Oxygen Reduction Reaction Catalysts For Fuel Cells Based On Heteroatom-doped Carbon Materials

With the rapid development of modern society,the overuse of traditional fossil energy leads to not only the global energy depletion crisis but also the serious environmental pollution.Therefore,searching for alternative clean energy is urgent.Fuel cells have attracted more and more attention of many researchers due to their advantages of high energy density,no pollution,low cost and wide source of raw materials.Oxygen reduction reaction?ORR?is a core reaction of new energy devices such as fuel cells and metal–air batteries.Owing to the slower kinetics in ORR,more Pt catalysts are needed in the cathode.Platinum catalyst is the most widely used ORR catalyst,but its poor resources,high cost and poor stability make it limited to achieve commercial application.Therefore,the development of low-cost,high-performance ORR catalysts remains a huge challenge.In this thesis,a variety of heteroatom-doped carbon catalysts were prepared by selecting different chemical substances as the precursor for the preparation of low cost electrocatalysts with high catalytic performance.These include a carbon-coated mesoporous Co/N-doped carbon material synthesized by using a metal organic framework?ZIF-67?as a precursor,3D porous Fe,N and S tri-doped carbon material prepared on the basis of glucosamine hydrochloride,and Fe and S co-doped N-enriched porous carbon materials prepared by using S spheres as templates.After the optimization experiment,the target catalyst materials prepared under the best conditions have good electrochemical activity.The main points of this thesis are presented as follows:?1?ZIF-67 was grown on the SiO₂ to obtain ZIF-67@SiO₂,which was then dispersed in a mixture of ionic liquid and methanol.After the polymerization of ionic liquid on ZIF-67@SiO₂ was completed,the sample was carbonized at high temperature.Finally,the target catalyst Co-N-C with hollow structure was obtained by HF acid etching.The structure and morphology of the materials were characterized by physical characterization.The catalytic activity,stability and resistance to methanol poisoning of the catalysts were characterized by electrochemical tests.The results showed that the ionic liquid polymer can maintain the stability of the structure of the material and further improve the catalytic performance of the catalyst.?2?Taking glucosamine hydrochloride as the substrate material,tripolythiocyanic acid as the source of N and S,NaCl,which is green,pollution-free and easy to remove,as a pore-forming agent,and FeCl₃ as the Fe source,Fe/N/S-C with 3D structure was prepared.The structure,morphology and composition of the materials were characterized by physical characterization.The catalytic activity,stability and resistance to methanol poisoning of the catalysts were characterized by electrochemical tests.The results indicated that the obtained Fe/N/S-C catalyst had better electrochemical activity than the sample without NaCl as template.The half-wave potential of Fe/N/S-C is more positive?positive shift 48 mV?compared to the commercial Pt/C in the alkaline environment,with better stability and methanol resistance.?3?Taking S sphere as template,pyrrole was polymerized on the surface with FeCl₃as polymerization catalyst.After high temperature carbonization,S was sublimed and then doped into carbon material,leaving pores to form 3D porous carbon material?Fe/S-NC?.The structure,morphology and composition of the materials were characterized by physical characterization.The catalytic activity,stability and resistance to methanol poisoning of the catalysts were characterized by electrochemical tests.The results showed that the catalysts with higher catalytic activity can be obtained by performing sulfur doping from the inside of the carbon material.Compared with Pt/C,the Fe/S-NC had a positive half-wave potential?-0.110 V?,and the catalyst had better stability and anti-methanol poisoning ability,due to the synergistic effect of Fe-N-C active site and C-S-C structure.