Preparation method of gradient pore structure carbon paper

Abstract

The invention discloses a preparation method of carbon paper with a gradient pore structure, which comprises the following steps: separately degumming and oxidizing carbon fibers with different length-diameter ratios, and respectively dispersing the treated carbon fibers in a dispersant solution to form carbon fiber slurry with different length-diameter ratios; sequentially carrying out gradient layering and inclined net forming on the carbon fiber slurry according to the length-diameter ratio of carbon fibers from high to low to obtain a carbon felt precursor with a three-dimensional net structure; dipping the carbon felt precursor in a resin solution, taking out the dipped precursor, and conducting drying to obtain a carbon felt; and firstly hot-pressing the carbon felt into carbon paper body paper, and then conducting carbonization and graphitization treatment to obtain the gradient pore structure carbon paper. According to the invention, gradient layering is carried out in sequence from high to low according to the length-diameter ratio of the slurry carbon fiber, so that the prepared carbon paper has a gradient pore structure, communicating pores are formed in the carbon paper, the pore diameter changes in a gradient manner along the normal direction on the plane of the carbon paper, a pressure gradient is formed in a diffusion channel, the gas conveying efficiency can be improved, and the mass transfer and heat transfer performances of the carbon paper are effectively improved.

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

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