Preparation And Study Ofnanofibers Catalyst Layer Of Fuel Cell

The proton exchange membrane fuel cells(PEMFC)are considered as one of the ultimate energy for automobile due to their advantages of zero emissions,high efficiency and low temperature.The catalyst layer(CL)is the dynamic reaction area of the fuel cell,which determines the performance and durability of the fuel cell.In this study,the nanofibers catalyst layer of fuel cell with high performance under low platinum loading was successfully prepared by electrospinning,and its structure and function were characterized by physical and electrochemical methods.At the same time,this study revealed the pre-conditioning mechanism of the nanofibers catalyst layer and determined the operating characteristics of the nanofibers catalyst layer under different temperature and humidity,which provided a new idea for the next generation catalyst layer of fuel cell.The following is the main research content:The first part is a preparation method and performance characterization section of nanofibers catalyst layer of fuel cell.In this part,the preparation procedure of the catalyst layer was determined through systematic experiments,which mainly included spinning solution formulation,preparation of uniforn electrospinning solution,and preparation of catalyst layer by electrospinning;finally,the catalyst layer with average fiber diameter of 200-800 nm was prepared.And it can be found that the Pt was dispersed evenly on the nanof-ibers without apparent agglomeration.Compared to the conventional catalyst layer with the same Pt loading,the thickness of the electrospinning nanofibers catalyst layer(17 ?m)is about 5 times that of the conventional catalyst layer(3 ?m),and the hydrophobicity of the electrospinning nanofibers catalyst layer(water contact angle is 146.05 °)slightly worse than the conventional catalyst layer(water contact angle 150.1 °).However,performance of the electrospinning nanofibers catalyst layer is still better than the conventional catalyst layer.There are two main reasons.On the one hand,the nanofibers has a larger specific surface area(the specific surface area of the electrospinning nanofibers catalyst layer is 22.96 m-g-1,The specific surface area of the conventional catalytic layer is 3.876 m·g-1,which provides more reactive sites for the catalyst layer(ECSAe/ECSAc=1.4).On the other hand,because the electrospinning nanofibers catalyst layer has more pore structure,these pores can promptly eliminate the water produced in cathode;so that the mass transport loss get lower at high current density.The second part is the mechanism analysis of the dramatic increase in the performance of the pre-conditioning process of the nanofibers catalyst layer.In this part,the electrochemical impedance spectroscopy and cyclic voltammetry were used to study the changes of impedance and electrochemical active area during the pre-conditioning process.At the same time,to analyze the change of components during the pre-conditioning process,the thermo gravimetric method was used to analyze the change of element content in the catalyst layer before and after water treatment.It was revealed that the PAA,which is a macromolecular organic material in the electrospinning nanofibers catalyst layer,gradually dissolves during the pre-conditioning process,and it finally improved performance.Subsequently,we characterized the performance of the two catalyst layers under multiple temperature and humidity conditions.It can be found that the performance of the two catalyst layers gradually increased with the increase of humidity when temperature is same.The performance of the two catalyst layers gradually reduced with the increase of temperature under low-mid-humidity conditions,the both of catalyst layers have the best performance at 70 ? under same high humidity environment.The optimum operating conditions for both catalytic layers are 70?-100%RH.In addition,this section compares the performance curves of the electrospinning nanofibers catalyst layer and the conventional catalyst layer at different temperatures and humidity;it can find that nanofibers catalyst layerhas higher performance than conventional catalyst layer at high temperature and high humidity.At the same time,the zero-dimensional electrochemical model was also used tovoltage losses for the polarization curve.The results show that the nanofibers catalyst layer has a lower activation overpotential.Finally,we conducted a preliminary exploration of an ordered nanofiber structure catalyst layer and a vertical staggered nanofiber structure catalyst layer.In this part,on the basis of the original electrospinning preparation method,the collection method of nanofibers was adjusted,the high-orientednanofibers catalyst layers were prepared by high-speedcollection device,and a vertical staggered nanofibers structure catalyst layer was further evolved.The experimental results show that the performance of the two new structures of the catalyst layer is lower than that of the original electrospinning nanofibers catalyst layer,however,both catalyst layers exhibit a higher electrochemical active area.The main innovation of this dissertation is that the nanofiber structure catalyst layer that can be comparable to the current domestic commercial catalyst layerunder low platinum loading.At the same time,this paper also further reveals the pre-conditioning mechanism of nanofibers catalyst layer.The nanofiber catalyst layer prepared in this study is expected to be the next generation catalyst layer for fuel cells.