Hydrogen fuel cell: function & types

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This type of fuel cell, which is classified as a low-temperature fuel cell, set a milestone in the development of fuel cell technology. Alkaline fuel cells were particularly successful in space travel and in the propulsion of submarines. The world's first fuel cell passenger boat was also powered by alkaline fuel cells. Despite its robust system, this type of fuel cell has a relatively short service life. The alkaline fuel cell does not achieve the high power density of today's widely used membrane fuel cells or PEM fuel cells.

No other type of fuel cell is as versatile as the membrane fuel cell or PEM fuel cell. Due to their highly dynamic power output, PEM fuel cells are often used in the mobile sector, e.g. in cars, vans and buses, but also for applications in aviation, aerospace and shipping. Another wide field of application for PEM fuel cells, which are classified as low-temperature fuel cells, is the emergency power supply, for example in rail transport and telecommunications, as well as the protection of critical industrial infrastructures or data centres.

Smaller fuel cell systems are used, for example, in portable generators or stationary domestic energy supply systems in combined heat and power plants. Larger PEM fuel cell systems can be found in hospitals, swimming pools and other municipal supply facilities, for example. The PEM fuel cell currently has the greatest potential of all types of fuel cells, especially in terms of mass production.

Thanks to their uncomplicated handling, direct methanol fuel cells are widely used. Direct methanol fuel cells are used for stationary applications such as off-grid power supplies for measuring stations, monitoring systems or communication equipment. In portable applications, direct methanol fuel cells are often used as range extenders for electric vehicles. But what are the advantages and disadvantages of direct methanol fuel cells? Firstly, the advantages: With its high storage density, the direct methanol fuel cell gives electric vehicles a long, environmentally friendly range. Furthermore, the reaction of methanol (CH4O) with oxygen in direct methanol fuel cells produces only a small amount of carbon dioxide (CO2) in addition to water vapour. In addition, liquid methanol is easy to store.

With regard to the disadvantages of direct methanol fuel cells, it should be noted that methanol is not only corrosive but also extremely toxic. The highest safety regulations must therefore apply to storage. Due to the operating temperatures of up to 120 °C, sufficient cooling must also be ensured. As a proportion of the methanol migrates from the anode to the cathode, the direct methanol fuel cell also has a low electrical efficiency. Another disadvantage of the direct methanol fuel cell is that carbon dioxide is produced in the cell during cold combustion.

As a medium-temperature fuel cell, this type of cell not only has a higher operating temperature than low-temperature fuel cells, but also has a certain tolerance to carbon monoxide (CO) and carbon dioxide, meaning that it can be operated primarily with reformed natural gas. However, due to its acidic, aggressive electrolyte, it also has a comparatively short service life. It is used in the field of combined heat and power generation, e.g. in stationary energy supply for industrial plants, shopping centres, hospitals or even housing estates.

As a high-temperature fuel cell, the molten carbonate fuel cell has the advantage of being insensitive to carbon monoxide and being able to utilise natural gas, coal, biogas and syngas directly without the process of reforming. However, the internal carbon dioxide cycle of the molten carbonate fuel cell requires additional electrolyte and carbon dioxide management. As with the medium-temperature fuel cell, the molten carbonate fuel cell prioritises heat production over electricity production. As it has a longer start-up phase and its service life is largely determined by the number of start-stop cycles, the molten carbonate fuel cell ideally works in base load operation in power stations and CHP plants.

Compared to molten carbonate fuel cells, oxide ceramic fuel cells are characterised by a comparatively simple system, long service life and high efficiency. The operating temperature of oxide ceramic fuel cells of up to 1000 °C predestines these powerful high-temperature fuel cells for the extraction of process heat and thus for stationary use in power stations and combined heat and power plants, but also for heating systems in detached and semi-detached houses. In combination with gas turbines, molten carbonate fuel cells are also used in smaller combined heat and power plants and large-scale power generation plants.