Enhanced generation of H2O2 and radicals on Co9S8/partly-graphitized carbon cathode for degradation of bio-refractory organic wastewater

Abstract

In electrochemical advanced oxidation processes (EAOPs), the hydrogen peroxide (H2O2) could be in-situ generated from the two-electron (2e−) oxygen reduction reaction (ORR), which was then converted to OH radicals in the role of cathode catalyst. To improve the efficiency of H2O2 generation, cobalt sulfide/partly-graphitized carbon (Co9S8/PGC) composites as EAOPs cathodes were synthesized via a simple simultaneous carbonization method. The structural and electrochemical properties of Co9S8/PGC were investigated. Results demonstrated that Co9S8 with coexistence of Co2+/Co3+ was tightly embedded into the PGC skeleton. Abundant oxygen-containing groups on the PGC surface could improve the wettability and hydrophilicity of the Co9S8/PGC (800°C), contributing to the formation of more catalytic active sites in the porous structure. Synergistic effect between Co9S8 and PGC could improve the electron transfer efficiency and O2 mass transfer by increasing the contact interface area between electrode and electrolyte, inducing the high selectivity for 2e−ORR. The mixed-valence nature of Co9S8 (Co2+/Co3+) exhibited high catalytic activity for promoting the OH generation from H2O2. Degradation rates of phenol and TOC removal rate of ceftazidime reached approximately 89.1 and 84.3% at 120 and 480min, respectively, indicating that Co9S8/PGC cathode had promise for further application.