Dynamic Molybdate Oxyanion Boosts Self-Optimization and Self-Healing on the NiMoFe Heterostructure for Water Splitting in Alkaline Media

Abstract

NiMo-based alloys and NiFe layered double hydroxides (NiFe-LDHs) are the most promising nonpreciousmetal electrocatalysts for hydrogen and oxygen evolution reactions (HER and OER) under alkaline conditions. However, the ready leaching of Mo and Fe during electrolysis may cause dynamic variation of the surface composition and structure of the catalysts. Here, we developed a NiMoFe heterostructure consisting of NiMoFe alloy and MoO 4 2− -intercalated NiFe-LDH (NiMoFe HI), which enables self-optimization of HER and self-healing of OER through the dynamic exchange of MoO 4 2− species. During the HER process, the leaching and readsorption of MoO 4 2− optimizes the electronic structure of NiFe-LDH, facilitating H 2 O adsorption and dissociation. Simultaneously, the repulsion of OH − by accumulated MoO 4 2− in the electric double layer can more rapidly drive the transfer kinetics of *OH + e ⇌ OH − to promote the desorption of *OH from the active sites, thus continuously enhancing the HER activity. During the OER process, the dynamic equilibrium of MoO 4 2− facilitates the readsorption of active Fe(OH) x species on the NiFeOOH surface and reduces the energy barrier of the OER rate-determining step, achieving self-healing of the OER activity. Benefiting from the self-optimization and self-healing properties for HER and OER, NiMoFe LDH exhibits promising performance in alkaline water splitting, with a low cell voltage of 1.528 V at 10 mA•cm −2 and stable operation at a high current density of 100 mA•cm −2 for 150 h.