Thermodynamic assessment of the solar-to-fuel performance of La0.6Sr0.4Mn1-yCryO3- perovskite solid solution series

Abstract

© 2019 In the search of new materials for the solar-to-fuel technology, we turn to the material class of perovskites that offer wide possibilities in manipulation of its chemistry and redox activity. Here, we access the role of Cr in the La0.6Sr0.4Mn1-yCryO3-δ perovskite solid solution hitherto unexplored for two-step solar thermochemical fuel production. A multi-component Calphad defect model for the system La–Sr–Cr–Mn–O is therefore optimized and used for computations of oxygen nonstoichiometries and redox thermodynamics of the La0.6Sr0.4Mn1-yCryO3-δ solution series in the temperature range of 1073–1873 K as a potential operation window for solar-to-fuel conversion. Modeling results reveal two advantages of substituting manganese by chromium. Firstly, it is possible to reduce the heat capacity with up to 10%, to a value of 132 J mol−1 K−1. Secondly, the thermodynamic driving force for solar-to-fuel conversion increases and the Cr-doped materials provide higher yield and efficiency at isothermal operation. The proposed model allows for continuous simulative scanning of redox thermodynamics from zero Cr-doping to a fully substituted chromite perovskite. For isothermal water splitting, the composition La0.6Sr0.4Mn0.2Cr0.8O3-δ displays the highest fuel yield and efficiency of 2.7% due to a high thermodynamic driving force at elevated temperature for this composition. These predictive insights give prospects for engineering the thermodynamics of the oxygen release reaction in perovskites towards higher fuel production and efficiency in solar-to-fuel reactors with isothermal operation.