Design and functional performance of polyaniline-carbon nanocomposites: synthesis, properties, and emerging applications

1 Introduction

A significant turning point occurred in materials science with the discovery of electrically conductive polymers in 1977, disproving the long-held belief that all polymers were insulators and leading to the Nobel Prize in Chemistry for Hideki Shirakawa, Alan Heeger and Alan MacDiarmid in 2000 (Shirakawa et al., 1977). The breakthrough demonstrated that organic polymers could exhibit electronic properties, similar to those seen in metals and semiconductors, while maintaining the processing and mechanical advantages inherent in plastics. Among the various conducting polymers PANI stands out for a unique set of desirable properties: low monomer cost, ease and scalability of synthesis, stability, electrical conductivity tunable and controllable via doping and oxidation states, reversible electroactivity and pH-response (Shirakawa et al., 1977; Heeger et al., 2002). PANI has a long history extending over 160 years, and was first synthesized by Henry Letheby in 1862, who produced “aniline black” through the anodic oxidation of aniline in sulfuric acid (Letheby, 1862; Cao et al., 2026). Nevertheless, only in the 1980s were the structure and doping mechanisms correctly elucidated by MacDiarmid and colleagues, revealing that PANI existed in 3 different oxidation states; fully reduced leucoemeraldine, half oxidized emeraldine and fully oxidized pernigraniline; and that the conductive emeraldine base is obtained by doping with protonic acids (MacDiarmid et al., 1987; Gojgić et al., 2022). In spite of such excellent potential PANI has failed to reach the commercial heights predicted, a consequence of inherent limitations which cannot be resolved simply by modifying the PANI itself. While the rigid conjugated backbone of the PANI polymer allows it to be electrically conductive, it has the associated drawback of being mechanically rigid and brittle leading to cracking and delamination when strained (Kim et al., 2013); thus, poor conductivity and electrical failure for flexible and wearable electronics applications. PANI has another major weakness, the highly conductive emeraldine salt form is only stable below pH 4 (MacDiarmid et al., 1987); this seriously limits its application in many biomedical and environmental applications operating around neutral pH values. Further to this the volume expansion associated with PANI during electrochemical cycles causes severe mechanical stress within the film, damaging the material and resulting in the rapid degradation of capacitance values after subsequent cycles (Banerjee et al., 2026). Another limiting factor for PANI performance is the strong aggregation behavior which causes the formation of densely packed granules and restricts the number of available electroactive sites (Wang et al., 2020a; Wang et al., 2020b). In this review, we demonstrate that the incorporation of carbon nanomaterials into PANI effectively overcomes its inherent limitations by creating synergistic interactions that significantly enhance the electrical conductivity, structural stability, mechanical strength, and electrochemical performance of the resulting composites. From one dimensional materials like carbon nanotubes (CNTs) to two dimensional materials like graphene and their derivatives (e.g. GO, rGO) and zero dimensional carbon dots and graphene quantum dots, through to three dimensional structures like activated carbons (Gao et al., 2021), all of these materials introduce new complementary characteristics and create strong interfacial interactions, specifically covalent, that enhance the electrical conductivity, specific capacitance and cycling stability (Rani and Ahlawat, 2024; Lu et al., 2016), as well as mechanical properties compared to a physical composite of the two materials (Wang et al., 2020a). There were significant recent studies on PANI-carbon nanocomposites (2024–2026). In the direction of energy storage, Ye et al. (2025) developed fiber supercapacitors made of PANI composite electrode which was enhanced with the graphene with high-energy density and good mechanical durability for flexible electronics. Chen et al. (2014) developed multifunctional carbon nanofibers (CNFs)/polyaniline (PANI) aerogels with good EMI shielding, flame retardancy, and thermal insulation performance. In addition, Several comprehensive reviews have addressed PANI-carbon composites, but they have been largely confined to specific applications and limited synthesis methodologies. Wang et al. (2019) provided a valuable overview of carbon/PANI hybrids for supercapacitors, focusing primarily on the classification of functionalized carbon materials and their electrochemical performance in energy storage applications. Similarly, Li and Gong (2020) reviewed PANI applications in electrochemical energy storage and conversion, covering supercapacitors, rechargeable batteries, and fuel cells, but with limited discussion of synthesis strategies and structure-property relationships. Reddy et al. (2023) examined the effect of conducting polymers on carbon-based electrodes for supercapacitors, yet their analysis remained confined to energy storage applications without exploring the broader potential of PANI-carbon composites. Other reviews have focused on even narrower domains. Shahat et al. (2025) specifically addressed PANI-based carbon composites for dye removal in water remediation, while Jiang et al. (2018) provided a mini-review on PANI-based adsorbents exclusively for hexavalent chromium removal. Despite these valuable contributions, the existing literature lacks a comprehensive and systematic analysis that compares multiple synthesis methods with evaluation of scalability and sustainability, establishes clear structure-property correlations linking carbon dimensionality to specific composite properties and covers the full spectrum of emerging applications beyond single-application studies. To address these gaps, the present review provides a critical and systematic analysis of PANI-carbon nanocomposites with several contributions: First, it comprehensively compares different synthesis methodologies. Second, it establishes structure-property correlations by linking carbon nanomaterial dimensionality and third, it provides a comprehensive application survey across five emerging fields, flexible supercapacitors, electrochromic devices, microbial fuel cells, CO₂ capture, and electromagnetic interference shielding. This article therefore explores PANI carbon nanomaterial composite materials in depth and provides an analysis of the influence of different types of carbon nanomaterial on the properties of PANI based composites. The review is organized as follows. Section 2 systematically classifies carbon nanomaterials by dimensionality. Section 3 compares different synthesis methodologies. Section 4 surveys emerging applications: flexible supercapacitors, electrochromic devices, microbial fuel cells, CO₂ capture, and EMI shielding. Section 5 identifies structure-property-performance correlations. Section 6 presents critical research gaps with actionable recommendations. Finally, Section 6 concludes with key findings and future perspectives for commercialization.

TABLE 1. Comparative properties of carbon nanomaterials for PANI composites.

2 Carbon nanomaterial types

This section provides a systematic differentiation of the major carbon nanomaterial types; namely carbon nanotubes (CNTs), graphene and its derivatives (graphene oxide, reduced graphene oxide), carbon dots (CDs), carbon nanofibers (CNFs), and porous carbons (including activated carbon and hierarchical porous structures) (Table 1; Figure 1).

2.1 Graphene and its derivatives

Graphene is a two-dimensional type of carbon material made up of one atomic layer of sp2 hybridized carbon atoms that are arranged in hexagonal (honeycomb) structure. Each individual carbon atom in the structure is bonded to three other neighboring carbon atoms via strong sigma (σ) in-plane bonds. This bonding forms a network of carbon-carbon bonds that are highly stable and extensive. The fourth electron of each carbon atom exists in delocalized (π) orbitals, which are perpendicular to the plane of the structure, creating a continuous cloud of electrons above and below the sheet. The delocalized electron-cloud provides graphene with its exceptional conductivity and fast charge transport. From a structural perspective, graphene is the primary building block for other forms of carbon nanomaterials. Carbon nanotubes are produced by rolling sheets of graphene into tubes, while graphite is produced by stacking many layers of graphene together using weak interactions between layers. The flat geometry and lack of dangling bonds in graphene provide it with strength, flexibility, and chemical stability, and they allow for effective interaction with polymer and other nanomaterials in composites (Geim and Novoselov, 2007).

Nevertheless, the surface of pristine graphene is hydrophobic because it consists of sp² carbons that have an inherently non-polar nature and no surface functional groups to be able to form hydrogen bonds with polar solvents like water, and polar monomer solution such as aniline. Therefore, graphene sheets aggregate together through strong van der Waals forces and π-π stacking interactions, resulting in graphene sheets restacking irreversibly into graphite-like structures. This aggregation reduces the surface area accessible to the solvents and thus diminishes the unique properties associated with individual layers of graphene (Geim and Novoselov, 2007). Graphene oxide (GO) is the chemical derivative of graphene that is commonly used, as it is composed of a high degree of oxygen-containing functional groups (hydroxyl, epoxy, carbonyl, carboxyl, etc.) that give GO a high degree of hydrophilicity and allow for excellent dispersion in water and other polar solvents (Milka et al., 2026; Hummers and Offeman, 1958). Unfortunately, the addition of oxygen functionalities to GO disrupts the π-conjugated system of graphene, thereby substantially decreasing GO’s electrical conductivity to essentially an insulator. Reduced GO (rGO) can be produced from the partial removal of the oxygen-containing functional groups from GO through chemical, thermal, or electrochemical reduction methods, resulting in an improvement in electrical conductivity from GO while maintaining some residual functional groups. The combination of PANI with graphene creates a synergistic interface that leverages the complementary properties of both materials: graphene provides a highly conductive scaffold with excellent mechanical strength, while PANI contributes reversible redox activity, pH-responsiveness, and biocompatibility (Stankovich et al., 2006). The synergistic combination of graphene’s high surface area and electrical conductivity with PANI’s redox activity and biocompatibility has opened new avenues for environmental remediation. This synergy is particularly evident in bioelectrochemical systems, where efficient electron transfer between microorganisms and electrodes is critical for pollutant degradation. In this context, Fang et al., 2025 demonstrated that utilizing the bioelectrochemical performance of co-contaminated wastewater streams (e.g., nitrobenzene, nitrate) can be significantly enhanced using GO/PANI coated carbon paper electrodes versus standard carbon papers. The authors attributed the enhanced bioelectrochemical removal to the establishment of a highly conductive and biocompatible interface between the electroactive bacteria and the electrode surface, which facilitated rapid extracellular electron transfer from electroactive bacteria to the electrode. In this way, graphene two-dimensional conductive structure provided a large surface area and multiple pathways for rapid electron transport; while polyaniline provided reversible redox capabilities and enhanced microbial adherence through its protonated amine groups.

2.2 Carbon nanotubes (CNTs)

Since their discovery by Iijima, 1991, they have attracted strong scientific interest due to their outstanding combination of electrical, mechanical, and thermal properties. Structurally, carbon nanotubes (CNTs) are seamless hollow cylinders composed of sp²-hybridized carbon atoms arranged in a hexagonal honeycomb lattice (Iijima, 1991). They are formed by rolling one or more graphene sheets into tubular structures with nanometer-scale diameters and lengths that can extend to several micrometers or even centimeters, and they exist mainly in two forms: single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) (Rathinavel et al., 2021). SWCNTs usually have diameters between 0.8 and 2 nm, while MWCNTs are composed of several concentric graphene layers with larger diameters ranging from about 5 to 50 nm (Rathinavel et al., 2021). Their electronic behavior is strongly dependent on structure, where SWCNTs may behave as either metallic or semiconducting depending on chirality, whereas MWCNTs are generally metallic because multiple walls provide parallel pathways for electron transport (Rathinavel et al., 2021). When integrated into PANI, CNTs act as efficient electron highways, enabling charge transport through the nanotube network instead of relying only on the polymer backbone. This significantly enhances conductivity, charge transfer, and overall electrochemical behavior (Xiong et al., 2011; Norfazlinayati et al., 2018; Dai et al., 2025; Kim et al., 2013). In addition to electrical improvements, CNTs also strengthen the structural stability of PANI composites. During repeated electrochemical cycling, PANI undergoes swelling and contraction due to doping and dedoping processes, which can lead to cracking and performance degradation. CNTs act as reinforcing nanofibers that absorb mechanical stress and maintain the integrity of the composite structure (Santino et al., 2016). Their high surface area also provides active sites for PANI growth, encouraging a more uniform and extended polymer morphology rather than agglomerated chains, which further improves ion transport and interfacial contact (Norfazlinayati et al., 2018). The practical benefits of CNT–PANI systems have been demonstrated in recent studies. Navatragulpisit et al. (2025) developed flexible thermoelectric fabrics based on PANI/CNT-coated cotton, achieving a power factor of about 9 μW m^-1 K⁻² and generating sufficient electrical output to power wearable devices. Despite these advantages, CNTs still face challenges that limit large-scale application. The most important issue is their strong tendency to aggregate due to van der Waals forces, which reduces dispersion quality and limits effective interaction with PANI (Huang et al., 2003).

2.3 Activated carbon from biomass

Activated carbon, one of the most frequently utilized porous carbon materials in energy storage and environment applications, possesses extremely large surface areas and well-developed pore structure and hierarchy structure combining micropores and mesopores. Activation carbon is normally produced by the two-step process involving the carbonization of the carbon-rich precursors in an inert atmosphere and followed by an activation procedure. Physical activation, which relies on oxidizing agents, such as CO₂ or steam, or chemical activation, which relies on chemical agents, such as KOH and ZnCl₂, will greatly enhance surface area, surface activity and pore structure (Mishra et al., 2024). Tomy et al. (2025) used coconut husk, a lignin-rich agricultural byproduct, to fabricate activated carbon, which was subsequently combined with PANI to achieve specific capacitance of 529 F g^-1 with outstanding stability of 98%–100% even after 50,000 cycles. Besides, Rahim et al. (2025) utilized date seeds to produce activated carbon by using ZnCl₂ as chemical activation agent and integrated this AC into PANI based composite material, which also demonstrates strong performance in carbofuran adsorption (327.6 mg g^-1). Balanites aegyptiaca stone was selected to develop activated carbon in Belhamdi et al. (2026) while date palm kernel biomass was used to create hybrid ACP@PANI-polypyrrole composites in Kalavani et al. (2026), revealing the flexibility in selecting diverse agricultural residues to fabricate functional materials. In order to develop efficient energy storage materials in a sustainable way, Ieamviteevanich et al. (2025) used sugarcane bagasse to produce nitrogen-doped carbon, followed by the integration with PANI to achieve flexible electrodes. The gamma radiation utilized to fabricate the electrodes provides crosslinks within the polymer matrix, which leads to improved mechanical properties. The optimized composite has significantly better electrochemical performance than those with other amounts.

2.4 Carbon nanospheres

Carbon nanospheres (CNS) are zero-dimensional carbon nanostructures with a spherical morphology and typical diameters ranging from about 50 to 500 nm (Yao et al., 2024). They occupy an important structural position between one-dimensional carbon nanotubes and two-dimensional graphene, offering isotropic geometry that is particularly useful in uniform composite formation (Yao et al., 2024). Carbon nanospheres can be divided into many types: solid carbon nanospheres, porous carbon nanospheres, core-shell carbon nanospheres, and hollow carbon nanospheres (Nieto-Márquez et al., 2011; Wang et al., 2016; sun et al., 2004). Solid carbon nanospheres have carbon densely packed with the fewest internal porosities. Therefore, this results in high structural integrity (Sun and Li, 2004). Porous carbon nanospheres have different sorts of pores like micropores, mesopores, and macropores which greatly increase the surface area and open up the surface sites for ion storage, molecular adsorption, and so on (Wickramaratne et al., 2014; Chen et al., 2014). Hollow carbon nanospheres have a hollow center surrounded by a thin carbon shell. The carbon shell allows for high guest molecule loading and the whole structure has an exceptionally high capacity for buffering volume expansions brought about by electrochemical cycling (Liu et al., 2011; Zhang et al., 2012). Core-shell structures have a carbon shell surrounding a functional core (metal, metal oxide, polymer), thereby producing multi-functional properties by combining features of core and shell (Wang et al., 2018; Zhao et al., 2012).

CNS can be synthesized through several methods, including hydrothermal carbonization of simple sugars such as glucose and sucrose, chemical vapor deposition (CVD), and arc-discharge techniques. Each method influences the degree of graphitization, particle size, and surface chemistry, which in turn determines their electrical and interfacial properties (Yao et al., 2024). Among these approaches, the arc-discharge method reported by Achutharao, 2025 stands out for producing highly graphitized carbon nanospheres. In this process, extremely high temperatures exceeding 3000 °C are generated during the discharge, leading to the formation of well-ordered sp² carbon structures. The resulting functionalized carbon nanospheres (f-CNS) exhibit superior crystallinity and relatively small particle sizes, around 74 nm. This high level of graphitization is particularly important because it ensures efficient charge transport across the spherical carbon network, thereby improving electrical conductivity (Achutharao, 2025). Carbon nanospheres are distinguished by their unique features, such as high surface area (e.g. the activated CNS can reach up to 3000 m²/g), surface chemistry is tunable via heteroatom doping (Chen et al., 2023; Ge et al., 2022; Wickramaratne et al., 2014), good dispersion since the geometry is isotropic, and the electrical conductivity is graphitization-dependent (Nieto-Márquez et al., 2011; Serafin and Dziejarski, 2024). In conjunction with PANI matrices, CNS facilitates efficient ion transport by forming well-separated inter-particle spaces, reinforces mechanical integrity via even stress distribution, provides uniform dispersion to prevent the materials from entanglement or restacking, and offers diverse functionalization possibilities to support strong interfacial bonding.

2.5 Carbon dots and graphene quantum dots

Carbon dots (CDs) and graphene quantum dots (GQDs) represent the smallest class of carbon-based nanomaterials, typically with lateral dimensions below the nanometer scale (Liu et al., 2026). Because of their small size, these materials have a much different electronic structure than larger carbon material, and therefore reduced electronic size effects cause all carriers of charge to be spatially restricted from all charges, creating band gaps rather than continuous bands of states as is seen in bulk carbon-based materials. The change in electronic structure of CDs creates localized electronic energy levels and therefore makes their photonic and electronic properties dependent on their size, surface chemistry, and chemical composition. Thus, the effective band structures for CDs can be modified, causing their emission and absorption to occur over a broad wavelength range across the visible spectrum.

The most common methods to produce carbon dots utilize inexpensive molecular precursors through hydrothermal, microwave-assisted, and thermal processing that incorporate only partial carbonization while maintaining a large number of oxygen and nitrogen functional groups on the surface (Liu et al., 2026; Zhao and Xie, 2017). Graphene quantum dots are produced mostly by the use of various controlled processing methods to produce a smaller form of previously characterized graphene. Banerjee et al. (2026) demonstrated that carboxyl-functionalized CDs can be covalently linked to aniline molecules through amide bond formation using carbodiimide chemistry. This allows CDs to act as multifunctional crosslinking nodes, where multiple aniline molecules are anchored onto each dot before polymerization. During oxidative polymerization, this results in a highly interconnected and branched PANI network, where CDs are structurally embedded within the polymer matrix rather than simply dispersed within it. This covalent integration has several important consequences. It prevents excessive aggregation of PANI chains, improves mechanical integrity, and ensures more efficient ion transport by maintaining open and accessible diffusion pathways. As a result, the CD–PANI composite reported by Banerjee et al. (2026) achieved a specific capacitance of 656 F g^-1 at 0.5 A g^-1, along with a high capacitance retention of 91% after 5000 cycles, reflecting excellent electrochemical stability. Beyond energy storage, CDs also introduce optical and sensing functionalities due to their intrinsic photoluminescence. Al Kiey et al. (2025) reported a microwave-assisted synthesis of nitrogen-doped carbon quantum dots embedded in a PANI/carboxymethyl cellulose hydrogel for L-arginine detection. The material exhibited a very low detection limit of 0.63 μM and a wide linear response range from 1 to 100 μM. Despite their promising features, CDs and GQDs still face several practical limitations. Their synthesis and purification can be relatively expensive when high-quality, uniform particles are required, especially at large scale. In addition, covalent integration with polymers often involves multi-step chemical processes, including functionalization, activation, and polymerization, which can increase complexity and reduce scalability.

3 Synthesis methods

3.1 In situ polymerization

In this method, aniline is polymerized directly in the presence of pre-dispersed carbon nanomaterials (Tkalya et al., 2012; Lei et al., 2010; Benahmed et al., 2018; Stejskal, 2002; Bekri-Abbes and Srasra, 2016; Sun et al., 2025). For instance, as shown in Figure 2, in situ chemical oxidation polymerization of aniline was used to produce a PANI/graphite flakes composite. Aniline and small graphite flakes (P50 μm) were first dissolved in diluted HCl to provide a uniform graphite-aniline monomer solution. An equal quantity of ammonium persulfate was independently prepared in deionized water to provide an oxidation agent for the polymerization and then added to the solution with continuous agitation to physically mix and adsorb the aniline molecules onto the graphite surface. The controlled addition of APS initiated the oxidation polymerization of aniline, resulting in the in-situ growth of polyaniline chains onto and encapsulating the graphite flakes. The reaction mixture was left undisturbed overnight to allow for uniformity of polymerization and completion of polyaniline chain growth, which resulted in the development of the composite network. Likewise, Gohar et al. (2025) employed in situ polymerization to fabricate CNT/PANI/epoxy nanocomposites for multifunctional smart materials, demonstrating clear improvements in mechanical strength, electrical conductivity, and long-term chemical stability. While in situ polymerization is a very effective technique, there are some limitations to consider. The process relies on the ability to obtain a uniform dispersion of carbon nanomaterials prior to polymer formation; however, it can be difficult to do this and oftentimes leads to the agglomeration of the carbon nanomaterials, which results in non-uniform coatings. Furthermore, the polymerization reaction is very sensitive to factors, such as temperature, pH, and concentration of oxidants; as a result, polymerization can be very difficult to reproduce. Excessive polymer growth can also cover up active sites, thus limiting the contribution of carbon surfaces to provide conductivity. In addition, after the polymerization reaction is complete there are residual oxidants and byproducts, which need to be removed from the resulting coating. This additional step for removing impurities can complicate the purification process and also alter the long-term electrochemical performance of the resulting composite materials.

3.2 Electrochemical polymerization

A completely different approach that bypasses many of the issues relating to heterogeneity associated with in situ polymerization is the electrochemical polymerization. This approach is initiated by preparing a carbon nanostructure-coated conductive substrate, e.g. A glassy carbon, FTO or carbon paper electrode (Figure 3). Uniform carbon layer can be formed through various methods, including dropping solution, electrophoretic deposition or by vacuum filtration and then transferring on the substrate (Adam et al., 2025; AbdulAlmohsin et al., 2012). Then, the carbon-modified electrode is immersed in a polymerization solution containing aniline monomer, and cyclic voltammetry (CV) was applied to drive the oxidative polymerization of aniline directly on the carbon surface. By controlling the number of CV cycles, the thickness and uniformity of the PANI coating were tuned. Key advantages include the formation of well-defined PANI-carbon interface under electrochemical control and fine tunability of the oxidation state and doping level of the polymer by control of applied potential. Recent examples show potential applications of the method. For example, electrodeposition of PANI/MWCNT/CuS nanocomposites on FTO substrates used as counter electrodes for CdS quantum dot-sensitized solar cells yielded energy conversion efficiency of 2.39% with a substantially reduced charge-transfer resistance (Tartuci et al., 2025). In another study, a poly (3-aminobenzylamine)/functionalized multi-walled carbon nanotube composite thin film was fabricated onto FTO glass by electrochemical polymerization, displaying sensitive detection of dopamine in artificial urine and achieving a limit of detection of 119.54 nM (Sriwichai and Thongnoppakhun et al., 2025).

However, this method possesses limitations that makes large scale production of composite powders unfeasible. They are fundamentally limited to use with conducting substrates and relatively small electrode.

3.3 Covalent conjugation

Covalent conjugation is a recent technique where chemical bonds are formed between carbon nanostructures and aniline molecules before polymerization (Xiong et al., 2011; Sun et al., 2024). This leads to a composite in which carbon acts not as a separate filler but rather as part of the chemical structure of the PANI. Such chemical linkages have definite advantages. They are efficient at preventing phase separation and delamination issues that usually plague non-covalently linked composites under mechanical load or repetitive electrochemical cycling. This method has been successfully used on a wide variety of carbon structures. For instance, amidation (-NH-CO-) reactions between PANI and carbon fibers have improved electron transfer and charge transfer kinetics as a result of enhanced -conjugation from the carbon surface to the PANI chains (Li et al., 2021). Similarly, covalent grafting of PANI onto carbon nanotubes yielded much higher values of ion diffusion, electrical conductivity and electrochromic performances in comparison with non-covalently integrated composites (Wang et al., 2020b). Excessive accumulation of PANI chains is prevented, thereby retaining large surface area and shallow diffusion pathways for ions. A covalently linked PANI-carbon material has delivered a capacitance of 656 F g^-1 at 0.5 A g^-1 and 286 F g^-1 at 5 A g^-1, along with a remarkable 91% retention of the initial capacitance after 5000 cycles (Banerjee et al., 2026). Water dispersible PANI-rGO and PANI-SWCNT nanocomposites were fabricated by covalent grafting onto amine-functionalized carbon surfaces and subsequently doped using macromolecular PS (Wang et al., 2020b). Compared with neat PANI, such a ternary composite achieved significantly higher optical contrast. In yet another case, high capacitance of 696.75 F g^-1 at 2 A g^-1 and an impressive cycling stability with 93.57% retention of capacitance over 3500 cycles were observed for PANI covalently anchored on a porous framework comprised of rGO and helical carbon nanotubes (Xuan et al., 2020).

3.4 Microwave-assisted synthesis

Microwave assistance is considered an energy efficient and rapid technique for preparation of carbon-PANI nanocomposites. Unlike the conventional thermal conduction method (using oil baths or hot plates), microwaves directly heat polar molecules and ions of reagents such as aniline, water and doping acids through the process of dieletric heating, thus providing an ultra-fast and uniform heating of the solution (Gizdavic-Nikolaidis et al., 2016) (Figure 4). Mi et al. (2007) presents a microwave-assisted method for synthesizing PANI and MWNT composites for use as supercapacitors. First, MWNTs were purified using a nitric acid reflux process to remove impurities from their surfaces while also adding functional groups to enhance their dispersion properties. Once the MWNTs were dried and cleaned, they were dispersed in a dilute acidic (H₂SO₄) aqueous solution with the aniline monomer. The resultant mixture was subjected to ultrasonication for approximately 30 min in order to achieve good dispersion of the nanotubes and to allow for adsorption of aniline molecules onto the surfaces of the MWNTs, which is critical for the formation of a uniform composite. Next, APS was added as an oxidant to initiate the polymerization process. Under microwave irradiation, aniline undergoes fast and uniform oxidative polymerization, which significantly decreases the synthesis time compared with traditional methods. Microwave-assisted synthesis provides rapid volumetric heating to accelerate the reaction kinetics of aniline, thereby facilitating the direct growth of polyaniline chains on the surfaces of MWNTs. These simultaneous chemical dissolution and physical coating processes create a well-integrated composite structure in which PANI is coated on the surfaces of the nanotubes. The prominent advantage of this method is the ultra-fast speed; for example, Qiu et al. (2025) reported synthesis of CNT/Ag/PANI composites in just 50 s.

3.5 Layer-by-layer assembly

Layer-by-layer (LbL) assembly is a controllable and versatile method to fabricate carbon/PANI composite thin films and complicated architectures based on sequential assembly of oppositely charged species onto a sacrificial template (Zhang et al., 2022). In typical approach, positively charged polyaniline (or aniline oligomers) and negatively charged functionalized carbon nanomaterials are alternately adsorbed onto template particles, predominantly, spherical beads made of polystyrene nanomaterial (Figure 5). The process is based on alternately dipping the templates into solution containing these components followed by rinsing for removed excessive species. After forming required bilayers, the sacrificial templates (e.g. Polystyrene which is soluble in tetrahydrofuran) are removed, yielding hollow spheres with multilayer structure consisting of alternative PANI and carbon layers. This LbL assembly has shown many potentials, such as Hyder et al., 2011 who constructed thin-film electrodes composed of PANI nanofibers and functionalized MWNT with interpenetrating nanoscale structure, achieving a high volumetric capacitance of 238 F cm^-3 and good energy density of 220 Wh L^-3 with a power density of ∼100 kW L^-3 in Li cell.

3.6 Cryo-polymerization

The technique of cryo-polymerization is a novel synthesis methodology, which carries out the oxidative polymerization of aniline under sub-zero conditions, typically between −20 to −78 °C. This technique relies on freezing of the solvent as a template to form macroporous cryogels or aerogels with well-defined hierarchically porous structure. As depicted in Figure 6, its mechanism differs significantly from traditional room temperature polymerization method. The growing ice crystals excluded dissolved components (aniline monomer, oxidant, dopant and carbon nano-fillers) and lead to high local concentration of these components between the ice crystals in the remaining liquid micro-phases. By eliminating the ice crystals (sacrifice template) under freeze-drying method, a three-dimensional interconnected macroporous framework is formed. Additionally, the very low polymerization temperature slows down the polymerization kinetics, controlling the growth of polymer chain and reducing the tendency to form uncontrolled aggregation, which is a common problem of normal PANI synthesis. The frozen solvent is then removed by sublimation under vacuum (freeze drying) after completion of polymerization to yield lightweight aerogels that inherit the ice-templated architecture. Milakin et al. (2024) utilized the one step method of oxidative cryopolymerization in 50:50 v/v water:isopropanol mixtures for the creation of double-porous PANI-poly (N-vinylpyrrolidone) cryogels with carbon nanofibres (PANI-CNF-PVP). Scan and transmission electron microscopies have shown the obtained aerogels have specific double-porous architecture, the overall 3D framework consisted of large macropores (5–35µm), mesopores of 200 nm–3 µm are formed on pore walls. The measured surface areas are in range of 13–25 m² g^-1. The surface area values are from 13 to 25 m² g^-1 which is typical of polymer cryogels. This relatively low surface area is due to the lack of microporosity (Vmicro = 0 cm³ g^-1) and the dominance of macroporous and mesoporous structures (Milakin et al., 2024). Compared to typical porous carbon with large surface area, such cryogels do not use high total surface area for fast ion transport but a hierarchically connected pore network. However, the PANI-CNF-PVP aerogels demonstrated excellent performance, gravimetric capacitance up to 201 F g^-1 at 1 A g (3-6-fold enhancement compared with CNF free materials). From Electrochemical impedance spectroscopy, the charge-transfer resistance was decreased and the cycling stability was improved with increasing CNF content. A key advantage is the one-step nature of cryo-polymerization, the cryogelation and the polymerization occur simultaneously and the distribution of all components is inherently homogeneous without the need for extra functionalization, activation or removing steps as needed in other complex approaches such as layer by layer or grafting on a preformed template.

3.7 Gamma radiation-assisted fabrication

Gamma radiation-assisted synthesis has become a promising alternative in creating carbon/PANI composites, as it is a clean, catalyst-free and scalable method compared to the traditional chemical synthesis. The high penetration capability of radiation is employed to directly create highly reactive free radicals within the material matrix. This makes it possible for them to initiate polymerization of PANI as well as crosslinking, eliminating the requirement of an oxidant or chemical crosslinking agent (Norfazlinayati et al., 2018) (Figure 7). Cleanliness and simplicity are among the main merits of using radiation-assisted method as the composite products are expected to be less impure. It is also conducted at room temperature so that polymers and carbon-based materials which sensitive to high temperature can preserve their structure. Furthermore, by utilizing radiation the process can affect the carbon precursors and the polymer matrix simultaneously leading to a synergistic design for the material structure (Ieamviteevanich et al., 2025). An exemplary application of this approach was done by Norfazlinayati et al. (2018), who successfully prepared a series of PVA/PANI/MWCNT composite films via gamma irradiation of a composite prepared from PVA, PANI and MWCNT, using Co-60 gamma source. The mixture of PVA, aniline hydrochloride, and functionalized MWCNTs was pre-mixed at room temperature through sonication and then fabricated into films by vacuum casting. These films were then dried at a mild temperature of 48°–50 °C for a night and then irradiating up to 50 kGy (around 25 h). Structural and chemical modification were observed after irradiation: an increase in PANI intensity in FTIR spectra indicates higher formation of PANI while the crystallinity of the material is decreased, confirmed by XRD results. The electron micrographs indicated that PANI was uniformly spread over the surface of MWCNTs, increasing the effective diameter. Optical studies demonstrated a shift of-transition and decrease of the band gap of PVA/PANI/MWCNT composites, suggesting improved electrical conductivity (Norfazlinayati et al., 2018). Very recently, the same research group, led by Ieamviteevanich et al. (2025), used the same approach with the combination of biomass waste to generate flexible energy storage material. They used sugarcane bagasse as carbon source, which was treated first by a low-dose irradiation (5 kGy) to improve the dispersion and breakdown of the cellulose structure. Then, melamin was added as the source of nitrogen and after being pyrolyzed at a high temperature (900 °C under nitrogen) and combined with PANI and flexible polymer matrix (PEBAX). Another irradiation was applied with a dose of 20 kGy to facilitate crosslinking, then freeze-dried and pressed to flexible films. Other than performance, another benefit of using irradiation-assisted crosslinking is it eliminated the use of chemical crosslinking agent which may leach out after a long use and it also enhanced the mechanical property of the materials. This material is particularly suitable for application in flexible and wearable device.

3.8 Scalability challenges of synthesis methods

While each synthesis method offers unique advantages for preparing PANI-carbon nanocomposites, their scalability varies significantly. Understanding these scalability challenges is essential for transitioning from laboratory research to industrial production. In situ polymerization is the most scalable synthesis method, as it employs simple equipment, mild reaction conditions, and commercially available reagents that are readily accessible at industrial scale. The method is already used in industrial production of PANI composites and can be readily adapted to large-scale batch or continuous flow reactors. However, scalability challenges include achieving homogeneous dispersion of carbon nanomaterials in large reaction volumes requires high-energy mixing that becomes energy-intensive and costly at industrial scale (Tkalya et al., 2012). Additionally, the exothermic nature of aniline polymerization requires precise temperature control to prevent runaway reactions, while the removal of residual oxidants and byproducts requires extensive washing, generating significant liquid waste and increasing production costs. Developing continuous flow reactors with efficient mixing and membrane-based purification systems can address these challenges (Ieamviteevanich et al., 2025). Electrochemical polymerization has limited scalability due to fundamental constraints. The method requires conductive substrates that must serve as working electrodes, restricting production to thin-film electrodes and preventing the production of freestanding composite powders. The electrode area limits production volume; scaling up would require large electrode arrays, increasing capital costs and process complexity (Adam et al., 2025). The method is inherently batch-based, making continuous production difficult. Consequently, this method is best suited for thin-film applications (sensors, electrochromic devices) rather than large-scale powder production. Roll-to-roll electrochemical deposition systems could enable continuous production for flexible electronics (Tartuci et al., 2025). Covalent conjugation offers excellent interfacial stability but faces major scalability barriers. The multi-step synthesis process adds time, cost, and potential for batch variation. Activation often requires expensive, hazardous reagents requiring careful handling and disposal (Banerjee et al., 2026). The use of organic solvents adds environmental and cost burdens, while extensive washing and purification generate significant solvent waste (Wang et al., 2020a). Currently, only milligram to Gram quantities have been reported, far from industrial needs. Developing aqueous-based conjugation chemistries and continuous flow reactors with in-line purification could reduce time from days to hours. Microwave-assisted synthesis offers energy efficiency and speed but faces scalability challenges. Microwave penetration depth limits the volume that can be uniformly heated; scaling to large reactors requires careful design to avoid temperature gradients (Gizdavic-Nikolaidis et al., 2016). Industrial microwave reactors are expensive, and most reported systems are batch-based; continuous flow microwave reactors are less common (Qiu et al., 2025). Current studies are at gram-kilogram scale, with large-scale validation lacking. Developing continuous flow microwave reactors with controlled residence time and heating profiles could enable large-scale production. Layer-by-layer assembly offers precise control but has poor scalability. Each bilayer deposition cycle requires multiple steps, making scale-up to thick films or large volumes impractical and generating significant liquid waste. The method is limited to flat surfaces or particulate templates, unsuitable for freestanding powder production (Hyder et al., 2011). Spray-assisted LbL assembly could accelerate production and enable roll-to-roll processing. Cryo-polymerization offers unique porous architectures but faces significant scalability challenges. Maintaining sub-zero temperatures (−20 to −78 °C) for extended periods requires substantial energy (Milakin et al., 2024). The prolonged polymerization time (days) limits throughput, and freeze-drying is energy-intensive. Studies are at gram-laboratory scale. Developing faster freeze-drying techniques could address these limitations. Gamma radiation-assisted fabrication offers clean, catalyst-free synthesis but faces constraints. Gamma irradiation facilities require substantial capital investment and specialized infrastructure (Norfazlinayati et al., 2018). Handling radioactive sources requires strict safety protocols, regulatory compliance, and trained personnel, increasing operational complexity (Ieamviteevanich et al., 2025). Current studies at gram-kilogram scale lack large-scale validation. Contract irradiation services could provide access to gamma facilities without capital investment.

3.9 Different criteria for synthesis method

The choice of synthesis method for PANI-carbon nanocomposites depends on multiple factors including the target application, required material properties, production scale, cost constraints, and available infrastructure. Application-driven selection is the primary consideration. Different applications require different material characteristics, which directly influence the choice of synthesis method. For supercapacitors requiring powder-form electrode materials with high capacitance and good conductivity, in situ polymerization is the most suitable method due to its scalability, cost-effectiveness, and established industrial protocols. Microwave-assisted synthesis offers an alternative when rapid preparation is prioritized, enabling synthesis in seconds to minutes. For thin-film devices such as sensors or electrochromic systems, electrochemical polymerization provides precise control over film thickness and uniformity, while layer-by-layer assembly enables the fabrication of highly ordered nanostructures with nanometer-scale precision. When mechanical stability and flexibility are critical for wearable electronics, covalent conjugation ensures strong interfacial bonding through chemical linkages, preventing delamination under mechanical stress, while gamma irradiation offers crosslinking that enhances mechanical integrity. For applications requiring lightweight porous structures such as aerogels or cryogels for advanced energy storage or CO₂ capture, cryo-polymerization is the method of choice, creating unique double-porous architectures with hierarchical pore networks that facilitate rapid ion transport. Scalability considerations are essential for transitioning from laboratory to industrial production. Production scale can be categorized into three levels: milligram to Gram for laboratory research, Gram to kilogram for pilot-scale production, and kilogram to ton for full industrial manufacturing. In situ polymerization is the only method currently suitable for kilogram to ton scale production, as it employs simple equipment, mild reaction conditions, and commercially available reagents. Microwave-assisted synthesis and gamma irradiation have been verified up to kilogram scale and show promise for further scale-up, though they require significant capital investment. Electrochemical polymerization, layer-by-layer assembly, covalent conjugation, and cryo-polymerization remain limited to milligram to Gram quantities due to substrate constraints, long processing times, multi-step synthesis, or energy-intensive conditions. Cost analysis reveals significant variation among synthesis methods. In situ polymerization offers the lowest cost due to inexpensive reagents and simple equipment. Microwave-assisted synthesis and electrochemical polymerization represent medium-cost options, with equipment and energy consumption being the primary cost drivers. Covalent conjugation and gamma irradiation involve high costs associated with hazardous reagents, specialized equipment, safety requirements, and waste treatment. Layer-by-layer assembly and cryo-polymerization fall in the medium-high range due to long processing times and intensive purification steps.

4 Emerging applications and properties

4.1 Flexible supercapacitors

Due to the growing demand for medical impalpable devices, wearable electronics, smart textiles, and common electronic devices with flexible displays, the flexible supercapacitor is one of the most popular research areas within energy storage (Thongsai et al., 2025). Flexible supercapacitors operate very much differently than traditional rigid supercapacitors. Flexible supercapacitors have to be able to maintain good electrochemical performance under various mechanical strains that must be considered when designing the flexible supercapacitor electrodes and devices (Gokul et al., 2026; Kayode et al., 2024). Among the various electrode materials explored for flexible supercapacitors, polyaniline (PANI)/carbon nanocomposites have attracted considerable attention because they effectively integrate the advantages of conducting polymers and carbon nanomaterials (Zhao et al., 2026). This improvement in performance is attributed to the porous structure of carbon derived from the biomass material, the redox activity of PANI, and the superior interfacial bond (radiation-induced cross-linking) (Wang et al., 2019). The failure of mechanical interaction between active materials and flexible substrates is a primary obstacle for building mechanical stable devices, so covalent bonding technique is generally used to strengthen the interfaces via chemical linkage. The study by Li et al. (2021) is a good example of covalent bonding between polyaniline and carbon fibers. A PANI- carbon fibers were synthesized and amide linkage were introduced at the interface, constructing stable covalent bond between polyaniline and carbon fibers which is helpful for interfacial mechanical stability. As a result, the performance loss of the fabricated device after 2000 folding cycles can be effectively suppressed to 92.9%, and the continuous π-conjugated network formed at the interface also sustained electrical path under the mechanical deformation to suppress the decrease of conductivity. Apart from the covalent strategies, layer-by-layer (LbL) technique also demonstrated to be a powerful method for fabricating highly ordered and mechanically stable electrochemical nanostructures. Alternating deposition of conducting polymer and porous carbon on various substrates enables the controlled fabrication of well-organized films with robust mechanical property.

Martire et al. (2026) reported a multilayer electrode based on polyaniline-polystyrene sulfonate (PANI-PSS)/porous carbon derived from ZIF-8 (PCZIF-8) (Figure 8). As more and more bilayers were deposited on the substrate, both the current response and the redox peak potential increased progressively and predictably, which is a sign of reliable film fabrication with well-maintained electrochemical contacts. A continuous increase in the peak current density as a function of bilayer number was observed and the electrochemically connected network-maintained integrity throughout the device during testing under varying conditions. Moreover, electric double-layer capacitance from porous carbon and pseudocapacitance from PANI contributed positively to the energy storage capability and the porous carbon was helpful for faster ion diffusion while PANI was responsible for rapid charge redox kinetics. Furthermore, the interlinked three-dimensional architectures are often more helpful to spread the stress over the electrode and therefore it is beneficial for achieving good mechanical flexibility. To improve the mechanical flexibility, a hybrid aerogel framework was employed with the presence of helical carbon nanotubes (Xuan et al., 2020). Helical carbon nanotubes enable the material to be mechanically stretchable due to their spring-like geometry, which can unwind and reform during deformation without breaking. The carbonized reduced graphene oxide/helical carbon nanotube/PANI (CRCP) aerogel developed was mechanically robust and showed high specific capacitance of 696.75 F g^-1 vs. 274.75 for pure PANI and with 93.57% retention over 3,500 cycles vs. 72.3% after 2500 charge/discharge cycles for pure PANI, as well as good performance even under a high degree of bending.

A self-healing system was developed to recover both the mechanical strength and electrical conductivity upon damage, for instance by using dynamic bonds which could break and reform reversibly under specific stimulus (Cheng et al., 2024). They used oxidized cellulose nanofibers and carbon nanotube as the structural support, and the MnO and PANI can provide supplementary pseudocapacitance, making it the hierarchically structured electrode. Due to the presence of the interdigitated configuration, ion transport paths are shortened. Self-healing property of borate ester bonds in the hydrogel allows the electrode material be repaired even after it is cut and then rejoined, thus making it desirable for wearable devices, which can potentially prevent device failure due to external damage. Sustainability is becoming increasingly crucial for energy storage materials. Low-cost biomass materials are commonly used to prepare porous carbons, which is the carbon support in most composite electrodes. Longan shell derived porous carbon used by Cui et al. (2024) achieved 486 F g^-1 and the performance remained 85% after 10,000 cycles, it also has a high energy density of 47.3 Wh kg^-1. The waste from agricultural production like olive stone can be successfully converted into activated carbon, which was combined with rGO and PANI to form a PANI-based electrode with high capacitance of 582.6 F g^-1 and 90.07% capacitance retention (Benchikh et al., 2024).

4.2 Electrochromic devices

Electrochromic devices (ECDs) are smart systems capable of reversibly changing their optical properties under an applied electrical voltage. This behavior makes them highly attractive for a wide range of applications. It includes smart windows, adaptive rearview mirrors, low-power displays, and thermal regulation systems in energy-efficient buildings (Shchegolkov et al., 2021). PANI has been extensively studied as an electrochromic material because of the extensive and reversible redox characteristics, changing from pale yellow leucoemeraldine in its completely reduced state to green in its emeraldine state and then to blue in its completely oxidized state called pernigraniline. Nevertheless, despite these advantageous characteristics, pure PANI still faces certain practical drawbacks, such as relatively low reaction rates, modest optical contrasts, and decreasing stability over time. Such issues have been attributed to the limited ion movement inside the dense structure of the polymer and poor electron mobility within the highly disordered polymer chains. As a result, such factors affect negatively the redox reactions necessary for the changes in the polymer’s color. In order to overcome the abovementioned drawbacks, the incorporation of carbon nanomaterials is utilized for producing composite materials based on PANI. Carbon nanomaterials help provide efficient electron movement via forming conductive channels. In addition, their high surface area provides access to electroactive sites and facilitates the process. Furthermore, carbon nanomaterials provide superior mechanical properties for the composite. The effects of carbon nanomaterials covalently incorporated into the matrix of electrochromic systems have been experimentally investigated by Wang et al. (2020b). It was shown that a ternary composition based on polyaniline, reduced graphene oxide, and SWCNTs exhibits a significantly improved contrast parameter compared to neat PANI (optical contrast increased from 0.38 to 0.52). Moreover, there is a pronounced increase in switching rates: from 2.59 s to 2.39 s for pure PANI to 1.33 s and 0.78 s, respectively. The reason for such an improvement is associated with the formation of a three-dimensional conductive structure that ensures fast electron transfer and stabilization of the π-conjugation in polyaniline. As shown in another work, a composition based on 0.6 wt% MWCNTs exhibited a significantly higher optical contrast of 0.78. More advanced multifunctional systems have also been developed by integrating electrochromism with energy storage. Chen et al. (2025a) reported a solid-state electrochromic supercapacitor based on PANI doped with carbon quantum dots, combined with a transparent V₂O₅@PEDOT counter electrode. This architecture enabled simultaneous energy storage and visual state indication. The device exhibited high areal energy density (up to 4.02 μWh cm^-2), ultra-fast switching times (0.75 s for coloration and 2.61 s for bleaching), and outstanding coloration efficiency (221.6 cm² C⁻¹). It also demonstrated excellent durability, maintaining performance over 5000 cycles. Notably, the device provided a direct visual correlation between stored energy and color state, transitioning from light yellow-green (discharged) to dark green (charged), enabling intuitive real-time energy monitoring. In another important development, Qin et al. (2024) focused on infrared-responsive electrochromic systems, which are essential for thermal management applications such as smart windows and thermal camouflage. They designed PANI/CQD composite films with improved porosity and ion transport pathways. The resulting material achieved a near-infrared optical contrast of 53% at 850 nm, along with significant emissivity modulation across multiple infrared regions (3–5 μm, 8–14 μm, and 2.5–25 μm). Switching times were also improved to 2.5 s for coloration and 3.6 s for bleaching, with excellent stability over repeated cycles. The enhanced performance was attributed to synergistic effects between CQDs and PANI, which improved both electron transport and electrolyte diffusion through a more open microstructure.

4.3 Microbial fuel cells

Microbial fuel cells (MFCs) are bioelectrochemical systems which utilize the metabolic activity of microorganisms to convert chemical energy present in organic matter to electrical energy (Dixit et al., 2025). Microorganisms in an MFC can oxidize organic substrates (waste water, organic waste) at the anode by releasing electrons and protons (Figure 9). The electrons then pass through an external circuit to the cathode where they reduce oxygen (or another electron acceptor) with protons to form water thus generating electricity. Performance of MFC strongly depends upon the cathode catalyst to catalyze the ORR efficiently and cost-effectively. Platinum-group metals are good catalysts but too expensive to use in wastewater treatment; PANI-carbon composites are thus developed as efficient and cost-effective cathode catalysts for MFCs. Sun et al., 2024 synthesized PANI@COF-CNT composite material as a cathode catalyst of MFC by chemical oxidation polymerization. Bone like coral architecture of COF and porous structure of CNTs were benefit for vast electroactive sites and high conductivity of PANI can largely enhance electron transfer rate, thereby significantly decrease the transport resistance. PANI@COF-CNT has surface area and pore diameter of 99.533 m²/g and 24.916 nm respectively, which were 13.220 times and 1.913 times higher than that of PANI@COF, respectively. PANI@COF-CNT MFC shows stable output voltage around 0.390 V for more than 120 h. The power density of PANI@COF-CNT MFC reach as high as 194.480 mW/m², which was 8.655 times of that of blank COF cathode MFC. Such striking improvement reveals the cooperative catalysis between PANI, COF and CNT where COF provides ordered pore channels and nitrogenous catalytic sites, CNT supports both efficient electron transfer channels and stable framework, and PANI exhibits electron transfer and additional redox capability. Authors hypothesized possible mechanism of electron transfer where PANI itself acts as electrons transfer pathway from electrode to oxygen molecules and the COF-CNT structure acts as electrons transmission network in cathode. In another study, the same group (Sun et al., 2025) carried out investigation about synergistic Uranium (VI) removal and bioenergy recovery using PANI-derived covalent organic framework-carbon nanotube (PANI@COF-CNT). The reactor can achieve U(VI) removal efficiencies from 97.22% to 98.99%. Importantly, the microorganisms showed adaptive responses under U(VI) stress including suppressed membrane transport, increased xenobiotics degradation and metabolism and altered lipid metabolism.

4.4 CO₂ capture and adsorption properties

4.4.1 CO₂ capture

Carbon dioxide (CO₂) capture from industrial emissions and directly from the atmosphere is an important climate change mitigation technique. Solid adsorbent adsorption technology has advantages over liquid amine scrubbing in terms of lower energy demand for regeneration, less equipment corrosion and easier handling. PANI is a nitrogen-rich polymer and nitrogen-containing functional groups (amine, imine, pyridinic, pyrrolic) have strong affinity for CO₂ molecules through acid-base and dipole-quadrupole interactions (Shahat et al., 2024). However, bulk PANI has low surface area and poor porosity that limits its CO₂ adsorption capacity. The introduction of carbon nanomaterials creates hierarchical porous structures with large surface area and defined pore network, which significantly enhances the CO₂ capture performance. Zhang et al. (2025) introduced an innovative cryo-polymerization method for creating “3D-stereoscopic printing-like” porous carbon aerogels based on PANI for effective CO₂ adsorption. This approach facilitated the structured “stereoscopic printing” of PANI on the surfaces of polyacrylamide (PAM) pores, successfully avoiding PANI clumping. The nitrogen-rich aerogel prepared by activation showed the even distributed nitrogen atoms within the aerogel structure and higher N doping amount. The prepared hierarchical pore had ultrmicropores with 0.54–0.64nm which was appropriate for the CO₂ adsorption because the confined pores structure had improved the binding energy of CO₂. High capacity of CO₂ adsorption with 6.04 mmol/g was achieved at 0 °C and 101 kPa, and the prepared aerogel showed CO/N selectivity with 23.07 which was very important for separating CO₂ from flue gas. It also revealed the outstanding regenerative ability after many cycles adsorption and desorption.

4.4.2 Adsorption properties

For pollutants adsorption application, the removal of insecticide Carbofuran (CF) from aqueous solutions onto activated carbon/polyaniline composite has been studied by Rahim et al. (2025) who prepared the activated carbon from the date seeds by the activation agent using ZnCl₂. Different percent of polyaniline is loaded onto the activated carbon 5%, 10% and 20%. From these results, it is found that 5% of polyaniline loaded on activated carbon gives optimum amount (327.6 mg/g) than higher loading that resulted pore blockage and reduced capacity.

The removal efficiency of the composite at 120 min was 98.6% compared to 97.4% at 360 min of AC. So, PANI coated on the activated carbon accelerate the kinetics of adsorption. Pseudo-second-order rate kinetic model fitted well the adsorption behavior (R = 0.999), it can show that chemical adsorption is responsible for the adsorption. Langmuir isotherm model is the suitable adsorption isotherm models. And thermodynamic parameters shown that adsorption process is endothermic and spontaneous. Youssif et al. (2026) used a magnetic activated carbon composite AC/FeO/PANI- sodium dodecyl sulfate (SDS) to efficiently remove Pb(II) ions from the aqueous solutions. Each part of the magnetic activated carbon composite has a role; AC offers a large surface area for adsorption, magnetic iron oxide (FeO) makes it easy to remove the magnetic material from water systems using a magnet and PANI combined with SDS makes the material’s capacity to attract Pb ions higher. Maximum adsorption capacity of AC/FeO/PANI-SDS towards Pb(II) ions was calculated to be 348.39 mg/g under optimum conditions, including pH 6 and 220 min contact time. The adsorption kinetic studies fit pseudo second-order model with strong correlation coefficient and isotherm analysis was in accordance with Langmuir model with highest correlation coefficient. Thermodynamic investigation proved that elimination of Pb ions is endothermic and spontaneous reaction.

4.5 Electromagnetic interference shielding

EMI shielding is essential for contemporary electronic systems as external electromagnetic waves may couple with the circuitry and affect signal integrity, resulting in either device failure or data loss. As devices become smaller and operate at higher frequencies, shielding materials must provide not only high levels of attenuation but also a lightweight, flexible and stable performance. In this context, composite systems such as carbon/polyaniline have been extensively studied. This was demonstrated by Patel et al. (2025) with the use of theoretical and simulation methods; they discovered that the EMI shielding is determined greatly by the relative contributions of the reflection and absorption mechanisms. At lower levels of carbon nanotube loading, the primary mechanism for shielding is absorption, thus, the electromagnetic waves dissipated energy within the material will primarily be through dielectric losses and interfacial polarization. As the content of MWCNTs increases, there is a newly developed continuous conductive network, thus, providing an increase in electrical conductivity and causing a shift in the primary shielding mechanism from absorption to reflection. This transition allows for the adjustment of the shielding based upon the application requirements. The performance of electromagnetic interference shielding has been enhanced with the use of magnetic and polymer components. According to Hu et al. (2026), flexible bucky paper films that are made of carbon nanotube sheets containing Fe₂O₃ nanoparticles and polyaniline, introduce two mechanisms for EMI shielding in this material: one is due to the electrical conductivity of the CNTs, and the other comes from the magnetic loss mechanisms associated with the presence of the Fe₂O₃ nanoparticles. The presence of magnetic domains within the material interacts with the alternating electromagnetic field to produce energy dissipated through magnetic relaxation processes. Polyaniline also enhances dielectric loss and provides additional sites for interfacial polarization. Furthermore, the interfaces between the CNTs, polyaniline and the magnetic nanoparticles contribute to the increased performance of EMI shielding. Heterogeneous interfaces generate substantial interfacial polarization as charge carriers accumulate and then decay (relax) when subjected to alternating electromagnetic fields. The dielectric loss is significantly enhanced through this process. While the change in surface modification produces a small reduction in saturation magnetization, the total shielding effectiveness improves as the mechanisms associated with conductive, dielectric and magnetic loss become more balanced against each other.

4.6 Sensors

PANI-carbon nanocomposites have emerged as highly promising sensing materials due to their tunable electrical properties, reversible redox behavior, ease of synthesis, and compatibility with flexible platforms (Jain et al., 2026). The incorporation of carbon nanomaterials significantly enhances sensor performance by providing high surface area, excellent electrical conductivity, and abundant active sites for analyte interaction.

4.6.1 Humidity sensors

PANI is a preferred candidate for humidity sensor materials due to its unique hydration properties and electrical conducting mechanism that relies on molecular interactions between water and the hydrophilic sites of PANI. The conductivity of PANI is highly dependent on the ambient relative humidity (RH), making it suitable for humidity sensing applications. To enhance the hydrophilic properties of PANI, it can be modified by forming composites with biopolymers, such as chitosan, cellulose, and other polysaccharides that facilitate hydrogen-bonded composite formation. The moisture-responsive mechanism of PANI/biopolymer systems depends on two factors: (i) electron/proton hopping between water molecules and acidic nitrogen groups of PANI; and (ii) morphology changes of the composites under the influence of relative humidity. Anisimov et al. (2021) reviewed PANI/biopolymer composite systems for humidity sensor applications, emphasizing the interrelationship between core properties and moisture responsiveness, including swelling, water vapor adsorption capacity, porosity, electrical conductivity, and enthalpies of adsorption and vaporization. The key performance parameters for humidity sensors include response time, recovery time, and hysteresis error. PANI composites with carbon nanomaterials such as graphene oxide and carbon nanotubes have shown significantly improved humidity sensing performance due to enhanced surface area and charge transport pathways.

4.6.2 Gas sensors

PANI-based composites have found extensive applications in gas sensing due to their tunable electrical properties, environmental stability, and compatibility with flexible platforms (Jain et al., 2026). The gas sensing behavior of PANI composites arises from a combination of physicochemical interactions and electronic structure modifications, with the dominant mechanism determined by the composite’s composition, morphology, and the nature of the target analyte. Three principal sensing pathways can be distinguished: electron transfer across heterojunctions, redox-induced modulation of conductivity, and surface adsorption effects. Recent studies have demonstrated the potential of PANI-carbon composites for gas sensing applications. The integration with AI and IoT platforms represents the next wave of development, where machine learning algorithms process multi-sensor arrays, extract signatures from noisy baselines, and adapt to environmental drift platforms (Jain et al., 2026). This integration is particularly promising for smart city networks and environmental monitoring applications. PANI-carbon composites have been employed for detecting toxic gases, humidity variations, and pollutants with high sensitivity and selectivity, as well as for real-time freshness assessment and spoilage detection in the food industry by monitoring volatile organic compounds.

4.7 Thermoelectric applications

Thermoelectric (TE) materials enable direct conversion of heat to electricity and vice versa, representing a promising renewable energy alternative. However, low conversion efficiency of thermoelectric materials has restricted their applications, primarily due to the conflicting association between electrical conductivity (σ), thermal conductivity (k), and Seebeck coefficient (S) (Ebrahimibagha et al., 2025). Conducting polymer-based composite have attracted significant attention since σ, k, and S can be somewhat independently tuned in engineered nanocomposites, and because of their potential in flexible electronics. Carbon nanotube and polyaniline nanocomposites present huge promise for thermoelectric applications due to controllable π-π interaction between components (Ebrahimibagha et al., 2025). The PANI typically displays a low intrinsic thermal conductivity due to irregular polymer chains in the molecular structure and lower lattice thermal conductivity efficiency, making it an ideal matrix for thermoelectric composites. However, its flexibility and mechanical strength are deficient in practical usage, necessitating composite formation with other materials (Ebrahimibagha et al., 2025). Recent studies have demonstrated significant improvements in thermoelectric performance. Qian et al. (2026) developed a superaligned carbon nanotube (SACNT)/polyaniline (PANI) generator with enhanced thermoelectric properties, featuring a Seebeck coefficient of 47.5 μV K⁻¹ based on a rational design of three-times polymerization of PANI. Furthermore, the generator offers a maximum power output of 2.95 nW at a temperature difference of 25 K.

4.8 Anti-corrosion applications

Corrosion of metals represents a significant economic and safety challenge across industries, with annual costs exceeding trillions of dollars globally. PANI-carbon nanocomposites have emerged as promising anti-corrosion coating materials due to their unique combination of properties: electrical conductivity, redox activity, barrier properties, and ability to form passive oxide layers on metal surfaces (Deshpande et al., 2013; Beygisangchin et al., 2024). The anti-corrosion mechanisms of PANI-carbon composites involve two primary pathways: corrosion barrier effect and anodic protection (Sathiyanarayanan et al., 2005). The barrier effect relies on carbon nanomaterials to create impermeable barriers that prevent diffusion of corrosive species (O₂, H₂O, Cl⁻) to the metal surface. The redox capability of PANI enables the formation of passive oxide layers on metal surfaces through electrochemical reactions, promoting anodic protection (Sazou and Deshpande, 2017). PANI-MWCNT composites have demonstrated significantly enhanced anti-corrosion performance. Deshpande et al. (2013) reported that PANI-MWCNT composites in epoxy coatings on low-carbon steel in 3.5 wt% NaCl exhibited a corrosion rate of 0.037 mm y^-1, about 5.2 times lower than that of unpainted steel and 3.6 times lower than that of epoxy painted steel (Deshpande et al., 2013). This enhanced performance was attributed to improved mechanical strength, strong interfacial interactions, and uniform fibrous morphology providing effective barrier properties (Mahmoudian et al., 2012). Carbon dots modified PANI nanocomposites in acrylic resin coatings have also shown remarkable improvements. Ren et al. (2023) demonstrated that nitrogen-doped carbon dots (N-CDs) introduced as hard templates in the aniline polymerization system produced small-sized, monodisperse, and highly conductive N-CDs/PANI nanocomposites (Ren et al., 2023). The protection efficiency of the acrylic resin coating was increased by 5 times, reaching 57.3% with N-CDs/PANI addition, compared to 37.0% with PANI alone (Ren et al., 2023). Additionally, the coating exhibited antifouling properties with an algae inhibition rate of about 24.6%, attributed to the redox property of carbon dots destroying the photosynthesis of microorganisms such as Chlorella (Ren et al., 2023). The N-CDs/PANI also demonstrated better dispersibility than PANI, resulting in improved adhesion of the N-CDs/PANI-AC coating compared to PANI-AC coating (Ren et al., 2023). Advanced theoretical evaluations using Molecular Dynamics (MD), Monte Carlo (MC), and Density Functional Theory (DFT) simulations have provided valuable insights into PANI composite coating design (Moradi et al., 2025). Moradi et al. (2025) demonstrated that additives such as polyaminophenol (PAP), graphene (G), and gabapentin (GP) significantly enhance wear resistance, tensile and shear strength, and reduce free volume by up to 11.8%, thereby increasing resistance to corrosive agents (Moradi et al., 2025). The interaction energy between modified PANI coatings and the Fe substrate increased by up to 61%, improving adhesion and reducing delamination risks (Moradi et al., 2025). The penetration of water and chloride ions in the PANI/PAP/G/GP coating was 3.3 and 1.2 times lower than in pure PANI, demonstrating superior barrier properties (Moradi et al., 2025). Furthermore, the addition of PAP and G enhanced PANI’s electroactivity, conductivity, and redox reactivity, promoting the formation of a stable passive film on the Fe substrate (Moradi et al., 2025). The future of polymeric corrosion inhibitors will be shaped by the integration of green chemistry, nanotechnology, and computational modelling, enabling the rational design of high-performance anti-corrosion coatings tailored to specific metal substrates and environmental conditions (Beygisangchin et al., 2024; Sathiyanarayanan et al., 2005).

5 Structure-property-performance correlations

Carbon nanostructures are materials with special properties such as the large specific surface area; surface chemistry can be tailored by means of heteroatom doping (Chen et al., 2023; Ge et al., 2022; Wickramaratne et al., 2014), excellent isotropic geometry which allows the materials to disperse easily, and graphitization-dependent electrical conductivity (Nieto-Márquez et al., 2011; Serafin and Dziejarski, 2024). In combination with PANI matrices, carbon nanostructures allow more ion diffusion via the inter-particle voids and allows the material to be physically very stable. The performance of PANI/carbon composites is strongly influenced by the properties of the carbon phase. In particular, the specific surface area, electrical conductivity, dimensionality, and surface chemistry of the carbon material play important roles in determining the overall performance of the composite. A high specific surface area provides more active sites for PANI deposition and facilitates ion adsorption, while high electrical conductivity promotes efficient electron transport. In addition, the dimensionality and morphology of the carbon structure can influence the diffusion of ions and electrons and the distribution of PANI within the composite. Surface chemistry is also important because functional groups on the carbon surface can improve the interaction between the carbon, PANI, and electrolyte. Therefore, tailoring the structural and surface properties of the carbon phase is essential for developing high-performance PANI/carbon electrodes for supercapacitor applications. Understanding the relation of properties and performance of their structures to the whole is vital for the scientific composite designing and development of specific applications. A high specific surface area of carbon nanomaterials provides a greater number of active sites for the nucleation and growth of PANI chains. This promotes a more uniform distribution of PANI over the carbon surface and increases the accessibility of electroactive sites to electrolyte ions, thereby enhancing ion and electron transport and ultimately improving the electrochemical performance of the PANI/carbon composite. For example, starch-based porous carbon with surface area of 1561.60 m² g^-1 allows for regular growth of PANI nanowire achieving a specific capacitance of 482.8 F g^-1 and only 93.32% loss at the 10,000-cycle stage (Zhu et al., 2026). In another study of chitosan-derived porous carbon (1305 m² g^-1) combined with PANI using in situ polymerization, the authors reported 434.73 F g^-1 and energy density reached 86.9 Wh kg^-1 (Gala et al., 2025). However, excessive PANI loading can block or partially fill the pores of the carbon material, reducing the accessible surface area and hindering electrolyte-ion diffusion. This effect is clearly demonstrated by the decrease in specific surface area from 1305 to 238 m² g^-1 as the PANI content increased, as reported by Gala et al. (2025). Therefore, an appropriate PANI loading is essential to balance the contribution of pseudocapacitance with the preservation of the porous structure and accessible surface area. Conductive carbon nanomaterials can act as efficient electron-transport pathways, facilitating rapid electron transfer within PANI/carbon composites. The electrical conductivity of the carbon phase therefore plays a critical role in determining the rate capability and charge-transfer characteristics of the electrode. For example, PANI/CNT composites exhibited the highest conductivity, reaching 7.58 S cm^-1 when CSA was used as the dopant, whereas PANI/graphite and PANI/carbon black showed lower conductivities of 0.07 and 0.03 S cm^-1, respectively (Jelmy et al., 2013). The enhanced electrical conductivity facilitates faster electron transport and can contribute to improved rate capability and reduced charge-transfer resistance. In addition, the morphology of the carbon phase plays a crucial role in determining the structural, electrical, and electrochemical characteristics of PANI/carbon composites, as it influences the distribution of PANI, ion diffusion, electron transport, and the accessibility of active sites. Another important consideration is the cost and sustainability of the carbon precursor. Biomass-derived activated carbon offers the combined advantages of low cost, abundant availability, and environmental sustainability, making it a promising option for large-scale production. For example, a sludge-derived activated carbon/PANI (SAC-PANI) composite demonstrated high adsorption capacities for heavy metals, reaching 128.5 mg g^-1 for Pb(II) and 115.7 mg g^-1 for Cd(II), while benefiting from the low-cost nature of the sludge-derived carbon precursor (Adaileh et al., 2026). Similarly, a PANI/oxidized porous activated carbon (PANI/OPAC) composite prepared from agricultural residues achieved a Pb(II) removal capacity of 6.81 mg g^-1, while also exhibiting improved thermal and electronic properties (Mohammad et al., 2019). The use of biomass- and waste-derived carbon materials therefore not only reduces the cost of electrode or adsorbent production but also contributes to waste valorization and supports the principles of green chemistry, enhancing the potential for sustainable and large-scale applications.

The preceding sections have demonstrated the remarkable versatility of PANI-carbon nanocomposites across diverse application domains, from energy storage and electrochromic devices to environmental remediation and corrosion protection. Figure 10 summarizes the most significant metrics for each application area. Figure 10 illustrates that PANI-carbon nanocomposites consistently outperform pristine PANI across all applications, with improvements ranging from moderate enhancements to orders-of-magnitude increases in performance metrics. The data presented collectively demonstrate that the synergistic integration of PANI with carbon nanomaterials effectively addresses the inherent limitations of the polymer while unlocking new functionalities unattainable with either component alone.

Table 2 provides a detailed quantitative comparison of the key performance metrics for PANI-carbon nanocomposites across all applications discussed in this review. For each application, the table lists the carbon component, synthesis method, specific performance metrics, comparison to pristine PANI (where available), and the corresponding reference.

TABLE 2. Summary of performance metrics by application.

6 Key research gaps and future directions

Despite significant progress in PANI/carbon composites, several challenges remain unresolved. First, long-term operational stability when using practical operating conditions. Second, scalable and low-cost fabrication methods for high-performance flexible electrodes are not yet fully developed. Third, the application of machine learning to facilitate faster predictions of properties.

6.1 Long-term operational stability

While polyaniline composites typically provide good cycling stability in low-current-density acidic aqueous electrolytes, their long-term durability in realistic operating scenarios is still a significant concern. Both supercapacitors and batteries must operate stably for an extremely high number of cycles at high-current densities and within large voltage ranges (Karami et al., 2024). Under such extreme operating conditions there are multiple degradation processes that will dominate the performance of the device. Chain scission of polyaniline, which involves the breakage of the polymer’s conjugated backbone, will occur during the redox cycling of polyaniline when the volume of the polymer expands and contracts, causing a loss of strength in the adhesive bond between the polymer’s active material and its conductive substrate, resulting in delamination and a loss of electrical connections. In addition, carbon components of supercapacitors and batteries can also experience slow corrosion or other forms of structural damage that contribute to the loss of performance. These types of degradation processes may be accelerated in the presence of more rigorous electrochemical conditions, but few systematic investigations of these degradation processes under conditions of accelerated aging have been conducted (Banerjee et al., 2026). Various strategies have been proposed to enhance the chemical, electrochemical and mechanical stability of PANI. One approach that has demonstrated enhanced stability at the conductive carbon–polymer interface is by employing covalent grafting of PANI to the supporting carbonaceous substrate. This method strongly anchors the PANI polymer chains to the conductive substrate, producing improved interfacial stability. Conductivity can also progressively improve via strengthening of the PANI conductivity through the electron-withdrawing effect of the carbon substrate, thereby improving resistance to deprotonation and structural degradation of the emeraldine salt form of PANI (Li et al., 2021). In order for PANI to retain its stability as a conductive polymer in flexible or wearable devices, additional problems arise during repeated mechanical deformation such as bending, folding and/or stretching. Notwithstanding the demonstration of mechanical stability to limited numbers of cycles in most studies, the long-term mechanical durability of PANI-based systems remains uncertain (Cheng et al., 2024). Overall, improving long-term operational stability requires a multi-level approach. First, standardized accelerated testing protocols should be developed that simultaneously combine electrochemical cycling, mechanical stress, and environmental factors such as humidity and temperature. Second, advanced in-situ characterization techniques (e.g., Raman spectroscopy, TEM, and XPS) are needed to directly monitor structural and interfacial degradation mechanisms during operation. Finally, robust molecular engineering strategies, such as multi-point covalent anchoring of polymer chains onto carbon frameworks, should be designed to suppress interfacial delamination and ensure durable electrical contact under long-term cycling conditions.

6.2 Scalable green synthesis routes

Most high-performance PANI–carbon composites can be fabricated at milligram-gram scales using synthetic routes that generate considerable chemical waste and consuming high energy. Among them, chemical oxidative polymerization is the most scalable synthesis method and typically yield heterogeneous composite that contains large amount of free PANI aggregates which cannot be well-connected with the carbon phase, hence additional purification step is required, this can reduce the yield and increase the cost. Covalent conjugation can lead to high interface quality and cycle stability, but involves the use of hazardous coupling reagents and organic solvents (DMF and DMSO), and requires multistep purification which cannot be scaled up to tonne scale synthesis (Banerjee et al., 2026). Microwave-assisted and gamma irradiation can be carried out rapidly with very little waste generation, but are restricted by high capital cost associated with the instruments; furthermore, these methods have only been verified up to kilogram level so far (Qiu et al., 2025; Ieamviteevanich et al., 2025). Green synthesis should primarily focus on substituting corrosive mineral acids (HCI and H₂SO₄) by solid reusable organic acids (citric acid and ascorbic acid), designing water-based, surfactant-free dispersion methods with non-covalent modifiers such as lignin or tannic acid, developing continuous flow reactors in covalent conjugation approach to minimize the reaction time from days to hours with on-line purification process (Ieamviteevanich et al., 2025).

6.3 Machine learning assisted property prediction

The design space for PANI-carbon composites is enormous, comprising not just carbon source (e.g., CNT, graphene, activated carbon, carbon dots, etc.), but also carbon dimension (0D, 1D, 2D, 3D), loading (0.1–50 wt%), surface functionalization, synthesis method, dopant acid, and processing parameters. The sheer magnitude of the high dimensional space prohibits efficient exploration by conventional experimental methods and requires the use of ML. Boublia et al., 2024 employed random forest and neural network models, training on ∼500 PANI-carbon composite systems and predicted electrical conductivity and gas sensing response with R > 0.85 respectively. Feature importance analysis indicated that carbon loading and aspect ratio predominantly determine conductivity whereas the oxygen content of the composite surface governs sensing properties. Future progress in this field requires: (i) the creation and open access provision of a database of PANI-carbon composite properties with appropriate metadata principles; (ii) incorporation of physics based descriptors (e.g., binding energies from DFT calculations, Monte Carlo simulation-predicted percolation thresholds); (iii) prediction of uncertainties to guide future experimental work and (iv) incorporation of a closed loop discovery paradigm in conjunction with robotic synthesis. Accurate prediction of cycling stability presents more of a challenge, requiring time-dependent (capacitance vs. cycle number) data which are typically poorly reported in a standardized manner. Collaboration between experimentalists and theorists is urgently needed to advance this field.

6.4 Environmental sustainability and lifecycle assessment

The increasing global demand for sustainable materials has placed environmental sustainability at the forefront of materials research. PANI-carbon nanocomposites, while offering exceptional performance across multiple applications, must be evaluated not only for their functional properties but also for their environmental footprint throughout their entire lifecycle. Traditional PANI synthesis relies on the oxidative polymerization of aniline using strong inorganic oxidants such as ammonium persulfate, which generates substantial amounts of toxic and carcinogenic waste (Galloni et al., 2025). This approach has become increasingly less practicable due to stricter environmental regulations and pollution limits. Recent studies have therefore focused on developing “green” synthesis routes using more environmentally friendly oxidants such as molecular oxygen or hydrogen peroxide, and alternative reaction mechanisms that avoid the production of toxic by-products. Galloni et al. (2025) developed a novel green catalytic method using N-phenyl-p-phenylenediamine as a sustainable reagent, demonstrating improved biocompatibility of the resulting PANI. Importantly, they conducted a comparative life cycle assessment (LCA) study on PANI synthesis, comparing the traditional method with the “green” one to determine whether the latter truly reduces environmental impact. The use of biomass-derived carbon precursors offers significant sustainability advantages over synthetic carbon sources. Agricultural waste materials such as coconut husk, date seeds, sugarcane bagasse, and olive stones can be converted into activated carbon with high surface area and porosity, providing a low-cost and renewable alternative to fossil-derived carbon (Tomy et al., 2025; Zhao et al., 2011). Tomy et al. (2025) demonstrated the development of sustainable biocarbon with a high surface area from coconut husk waste for AC/PANI composite synthesis, confirming excellent specific capacitance with good cyclic stabilities. Zhao et al. (2011) employed lightweight balsa wood as a sustainable precursor for phosphoric acid-activated carbon modified with PANI, achieving a high specific capacitance of 539 F g^-1 at 0.5 A g^-1. Cow dung-derived carbons have also shown exceptional promise, developing high specific surface areas (>1000 m²/g) and hierarchical micro/mesoporous structures advantageous for both ion adsorption and charge storage, while valorizing a major husbandry waste stream. The end-of-life phase of PANI-carbon composites remains a critical and largely unexplored area. Carbon fibre reinforced polymer composites are notoriously difficult to recycle due to their permanent crosslinked networks, which resist conventional recycling methods and trap valuable nanomaterials within non-degradable matrices.

7 Conclusion

PANI-carbon nanomaterial composites represent a functional family of materials that successfully overcome several inherent disadvantages of pristine PANI. They include poor mechanical flexibility, negligible conductivity at neutral pH, and rapid capacitance decay during electrochemical cycling. The electrical, electrochemical, and electrochromic behaviors of these composites are tunable by varying the dimension and surface chemistry of carbon nanomaterials,ranging from 0D carbon dots and graphene quantum dots to 1D carbon nanotubes, 2D graphene and its derivatives, and 3D porous carbons. Each type of the carbon component imparts specific benefits: 0D particles facilitate the occurrence of quantum confinement phenomena and create many more edges; 1D nanotubes generate high-aspect-ratio conductive pathways; 2D graphene brings in excellent surface area and a great degree of charge mobility; and 3D porous structures help in good ion diffusion and mechanical stability. The use of covalent bond strategies and porous hierarchical structures have led to the realization of novel functionalities and excellent performance beyond normal supercapacitors such as microbial fuel cells, CO₂ capture, the application in shielding from electromagnetic interference, and in electrochromic devices that are flexible. The cooperation between PANI pseudocapacitive properties and carbon double-layer capacitance along with reinforcing effects has produced materials with highly improved properties: longevity, capability for fast charging/discharging and overall device performance. Despite these significant advances, three main issues have to be handled in order to speed up commercialization of the results: First, long-term operational stability under practical conditions, neutral pH environments, mechanical strain, and high current densities, requires more investigation by using uniform aging accelerated tests. Most of the research nowadays is carried out in lab settings, however, the durability aspect needs to be tested on material subjected to electrochemical and mechanical fatigue simultaneously. Second, scalable and green synthesis approaches are urgently needed to replace current energy-intensive and waste-producing routes. Third, the application of machine learning in material design would facilitate the identification of the best mix of ingredients and processes, and minimize the expense of trial-and-error methods. Collaborative efforts between experimentalists and computational scientists are essential to build comprehensive databases and develop predictive models for targeted material properties.

The development and commercialization of PANI-carbon nanocomposites carry significant policy implications across environmental, funding, and standardization domains. The shift toward biomass-derived carbon precursors and green synthesis aligns with the United Nations Sustainable Development Goals (SDGs), particularly SDG 7 (Clean Energy), SDG 9 (Innovation), SDG 12 (Responsible Consumption), and SDG 13 (Climate Action). Policymakers should incentivize green synthesis through tax benefits, research grants, and regulatory frameworks that replace hazardous chemicals with sustainable alternatives. Government agencies should prioritize interdisciplinary research integrating materials science, environmental science, and data science, while public-private partnerships can accelerate technology transfer and scale-up. International organizations such as ISO and ASTM should develop standardized testing protocols for PANI-carbon composites to enable fair comparison and regulatory approval.

The interplay between sustainable synthesis, advanced interfacial engineering, and machine learning-based prediction will be crucial for realizing the full potential of PANI-carbon nanocomposites. With continued interdisciplinary collaboration, these materials are poised to become key components in next-generation energy storage, environmental remediation, and smart electronic devices.

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Footnotes

Edited by: Mustapha Balarabe Idris, Federal University, Dutse, Nigeria

Reviewed by: Salamon Jonas, St Joseph’s College Tiruchirappalli Department of Chemistry, India

Magaji Ladan, Bayero University Faculty of Physical Sciences, Nigeria

Najlaa Jerjack, Wasit University College of Science, Iraq