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 (MnOx) on a stainless steel (SS) substrate followed by high-temperature calcination at 480 °C. The MnOx–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 MnOx–SS electrode compared to both the Pt/C–SS electrode and a carbon-based electrode with MnOx and Ni catalysts. This can be rationalized by the carbon-free nature of the MnOx–SS electrode which circumvents carbon corrosion at the high electrochemical potentials during water oxidation and O2 reduction. Integrating the MnOx–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 MnOx–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.
