Electrochemical Reduction Of N₂ On Nanocarbon Based Cathode Coupled With Electrochemical Oxidation Of Perfluoro Octanoic Acid On Sb-SnO₂ Anode

Ammonia（NH₃）is the world’s second largest chemical product,but industrial synthesis of ammonia has harsh reaction conditions.The reaction process will generate a large amount of Carbon dioxide（CO₂）,putting a heavy burden on the environment.While the electrochemical ammonia synthesis has ambient operation conditions and no CO₂ output,which is a very promising technology for Nitrogen（N₂）resource utilization.However,the process of the electrocatalytic N₂ reduction reaction（NRR）to NH₃ has low NH₃yield and low Faradaic efficiency,which is still hard to overcome in this field.Meanwhile,the electrochemical nitrogen fixation process will be accompanied by the oxygen evolution reaction at the anode,which will consume a large amount of electrical energy,resulting in energy waste.Electrochemical oxidation technology has a good mineralization effect on persistent organic pollutants.The electrochemical reduction of N₂ coupled with electrochemical oxidation of organic pollutants can make full use of the electric energy in the electrochemical cell.However,the electrochemical oxidation of persistent organic pollutants generally suffers from high voltage or current.Therefore,how to improve electrocatalytic activity and reduce energy consumption are the main challegens for electrochemical oxidation of persistent organic pollutants.In this study,we designed Co single atom embedded N-doped porous carbon（CSA/NPC）、sp²/sp³ core-shell hybrid carbon catalysts and Ti/SnO₂-Sb nanoneedle array electrode.We studied the electrochemical nitrogen fixation performance of sp²/sp³ core-shell hybrid carbon catalysts and explored methods to enhance nitrogen fixation performance.Moreover,we investigated the degradation performance of perfluoro octanoic acid（PFOA）by Ti/SnO₂-Sb nanoneedle array electrode,and verified the improvement of PFOA degradation performance via nanoneedle array.And the electrochemical nitrogen fixation on sp²/sp³ core-shell hybrid carbon was coupled with the electro-oxidation degradation of PFOA on nano-tip array Ti/SnO₂-Sb to achieve nitrogen fixation at the cathode and simultaneously pollutant degradation at the anode.The research results obtained are as follows:（1）We prepared the CSA/NPC.The effect of Co single atom and N doping on the performance of electrochemical reduction of N₂ to NH₃ on CSA/NPC were studied.The results showed that the introduction of Co single atom and N doping could promote electrocatalytic N₂reduction to NH₃ on CSA/NPC.Under the optimized conditions,NH₃ production rate of 0.86mmol?cm^-2?h^-1 and the Faradaic efficiency of 10.5%could be achieved at-0.2 V.Co single atom and N doping could effectively improve the N₂ adsorption and activation performance of CSA/NPC and accelerated the rate of its NH₃ synthesis.（2）The sp²/sp³ core-shell hybrid carbon was prepared through high-temperature calcination.Subsequently,the effects of its oxygen-containing functional groups,sp²/sp³ ratio and B doping on the performance of electrochemical reduction of N₂ to NH₃ on sp²/sp³ core-shell hybrid carbon were studied.The results showed that the sp²/sp³ core-shell hybrid carbon synthesized at 900℃（I_D?I_G=0.92）has the best NRR performance with the NH₃ productiion rate of 0.16μg?h^-1?cm^-2 and the Faradaic efficiency of 13.5%at-0.1V.The B doped sp²/sp³ core-shell hybrid carbon with 3.19%B content has the best NRR performance with the NH₃production rate of 0.53μg?h^-1?cm^-2 and the Faradaic efficiency of 46.9%at 0V.This result indicated that B doping could introduce a large number of defects and active sites,which inhibited the hydrogen evolution reaction（HER）to a certain extent and improved the NRR activity of BDHC.（3）The Ti/SnO₂-Sb nanoneedle array electrode was prepared by electrophoresis.Its performance for PFOA degradation was invertigated at a current density of 10 m A?cm^-2,99.5%PFOA(100 mg?L^-1)was degraded by Ti/SnO₂-Sb nanoneedle array electrode after 3 h with the first-order kinetic constant of 1.92?h^-1.The first-order kinetic constant of Ti/SnO₂-Sb nanoneedle used to degrade PFOA is 1.6 times that of Ti/SnO₂-Sb.When electrochemical reduction of N₂ on sp²/sp³ hybrid carbon cathode coupled with electrochemical oxidation of organic pollutants on Ti/SnO₂-Sb nanoneedle array anode,the degradation efficiency of 100mg?L^-1 PFOA can reached 98.6%in 3 hours,and the NH₃ yield reached 0.43～0.46μg?h^-1?cm^-2.In summary,the single metal atom,B-doping and N-doping can effectively enhance the NH₃ yield and Faradaic efficiency for electrochemical reduction of N₂ on nanocarbon.The Ti/SnO₂-Sb with nanoneedle array morphology can enhance the degradation rate and reduce the energy consumption for PFOA degradation.The research has realized the high-efficiency electrochemical reduction of N₂ to synthesize NH₃ and simultaneous oxidation and degradation of PFOA.It provided new ideas for the design of electrocatalysts,electrooxidation and electroreduction performance optimization.