van der Waals Heterojunction between a Bottom-Up Grown Doped Graphene Quantum Dot and Graphene for Photoelectrochemical Water Splitting.

van der Waals heterojunctions (vdWHs) formed between 2D materials have attracted tremendous attention recently due to their extraordinary properties, which cannot be offered by their individual components or other heterojunctions. Intriguing electronic coupling, lowered energy barrier, intimate charge transfer, and efficient exciton separation occurring at the atomically sharp interface promise their applications in catalysis, which, however, are largely unexplored. Herein, we demonstrate a 0D/2D vdWH between 0D graphene quantum dots (GQDs) and 2D pristine graphene sheets, simply prepared by ultrasonication of graphite powder using GQDs as intercalation surfactant. Such an all-carbon Schottky-diode-like 0D/2D vdWH is employed for the emerging photoelectrochemical catalysis (water splitting) with high performance. The demonstrated low-cost and scalable bottom-up growth of heteroatom-doped GQDs will greatly promote their widespread applications. Moreover, the mechanisms underlying GQD growth and heterojunction-mediated catalysis are revealed both experimentally and theoretically.