Synthesis And Eiectrocatalytic Property Study Of Cobalt Based Compouds/carbon Composite Materials

Oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)are critical paired reactions for both energy conversion and storage.At present,the most effective catalysts for OER and ORR reactions are noble metal catalyst,including Pt,Ru and Ir.However,high cost,poor stability and other issues seriously hampered their industrial application.Therefore,non-noble metal catalysts,which have low cost,excellent performance and good stability,has become one of the main objectives of the battery research.This thesis contains the synthesis of several different composites of carbon materials and cobalt-based compounds,which combine the advantages of them in the electrocatalytic reaction.Their morphology,structures and electrocatalytic properties in OER or ORR as well as in the zinc-air batteries were investigated.The details are listed as follows:1.A simple method for preparing electrochemical catalysts without high temperature calcination is proposed.Cobalt-nitrogen-carbon/graphene composites(Co-NC/RGO)have been prepared by mixing graphene oxide,formamide and cobalt salt at a certain temperature.Compared with the traditional Co-NC materials,Co-NC/RGO can not only effectively prevent the agglomeration of cobalt particles and retain more active sites,but also provide the material excellent conductivity.When tested in the alkaline solution,Co-NC/RGO showed excellent catalytic activity and stability as the electrode materials for both ORR and OER reactions.At the same time,it also showed excellent performance as air electrode in metal-air batteries.2.Cobalt-aluminum hydrotalcite/graphene aerogels(CoAl-LDH/GA)have been successfully prepared via a facile hydrothermal process with the composite of CoAl-LDH and GO.After high temperature calcination process,cobalt aluminum oxide/graphene aerogel(CoAl2O4/GA)was prepared.In order to increase the catalytic activity,moderate ammonia and hydrazine hydrate are added into the composites during the hydrothermal process.Results show that the optimal catalyst exhibits high activity,which is close to commercial Pt/C and Ir/C catalysts,while its cycle stability is much higher than the commercial one.Therefore,the CoAl2O4/GA composites are a perfect bifunctional electrocatalyst materials for OER and ORR.3.A novel method for the synthesis of hollow N-doped carbon networks(N-CNs)via interfacial dehalogenation of poly(vinylidene chloride)(PVDC)on 2D CoAl-LDH with the presence of N dopant is proposed.Optimally synthesized N-CNs showed highly comparable performance of promoting ORR/OER relative to PtRu catalyst.Zn-air battery(ZAB)assembled using N-CNs performed very good rate capability and cycling stability.We believe that interfacial dehalogenation reactions on dimensional metal hydroxides could provide more opportunities for precisely adjusting the composition,structure,and porosity of carbon materials.