A unitized regenerative fuel cell (URFC) that uses a single cell that functions in electrolysis or fuel cell mode provides potential advantages including lower cost, mass, and volume compared with discrete electrolyzer and fuel cell systems. However, significant challenges for URFCs include lower performance, lower round-trip efficiency, and higher stability/degradation issues compared with separate systems. The lower performance and enhanced degradation of URFCs results from a combination of factors including catalyst degradation and water management issues that result from switching between electrolyzer and fuel cell modes. To address these challenges and improve performance of proton-exchange membrane (PEM) URFCs in both fuel cell and electrolyzer modes, we evaluated the effects of catalyst and electrode composition of the bifunctional oxygen electrode. To improve catalyst activity and efficiency of the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), we explored using bifunctional oxygen catalysts composed of bimetallic nanoframes derived from our prior studies.^1,2 Electrochemical testing using a rotating disk electrode configuration showed that the nanoframe bifunctional oxygen electrocatalysts have higher ORR mass activity, OER mass activity, and round-trip efficiency and reasonable stability compared with baseline Pt-IrO₂ catalysts. URFC membrane electrode assemblies (MEAs) were fabricated and tested to determine the effect of the composition of the oxygen electrode on fuel cell and electrolyzer performance and evaluate the effect of switching between operating in fuel cell and electrolyzer modes. Performance comparisons were made with MEAs composed of baseline commercial Pt black-IrO₂ catalysts.

References

1. Godinez-Salomon, F.; Mendoza-Cruz, R.; Arellano-Jimenez, M. J.; Jose-Yacaman, M.; Rhodes, C. P., Metallic Two-Dimensional Nanoframes: Unsupported Hierarchical Nickel-Platinum Alloy Nanoarchitectures with Enhanced Electrochemical Oxygen Reduction Activity and Stability. ACS Appl. Mater. Interfaces 2017, 9, 18660-18674. DOI: 10.1021/acsami.7b00043
2. Godínez-Salomón, F.; Albiter, L.; Alia, S. M.; Pivovar, B. S.; Camacho-Forero, L. E.; Balbuena, P. B.; Mendoza-Cruz, R.; Arellano-Jimenez, M. J.; Rhodes, C. P., Self-Supported Hydrous Iridium–Nickel Oxide Two-Dimensional Nanoframes for High Activity Oxygen Evolution Electrocatalysts. ACS Catal. 2018, 8, 10498-10520. DOI: 10.1021/acscatal.8b02171