Hydrogen peroxide (H 2 O 2) has received increasing attention as an energy carrier. To achieve a sustainable energy society, photocatalytic H 2 O 2 splitting (H 2 O 2 (l) → H 2 (g) + O 2 (g); ΔG°= + 131 kJ mol −1) is a desirable reaction for on-site H 2 generation. However, this reaction has not been reported because conventional photocatalysis decomposes H 2 O 2 by disproportionation (H 2 O 2 (l) → H 2 O (l) + 1/2O 2 (g); ΔG°= −117 kJ mol −1) and by promoting H 2 O 2 reduction instead of H + reduction. Here we report the successful example of H 2 O 2 splitting. Visible light irradiation of a graphitic carbon nitride loaded with graphene quantum dots as co-catalysts (GQDs/g-C 3 N 4) in a H 2 O 2 solution containing phosphoric acid (H 3 PO 4) produces H 2. H 3 PO 4 associates with H 2 O 2 via hydrogen bonding, and this stabilization of H 2 O 2 suppresses its reduction, thus promoting H + reduction. The all-organic photosystem with H 3 PO 4 as a stabilizer may provide a basis of photocatalytic H 2 O 2 splitting.

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