Enhanced Hot/Free Electron Effect for Photocatalytic Hydrogen Evolution Based on 3D/2D Graphene/MXene Composite

Photocatalytic hydrogen production through water splitting represents a promising strategy to store solar energy as chemical energy. Current photocatalysts primarily focus on traditional semiconductor materials, such as metal oxides, sulfides, nitrides, g-C₃N₄, etc. However, these materials often suffer from large bandgap and fast charge recombination, which limit sunlight utilization and result in unsatisfactory photon conversion efficiency. Here, a novel 3D/2D graphene/MXene (3DGraphene/MXene) photocatalyst without metal semiconductor participant is designed, and an enhanced hot/free electron catalytic mechanism for photocatalytic hydrogen evolution is proposed. The hot/free electrons, ejected out from 3DGraphene based on an Auger-like light induced electron emission mechanism and enhanced by the cocatalyst MXene Ti₃C₂T_x, exhibit exceptional catalytic activity under wide spectrum range from ultraviolet to visible light. The optimized 3DGraphene/MXene composite catalyst achieves an average hydrogen production rate of 1.4 mmol h^-1 g_cat ^-1. Furthermore, consistent with the proposed hot/free electron emitting mechanism, the photocurrent rises with increasing the photon energy from visible to ultraviolet light and the light intensity under the same frequency range. These results indicate that using the hot electron generated from graphene and enhanced by other 2D materials might be an effective strategy for enhancing the activity of the photocatalytic materials for water splitting.