Studies On Preparation And Co₂ Electroreduction Property Of NiO/N-Doped Mesoporous Graphene Catalyst

Direct electrochemical CO₂reduction（CO₂RR）could convert CO₂to value-added chemicals,such as CO,which can significantly alleviate the energy crisis and environmental pollution.Unfortunately,the industrial application of CO₂RR is limited by high overpotential,low product selectivity and fierce competition.Transition metal oxides/nitrogen-doped graphene composites are promising CO₂RR electrocatalysts,however,it is still challenging to determine which nitrogen configuration（pyridinic-N,pyrrolic-N or graphitic-N）can significantly enhance the activity of the catalyst.In this thesis,a strategy based on LI-PLI and direct pyrolysis is developed for the synthesis of NiO/N-doped mesoporous graphene with adjustable types of N configurations.The relationship between the activity of NiO/NLG-x catalyst for CO₂RR and different N configurations and contents are studied.The results show that,with the increase of laser energy,the pore density of NiO/NLG-x increases,and the content of pyridinic-N in graphene also increases.The coordination structure of Ni-pyridinic-N results in partial electron transfer from Ni to pyridinic-N.The results of electrochemical tests show that the activity of CO₂RR improves gradually with the increase of pyridinic-N content,which is not related to the pyrrolic-N and graphitic-N contents.For laser energy exceeding 245 m J,although the content of pyridinic-N continues to increase,the CO₂RR activity gets worse due to increasing of charge transfer resistance on the electrode surface.The reduction current density of CO₂on the electrode surface of NiO/NLG-245 reaches 35 m A cm^-2and the Faraday efficiency of CO achieves 87.5%at-0.74 V vs.RHE.The Tafel slope is 116 m V dec^-1.The excellent CO₂RR activity of NiO/NLG-245 could be ascribed to the followings.1)Laser-induced mesopores in the graphene are favorable for the formation of pyridinic nitrogen and pyridinic-N-Ni active sites,which could accelerate the adsorption of CO₂molecules and the desorption of*CO and reduce the overpotential;2)The mesopores in graphene are favorable for rapid penetration of electrolyte and the diffusion of CO₂molecules,thus improving the catalytic efficiency.