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

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 MoO 4 2- in CoMoO 4 boosts spontaneous surface reconstruction in an alkaline medium. Our results reveal that CoMoO 4 microrod arrays function as precatalysts that undergo spontaneous surface reconstruction under alkaline conditions, forming a layer of Co 3 O 4 /CoMoO 4 and CoOOH/CoMoO 4 heterostructures. X-ray photoelectron spectroscopy (XPS) combined with in situ Raman spectroscopy reveals that in such activated CoMoO 4 (A-CoMoO 4 ), the partial electron transfer from Co to Mo sites helps induce a higher valence state of Co centers and the heterostructure of Co 3 O 4 /CoMoO 4 may promote the generation of CoOOH, which is very likely the precursor to the active Co 4+ species for oxygen evolution reaction (OER) catalysis. During the hydrogen evolution reaction (HER), Co 3 O 4 generated after surface reconstruction can promote the dissociation of water, which is considered the rate-determining step of the alkaline HER. Hence, A-CoMoO 4 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-CoMoO 4 as both anode and cathode shows an appealing potential of 1.51 V to deliver 10 mA cm -2 for overall water splitting. Similarly, CoVO x also shows the spontaneous surface reconstruction behavior in the alkaline medium, which we propose can be extended to a series of oxometalate catalysts.