Simultaneous nanoporous and intermetallic engineering of NiMo electrodes for efficient and stable alkaline water electrolysis

Ni-Mo alloys are highly promising low-cost electrode materials for alkaline water electrolysis (AWE), but their activity and stability often appear to be mutually exclusive due to undesirable dissolution of Mo. Here we address this challenge by applying a high-temperature gaseous oxidation-reduction (GOR) treatment to commercial Ni-Mo/Ni foam. This treatment in situ generates nanopores within the originally hundred-micron porous skeleton of Ni-Mo/Ni foam, while transforms the solid-solution Ni-Mo alloy into intermetallic Ni₄Mo. The intermetallic Ni₄Mo effectively suppresses Mo dissolution. Additionally, the hierarchical pores facilitates the rapid formation of a protective NiOOH layer that traps dissolved Mo species in the oxygen evolution reaction. Consequently, the hierarchical porous Ni₄Mo/Ni electrode achieves efficient AWE activity and stability, maintaining performance over 2200 h with negligible Mo dissolution (∼0.13 μg mL^–1). This study highlights that the GOR treatment is an effective “structure-phase" synergistic regulation for designing electrode materials with both long-term stability and high catalytic efficiency.