Hydrogen fuel cell: function & types

This type of fuel cell, which belongs to the low-temperature fuel cells, set a milestone in the development of fuel cell technology. The alkaline fuel cell was particularly successful in space travel and in powering 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 lifetime. 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 fuel cell type can be used in as many ways as the membrane fuel cell or PEM fuel cell. Due to the high dynamics of the 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, space travel and shipping. A wide field of application for PEM fuel cells, which belong to the 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 in the area of domestic energy supply through combined heat and power plants. Larger systems of PEM fuel cells can be found, for example, in hospitals, public swimming pools or other municipal supply facilities. Currently, the PEM fuel cell has the greatest potential of all types of fuel cells, especially in terms of mass production.

Thanks to their straightforward handling, direct methanol fuel cells are widely used. In stationary applications, direct methanol fuel cells are used for off-grid power supply of measuring stations, monitoring systems or communication equipment. Direct methanol fuel cells are used as portables, e.g. in the leisure sector, and often as range extenders for electric vehicles. But what are the advantages and disadvantages of the direct methanol fuel cell? First of all, the advantages: With its high storage density, the direct methanol fuel cell enables electric vehicles to have a long, environmentally friendly range. Moreover, 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. Moreover, liquid methanol can be easily stored.

With regard to the disadvantages of the direct methanol fuel cell, it should be noted above all that methanol is not only corrosive, but also extremely toxic. Therefore, the highest safety regulations must apply during storage. Due to the working temperatures of up to 120 °C, sufficient cooling must also be ensured. Since a portion of the methanol migrates from the anode to the cathode, the direct methanol fuel cell also has only 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 a certain tolerance to carbon monoxide (CO) and carbon dioxide, so that it can be operated primarily with reformed natural gas. However, due to its acidic, aggressive electrolyte, it also has a comparatively short lifetime. 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 of being able to use natural gas, coal, biogas and synthesis gas 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 prioritizes heat production over electricity production. Since it has a longer start-up phase and its lifetime is largely determined by the number of start-stop cycles, the molten carbonate fuel cell ideally operates in base load mode in power plants and CHP plants.

Compared to the molten carbonate fuel cell, the solid oxide fuel cell is characterized by a comparatively simple system, a long lifetime and high efficiencies. The operating temperature of solid oxide fuel cells of up to 1,000 °C qualifies these high-performance, 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.