Electrochemical catalytic mechanism of N-doped graphene for enhanced H2O2 yield and in-situ degradation of organic pollutant

摘要

Highly efficient electrochemical advanced oxidation processes (EAOPs) based on carbon catalysts are promising and green technologies for environmental remediation. Herein, for the purpose of cost-effectiveness, wide pH suitability and excellent reusability, graphite felt modified with regulatable N-doped graphene was developed as a cathode to electrochemically generate H2O2 with high yield and selectivity, and efficiently catalyze H2O2 to form (OH)-O-center dot for organic pollutants degradation by in-situ metal-free EAOPs. Particularly, the catalytic mechanism of N-doped graphene for enhanced performance was explored. Optimized N-doped graphene showed a very high H2O2 generation rate of 8.6 mg/h/cm(2), low electric energy consumption (9.8 kW h/kg) and high H2O2 selectivity of 78.02% in neutral pH solution. Compared with electro-Fenton (EF), this in-situ metal-free EAOPs on N-doped graphene displayed significant improvement on the degradation performance of organic pollutants in neutral and alkaline solutions, and was certified to be less affected by initial pH. The pyridinic N and C=C in N-doped graphene enhanced the onset potential while graphite N determined the disk current of oxygen reduction reaction (ORR) process. Most importantly, it proved that the introduction of graphite N could promote the 2e- ORR process for H2O2 generation, and the presence of pyridinic N could catalyze H2O2 to the production of (OH)-O-center dot. Taken phenol as target pollutant, 'OH generated by N-doped graphene accounted for 80.72% while O-2 contributed 19.28% to its degradation, based on which a possible mechanism for phenol degradation was proposed. Moreover, in-situ metal-free EAOPs showed excellent stability, reusability and performance for various organic pollutants degradation. This work would shed light on the catalytic mechanism for metal-free EAOPs, and thus promote its application for organic pollutants degradation.