How are hydrogen fuel cells stored


The element hydrogen

Hydrogen is present in almost unlimited quantities on earth, but almost exclusively in chemical compounds (water, acids, hydrocarbons and other organic compounds). Hydrogen is a colorless and odorless gas and with a specific weight of 0.0899 g / l it is lightweight compared to air. Rule of thumb: 1 kg of hydrogen contains as much energy as 2.8 kg of gasoline.

Hydrogen is not an energy source but an energy carrier that can be used to store and transport energy. Hydrogen is therefore a secondary energy, since primary energy must first be used for production in all types of production. Environmentally friendly energy generation using hydrogen only takes place if the hydrogen is generated using regenerative energy sources.

Generation of hydrogen

The most advanced processes for producing hydrogen are the reforming process and water electrolysis.

- reforming process
Most of today's hydrogen production occurs as a by-product in processes in the chemical industry and is usually consumed again there. On an industrial scale, hydrogen is currently mainly produced by reforming natural gas. But light hydrocarbons from other sources can also be used, such as gasoline, coal, methanol or biomass. In the various reforming processes, the hydrogen is extracted from the fossil fuels consisting of carbon-hydrogen chains in several steps. Carbon monoxide, nitrogen oxides and sulfur dioxide are produced as by-products.

- water electrolysis
Another manufacturing process that is already in use is electrolysis. During electrolysis, water (H2O) is mixed with a liquid that enables ion transport. Using electricity, water is broken down into the components hydrogen (H2) and oxygen (O2). The electrical energy is converted into chemical energy and stored in the hydrogen. In a fuel cell, the reverse principle can be used to recover the energy previously chemically stored in hydrogen back into electrical energy.

Other types of production are the fermentation of biomass, the Kvæner process and the production of hydrogen from green algae. However, these technologies are still in the testing phase.

Storage of hydrogen

As an energy carrier, hydrogen can be transported relatively easily. Like natural gas, hydrogen can be compressed under high pressure or stored in liquid form. Pressure accumulators are available in different designs, from ten-liter gas bottles to large storage tanks with 100,000 cubic meters. Tank pressures of 700 bar are being tested for fuel cell cars. There are also other storage options that are still under development. There are basically three different storage options for hydrogen: gaseous in pressure vessels, liquid in vacuum-insulated containers and storage in metals on a molecular level.

Hydrogen economy

Hydrogen is an important industrial product. It is the starting element in the synthesis of ammonia, in the refining of mineral oil, the synthesis of methanol and in many metallurgical manufacturing processes. The importance of hydrogen in the energy industry is also steadily increasing. The use of the energy carrier hydrogen in connection with fuel cell systems is currently being tested in a wide variety of areas. These include the automotive and shipping industries, portable power supplies for electrical appliances and camping, as well as use in small power plants.

The advantage of hydrogen as an energy carrier lies in its storability and transportability, although there are still some problems to be solved for a functioning hydrogen economy. The production of hydrogen from fossil fuels produces carbon monoxide or carbon dioxide, i.e. a greenhouse gas. Problems for a market launch include the short service life, the comprehensive supply (e.g. hydrogen filling stations), emissions during production, the weight of some storage media and the still relatively high costs. With stationary fuel cells, natural gas is an energy source that can be used in almost every House is enough. The supply is still a crucial aspect for the mobile use of the fuel cell. So far, for example, there is no hydrogen filling station network in Germany. Without these hydrogen filling stations, the technology will find it difficult to establish itself in the automotive sector (more information on alternative fuels -> biodiesel, pure vegetable oil, natural gas and LPG). Likewise, there will probably not be a nationwide filling station network as long as there are no fuel cell cars ready for series production.

© Copyright: IWR - International Economic Forum for Renewable Energies 2005