Electro-oxidation　(EO)　is　an　efficient　approach　to　removing　refractory　organics　in　wastewater.　However,　the　interference　from　chlorine　ions　(Cl-)　can　generate　reactive　chlorine　species　(RCS),　potentially　leading　to　the　production　of　undesirable　chlorinated　byproducts.　A　novel　approach　involving　the　cathodic　oxygen　reduction　reaction　(ORR)　for　in　situ　H2O2　production　has　emerged　as　a　promising　strategy　to　counteract　this　issue.　This　study　systematically　investigated　the　dynamics　and　transformation　of　RCS　and　reactive　oxygen　species　(ROS)　in　an　ORR/chloride-containing　EO　(EO-Cl)　system,　elucidating　their　respective　roles　in　organic　removal　and　chlorinated　byproduct　minimization.　Distinct　generation　rates　and　patterns　were　observed　for　free　chlorine　and　H2O2　in　the　ORR/EO-Cl　system.　The　rapid　generation　of　free　chlorine　at　the　anode　quickly　reached　a　dynamic　equilibrium,　which　contrasted　with　the　moderate,　continuous　cathodic　production　of　H2O2,　resulting　in　considerable　H2O2　accumulation　over　time.　This　difference　established　kinetics-driven　ROS　and　RCS　formation　and　distribution,　influencing　the　subsequent　organic　degradation　process.　Three　distinct　stages　were　identified　in　the　degradation　process.　In　stage　I,　free　chlorine　was　the　primary　species,　along　with　reactive　species　including　Cl2•-　1O2,　ClO•,　HO•,　and　Cl•.　In　stage　II,　the　gradual　accumulation　of　H2O2　consumed　free　chlorine,　favoring　the　formation　of　1O2　and　HO•.　In　stage　III,　excessive　H2O2　quenched　the　free　radicals.　Insights　into　these　multistage　mechanisms　reveal　that　the　rapid　degradation　of　chlorinated　byproducts　by　1O2　and　HO•　occurs　in　stage　II　of　the　ORR/EO-Cl　system.　©　2024　American　Chemical　Society.