Ultra-thin carbon layer encapsulated NiCoP coralline-like catalysts for efficient overall water electrolysis

Abstract

Bimetallic phosphides exhibit excellent catalytic performance for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) because the adsorption/desorption energies of reactants are optimized by charge redistributions among metals and phosphorus. However, their wide application is limited due to unsatisfactory stability, inappropriate reaction intermediates' adsorption/desorption capacities, and a lack of activation study. Herein, a coralline-like nano-composite catalyst, NC@NiCoP@NF, is synthesized through coupling a bimetallic phosphide (NiCoP) and N-doped carbon layer (NC layer) on a Ni foam. The hierarchical structure and carbon coating result in modified electronic structures, improved adsorption/desorption capacities of intermediates, abundant active sites, and well-defined electron/electrolyte pathways, thus exhibiting optimal performance to catalyze the HER, the OER, and water electrolysis. The analysis after a long-term reaction gives an insight into the surface activation process of the catalyst, in which NiCoP evolves to hydroxide (HER) and oxyhydroxide (OER) to form new heterostructures (NiCoP/M–OH or NiCoP/MOOH) on surfaces. Density functional theory (DFT) calculations prove that the interaction between NiCoP and M–OH in the new heterostructure reaction system greatly improves the HER performance through promoting electronic conductivity, lowering the adsorption/dissociation energy barrier for H₂O molecules, and optimizing the free energy of hydrogen adsorption (ΔG_H*). This paper reports innovative methods to design and develop advanced high-performance catalysts for renewable energy generation.