Preparation of Yolk–Shell-Structured CoxFe1−xP with Enhanced OER Performance

Graphical Eggselent electrocatalysts : Yolk–shell Co x Fe 1− x P microspheres are fabricated by phosphidation of cobalt ferrite precursors and used as electrocatalysts for the oxygen evolution reaction (OER). Among the as-prepared Co x Fe 1− x P with various Co/Fe ratios, CoP, FeP, solid CoFeP, cobalt ferrite microspheres, and commercial IrO 2 , Co 0.47 Fe 0.53 P exhibits the best OER performance, including small overpotential, low Tafel slope, and high stability in alkaline medium. The design and development of low-cost, highly efficient, and stable electrocatalysts to take the place of noble-metal catalysts for the oxygen evolution reaction (OER) remain a significant challenge. Herein, the synthesis of yolk–shell-structured binary transition metal phosphide Co x Fe 1− x P with different Co/Fe ratios by phosphidation of a cobalt ferrite precursor is reported. The as-synthesized Co x Fe 1− x P catalysts were used for the OER. All yolk–shell Co x Fe 1− x P catalysts with different Co/Fe ratios showed much better performance than the corresponding solid catalyst. The formation of Co oxides on the catalyst surface during OER and the optimal Co/Fe ratio were found to be critical to their activity. Among the as-prepared Co x Fe 1− x P catalysts, that with a Co/Fe ratio of 0.47/0.53 (Co 0.47 Fe 0.53 P) exhibited the best performance. Co 0.47 Fe 0.53 P has an overpotential of 277 mV at a current density of 10 mA cm −2 , a Tafel slope of 37 mV dec −1 , and superior stability in alkaline medium. The outstanding performance is partly ascribed to the transfer of valence electrons from Co to P and Fe. The Co 0.47 Fe 0.53 P matrix with excellent conductivity and Fe phosphate that is stable on the surface of the catalyst are also helpful for the OER performance. In addition, the yolk–shell structure of Co 0.47 Fe 0.53 P increases the contact area between electrolyte and catalyst. These characteristics of Co 0.47 Fe 0.53 P greatly improve its OER performance. This optimized binary transition metal phosphide provides a new approach for the design of nonprecious-metal electrocatalysts.