Modeling Thermochemical Solar-to-Fuel Conversion: CALPHAD for Thermodynamic Assessment Studies of Perovskites, Exemplified for (La, Sr)MnO3

Two-step solar thermochemical fuel production has the potential to reduce global greenhouse gas emissions and replace fossil fuels. The success of the technology relies on the development of materials with high thermochemical efficiency. Perovskites with the general structure ABO(3) have received much attention recently due to impressive fuel productivity and their amenability of substituting and doping both A-and B-site. Despite the potential of perovskites for solar-to-fuel conversion, literature on their solar thermochemical efficiency is scarce and finding the best chemical composition and optimum operation conditions is unknown. For this purpose, this study suggests to use Computer Coupling of Phase Diagrams and Thermochemistry (CALPHAD) data libraries to access the relevant thermodynamic properties of perovskites. This work demonstrates the usefulness of employing CALPHAD data by a full thermodynamic study of the model case compositions of La1-xSrxMnO3-delta. This study uses data on oxygen-nonstoichiometry and heat capacity in the temperature range of 1073-1873 K relevant for solar-to-fuel. Unlike earlier thermodynamic assessments of perovskites that rely on a single literature source and a limited temperature range, the CALPHAD approach takes all available data in literature into consideration. Thermochemical equilibrium models of fuel yields are accompanied by validations toward experimental results in literature, and this study highlights the effects of strontium doping level on the efficiency.