Controllable Assembly Of Multi-dimensional Doped Carbon Materials And Their Oxygen Reduction Reaction Properties

Electrocatalytic oxygen reduction reaction（ORR）is one of the most important reactions in the cathode of fuel cell,which is the key step to improve the performance of fuel cell due to the sluggish kinetics.Therefore,it is vital to develop high performance oxygen reduction catalysts.For the ORR,it can be mainly divided into two ways: high efficient single-step four electron process that can hard to happen for the great free energy and low efficient two-step with sluggish two electron process.The two-step two electron process was more difficult to occur,and the intermediate product of H₂O₂ have strong toxicity to the catalyst,so it is important to prepare the ORR catalyst with four electron reaction selectivity,high efficiency,low cost as well as high stability.This paper is committed to the development of carbon based catalysts exhibited excellent electrocatalytic performance for oxygen reduction,introduced catalytic active sites by doping;building multi-dimensional structure and improve the conductivity in bulk catalyst.Besides,reducing the surface energy by drilling as well as the formation of folds can not only enhance the ability to absorb oxygen,but also increasing the specific surface area of the material.Accordingly,a series of multi dimensional high performance carbon based ORR catalyst are constructed by the electrostatic interaction of the polymer with electronegativity carbon,and the high efficiency four electron oxygen reduction process is realized.In the first part of the thesis,we use PPV-precursor which is a water soluble polymer with electropositivity to form polymer spheres on the surface of graphene by intercalation modification method as well as hydrothermal self-assembly process.After that,the pre-material is calcined in ammonia atmosphere under high temperature,and finally,nitrogen doped porous graphene sheet with abundant folds was prepared.It is found that the catalyst achieves an advanced activity of ORR and cycle stability.Three dimensional carbon nanostructures exhibit better properties than 2D structures due to their structural advantages（greater specific surface area and more stable catalyst structure）.In the second part,we study the effect of PPV-precursor by constructing the 3D N-RGO-PPV（c）-CNTs materials.In that case,we obtained the ORR catalyst with more stable structure,larger surface area as well as more active sites.As a non platinum ORR materials,N-RGO-PPV（c）-CNTs has the initial potential close to the commercial platinum carbon（0.92V）and the limit current density is higher than that of commercial platinum carbon（5.7m A*cm-2）.In addition,the catalyst also has excellent methanol resistance performance and cycle stability,which reveals the large application foreground in ORR field.In the third part of the paper,we use electropositive polymer PEI as coupling agent,which can make GQDs and graphene combined effectively,and then form a two-dimensional structure of ORR catalyst.The introduction of carbon prevent the graphene layers from reuniting,resulting in the enlargement of catalyst specific surface area.Whereas the small size GQDs could provide more active sites,thus improving the adsorption of oxygen molecule.At the same time,we have accomplished the doping of boron and nitrogen atoms by one-step hydrothermal method,and prepared a new type of B/N co-doping graphene quantum dots（GQDs）/ graphene composites.