A comparative study of electrochemical properties of CBD and SILAR grown Zn(OH) 2 thin films

This study investigates the electrochemical properties of zinc hydroxide (Zn(OH) 2) thin films synthesized through two distinct methods: chemical bath deposition (CBD) and successive ionic layer adsorption and reaction (SILAR). Notable variations in crystallite size, morphology, and bandgap energy were observed between the films synthesized using two methods. Specifically, a reduction in crystallite size was evident in films produced via the SILAR method, accompanied by an increase in bandgap energy. Morphological analysis revealed that CBD-deposited films exhibited a needle-like structure, while SILAR-synthesized films displayed a microflower-like texture. Electrochemical characterization in a 2 M KOH solution indicated that the Zn(OH) 2 needles and microflowers thin film electrodes achieved remarkable specific capacitances of 329 F/g and 179 F/g at a current density of 1 A/g, respectively. Furthermore, both films demonstrated impressive cycling stability, retaining 78% and 74% of their original capacitance after 3,000 cycles at a scan rate of 100 mV/s. The findings of this study elucidate the significant impact of growth methods on the electrochemical properties of Zn(OH) 2 thin films, providing valuable insights for the advancement of materials science and electrochemistry.

The rapid escalation in global energy consumption, driven by the continuous expansion of industrialization, urbanization, and technological advancement, has intensified the demand for efficient, sustainable, and high-performance energy storage systems (Mahanty et al., 2025; Mendoza et al., 2022). Traditional fossil-fuel-based energy sources are becoming increasingly unsustainable due to environmental concerns and limited availability, necessitating the exploration of clean, renewable alternatives (Tamoor and Zhang, 2025; Singh et al., 2025). In this context, advanced electrochemical energy storage devices, such as batteries and supercapacitors, have emerged as crucial components for bridging the gap between energy generation and utilization (Yi et al., 2021; Chodankar et al., 2023; Schoetz et al., 2022). Among these systems, supercapacitors, also known as electrochemical capacitors, have attracted significant attention owing to their superior power density, rapid charge–discharge performance, long cycle life, and cost-effectiveness compared to conventional batteries. Their ability to deliver high power within a short time frame makes them ideal candidates for applications in hybrid electric vehicles, portable electronics, and grid-stabilization systems (Pameté et al., 2023; Pawar et al., 2025). Unlike batteries, which rely on bulk diffusion processes for energy storage, supercapacitors store and release energy through surface or near-surface electrochemical processes, leading to enhanced reversibility and stability during extended cycling (Zhang et al., 2022; Cui et al., 2022).

Fundamentally, supercapacitors can be categorized based on their charge-storage mechanisms into two main types: electrochemical double-layer capacitors (EDLCs) and pseudocapacitors (Bachankar et al., 2024). EDLCs store energy via the physical adsorption and desorption of electrolyte ions at the electrode–electrolyte interface, forming an electrostatic double layer without involving any faradaic charge transfer. In contrast, pseudocapacitors operate via fast, reversible surface or near-surface redox reactions between electrolyte ions and the electrode active sites of materials, thereby providing higher energy densities than EDLCs (Kumbhar et al., 2025). The rational design and development of electrode materials that can effectively combine both mechanisms, offering high energy density while maintaining rapid charge kinetics, remain at the forefront of current research in electrochemical energy storage (Patil et al., 2023). In particular, transition metal oxides and hydroxides, including MnO 2, NiO, Ni(OH) 2, and Co(OH) 2 have been extensively explored due to their multiple oxidation states and fast reversible redox activity. These materials offer enhanced energy storage capabilities, positioning them as promising candidates for next-generation pseudocapacitors (Yue X. et al., 2023).

Among various hydroxides, zinc hydroxide (Zn(OH) 2) has emerged as a particularly attractive option due to its cost-effectiveness, abundance, facile synthesis, and favorable electrochemical performance (Elumalai et al., 2023; Huang et al., 2021; Mancharkar et al., 2024; Sasirekha and Arumugam, 2017). Zn(OH) 2 can be synthesized by diverse techniques such as chemical vapor deposition (CVD), chemical bath deposition (CBD), hydrothermal synthesis, electrodeposition, spin coating, and successive ionic layer adsorption and reaction (SILAR) (Gao et al., 2024; Jeong et al., 2022; Ulum and Kurniawan, 2017; Bazrafshan et al., 2015). Notably, the SILAR method is recognized for its low cost, reduced material wastage, and ability to prevent unwanted precipitation, making it highly suitable for large-scale applications (Gao et al., 2024; Bazrafshan et al., 2015) Likewise, the CBD method is advantageous for its simplicity, eco-friendliness, and scalability. The SILAR method is often regarded as a modified form of the CBD method (Li et al., 2025; Toma et al., 2025). Depending on the synthesis method and strategy, Zn(OH) 2 can be obtained in various nanostructures, including nanorods, nanotubes, and nanosheets, providing versatility for diverse electrochemical applications (Gao et al., 2024; Bazrafshan et al., 2015; Ulum and Kurniawan, 2017).

In this study, we present a facile and cost-effective strategy to fabricate zinc hydroxide thin films on stainless steel (SS) substrates via CBD and SILAR methods. Both techniques offer simple, low-temperature synthesis routes suitable for large-scale applications. Despite utilizing similar precursor systems, the two methods produce distinct film morphologies, mass loadings, and crystallinities, significantly influencing the electrochemical behavior of Zn(OH) 2. The CBD-derived Zn(OH) 2 film demonstrated higher specific capacitance and superior cycling stability compared to the SILAR counterpart, owing to its uniform growth and enhanced ion transport. This comparative approach highlights the importance of deposition technique in tailoring electrode properties for advanced supercapacitor applications.

Chemicals and materials

In this work, all chemicals utilized were of analytical grade. Zinc acetate Zn(C 4 H 6 O 4) 2 was selected as the source of zinc ions, and ammonium hydroxide (NH 4 OH) acted as the complexing agent during synthesis. Double-distilled water (DDW) was used as the solvent throughout the experimental procedure. SS (grade 304) foils with a thickness of 0.1 mm were obtained from a local supplier and employed as the substrate material.

Synthesis Zn(OH) 2 using CBD method

Zn(OH) 2 thin films were deposited onto SS substrates (dimensions: 5 × 1 cm 2, grade 304). An aqueous bath containing 0.1 M Zn(C 4 H 6 O 4) 2 and an optimized amount of NH4OH was prepared and stirred for 20 min. During the initial mixing process, a white precipitate appeared but gradually dissolved after adding excess ammonia, yielding a clear solution with a pH of approximately 12 ± 0.1. Ammonia functioned as a complexing agent, preventing rapid precipitation and facilitating controlled nucleation and uniform film growth on the substrate surface. The prepared solution was then poured into a beaker containing pre-cleaned SS substrates, which were positioned vertically in the bath. The reaction was maintained at 50 °C for 2 h, allowing the direct formation of Zn(OH) 2 films on the SS surface. A schematic illustration of the CBD process for Zn(OH) 2 deposition on SS is presented in Figure 1a. After deposition, the films were thoroughly rinsed with DDW, air-dried at room temperature, and designated as Zn−C for subsequent analyses. The mass loading of the Zn−C electrode was determined using the gravimetric (weight difference) method by measuring the weight of the cleaned SS substrate before deposition and after complete film growth using a high-precision analytical balance. The mass loading of the Zn−C electrode was found to be ∼0.8 mg cm −2.

Synthesis of Zn(OH) 2 using SILAR method

For the fabrication of Zn(OH) 2 thin films by the SILAR technique, three separate solutions were prepared. Beaker A contained 50 mL of 0.1 M zinc acetate [Zn(C 4 H 6 O 4) 2 ], beaker B contained 50 mL of double-distilled water (DDW), and beaker C contained 50 mL of 2 M aqueous ammonia solution. Throughout the deposition process, the ammonia bath (beaker C) was maintained at 50 °C. The pre-cleaned SS substrates were first immersed in the zinc precursor solution for 5 s to allow adsorption of Zn 2+ ions, followed by rinsing in DDW for 5 s to remove loosely bound species. The substrates were then transferred to the heated ammonia solution for 10 s to facilitate the formation of Zn(OH) 2. This sequence constituted a single SILAR cycle. A total of 50 deposition cycles were carried out to achieve uniform film growth on the SS substrates. A schematic representation of the deposition procedure is provided in Figure 1b. After deposition, the films were thoroughly washed with DDW to remove any residual precursors, allowed to dry naturally at ambient conditions, and subsequently subjected to further characterization. The Zn(OH) 2 thin films prepared via the SILAR route were designated as Zn−S. The mass loading of the Zn−S electrode was found to be ∼1 mg cm −2.

Characterizations

The structural properties of the Zn(OH) 2 thin films were characterized by X-ray diffraction (XRD) using a Bruker D8 diffractometer with Cu Kα radiation (λ = 1.5406 Å), and the diffraction patterns were recorded over a 2θ range of 20°–80°. Chemical bonding and functional groups were analyzed through Fourier-transform infrared (FTIR) spectroscopy in the wavenumber range of 4,000–450 cm −1. Optical absorption behavior was investigated using a JASCO V-670 UV–visible spectrophotometer. The surface morphology and elemental distribution of the films were examined using a JEOL JSM-6360A scanning electron microscope equipped with an Oxford energy-dispersive X-ray spectroscopy (EDS) detector. Electrochemical measurements were carried out on a ZIVE BP2 electrochemical workstation employing a conventional three-electrode configuration. In this setup, the synthesized Zn(OH) 2 thin films acted as the working electrode, a platinum wire served as the counter electrode, and a Hg/HgO electrode was used as the reference electrode. All electrochemical tests were performed in 2 M KOH aqueous electrolyte. The charge-storage behavior was evaluated by cyclic voltammetry (CV) at scan rates between 5 and 100 mV/s. Galvanostatic charge–discharge (GCD) measurements were conducted at applied current densities of 1, 2, 3, and 4 A/g. Electrochemical impedance spectroscopy (EIS) was performed at open-circuit potential across a frequency range extending from 100 kHz to 100 mHz to assess the charge-transfer and ion-transport characteristics. The durability of the electrodes was further examined through prolonged cycling tests, where the capacitance retention was monitored over 3,000 consecutive cycles at a scan rate of 100 mV/s.

Reaction mechanism

The CBD process involves the generation of a solid phase from a liquid precursor and typically progresses through two fundamental steps: nucleation and subsequent growth (Toma et al., 2025). In the nucleation stage, molecular species present in the solution undergo controlled decomposition under appropriate pH and temperature conditions, leading to the formation of stable nuclei on the substrate surface through heterogeneous nucleation. These nuclei subsequently grow by the continuous incorporation of Zn 2+ and OH − ions, resulting in the formation of a continuous Zn(OH) 2 thin film (Sengupta et al., 2023; Oliva et al., 2022). In the present work, zinc acetate and aqueous ammonia constitute the precursor system, where ammonia plays a dual role as both a complexing agent and an OH − source. Initially, Zn 2+ ions form soluble zinc–ammonia complexes (e.g., [Zn(NH 3) 4 ] 2+), which effectively regulate the free Zn 2+ ion concentration in the solution. This controlled complexation suppresses rapid homogeneous precipitation and enables the gradual release of Zn 2+ ions as the equilibrium shifts during deposition. Simultaneously, NH 4 OH provides OH − ions through partial dissociation, maintaining a highly alkaline environment (pH ≈ 11–12), which promotes the controlled formation of Zn(OH) 2 according to the following reaction:

The sustained release of Zn 2+ ions from the zinc–ammonia complexes, together with the continuous supply of OH − ions, results in a relatively low supersaturation level that favors heterogeneous nucleation on the SS substrate over homogeneous precipitation in the bulk solution. Because the entire deposition bath is maintained at 50 °C throughout the reaction, nucleation and crystal growth occur continuously, allowing the nuclei to grow into well defined needle-like Zn(OH) 2 nanostructures with improved crystallinity, high porosity, and strong adhesion to the substrate. The resulting Zn(OH) 2 is deposited as a white film on the SS substrate.

In contrast, the SILAR process follows a stepwise adsorption–reaction mechanism rather than continuous crystal growth. During each deposition cycle, the substrate is first immersed in the zinc precursor solution, where Zn 2+ ions are adsorbed onto the substrate surface. The subsequent rinsing step with deionized water removes weakly adsorbed ions and prevents unwanted homogeneous precipitation. The substrate is then immersed in the NH 4 OH solution maintained at 50 °C, where the adsorbed Zn 2+ species react with OH − ions to form Zn(OH) 2. Since each deposition cycle is separated by rinsing and repeated adsorption, nucleation is repeatedly initiated rather than continuously sustained, resulting in discontinuous crystal growth. Furthermore, unlike the CBD process, only the alkaline solution is maintained at an elevated temperature, while the adsorption and rinsing steps occur at room temperature. Consequently, crystal growth kinetics are comparatively slower, producing microflower-like Zn(OH) 2 structures with relatively lower crystallinity and a smaller specific surface area. Therefore, the differences in zinc–ammonia complex chemistry, pH-controlled ion release, and nucleation kinetics between the CBD and SILAR methods play a decisive role in determining the final morphology, crystallinity, and electrochemical properties of the Zn(OH) 2 thin films.

Physicochemical study

The crystal structure of the Zn(OH) 2 thin films prepared by different deposition routes was investigated through XRD analysis, and the corresponding patterns are presented in Figure 2a. All observed diffraction peaks can be indexed to the orthorhombic phase of Zn(OH) 2, in good agreement with the standard reference data (JCPDS No. 00-048-1066). The diffraction patterns of both Zn-C and Zn-S films exhibit prominent reflections associated with the (100), (002), (101), (102), (110), and (103) crystallographic planes, confirming the successful formation of Zn(OH) 2. Compared with the SILAR-derived film, the Zn-C sample synthesized by the CBD method shows stronger diffraction intensities, indicating a higher degree of crystallinity. This enhancement is likely related to the continuous growth process characteristic of the CBD technique, which promotes improved crystal development. The peaks identified by the symbol (#) are attributed to the underlying SS substrate. The average crystallite size of the Zn(OH) 2 films was subsequently estimated using the Scherrer equation (Equation 2) (Malavekar et al., 2020),

In this equation, D denotes the average crystallite size, K represents the shape factor (typically assumed to be 0.94), λ is the wavelength of the incident X-rays (1.54 Å for Cu Kα radiation), β corresponds to the full width at half maximum (FWHM) of the selected diffraction peak, and θ is the Bragg angle associated with that reflection. Based on the Scherrer analysis, the average crystallite sizes of the Zn-C and Zn-S thin films were estimated to be 34 nm and 27 nm, respectively. These results suggest that the choice of deposition technique has a pronounced effect on the crystallite growth and microstructural characteristics of the resulting films.

Figure 2b displays the FT-IR spectra of the Zn-C and Zn-S thin films, providing information on the vibrational characteristics of the chemical bonds present in the materials. FT-IR spectroscopy identifies functional groups through their characteristic absorption of infrared radiation at specific frequencies. The broad absorption features observed in the 3,806–3,793 cm −1 region are associated with O–H stretching vibrations originating from structural hydroxyl groups and physically adsorbed water molecules (Gao et al., 2024). The band located near 1,607 cm −1 is assigned to the bending vibration of adsorbed water, whereas the peaks appearing around 1,033, 896, and 856 cm −1 correspond to Zn–OH bending modes, confirming the hydroxide nature of the films (Faheem et al., 2022; Rauf et al., 2021). Furthermore, the absorption signal detected at approximately 2340 cm −1 is attributed to atmospheric CO 2 molecules adsorbed on the sample surface (Gordeeva et al., 2020; Khanom and Hayashi, 2021). The optical properties of the Zn(OH) 2 thin films were further examined using UV–visible absorption spectroscopy in the wavelength range of 400–750 nm, as illustrated in Figure 2c. The optical band gap values were estimated from Tauc plots derived from the absorption data. The calculated band gap energies were 3.19 eV for the CBD-grown Zn-C film and 3.34 eV for the SILAR-derived Zn-S film, indicating a slight variation in the electronic structure resulting from the different deposition methods.

The influence of the deposition technique on the surface morphology of the films was investigated by SEM analysis, and the corresponding micrographs are presented in Figure 3. The Zn-C film synthesized through the CBD process consists of densely packed, vertically aligned needle-like structures that are uniformly distributed across the SS substrate. Such a morphology is advantageous for electrochemical applications, as it offers a larger surface area and a greater number of electrochemically active sites, facilitating efficient charge storage. The average width of these needle-like features was found to be approximately 0.5 μm. In comparison, the Zn-S film exhibited a distinct microflower-like architecture composed of uniformly dispersed flower-shaped assemblies with lateral dimensions ranging from 300 to 600 nm. These interconnected microflowers create a porous network with abundant accessible surface sites that can contribute to charge accumulation. Energy-dispersive X-ray spectroscopy (EDS) analysis of both samples verified the presence of zinc and oxygen as the major constituents, with elemental ratios consistent with the formation of Zn(OH) 2. The corresponding atomic percentages of Zn and O are provided in the insets of the respective EDS spectra.

The BET analysis of the Zn−C and Zn−S films, shown in Figure 4, demonstrates the significant influence of the deposition technique on the textural properties of the materials. The N 2 adsorption–desorption isotherms of both samples display typical type−IV behavior accompanied by an H3 hysteresis loop, indicating the presence of mesoporous structures. The calculated specific surface areas were 17.63 m 2 /g for Zn−C and 8.59 m 2 /g for Zn−S, revealing a substantially larger accessible surface in the Zn−C film (Figure 4a). In addition, pore-size distribution analysis based on the Barrett–Joyner–Halenda (BJH) model, using the desorption branch of the isotherm, yielded average pore diameters of 16.34 nm for Zn−C and 17.89 nm for Zn−S (Figure 4b). The enhanced surface area observed for the CBD-derived Zn−C sample is likely associated with its highly crystalline nature and distinctive needle-like architecture, which provide a greater number of exposed surface sites.

Electrochemical performance

The CV responses of the Zn-C and Zn-S thin-film electrodes measured at various scan rates are displayed in Figures 5a,b. Among the two electrodes, the Zn-C film demonstrates a higher current response at a scan rate of 100 mV/s, indicating enhanced electrochemical activity. The overall shape of the CV curves remains largely unchanged with increasing scan rate for both electrodes, suggesting favorable reversibility and stable charge-storage behavior. The well defined redox peaks observed in the CV curves indicate that the charge-storage behavior of the Zn(OH) 2 electrodes is predominantly governed by reversible Faradaic redox reactions occurring at the electrode/electrolyte interface. In the alkaline electrolyte, OH − ions actively participate in the charge storage process through the reversible oxidation and reduction of Zn(OH) 2, which can be represented by the following reaction (Equation 3) (Mancharkar et al., 2024; Sasirekha and Arumugam, 2017).

During the charging process, Zn(OH) 2 is oxidized to ZnOOH with the release of an electron, while the reverse reduction reaction occurs during discharge, regenerating Zn(OH) 2. This reversible redox process is responsible for the pronounced redox peaks in the CV curves and the distinct voltage plateaus observed in the GCD profiles, confirming the pseudocapacitive charge-storage mechanism of the Zn(OH) 2 electrodes.

The specific capacitance values of the Zn-C and Zn-S thin films were determined from the CV data using the following Equation 4 (Malavekar et al., 2024): where ∫ i dν (AV) denotes half of the integrated area enclosed by the CV curve, m (g) corresponds to the mass of the electroactive material coated on the current collector, ν (mV/s) represents the scan rate employed during the CV measurement, and Δ V (V) is the applied potential window. Based on the CV analysis, the specific capacitance values of the Zn-C and Zn-S electrodes were calculated to be 402 and 238 F/g, respectively, at a scan rate of 5 mV/s. The reproducibility of Zn-C and Zn-S electrodes for the stable electrochemical performance was assessed by independently fabricating five Zn(OH) 2 electrodes under identical synthesis conditions. The specific capacitance values obtained from CV curves of these electrodes measured at scan rate of 5 mV/s showed only slight deviations, indicating excellent fabrication reproducibility and measurement reliability. The Zn-C electrodes exhibited specific capacitance values ranging from 392 to 410 F/g, whereas the Zn-S electrodes displayed specific capacitance values in the range of 230–242 F/g, demonstrating excellent electrode-to-electrode reproducibility for both fabrication methods. The corresponding reproducibility data are provided in the Supplementary Material (Supplementary Figure S1), demonstrating that the reported electrochemical performance is consistent of the prepared electrodes.

To further elucidate the charge-storage kinetics and distinguish the contributions from different electrochemical processes in the electrodes prepared by the two deposition techniques, the power-law model was subsequently applied as Equation 5 (Banerjee et al., 2025):

The dependence of current density on scan rate was further examined using a logarithmic plot, as presented in Figure 5c. The calculated b -values were found to be 0.66 for the Zn–C electrode and 0.73 for the Zn–S electrode. Since both values lie between 0.5 and 1.0, the charge storage process is governed by a combination of diffusion-limited ion transport and surface-controlled capacitive effects. The relatively lower b -value of Zn–C suggests a greater contribution from diffusion-controlled charge storage compared with Zn–S. To gain further insight into the charge storage kinetics, the current response was subsequently evaluated using the modified power-law relationship given in Equation 6 (Liu et al., 2025):

The relationship between i / v 0.5 against v 0.5, shown in Figure 5d, was utilized to determine the k 1 and k 2 parameters, enabling the separation of capacitive and diffusion-governed charge storage contributions. Analysis revealed that the Zn–C electrode possessed a greater diffusion-controlled contribution to charge storage, accounting for nearly 78% of the total current at a scan rate of 5 mV/s, whereas the corresponding contribution for the Zn–S electrode was approximately 71% (Figures 5e,f). As the scan rate increased, the proportion of surface-controlled capacitive processes became more pronounced for both electrodes. Nevertheless, at 100 mV/s, the Zn–S electrode exhibited a larger capacitive contribution of 64%, compared to 56% for the Zn–C electrode, indicating a stronger surface-controlled charge-storage behavior at higher scan rates.

In addition, the charge–discharge behavior of the electrodes was investigated at various applied current densities using GCD measurements. As illustrated in Figures 6a,b, both Zn-C and Zn-S electrodes exhibit characteristic non-linear charge–discharge curves, confirming the predominance of pseudocapacitive charge-storage mechanisms. The specific capacitance values of the electrodes were subsequently calculated from the GCD data using Equation 7 (Thomas et al., 2024; Nabeel et al., 2025). where Δ t (s) represents the discharge duration, Δ V (V) denotes the applied potential window during the GCD measurement, i (A/g) is the applied current density, and m (g) corresponds to the mass of the electrochemically active material. The variation of specific capacitance with current density for the Zn-C and Zn-S electrodes is presented in Figure 6c. At a current density of 1 A/g, the Zn-C electrode exhibits a significantly higher specific capacitance of 329 F/g, whereas the Zn-S electrode delivers a lower capacitance value of 179 F/g, indicating the superior charge-storage capability of the Zn-C thin film.

Figure 6d shows the Nyquist spectra of the Zn-C and Zn-S thin-film electrodes recorded within a frequency range of 100 kHz to 100 mHz. These spectra were analyzed to investigate the charge transport and interfacial kinetics of the electrodes. The point where the impedance curve intersects the real axis (Z′) in the high frequency region represents the equivalent series resistance (R s). The semicircular feature appearing at high frequencies corresponds to the charge-transfer resistance (R ct), whereas the sloped region at lower frequencies is associated with the Warburg diffusion impedance (W), reflecting ion transport within the electrode/electrolyte interface (Lazanas and Prodromidis, 2023; Perdana et al., 2024; Panchal et al., 2025; Anantharaj and Noda, 2020). The Zn-C and Zn-S electrodes exhibited comparable R s values of 0.72 and 0.78 Ω/cm 2, respectively, indicating similar intrinsic and contact resistances. In contrast, noticeable differences were observed in their charge-transfer behavior. The R ct values were determined to be 25.36 Ω/cm 2 for Zn-C and 31.98 Ω/cm 2 for Zn-S, suggesting more favorable electron-transfer kinetics in the Zn-C electrode. Likewise, the calculated Warburg impedance values were 0.0015 Ω/cm 2 and 0.0082 Ω/cm 2 for Zn-C and Zn-S, respectively, indicating faster ion diffusion in the Zn-C thin film.

The cyclic stability of the electrodes was further assessed through repeated charge–discharge measurements at a scan rate of 100 mV/s, as illustrated in Figures 7a,b. A gradual decline in specific capacitance was observed for both samples as the number of cycles increased, which may be related to irreversible electrochemical processes and partial loss of active sites during prolonged cycling. After 3,000 cycles, the Zn−S electrode maintained 74% of its original capacitance, whereas the Zn−C electrode preserved 78%, indicating slightly improved cycling stability for Zn−C. Overall, the results demonstrate that the Zn−C thin film combines higher capacitance with enhanced long-term electrochemical stability compared to the Zn−S electrode. The electrochemical performance of representative Zn−based electrode materials reported in the literature is compared in Table 1, considering their morphology, electrolyte, and charge-storage characteristics.

The superior electrochemical performance of the CBD-grown Zn(OH) 2 electrode can be attributed to its distinct growth mechanism. In the CBD process, the gradual release of Zn 2+ ions from zinc–ammonia complexes promotes controlled nucleation and crystal growth, resulting in a highly porous needle-like structure with improved crystallinity and larger specific surface area. These characteristics enhance electrolyte penetration, increase the number of electroactive sites, and facilitate rapid ion diffusion, leading to a higher specific capacitance (329 F g −1 at 1 A g −1) and better cycling stability (78% retention after 3,000 cycles). In contrast, the SILAR process produces microflower-like structures through successive adsorption and reaction cycles, resulting in comparatively lower crystallinity and surface area. Consequently, the SILAR-grown electrode exhibits reduced electrolyte accessibility and electrochemical activity, yielding a lower specific capacitance (179 F g −1 at 1 A g −1) and slightly lower capacitance retention (74% after 3,000 cycles). These results demonstrate that the growth mechanism plays a crucial role in determining the structural and electrochemical properties of Zn(OH) 2 electrodes.

This study highlights the significant influence of the deposition technique on the structural, morphological, and electrochemical characteristics of Zn(OH) 2 thin films. Although both samples crystallized in the same orthorhombic phase, notable differences in morphology and electrochemical behavior were observed. The film prepared via the CBD route developed a needle-like architecture and delivered a superior specific capacitance of 329 F/g, along with a capacitance retention of 78% after 300 charge–discharge cycles. In contrast, the SILAR-derived microflower-structured film exhibited a lower specific capacitance of 179 F/g and retained 74% of its initial capacitance under identical cycling conditions. The superior electrochemical performance of the CBD-grown Zn(OH) 2 film can be attributed to its highly porous needle-like morphology, enhanced crystallinity, larger specific surface area (17.59 m 2 /g), and greater abundance of electrochemically active sites, all of which facilitate efficient electrolyte penetration, rapid ion diffusion, and improved charge storage. Despite these differences, both electrodes demonstrated satisfactory cycling durability, indicating their suitability for prolonged energy-storage operation. These results emphasize that precise control over synthesis methodology is essential for improving the electrochemical performance of Zn(OH) 2 -based electrodes and advancing their application in high performance supercapacitor systems.