Colloidal Ni2-xCoxP nanoparticles for the hydrogen evolution reaction

A cost-effective and scalable approach was developed to produce monodisperse Ni2-xCoxP nanoparticles (NPs) with composition tuned over the entire range (0≤x≤2). Ni2-xCoxP NPs were synthesized using lowcost, stable and low-toxicity triphenyl phosphite (TPOP) as phosphorous precursor, metal chlorides as metal precursors and hexadecylamine (HDA) as ligand. The synthesis involved the generation of intermediate Ni-P amorphous NPs and the posterior crystallization and simultaneous incorporation of Co. The composition, size and morphology of the NPs could be controlled simply by varying the ratio of Ni and Co precursors and the amount of TPOP and HDA. Ternary Ni2-xCoxP based electrocatalysts exhibited enhanced electrocatalytic activity toward hydrogen evolution reaction (HER) compared to binary phosphides. In particular, NiCoP electrocatalysts displayed the lowest overpotential of 97 mV at J=10 mA cm -2 and an excellent long-term stability. DFT calculations of the Gibbs free energy for hydrogen adsorption at the surface of Ni2-xCoxP NPs showed NiCoP to have the most appropriate composition to optimize this parameter within the whole Ni2xCoxP series. However, the hydrogen adsorption energy was demonstrated not to be the only parameter controlling HER activity in Ni2-xCoxP.