Graphene Quantum Dot-Modified Mn0.2Cd0.8S for Efficient Overall Photosynthesis of H2O2

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 MnxCd1-xS solid solution nanowires to enable overall H2O2 photosynthesis in pure water under an air atmosphere. The optimized Mn0.2Cd0.8S/NGQDs (M0.2NG5) composite achieves a high yield of 6885 mu mol g-1 h-1, which is 10.4 times and 4.5 times higher than that of CdS (661 mu mol g-1 h-1) and Mn0.2Cd0.8S (1522 mu mol 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 <middle dot>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.