Abstract: Design of electrode materials for stable and efficient electrocatalytic oxidation of As(Ⅲ) in arsenic-contaminated groundwater poses a great challenge due to the rapid deactivation of catalysts resulting from the high oxygen evolution potential (OEP) and considerable barrier to generating reactive oxygen species (ROS). Herein, an innovative TNAs/SnO₂/PEDOT/Fe(III)-RuO₂ multilayer electrode was synthesized by utilizing a PEDOT-coated SnO₂ interlayer as a supportive framework to combine Fe-doped amorphous RuO₂ catalytic layer with TiO₂ nanotube array substrate. Such electrode exhibited high activity and stability for the oxidation of As(III) to As(V) due to the large surface area provided by the TiO₂ nanotube arrays and the SnO₂/PEDOT interlayer for facilitating the growth of the catalytic layer. The electrochemically active surface area of the electrode reached as high as 31.7 mF/cm². Impressively, the doping of Fe into RuO₂ layer led to a remarkable increase in the OEP value to 3.12 V, which boosted the indirect oxidation process mediated by ROS at a lower potential to achieve the As(III) oxidation ratio of 98.5%. DFT calculations revealed that the Fe-doped amorphous RuO₂ weakened the adsorption strength of ·OH and ·SO₄^- intermediates and lowered the energy barrier for generating ROS. Combined with ESR results, the formation of ·OH and ·SO₄^- with strong oxidizing properties was fully verified, providing further evidence for the involvement of ROS as the main mediator of the oxidation mechanism of As(III). This work may provide valuable perspectives into the design of catalytic layer structures and heteroatom doping modifications for composite-coated electrodes.

Key words: Arsenite, Electrocatalytic oxidation, Iron-doped ruthenium oxide, AnodeReactive oxygen species