Modulating positive charge sites generations and iron oxidation state transitions in FeP4/CoP/C p-n heterojunction toward efficient oxygen evolution

Abstract

Promoting the formation of positive charge active sites and high oxidation state FeOOH in the heterojunction electrocatalyst can enhance its intrinsic activity for oxygen evolution reaction (OER). However, the current synthesis methods that can simultaneously achieve both properties remain a great challenge. In this work, a feasible strategy for concurrently promoting the generation of positive charge active sites and high oxidation state metal species by constructing a heterojunction between FeP4 and CoP is proposed. Specifically, the p-n heterojunction between FeP4 and CoP is constructed by pyrolysis of MIL88A@FeCoLDH prepared by introducing Co through cation exchange using MIL88A as a template. The experimental and density functional theory calculation analyses suggest the construction of p-n heterojunction can effectively modulate the electron structure, optimize the d-band center, induce the generation of strong space charge region, and shorten the bond length of Fe-O, thus promoting the formation of positive charge active sites and high active species FeOOH and the adsorption ability of oxygen-containing intermediates for enhancing the OER performance. Benefiting from the synergistic effect between positive charge active sites and FeOOH, the obtained FeP4/CoP/C electrocatalyst exhibits a low overpotential of 258 mV for the OER at a current density of 10 mA cm−2 and superior stability at 20 mA cm−2 for 52 h. This work gives insights into the charge regulation effect in the heterojunction for enhancing the OER catalytic activity and provides a general strategy for designing more efficient oxygen evolution electrocatalysts.