Nickel And Nitrogen Co-doped Carbon Composites For CO₂ Electroreduction

A large amount of CO₂ released by fossil fuel combustion has caused more and more serious environmental problems.Electrochemical reduction of CO₂ to high value-added chemicals and fuels is an ideal way to solve the problems of climate warming and energy crisis.However,CO₂ is a highly stable molecule,which needs appropriate catalyst to be activated.It is no doubt that electrocatalysts with high activity and selectivity have become the research focus in the field of electrochemical reduction of CO₂.Transition metals and nitrogen co-doped carbon composites are favored by many researchers because of their low price,abundant reserves and controllable structure.They are expected to become the main force of the future catalysts for electrochemical reduction of CO₂.Based on this,this thesis focuses on nickel and nitrogen co-doped carbon electrocatalysts.The main works of this paper are as follows:1.The pore structure of XC-72 is pretty good,with both mesopores and micropores.By chemically modifying XC-72,oxidized carbon black rich in organic groups can be obtained,and nitrogen doping can be achieved.Therefore,oxidized carbon black is used as the support of the electrocatalyst.Using nickel chloride as the nickel source and melamine as the nitrogen source.A series of experimental operations including ultrasonic dispersion,stirring overnight,freeze-drying,and high-temperature calcination were used to prepare the nickel and nitrogen co-doped carbon electrocatalyst Ni/N-C.In CO₂-saturated 0.5 mol/L KHCO₃ electrolyte,the Ni/N-C catalyst can achieve 98%CO selectivity with a high current density of 16m A/cm² at-0.74 V?vs.RHE?,which is comparable to those of the single-atom nickel electrocatalysts reported previously.Moreover,we investigated the effects of experimental parameters such as metal content,drying method and calcination temperature on catalytic performance,and provided reasonable explanations.2.Sodium tetraborate was used as structure directing agent to catalyze the hydrothermal carbonization of glucose.As-prepared polysaccharide was used as the support of electrocatalysts and their abundant organic groups could provide favorable sites for nitrogen doping.The mononuclear nickel complex Ni TPP was used as the nickel source to prevent the transfer and aggregation of Ni atoms thus improve its utilization.After a series of experimental operations,such as ultrasonic dispersion,stirring overnight,freeze-drying,and high-temperature calcination,the nickel and nitrogen co-doped carbon electrocatalyst Ni TPP/N-G-750 was finally obtained.The Ni TPP/N-G-750 catalyst exhibited good activity with a Faradaic efficiency for CO production of about 95%and a current density of approximately 8 m A/cm² at a potential of-0.87 V?vs.RHE?.The catalytic performance of Ni TPP/N-G-750 is relatively close to those of most of the single-atom nickel electrocatalysts reported previously.