Two‐Dimensional Materials and their Hetero‐Superlattices for Photocatalytic Hydrogen Evolution Reaction

Abstract Since the discovery of graphene, there has been intensive research on other two‐dimensional (2D) analogues. Some of them are elemental 2D materials such as phosphorene and bismuthene. Others are binary compounds fascinating in terms of energy applications are transition metal dichalcogenides (TMDCs: MoS₂, MoSe₂) and MXenes (Ti₃C₂, Nb₂C₃). 1T‐forms of MoS₂ and MoSe₂ are probably the best materials reported for dye‐sensitized photocatalytic hydrogen evolution reaction (HER). Here, we first highlight the phase engineering in 2D‐TMDCs to enhance hydrogen evolution activity. Generation of hetero‐superlattices of TMDCs with other HER active materials such as graphene, carbon nitride and borocarbonitrides, by utilizing coupling and electrostatic restacking strategies, appears to be advantageous for photocatalytic application. These hetero‐superlattices provide a counterpoint to the van der Waals heterostructures by means of covalent bonds. Ladder‐like networks of heterolayers generated due to cross‐linking enhance the interfacial area and charge‐transfer interactions, thereby improving HER activity. The use of 2D phosphorene as a photocatalytic material is limited by its ambient instability. Covalent functionalization of phosphorene surface with tris(pentafluorophenyl) borane and benzyl group increases ambient stability and dispersibility. The functionalized surface can be further utilized to cross‐link with amine or acid‐modified TMDCs. The HER activity obtained with phosphorene‐MoS₂ superlattices is the highest reported among the phosphorene‐based systems, thus setting a new example for metal‐free catalysis. The ambient instability of MXenes and other related 2d materials under photocatalytic conditions can be resolved either by functionalization or by forming hetero‐superlattices.