High-performance water electrolyzer with minimum platinum group metal usage: Iron nitride-iridium oxide core-shell nanostructures for stable and efficient oxygen evolution reaction

To reduce the usage of rare-earth metals in a proton-exchange-membrane water electrolyzer (PEMWE), a highly active water-oxidizing anode based on a core-shell catalyst structure was developed. Earth-abundant metalbased iron-nitride nanostructure was adopted to support thin, electrodeposited iridium-oxide films. PEMWEs with core-shell nanostructure has substantially low ohmic and mass-transfer resistances, suggesting that the introduction of Fe2N nanostructure on Ti PTL enhances the transfer of protons, water, and oxygen on the catalyst layer. Furthermore, a high Ir mass activity of 103 A/mgIr was achieved with reduced Ir loading of 0.036 mg/cm2 on the Ti PTL. The well-known weakness of transition-metal nitrides (TMNs) for use in PEMWEs, that is, their chemical instability in corrosive acidic environments, was overcome by carefully passivating the surfaces of the TMNs with chemically stable Ir catalyst layers. As a result, the prepared core-shell-structured catalysts were stable under the PEMWE operating condition.