A carbon-free, precious-metal-free, high-performance O2 electrode for regenerative fuel cells and metal–air batteries

Abstract

The development of high-performance and cost-effective electrodes for oxygen evolution and oxygen reduction is critical for enabling the use of energy storage devices based on O₂–H₂O chemistries such as metal–air batteries and unitized regenerative fuel cells (URFCs). Herein, we report a precious-metal-free and carbon-free O₂ electrode synthesized via electrodeposition of manganese oxide (MnO_x) on a stainless steel (SS) substrate followed by high-temperature calcination at 480 °C. The MnO_x–SS electrode displays high oxygen reduction and water oxidation activities when tested in an electrochemical cell, comparable to that of a precious-metal based electrode, Pt/C–SS. Accelerated durability testing reveals the excellent stability of the MnO_x–SS electrode compared to both the Pt/C–SS electrode and a carbon-based electrode with MnO_x and Ni catalysts. This can be rationalized by the carbon-free nature of the MnO_x–SS electrode which circumvents carbon corrosion at the high electrochemical potentials during water oxidation and O₂ reduction. Integrating the MnO_x–SS electrode as the O₂ electrode into an anion exchange membrane (AEM) URFC produces round-trip efficiencies of 42–45% at 20 mA cm⁻² over 10 cycles, and exhibits significantly enhanced durability compared to the carbon-based analogue. This work demonstrates the MnO_x–SS electrode's potential for use as a high performance, scalable, precious-metal-free and carbon-free O₂ electrode in AEM-URFCs and metal–air batteries.