Hydrogen solubility in aqueous solutions: A thermodynamic modeling approach using electrolyte equation of state

Accurate prediction of hydrogen solubility in aqueous solutions is essential for evaluating the feasibility and safety of underground hydrogen storage. This study applies an electrolyte version of the Cubic-Plus-Association (eCPA) Equation of State to model hydrogen solubility in both pure water and aqueous sodium chloride solutions. For hydrogen solubility in pure water (up to 497.5 K and 102.7 MPa), the model achieves a relative average deviation of 3.6%. In sodium chloride solutions (up to 373.9 K, 20.1 MPa, and 5.3 mol/kg), the deviation is further reduced to 2.7%. The model effectively captures key thermodynamic behaviors, including the salting-out effect, where ion hydration reduces gas solubility, and the temperature inversion phenomenon observed in pure water. This work establishes a robust thermodynamic framework for hydrogen storage applications and provides a foundational tool for analyzing phase equilibria in aqueous hydrogen systems.