Ultra-stable self-supported bifunctional iron phosphide catalysts for anion exchange membrane water electrolyzer at industrial-scale current density

Catalysts and catalytic electrodes for anion exchange membrane water electrolyzers (AEMWEs) face challenges including ionomeric binder instability, high cost of noble metal-based catalysts, and insufficient activity of non-noble metal alternatives. Herein, we report a low-cost strategy to prepare ultra-stable self-supported bifunctional iron phosphide (FeP) catalysts for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The catalysts were fabricated via facile high-temperature oxidation of industrial stainless-steel felts (SSFs) followed by phosphating. Oxidation promotes the following phosphidation with high surface area exposure and conducts robust interfacial bonding between the FeP layer and SSF substrate, ensuring stable operation at high current densities and long-term durability. Phosphidation optimizes the surface electronic structure and enhances the synergistic effect of multiple metals from SSFs, endowing the catalysts with excellent alkaline catalytic activity. Notably, FeP/SSF-700-5 exhibits superior bifunctional performance, achieving 10 mA cm −2 at overpotentials of 297 mV (OER) and 105 mV (HER). When used as the anode in an AEM electrolyzer, it reached the industrial current density of 1 A cm −2 at 1.7693 V; as the cathode, 1.8729 V was required for the same current density. Both configurations showed no obvious degradation after 4000 h electrolysis at 1 A cm −2 . When employed as both anode and cathode, FeP/SSF-700-5 enabled the electrolyzer to operate at 1.9414 V at 1 A cm −2 , with an ultra-low degradation rate of −3.8 μV/h. This study provides a high-performance, stable self-supported bifunctional catalyst, laying a solid foundation for the rational design of non-precious metal catalysts in large-scale industrial applications.