Computational Investigation of Metal Oxides as Candidate Hydrogen Storage Materials

Materials-based approaches are needed to achieve high volumetric density for the storage and release of hydrogen. In this work, we investigate metal oxides for their ability to store hydrogen, based on the idea that the known reduction potentials of proton-coupled electron transfer in metal oxides are in a range that suggests these materials could have suitable energetics for hydrogen storage and release at near-ambient temperature. We hypothesize that the more positive (or less negative) is the reduction potential, the greater is the favorability to absorb hydrogen. To test this idea, the absorption of atomic hydrogen (which can be derived from molecular hydrogen with a suitable catalyst) in six metal oxides (MnO2, MoO3, SnO2, TiO2, WO3, and ZrO2) is studied using density functional theory at the PBE-D3(BJ), PBE-D3(BJ)+U, and PBE0 levels of theory. A correlation between reduction potentials and the energies of absorption (relative to free H2) is found, and three of the metal oxides are predicted to absorb hydrogen at storage-relevant temperatures and pressures, with MoO3 showing the most promise.