Doping unary transition-metal phosphides (TMPs) by secondary metal is a powerful method to improve their catalytic activity for electrochemical oxygen evolution reaction (OER). However, the composition-activity relationship of such doping has not been systematically investigated yet because of the challenge in constructing bimetal TMPs with continuously variable composition while keeping homogenous elemental distribution. Herein, we develop a strategy of using bimetal Prussian blue analogues with homogenous elemental distribution at molecular scale as an ideal platform to achieve bimetal cobalt-iron phosphides (Co1- xFe xP) with a continuously changeable Co/Fe ratio (0 < x < 1) and uniform metal distribution. Such a system allows us to draw out a composition-activity volcano profile of Co1- xFe xP for OER. By optimizing the composition, the best catalytic activity is obtained at the Co/Fe ratio of 1.63 in Co1- xFe xP with small overpotentials of 230 and 268 mV at 10 and 100 mA cm-2, respectively, which outperform most of the reported TMPs. These results may inspire the use of multicomponent molecular platforms to understand composition-dependent performance and explore highly efficient catalysts for diverse applications.
Keywords: Prussian blue; electrocatalysis; oxygen evolution reaction; phosphides; water splitting.