Unlocking the synergy of interface and oxygen vacancy by core-shell nickel phosphide@oxyhydroxide nanosheets arrays for accelerating alkaline oxygen evolution kinetics

Abstract

Oxygen evolution reaction (OER) as a key process is of vital importance to sustainable and green hydrogen energy scenario. Its sluggish kinetics is tightly associated with stubborn O-O bond formation, where constructing stable superoxo/peroxo-like (O2)n− species (typically e.g. NiOO*) and activating them on the catalyst surfaces have been considered as one of most efficient strategies to accelerate oxygen evolution kinetics. Herein, we have purposely designed core-shell Ni5P4@NiOOH heterostructure nanosheet arrays, which are constructed by an in-situ electrochemical self-adaptive process of the corresponding Ni5P4 precursor, and therefore demonstrate a sharp rise in activation of NiOO* on surfaces by the synergy between interface and oxygen vacancy (Vo) created during OER. By the combination studies of contrast experiments with or without interface or oxygen vacancies and theoretical calculations, we find that the interface between Ni5P4 and amorphous NiOOH ultrathin layer can promote the redistribution of electron density on the catalyst surface and optimize the Gibbs free energy of multiple adsorbed intermediates, while the numerous Vo activates NiOO* species in the Ni5P4@NiOOH catalyst. The interface-Vo synergy therefore enables an ultralow overpotential of only 273 mV@50 mA cm−2 and a superior OER activity with up to 21- and 70-fold rise in kinetic current density under the overpotential of 270 mV over those of Ni(OH)2@NiOOH and NiO@NiOOH counterparts, respectively.