MXenes for electrocatalysis applications: Modification and hybridization

Two-dimensional carbides, nitrides, and carbonitrides (MXenes) play important roles in promoting the development of sustainable energy because they have abundant reactive sites on their surfaces. An increasing number of MXenes with diverse elements and composites have been predicted and synthesized for electrocatalysis applications since the first report of a Ti-Mo-based MXene for the hydrogen evolution reaction (HER). Herein, we summarize the progress of MXene-based electrocatalysts for the HER, the oxygen evolution reaction, and the oxygen reduction reaction, including regulated pristine MXenes and modified hybrid MXenes, from both theoretical and experimental perspectives. A brief overview on MXene synthesis is presented first, accompanied by a discussion on the relationship between electrocatalytic properties and M, X, T, vacancies, and morphologies. After reviewing strategies in terms of atom substitution, functional modification, defect engineering, and morphology control, we emphasize the construction of heterojunctions between MXenes and other nanostructures, such as metal nanoparticles, oxides, hydroxides, sulfides, and phosphides. We finally discuss prospects for the future development of MXene-based electrocatalysts.