Influence of Ni to Co ratio in mixed Co and Ni phosphides on their electrocatalytic oxygen evolution activity

Prompted by the impact of Ni-based support materials on the intrinsic activity of electrocatalysts, we investigated the influence of partial Co substitution by Ni during the reductive thermal synthesis of cobalt-cobalt phosphide nanoparticles from triphenylphosphine complexes. The obtained catalysts were characterised by X-ray diffraction and electrochemistry. Increasing the amount of Ni in the precursor complexes leads to materials with lower overpotential for the OER at low current densities, and lower Tafel slopes. Co nanoparticles, which are only formed in materials with low Ni content, increase the intrinsic material conductivity and reduce the OER overpotential at high current densities. Keywords: Electrocatalysis, Oxygen evolution reaction, Co phosphide, Ni phosphide, Transition metal phosphide