Search for: All records

We identified the perovskite oxides LaMn0.5Ni0.5O3 (L2MN), Gd0.5La0.5Mn0.5Ni0.5O3 (GLMN), and GdMn0.5Ni0.5O3 (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. 

Non-stoichiometric perovskite oxides have been studied as a new family of redox oxides for solar thermochemical hydrogen (STCH) production owing to their favourable thermodynamic properties. However, conventional perovskite oxides suffer from limited phase stability and kinetic properties, and poor cyclability. Here, we report a strategy of introducing A-site multi-principal-component mixing to develop a high-entropy perovskite oxide, (La1/6Pr1/6Nd1/6Gd1/6Sr1/6Ba1/6)MnO3 (LPNGSB_Mn), which shows desirable thermodynamic and kinetics properties as well as excellent phase stability and cycling durability. LPNGSB_Mn exhibits enhanced hydrogen production (∼77.5 mmol/mol-oxide) compared to (La2/3Sr1/3)MnO3 (∼53.5 mmol / mol-oxide) in a short 1 hour redox duration and high STCH and phase stability for 50 cycles. LPNGSB_Mn possesses a moderate enthalpy of reduction (252.51–296.32 kJ / mol-oxide), a high entropy of reduction (126.95–168.85 J / mol-oxide), and fast surface oxygen exchange kinetics. All A-site cations do not show observable valence changes during the reduction and oxidation processes. This research preliminarily explores the use of one A-site high-entropy perovskite oxide for STCH.