Defect Chemistry and Transport Properties of Lanthanum Cerate as an Electrolyte Membrane in Protonic Ceramic Electrolysis Cells

Lanthanum cerate La 2 Ce 2 O 7 (LCO) (or lanthanum-doped ceria Ce 0.5 La 0.5 O 2− δ , LDC50) can serve as a proton-conducting electrolyte membrane in fuel-cell or electrolysis applications. The primary purpose of this paper is to develop thermodynamic and transport properties, based on fits to previously published conductivity and water-uptake measurements. The properties include reaction enthalpies and entropies for three defect-incorporation reactions and four mobile charged-defect diffusion coefficients. In addition to protons and oxygen vacancies, the analysis considers two small polarons. The analysis is motivated, in part, by the application of LDC as a thin barrier layer in a dual-layer composite electrolysis membrane that protects a high proton-conductivity BaCe 0.7 Zr 0.1 Y 0.1 Yb 0.1 O 3− δ (BCZYYb7111) from degradation in high steam environments. The paper uses the best-fit LDC properties in a physics-based model to predict defect transport within LDC and composite LDC/BCZYYb membranes.