Hollow FeP/Fe₃O₄ Hybrid Nanoparticles on Carbon Nanotubes as Efficient Electrocatalysts for the Oxygen Evolution Reaction

We develop a method to prepare hollow FeP/Fe₃O₄ hybrid nanoparticles supported on carbon nanotubes (CNTs), which could be used as highly active and efficient electrocatalysts. The Fe@Fe₃O₄/CNT hybrids were first synthesized by annealing the CNTs adsorbed with Fe­(NO₃)₃, followed by controlled phosphorization treatment. They exhibit an outstanding catalytic activity for oxygen evolution reaction (OER) with a low overpotential of 229 mV at a current density of 10 mA cm^–2, a high turnover frequency value of 0.35 s^–1 at an overpotential of 300 mV, and an ultralow Tafel slope of 27.6 mV dec^–1, which is much better than that of FeP/Fe₃O₄, FeP/CNTs, Fe₃O₄/CNTs, and the commercial RuO₂ electrocatalyst. More importantly, the Tafel slope is much lower than most non-noble metal-based OER electrocatalysts reported in the previous literature studies as far as we know. The excellent OER performance benefits from the electron transfer from Fe₃O₄ to FeP confirmed by X-ray photoelectron spectroscopy, together with good conductivity of CNTs. This hybrid structure supported on conductive CNTs may offer an efficient method to design earth-abundant and low-cost electrocatalysts for OER in practical applications.