Co-deficient PrBaCo2−xO6−δ perovskites as cathode materials for intermediate-temperature solid oxide fuel cells: Enhanced electrochemical performance and oxygen reduction kinetics

Abstract

Co-deficient PrBaCo2−xO6−δ perovskites (x = 0, 0.02, 0.06 and 0.1) are synthesized by a solid-state reaction, and the effects of Co-deficiency on the crystal structure, oxygen nonstoichiometry and electrochemical properties are investigated. The PrBaCo2−xO6−δ samples have an orthorhombic layered perovskite structure with double c axis. The degree of oxygen nonstoichiometry increases with decreasing Co content (0 ≤ x ≤ 0.06) and then slightly decreases at x = 0.1. All the samples exhibit the electrical conductivity values of >300 S cm−1 in the temperature range of 100–800 °C in air, which match well the requirement of cathode. With significantly enhanced electrochemical performance and good chemical compatibility between PrBaCo2−xO6−δ and CGO, this system of Co-deficient perovskite is promising cathode material for IT-SOFCs. Among all these components, PrBaCo1.94O6−δ gives lowest polarization resistance of 0.059 Ω cm2 at 700 °C in air. When tested as cathode in fuel cell, the anode-supported Ni-YSZ|YSZ|CGO|PrBaCo1.94O6−δ cell delivers a maximum peak power density of 889 mW cm−2 at 650 °C, which is higher than that of PrBaCoO6−δ cathode-based cell (764 mW cm−2). The oxygen reduction kinetics at the PrBaCo1.94O6−δ cathode interface is also explored, and the rate-limiting steps for oxygen reduction reaction are determined.