NiMoO₄ Nanowires Supported on Stainless-Steel, Carbon, and Nickel Fiber Papers as Catalysts for the Oxygen Evolution Reaction in Anion Exchange Membrane Water Electrolysis

Designing efficient and durable anodes remains a key challenge for anion exchange membrane water electrolysis (AEMWE), where catalyst layer/porous transport layer (CL/PTL) integration critically governs interfacial resistance, electronic coupling, and long-term stability. Here, NiMoO4 nanowires were hydrothermally grown in situ on carbon paper (CP), stainless steel fiber paper (SSP), and nickel fiber paper (NFP) to fabricate binder-free CL/PTL electrodes. Among these substrates, SSP provided the most favorable interfacial environment, where Fe incorporation during hydrothermal growth enriched Ni3+ species and defect oxygen while maintaining a balanced Mo5+/Mo6+ ratio. As a result, NiMoO4/SSP achieved 2.67 A cm–2 at 2.0 V under cathode-wet operation at 70 °C and maintained 1.83 A cm–2 under cathode-dry conditions, significantly outperforming NiMoO4/CP and NiMoO4/NFP. Durability tests confirmed stable operation with only a minor voltage increase over 60 h, and post-durability analyses revealed Mo leaching and the self-reconstruction of NiMoO4 into γ-NiOOH, the catalytically active phase. This study demonstrates substrate engineering, integrating interfacial coupling with substrate-derived doping, as an effective strategy for advancing high-performance and durable AEMWE anodes.