Synthesis And Oxygen Reduction Performance Of Special Structure N-doped Carbon-supported Transition Metal Electrocatalyst

The slow kinetics of the oxygen reduction reaction（ORR）is a key factor affecting the performance of fuel cells.At present,Pt-based catalysts commonly used in fuel cell cathodes have severely hindered the wide application of related new energy equipment due to low reserves and high price.Therefore,it is of great significance to develop efficient and inexpensive non-noble metal oxygen reduction catalysts.Among them,transition metal-nitrogen-carbon（M-N-C）catalysts are the most promising candidates that replace with Pt-based catalysts,but they have problems such as poor stability and low volume activity.This paper aims to prepare low-cost and high-performance M-N-C catalysts.By adjusting the morphology of the carbon support and the active components and morphology of the catalyst,the activity and stability of the catalyst can be improved.The structure and catalytic performance have been systematically analyzed.This paper mainly includes the following contents.（1）Cheap carbon black and glucose were used as carbon source and melamine was used as nitrogen source,respectively.Then,the catalysts(Fe_xCo_2-x-N-C,x=0,0.5,1.5,1,2)for in-situ growth of nitrogen-doped carbon nanotubes containing iron and cobalt nanoparticles was prepared by the catalyzation of Fe and Co species.The results show that the oxygen reduction activity of catalysts with FeCo nanoparticles is significantly higher than that of Fe-N-C and Co-N-C catalysts under alkaline conditions.Among them,the half-wave potential of Fe₁Co₁-N-C is as high as 0.864V vs.RHE.In addition,the encapsulation of carbon nanotubes is not only beneficial to improve the electrical conductivity and electron transport performance of the catalyst,but also to realize the protection of metal nanoparticles,thus improving the stability of the catalyst.（2）Nitrogen-containing hypercrosslinked porous polymers hollow spheres（HTPP）was obtained through phenyl functionalized silica nanoparticles spheres as template.After introducing appropriate amounts of cobalt and iron metal ions into the HTPP by chemical doping method,the transition metal-nitrogen-doped hollow carbon spheres was obtained through high temperature pyrolysis.Among them,the specific surface area of the cobalt-nitrogen-doped hollow carbon spheres（C-HTPP-Co）catalyst was up to 529 m² g^-1,and the catalyst showed excellent oxygen reduction activity under alkaline conditions（half-wave potential is 0.828V vs.RHE）.The results show that the high activity of the catalyst is mainly derived from the Co-N active species formed after the introduction of Co,and the hollow spherical structure is beneficial to the diffusion of the electrolyte and the transport of the reactants.On the other hand,pre-doped cobalt ions can promote the graphitization of HTPP during the high-temperature pyrolysis process,thus improving the cycle stability and corrosion resistance of polymer-derived carbon.