Ultra-small intermetallic NiZn nanoparticles: a non-precious metal catalyst for efficient electrocatalysis

Intermetallics are long-range-ordered alloys traditionally synthesized by annealing nanoparticles of a random alloy, which results in the sintering of the nanoparticles and leads to the formation of polydispersed samples. It thus remains a challenge to achieve a monodispersion of tiny intermetallics. In the current work, ultra-small monodisperse intermetallic NiZn nanoparticles were synthesized based on a low-temperature solution chemistry route involving the chemical conversion of metal nanoparticles into an ordered alloy using an organometallic zinc precursor. During the transformation of single metal nanoparticles into the corresponding alloy, the particles retained their morphology. The resulting ordered alloy made up of earth-abundant materials demonstrated high electrocatalytic performance for the oxygen evolution reaction (OER) with a low overpotential of 283 mV at a current density of 10 mA cm^-2 and a small Tafel slope of 73 mV dec^-1, along with excellent stability and durability. The prepared intermetallic NiZn exhibited outstanding OER efficacy, better than those of a Ni_0.7Zn_0.3 alloy, pure Ni nanoparticles and even state-of-the art RuO₂. The atomic ordering as well as the modification of the electronic structure of Ni upon becoming alloyed with Zn, together with an atomic-scale synergistic effect produced from Ni and Zn, led to the enhanced intrinsic catalytic activity. The present findings point to a general route to produce nanoscale tiny alloys and also provide excellent electrocatalysts having exceptional energy conversion efficiency.