Carbothermal-Reduction-Assisted Phosphidation of Cobalt Affords Mesoporous Nitrogen-Doped Carbon-Embedded CoP Nanoelectrocatalysts for the Oxygen Reduction Reaction

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.