Molecular insights into hydrogen solubility in water under pore confinement

doi:10.21203/rs.3.rs-3340584/v1

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Molecular insights into hydrogen solubility in water under pore confinement

https://doi.org/10.21203/rs.3.rs-3340584/v1

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published 01 Feb, 2024

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Underground hydrogen storage in geological formations has gained significant interest as a potential solution to global energy transition. Among the technical challenges related to underground hydrogen storage, one key fundamental problem is the solubility change due to the confinement, which is highly relevant to safety and efficiency. Though solubility enhancement has been extensively reported in multiple systems, hydrogen displays undersolubility under the nanoconfinement of clay. In this study, we use molecular dynamic simulations to study the hydrogen solubility in water at realistic storage conditions under the confinement of kaolinite. We find a solubility enhancement of 10-fold compared with that in the bulk for both hydrophobic and hydrophilic systems. Furthermore, we identify the major driving mechanism and show that the over-solubility is driven by adsorption and confinement.

Renewable energy plays a growing role in the energy transition as global warming has posed significant challenges to human lives (Osman et al. 2022; Chen et al.2022; Srivastava et al. 2020; Osman et al. 2023). Underground hydrogen storage has been considered a promising approach to compensate for the seasonal instability of renewable energy for mainly two reasons: (i) it is a clean energy carrier, the combustion product of hydrogen has no carbon dioxide (CO₂) or other greenhouse gas, (ii) subsurface systems have large storage capacity, high integrity with low oxygen level which enables large-scale storage(Muhammed et al. 2022; Zivar et al. 2021; Chen et al. 2023). Although significant efforts have focused on a similar system-subsurface CO₂ sequestration (Benson and Cole 2008; Rutqvist 2002; Liu et al. 2014 ), new technical challenges are stemmed due to the fundamental differences between these two gases (Blunt 2022; Hematpur et al. 2023; Tarkowski et al. 2022; Miocic et al. 2023; van Rooijen et al. 2023). Hence, it is crucially important to address the new challenges to deploy underground hydrogen storage safely and efficiently.

One important aspect is the solubility of hydrogen in the porous media. Not only does the dissolution of hydrogen in the water phase lead to potential hydrogen loss, but also the dissolved hydrogen is more likely to undergo geochemical and bio-mediated reactions (Liu et al., 2023) as well and further affects the storage seal integrity as illustrated in Fig. 1. The uniqueness of solubility in the porous media is that the wide range of pore sizes can have non-negligible confinement effect, which will lead to solubility change. Hence, it is of critical importance to understand the solubility of hydrogen under pore confinement and elucidate the underlying mechanisms. To clarify, solubility is commonly defined in two ways (Hu et al., 2016). The first definition is ${S}_{1}={N}_{1}/V$, where, ${N}_{1}$ is the amount of solute in the pore. It is based on the density of solute in the pore and usually expressed in $mmol/c{m}^{3}$. The second definition considers the mole fraction of solute in the solvent, ${S}_{2}={N}_{1}{/N}_{2}$. Here, ${N}_{2}$ is the amount of solvent in the pore. These two definitions are consistent in the bulk conditions but become different under confinement as the solvent density varies under confinement.

The impact of confinement on solubility is not a new problem. Over the past few decades, pioneering studies have been dedicated to investigating the uptake phenomenon of CO₂. It has been extensively reported that CO₂ exhibits over-solubility under confinement for both definitions in various combinations of porous media and solvent (Ho et al., 2021; Sánchez-Bautista, 2019; Soubeyrand-Lenoir et al., 2012; Ali et al., 2021; Myshakin et al., 2013). The underlying mechanism of enhanced CO2 solubility is an interplay of adsorption-driven mechanism and confinement effect (Li et al., 2020). However, the phenomenon has not been fully understood for H_2, given the fundamental difference between CO₂ and H₂. Experiments indicate that the H₂ solubility in n-hexane and ethanol will be enhanced in a pore with a silica surface when the pore size is less than 3nm (Clauzier et al., 2012; Clauzier et al., 2014). There is also experimental evidence on the over-solubility of H₂/CCl₄ on $\gamma$-alumina and H₂/CS₂ on $\gamma$-alumina (Miachon et al., 2008). Studies by molecule simulations also indicate the over-solubility phenomenon of H₂/octamethylcyclotetrasiloxane (OMCTS) on multiple surfaces, including alumina and Mobil Composition of Matter No. 41 (MCM-41) surface (Ho et al., 2013; Coasne et al., 2019). Despite these findings on H₂ consistent with the solubility increase for CO₂, it has also been reported that H₂ only displays over-solubility with the first definition of solubility while it shows an under-solubility instead if the second definition is used. More recently, a pioneering work reports that hydrogen shows under-solubility in water due to the nanoconfinement of clay minerals, which contrasts with previous knowledge on CO₂ and H₂ (Ho et al., 2023). Since this is the only publication reporting H₂ solubility in water under clay confinement to the best of our knowledge, further studies are needed to clarify whether it should be over-solubility or under-solubility in H₂/water systems for a realistic environment in underground hydrogen storage. Yet, the underlying mechanism to drive the solubility change is not fully understood, as two different mechanisms are proposed to enhance CO₂ solubility.

In our study, we specifically focus on H₂ solubility in water under the confinement of kaolinite. Kaolinite is considered to be a promising storage formation as it is the principal representative of the major clay mineral groups (Al-Yaseri et al., 2021; Yekeen et al., 2022). Furthermore, kaolinite has both hydrophobic and hydrophilic surfaces, encompassing all the wettability conditions. To address the problem, we conduct molecular simulations to quantify the solubility in confined kaolinite and use that in bulk water as a benchmark. We then propose a method to perform a detailed analysis of the results to understand the dominant driving mechanism.

The kaolinite unit cell is built using X-ray diffraction data (Bish, 1993). As shown in Fig. 2(a), the unit cell comprises a gibbsite (Al-OH) sheet and a siloxane (Si-O) sheet, resulting in hydrophilic and hydrophobic surfaces, respectively. The bulk system is set up as Fig. 2(b) indicates. The water slab is 6nm long with two 12nm hydrogen slabs on two sides. The dimension for the y direction is 5nm. In the confinement system, a water slab with a length of 6.7nm is confined in a 2nm slit pore with three layers of kaolinite. Two water slabs function as the buffer to mitigate the entrance effect and prevent the bulk gas from entering the pore. There are two 6nm H₂ slabs outside the kaolinite confinement.

All MD simulations are conducted by the LAMMPS (Plimpton, 1995). The simulation conditions are selected similarly to the geological storage conditions where the temperature is up to 373K, and pressure can be up to 400 bar. During the simulation, the kaolinite wall is fixed for both hydrophilic and hydrophobic confinement. The mobile phase (water and hydrogen) is first generated randomly with a specified number calculated from the experimental density(Wagner et al., 2002; Leachman et al., 2009). For both hydrophobic and hydrophilic systems, we start with a supersaturated configuration to allow the systems to reach equilibrium quickly. The temperature of the system is initialized with velocity created at 300K. Water and H₂ molecules are first relaxed with a microcanonical ensemble(NVE ensemble) for 1ns and then by a canonical ensemble (NVT ensemble) for 1ns to reach the desired temperature. A 10ns isothermal-isobaric ensemble (NPT ensemble) calculates the density profile since the solubility is more pressure-sensitive. Results of the last 5ns are averaged to obtain the solubility. We checked the density profile to ensure the system reached equilibrium.

The forcefield of kaolinite is modeled by CLAYFF (Cygan et al., 2004), which is widely used for simulating the interaction between clay and water. The SPC model (Berendsen et al., 1984) is selected to simulate the water as the performance with CLAYFF has been demonstrated in previous studies (Berendsen et al., 1981). A single-site model is selected to represent H₂ molecules for simplification, which has been reported to be capable of providing accurate predictions for solubility(Rahbari et al., 2019). This single-site model is validated by comparing the bulk solubility with experimental data. The long-range interaction is handled by the particle-particle particle-mesh solver.

Density profile

The solubility is estimated from the density profile of both H₂ and water.

As shown in Fig. 3(a), there are two adsorption peaks for both water and H₂. For a hydrophilic surface, adsorption peaks are closer to the solid wall because of the stronger interaction between Al-OH and water molecules. Due to the smaller size, the location of the adsorption layer of H₂ is closer to the wall compared with that of water. The density profile along the z direction indicates that adsorption is not negligible in the confined space for our system. Based on the profile along the z direction, the contribution of adsorption can be quantified by evaluating the excess amount of hydrogen over the bulk density. The contribution of adsorption on the solubility can be expressed as

$$\begin{array}{c}{\eta }_{a}=\frac{\int \left({\rho }_{H}-{\rho }_{b}\right)dz}{\int {\rho }_{H}dz}. \#\left(1\right)\end{array}$$

Here, ${\rho }_{H}$ is the number density of hydrogen and ${\rho }_{b}$ is the number density of hydrogen in the center region as denoted in Fig. 3(a). Since the contribution of adsorption can be quantified by Eq. (1), the solubility under confinement, excluding the effect of adsorption ${S}_{i}^{ex}$ is described as

$$\begin{array}{c}{S}_{i}^{ex}={S}_{i}*\left(1-{\eta }_{a}\right). \#\left(2\right) \#\end{array}$$

Here, subscript $i$ can be 1 and 2.

Solubility of confined fluids

With definitions of solubility, we first compare the solubility in bulk water obtained from MD simulation with that of experiments. The bulk solubility is determined from Henry’s law, and Henry’s constant is obtained from the NIST chemistry webbook. A good agreement is observed for both ${S}_{1}$ and ${S}_{2}$ between our simulation results and the experimental data, as shown in Fig. 4(b)-(c), which validates our model parameters for H₂ and water molecules.

In Fig. 4(a), the impact of confinement on the water density is quantitatively compared. The strong interaction between the hydrophilic wall and water molecule gives rise to the highest water density for the hydrophilic confinement, while the repulsion effect of hydrophobic leads to the lowest water density for the hydrophobic confinement. The bulk density from MD simulations also corresponds to experimental results obtained from the NIST chemistry webbook. The water density indicates that the confinement effect on the water will cause a 4% difference based on different solubility definitions due to the water density variation.

Figure 4(b) and (c) indicate an over-solubility of hydrogen in water for both the hydrophilic and hydrophobic confinement. The enhancement of solubility due to the confinement can be approximately 10 times the bulk water for the hydrophobic surface, which increases by an order of magnitude. Additionally, hydrophobic surfaces display a more significant over-solubility phenomenon than the hydrophilic surface. The results directly shed light on the conclusion that about 10 times hydrogen molecules will be contained in the water because of confinement.

To better understand the underlying mechanism, we sort out the contributions of the aforementioned adsorption-driven mechanism and the confinement-driven mechanism by Eq. (1)-Eq. (2). After we exclude the adsorption by ruling out the excess amount in the density profile, the solubility is still 4 times that in the bulk water as the curves plotted in diamond markers indicate in Fig. 4(b) and (c). This provides evidence that the overall enhancement of solubility is driven by both mechanisms in our system. The direct adsorption interaction between hydrogen and kaolinite confinement accounts for about 60% of the over-solubility. Yet, the remaining 40% results from increased effective pressure inside the confinement space. The pressure is uniform throughout the simulation since the mobile phase is under the NPT ensemble. However, molecules inside the confinement are more likely to collide with each other because the confinement limits the mean free path (Baek and Yucel Akkutlu 2019; PD et al. 2015; Barisik and Beskok 2015). Furthermore, this increases the effective pressure for the confined water to hold more hydrogen molecules (Barsotti et al. 2016; Gubbins et al. 2014).

Increasing one order of magnitude in solubility in confined water has great implications for underground hydrogen storage. First, there will be a significant underestimation of the hydrogen loss because of dissolution in a nanopore if the bulk properties are used. Second, aqueous geochemical and bio-mediated reaction rates might be significantly higher than bulk studies predict. Third, there will be a faster leakage rate through the caprock, which poses a greater challenge to seal integrity.

In this study, we quantified the impact of pore confinement on the H₂ solubility and identified the main underlying mechanisms under realistic conditions for underground hydrogen storage. The results reveal that the solubility enhancement can be up to 10 times in an H₂/water system confined by hydrophilic and hydrophobic surfaces. Over-solubility in this system is driven by both adsorption and confinement, though adsorption plays a major role. Our results are essential for evaluating the hydrogen loss during the injection/extraction cycles and assessing seal integrity for underground hydrogen storage.

Funding

This work was supported by Laboratory Directed Research and Development, Los Alamos National Laboratory, USA.

Competing Interests

The authors have no relevant financial or non-financial interests to disclose.

Author Contributions

All authors contributed to the study conception and design. Model design, data collection and analysis were performed by Siqin Yu and Mohamed Mehana. The first draft of the manuscript was written by Siqin Yu, and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Al-Yaseri, A., Wolff-Boenisch, D., Fauziah, C. A., & Iglauer, S. (2021). Hydrogen wettability of clays: Implications for underground hydrogen storage. International Journal of Hydrogen Energy, 46(69), 34356-34361.
Ali, A., Striolo, A., & Cole, D. R. (2021). CO2 solubility in aqueous electrolyte solutions confined in calcite nanopores. The Journal of Physical Chemistry C, 125(22), 12333-12341.
Baek, S., & Yucel Akkutlu, I. (2019). Mean free path of gas molecules in organic nanochannels using molecular simulations. SPE Journal, 24(06), 2555-2573.
Barisik, M., & Beskok, A. (2015). Molecular free paths in nanoscale gas flows. Microfluidics and Nanofluidics, 18, 1365-1371.
Barsotti, E., Tan, S. P., Saraji, S., Piri, M., & Chen, J. H. (2016). A review on capillary condensation in nanoporous media: Implications for hydrocarbon recovery from tight reservoirs. Fuel, 184, 344-361.
Benson, S. M., & Cole, D. R. (2008). CO2 sequestration in deep sedimentary formations. Elements, 4(5), 325-331.
Berendsen, H. J., Postma, J. P., van Gunsteren, W. F., & Hermans, J. (1981). Interaction models for water in relation to protein hydration. In Intermolecular forces: proceedings of the fourteenth Jerusalem symposium on quantum chemistry and biochemistry held in jerusalem, israel, april 13–16, 1981 (pp. 331-342). Springer Netherlands.
Berendsen, H. J., Postma, J. V., Van Gunsteren, W. F., DiNola, A. R. H. J., & Haak, J. R. (1984). Molecular dynamics with coupling to an external bath. The Journal of chemical physics, 81(8), 3684-3690.
Bish, D. L. (1993). Rietveld refinement of the kaolinite structure at 1.5 K. Clays and Clay Minerals, 41, 738-744.
Blunt, M. J. (2022). Ostwald ripening and gravitational equilibrium: Implications for long-term subsurface gas storage. Physical Review E, 106(4), 045103.
Chen, L., Msigwa, G., Yang, M., Osman, A. I., Fawzy, S., Rooney, D. W., & Yap, P. S. (2022). Strategies to achieve a carbon neutral society: a review. Environmental Chemistry Letters, 20(4), 2277-2310.
Chen, Y., Jin, X., Zeng, L., Zhong, Z., Mehana, M., Xiao, W., ... & Xie, Q. (2023). Role of large-scale underground hydrogen storage and its pathways to achieve net-zero in China. Journal of Energy Storage, 72, 108448.
Clauzier, S., Ho, L. N., Pera-Titus, M., Coasne, B., & Farrusseng, D. (2012). Enhanced H2 uptake in solvents confined in mesoporous metal–organic framework. Journal of the American Chemical Society, 134(42), 17369-17371.
Clauzier, S., Ho, L. N., Pera-Titus, M., Farrusseng, D., & Coasne, B. (2014). Enhanced H2 uptake of n-alkanes confined in mesoporous materials. The Journal of Physical Chemistry C, 118(20), 10720-10727.
Coasne, B., & Farrusseng, D. (2019). Gas oversolubility in nanoconfined liquids: Review and perspectives for adsorbent design. Microporous and Mesoporous Materials, 288, 109561.
Cygan, R. T., Liang, J. J., & Kalinichev, A. G. (2004). Molecular models of hydroxide, oxyhydroxide, and clay phases and the development of a general force field. The Journal of Physical Chemistry B, 108(4), 1255-1266.
Farghali, M., Osman, A. I., Umetsu, K., & Rooney, D. W. (2022). Integration of biogas systems into a carbon zero and hydrogen economy: a review. Environmental Chemistry Letters, 20(5), 2853-2927.
Gubbins, K. E., Long, Y., & Śliwinska-Bartkowiak, M. (2014). Thermodynamics of confined nano-phases. The Journal of Chemical Thermodynamics, 74, 169-183.
Hematpur, H., Abdollahi, R., Rostami, S., Haghighi, M., & Blunt, M. J. (2023). Review of underground hydrogen storage: Concepts and challenges. Advances in Geo-Energy Research, 7(2), 111-131.
Ho, L. N., Clauzier, S., Schuurman, Y., Farrusseng, D., & Coasne, B. (2013). Gas uptake in solvents confined in mesopores: Adsorption versus enhanced solubility. The Journal of Physical Chemistry Letters, 4(14), 2274-2278.
Ho, L. N., Perez Pellitero, J., Porcheron, F., & Pellenq, R. J. M. (2011). Enhanced CO2 solubility in hybrid MCM-41: molecular simulations and experiments. Langmuir, 27(13), 8187-8197.
Ho, T. A., Jove-Colon, C. F., & Wang, Y. (2023). Low hydrogen solubility in clay interlayers limits gas loss in hydrogen geological storage. Sustainable Energy & Fuels.
Hu, Y., Huang, L., Zhao, S., Liu, H., & Gubbins, K. E. (2016). Effect of confinement in nano-porous materials on the solubility of a supercritical gas. Molecular Physics, 114(22), 3294-3306.
Huang, R., Herring, A., & Sheppard, A. (2020, December 11). High-resolution scans of Bentheimer sandstone core for imbibition experiments. Retrieved August 10, 2023, from www.digitalrocksportal.org
Leachman, J. W., Jacobsen, R. T., Penoncello, S. G., & Lemmon, E. W. (2009). Fundamental equations of state for parahydrogen, normal hydrogen, and orthohydrogen. Journal of Physical and Chemical Reference Data, 38(3), 721-748.
Li, W., Nan, Y., Zhang, Z., You, Q., & Jin, Z. (2020). Hydrophilicity/hydrophobicity driven CO2 solubility in kaolinite nanopores in relation to carbon sequestration. Chemical Engineering Journal, 398, 125449.
Liu, H., Valocchi, A. J., Werth, C., Kang, Q., & Oostrom, M. (2014). Pore-scale simulation of liquid CO2 displacement of water using a two-phase lattice Boltzmann model. Advances in water resources, 73, 144-158.
Liu, N., Kovscek, A. R., Fernø, M. A., & Dopffel, N. (2023). Pore-scale study of microbial hydrogen consumption and wettability alteration during underground hydrogen storage. Frontiers in Energy Research, 11, 1124621.
Miachon, S., Syakaev, V. V., Rakhmatullin, A., Pera‐Titus, M., Caldarelli, S., & Dalmon, J. A. (2008). Higher gas solubility in nanoliquids?. ChemPhysChem, 9(1), 78-82.
Miocic, J., Heinemann, N., Edlmann, K., Scafidi, J., Molaei, F., & Alcalde, J. (2023). Underground hydrogen storage: a review. Geological Society, London, Special Publications, 528(1), SP528-2022.
Muhammed, N. S., Haq, B., Al Shehri, D., Al-Ahmed, A., Rahman, M. M., & Zaman, E. (2022). A review on underground hydrogen storage: Insight into geological sites, influencing factors and future outlook. Energy Reports, 8, 461-499.
Myshakin, E. M., Saidi, W. A., Romanov, V. N., Cygan, R. T., & Jordan, K. D. (2013). Molecular dynamics simulations of carbon dioxide intercalation in hydrated Na-montmorillonite. The Journal of Physical Chemistry C, 117(21), 11028-11039.
Osman, A. I., Chen, L., Yang, M., Msigwa, G., Farghali, M., Fawzy, S., ... & Yap, P. S. (2023). Cost, environmental impact, and resilience of renewable energy under a changing climate: a review. Environmental Chemistry Letters, 21(2), 741-764.
Osman, A. I., Mehta, N., Elgarahy, A. M., Hefny, M., Al-Hinai, A., Al-Muhtaseb, A. A. H., & Rooney, D. W. (2022). Hydrogen production, storage, utilisation and environmental impacts: a review. Environmental Chemistry Letters, 1-36.
PD, S. H., Prabha, S. K., & Sathian, S. P. (2015). The effect of characteristic length on mean free path for confined gases. Physica A: Statistical Mechanics and its Applications, 437, 68-74.
Plimpton, S. (1995). Fast parallel algorithms for short-range molecular dynamics. Journal of computational physics, 117(1), 1-19.
Rahbari, A., Brenkman, J., Hens, R., Ramdin, M., Van Den Broeke, L. J., Schoon, R., ... & Vlugt, T. J. (2019). Solubility of water in hydrogen at high pressures: a molecular simulation study. Journal of Chemical & Engineering Data, 64(9), 4103-4115.
Rutqvist, J. (2012). The geomechanics of CO 2 storage in deep sedimentary formations. Geotechnical and Geological Engineering, 30, 525-551.
Sánchez-Bautista, J. E., Landeros-Rivera, B., Jurado-Vázquez, T., Martínez, A., González-Zamora, E., Balmaseda, J., ... & Ibarra, I. A. (2019). CO 2 capture enhancement for InOF-1: confinement of 2-propanol. Dalton Transactions, 48(16), 5176-5182.
Soubeyrand-Lenoir, E., Vagner, C., Yoon, J. W., Bazin, P., Ragon, F., Hwang, Y. K., ... & Llewellyn, P. L. (2012). How water fosters a remarkable 5-fold increase in low-pressure CO2 uptake within mesoporous MIL-100 (Fe). Journal of the American Chemical Society, 134(24), 10174-10181.
Srivastava, R. K., Shetti, N. P., Reddy, K. R., & Aminabhavi, T. M. (2020). Biofuels, biodiesel and biohydrogen production using bioprocesses. A review. Environmental Chemistry Letters, 18, 1049-1072.
Stukowski, A. (2009). Visualization and analysis of atomistic simulation data with OVITO–the Open Visualization Tool. Modelling and simulation in materials science and engineering, 18(1), 015012.
Tarkowski, R., & Uliasz-Misiak, B. (2022). Towards underground hydrogen storage: A review of barriers. Renewable and Sustainable Energy Reviews, 162, 112451.
Theerthagiri, J., Karuppasamy, K., Park, J., Rahamathulla, N., Kumari, M. A., Souza, M. K., ... & Choi, M. Y. (2023). Electrochemical conversion of biomass-derived aldehydes into fine chemicals and hydrogen: A review. Environmental Chemistry Letters, 21(3), 1555-1583.
van Rooijen, W. A., Habibi, P., Xu, K., Dey, P., Vlugt, T. J. H., Hajibeygi, H., & Moultos, O. A. (2023). Interfacial tensions, solubilities, and transport properties of the H2/H2O/NaCl system: A molecular simulation study. Journal of Chemical & Engineering Data.
Wagner, W., & Pruß, A. (2002). The IAPWS formulation 1995 for the thermodynamic properties of ordinary water substance for general and scientific use. Journal of physical and chemical reference data, 31(2), 387-535.
Yekeen, N., Al-Yaseri, A., Negash, B. M., Ali, M., Giwelli, A., Esteban, L., & Sarout, J. (2022). Clay-hydrogen and clay-cushion gas interfacial tensions: Implications for hydrogen storage. International Journal of Hydrogen Energy, 47(44), 19155-19167.
Zivar, D., Kumar, S., & Foroozesh, J. (2021). Underground hydrogen storage: A comprehensive review. International journal of hydrogen energy, 46(45), 23436-23462.

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You are reading this latest preprint version

Molecular insights into hydrogen solubility in water under pore confinement

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Abstract

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Introduction

Method

Results and discussion

Density profile

Solubility of confined fluids

Conclusion

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References

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