Carbon-coated cobalt iron bimetallic phosphide as a bifunctional electrocatalyst for overall water splitting

Abstract

Transition metal phosphides have been widely used in the design of water splitting electrodes because of their high catalytic activity. However, due to the different reaction kinetics of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in different media, a major challenge is how to achieve the transition metal phosphides electrocatalysts afford high performance of both HER and OER in the same electrolyte. Herein, a novel bifunctional electrocatalyst with carbon-coated cobalt iron bimetallic phosphide (CoFeP@C/NF-2) was self-assembled on nickel foam by hydrothermal and phosphidation pathway. Benefiting from its unique flower-like structure, and the synergistic effect of bimetallic phosphides and carbon coated, which not only offered abundant catalytic active sites but also accelerated electronic transmission, the CoFeP@C/NF-2 could act a bifunctional electrocatalyst that was simultaneously used for OER and HER. The CoFeP@C/NF-2 hybrid delivered a high OER catalytic activity in alkaline electrolyte, with a low overpotential of 119 and 217 mV at current densities of 10 and 50 mA cm−2, respectively. The CoFeP@C/NF-2 electrode also exhibited a considerable OER stability over 20 h. Meanwhile, when serving as a catalyst for the HER under alkaline condition, it showed an overpotential of 155 mV at a current density of 10 mA cm−2. Furthermore, the assembled electrolytic cell using CoFeP@C/NF-2 only required a voltage of 1.59 V to achieve the current density of 10 mA cm−2 for the overall water splitting. This work provides a general strategy for improving the water splitting performance of phosphides, which can be applied to the preparation of other transition metal catalysts.