Insight into the Real Efficacy of Graphene for Enhancing Photocatalytic Efficiency: A Case Study on CVD Graphene-TiO₂ Composites

Construction of graphene-based composites has been a popular theme in solar energy harvesting and conversion, yet the understanding of the real efficacy of graphene for enhancing photocatalytic efficiency is hampered by the gap of physicochemical properties between the defined graphene and the graphene used in research laboratories. Here, we purposely synthesize a high-quality chemical vapor deposition graphene (CVDG) as a model material to integrate with TiO2, which demonstrates that photocatalytic performance can be greatly improved by controlling the quality of graphene. Under the same reaction conditions, the as-prepared CVDG-TiO2 displays a 26.2-times and 10-times higher photocatalytic hydrogen evolution activity than bare TiO2 and its counterpart, reduced graphene oxide (RGO)-TiO2, respectively. Experimental characterization reveals that the few-layer CVDG with a low defect density is able to better unleash the excellent electrical conductivity potential of graphene, by which the separation and lifetime of photoexcited charge carriers of graphene-TiO2 could be improved more efficiently. The research highlights the significant effect of the quality of graphene for the construction of more efficient semiconductor-graphene composites, which is anticipated to inform ongoing efforts on exploiting high-quality graphene to advance solar energy harvesting and conversion.