Metallic bipolar plates are an important element of fuel cells used in vehicles. They could therefore play a major role in the future of fuel cell technology. The article explains why this is so, what other advantages bipolar plates have and what applications they serve in the context of the increasingly popular fuel cell technology.
Bipolar plates are a key element of hydrogen fuel cells and direct methanol fuel cells. While the fuel cells, layered into stacks, form the most important element of the fuel cell system, the plates, as integrated components of the cells, fulfill various significant tasks. For example, they are responsible not only for the electrical connection of the fuel cells and the distribution of gases over the plate surface, but also for gas separation between adjacent cells, cooling and sealing to the outside.[1]
The bipolar plate structure looks as follows: As the name "bi" implies, the bipolar plate serves as a carrier plate for the two poles of the fuel cell. These poles are the negatively charged, H2-carrying anode plate and the positively charged, O2-carrying cathode plate.[1] As the heart of the fuel cell, the bipolar plate thus plays the central role in the conversion of hydrogen (H2) with oxygen (O2) from the air to water.[2]
Fuel cells have numerous membrane electrode units arranged in the stack that generate electrical power. Between every two of these units in the fuel cell is a bipolar plate.[1]
The bipolar plate in the fuel cell fulfills several important functions. Firstly, it provides the physically and electrically conductive connection between the anode of a cell and the cathode of its neighboring cell. In addition, the bipolar plate has the task of conducting the gases O2 and H2 produced during the reaction into the so-called reaction zone. For this purpose, the plates have flow profiles that were milled or pressed into the plates on both sides during their manufacture. This allows air to be supplied on one side of the plate and hydrogen to flow on the other. In addition, bipolar plates control the removal of water vapor and the release of electrical and thermal energy. Thus, the plates perform three functions at once: gas supply, cooling, and electrical connection in the fuel cell.[1]
Just like the membrane electrode units, bipolar plates are indispensable components of fuel cells. In addition to supplying water and oxygen, the plates are responsible for water removal and cooling. Furthermore, they absorb the discharged electrons on the hydrogen side and – after they have fulfilled their task in the drive – supply them again on the oxygen side.[3]
Major advantages of bipolar plates are therefore that they reliably remove the water produced during the reaction and also dissipate the heat of reaction in an efficient manner. They also distribute the reaction gases – i.e. H2 and O2 – evenly and feed them to the catalyst layer. In addition, the plates conduct the current generated during the reaction from cell to cell within the stack.[2]
In order for the bipolar plates to meet the above requirements, they must be made of very specific materials. The most important material requirement is excellent electrical conductivity, which does not decrease significantly even during the electrochemical processes in the fuel cell.[3] Therefore, the plates are made of graphite, graphite-polymer compound, (coated) metal or else ceramic.
The different materials bring different properties and advantages for the functionality of the plates. For example, metallic bipolar plates are often assumed to be more suitable than plates made of graphite. The reason is that they not only weigh less, but also have a smaller volume and also better cold-start capability. In addition, the cost of metallic bipolar plates would be significantly lower than that of graphite plates for high volumes. However, the latter are more suitable when aiming to achieve the highest possible lifetime of more than 40,000 hours.[1]
Sustainable, non-fossil energy sources are playing an increasingly important role in the power supply of the future. Unfortunately, electricity generated from wind and solar power is often subject to weather-related fluctuations, which is why it requires various means of intermediate storage in the medium and long term.[4]
Direct methanol and hydrogen fuel cells represent one option for storing electricity. These convert sustainable fuels, for example hydrogen, into electrical energy. Fuel cells are becoming increasingly popular, particularly for mobile applications, and are already being used, for example, in vehicle construction and in the energy supply of buildings (combined heat and power). Powerful fuel cells are used, for example, in cars, trucks, trains and ships. Fuel cells are also playing an increasingly important role in independent power supply systems, for example for data centers.[4]
For this technology – and thus a sustainable supply of sufficient electricity – to become established, bipolar plates must be researched and further developed as a key functional element of fuel cells.[4] There is a need for research, for example, in the production of bipolar plates that is suitable for series production and inexpensive. The reason: Bipolar plates still account for a large part of the weight of fuel cells. They also account for up to 45 percent of the production costs of the cells. If, on the other hand, bipolar plates were manufactured in series and in large quantities, the potential savings would be enormous.[1]
Bipolar plates are an important element of fuel cells and serve as a carrier plate for both poles of the cells. They thus play a central role in the conversion of hydrogen with oxygen to water. As fuel cell technology is becoming increasingly popular, particularly for mobile applications, and is already being used in vehicle construction, for example, research into the possibilities of manufacturing low-cost bipolar plates also offers potential for generating sustainable electricity.
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