Rational green design of porous iron oxide/phosphide heterogeneous nanospheres embedded in hybrid graphene for efficient water oxidation

Abstract

Considering the rapidly growing energy demand, electrocatalytic decomposition of water is much promising as an ideal cleaning energy to help mankind energy conservation and emission reduction. However, the inadequate intrinsic activity and slow kinetics of precious-metal-free electrocatalysts in water oxidation processes are still limited. Herein, porous iron oxide/iron phosphide heterostructure packaged in nitrogen, sulfur co-doped graphene (labeled as p-Fe₃O₄/FeP@N,S-Gr) with mesoporous morphology and abundant interface is prepared using facile electronic and structural engineering for efficient electrochemical water oxidation. The catalyst of p-Fe₃O₄/FeP@N,S-Gr showed superior electrocatalytic activity and kinetic compared with porous iron oxide packaged in nitrogen, sulfur co-doped graphene (p-Fe₃O₄@N,S-Gr), and porous iron oxide (p-Fe₃O₄) catalyst for oxygen evolution reaction (OER). The overpotential (240 mV at 10 mA/cm²) and the tafel slope (45.1 mV dec^-1) of p-Fe₃O₄/FeP@N,S-Gr in OER process is significantly lower than that of p-Fe₃O₄ (289 mV at 10 mA/cm² and 63.5 mV dec^-1), p-Fe₃O₄@N,S-Gr (257 mV at 10 mA/cm² and 61.3 mV dec^-1), RuO₂ (308 mV at 10 mA/cm² and 99.0 mV dec^-1) and other reported relevant literature. Meanwhile, theoretical calculations indicate that constructing heterojunctions can significantly increase electron transfer capability and effectively reduce the adsorption energy barrier of intermediates (OH*→O* and O*→OOH*). This work demonstrates a practical and economical strategy toward the fabrication of transition metal catalysts for water oxidation.