Synthesis Of Carbon Nanofiber-based Catalyst For Oxygen Reduction Reaction And Zn-air Battery

Developing an inexpensive and efficient oxygen reduction/evolution catalysts is crucial for the next generation energy conversion de storage devices?fuel cells,metal-air batterys etc.?.As one of the promising candidates for noble metal catalysts,transition metal-nitrogen-carbon materials?M-N-C?are of interest due to their low cost,high performance and high durability.The synthesis and regulation of the catalyst structure of M-N-C are hot research field among past decades.Due to the catalytic reaction taken placed in the three-phase interface,involving a variety of mass transfer and interface transfer process.Rational design of the catalyst components,as well as the construction of an effective catalytic interface has become a key factor affecting the catalytic activity of the material.In response to these problems,we prepared a series of M-N-C nanofibers with different microstructures and compositions by electrospinning method.The effects of the structure and composition of the catalyst on the catalytic activity were studied.In order to provides the experimental basis for the preparation of high performance M-N-C.The specific research contents are as follows:?1?Hierarchically porous carbon nanofibers simultaneously doped with nitrogen and iron?HP-Fe-N/CNFs?were fabricated by facile pyrolysis of polypyrrole-coated electrospun polystyrene/FeCl3fibers.We found the introduction of PS is the key factor to from the hierarchically porous structures in nanofeibers.Benefiting from the improved mass transfer and utilization of active sites attributed to interconnected hierarchical porous structures,HP-Fe-N/CNFs display excellent ORR catalytic activity in alkaline media,the onset potential,half-wave potential and limited current density are 0.93 V,0.80V and 5.69 mA·cm^-2,respectively.Particularly,when applied in an assembled Zn-air battery,HP-Fe-N/CNFs outperform 30 wt%Pt/C in power density and long-term stability??2?We developed a PVP assistant in-situ growth method to achieve one dimensional structure-controllable zeolitic imidazolate frameworks?ZIFs?/polyacrylonitrile?PAN?core/shell fiber?PAN@ZIFs?.Subsequent pyrolysis of this precursor can obtain cobalt,nitrogen codoped carbon nanofiber network as an efficient oxygen electrocatalyst.During the experiment,we proposed the law of morphology evolutions of PAN@ZIFs by investigated the influence of the composition of PAN fibers and the order of ligands.By adjust the cobalt content in the precursor fiber,the graphitization degree and nitrogen content of the catalysts can be regulated.Due to the one-dimensional core-shell structure of the catalysts.The onset potential,half-wave potential and limited current density of optimized CNF@Zn/CoNC reached 0.91 V,0.82 V and 5.62 mA·cm^-2,respectively.Meanwhile,the catalyst had good catalytic OER performance.In addition,the corresponding rechargeable zinc-air cells also have excellent performance and cyclic stability over 150 h.?3?Single-metal components of Fe,Co and bimetallic components of CoFe loaded on nitrogen doped carbon nanofibers were prepared.The effects of different metals on the structure and composition of the fibers and the sources of ORR/OER performance were investigated.At the same time,reductive hydrogen was introduced into the heat treatment process.It was found that the etching effect of hydrogen on the carbon fiber enhanced the porosity,graphitization degree of fiber.Ultimately,CoFe-NCNF-H₂ possesses excellent ORR/OER performance reflected by the lowest?E values.In addition,controlling the catalyst loadings on RRDE,the ORR reaction process on the catalyst was studied.It was found that the introduction of Co and Fe bimetallics may change the reaction process by influencing the desorption of the reaction intermediates,and the synergistic catalysis between the bimetallics improved its ORR activity.We hoped this experiment could provide a feasible idea for the component design of M-N-C catalysts with highly activity.