Preparation of Hollow Cobalt-Iron Phosphides Nanospheres by Controllable Atom Migration for Enhanced Water Oxidation and Splitting.

Transition metal phosphides (TMPs), especially the dual-metal TMPs, are highly active non-precious metal oxygen evolution reaction (OER) electrocatalysts. Herein, an interesting atom migration phenomenon induced by Kirkendall effect is reported for the preparation of cobalt-iron (Co-Fe) phosphides by the direct phosphorization of Co-Fe alloys. The compositions and distributions of the Co and Fe phosphides phases on the surfaces of the electrocatalysts can be readily controlled by Co Fe alloys precursors and the phosphorization process with interesting atom migration phenomenon. The optimized Co Fe phosphides exhibit a low overpotential of 225 mV at 10 mA cm in 1 m KOH alkaline media, with a small Tafel slope of 37.88 mV dec and excellent durability. It only requires a voltage of 1.56 V to drive the current density of 10 mA cm when used as both anode and cathode for overall water splitting. This work opens a new strategy to controllable preparation of dual-metal TMPs with designed phosphides active sites for enhanced OER and overall water splitting.