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

We show that Co2-xRhxP 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 degrees 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 Co2-xRhxP 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 Co1.75Rh0.25P, where a current density of 10 mA cm(-2) was achieved at an overpotential of 0.29 V.