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A.H. Bork, E. Povoden-Karadeniz, J.L.M. Rupp:
"Two-step thermochemical solar-to-fuel efficiency CALPHAD computation for strontium and chromium doped lanthanum manganite perovskite oxides";
Poster: Calphad XlV, Awaji Island, Hyogo, Japan; 2016-05-29 - 2016-06-03.

A key to ensuring a sustainable energy future is to develop technologies producing sustainable fuels and reducing greenhouse gas emissions. Two-step thermochemical fuel production, is an energy conversion technology utilizing solar thermal energy to heat a solid which catalyses conversion of water and carbon dioxide into syngas, a renewable fuel that can replace fossil fuels and mitigate CO2 emissions [1].

Practical implementation of the technology is predicated on the discovery of materials with a high thermochemical solar-to-fuel conversion efficiency. Perovskites have attracted much attention recently due to impressive fuel productivity [2,3]. A high fuel productivity shows the viability of a material, but it does not imply that it is the material with highest efficiency [4]. Literature on solar thermochemical efficiency of perovskites is scarce and none of the existing studies determine the input data, such as heat capacity and oxygen nonstoichiometry, in the entire technological relevant temperature range of 1000-1800K. One can expect discrepancies in the oxygen nonstoichiometry and heat capacity when the data is extrapolated over a wide temperature range, which results in less reliable estimates of the actual efficiency.

Here, we use CALPHAD data libraries on heat capacity and oxygen nonstoichiometry data of the compositions La1-xSrxMn1-yCryO3-δ in the entire relevant temperature range of 1073-1873K for the solar-to-fuel application. Thermochemical equilibrium models of fuel productivity are accompanied by validations with experimental results in literature. Further, we make predictions on the most efficient material in the composition space La1-xSrxMn1-yCryO3-δ for different conditions, e.g. water partial pressure and operation temperature. The models reveal that the optimum material is highly dependent on the solar reactor operating conditions. Due to the wide possibilities of doping in perovskites, there is great need for mapping their thermodynamic properties in the temperature range of 1000-1800K. The necessary key experiments for CALPHAD modelling extended to further promising perovskite candidates with high potential for this appealing renewable energy technology are discussed.