| Among various renewable clean energy technologies,the direct methanol fuel cells（DMFC）have attracted worldwide attention in recent years,due to their unique advantagessuch as the use of carbon neutral and renewable fuels,high energy density,high power density,relatively simple structure,low noise and operating costs,easy operation and transportation However,in order to achieve the commercialization of DMFC,some key issues need to solve:1)the kinetics of methanol oxidation reaction in anode is slow;2)fuel loss and cathodemixed-potential caused by methanol crossover;3)the so-called"water flooding"caused by the accumulation of liquid water at the cathode.At present,in order to alleviate polarization loss and voltage fluctuation caused by flooding,conventional gas diffusion layer（GDL）materials（such as carbon cloth,carbon paper,etc.）usually require hydrophobic treatment and an addition of a hydrophobic microporous layer to regulate the content and distribution of liquid water in the electrode.However,these measures not only change the pore structure and interfacical morphology of the pristine GDL,but also increase the manufacturing process and cost.Therefore,one of the main directions of current research is to design and develop a new type of GDL to improve its oxygen transfer capacity and reduce costs.In this paper,a series of three-dimensional porous,free-standing carbon fiber mats were prepared by heat treatment of electrospun polyacrylonitrile（PAN）and the physical and chemical properties of carbon fiber mats were experimentally investigated.Meanwhile the feasibility of electrospun carbon fiber mat as the GDL were studied in a DMFC,which provides guidance for the optimal design of the GDL structure.The contents and the main conclusions were as follows.（1）PAN based electrospun GDL.Firstly,The PAN carbon fibers was prepared by electrospinning with different concentrations of PAN/DMF（N,N-Dimethylformamide）and the influences of solution concentration,carbonization temperature,spinning speed and mat thickness on the fiber morphology and cell performance were investigated.The results showed that the carbon fiber prepared with 14 wt.%PAN concentration,1100°C carbonization temperature and a rotation rate of 1000 RPM exhibited the best performance among various prepared samples,suggesting its low Ohmic resistance and mass-transfer resistance as well as no need for an additional hydrophobic treatment.（2）PAN based electrospun GDL with polylactic acid（polylactic acid）as pore former.In order to reduce the concentration polarization,the pore structures of the carbon fiber were modified.The PAN/DMF and PLA/DMF mixture solutions of different ratio were used as the precursor for electrospinning.The electrospun fibers were then sonicated with chloroform to remove PLA,followed by a heat treatment to obtain the porous carbon fibers.Such porous carbon fibers mats were used as the cathode GDL to investigate its fuel cell performance.The results showed that as compared with the commercialized carbon paper and 14 wt.%PAN carbon mat,the PAN/PLA porous carbon mat was only slightly better.（3）PAN based electrospun GDL with SiO2 as pore former.In order to further reduce the concentration polarization,the hard template method was used to fabricate the porous carbon mat.The PAN/DMF and SiO2/DMF mixture solutions of different ratio were used as the precursor forelectrospinning,followed by heat treatment.Then,the carbon fibers mat were immersed in hydrofluoric acid for 24 h to remove SiO2 to form interconnected pores,.Through the TEM characterization,it was confirmed that the prepared fibers exhibited three-dimensional interconnected porous structure.Through the fuel cell performance test,it was found that the PAN/SiO2 GDL showed a higher voltage in the concentration polarization zone as compared with other carbon fibers mats,indicating its capability of improving oxygen transfer and promising application in fuel cell. |
