Comparative study on the electrochemical properties of scandium doped CaHfO3 and CaZrO3 perovskite proton conductors in medium temperature electrochemical devices

This study investigates the electrochemical properties of two perovskite-type proton conductors, CaHf 0.82 Sc 0.18 O 2.91 (CHSc) and CaZr 0.82 Sc 0.18 O 2.91 (CZSc), synthesized via a high-temperature solid-state reaction method. The materials were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and AC impedance spectroscopy to evaluate their phase structure, morphology, and electrical conductivity. Both compositions formed dense, single-phase orthorhombic perovskite structures. The research systematically compares their performance, focusing on proton conductivity, chemical stability, and chemical diffusion coefficients. Key analyses, including the H/D isotope effect and electromotive force (EMF) measurements, were conducted to delineate the dominant charge carriers and optimal operating temperature ranges. Results demonstrate that both materials function as proton conductors below 1173 K, with proton transport numbers exceeding 0.90. Notably, the CHSc electrolyte exhibited superior overall electrochemical performance, including higher conductivity and chemical diffusion coefficient, compared to its zirconium-based counterpart. This enhanced performance is attributed to CHSc exhibiting higher chemical diffusion coefficient, proton transport number, and water hydration ability in the range of 873-1173 K. These findings underscore the potential of Sc-doped CaHfO 3 (CHO) as a promising electrolyte for intermediate-temperature electrochemical devices like hydrogen sensors and fuel cells.