Preparation And Properties Of Bifunctional Electrocatalyst Of Biomass Based Carbon Composite Transition Metal Compounds

With the large amount of carbon dioxide produced by the combustion of non renewable fossil resources continuously injected into the ecological environment and human life,it has caused huge environmental problems on a global scale.Moreover,the impact of our unrestricted discharge of waste to the environment and human beings has become more obvious,so we need to find a way to turn from non renewable energy to renewable energy in order to reduce the impact of excessive use of non renewable resources on the environment.Among the renewable resource candidates,biomass is one of the alternatives to meet the demand for carbon based chemicals and energy.Therefore,we use green carbon-based precursors and environmentally friendly preparation processes to design heteroatom doping and composite transition metal methods from the molecular level to enhance the activity and stability of carbon materials,making them suitable for zinc-air batteries（ZAB）has the potential for practical applications.In this paper,we focused on the introduction of heteroatoms and transition metals into the carbon lattice by direct pyrolysis of catkins as precursors,and explored the electrocatalytic performance of oxygen reduction reaction（ORR）/oxygen evolution reaction（OER）and ZAB performance of the materials.The research content and results of the paper are as follows:1.Iron-cobalt composite nitrogen-doped carbon material for ORR/OER bifunctional electrocatalyst.Fe Cl₃·6H₂O,Co（NO₃）₂·6H₂O are selected as the metal precursors of Fe and Co,and dicyandiamide is used as the precursor of the foreign doping element N.Through the direct pyrolysis process,the nitrogen-doped carbon nanometer is realized The hollow carbon fiber structure of the carbon tube（FeCo/N-CNT@HCF）,the doped nitrogen can coordinate with the transition metal to form TM-Nx,thereby increasing the active center and promoting the electrochemical reaction together with the metal oxide.The ORR catalytic activity of FeCo/N-CNT@HCF is equivalent to that of Pt/C.The half-wave potential(E_1/2)and initial potential（E₀）are 0.86 V and 0.95 V,respectively.After5000 cycles,FeCo/N-CNT@The negative shift of E_1/2 in the HCF LSVs curve by 9 m V is the same as the negative shift of E_1/2 of 20%Pt/C.At a current density of 10 m A cm^-2,the overpotential of OER(E_j=10)is 1.678 V,which is close to the overpotential of Ru O2(E_j=10=1.62 V),and the potential difference between（ΔE）E_1/2 and E_j=10 of FeCo/N-CNT@HCF is 0.897 V,so the synthesized FeCo/N-CNT@HCF exhibits good ORR and OER dual-function electrocatalytic performance.This work provides a simple and economical method for preparing porous materials using biomass derivatives as precursors.2.Iron-cobalt composite nitrogen-sulfur-doped carbon material used as cathode catalyst for zinc-air battery.Using biomass catkins as the substrate,thiourea as the precursor of element S,and dicyandiamine as the precursor of element N,the doping of multiple heteroatoms not only increases the specific surface area of the catalyst,but also effectively improves the transition metal doping The content of miscellaneous.By changing the molar ratio of transition metal iron salt and cobalt salt,we obtain the optimal iron-cobalt co-doped nitrogen-sulfur hollow carbon material（Fe_xCo_y/NS-CNT@HCF）.The E₀ and E_1/2of Fe₁Co₁/NS-CNT@HCF are 0.963 V and 0.863 V,respectively,which are slightly higher than the E₀ and E_1/2 of Pt/C.After 5000 cycles of testing,the E_1/2 of Fe₁Co₁/NS-CNT@HCF is only negatively shifted by 5 m V.The E_j=10 of Fe₁Co₁/NS-CNT@HCF is 1.585 V,which is 32 m V lower than the E_j=10 of Ru O₂.It exhibits excellent ORR and OER dual-function electrocatalytic activity and excellent stability,and it can also be applied to rechargeable ZAB.ZAB was assembled based on Fe₁Co₁/NS-CNT@HCF catalyst,and the electrochemical performance of ZAB was tested.At a current density of 5 m A cm^-2,the charge-discharge cycle lasted 165 h,showing a good battery cycle life.Through the above exploration,we modified the carbon materials from multiple heteroatom doping and composite transition metals,which improved the ORR and OER bifunctional electrocatalytic activity of the catalyst,and provided the potential for practical application of rechargeable ZAB.