Synthesis and characterization of Co2−xRhxP nanoparticles and their catalytic activity towards the oxygen evolution reaction

Abstract

We show that Co_2−xRh_xP ternary phase nanoparticles can be synthesized using the arrested precipitation technique, via a requisite low temperature co-reduction of Co²⁺ and Rh³⁺ ions, followed by phosphidation of the resulting intermediate product at above 300 °C. The most unique aspect of our synthesis protocol is the fact that we are able to solubilize both cubic antifluorite and orthorhombic crystal systems, into uniform solid solutions of Co_2−xRh_xP nanoparticles under mild reaction conditions. These nanoparticles are active towards the oxygen evolution reaction and deliver higher electrolytic activities as compared to those of Co₂P and Rh₂P binary phases. Cobalt-rich compositions were found to be the most active, with a sweet spot occurring at a target composition of Co_1.75Rh_0.25P, where a current density of 10 mA cm⁻² was achieved at an overpotential of 0.29 V.