Hydrogen and Fuel Cells

Fuel cells will play a key role in future energy supplies as an efficient, flexible in use and silent system. They produce electricity by means of a chemical and direct conversion of the fuel's energy without any thermic intermediate steps like in nowadays power plants.

Depending on the type fuel cells can run on hydrogen or methane (from natural gas, biogas or gas from sewage treatment plants), mixtures of both or liquid methanol. All fuels do not react directly with oxygen, but are being separated by an appropriate electrolyte (see figure). The electrolyte is only permeable for certain ions. Only when ions are exchanged over an external connection the reaction starts. The resulting electricity is the desired fuel cell process.

With hydrogen as a fuel there are no harmful emissions whatsoever, only steam as an "exhaust fume". The process in the fuel cell thereby represents a reverse electrolysis. Hydrogen ions combine with oxygen to form water or steam respectively, producing electricity and heat.

Hydrogen + Oxygen → electrical Energy + Water + Heat

In this process relatively high electrical efficiencies of 30% up to 55% can be gained depending on the fuel cell type. Fuels cells can be utilised for a wide range of tasks:

Today mainly four fuel cell types are being developed and used, depending on the purpose of use and the fuel type or grade of purity available. The names of the different types mostly conform to the used electrolytes with direct-methanol-fuel cells being an exception.

Low-temperature fuel cells work at temperatures between 60°C and 120°C. Hydrogen and methanol act as a fuel. These fuel cells require a high degree of purity of the fuels and have an efficiency between 30% (methanol) and 45% (hydrogen). For the membrane that separates the two gases synthetic materials are used, which is why they are called polymer-electrolyte fuel cells (PEFC).

While PEFCs are operated with gaseous fuels, the direct methanol fuel cells (DMFC) uses an aqueous methanol solution.

High-temperature fuel cells work at temperatures between 550°C and 1100°C. This has the advantage that the fuel's degree of purity needs to be considerably lower and, at the same time, methane and carbon monoxide can be used as fuels directly. The electrical efficiency lies between 50% - 55% and, in conjunction with a downstream gas turbine that uses the exhaust fumes, can go up to 65% for the entire process. This is the best value for efficient power production.

High-temperature fuel cells are made from ceramics with either ceramic or metal connection plates. One can distinguish between solid oxide fuel cells (SOFC) and molten carbonate fuel cells (MCFC).  

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Function diagram of a Fuel Cell

Selected publications on this topic

R. Steinberger-Wilckens
Hochtemperatur-Brennstoffzellen als Verbindungsglied zwischen Erdgas- und Wasserstoffwirtschaft
Deutscher Wasserstoff-Energietag, Essen, November 2002.

R. Steinberger-Wilckens
Not Cost Minimisation But Added Value Maximisation
GEE Conference “Market Challenges of Fuel Cell Commercialisation”, Berlin, September 2002,
Überarbeitete Version in: International. Journal of Hydrogen Energy 28 (2003) 763-770.

Th. Feck, R. Steinberger-Wilckens
Status und Perspektiven der Nutzung biogener Gase in Brennstoffzellen
Tagung der Deutschen Gesellschaft für Erdöl, Erdgas und Kohle e. V. (DGMK), Velen, April 2002.

more publications


Two further types of fuel cells are the alkaline fuel cell (AFC), which is mainly being used in aeronautics, and phosphoric acid fuel cell (PAFC) with - from today's perspective - a low potential for any further development.