Accumulation of high-arsenic fly ash (HAFA) poses a serious environmental threat due to the toxicity of As and release of other heavy metals especially Cr. In this work, a novel graphite felt (GF) cathode modified with the nanoscale MoS2/reduced graphene oxide (rGO) heterojunction is prepared by blending with PTFE emulsion for efficient synergistic oxidative dissolution of As(III) and Cr(III) in HAFA. By taking advantage of the p-n junction characteristics of the heterojunction and appropriate hydrophobicity of the PTFE coating, the modified GF efficiently utilizes both dissolved O-2 and gaseous O-2 in the 2e(-) oxygen reduction reaction (ORR). Our theoretical assessment indicates that gaseous O-2 adsorbs stably on sulfur vacancies and is reduced by electrons transmitted from rGO. Experimentally, the modified GF shows superior ORR catalytic activity as exemplified by a high peak current density of 8.41 mA cm(-2) and onset potential of 0.53 V vs. RHE. center dot OH generated by the Cr and Fe-triggered autocatalysis mechanism promotes oxidization of As(III) and Cr(III) in detoxification of HAFA resulting in 96.1% As removal as well as 70.74% Cr removal in 135 min. The modified GF with excellent stability and durability has immense industrial prospect in detoxification of HAFA and treatment of other types of As-containing hazardous wastes.