Preparation And Electrochemical Properties Of N,P-codoped Carbon And Carbon-coated Nanomaterials

Recently,under the great pressure of energy requirement and environmental pollution,green and sustainable energy resource is a common goal for the current human society.Fuel cells and Lithium-ion batteries have been extensively developed due to their enviroment friendliness and renewability.For fuel cells,metal-free catalysts based on carbons for oxygen reduction reaction?ORR?possess high energy dencity and conversion,low CO poisoning,and low methanol crossover effects.For spinel Li₄Ti₅O₁₂,which is designated by the US Department of Energy as the second-generation negative electrode material for lithium-ion batteries,the raw materials are provided with low cost,high safety,and high energy/powder density.Based on above mentioned,this thesis includes two study aspects as following:?1?N,P co-doped carbon nanofibers were prepared by simple electrospinning and high-temperature pyrolysis.Firstly,the precursor were electrospun from a solution of polyacrylonitrile?PAN?,triphenyl phosphate?TPP?and N,N-dimethylformamide?DMF?.Then,the precursor was annealed at 800,900 and 1000?in an Ar atmosphere to obtain N,P co-doped carbon nanofibers?NPC NFs-x?.Among the three homemade samples,the NPC NFs-900 showed the best electrocatalytic performance toward oxygen reduction reaction?ORR?in0.1 M KOH solution,with an onset potential of 0.93 V,and large current density(4.6 mA cm^-2).Notably,the number of electron transfer was 3.98 on NPC NFs-900,much closed to four-electron pathway on the Pt/C benchmar.The excellent catalytic performance would be contributed to synergistic effect of the active sites produced by pyridinic N and P-C.Additionally,the tolerance of methanol is better than commercial Pt/C.?2?The spinel Li₄Ti₅O₁₂ was treated in triethanolamine,then followed by pyrolysis at high temperature to obtain a carbon-coated Li₄Ti₅O₁₂ sample?LTO-1?.From the EDS and XPS,the peaks of the element C was observed,confirming successful C-coated on spinel Li₄Ti₅O₁₂.The high-resolution XPS shows there exhibit Ti³⁺and graphitization of carbon,which have been verified to improve the performance of lithium-ion batteries.LTO-1 possesses very small impedance,with an initial discharge capacity of 172.5 mAh g^-1 and a retention of 121.7 mAh g^-1 after 50 cycles.The rate capability of LTO-1 at high current densities is higher than spinel Li₄Ti₅O₁₂.The charging and discharging platform enhances the safety during charge and discharge.