Degradation mechanism of methylene blue by heterogenous electro-Fenton with CeO2/rGO composite cathode

The noble materials have been regarded as the best catalysts for electro-generating H2O2 in electro-Fenton (EF) process, but their high cost is daunting. Herein, a noble-metal-free catalyst of CeO2/reduced graphene oxide (CeO2/rGO) was prepared for electro-generating H2O2 in this study. Due to a synergistic effect between the excellent electronic mobility of CeO2 and the unique interconnected electrical transmission channels of rGO, the CeO2/rGO composite exhibited superior electrocatalytic activity than CeO2 and rGO towards the electro-generation of H2O2. In EF experiments, the degradation rate constant of methylene blue (MB) at the CeO2/rGO cathode (0.025 min–1) was 2.27 times and 2.78 times that of CeO2 (0.011 min–1) and rGO (0.009 min–1), respectively. The investigation of reaction mechanism in EF process showed that the •OH radical was the major contributor, while the •O2– radical played an important role but was not the primary active species. In addition, the vulnerable sites and the possible degradation pathways of MB in EF process were proposed according to the density functional theory (DFT) calculation and experimental results of liquid chromatography-mass spectrometry.