The Preparation Of Co(CoFe)-nitrogen Doped Carbon Nanofibers And Their Electrocatalysis Performance

As an emerging chemical energy replacement device and secondary battery,fuel cells and metal air batteries are characterized by clean and efficient performance which can mitigate the increasingly prominent energy and environmental issues.However,their slow cathode kinetics and expensive catalyst costs constrain their large-scale applications.Therefore,it is necessary to develop an oxygen electrode catalyst which is economical and efficient and easy to scale.Transition metals,instead of noble metals,have demonstrated their potential in oxygen electrode catalysts.As a method for fabricating one-dimensional nanofibers,the electrospinning technology is easy to enlarge industrialization.At present,in the manufacture of carbon nanofiber electrocatalysts,researchers mostly use organic solvents that will cause the environment to be polluted.Therefore,it is necessary to develop environmental-friendly electrospinning technology for the preparation of carbon nanofiber-based materials.In this research work,biomass-derived chitosan was used as carbon source,and carbon nanofibers were prepared by aqueous solvent electrospinning.The pyrolysis characteristics of nanofibers in inert atmosphere were studied by comprehensive thermal analysis.The slow-rate pyrolysis procedure was designed.The program controls the agglomeration of metal in the pyrolysis process of nanofibers.These strategy were also used in the synthesis of various carbon nanofibers with different type and amount of metal.Their catalytic performance for oxygen reduction or oxygen evolution/oxygen reduction reactions were also investigated.The main research contents and conclusions are as follows:?1?By analyzing the complex influence of the ratio of the precusors on the electrospinning process parameters,the boundary conditions and exploration experiments was rationally designed,and the linear programming method was used to obtain the morphological-feasible operating range of the ratio of the precusors.The optimal precursor prescription is selected in the operating region from the perspective of optimizing the ORR performance with PEO:chitosan:cobalt source:PEI?50%?=1.4:1:0.1:0.8.By analyzing the pyrolysis of each precursor and its complex under inert atmosphere,a slow-rate pyrolysis procedure was designed.Using this procedure,with the optimal precursor prescription,Co-N-CNFs-LM with well dispersed cobalt?0.71at%?can be obtained.In alkaline solution,Co-N-CNFs-LM shows comparable ORR catalytic performance to commercial Pt/C with the electron transfer number of 3.70,the kinetic current density of 24.43 mA cm^-2,and the Tafel slope of-48.5 mV dec^-1 and shows better methanol tolerance than Pt/C.?2?The above-mentioned aqueous solvent electrospinning combined with slow-rate pyrolysis procedure was extended to the preparation of cobalt-iron bimetallic-doped carbon fiber CoFe/CoFe₂O₄-CNFs.The pyrolysis method,the ratio of the two metal precursors and the amount of the two kinds of metal precursors on the particle size of CoFe alloy particles and CoFe₂O₄ particles,and their effects on the electrocatalytic performance of OER/ORR were studied.The addition of PEI and slow-rate pyrolysis procedure are beneficial to the increase of ECSA for OER and the performance of ORR and OER.The best sample Co₁₂Fe₁₈-CNF shows potential difference??E?of 0.979 V between the OER potential at 10 mAcm^-2(E₁₀)and ORR potential at E_1/2,which is slightly worse than Pt/C+RuO₂ with 64 mV difference.