Geologic H₂ generation with simultaneous CO₂ mineralization: A dual strategy for energy decarbonization

Ultramafic formations are ideal for generating geologic H₂ and mineralizing CO₂. The prospect of combining both processes is examined using geochemical kinetic modeling. Simulations show that CO₂ promotes H₂ generation up to 31% at depths where the temperature is less than ∼150 °C by enhancing Fe(II) dissolution. A key feature of this model is that porosity, which controls water availability for H₂ generation, evolves with mineral assemblage. This reveals that adequate flow is critical in sustaining the positive effect of CO₂. We also report that magnesium promotes H₂ generation by scavenging SiO₂, which broadens implementation options given that ultramafic rocks are replete with Mg. CO₂ is mainly mineralized in magnesite, rather than as siderite, thereby keeping Fe(II) available for H₂ generation. Relative to the H₂ generation target proposed in the IEA net-zero-emissions scenario, the CO₂-enhanced H₂ generation could significantly reduce needed reactive formation volume while contributing to the CO₂ capture goal.