Vacancy-induced high activity of MoS2 monolayers for CO electroreduction: a computational study

The electroreduction of CO (COER) to valuable carbon-based chemicals is an attractive alternative to the traditional Fischer–Tropsch process, in which the development of electrocatalysts with high activity and high selectivity still remains a huge challenge. Herein, by means of density functional theory (DFT) computations, we systematically explored the potential of defective MoS2 monolayers with sulfur vacancies, including mono-sulfur (VS), di-sulfur (VS2 and V2S), and tri-sulfur (V3S), as COER electrocatalysts. Our results revealed that these defective MoS2-based candidates exhibit low formation energies and high stability, holding great promise for experimental synthesis and practical applications. In particular, according to the computed free energy changes, we found that the catalytic activity of these considered defective MoS2 monolayers for COER is highly dependent on the size of sulfur vacancies in MoS2 monolayers, among which V3S exhibits the best COER catalytic performance, and CH4 is identified as the main product. Interestingly, the difference between the adsorption strength of *CH2 and *CH3 species can be used as a rational descriptor to evaluate the COER catalytic activity of these defective MoS2 monolayers. Thus, controlling the size of S-vacancies can make MoS2 monolayers a promising electrocatalyst for COER, which not only further widens the potential of MoS2 monolayers in electrocatalysis, but also opens a new door for CO reduction for renewable energy supply.