Enhanced Photocatalytic Production of H2O2 by Nafion Coatings on S,N-Codoped Graphene-Quantum-Dots-Modified TiO2

Photocatalytic production of H2O2 requires simultaneous promotion of the formation and the suppression of the decomposition of H2O2. This work explored a promising strategy of Nafion (perfluorinated polymer with sulfonate groups) coatings to enhance photocatalytic H2O2 production. The presence of Nafion layer on the S,N-codoped graphene-quantum-dots-modified TiO2 was characterized by transmission electron microscopy, Fourier transform infrared, and X-ray photoelectron spectroscopy measurements. The incorporation of Nafion coatings significantly improves the photocatalytic production of H2O2 (373 μM/h under simulated sunlight irradiation), which is about 70% higher than that without Nafion coatings. Both accelerated formation (34.8 μM/min) and dramatically inhibited decomposition (0.003 min–1) of H2O2 contribute to the efficient production of H2O2. Moreover, the ratios of H2O2 formation rate in the presence and absence of Nafion layers are more significantly improved at the neutral pH, which are 1.2 and 1.7 at pH 3 and 6.5, respectively. Nafion coatings show the abilities to induce a strongly negative charged hydrophobic surface, which can enhanced the local proton activity and oxygen concentration on the catalyst surface. The enhanced production of H2O2 by Nafion coatings can be attributed to the unaltered two-electron oxygen reduction reaction (ORR) pathway, the promoted charge transfer, the enhanced proton activity and oxygen diffusion, and the blocked formation of surface peroxide complexes. This work provides an insight for the modulation of proton-coupled electron-transfer-dominated ORR in photocatalysis through surface modification of Nafion coatings.