Core-Shell-Structured Prussian Blue Analogues Ternary Metal Phosphides as Efficient Bifunctional Electrocatalysts for OER and HER.

Electrochemical water splitting is regarded as the most potential sustainable hydrogen production technology. However, the slow reaction kinetics and high overpotential of this process will result in low energy conversion efficiency. Therefore, it is of great practical value to research low-cost, efficient, and stable transition-metal-based bifunctional electrocatalysts. Herein, Fe-Co Prussian blue analogue (PBA) was coated with Ni-Co PBA to prepare the trimetallic PBA precursor, and the trimetallic phosphate (Fe-Co-Ni-P-1) has been prepared via the low-temperature phosphating process. The effects of metal ratios, the amount of sodium hypophosphite, and phosphating temperature on the catalytic performances were studied. When Fe-Co-Ni-P-1 was used as an electrocatalyst, the overpotential of oxygen evolution reaction and hydrogen evolution reaction was 247 and 215 mV, respectively, at a current density of 10 mA cm-2. At the same time, Fe-Co-Ni-P-1 showed faster kinetics and better long-term stability in the catalytic process. The catalytic performances of unary metal, binary metal, and ternary metal phosphides, oxides, and sulfides were systematically studied. It is demonstrated that the ternary metal phosphide Fe-Co-Ni-P-1 manifests the best catalytic performance, which is mainly attributed to the monodisperse core-shell structure, low resistance, large electrochemical active area, and the synergistic effect among metals.