Encapsulation of NiCo nanoparticles into foam-like porous N,P-codoped carbon nanosheets: Electronic and architectural dual regulations toward high-efficiency water electrolysis

Abstract

The rational design of earth-abundant and high-efficiency bifunctional electrocatalysts for expediting the sluggish kinetics of both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is imperative to fulfill the sustainable hydrogen-based energy electrochemical devices. The design rationale for advanced catalyst requires to simultaneously take into account both thermodynamic and kinetic aspects. Herein, a feasible and scalable hydrogel-bridged pyrolysis strategy is developed to directly immobilize uniform NiCo nanoparticles into 2D foam-like porous N,P-codoped carbon nanosheets (abbreviated as NiCo@N,P-CNSs hereafter). The bimetallic alloy synergy, well confined active sites and highly porous nanosheet architecture collaboratively afford modulated electronic structure, abundant active sites, and multidimensional mass diffusion pathways, which are thermodynamically and kinetically favorable for catalytic performance. Consequently, the as-fabricated NiCo@N,P-CNSs exhibit distinguished bifunctional performance in alkaline medium, requiring overpotentials of only 99 and 226 mV at a current density of 10 mA cm−2 for HER and OER, respectively. Furthermore, when equipped in a two-electrode electrolyzer, the NiCo@N,P-CNS electrode couple displays a low cell voltage of 1.57 V at 10 mA cm−2 and outstanding stability, outperforming a majority of the recently reported non-precious electrocatalysts and representing a competitive candidate for practical water electrolysis. Density functional theory (DFT) simulations further corroborate that the bimetallic NiCo alloy possesses favorable Gibbs free energies of water and hydrogen adsorption, which are beneficial for enhancing its intrinsic activity. More importantly, the developed methodology for the simultaneous realization of electronic modulation, nanostructure engineering and nanocarbon hybridization may provide new perspectives for future exploration of high-efficiency electrocatalysts for a range of energy conversion applications and beyond.