Synthesis and characterization of Ce1–x(Gd1/5Sm1/5Er1/5Y1/5Bi1/5)xO2–δ solid electrolyte for SOFCs

Abstract

This study focuses on the impact of Gd3+, Sm3+, Er3+, Y3+, and Bi3+ multi-doping on the crystal structure, microscopic surface features, and ionic conductivity of cerium dioxide in the Ce1–x(Gd1/5Sm1/5Er1/5Y1/5Bi1/5)xO2–δ (GSEYB) system. This system holds promise as a solid electrolyte material for low and medium-temperature solid oxide fuel cells. The powders of Ce1–x(Gd1/5Sm1/5Er1/5Y1/5Bi1/5)xO2–δ (x = 0, 0.10, 0.15, 0.20, 0.25, 0.30) were synthesized using the solid-phase reaction method. The GSEYB electrolytes were comprehensively investigated for their phase structure, microstructure, oxygen vacancy concentration, and ionic conductivity using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and impedance spectroscopy. XRD diffraction patterns confirm a cubic fluorite-type structure with Fm3m space groups in all multi-doped systems. After sintering at 1400 °C for 10 h, the relative density of doped samples exceeds 96%. In terms of electrical properties, the Ce0.75Gd0.05Sm0.05Er0.05Y0.05Bi0.05O2–δ (x = 0.25) electrolyte exhibits the highest ionic conductivity (σt = 4.45 × 10−2 S/cm) and the lowest activation energy (Ea = 0.79 eV) at 800 °C. The coefficient of thermal expansion of the developed electrolyte aligns well with that of the commonly used electrode materials. This compatibility positions it as a highly promising candidate for utilization as an electrolyte material in solid oxide fuel cells (SOFCs).