Hydrophobic Treatment Of Carbon Paper And Its Impact On The Performance Of Proton Exchange Membrane Fuel Cells

Proton exchange membrane fuel cell(PEMFC)is a power generation device that directly converts chemical energy into electric energy.Due to the characteristics of high energy density,fast starting speed,low working temperature and zero product pollution,PEMFC is widely used in transportation,portable power generation and fixed power supply.As the core component of PEMFC,the gas diffusion layer(GDL)has the functions of gas supply,water discharge,and electron conduction,which is the key factor affecting the performance of PEMFC.GDL is composed of gas diffusion back layer(GDBL)and microporous layer(MPL).Carbon paper(CP)is the preferred material for GDBL because of its excellent conductive performance and uniform pore structure.However,CP is highly hydrophilic,so it must be hydrophobic treatment to enhance the drainage capacity.Based on the hydrophobic treatment process,this paper studies the influence of hydrophobic concentration,the bulk density of CP on the structure and performance of carbon paper,and further explores the application of hydrophobic treatment carbon paper in PEMFC.The main contents are as follows:Firstly,we used PTFE emulsion with different concentrations to prepare CP with different PTFE loads,studied the effect of PTFE concentration on PTFE load and structure and performance of CP,and obtained GDL after further coating on the surface,and studied the effect of carbon paper PTFE load on PEMFC performance.The results show that: in the hydrophobic time,with the increase of hydrophobic concentration,the PTFE load of CP increased,resulting in the increase of CP surface density and bulk density,the corresponding surface element content also changed,the hydrophilic carbon element content,the content of hydrophobic fluorine,thus changing the hydrophilic and hydrophobic properties of CP,the surface contact angle from 125°to 152°.Meanwhile,with the increase of trap concentration,the TP resistivity of CP gradually increases and the TP permeability gradually decreases.The CP treated with 10 wt % PTFE has the best single cell performance with the surface contact angle of 133°,the TP resistivity of 10.07 mΩ·cm2 at 1 MPa,and the TP permeability of181.80 ml mm /(cm2·h·Pa).Secondly,due to the CP with different density has different surface pore structure and size,it may affect the hydrophobic process.Therefore,we do hydrophobic treatment by using CP of different bulk density,the influence of density of CP on the hydrophobic treatment process was studied by comparing the PTFE loads 、 strcuture and performance.Then the corresponding GDL was prepared by the microporous layer coating process,and the difference of GDL prepared after the hydrophobic performance was compared.The results show that when the hydrophobic concentration is the same,the PTFE load of CP with low bulk density is greater than that of CP with high bulk density,resulting in the hydrophobic fluorine content on the surface of CP with high bulk density is greater than that of CP with high bulk density,so that the hydrophobic angle on the surface of CP with low bulk density is greater than that of CP with high bulk density.With the increase of hydrophobic concentration the increase of PTFE load of CP with low bulk density is higher than that of CP with high bulk density,resulting in the increase of contact angle,TP resistivity and TP permeability of CP with low bulk density is greater than that of CP with high bulk density.In the single cell performance test,the GDL prepared from carbon paper with a bulk density of 0.3 g/cm3 has a better single battery performance.Finally,by changing the hydrophobic treatment method,the CP with hydrophilic and hydrophobic alteration was obtained,and the corresponding GDL was prepared by the MPL coating process,under which the influence of the hydrophobic treatment on the structure and performance of CP and the performance of PEMFC were studied.The results show that by changing the hydrophobic treatment method,the CP forms a stripe of light and dark,and the content of hydrophobic agent at the light and dark stripes is significantly different,thus forming the difference of hydrophobic nature of CP.This difference reduces the resistance of the hydrophilic area of CP and improves the overall gas transmittance of CP.Compared with GDL with conventional hydrophobic treatment,the GDL with hydrophilic and hydrophobic alteration increased the voltage and power density by 12.5% and 13.5% respectively.By changing the hydrophobic treatment,the CP paper formed the hydrophilic zone and hydrophobic zone,thus improving the hydration of PEM to improve the proton conductivity of PEM,while reducing the contact resistance between GDL and the bipolar plate and enhancing the gas transfer of GDL.