Revealing the electrocatalytic mechanism of layered crystalline CoMoO4 for water splitting: A theoretical study from facet selecting to active site engineering

Deciphering the atomic-level properties and mechanism of electrocatalysts for water splitting is vital for the development of highly active non-noble-metal catalysts. Herein, we conduct a detailed study of layered crystalline CoMoO4 using density functional theory (DFT) calculations. The layered arrangement of CoMoO4 along the [110] lattice direction is observed, and the two thermodynamically stable and most exposed (110)A and (001)A crystal facets are selected among all low-index facets by surface energy calculations and Wulff construction to study the electrocatalytic activity for alkaline water splitting and corresponding mechanism. CoMoO4 with an exposed (110)A facet (i.e., CMO (110)A) exhibited a high hydrogen evolution reaction (HER) activity, with a ΔGH* of 0.22 eV, which is similar to that of Pt because the adsorbed H is allowed to interact with two oxygen atoms (O3 and Oadj). The (110)A facet also possesses better H2O adsorption and dissociation abilities than the (001)A facet, benefiting the HER performance in alkaline solutions. Moreover, the overpotential of the (110)A facet for the electrocatalytic oxygen evolution reaction (OER) is only 0.74 V according to the Gibbs free-energy calculation, this overpotential is lower than that of the (001)A facet (0.84 V) owing to the stronger binding and more stable adsorption states between Co and O for the intermediate *O. By allowing us to identify highly active facets and sites, this approach guided the selective synthesis of CoMoO4 and its isostructural substances, such as Mn(Ni, Fe)MoO4 nanocatalysts, for alkaline water splitting.