Single atom supported on MXenes for the alkaline hydrogen evolution reaction: species, coordination environment, and action mechanism

Abstract

The electrochemical hydrogen evolution reaction (HER) in alkaline media provides an environmentally friendly industrial application approach to replace traditional fossil energy. The search for efficient, low-cost, and durable active electrocatalysts is central to the development of this area. Transition metal carbides (MXenes) have been emerging as a new family of two-dimensional (2D) materials that have great potential in the HER. Herein, density functional theory calculations are performed to systematically explore the structural and electronic properties and alkaline HER performances of Mo-based MXenes, as well as the influence of species and the coordination environment of single atoms on the improvement of the electrocatalytic activity of Mo₂Ti₂C₃O₂. The results show that Mo-based MXenes (Mo₂CO₂, Mo₂TiC₂O₂, and Mo₂Ti₂C₃O₂) exhibit excellent H binding ability, while slow water decomposition kinetics hinders their HER performance. Replacing the O-terminal of Mo₂Ti₂C₃O₂ with a Ru single-atom (Ru_S–Mo₂Ti₂C₃O₂) could promote the decomposition of water owing to the stronger electron-donating ability of the atomic state Ru. In addition, Ru could also improve the binding ability of the catalyst to H by adjusting the surface electron distribution. As a result, Ru_S–Mo₂Ti₂C₃O₂ exhibits excellent HER performance with a water decomposition potential barrier of 0.292 eV and a H adsorption Gibbs free energy of −0.041 eV. These explorations bring new prospects for single atoms supported on Mo-based MXenes in the alkaline hydrogen evolution reaction.