Photocatalytic hydrogen peroxide splitting on metal-free powders assisted by phosphoric acid as a stabilizer

Hydrogen peroxide (H₂O₂) has received increasing attention as an energy carrier. To achieve a sustainable energy society, photocatalytic H₂O₂ splitting (H₂O₂ (l) → H₂ (g)⁺O₂ (g); ΔG° = + 131 kJ mol^-1) is a desirable reaction for on-site H₂ generation. However, this reaction has not been reported because conventional photocatalysis decomposes H₂O₂ by disproportionation (H₂O₂ (l) → H₂O (l) + 1/2O₂ (g); ΔG° = -117 kJ mol^-1) and by promoting H₂O₂ reduction instead of H⁺ reduction. Here we report the successful example of H₂O₂ splitting. Visible light irradiation of a graphitic carbon nitride loaded with graphene quantum dots as co-catalysts (GQDs/g-C₃N₄) in a H₂O₂ solution containing phosphoric acid (H₃PO₄) produces H₂. H₃PO₄ associates with H₂O₂ via hydrogen bonding, and this stabilization of H₂O₂ suppresses its reduction, thus promoting H⁺ reduction. The all-organic photosystem with H₃PO₄ as a stabilizer may provide a basis of photocatalytic H₂O₂ splitting.