Two-dimensional photocatalysts often suffer severe aggregation due to the inevitable van der Waals forces between nanosheets, which limits their photocatalytic water-splitting efficiency. Herein, a rational design of confined synthesis of g-C3N4 nanomeshes (GCN) on N-doped vertically-oriented graphene (NVG) arrays for enhanced hydrogen evolution is reported. The aggregation of 2D g-C3N4 nanosheets is effectively avoided via physical separation by electrically conductive NVG networks. Well-defined hierarchical architecture of the GCN/NVG photocatalyst endows with superaerophobicity and simultaneously enhanced light absorption. Experimental and ab initio simulation results suggest that the protruding graphene edges induce charge redistribution, thus enhancing interfacial charge separation. The GCN/NVG samples demonstrate a high areal hydrogen evolution rate of 41.7 μmol h−1 cm−2 (225 L m−2 in 24 h, STP) in water and 45.8 μmol h−1 cm−2 (246.2 L m−2 in 24 h, STP) in simulated seawater. This work creates further opportunities for the development of earth-abundant photocatalysts.