The promotion mechanism of different nitrogen doping types on the catalytic activity of activated carbon electro-Fenton cathode: Simultaneous promotion of H2O2 generation and phenol degradation ability.

Doping with nitrogen atoms can improve the catalytic activity of activated carbon cathodes in electro-Fenton systems, but currently there is a lack of understanding of the catalytic mechanism, which limits the further development of high-performance activated carbon cathodes. Here, a multi-scale exploration was conducted using density functional theory and experimental methods to investigate the mechanism of different nitrogen doping types promoting the redox performance of activated carbon cathodes and the degradation of phenol. The density functional theory results indicate that the introduction of nitrogen atoms enhances the binding ability between carbon substrates and oxygen-containing substances, promotes the localization of surrounding electrons, and makes it easier for O2 to bind with protons and catalyze the hydrogenation reaction of *OOH. Due to its weak binding ability with oxygen-containing substances, AC is difficult to form H2O2, resulting in a tendency towards the 4e-ORR pathway. The binding energy between graphite-N carbon substrate and pyridine-N carbon substrate with *OOH is closer to the volcano top, so graphite n and pyridine n can better promote the selectivity of activated carbon for 2e-ORR. In addition, the calculation results also indicate that pyrrole-N and graphite-N are more capable of catalyzing the reaction energy barrier between ·OH and phenol. Finally, the simulation results were used to guide the modification of nitrogen doped activated carbon and experimental verification was carried out. The degradation results of phenol confirmed the efficient synergistic effect between different types of nitrogen doping, and the NAC-800 electrode exhibited efficient and stable characteristics. This work provides a guiding strategy for further developing stable and highly selective activated carbon cathode materials.

Investigation of the Mechanisms of CO2/O2 Adsorption Selectivity on Carbon Materials Enhanced by Oxygen Functional Groups.

Power plant flue gas and industrial waste gas are produced in large quantities. Using these as feedstocks for CO2 electroreduction has important practical significance for the treatment of excessive CO2 emissions. However, O2 in such sources strongly inhibits the electrochemical conversion of CO2. The inhibitory effect of O2 can be mitigated by constructing CO2-enriched regions on the surface of the cathode. In this study, the reaction zone was controlled by the selective adsorption of CO2 on oxygen-functionalized carbon materials. The results of quantum chemical simulations showed that CO2 adsorption was mainly influenced by electrostatic interactions, whereas O2 adsorption was completely regulated by dispersion interactions. This distinction indicated that introducing polar oxygen functional groups at the edge of the carbon plane can significantly enhance the selectivity for CO2/O2 adsorption. The difference in the adsorption energy between CO2 and O2 increased most noticeably after the carboxyl groups were introduced. The results of the adsorption experiments showed that oxygen-functionalization increased the CO2/O2 selectivity of the carbon material under an atmosphere of multicomponent gases by more than 4.9 times. The carboxyl groups played a dominant role. Our findings might act as a reference for the selective adsorption of polar molecules over nonpolar molecules.