Carbon fiber and graphene compounded high-strength porous material, and gas diffusion layer and preparation method therefor
A carbon fiber and graphene compounded high-strength porous material, and a gas diffusion layer and a preparation method therefor are provided. The carbon material integrates respective structures and characteristic advantages of a carbon fiber and graphene, complements each other, and has characteristics such as high mechanical strength (the carbon fiber is not cut off), hierarchical pore gradient distribution, good air permeability, good electric conductivity, good thermal conductivity, light weight, and high stability. The preparation method includes process steps such as graphene preparation, filament split of a carbon fiber bundle by spreading a liquid film, adsorption and anchoring of a filament by means of graphene, graphene coating, and high-temperature treatment. In the preparation process of the carbon-based gas diffusion layer, the carbon fiber is not cut off, the strength of the carbon fiber is kept, and the carbon-based gas diffusion layer is suitable for roll-to-roll batch preparation.
1 . A gas diffusion layer formed by combining a carbon fiber and graphene, comprising a porous and air-permeable conductive carbon material layer formed by compounding a carbon fiber monofilament with graphene and having a porosity of greater than or equal to 70%; wherein the conductive carbon material layer comprises a support layer and a microporous layer on the support layer; the support layer comprises a porous material layer formed by compounding the carbon fiber monofilament with large graphene, the large graphene is of 1-5 graphene atomic layers, and single nanosheet graphene has an area greater than 50 square micrometers; the carbon fiber monofilament has a diameter of 5-7 micrometers and a length greater than 10 centimeters;
a method for preparing the gas diffusion layer comprises: splitting a tow into filaments by spreading a liquid film to form a liquid film for infiltrating the filaments, wherein the filaments and the filaments form a network infiltrated and covered by the liquid film, and an area of filament-liquid film is enlarged to more than 10 times relative to that of the tow;
an oxygen-containing hydrophilic functional group on a surface of a carbon fiber filament is compatible with an aqueous solution to form a solid-liquid film, the solid-liquid film has a thickness of 0.5-500 micrometers, and two sides of a film surface of the solid-liquid film are in contact with air; a liquid film is formed between the carbon fiber filaments has a viscosity of 1.7-1000 Pa·s; the solid-liquid film is expanded by more than 10 times, an area of the liquid film is expanded by receiving a liquid, and a distance between the carbon fiber filaments is synchronously increased along with an expansion of the area of the liquid film;
a method for preparing the liquid film comprises the following steps: (1) preparing a solution, wherein components of the solution comprise polymers, a solvent is water, a total mass percentage concentration of the polymers is 0.1-5%, and the polymers are 1-4 of sodium carboxymethyl cellulose, polyvinyl alcohol, polyacrylic acid, and waterborne polyurethane; (2) performing oxidation hydrophilicity of carbon fiber bundles, removing a sizing agent, and then performing heat oxidation or electrochemical oxidation in concentrated nitric acid; (3) soaking the carbon fiber bundles in the solution on a water-permeable base film together, so as to infiltrate carbon fiber bundle filaments in the solution; and (4) stretching the carbon fiber bundles towards two sides at a controlled speed, supplying the solution to the liquid film, and keeping the area of the liquid film from being broken during an increase.
2 . The gas diffusion layer according to claim 1 , wherein the support layer is carbon fiber filaments absorbed and anchored with graphene, and an intersection point of the filaments covers the graphene to form a porous frame structure; and the support layer has a tensile strength greater than or equal to 100 Mpa and a porosity greater than or equal to 70%, and is stretched roll-to-roll and transported in rolls.
3 . The gas diffusion layer according to claim 1 , wherein the microporous layer is a layer formed from raw materials comprising the large graphene, small graphene, and graphene with a void; the small graphene is of 1-9 graphene atomic layers, and a length and a width of a single sheet of the small graphene are less than 1 micrometer; and the graphene with the void is provided with a void with a size of 1-300 nanometers on a surface of single-sheet graphene.
4 . The gas diffusion layer according to claim 1 , wherein the gas diffusion layer has a layered network air-permeable structure with pore diameters in gradient distribution, the pore diameters are in layered gradient distribution from millimeter to micrometer to nanometer, millimeter and micrometer pores are formed by compounding the carbon fiber filaments and graphene, nanometer pores are formed by graphene, the distance between the carbon fiber filaments and a density of the carbon fiber filament are in layered gradient distribution, a surface density of each layer of carbon fiber monofilaments ranges from 20 monofilaments to 500 monofilaments per square centimeter, and a surface density between layers is arranged unidirectionally from high to low.
5 . The gas diffusion layer according to claim 1 , wherein an interfacial force between the liquid and the carbon fiber filament in the support layer drives a carbon fiber bundle to split into and spread filaments to form a combined filament-to-filament network structure, an area of which is enlarged by more than 20 times relative to a carbon fiber tow.
6 . The gas diffusion layer according to claim 1 , wherein in the support layer, the large graphene has a crystal characteristic and a carbon element content greater than or equal to 88 wt %, has an oxygen-containing chemical functional group and a carbon-oxygen-hydrogen-containing solid electrolyte interface, and is dispersed in water, alcohol, and dimethylformamide (DMF) to form a slurry; the slurry is sprayed to form a film and a coating and is self-absorbed to form a film after dried; a method for preparing the large graphene comprises the following steps: (1) taking a graphite paper as an electrode, or taking a graphite film prepared from vermicular graphite as an electrode, wherein a single electrode has a thickness of 0.5-2 mm; cutting the graphite paper or the graphite film into comb-shaped strips, wherein each strip has a width of 1-3 cm; (2) electrifying by using an electrolyte to drive graphite to expand; (3) performing electrifying under conditions that a voltage of a direct current power supply is charged for 3-8 V, a temperature is 0-40° C., a software program controls a current to be positive current, standing, reverse current, and standing alternately performed; and (4) performing filter pressing after electrolysis, and recovering the electrolyte for recycling electrolytic graphite paper/film; then soaking and stirring with alkaline aqueous solution, filtering, stirring, washing, and washing with water to pH of 8-10; the electrolyte used for preparing the large graphene comprises perchlorate ions at a concentration of 5-10 wt % and lithium ions at a concentration of 1-5 wt %, a solvent comprises dimethyl carbonate (DMC) and water, a content of the water is 0.02-2 wt %, and a content of the DMC is greater than or equal to 50 wt %; the solvent further comprises at least one of ethylene carbonate (EC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and an imidazolium perchlorate ionic liquid.
7 . The gas diffusion layer according to claim 3 , wherein the graphene with the void is prepared by the following steps: preparing an aqueous solution of metal ions, adding graphene to form a graphene dispersion; drying the dispersion, then putting a solid into a furnace for heating, introducing 5% of argon with hydrogen H 2 , heating at a rate of 10° C./min to 900° C., and keeping a temperature at 900° C. for 1 h; then soaking a mixture in 3.0 wt % of nitric acid solution, filtering, centrifuging, washing with water, collecting a solid, and drying the solid at 80° C.; and the graphene dispersion is prepared: a dispersion concentration of graphene in water is 5 wt %, a concentration of calcium chloride is 0.01 wt %, and a concentration of magnesium chloride is 0.02 wt % relative to a mass of water.
8 . A preparation method for the gas diffusion layer according to claim 1 , comprising the following process units: preparation of the large graphene, filament split of a carbon fiber tow by spreading the liquid film, compounding of a carbon fiber filament with graphene, preparation of a graphene microporous layer, programmed heat treatment, and forming and surface strengthening.
9 . The preparation method for the gas diffusion layer according to claim 8 , wherein the compounding of the carbon fiber filament with the graphene comprises: spraying and drying a slurry of large graphene, and cross-overlapping and compacting two rolls of filament films; the programmed heat treatment comprises: heating at 900-1100° C. for 1-2 h, and heating at 2500±100° C. for 30 min in an argon atmosphere; and the forming and surface strengthening comprises: increasing hydrophobicity and bonding the microporous layer by using polyvinylidene fluoride (PVDF), and performing rolling or hot pressing.