The bipolar plate is one of the core components of the hydrogen fuel cell, and its functions include providing an air flow channel to prevent the hydrogen and oxygen in the battery gas chamber from interacting with each other, evenly distributing the gas to the reaction layer of the electrode for reaction, maintaining the temperature field equilibrium inside the battery by discharging heat, and establishing an electrical connection between the Yin and Yang poles to form a continuous current path.
In general, in a hydrogen fuel cell pile, the bipolar plate accounts for more than 80% of the total mass of the pile and about 30% of the total cost, and the volume of the pile is basically occupied by the bipolar plate. Therefore, improving the performance of bipolar plates and reducing their manufacturing costs have become the technical development direction of widespread attention and efforts in the field of hydrogen energy.
Bipolar plate function and classification
In the design of hydrogen fuel cells, bipolar plates have six basic functions:
(1) Realize the isolation of the battery unit
(2) Transport reaction gas
(3) Ensure electrical connectivity
(4) Remove the resulting water byproducts
(5) Dissipate the heat generated by the reaction
(6) Resist structural fastening force
According to the different materials, there are three main types of hydrogen fuel cell bipolar plates on the market at present: graphite bipolar plates, metal bipolar plates and composite bipolar plates. Among them, the graphite bipolar plate occupies a dominant position in the application field because of its high technical maturity.
Graphite bipolar plate includes hard graphite plate and flexible graphite plate. Hard graphite plate has long processing time, high difficulty, high production cost and easy fracture. Metal bipolar plates face the problem of insufficient corrosion resistance, which limits their service life. As for composite bipolar plates, despite their unique advantages, their use has been restricted to a certain extent due to the complexity of their production process and high cost.
Flexible graphite plate bipolar plate
Flexible graphite plate bipolar plate is a kind of bipolar plate based on expandable graphite and supplemented by composite material modification, which is derived from the type of composite bipolar plate and has wide application potential. This bipolar plate takes advantage of the lightweight porous properties of expanded graphite, and its internal graphite layer structure gives the plate good electrical conductivity.
According to the different materials, there are three main types of hydrogen fuel cell bipolar plates on the market at present: graphite bipolar plates, metal bipolar plates and composite bipolar plates. Expanded graphite, also known as flexible graphite or worm graphite, is a new type of carbon material. Expanded graphite has many advantages, such as large specific surface area, high surface activity, good chemical stability and high temperature resistance.
The common preparation process of expanded graphite is natural flake graphite, which is first oxidized to produce expandable graphite, and then expanded to become expanded graphite.
When exposed to high temperatures, the expanded graphite can rapidly expand its volume by 150 to 300 times, and the shape changes from sheet to worm-like structure, thus the structure is loose, porous and curved, the surface area is expanded, the surface energy is improved, and the adsorption capacity of the flake graphite is enhanced. The wormlike graphite can be self-chimeric, giving the material flame-retardant, sealing and adsorption properties, and is widely used in many fields such as life, military, environmental protection and chemical industry.
Among them, the graphite bipolar plate occupies a dominant position in the application field because of its high technical maturity.
Graphite bipolar plate includes hard graphite plate and flexible graphite plate. Hard graphite plate has long processing time, high difficulty, high production cost and easy fracture. Metal bipolar plates face the problem of insufficient corrosion resistance, which limits their service life. As for composite bipolar plates, despite their unique advantages, their use has been restricted to a certain extent due to the complexity of their production process and high cost.
Flexible graphite plate bipolar plate
Flexible graphite plate bipolar plate is a kind of bipolar plate based on expandable graphite and supplemented by composite material modification, which is derived from the type of composite bipolar plate and has wide application potential. This bipolar plate takes advantage of the lightweight porous properties of expanded graphite, and its internal graphite layer structure gives the plate good electrical conductivity.
According to the functional requirements of bipolar plates, and considering that the electrochemical reaction environment of PEMFC is acidic, the bipolar plates are required to have high requirements on conductivity, air tightness, mechanical properties, corrosion resistance, etc. On December 22, 2023, the Ministry of Industry and Information Technology issued the notice of "The First Batch of Application Demonstration Guidance Catalogue of Key New Materials (2024 version)". Among them, the standards for flexible graphite bipolar plates for hydrogen energy fuel cells are as follows:
Density ≥1.9g/cm3, conductivity ≥100S/m, compressive strength ≥100MPa, corrosion current ≤0.016mA/cm2, thermal conductivity ≥10W/(m·K), bending strength ≥50MPa, air permeability ≤2×10-6cm3/scm2.
In 2024, the industrialization of flexible graphite bipolar plates for hydrogen energy fuel cells continues to "heat up". On March 27, the second phase of the industrialization project of flexible graphite bipolar plate materials for hydrogen fuel cells of Guotai Xiaoxing was officially announced to the public; Meimiao Energy storage 400,000 graphite composite bipolar plate project is also in intensive progress...... The overall trend of the market shows that the bipolar plate market is expanding, whether it is based on graphite, metal or composite materials, the bipolar plate is everywhere. In contrast, there are more domestic enterprises that do graphite bipolar plates, and the technology is more mature. In the future, the domestic bipolar plate production capacity is expected to achieve explosive growth, and the technical level will also accelerate.
