Experimental investigation of hydrogen solubility in water, NaCl solutions, and deep saline reservoir fluids from the Ketzin site under subsurface conditions

1 Introduction

Hydrogen (H 2) is increasingly recognized as a key energy carrier for a low-carbon energy transition due to its flexibility to balance fluctuations in renewable energy supply and its potential for large-scale storage. Subsurface hydrogen storage (UHS) in deep geological formations is considered a promising solution because of the large storage capacity and structural integrity of saline aquifers. A critical factor influencing storage performance is the solubility of hydrogen in formation fluids, as the dissolved fraction affects gas phase behavior, effective storage capacity, and possible geochemical interactions with reservoir waters. Hence, accurate solubility data under reservoir-relevant pressures, temperatures, and salinities are essential for reliable site assessment and predictive modeling.

Hydrogen’s non-polar nature leads to relatively low solubility in water compared to other gases such as SO 2 or H 2S. Solubility generally increases with pressure and decreases with temperature and salinity due to the salting-out effect (Wiebe and Gaddy, 1934; Morrison and Billett, 1952). Early experimental datasets, including the classical measurements by Wiebe and Gaddy (1934), Morrison and Billett (1952), and Crozier and Yamamoto (1974), provided the basis for empirical correlations but are limited in their range of pressure and salinity. More recent high-pressure measurements have significantly extended the available data. Chabab et al. (2020) measured high-pressure H 2 solubility in H 2O + NaCl brine under conditions relevant for geological hydrogen storage and developed predictive models incorporating salting-out effects. Torin-Ollarves and Trusler (2021) conducted high-pressure solubility experiments and provided correlations describing combined temperature, pressure, and salinity. Chabab et al. (2024) later expanded this dataset to a wider range of temperatures, pressures, and molalities, refining thermodynamic models for reservoir applications.

Beyond experimental approaches, thermodynamic and molecular simulation studies have enhanced predictive capability for hydrogen solubility in brines (Li et al., 2018; Dehghani et al., 2024). Molecular simulations and machine learning models, in combination with Krichevsky–Kasarnovsky-based thermodynamic frameworks, have extended solubility predictions to higher temperatures and pressures beyond the current experimental range (Dehghani et al., 2024). Experimental high-pressure datasets, such as those reported by Torin-Ollarves and Trusler (2021), provide essential validation for these models and highlight the salting-out effect of NaCl. Overall, these modeling efforts consistently indicate the dominant control of salinity on hydrogen solubility, while highlighting persisting uncertainties due to the limited availability of authentic reservoir fluid data.

Despite these advances, most available data pertain to simplified water–NaCl systems or modeled estimates, leaving questions about H 2 behavior in natural formation fluids that typically contain multiple ions and minor components potentially affecting solubility and transport. Therefore, experimental validation using genuine reservoir brines is essential to calibrate thermodynamic models and quantify realistic dissolved hydrogen fractions.

The Ketzin pilot site in Germany, originally developed for CO 2 storage research, provides a well-characterized deep saline reservoir condition suitable for hydrogen storage investigations. Its detailed geological and geochemical site characterization offers a robust framework for evaluating hydrogen solubility in reservoir-relevant brines. In this study, we present laboratory investigations of hydrogen solubility in water, NaCl solutions, and Ketzin deep saline reservoir fluids under subsurface-relevant pressure and temperature condition. The generated dataset includes, for the first time, experimentally determined hydrogen solubility data for multi-ion reservoir brines. Our results advance the understanding of H 2 dissolution in realistic reservoir environments and provide a valuable basis for future assessments and modeling studies of hydrogen storage at the Ketzin site.

2 Experimental methods and materials

The experimental investigations are based on a closed, isothermal system to determine the solubility of hydrogen in pure water or brine solutions. A known volume of brine is placed in a sealed reactor and subsequently pressurized with hydrogen to a target pressure. The system is stirred to ensure homogeneous mixing and to facilitate gas–liquid mass transfer. Hydrogen dissolves in the liquid phase until thermodynamic equilibrium is reached, at which point the partial pressure of hydrogen in the gas phase remains constant. The solubility of hydrogen was determined from the measured initial and final pressures, taking into account the known total reactor volume, the volume of the liquid, and the system temperature. From these values, the actual hydrogen solubility was calculated. This approach allows a determination of hydrogen solubility under controlled p-T-conditions.

The experiments in this work were conducted in four series, as summarized in Table 1. The measurements were performed under isothermal conditions (295.15 K, 323.15 K, 348.15 K and 373.15 K) and ranged from 50 to 200 bar including four pressure steps. Each experiment was conducted with a constant stirring speed of 800 rpm during hydrogen dissolution. Due to the limited amount of well brine available, only two temperature steps were measured in this measurement series.

TABLE 1. Summary of the experimental series conducted in this work.

For the calculation of solubility from the experimental data, it was first necessary to determine the exact volume of the reactor, including all components such as fittings, manometers, valves and tubing. For this approach, an ISCO pump (Teledyne LABS) was connected to the reactor’s free outlet valve. Water was injected into the reactor in several steps, which increased the gas pressure (maximum pressure was 30 bar). The amount of water added at each step was recorded directly from the pump. Using the Boyle–Mariotte law from Equation 1, the reactor volume was then calculated from the measured pressure changes and the corresponding water volumes, where: V 1 = initial gas volume (target reactor volume), V 2 = V 1 – amount of water added, P 1 = initial pressure, P 2 = pressure after water injection.

P 1 V 1 = P 2 V 2 (1)

The experimentally determined reactor volume of ∼ 666 ml was used in subsequent hydrogen solubility calculations (see Section 3).

2.1 Materials

Suppliers and purities of gases and chemicals used in this work are given in Table 2. Brines were prepared using deionized and degassed water. The synthetic brine was used immediately after preparation, and a fresh batch was prepared for each experiment. Table 3 summarizes the elemental composition of the Ketzin synthetic brine compared with the Ketzin well brine obtained by ICP–OES (Inductively Coupled Plasma–Optical Emission Spectroscopy). The measured densities of both brines at 293.15 K are also given. The elemental composition of the synthetic brine agrees well with the ICP-OES analysis of the natural well brine. The slightly higher density of the well brine (1.151 g cm^-3) compared with the synthetic brine (1.134 g cm^-3) indicates a modestly higher overall salinity, consistent with concentration effects during storage.

TABLE 2. Chemicals and gases used in this work: purities and suppliers.

TABLE 3. Composition of Ketzin synthetic brine (SB) and well brine (WB) (analyzed with ICP–OES).

2.2 Experimental setup

The experimental setup consists of a novoclave reactor system (Büchi AG, Uster, Switzerland) which allows operating pressures up to 500 bar and temperatures up to 673.15 K. A schematic overview of the apparatus is presented in Figure 1. The pressure vessel, manufactured from Hastelloy C22 and sealed with a nickel gasket, has a nominal internal volume of 600 mL. Temperature control is provided by a 2000 W electric heating unit equipped with an integrated water circulation system. The temperature control within the reactor was maintained with an accuracy of ± 0.5 %, and pressure was measured using a reactor pressure transducer with an accuracy of ± 0.1 %.

The reactor is additionally fitted with a pressflow gas controller (Büchi VD Block, overall accuracy of ± 2 %) with an integrated gas feed regulator, a temperature cascade controller, and a cyclone 075 dc magnetic stirrer M. System operation and data acquisition are performed using the provided bls 3 software (Büchi, 2021).

The measurement of H 2 solubility was performed according to the following standard procedure (with reference to Figure 1):

• Charge the reactor (pressure vessel) with 550 g of distilled water/brine solution.
• Set the desired operating temperature.
• Purge the reactor three times with nitrogen (5 bar) to remove air (for safety reasons).
• Purge the reactor with hydrogen (4 bar).
• Pressurize the reactor with H 2 until the first target pressure is reached and wait for temperature stabilization
• Close the inlet valve V1.
• Start the magnetic stirrer M at 800 rpm.
• Wait until the system reaches equilibrium.
• Stop the magnetic stirrer.
• Open the inlet valve V1 and pressurize the reactor to the next target pressure.

The experimental setup did not allow evacuation of the autoclave prior to the measurements. Therefore, a sequential purging procedure consisting of three nitrogen purges (5 bar) followed by a hydrogen purge (4 bar) was applied to remove residual atmospheric gases from the gas phase. Since the brines were prepared using degassed water and the gas phase was replaced by hydrogen before pressurization, the amount of residual dissolved gases is expected to be minor. In addition, the experimental hydrogen pressures (50–200 bar) were substantially higher than the purging pressure, so that any remaining residual gases are expected to have a negligible influence on the measured pressure decrease and the calculated hydrogen solubility.

Figure 2 shows a typical pressure–time profile of a hydrogen solubility experiment conducted at 100 °C over a pressure range of 50–200 bar. After the attainment of solubility equilibrium at each pressure step (typical equilibration time was 30–40 min), the system was maintained under isobaric conditions for several hours to ensure that the dissolution process was finished. The absence of any significant pressure loss during these holding periods verifies the tightness of the experimental setup and the reliability of the measurement system under high-pressure conditions.

3 Experimental results and discussion

The experimental results of this work are divided in three experimental series: Hydrogen solubility in water (Section 3.1), Hydrogen solubility in 3 M NaCl brine (Section 3.2) and Hydrogen solubility in Ketzin synthetic and well brine (Section 3.3). All experiments were carried out in a closed system under non-ideal conditions with pressures ranging from 50 to 200 bar and temperatures between 295.15 and 373.15 K. Since the applied pressures and temperatures exceed the validity limits of ideal gas assumptions, a real gas behavior of hydrogen was taken into account.

The calculation of the dissolved hydrogen amount was based on the mass balance of hydrogen in the closed system before and after dissolution into the liquid phase. Instead of using ideal gas relations, real hydrogen densities were employed to accurately describe the thermodynamic state of hydrogen at elevated pressures. For each experiment, the hydrogen density corresponding to the measured pressure and temperature was obtained from the NIST database nis (2025). The total amount of hydrogen present in the system was calculated from the gas volume and the corresponding hydrogen density. By comparing the hydrogen content before and after dissolution, the amount of hydrogen transferred into the liquid phase was determined. The density of the liquid phase (e.g., water) at the respective temperature was also obtained from the NIST database, enabling precise calculation of the water mass present. The density of the Ketzin formation brine was estimated using a linear isothermal compression model. Reference densities at a pressure of 63 bar were derived from the measured salinity of the Ketzin formation water (234 g/L TDS (Förster et al., 2006)) and published density data for the Ketzin CO 2 storage site. Pressure-dependent densities were calculated assuming a constant isothermal compressibility of β = 4.5 × 1 0 − 5 b a r − 1, consistent with reported values for highly saline Na–Cl-dominated formation waters (Batzle and Wang, 1992). The brine density at pressure p was calculated as Equation 2:where ρ p 0 denotes the reference density at p 0 = 63 bar. This approach provides a first-order approximation of density variations with pressure and temperature for the Ketzin reservoir conditions. The molar amount of dissolved hydrogen was calculated (Equation 3) from the density-based mass difference and the molar mass of hydrogen. Finally, the real hydrogen solubility was expressed as the molar amount of dissolved hydrogen normalized to the mass of water:

ρ p = ρ p 0 1 + β p − p 0 , (2)

S H 2 = n H 2 , d i s s o l v e d m water (3)

For plotting solubility as a function of pressure, the calculated (Equation 4) data points were fitted using a linear regression with the general mathematic expression:

S H 2 = k H ⋅ P (4)

A quadratic regression was applied (Equation 5) to describe the nonlinear dependence of solubility on temperature:

S H 2 T = a T 2 + b T + c (5)

The corresponding fitting parameters are summarized in Table 4.

TABLE 4. Fitting parameters for solubility as a function of pressure and temperature.

3.1 Hydrogen solubility in water

Figure 3 presents the experimentally determined hydrogen solubility in pure water as a function of pressure at four representative temperatures (295, 323, 348, and 373 K). For comparison, data points from Wiebe and Gaddy (1934) are represented as open circles for 50, 100 and 200 bar at 323, 348 and 373 K. The data clearly demonstrate a strong pressure dependence: for example, at 295 K the solubility rises from ∼ 0.038 m o l k g − 1 at 45 bar to ∼ 0.080 m o l k g − 1 at 95 bar, reaching ∼ 0.159 m o l k g − 1 at 196 bar (corresponding numerical values are summarized in Table 5).

TABLE 5. Experimental solubilities of hydrogen in different aqueous solutions.

Abbreviations: SB, Ketzin synthetic brine; WB, Ketzin well brine.

Comparison with earlier literature further confirms the reliability of these measurements. Wiebe and Gaddy (1934) report solubilities of ∼ 0.077 m o l k g − 1 at ∼100 bar and 298 K, in good agreement with the present value of ∼ 0.079 m o l k g − 1 (Figure 3). The correlation based on the Krichevsky–Kasarnovsky (KK) model by Torin-Ollarves and Trusler (2021) predicts hydrogen solubilities of similar order under comparable temperature and pressure conditions. For example, at ∼150 bar and 323.15 K they report a solubility of 0.1121 m o l k g − 1, which is in good agreement with our experimental value of 0.103 m o l k g − 1 at 145 bar Chabab et al. (2020) report ∼ 0.076 m o l k g − 1 at 372 K and ∼93 bar, further validating the dataset. The present measurements, which include pressures up to ∼196 bar, complement previous high-pressure studies (Wiebe and Gaddy, 1934; Torin-Ollarves and Trusler, 2021), providing additional high-precision data for modeling hydrogen solubility under storage-relevant conditions.

The temperature dependence of hydrogen solubility shown in Figure 4, exhibits a non-monotonic trend with a minimum around 323 K. It is clearly shown, that at constant temperature, hydrogen solubility increases with increasing pressure. But at constant pressures, the solubility first decreases and then increases as temperature rises. This phenomenom is reported as “temperature inversion of solubility” (Sun et al., 2026). At lower temperature, the solubility is mainly controlled by molecular motion and follows the typical behavior of most gases in water, where gas molecules have the tendency to escape from the liquid phase to the vapor phase. At higher temperatures, an opposite trend can be observed, where solubility increases with temperature. Several thermodynamic interpretations have been proposed. Tamman (1926) suggested that temperature changes the balance between vacancy formation and solvation in water, producing a minimum in the solubility curve. It has also been proposed that stronger gas–water interactions (e.g., dipole interactions) at high temperature and pressure may enhance dissolution (Zhang et al., 2018). From a molecular thermodynamics perspective, the phenomenon results from competition between two processes: breaking the hydrogen-bond network of water (endothermic) and the formation of gas–water interactions (exothermic) (Sun et al., 2026). At low temperatures, the exothermic contribution dominates, so solubility decreases with temperature. As temperature increases, structural constraints in water weaken and entropy effects become more important, causing the overall dissolution enthalpy to change sign. The solubility minimum corresponds to this transition point.

The hydrogen solubility measurements in pure water were used to validate the experimental methodology, ensuring that the setup produces reliable and accurate results across a wide range of pressures and temperatures. These validated measurements provide a solid basis for interpreting the newly obtained Ketzin brine results, ensuring that the unpublished data meet the accuracy requirements for application in predictive modeling. Consequently, the dataset enhances the robustness of simulations describing hydrogen transport and dissolution in the Ketzin reservoir, thus supporting the reliable design and evaluation of underground hydrogen storage systems using experimentally grounded solubility parameters.

3.2 Hydrogen solubility in NaCl brine

Hydrogen solubility in 3 M NaCl brine (175.3 g/L TDS) is systematically lower than in pure water (Table 5; Figure 5), reflecting the well known salting-out effect, in which dissolved ions reduce the availability of solvent for gas dissolution (Chabab et al., 2020; Torin-Ollarves and Trusler, 2021). In brine solutions, the formation of hydration shells around dissolved ions effectively decreases the amount of free water available for the dissolution process. As a result, there is less accessible volume for gas molecules and atoms, leading to a diminished gas solubility (Seibt et al., 1999). According to the Sechenov relationship, first proposed more than a century ago (Sechenov, 1877a; Sechenov, 1877b; 1889), the logarithm of gas solubility at constant temperature is a linear function of salt concentration. The salting-out effect can be described by the Sechenov equation as follows Equation 6:lg denotes the common (base-10) logarithm and C denotes the concentration variable used in the Sechenov relationship (e.g., ionic strength, molality or molarity, depending on the formulation), S i 0 ( T ) is the solubility of a non-electrolyte i in pure water at temperature T, S i ( T ) is the solubility of the non-electrolyte in the salt solution at temperature T, and K i ( T ) is the empirical salting coefficient at temperature T.

l g S 0 i T / S i T = C ⋅ K i T (6)

Smaller ions or ions with higher charge density induce a more pronounced decrease in solubility compared to larger or monovalent ions. For CaCl 2 solutions and NaCl/CaCl₂ mixtures, an empirically determined factor of 1.8 was obtained. Multiplying the molality of CaCl 2 by this factor yields the equivalent NaCl concentration that produces an identical reduction in solubility (Seibt et al., 1999).

Weisenberger and Schumpe extended an empirical model for predicting gas solubility in electrolyte solutions by explicitly incorporating temperature dependence. For most gases, a nearly linear decrease of the Sechenov constant with increasing temperature is observed, indicating that the salting-out effect becomes weaker at higher temperatures. However, exceptions exist, most notably helium and sulfur dioxide, for which salting-out becomes stronger as temperature increases (Weisenberger and Schumpe, 1996).

The temperature dependence of hydrogen solubility in 3 M NaCl brine exhibits a slightly non-monotonic behavior (Figure 6), comparable to that observed in pure water, with a weakly pronounced minimum in the intermediate temperature range (∼ 320–340 K). Although the same general temperature dependence can still be observed in NaCl brine, it occurs at a much lower overall solubility level. Interestingly, the salting-out effect is more pronounced at lower temperatures and pressures. This is mainly due to the increased structural order of water: at low temperatures, hydration shells around ions are more stable, meaning water molecules are more strongly bound and effectively “blocked” from interacting with hydrogen. In addition, cold water is denser and leaves less free space between molecules, further limiting hydrogen dissolution. At higher temperatures, this ordered structure breaks down, water expands slightly, and more transient free volume becomes available. At the same time, entropy becomes a stronger driving force for mixing, partially overcoming the repulsive effect of the ions. Pressure further influences this behavior. At high pressures (around 200 bar), the minimum in solubility becomes more pronounced, indicating a stronger dependence on the structural properties of the solvent. Under these conditions, compression of the liquid reduces the number of transient cavities that are needed to accommodate nonpolar molecules such as H 2. Above the solubility minimum, increasing temperature leads to a stronger increase in solubility at high pressure compared to lower pressures. This suggests that thermal disruption of the solvent structure, including hydration shells around ions, has a greater relative effect when the liquid is already compressed (Sun et al., 2026; Kerle et al., 2017; Chabab et al., 2024).

Overall, these results demonstrate that hydrogen solubility in 3 M NaCl brine is governed by a complex interplay of pressure and temperature, emphasizing the importance of accurate, high-pressure, temperature-resolved measurements for reliable modeling of underground hydrogen storage.

3.3 Hydrogen solubility in Ketzin brine

Hydrogen solubility in the Ketzin brines, which are dominated by NaCl, is systematically lower than in pure water due to the salting-out effect, where the presence of dissolved Na⁺ and Cl⁻ ions reduces the availability of solvent for gas dissolution (Chabab et al., 2020; Torin-Ollarves and Trusler, 2021) (Figures 7, 8). The Ketzin synthetic brine exhibits solubility values comparable to those measured in our laboratory 3 M NaCl solution, confirming the expected salt induced reduction and validating the experimental approach. The Ketzin well brine shows slightly lower solubility at similar pressures and temperatures, consistent with its modestly higher salinity resulting from prolonged storage and partial evaporation.

In contrast to the behavior observed in 3 M NaCl brine, experiments with multi-electrolyte brines reveal a change in the temperature dependence of hydrogen solubility (Figure 9). While the 3 M solution exhibits a pronounced non-monotonic behavior with a minimum in the intermediate temperature range, this minimum progressively disappears with increasing overall ionic complexity. Instead, the solubility becomes a weakly monotonic function of temperature over the entire investigated range.

In the intermediate temperature regime (around 320–340 K), where a minimum would be expected based on the behavior of NaCl brines, the multi-electrolyte solutions show slightly higher hydrogen solubility than the 3 M NaCl brine. This suggests that the structural mechanism responsible for the formation of the solubility minimum in water-rich and moderately saline systems is suppressed at high ionic strength and in multi-electrolyte environments. In particular, the presence of additional cations such as Mg 2 +, Ca 2 +, and K + modifies the water structure compared to a pure NaCl system. While Na + exhibits moderate hydration strength, the divalent ions Mg 2 + and Ca 2 + strongly bind surrounding water molecules and form highly stable, extended hydration shells, thereby effectively reducing the fraction of dynamically available water. In contrast, K + is more weakly hydrated than Na + and contributes less to local water structuring, but still alters the distribution of water molecules across different ionic species. The resulting mixture leads to a heterogeneous hydration environment in which water is partitioned between ions with differing hydration strengths. This compositional complexity, together with the high ion density, leads to a saturation of hydration structures and a reduced sensitivity of the solvent network to temperature-induced rearrangements.

At higher temperatures (348–373 K), however, this trend reverses, and the hydrogen solubility in the highly saline brine becomes lower than in the 3 M NaCl solution. This behavior is consistent with a stronger effective salting-out effect in the more complex brine composition, where reduced water availability, lower water activity, and ion-specific interactions increasingly dominate the thermodynamic balance. In particular, the strong hydration of Mg 2 + and Ca 2 + further reduces the amount of free or weakly bound water available for hydrogen dissolution compared to NaCl-dominated systems. As temperature increases, thermal disruption of hydration structures and enhanced molecular motion promote gas dissolution in both systems; however, this effect is comparatively weaker in the highly saline, multi-ion solution due to the already highly constrained and heterogeneously structured solvent environment. Consequently, the difference between both systems becomes strongly temperature dependent and changes sign across the investigated range. (Görgenyi et al., 2006).

Overall, the present observations suggest that at very high salinities and in mixed-electrolyte brines, the characteristic non-monotonic temperature dependence of hydrogen solubility becomes less pronounced. This interpretation is primarily supported by the complete temperature series obtained for the Ketzin synthetic brine, which consistently shows a reduced temperature sensitivity compared to the NaCl system. Although the measurements of the natural Ketzin well brine at 295.15 K and 348.15 K are consistent with this trend, the limited number of investigated temperatures does not allow a definitive assessment of the temperature dependence in the reservoir fluid. Additional measurements covering the full temperature range are therefore required to verify whether the suppression of the solubility minimum also occurs in the natural Ketzin well brine. Overall, the available data indicate a transition towards a regime governed by a competition between entropic contributions favoring dissolution and strong, ion-specific salting-out effects arising from the combined influence of Na +, Mg 2 +, Ca 2 +, and K +, which increasingly reduce hydrogen solubility with rising ionic strength, particularly at elevated temperatures.

4 Conclusion

The experimentally determined hydrogen solubilities in pure water, 3 M NaCl, and Ketzin brines provide a consistent dataset for evaluating hydrogen behavior under subsurface storage conditions. Across the investigated pressure and temperature range (up to ∼200 bar and 295–373 K), hydrogen solubility shows a strong and systematic increase with pressure, while temperature effects remain comparatively moderate and, in several cases, non-monotonic. In pure water, the results reproduce literature data and reveal a distinct temperature inversion behavior, confirming the validity of the measurements and the presence of competing thermodynamic contributions controlling dissolution.

In saline systems, a clear salting-out effect is observed, with hydrogen solubility significantly reduced relative to pure water. The 3 M NaCl brine exhibits a pronounced pressure dependence together with a temperature-dependent minimum, reflecting the interplay between ion hydration, structural changes in water, and thermal disruption of hydrogen-bond networks. In contrast, the Ketzin brines exhibit a further reduction in hydrogen solubility compared with the NaCl system. The complete temperature series obtained for the synthetic Ketzin brine indicates that the characteristic solubility minimum becomes less pronounced at high salinity and increased ionic complexity. Because the Ketzin well brine could only be measured at two temperatures, additional experimental data covering the full temperature range are required to verify this behavior for reservoir brine.

At conditions relevant to the Ketzin reservoir, the measurements confirm that only a small fraction of injected hydrogen dissolves into the formation brine. This is consistent with the dominant salting-out behavior and the relatively low equilibrium solubilities observed even at elevated pressures. However, given the large pore volumes and long operational timescales associated with subsurface storage, these dissolved fractions may still accumulate and become relevant for overall mass balance considerations.

Overall, the agreement with available literature data and model predictions demonstrates the reliability of the experimental methodology and confirms the applicability of the results to reservoir-scale conditions. A key outcome of this work is the generation of the first experimentally determined hydrogen solubility dataset for natural multi-ion reservoir brines. These data fill a gap in the currently available database and provide an experimental foundation for future thermodynamic and reservoir-scale modeling studies, particularly for assessing dissolution-driven hydrogen losses in underground storage reservoirs. Future work should extend these investigations to additional reservoir brines with varying salinities and ionic compositions to improve the understanding of ion-specific effects on hydrogen solubility and to further support the validation of thermodynamic models. The dataset thereby contributes to reducing uncertainties in predictive simulations and supports the safe and efficient deployment of underground hydrogen storage in saline aquifers.

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Footnotes

Edited by: Reza Derakhshani, Utrecht University, Netherlands

Reviewed by: Kwamena Opoku Duartey, New Mexico Institute of Mining and Technology, United States

Dawid Gajda, University of Texas at Austin, United States