Preparation Of One Dimension Carbon Based Transition Metal Catalysts By Electrospinning And Their Performance For Oxygen Reduction Reaction

Platinum-based precious metal catalysts are most commonly used in fuel cells for oxygen reduction reaction,but its high production costs and limited life seriously restrict the commercialization process.The non-precious metal electrocatalysts,such as transition metal and late-model carbon materials,are regarded as one of the best potential alternatives to platinum-based catalysts.However,the advantages of these catalyst materials are weakened by the complex preparation process and lower utilization ratio of the catalytic active sites and the bad catalytic activity and stability make them hard to meet the actual demand.In this dissertation,we prepared one-dimensional carbon-based materials using different polymers and introducd transition metals as the catalytic active sites.All the experiments are based on the electrospinning technique.Further,the effect of catalysts’ structure and composition on the electrocatalytic performance has been investigated systematically,providing the basis for deep reveal of real active sites and catalytic mechanism for ORR.(1)In this experiment,we built diversified structures of carbon nanofibers using different polymer blends system by electrospinning and studied the relationship between fiber morphologies and PAN,PAN/PVP,PAN/PMMA system.It is found that the multi-channel carbon nanofibers,CNFs-3,which have open architecture and large surface area,showed better catalytic activity and current efficiency.The limiting current density of CNFs-3 was 4.06 mA/cm2 and electron transfer number was 3.44.By revealing the mechanism of building diversified carbon nanofibers through electrospinning,we clarified the effect of precursors’ composition on the structures.This result provided a novel reference template for follow-up experiments.(2)In this experiment,Co(acac)2 was introduced into PAN/PVP electrospinning system,resulting in phase-separated precursors.Then we prepared cobaltosic oxide doped spongy carbon nanofibers,Co3O4-SCNFs and studied the influence of different Co loading on the electrocatalytic performance.The porous Co3O4-SCNFs have got highly opened sponge-like structures which helps to increase the contact area between spinel Co3O4 nanoparticles and O2.The utilization of catalytic active sites are significantly improved and more transmission and diffusion channels are formed for materials.In optimal conditions,the limiting current density of Co3O4-SCNFs reached 5.89 mA/cm2,the electron transfer number was 3.75,which make it comparable to commercial Pt/C catalyst.(3)In this experiment,we prepared cobaltosic oxide doped hollow carbon nanofibers,Co3O4-HCNFs,by coaxial electrospinning.The hollow structure obtained by removing the core material improved the utilization rate of the internal space of the one-dimension carbon-based material.Co3O4 nanoparticles located in the shell can contact with O2 in both inner and outer walls,which increased the reaction area.Besides,the hollow structure can be used as the transmission channel of reactants and reaction products.The onset potential of Co3O4-HCNFs reached-0.12 V,which was the same as commercial Pt/C.The electron transfer number is 3.75,much close to four electron process.The current retention rate reached 93.6%,showing a great improvement in stability.After all,Co3O4-HCNFs is an excellent oxygen reduction reation catalyst with high activity and long life and make it possible to replace commercial Pt/C catalyst.