Mechanistic insights into hydrogen production from aluminum and alkaline solution under high temperature and pressure conditions: A ReaxFF molecular dynamics study

The aluminum–water reaction is a promising low-carbon route to hydrogen, yet its molecular-scale mechanism under combined high temperature, pressure, and alkaline conditions remains unclear. Using ReaxFF reactive molecular dynamics, we systematically investigate this reaction for 2.4 nm aluminum nanoparticles, quantifying the effects of hydroxide concentration (1.0–3.0 M), temperature (800–1600 K), and pressure. Our simulations reveal a three-stage mechanism: water adsorption/dissociation, boehmite (AlOOH) intermediate formation, and thermal dehydration to alumina (Al₂O₃) with H₂ release. We find that increasing hydroxide concentration lowers the activation energy from 23.08 to 18.32 kJ/mol, while a medium-pressure regime maximizes the hydrogen yield (∼44 %) by optimally balancing reactant proximity and ionic mobility. These insights are validated by batch experiments, which confirm the non-monotonic effect of pressure and a ∼ 35 % yield increase at higher NaOH concentrations, underscoring the critical role of hydroxide ions in facilitating H₃O⁺-mediated proton transfer. Our results establish a quantitative, molecular-level framework for optimizing hydrogen production from aluminum under extreme conditions.