Fuel cells

The function of a fuel cell differs depending on the type and the fuel and electrolyte used. In the following, the functional principle is explained on the basis of the proton exchange membrane fuel cell (PEMFC).

The structure of a proton exchange membrane fuel cell consists of a bipolar plate, a gas diffusion layer (GDL for short, ensures the controlled entry of hydrogen or oxygen into the cell) followed by the anode. Then comes a thin proton-conducting membrane. On the other side of the membrane comes the cathode, another GDL and finally another bipolar plate.

On the anode side, hydrogen is supplied to the cell. This splits at the membrane so that the positive hydrogen ions can migrate through the membrane to the cathode side. The membrane does not allow the negative electrons from the hydrogen to pass through and they have to take a detour to the cathode, creating an electric voltage. On the cathode side, (air) oxygen is supplied and the positive hydrogen ions combine with the oxygen and the negative electrons. The emission of this reaction is pure water.

The DMFC (Direct Methanol Fuel Cell) is operated between 60 and 120 °C and thus belongs to the low-temperature fuel cells. The fuel is methanol together with water, which is fed to the anode and then oxidised. At the cathode, (air) oxygen is added and electrical energy is produced, as well as water as a waste product. Direct methanol fuel cells are used for small emergency power generators in camping or for remote measuring stations.

The PEMFC (Proton Exchange Membrane Fuel Cell) belongs to the low-temperature fuel cells at an operating temperature between 70 - 90 °C. However, there are also PEM fuel cells that are operated at an operating temperature of approx. 180 °C as high-temperature fuel cells.

Through a chemical reaction within the cell of hydrogen and oxygen, an electrical voltage is generated. Here, too, the waste product of the reaction is pure water. Platinum is often used as the catalyst in the membrane for the reaction. Due to the simple and light construction of this type of fuel cell, the PEMFC is the most produced and used fuel cell worldwide.

The SOFC (Solid Oxid Fuel Cell) is operated at a temperature between 650 and 1,000 °C and thus belongs to the high-temperature fuel cells. A solid ceramic material serves as the electrolyte. Hydrogen as well as natural gas or biogas can be used as fuel. Depending on the use of the fuel, either water or surplus fuel gas remains as waste product.

Due to the high operating temperature, the SOFC has a high electrical efficiency of up to 60%. This makes this type of fuel cell particularly well suited for use as a combined heat and power plant in the form of a cogeneration plant (in short: CHP). The SOFC is the second most produced and used fuel cell in the world after the PEMFC.

The mobile applications of fuel cells are particularly in the public focus due to the ambitious climate targets and the automotive location Germany. Fuel cells can be used as energy converters in cars and trucks and the electricity generated by the fuel cell can be used to power an electric motor. If the hydrogen used is green, i.e. produced from renewable energy sources with the help of electrolyzers, the cars and trucks run without CO2 emissions. In cars and trucks, the PEMFC with lightweight metallic bipolar plates are used due to their light weight.

In addition, the fuel cell offers further possibilities in mobile applications. For example, it can be used to power trains that run on non-electrified lines. The first hydrogen train from the French company Alstom has already been running in northern Germany since 2019. But ships can also be powered by fuel cells in the future. Various research projects with PEMFC or DMFC fuel cells are already underway in order to convert shipping to an environmentally friendly drive.

Although the functional principle has been known since the 19th century, the safe and efficient application of this technology still requires a lot of research. Due to the high complexity of the fuel cell in construction and operation, many problems still need to be solved. However, much progress has been made in recent years. The fact that hydrogen technologies and thus also the fuel cell have moved considerably into the public focus since 2019 means that a significant push in the further development of this technology can be expected in the next few years.

A particularly interesting field of research is the combination of electrolysis and fuel cells in one and the same system. This is possible with so-called reversible fuel cells. They can be operated bidirectionally and have a fuel cell mode in which you generate electricity from hydrogen and a electrolysis mode in which you generate hydrogen from electricity and water. Otto-von-Guericke University Magdeburg, together with a consortium from industry and research, is researching such a reversible fuel cell based on PEM technology in the research project RE-FLEX (Unitary REversible PEM fuel cells for FLEXible energy storage).

In addition to basic scientific research, such as in the RE-FLEX project, a lot of work is also being done in the economy on the practical use of fuel cells and hydrogen technologies. DILICO engineering was able to plan and build the Energy Pavilion in Bitterfeld-Wolfen on the test site of MITNETZ GAS GmbH as part of the HYPOS projects H2-Netz and H2-Home with its many years of experience in the field of hydrogen as service provider. In this exhibition pavilion, the project participants will show how the supply of buildings with heat and electricity from hydrogen can look in the future. The focus is also on the integration of hydrogen into the natural gas network or the transport of pure hydrogen via a gas network.

An important research focus in the field of fuel cells is the improvement of the service life of fuel cells. Particularly in stationary applications, such as fuel cell-based heating, the service life is a very important factor for the economic success of the technology. While mobile applications require relatively few operating hours over the entire product lifetime, in the stationary sector fuel cell heating systems must enable up to 80,000 operating hours and more.

To achieve these operating hours, the individual cells of a fuel cell stack must be permanently monitored during operation. Because if just one cell fails, the entire fuel cell fails. The DILICO cell voltage measuring system is designed precisely for this application. It monitors the individual cells of a stack and can send a signal to the system's controller in case of deviations to change the operation and avoid failure of the fuel cell. This is a particular advantage for the customer, as his system does not fail.