Using density functional theory to evaluate Ca-Ce-M-O (M = 3<i>d</i> transition metal) oxide perovskites for solar thermochemical applications

Solar thermochemical (STC) processes that use redox-active, off-stoichiometric, transition-metal oxide substrates to split water and/or CO₂ are an efficient way to generate reusable fuels or fuel precursors using concentrated solar flux. However, STC processes require oxides that are thermally stable, tolerate high oxygen off-stoichiometry, and be resistant to adverse phase transformations. In this work, we explore the chemical space of Ca-Ce-M-O (M=3d transition metal) oxide perovskites as potential STC candidates using density functional theory based calculations. Specifically, we use the strongly constrained and appropriately normed (SCAN) functional, with an appropriately determined Hubbard U correction to reduce the self-interaction errors of the highly-correlated 3d and 4f electrons within M and Ce, respectively. While, we consider Ca and Ce on the A site (in an ABO₃ perovskite framework) because of their similar ionic radii and the potential redox-activity of Ce, we consider all 3d transition metals except Zn on the B-site. Subsequently, we evaluate the oxygen vacancy formation energy, electronic properties, and thermodynamic stability of ternary Ca-M-O, Ce-M-O, and quaternary Ca-Ce-M-O perovskites and identify promising candidates that can improve STC efficiencies.