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

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 O-2-H2O chemistries such as metal-air batteries and unitized regenerative fuel cells (URFCs). Herein, we report a precious-metal-free and carbon-free O-2 electrode synthesized via electrodeposition of manganese oxide (MnOx) on a stainless steel (SS) substrate followed by high-temperature calcination at 480 degrees 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 O-2 reduction. Integrating the MnOx-SS electrode as the O-2 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 O-2 electrode in AEM-URFCs and metal-air batteries.