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

Area of Science:

• Materials Science
• Electrochemistry
• Energy Conversion and Storage

Background:

• Commercialization of reversible solid oxide cells (Re-SOCs) hinges on developing oxygen electrodes with high oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activity.
• Existing oxygen electrodes often suffer from poor tolerance to contaminants like chromium, limiting their practical application.
• The need for stable, efficient, and poisoning-tolerant oxygen electrodes is critical for advancing Re-SOC technology.

Purpose of the Study:

• To design and synthesize a novel medium-entropy oxygen electrode material for Re-SOCs.
• To evaluate the performance of the new electrode in both fuel cell (FC) and electrolysis (EC) modes under various conditions, including chromium contamination.
• To demonstrate the stable and efficient operation of Re-SOCs utilizing the developed oxygen electrode.

Main Methods:

• Synthesis of a medium-entropy oxygen electrode with the composition Pr$_{0.5}$Ba$_{0.2}$Sr$_{0.2}$Ca$_{0.1}$CoO$_{3-δ}$ (ME-PBSCC).
• Characterization of the ME-PBSCC electrode's properties, including surface oxygen vacancy concentration, electrical conductivity, oxygen exchange kinetics, and structural stability.
• Integration of the ME-PBSCC electrode into Re-SOC devices and testing of their performance in FC and EC modes in ambient air and Cr-contaminated air.

Main Results:

• The ME-PBSCC electrode exhibits high surface oxygen vacancy concentration, excellent electrical conductivity, and rapid, stable oxygen exchange kinetics.
• Re-SOCs with ME-PBSCC electrodes achieved maximum power densities of 2.239 W cm$^{-2}$ (air) and 1.859 W cm$^{-2}$ (Cr-contaminated air) at 750 °C in FC mode.
• In EC mode, Re-SOCs demonstrated current densities of 1.10 A cm$^{-2}$ at 1.3 V and 700 °C under 50% H$_{2}$O in Cr-contaminated air, with stable operation in FC, EC, and reversible modes.

Conclusions:

• The developed ME-PBSCC oxygen electrode offers efficient and poisoning-tolerant ORR/OER performance, crucial for Re-SOC commercialization.
• The material's stability and high activity under chromium contamination highlight its potential for practical Re-SOC applications.
• This work presents a promising pathway for achieving robust and high-performance Re-SOCs capable of operating reliably in contaminated environments.