Application Of 3D Porous Nitrogen-doped Carbon Catalysts In CO₂ Electroreduction

The human existence is increasingly threatened by resource shortage and environmental problems.Carbon neutrality is the only way out of the current economic and ecological dilemma for us.With the serious commitment to peak carbon dioxide emissions and carbon neutrality,CO₂ capture and conversion technology is an efficient way to finish this task.Among the various techniques,CO₂ electroreduction into high value-added fuels at moderate temperature and pressure is promising due to its higher cost-effectiveness than that of typical thermochemical method.It is very important to select a satisfactory catalyst which is very important for the development of CO₂ electroreduction reaction.Many metal catalysts show the same shortcomings,including unstable chemical properties and high cost.However,some carbon-based metal free catalysts,such as heteroatom doped nano-diamond,graphene and carbon nanotube,show high performance at the expense of high cost.Therwfore,we are aimed to develop new catalysts with high CO₂RR performance and low cost.Based on this,we tried to prepare carbon-based catalysts with high selectivity,high stability and high activity through heteroatom doping and pore engineering.The main research tasks are as follow:（1）We prepared a series of nitrogen-doped carbon gel electrocatalysts by pyrolysis of agarose-based gel precursors,which was systhesized via a sol-gel method using agarose as carbon source,ammonium chloride as nitrogen source,and zinc chloride as pore-forming agent.The catalysts with different catalytic properties were obtained by changing the carbonization temperature.Among them,NZn CA-1000 showed the best electroreduction activity for CO₂ to CO with a high Faradic efficiency（93%）at the current density of-6.4 m A cm^-2when the potential was set to-0.65 V vs.RHE.The Faradic efficiency of CO decreased to 85%after continuous electrolysis for 11 h,and recovered to 90%after changing the fresh electrolyte.As for the frozen aerogel electrocatalyst,pyrrole nitrogen is the main factor of CO2RR efficiency,and the 3D porous network structure is conducive to the exposure of active sites.（2）The nitrogen doped carbon catalyst for electrocatalyzing CO₂ reduction reaction was synthesized by pyrolysis of polyacrylonitrile precursors via the double templates method using polyacrylonitrile as carbon and nitrogen sources,zinc oxide and sodium chloride were used as double templates.In the catalytic system,polyacrylonitrile was used as a source of nitrogen and carbon sources.During the preparation,the templates were removed using high temperature carbonization and following dilute hydrochloric acid treatment.The carbonization temperature was optimized,obtaining several catalysts.Among them,the catalyst prepared at 1100℃shows the best performance for electroreduction of CO₂.When the potential of-0.6V vs.RHE is applied,CO₂can be effectively reduced to CO with 95%Faradic efficiency at the current density of-4.2 m A cm^-2.The Faradic efficiency remained at 90%after the electrolysis for 16 h,and recovered to 94%after reusing new electrolyte,showing excellent stability.In all,the hierarchical porous structure of micropore-mesopore-macropore can promote the mass transfer of catalytic reaction and reduce CO₂ with high efficiency.