New Electro-Fenton Gas Diffusion Cathode based on Nitrogen-doped Graphene@Carbon Nanotube Composite Materials

• A new nitrogen-doped graphene@carbon nanotube (N-G@CNT) cathode is used for the e-Fenton process.
• ORR activity is significantly improved mostly due to the bridge graphene—CNT and to N doping.
• The DMP degradation rate, compared to graphite cathode, is 14 times higher.
• At t1/2 of DMP degradation, the energy consumption is much less of that required on other GDEs.

For the development of a highly active and energy-effective electro-Fenton process, a novel nitrogen-doped graphene@carbon nanotube composite material (N-G@CNT) is prepared, characterized, investigated for the oxygen reduction reaction (ORR), and employed for dimethyl phthalate (DMP) degradation in aqueous solution. It is found that N-G@CNT’s ORR activity towards H2O2 production is significantly improved in terms of increased current density and more positive onset potential. Moreover, −0.2 V (vs. SCE) is the lowest cathodic potential, to our best knowledge, in which DMP degrades over N-G@CNT GDE (Gas Diffusion Electrode) more effectively than over: i) graphite GDE or ii) graphene GDE or iii) CNT GDE. The apparent rate constant of DMP degradation is found to be 0.0322 min−1, about 14, 19, and 54 times higher than those measured on the above three types of GDEs, respectively. It is also found that, at the lower potential (−0.2 V), the energy consumption (EC) for the half-life time degradation of DMP over the studied GDEs, is as follows (in J mg−1): N-G@CNT = 2.56 < graphite = 10.61 < graphene = 12.23 < CNT = 38.35. The lower onset potential could be attributed to both the bridge between graphene and CNT and the nitrogen doping. The as-prepared N-G@CNT exhibits high activity and desirable stability, and represents a potential candidate material as electro-Fenton cathode for energy-effective wastewater treatment.

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