A medium-entropy oxygen electrode enables high-performance and contaminant-tolerant reversible solid oxide cells

The development of oxygen electrodes with sufficient oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activity, as well as good tolerance to contaminants, is crucial for promoting the commercialization of reversible solid oxide cells (Re-SOCs) technologies. Herein, we design and synthesize a medium-entropy oxygen electrode with a formula of Pr0.5Ba0.2Sr0.2Ca0.1CoO3-δ (ME-PBSCC). The abundant surface oxygen vacancy concentration, high electrical conductivity, rapid and stable oxygen exchange kinetics, and structural stability of the ME-PBSCC oxygen electrode ensure the efficient and poisoning-tolerant ORR/OER in ambient air and Cr-contaminated atmosphere. Specifically, Re-SOCs incorporating the PBSCC oxygen electrodes exhibit maximum power densities of 2.239 (in ambient air) and 1.859 W cm-2 (in a Cr-contaminated air) at 750 oC in fuel cell (FC) mode, and current densities of 1.10 A cm-2 at 1.3 V and 700 oC under 50% H2O (in a Cr-contaminated air) in electrolysis (EC) mode, demonstrating competitive performance for Re-SOCs. More importantly, the developed ME-PBSCC oxygen electrode has achieved the highly promising stable operation of Re-SOCs in FC, EC, and reversible modes in the presence of Cr contamination. Reversible solid oxide cells are hindered by inadequate electrode activity and tolerance against contaminants. Here, the authors present an oxygen electrode delivering promising electrochemical performance and stable operation in fuel cell, electrolysis cell, and reversible cycling modes with Cr contaminations.