Insights into the Effect of Precursors on the FeP-Catalyzed Hydrogen Evolution Reaction

Iron phosphide nanoparticles (NPs) are promising noble metal-free electrocatalysts for the hydrogen evolution reaction (HER), but they usually show inferior activity due to the limited surface area and oxidative passivation. We reported a facile synthetic method to prepare FeP hollow NPs (HNPs) with various precursors. It was proven that the structural parameters (i.e., size, phosphating temperature, phase, and surfactant) of oxide precursors were correlated to the electrochemically active surface area (ECSA), phase purity, surface oxidation, and hollow morphology of FeP HER catalysts, thus affecting the HER activity. Among the three FeP HNPs, the 9 nm FeP HNPs prepared using the Fe₃O₄ precursor exhibited the highest overall activity with the lowest overpotential of 76 mV to drive a cathodic current density of 10 mA·cm^–2 due to the highest ECSA, while 25 nm FeP prepared using the Fe₂O₃ precursor showed the highest turnover frequency because of the high phase purity and low surface oxidation degree.