Fabrication of nickel–cobalt bimetal phosphide nanocages for enhanced oxygen evolution catalysis

Abstract

Replacement of precious metals with earth-abundant electrocatalysts for oxygen evolution reaction (OER) holds great promise for realizing practically viable water-splitting systems. It still remains a great challenge to develop low-cost, highly efficient, and durable OER catalysts. Here, the composition and morphology of Ni–Co bimetal phosphide nanocages are engineered for a highly efficient and durable OER electrocatalyst. The nanocage structure enlarges the effective specific area and facilitates the contact between catalyst and electrolyte. The as-prepared Ni–Co bimetal phosphide nanocages show superior OER performance compared with Ni2P and CoP nanocages. By controlling the molar ratio of Ni/Co atoms in Ni–Co bimetal hydroxides, the Ni0.6Co1.4P nanocages derived from Ni0.6Co1.4(OH)2 nanocages exhibit remarkable OER catalytic activity (η = 300 mV at 10 mA cm−2) and long-term stability (10 h for continuous test). The density-functional-theory calculations suggest that the appropriate Co doping concentration increases density of states at the Fermi level and makes the d-states more close to Fermi level, giving rise to high charge carrier density and low intermedia adsorption energy than those of Ni2P and CoP. This work also provides a general approach to optimize the catalysis performance of bimetal compounds.