•B,Cs co-doped g-C3N4 nanosheets successfully were synthesized.•B,Cs co-doped g-C3N4 nanosheets showed H2 evolution rate of 1120 μmolg-1h−1.•The optimized structure showed H2O2 production rate of 113 μmolg-1h−1.•B and Cs doping increased charge carrier mobility in g-C3N4 structure.•Thin nanosheets decreased diffusion distance for the charge carriers and reactants. This study reports the synthesis of a highly efficient visible-light-driven photocatalyst for hydrogen evolution and H2O2 production by manipulating the electronic band structure and surface properties of g-C3N4. Boron and caesium co-doped g-C3N4 porous and wrinkled nanosheets were nobly synthesized by using recrystallization of melamine in water in the presence of boric acid and CsCl followed by calcination and thermal etching. The prepared nanosheets showed an extremely porous and wrinkled structure with high surface area and edge sites. The optimized B, Cs co-doped g-C3N4 nanosheets exhibited a stable hydrogen evolution rate of 1,120 μmolg-1h−1 in the presence of triethanolamine, which is 7.7 times higher than that of the bulk. Moreover, this optimized structure showed a greatly increased hydrogen peroxide production rate of 113 μmolg-1h−1 compared to that (19 μmolg-1h−1) of the bulk GCN-B. Meanwhile, the optimized structure showed a high photooxidation ability toward RhB oxidation. This outstanding improvement in photocatalytic performance is attributed to the enhanced charge carrier mobility in the π-conjugated structure and increased accessible reaction sites for photocatalytic reactions originated from the synergetic effect of co-doping and formation of the porous and wrinkled nanosheets.