Tailoring hollow structure within NiCoP nanowire arrays via nanoscale Kirkendall diffusion to enhance hydrogen evolution reaction.

Hollow structured nanomaterials with void space available inside the shells can effectively enhance electrocatalytic activity due to their high specific surface area, volume buffer and shell permeability properties. In this study, low-cost and hollow structured bimetal phosphide nanowires are synthesized directly on Ni foam via the Kirkendall effect by using NaH2PO2 as a phosphorizing agent at 350 °C. Both the crystal and hollow structures of the obtained phosphide can be efficiently tuned by controlling the amount of phosphorizing agent and the phosphorizing time. The morphology and microstructure of the obtained phosphides are characterised using various techniques, which indicate that the formation mechanism of the hollow structure is consistent with the Kirkendall effect. The optimized bimetal phosphide sample demonstrates a low onset potential (59 mV) at a current density of 10 mA cm-2, low charge transfer resistance (0.83 Ω) and superior durability in the hydrogen evolution reaction (HER) for water electrolysis. The electrochemical results clearly demonstrate that the hollow structure can efficiently improve the HER properties and the obtained phosphide is a promising HER catalysts for water splitting in KOH or seawater electrolytes.