Spontaneous Dissolution of Oxometalates Boosting the Surface Reconstruction of CoMOx (M = Mo, V) to Achieve Efficient Overall Water Splitting in Alkaline Media

Abstract

Bimetallic materials have been regarded as promising catalysts for efficient alkaline water splitting. However, the spontaneous reconstruction of the surface structures of the catalysts before catalysis has long been overlooked. Here, we present that in situ dissolution of MoO42- in CoMoO4 boosts spontaneous surface reconstruction in an alkaline medium. Our results reveal that CoMoO4 microrod arrays function as precatalysts that undergo spontaneous surface reconstruction under alkaline conditions, forming a layer of Co3O4/CoMoO4 and CoOOH/CoMoO4 heterostructures. X-ray photoelectron spectroscopy (XPS) combined with in situ Raman spectroscopy reveals that in such activated CoMoO4 (A-CoMoO4), the partial electron transfer from Co to Mo sites helps induce a higher valence state of Co centers and the heterostructure of Co3O4/CoMoO4 may promote the generation of CoOOH, which is very likely the precursor to the active Co4+ species for oxygen evolution reaction (OER) catalysis. During the hydrogen evolution reaction (HER), Co3O4 generated after surface reconstruction can promote the dissociation of water, which is considered the rate-determining step of the alkaline HER. Hence, A-CoMoO4 exhibits superior bifunctional electrocatalytic activities that the overpotentials at a working current density of 10 mA cm-2 for the HER and OER are only 13 and 264 mV, respectively. Inspired by the remarkable bifunctionality, the electrolytic cell employing A-CoMoO4 as both anode and cathode shows an appealing potential of 1.51 V to deliver 10 mA cm-2 for overall water splitting. Similarly, CoVOx also shows the spontaneous surface reconstruction behavior in the alkaline medium, which we propose can be extended to a series of oxometalate catalysts.