Preparation Of Transition Metal/Heteroatom Doped Carbon Materials And Their Electrocatalytic Properties For Oxygen Reduction Reaction

Oxygen reduction reaction is an important reaction process of fuel cell and metal-air battery cathodes.The kinetic reaction rate is low,which seriously affects the energy conversion efficiency of the battery.Therefore,it is necessary to use a catalyst to accelerate the reaction process.As the current mainstream oxygen reduction catalyst,platinum-based catalysts have excellent oxygen reduction catalytic activity,but their high cost,poor stability and catalytic selectivity are not conducive to large-scale commercial application of fuel cells.An effective way to solve these problems is to prepare highly efficient and stable non-Pt-based catalysts using low-cost raw materials and simple preparation methods.The performance of the catalyst is related to the intrinsic catalytic activity of the active site and the number of effective active sites,wherein the intrinsic catalytic activity is determined by the composition of the catalyst,and the number of effective active sites is related to the porous structure and specific surface area of the catalyst.Therefore,in order to explore the highly active catalytically active center and to construct an excellent catalyst structure,a series of transition metal/heteroatom doped carbon-based catalysts were synthesized by various strategies,and the morphology,structure,composition and oxygen reduction catalytic performance of the materials were characterized.The main contents and results are as follows:?1?Fe/Fe₃N-NC,Co-NC and Ni-NC catalysts were prepared by one-step calcination method using C₃N₄,citric acid and transition metal salt as precursors.C₃N₄ was carbon and nitrogen sources,and citric acid was used as the complexing agent to promote the dispersion of metal ions,and the transition metal salt was a doped metal source.The results of oxygen reduction test show that Fe/Fe ₃N-NC has the best catalytic performance,followed by Co-NC,Ni-NC,and Fe/Fe₃N-NC and Co-NC have better oxygen reduction catalytic performance than commercial Pt/C catalyst.Physical characterization results further reveal that different transition metal doping leads to different morphology,defect,metal compound,nitrogen content and reactive nitrogen content.The combined effects of these factors lead to different oxygen reduction catalytic characteristics of Fe/Fe₃N-NC,Co-NC and Ni-NC catalysts.?2?The fibrous composite formed by methyl orange?MO?and FeCl ₃ was used as a reactive self-degradation template to polymerize the pyrrole monomer in situ on the template to form polypyrrole?PPy?nanotubes.In the subsequent calcination process,MO and Fe substances are doped as S source and Fe source.At the same time,the iron compound also has pyrolysis catalytic activation,and finally Fe/N/S doped porous carbon nanotubes?Fe/N/S-PCNT?)is obtained.The results show that Fe/N/S-PCNT has high-efficiency oxygen reduction catalyzed Fe-N-C and C-S-C active sites.The catalytic activation of iron compounds to carbon nanotubes promotes the development of micropores and increases the specific surface area,thus espousing more active sites and promoting the transfer of substances and electrons.Electrochemical performance tests show that the Fe/N/S-PCNT catalyst exhibits effective ORR electrocatalytic activity in both alkaline and acidic media,as well as excellent cycle stability and methanol tolerance.?3?Fe/N-doped three-dimensional porous carbon material?FeZnA-NC?was prepared by the cocatalytic activation of FeCl₃ and ZnCl₂ with chitosan as carbon source and nitrogen source.The coordination of the amino group and the hydroxyl group on the chitosan chain to Fe³⁺or Zn²⁺can achieve uniform dispersion of metal ions in the precursor,and ZnCl₂ volatilizes during high temperature activation.FeCl₃is both an activator and a dopant.The results show that the carbon material prepared by the synergistic action of ZnCl₂ and FeCl₃ forms Fe-N active center,and has a high degree of graphitization and porosity,which is beneficial to electron transfer and material diffusion.The FeZnA-NC catalyst exhibits good ORR electrocatalytic activity in an alkaline medium,as well as excellent cycle stability and methanol tolerance,and also has an effective oxygen reduction catalytic activity in acidity.