Modeling the reduction thermodynamics of simple and Ruddlesden-Popper cerium-doped perovskites for solar thermochemical hydrogen production

Abstract

In this work, the compositional families Sr1-xCexMnO3−δ (SCMX, X = 100x,x= 0.10, 0.20, & 0.30) and CexSr2-xMnO4−δ (CSMX, X=100x, x= 0.10, 0.20, & 0.30) are studied to determine the effects of perovskite structure and cerium content on the thermal reduction thermodynamics and the resulting impact on solar thermochemical hydrogen-production (STCH). Relying on thermogravimetric results from oxygen nonstoichiometry experiments, fits for various thermodynamic quantities, including defect-reaction specific enthalpy and entropy, ∆H◦ and ∆S◦, as well as theδ-dependent standard partial molar enthalpy and entropy of oxygen, ∆ ̄h◦O and ∆ ̄s◦O, are produced as a function of composition within these two perovskite families using a thermodynamic model developed herein. The results of this thermodynamic study in the context of structure and cerium dopant level are discussed, and several improvements to the model are proposed and explored. Experimental hydrogen production results show that the SCM family produces slightly larger amounts of hydrogen per mole of oxide compared to the CSM family under similar reduction and oxidation temperature conditions, however a direct correlation between structure, cerium content and water-splitting capacity could not be discerned. Lastly, compositions of Ca1-xCexMnO3−δ(CCMX, X = 100x, x= 0, 0.10 & 0.20) are explored for the composition’s predicted ability to reduce on both the A- and B-sites of the simple perovskite oxide material, however low melting temperatures prevent further study of this compositional family for STCH purposes.