In-situ structure reconstitution of NiCo₂P_x 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, NiCo₂P_x nanowires (NWs) vertically grown on Ni foam were adopted as the target to explore the in-situ morphology and chemical component reconstitution during the anodic oxidation. The major factors causing the transformation from NiCo₂P_x into the hierarchical NiCo₂P_x@CoNi(OOH)_x NWs are two competing reactions: the dissolution of NiCo₂P_x NWs and the oxidative re-deposition of dissolved Co²⁺ and Ni²⁺ ions, which is based primarily on the anodic bias applied on NiCo₂P_x NWs. The well balance of above competing reactions, and local pH on the surface of NiCo₂P_x NW modulated by the anodic oxidation can serve to control the anodic electrodeposition and rearrangement of metal ions on the surface of NiCo₂P_x NWs, and the immediate conversion into CoNi(OOH)_x. Consequently, the regular hexagonal CoNi(OOH)_x nanosheets grew around NiCo₂P_x NWs. Benefiting from the active catalytic sites on the surface and the sufficient conductivity, the resultant NiCo₂P_x@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 electrocatalytic applications.