Computationally Guided Discovery of Mixed Mn/Ni Perovskites for Solar Thermochemical Hydrogen Production at High H₂ Conversion

We identified the perovskite oxides LaMn_0.5Ni_0.5O₃ (L2MN), Gd_0.5La_0.5Mn_0.5Ni_0.5O₃ (GLMN), and GdMn_0.5Ni_0.5O₃ (G2MN) as candidate solar thermal chemical hydrogen (STCH) redox mediators from their density functional theory (DFT)-computed electronic and oxygen vacancy properties following a high-throughput computational screening of AA′BB′O₆ compositions that are likely to form as perovskites and split water. At a thermal reduction temperature of 1350 °C and a water splitting temperature of 850 °C, the L2MN and GLMN perovskites produced ∼65 μmol g^-1 of hydrogen per cycle with no phase degradation over three redox cycles at 40 mol % steam, while the G2MN perovskite did not produce STCH under these conditions. When reoxidized by exposure to a gas flow with a H₂O:H₂ molar ratio of 1333:1, which represents operating conditions where the thermodynamic driving force of water splitting is lowered by orders of magnitude relative to 40 mol % steam, the L2MN and GLMN perovskites each produced ∼35 μmol g^-1 of hydrogen per cycle. Guided by DFT, we propose that L2MN and GLMN’s STCH activities arise from B-site cation antisite defects that facilitate oxygen vacancy formation and thus redox cycling, whereas the synthesized G2MN has few antisite defects and is therefore inactive for STCH.