Hollow FeP/Fe3O4 hybrid nanoparticles on CNTs as efficient electrocatalysts for 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/CNTs hybrids were firstly synthesized by annealing the CNTs adsorbed with Fe(NO3)3, followed by controlled phosphorization treatment. They exhibit an outstanding catalytic activity for OER with a low overpotential of 229 mV at the current density of 10 mA cm-2, a high TOF 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 literatures as far as we known. The excellent OER performance benefits from the electron transfer from Fe3O4 to FeP confirmed by XPS, together with good conductivity of CNTs. This hybrid structure supported on conductive CNTs may offer an efficient method to design earth-aboundant and low-cost electrocatalysts for OER in practical applications.