| Proton exchange membrane fuel cell gas diffusion layer is mainly composed of a base layer and a microporous layer.It is usually prepared by coating carbon black particles on the surface of carbon paper.Currently,due to the poor dispersion and paper uniformity of carbon fiber pulp,the pore structure and performance indicators of carbon paper are difficult to control stably.Therefore,this paper carries out the following research work for the dispersion of carbon fibers in water and the preparation of high uniformity carbon paper:Firstly,to address the problem of difficult dispersion of carbon fibers,the effects of fiber length,alkali treatment,single dispersion system and composite dispersion system on the dispersion performance and stability of carbon fiber pulp were investigated.By examining the degree of carbon fiber dispersion in the pulp under different conditions,as well as the TSI stability index of the carbon fiber pulp suspension,the backscattering light reference intensity and the dynamic distribution of carbon fibers,the effects of different conditions on the dispersion of carbon fibers and the stability of the pulp were studied.It was found that when alkali treatment and anionic polyacrylamide(APAM)are used as dispersants,as the length of carbon fibers changes from 8 mm to 2 mm,the TSI stability index of the slurry decreases from 31.46to 19.40,and the dispersion stability of the slurry gradually increases.The TSI stability index of the anionic polyacrylamide and carbomer dispersion system was the smallest,with a value of 1.75.Based on the above research,a new p H-responsive dispersion system was proposed for the dispersion of carbon fiber pulp,and the uniformity index of the prepared carbon paper was improved by about 60%.Secondly,the influence of preparation conditions of highly homogeneous carbon paper on its performance was studied,focusing on conditions such as carbon fiber length,polyvinyl alcohol fiber and polyvinyl alcohol dosage,drying pressure,and uniformity index.The study found that with the improvement of the uniformity index,the tensile strength and conductivity of the carbon paper improved,while the air permeability decreased.Specifically,when the uniformity index of the raw paper was less than 7,the carbon paper showed better uniformity characteristics,with optimal performance indicators of thickness of 175μm,electrical resistivity of 51.78 mΩ·cm,air permeability of 1213 L/(m~2·s),tensile strength of 1.88 k N/m,and porosity of 91.20%.In addition,there was a positive correlation between carbon fiber length and raw paper thickness,air permeability,porosity,electrical resistivity,and tensile strength.The minimum thickness of raw paper prepared with 2 mm carbon fiber was 168μm.The2mm and 4mm compounded carbon paper had the lowest electrical resistivity of 77.65mΩ·cm,and the 4 mm and 8 mm compounded carbon paper had the highest tensile strength of 2.67 k N/m.There was a negative correlation between polyvinyl alcohol fiber dosage and raw paper thickness,air permeability,porosity,and electrical resistivity,while there was a positive correlation between polyvinyl alcohol fiber dosage and tensile strength.When the polyvinyl alcohol fiber dosage in the slurry was1 wt%,the minimum thickness was 167μm,and the tensile strength reached the maximum of 2.98 k N/m.At this point,the porosity and air permeability both reached their minimum,at 91.44%and 1100 L/(m~2·s),respectively,and the electrical resistivity also reached its minimum at only 50.79 mΩ·cm.There was a negative correlation between drying pressure and raw paper thickness,air permeability,porosity,and electrical resistivity,while there was a positive correlation between drying pressure and tensile strength.When the drying pressure was 1.00 MPa,the raw paper thickness and electrical resistivity reached their minimum,at 170μm and 68.18 mΩ·cm,respectively,and the tensile strength also reached its maximum of 1.11 k N/m.The porosity and air permeability both reached their minimum at 92.68%and 1372 L/(m~2·s),respectively.Finally,the preparation process and properties of gradient pore high uniformity carbon paper were studied,and the effects of uniformity index,interlayer bonding method,and fiber length on the properties of carbon paper were investigated.It was found that when the uniformity index of the raw paper was less than 7,the thickness,resistivity,air permeability,and tensile strength of the carbon paper were all better.Specially,with thickness concentrated in the range of 151-175μm,resistivity concentrated in the range of 49.00-55.85 mΩ·cm,air permeability less than 1000L/(m~2·s),and tensile strength concentrated in the range of 0.25～0.54 k N/m.The increase in bulk density continued to increase with the improvement of uniformity.Different interlayer bonding methods had a significant impact on the strength and conductivity of carbon paper.The gradient pore carbon paper prepared by wet paper stacking had better performance due to tighter interlayer bonding.Among them,the tensile strength of the three-layer gradient pore carbon paper prepared by wet paper stacking was 0.41 k N/m,which was much higher than that of the carbon paper prepared by raw paper stacking.Its resistivity was also the lowest among all groups,only 19.53mΩ·cm.Fiber length had a significant impact on the pore characteristics of gradient pore carbon paper.When carbon paper was prepared by stacking wet paper with different lengths of fibers,there was a significant difference in pore size characteristics between the front and back of the carbon paper.The air permeability of the 2 mm and8 mm double-layer carbon paper was the highest at 1230 L/(m~2·s),and the bulk density increase of the 4 mm and 8 mm three-layer gradient pore carbon paper was the highest at 35.49%,with a bulk density of 0.25 g/cm~3. |
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