Systematic Studies of Phase Relation and Thermodynamic Stability of Ln-Rh-O System for Catalysis and Electrochemical Devices

Abstract

Ln-Rh-O systems show potential interest in different catalytic applications. Phase diagram of these systems revealed that only LnRhO3, an orthorhombic perovskite structure, has been found as stable ternary oxide. Employed solid-state electrochemical cell to determine the thermodynamic parameters of LnRhO3 compounds from their binary oxides Rh2O3 and Ln2O3. Calcia stabilized and yttria stabilized zirconia has been used as solid electrolytes in these cells. Ternary phase relation for Ln-Rh-O systems is established using isothermal equilibration technique. Phase diagram of few Ln-Rh-O systems are computed with the help of supplementary data for other binary phases (Ln-Rh) from the literature and thermodynamic data for LnRhO3 from experiment at high temperature. At 298.15 K, 〖∆H〗_f^0and S^0for LnRhO3are calculated from its constituting elements. Thermodynamic data has been used to compute an oxygen potential ‒ composition and three-dimensional chemical potential diagram for the system Ln-Rh-O.