Dynamic Molybdate\nOxyanion Boosts Self-Optimization\nand Self-Healing on the NiMoFe Heterostructure for Water Splitting\nin Alkaline Media

NiMo-based alloys and NiFe layered double hydroxides\n(NiFe-LDHs)\nare the most promising nonprecious-metal electrocatalysts for hydrogen\nand oxygen evolution reactions (HER and OER) under alkaline conditions.\nHowever, the ready leaching of Mo and Fe during electrolysis may cause\ndynamic variation of the surface composition and structure of the\ncatalysts. Here, we developed a NiMoFe heterostructure consisting\nof NiMoFe alloy and MoO<sub>4</sub><sup>2–</sup>-intercalated\nNiFe-LDH (NiMoFe HI), which enables self-optimization of HER and self-healing\nof OER through the dynamic exchange of MoO<sub>4</sub><sup>2–</sup> species. During the HER process, the leaching and readsorption of\nMoO<sub>4</sub><sup>2–</sup> optimizes the electronic structure\nof NiFe-LDH, facilitating H<sub>2</sub>O adsorption and dissociation.\nSimultaneously, the repulsion of OH<sup>–</sup> by accumulated\nMoO<sub>4</sub><sup>2–</sup> in the electric double layer can\nmore rapidly drive the transfer kinetics of *OH + e ⇌ OH<sup>–</sup> to promote the desorption of *OH from the active sites,\nthus continuously enhancing the HER activity. During the OER process,\nthe dynamic equilibrium of MoO<sub>4</sub><sup>2–</sup> facilitates\nthe readsorption of active Fe(OH)<sub><i>x</i></sub> species\non the NiFeOOH surface and reduces the energy barrier of the OER rate-determining\nstep, achieving self-healing of the OER activity. Benefiting from\nthe self-optimization and self-healing properties for HER and OER,\nNiMoFe LDH exhibits promising performance in alkaline water splitting,\nwith a low cell voltage of 1.528 V at 10 mA·cm<sup>–2</sup> and stable operation at a high current density of 100 mA·cm<sup>–2</sup> for 150 h.