Design and synthesis of efficient photocatalysts for hydrogen production via water splitting are of great importance from both theoretical and practical viewpoints. Many metal-based semiconductors have been explored for this purpose in recent decades. Here, for the first time, an entirely carbon-based material, bulk three-dimensionally cross-linked graphene (3DG), has been developed as a photocatalyst for hydrogen production. It exhibits a remarkable hydrogen production rate of 270 μmol·h⁻¹·g_cat⁻¹ under full-spectrum light via a hot/free electron emission mechanism. Furthermore, when combined with the widely used semiconductor TiO₂ to form a TiO₂/3DG composite, it appears to become a more efficient hydrogen production photocatalyst. The composite achieves a production rate of 1, 205 μmol·h⁻¹·g_cat⁻¹ under ultraviolet–visible (UV–vis) light and a 7.2% apparent quantum efficiency at 350 nm due to the strong synergetic effects between TiO₂ and 3DG.