Graphene Quantum Dot‐Modified Mn_0.2Cd_0.8S for Efficient Overall Photosynthesis of H₂O₂

Abstract The photosynthesis of hydrogen peroxide (H₂O₂) via the selective two‐electron oxygen reduction reaction (ORR) is emerging as a promising method for producing this important chemical. However, the reliance on sacrificial agents has limited the practical application of many photocatalysts. Herein, nitrogen‐doped graphene quantum dots (NGQDs) are loaded onto the surface of Mn_xCd_1‐xS solid solution nanowires to enable overall H₂O₂ photosynthesis in pure water under an air atmosphere. The optimized Mn_0.2Cd_0.8S/NGQDs (M_0.2NG5) composite achieves a high yield of 6885 µmol g⁻¹ h⁻¹, which is 10.4 times and 4.5 times higher than that of CdS (661 µmol g⁻¹ h⁻¹) and Mn_0.2Cd_0.8S (1522 µmol g⁻¹ h⁻¹), respectively. The NGQDs act as co‐catalysts, enhancing the conductivity of the system. The strong electronegativity and polarity of the incorporated nitrogen and functional groups on the NGQDs edges enhance the ability of carbon atoms to activate O₂ into ·O₂⁻. The mechanism of H₂O₂ photosynthesis is investigated using in situ Fourier transform infrared spectroscopy, intermediate trapping experiments, and theoretical calculations. This work offers new insights into the design of non‐noble metal co‐catalyst‐modified photocatalysts for sacrificial‐agent‐free H₂O₂ production.