The Study Of Flame Synthesis Of Heteroatom Co-doped Carbon Materials For Oxygen Reduction Reaction

Heteroatom doped carbon materials have become the most promising alternative to precious metal Pt because of their low cost,high ORR performance,excellent methanol tolerance,and high stability.It has a broad application prospect in fuel cells.At present,methods for preparing hetero atom-doped carbon materials include chemical vapor deposition(CVD),templating,pyrolysis and hydrothermal methods,but these methods require specific experimental conditions and complicated pre-and post-treatment processes.The development of a fast,economical and efficient method for the preparation of heteroatom-doped carbon materials is of great significance for the study of heteroatom-doped carbon materials in non-precious metals.As a simple and rapid preparation method,flame synthesis is gradually applied to the preparation of heteroatom-doped carbon materials.And the prepared doped carbon material exhibits good catalytic activity in the cathode oxygen reduction reaction(ORR)of the fuel cell.Therefore,the research and development of heteroatom-doped carbon materials by flame method is of great significance for the commercial development of fuel cells.In this thesis,the main goal is to prepare a catalyst with low cost,high catalytic activity,good selectivity and stability.The simple flame synthesis method is used to optimize the precursor selection and carbonization conditions by using the advantages of heteroatom doping carbon materials.Nitrogen,boron co-doped carbon materials(NBC,NBC)and nitrogen and phosphorus,co-doped carbon materials(NPC)were successfully prepared and used as ORR reaction catalysts under alkaline conditions.The main research content is divided into the following three parts:Part ?: Flame synthesis of N,B co-doped carbon material by pyrrole as raw material and its electrocatalytic performance for oxygen reduction reactionIn this part,pyrrole was used as the nitrogen source and acetone was used as the carbon source.The nitrogen-doped carbon material is prepared by simple flame synthesis method,and then combined with boric acid in a certain ratio to prepare nitrogen and boron co-doped carbon material(NBC).The results of ORR electrocatalytic activity test showed that after 30 000 s chronoamperometry,the current retention rate was 86.0% and 1000 cycles of cycling test,the half-wave potential was only shifted by 3.1 m V,showing good stability and anti-methanol test results showed strong methanol tolerance.The high ORR performance of NBC may be due to the strong synergistic effect between nitrogen and boron atoms.XPS characterization showed that the content of nitrogen and boron in NBC reached 2.85 at% and 9.53 at%,respectively,indicating that the method can successfully prepare heteroatom co-doped carbon materials.Part ? Flame synthesis of N,B co-doped carbon material by acetonitrile as raw material and its electrocatalytic performance for oxygen reduction reactionBased on the research content of the previous part,the acetonitrile was used as the nitrogen source,and the ratio of precursor,carbonization temperature and carbonization time were regulated.Among many as-prepared samples,the N-B-C catalyst which prepared under carbonization temperature of 1000 ? for 3 h with acetonitrile/acetone precursor ratio of 1:1 exhibits the best catalytic activity,the half-wave potential differs from Pt/C by 49 m V,and has good stability and resistance to methanol poisoning.The electron transfer number of oxygen reduction reaction is 3.9,which has a fast ORR reaction kinetics.Part ?: Flame synthesis of N,P co-doped carbon material and its electrocatalytic performance for oxygen reduction reactionBased on the first two parts,the N,P co-doped carbon material(N-P-C)was successfully prepared by the change of dopant atoms and the optimization of the preparation process.Electrochemical tests show that,compared with Pt/C,the prepared NPC catalyst has good resistance to methanol poisoning in ORR and has a high current retention rate of 92.6%,showing excellent stability.The results of rotating ring electrode test(RRDE)showed that the electron transfer number was 3.53,indicating that N-P-C catalyzes the four-electron reaction process of ORR in alkaline medium.The BET test results show that the N-P-C catalyst has a graded porous structure.The XPS characterization shows that the content of nitrogen and phosphorus in NBC reaches 1.68 at% and 1.98 at%,respectively,indicating that the flame synthesis method can successfully achieve doping of heteroatoms.A good synergistic effect between N and P promotes an increase in the activity of the catalyst ORR.