A kind of preparation method of gradient pore structure carbon paper

Abstract

The invention discloses a preparation method of carbon paper with gradient pore structure: after degumming and oxidation treatment of carbon fibers with different length-to-diameter ratios, they are respectively dispersed in dispersant solutions to form carbon fiber slurries with different length-to-diameter ratios; The slurry is layered sequentially according to the length-to-diameter ratio of the carbon fiber, and the inclined mesh is formed to obtain a carbon felt precursor with a three-dimensional network structure; the carbon felt precursor is immersed in the resin solution, taken out, and dried. The carbon felt is obtained; the carbon felt is first hot-pressed into a carbon paper base paper, and then carbonized and graphitized to obtain a gradient pore structure carbon paper. According to the present invention, the carbon fiber aspect ratio of the slurry is layered sequentially from high to low, so that the prepared carbon paper has a gradient pore structure, and interconnected pores are formed inside the carbon paper, and the pore diameter changes along the normal direction of the carbon paper plane. A pressure gradient is formed in the diffusion channel, which can improve the gas delivery efficiency and effectively improve the mass transfer and heat transfer performance of carbon paper.

Description

technical field [0001] The invention belongs to the technical field of fuel cells, in particular to a method for preparing carbon paper with gradient pore structure. Background technique [0002] Carbon paper is an ideal substrate material for the gas diffusion layer of fuel cells. Its porosity and pore structure directly affect the mass transfer and conductivity of the diffusion layer, that is, the transmission efficiency of product water and reaction gas, and affect the performance of the battery. [0003] At present, the method of preparing carbon paper is generally to degumming the chopped carbon fiber bundles first, removing the surface sizing agent, and then modifying the carbon fibers by gas phase or liquid phase oxidation, introducing oxygen-containing functional groups to improve hydrophilicity, and then pre- Treat the carbon fiber and add it to the dispersant solution, stir and disperse until the fiber is completely dispersed, and form a stable papermaking slurry f...

AI Technical Summary

Problems solved by technology

[0004] 1. The pore structure cannot meet the requirements of high energy efficiency of the battery

Carbon paper made of carbon fibers with a single aspect ratio, the pore size and porosity often cannot meet the mass transfer requirements of the diffusion layer

When the fiber length is too long, larger network pores will be formed on the carbon paper, resulting in too strong drainage, which will easily cause the dehydration of the proton exchange membrane and reduce the mass transfer efficiency; when short carbon fibers are used, the carbon paper network pores will be smaller, Insufficient porosity and poor permeability lead to product water clogging and slow gas transport, causing water flooding and mass transfer polarization

If the papermaking method of mixing carbon fibers with different aspect ratios is used, although the effective overlap between fibers can be increased, the uniformity and density of the precursor carbon paper can be improved, and the resistivity can be reduced; but the carbon paper prepared by this method The pore size is difficult to keep consistent, the porosity is low, the overall mass transfer capacity is not good, and the flow rate of the gas passing through each position in the surface is different, which causes the uneven distribution of the reactant gas on the catalyst surface and mass transfer polarization.

[0005] 2. The density of carbon paper is low, which affects the internal and longitudinal conductivity of carbon paper

However, the carbon content of phenolic resin itself generally does not exceed 40%, even if it is modified, it can only be close to 50%, and the phenolic resin is reduced to resin carbon during high-temperature carbonization, and carbon oxides are released in the form of gas. If the carbonization rate is high, the volume of the resin will shrink a lot after carbonization, causing a huge area of ​​holes, which will lead to a sharp drop in strength and electrical conductivity. This will lead to a further densification process for carbon paper and prolong the production line, which is not conducive to industrialization efficiency.

[0006] 3. High graphitization temperature

Since the graphitization temperature is above 2200 °C, many heating equipment often fail to meet the parameter requirements, resulting in difficulties in heat treatment and increased costs

Images