In-situ structure reconstitution of NiCo2Px for enhanced electrochemical water oxidation

Gaining insight into the structure evolution of transition-metal phosphides during anodic oxidation is significant to understand their oxygen evolution reaction （OER） mechanism, and then design high- efficiency transition metal-based catalysts. Herein, NiCo2Px nanowires （NWs） vertically grown on Ni foam were adopted as the target to explore the insitu morphology and chemical component reconstitution during the anodic oxidation. The major factors causing the transformation from NiCo2Px into the hierarchical NiCo2Px@CoNi（OOH）x NWs are two competing reactions： the dissolution of NiCo2Px NWs and the oxidative re-deposition of dissolved Co^2＋ and Ni^2＋ ions, which is based primarily on the anodic bias applied on NiCo2Px NWs. The well balance of above competing reactions, and local pH on the surface of NiCo2Px NW modulated by the anodic oxidation can serve to control the anodic electrodeposition and rearrangement of metal ions on the surface of NiCo2Px NWs, and the immediate conversion into CoNi（OOH）x. Consequently, the regular hexagonal CoNi（OOH）x nanosheets grew around NiCo2Px NWs. Benefiting from the active catalytic sites on the surface and the sufficient conductivity, the resultant NiCo2Px@CoNi（OOH）x arrays also display good OER activity, in terms of the fast kinetics process, the high energy conversion efficiency, especially the excellent durability. The strategy of in-situ structure reconstitution by electrochemical reaction described here offers a reliable and valid way to construct the highly active systems for various electrocatalvtic applications.