Preparation Of Transition Metal And Nitrogen Doped Carbon Materials And Their Electrocatalytic Oxygen Reduction Performance

Fuel Cells（FC）is a chemical device that converts the chemical energy of fuel into electric energy.It is widely used in the fields of military,space and power plants,as well as in the fields of motor vehicles,mobile devices and households.It is one of the directions of clean energy development in the future.Among them,proton exchange membrane fuel cells（PEMFCs）and hydrogen and oxygen fuel cells have the advantages of low operating temperature and high energy density,which are the fuel cells closest to commercial application at present.The cathode reaction of this kind of battery is oxygen reduction reaction（ORR）with very slow kinetic process.At present,platinum（Pt）catalyst is mainly used to catalyze the reaction to improve the discharge efficiency of the battery.However,the scarcity and high cost of Pt greatly limit the large-scale application and development of fuel cells.Therefore,it is urgent to develop clean and efficient non-noble metal（NPMC）ORR catalysts.This paper mainly studies highly active,low cost of non-noble metal catalyst for ORR as a starting point.About non-noble metal catalyst carbon-based electrode polarization and active site of low density and mass transfer problem,we put forward building many active sites and porous structure of catalyst design strategy,which promote non-noble metal carbon catalyst activity,stability,and methanol tolerance.And we use physical characterization and electrochemical testing technology to the morphology,structure of the material and ORR catalytic activity was studied,the results are as follows:（1）Due to most carbon-based catalysts have low density of active sites for oxygen reduction.We prepared carbon-based nanomaterials by one-step hydrothermal method using polyvinyl alcohol（PVA）and sodium hydroxide（NaOH）as precursors.B,N and Co were doped by introducing ammonium borate（NH₄HB₄O₇·3H₂O）and cobalt nitrate（Co（NO₃）₂）of rich in B and N,and the Co-doped carbon nanosheets were prepared by high temperature calcination.It was found that B,N-Co/CNFs were rich in Co-N_x,B-C and other active sites,which contributed to the rapid ORR process.The ORR half-wave potential(E_1/2)in 0.1 mol/L KOH electrolyte was 0.83 V.Compared with the contrast samples of CNFs and Co/CNFs,the catalytic activity and stability of ORR were significantly improved.（2）In order to investigate the effects of different transition metals on the catalytic activity of ORR,we designed a simple and feasible construction method for the active site of oxygen reduction reaction（Fe-N_x）,and explored the efficient catalytic mechanism of Fe-N_xactive site in oxygen reduction reaction.Fe-N/C catalyst was obtained by adjusting the reaction temperature and the proportion of doping metal.Fe-N/C SACs was prepared by etching Fe-N/C.Compared with commercial Pt/C catalysts,Fe-N/C SACs have excellent catalytic activity for oxygen reduction reaction,higher electrochemical stability and methanol tolerance due to the uniform distribution of Fe-N_x active sites and porous structure in Fe-N/C SACs.It was found that the half-wave potential(E_1/2)of Fe-N/C SACs catalyzed ORR in 0.1mol/L KOH electrolyte was 0.845 V.Compared with the sample N/C and Fe-N/C,the catalytic activity and stability of Fe-N/C SACS for ORR were significantly improved.（3）Based on the active site density and porous structure design of non-noble carbon-based catalyst,SiO₂/PAN/PANI nanofibers were prepared by electrospinning polyacrylonitrile（PAN）,polyaniline（PANI）and SiO₂ which use SiO₂ as hard template.After high temperature treatment and pre-oxidation,stable carbon nanofibers were formed.Porous carbon nanofibers were formed by NaOH etching silicon dioxide particles and high temperature calcination,which constructed with porous structure of iron and nitrogen doped carbon nano fiber catalyst.Due to the larger specific surface area the catalyst can carry more active sites,and in 0.1 mol/L KOH electrolyte initial potential E₀（0.983 V vs.RHE）and half wave potential E_1/2（0.837 V vs.RHE）are similar to 20%Pt/C,but have better electrochemical stability.