Carbothermal-reduction-assisted phosphidation of cobalt affords mesoporous nitrogen-doped carbon-embedded CoP nanoelectrocatalysts for the oxygen reduction reaction

Abstract

We demonstrate a new facile single-step synthesis of mesoporous nitrogen-doped carbon-embedded cobalt phosphide (NC-CoP) nanoparticles using a single-source precursor of the cobalt(II) bis(terpyridine)-based complex ([Co(pyterpy)₂](PF6)₂) by carbothermal reduction. Phosphidation of cobalt is achieved with the hexafluorophosphate counteranion of the precursor complex for the first time. Polypyridyl complexes such as [Co(bpy)₃](PF₆)₂ and [Co(terpy)₂](PF₆)₂ do not yield the desired CoP. The atomic percent of carbon in the precursor complex controls the growth of CoP. The as-synthesized NC-CoP has a large surface area of 120 m²/g and shows excellent electrocatalytic activity toward the oxygen reduction reaction (ORR). It is highly durable and favors the four-electron pathway for the reduction of oxygen to water at low overpotential. The synergistic effect between NC and CoP facilitates the electron-transfer kinetics for ORR.