In situ topologically induced metastable phase Ni/r-Ni(OH)2@C heterostructures with abundant oxygen vacancies as efficient bifunctional electrocatalysts for energy-saving hydrogen production

Abstract

To simultaneously accelerate both sluggish hydrogen evolution reaction (HER) and urea oxidation reaction (UOR) kinetics, strongly coupling of transition metal hydroxides of high UOR activity with the transition metals of low hydrogen adsorption barrier for highly active HER is a promising strategy. Herein, a tractable hydrothermal protocol and a partial in-situ topological reduction strategy are developed to synthesize hcp Ni/r-Ni(OH)2 nanosheets containing abundant oxygen defects with an ultrathin carbon layer, which are utilized as the new bifunctional catalysts for both HER and UOR. As for HER, the surface electronic structure of Ni is optimized by introducing the oxygen defects coupling with hcp Ni with excellent electronic structure, which greatly enhances the dissociation ability of H2O and reduces the Ni-H bond strength, thus acquiring the optimized H* Gibbs free energy (∆GH*). As for UOR, abundant interfaces and the electron transfer between transition metal hydroxides/transition metal are favorable to regulate the urea adsorption. As expected, the hcp Ni/r-Ni(OH)2/C electrocatalyst shows good activity for HER (70.7 mV @ 10 mA cm−2), UOR (1.36 V @ 10 mA cm−2), and urea electrolysis (1.45 V @ 10 mA cm−2). This facile strategy provides a novel way to design high-performance electrocatalysts towards urea splitting, which can utilize to generate hydrogen as well as eliminate urea in water.