Preparation Of Heteroatom-doped Carbon Nanofibers For Application In Zn-Air Batteries

Zinc-Air Battery(ZAB),a new energy conversion device,has the advantages of green and high efficiency.However,the energy conversion efficiency of zinc-air battery is restricted by the kinetics of reaction at the cathode.At present,the large-scale production and application of zinc-air batteries are seriously limited as the noble metal catalysts used in cathode are scarce,expensive and poor in stability.Therefore,it is important to develop stable,efficient and low-cost cathode catalysts for the commercialization of zinc-air batteries.Heteroatom-doped carbon is considered to be a class of materials that can replace noble metal catalysts.In this paper,a series of one-dimensional heteroatom-doped carbon nanofibers electrocatalysts were prepared by electrospinning,and the catalysts were applied in zinc-air batteries,the main findings are as follows:(1)Nitrogen and sulfur co-doped carbon nanofibers(N,S-CNF)was prepared via electrospinning and multi-step heat treatment by using polyacrylonitrile and thiourea as raw materials.Due to the three-dimensional conductive network structure and high proportion of active sites of N,S-CNF,it shows superior electrochemical performance than commercial Pt/C in electrocatalytic oxygen reduction activity,electrochemical stability and methanol resistance in alkaline media.When it is used as cathode catalyst in zinc-air battery,it shows higher power density and specific capacity than Pt/C-based ZAB.During the mechanical charge-discharge test,the battery maintains continuous discharge for 135 hours with the voltage does not decrease significantly.(2)Nitrogen and sulfur co-doped carbon nanofibers(N,S-CNF-1-900)was prepared by electrospinning of polyacrylonitrile and thiocyanuric acid and further one-step pyrolysis.During the pyrolysis process,gas generated by the decomposition of thiocyanuric acid was used to in-situ doping N and S into the carbon skeleton,which also effectively avoided sintering between nanowires and maintained a high specific surface area of the material.In addition,the effects of pyrolysis temperature and the amount of thiocyanuric acid on the catalytic ORR performance were investigated,too.The onset potential and half-wave potential of N,S-CNF-1-900 are 0.96 V(vs.RHE)and 0.83 V(vs.RHE)in alkaline media,which close to commercial Pt/C.N,S-CNF-1-900-based ZAB also shows higher power density,specific capacity and stability.(3)Cobalt and nitrogen co-doped carbon nanofibers(Co-NTA/PAN-900)was synthesized by electrospinning polyacrylonitrile and Co-NTA.1D Co-NTA was decomposed to produce gas and reduced to Co which embedded in carbon nanofibers during pyrolysis.Acid treatment can remove the excess Co on the surface of carbon nanofibers and further increase the specific surface area.Due to its abundant electrocatalytic active sites(Co-N,pyridine nitrogen,graphite nitrogen)and continuous conductive network,Co-NTA/PAN-900 shows excellent ORR and OER bifunctional catalytic activity(E_J10-E_1/2=0.75 V)in alkaline media.The rechargeable ZABs,using Co-NTA/PAN-900 as cathode catalyst,also shows a low charge-discharge gap and cycles stability.