Green synthesis of FeNi₃/FeNiOₓ nanosponges via aluminum cementation for PGM-free anion exchange membrane water electrolysis

Low-temperature anion exchange membrane water electrolyzer (AEMWE) is widely recognized as a highly promising approach for sustainable hydrogen production. Nevertheless, current membrane–electrode assemblies (MEAs) still achieve their best performance when employing platinum group metal (PGM)-based electrocatalysts, while PGM-free alternatives generally exhibit inferior activity. In this study, a straightforward and unified synthetic route is presented for the preparation of non-noble metal electrocatalysts suitable for both the hydrogen and oxygen evolution reactions (HER and OER). The resulting electrocatalysts are composed of FeNi₃/FeNiOx nanosponges and were produced by a straightforward two-step synthetic route in aqueous solution, exploiting aluminum powder as a cementation agent. The developed electrocatalyst delivers overpotentials of 97 mV for the HER and 254 mV for the OER at a current density of 10 mA cm⁻² in 1 M KOH, enabling a direct assessment of both mass-specific and geometric activities in comparison with PGM-based electrocatalysts. Beyond the initial electrochemical evaluation of the FeNi₃/FeNiOx material, the electrocatalyst was integrated into an MEA, operating as both the anode and the cathode and tested in an AEMWE. Under these conditions, the device achieved a cell voltage of 2.037 V at 1 A cm⁻² and 50 °C, without iR correction. Notably, the resulting PGM-free MEA exhibited superior performance relative to a benchmark configuration employing Pt/C at the cathode and RuO₂ at the anode, with a voltage reduction of 105 mV at 1 A cm⁻². Long-term operation was evaluated over 150 h under a discontinuous power profile to gain insight into degradation behavior relevant to industrial operation. These results highlight a simple and scalable approach to the synthesis of earth-abundant electrocatalysts enabling high-performance AEMWE.