Sulfate ion-mediated electron transfer process on Ti/RuO2-MOx electrodes for ultra-low energy degradation of organic pollutants

The treatment of high-salinity organic wastewater (HSOW) poses severe challenges, with sulfate ions (SO 4 2− ) playing a critical role in electrocatalytic oxidation processes. In this study, a series of Ti/RuO 2 -MO x electrodes were fabricated by coating composite metal oxides onto titanium substrates, and the SO 4 2− -mediated electron transfer mechanism on the electrode surface was elucidated. We reveal that surface metal atoms form M O S electron channels with SO 4 2− , facilitating direct electron transfer for organic oxidation. The oxidation state of metal ions exerts a significant regulatory effect on electron transfer processes. Specifically, composite formation with metal oxides (i.e., Sn 4+ , Ce 4+ , Mn 4+ ) exhibiting valence state matching with Ru 4+ optimizes surface electron distribution, expands electron channels, and enhances SO 4 2− adsorption stability, thereby exerting a positive promotional effect on electron transfer. Conversely, composite systems involving metal oxides with significant valence state discrepancies from Ru 4+ (i.e., Cu 2+/3+ , Co 2+/3+ , Fe 2+/3+ ) disrupt surface electron distribution, shrink electron channels, and reduce SO 4 2− adsorption stability, leading to impaired charge transfer kinetics. Notably, via the SO 4 2− -mediated electron transfer process, the Ti/RuO 2 -SnO 2 electrode with outstanding electron transfer properties achieved ultra-low energy consumption (0.0022 kwh‧g −1 ) degradation of organic pollutants, with a carbon footprint of 0.68 kg CO 2 ‧m −3 . This study provides novel insights for the ultra-low energy treatment of HSOW.