Polymethylhydrosiloxane-modified gas-diffusion cathode for more efficient and durable H2O2 electrosynthesis in the context of water treatment

On-site H2O2 electrosynthesis via two-electron oxygen reduction reaction (ORR) is attracting great interest for water treatment. The use of carbon black-based gas-diffusion electrodes (GDEs) is especially appealing, but their activity, selectivity and long-term stability must be improved. Here, a facile GDEs modification strategy using trace polymethylhydrosiloxane (PMHS) allowed reaching a outstanding H2O2 production, outperforming the conventional polytetrafluoroethylene (PTFE)-GDE (1874.8 vs 1087.4 mg L-1 at 360 min). The superhydrophobicity conferred by PMHS endowed the catalytic layer with high faradaic efficiencies (76.2%-89.7%) during long-term operation for 60 h. The electrochemical tests confirmed the high activity and selectivity of the PMHS-modified GDE. Moreover, the efficient degradation of several micropollutants by the electro-Fenton process demonstrated the great potential of the new GDE. An in-depth understanding of the roles of PMHS functional groups is provided from DFT calculations: the -CH3 groups contribute to form a superhydrophobic interface, whereas Si-H and as-formed Si-O-C sites modulate the coordination environment of active carbon centers.