Molecular Covalent Functionalization of Graphene and Its Derivatives: An Effective Strategy to Boost Electrocatalytic HER.

Graphene-based electrocatalysts have been developed, and they exhibited enhanced activity due to their superior electronic conductivity. The robustness of such graphene materials can be further enhanced by altering their chemical and physical properties using different techniques. Molecular covalent functionalization is one of the effective strategies to alter the chemical composition, electronic structure, surface area, as well as dispersibility of graphene materials. Despite the significant literature on its contribution to improving the electrocatalytic activity for the hydrogen evolution reaction (HER), there is no review article available. Therefore, we have tried to fill this void by examining recent developments in the field of molecular covalent functionalized graphene and its derivatives for water electrolysis. We have also thoroughly discussed the role of individual components (graphene support, linker, and functional molecules bearing the main active sites) to improve the performance of the electrocatalyst by inducing synergistic effects and enriching surface properties. Moreover, the main characteristics of effective electrocatalysts, such as the surface area, functionality, dispersibility, conductivity, stability, and electronic structure, have also been reviewed. Finally, challenges and future perspectives are outlined to assist researchers in designing more effective electrocatalysts for the HER.