Prepration And Properties Research Of Carbon Based Electrocatalysts Derived From MOF Based Hierarchical Structure Materials

Fuel cells and metal-air batteries have the advantages of high energy density,clean and pollution-free,and become the preferred solution to solve the current energy and environmental problems.However,their energy conversion efficiency were limited by oxygen reduction reaction(ORR)and oxygen evolution reaction(OER).By far,the most efficient commercial oxygen electrocatalysts are mainly precious metal(Pt,Ru,Ir)based catalysts.However,their large-scale commercial application was restricted by the resource scarcity,high cost,and poor stability seriously.Therefore,it is very important to develop cheap,efficient,and stable non-precious metal oxygen catalysts for the wide application of fuel cells and metal-air batteries.The Work of this thesis are mainly to non-precious metal carbon based catalysts as the research object,through combining the bimetallic zeolitic imidazolate frameworks(ZIF)with graphene oxide(GO)and electrospun nanofibers to construct some nanocomposite precursors with different structures and composition.By adjusting the composition and carbonization process of catalysts,several pairs of transition metal and heteroatoms doped carbon based electrocatalysts were obtained.A variety of techniques have been characterized and investigated the construction,phase composition,and electrochemical properties of the catalysts.The main research work of this thesis are as follows:1.The sandwich Fe-Co-ZIF/GO nanocomposite precursors were prepared by in-situ solvent thermal growth method.The surface porous rGO nanosheets with bimetallic(Fe,Co)and N elements co-dopping were obtained after carbonization treatment and acid etching process,and their ORR properties were investigated.By adjusting the molar ratio of Fe/Co,the mass ratio of metal/ligand,and the mass of GO,it was found that when Fe/Co molar ratio was 0.4,the mass ratio of metal/ligand was 1:1,50 mg GO was added,it had higher ORR catalytic activity,good cyclic stability and methanol tolerance.2.The first time,Zn-Co-ZIF/PAN core-shell structure nanofiber precursor was constructed through in-situ growth method using electrospun MIM/PAN composite nanofibers as base materials.Carbon coated bimetallic elements(Zn,Co)nanoparticles and N-doped core-shell carbon nanofibers were obtained after high temperature carbonization,and their ORR properties were investigated.Further improved ORR performance,good cyclic stability and methanol tolerance were obtained.3.In Further,using Zn/Co-ZIF nanoparticles as internal dopant and self-sacrifice template,Zn/Co-ZIF/PAN composite nanofiber precursor was prepared by simple mixing electrospinning method.A novel flexible,hierarchical pore structure,bimetallic element(Zn,Co)nanoparticles and N element doped carbon nanofibers was prepared by high temperature carbonization,and the changes of morphology and the structure under different ZIF loading and different carbonization temperature were investigated systematically,their ORR and Zn-air battery performances were also investigated.The results showed that when the precursor with 200 wt%Zn/Co-ZIF loading was carbonized at 800℃,the obtained catalysts had the better performance than 20 wt%Pt/C catalyst,and also showed good cyclic stability,methanol tolerance,and excellent performance in Zn-air single battery.4.Using the as-prepared Zn/Co-ZIF/PAN composite nanofibers as precursor in the last chapter,introducing active H2S gas in traditional high temperature carbonization process,the transition metal sulfide nanoparticles and N,S co-doped porous carbon nanofibers was prepared by one step carbonization/sulfurization,and their ORR and OER catalytic performances were investigated.The results showed that the catalysts obtained by Zn/Co-ZIF/PAN at 800℃ carbonization/sulfurization has bifunctional ORR and OER properties comparable to commercial 20 wt%Pt/C and RuO2 catalysts.One step carbonization/sulfurization method realizes the rapid phase transformation from metal to metal sulfide and synchronous sulfur doping,providing a new idea for the preparation of high-performance catalyst.