Fraunhofer scientists develop ethanol fuel cells

The hydrogen economy has been on the back burner for quite a while now, mainly because producing, storing and distributing the clean gas is problematic (earlier post). Moreover, when biomass-to-hydrogen is used as a production path, well-to-wheel analyses show that the biomass can be used more efficiently for other fuel paths (earlier post).

One element of hydrogen systems that remains on the radar of research are fuel cells which convert the hydrogen contained in gaseous or liquid fuels into electricity that can be used for stationary or mobile applications. Earlier, we reported about an Italian group of researchers who have developed cheap non-platinum catalysts for fuel cells that can work on a range of fuels (including biofuels, and probably on butanol too). And now, researchers from one of Europe's main R&D institutions, the Fraunhofer Institute, are working on direct-alcohol fuel cells (DAFC, also known as direct-ethanol fuel cells: DEFC).

The cells work on ethanol without the need for prior reforming of the fuel. Instead, the alcohols are directly converted into energy via the cell's membrane [picture] and catalysts under development. The advantage of DAFCs is that they use fuels that are easy to produce, store and distribute and which have a higher energy density than hydrogen.

The development of such a DAFC is in its infancy, says Michael Krausa who heads the research at the Fraunhofer Institute's dept. for Chemical Technologies: we are in a phase where research into direct-methanol fuel cells (DMFCs) was about 10 years ago. In DMFCs, methanol reacts directly with oxygen from the air at the membrane, with the reaction delivering electricity. But because ethanol differs considerably from methanol, the DAFC has to be built from scratch. The main challenge lies in the fact that ethanol consists of two strongly bonded carbon atoms, that have to be broken down. Methanol only contains one such an atom.

Central to the development of the DAFC is the membrane: it should be impermeable for the ethanol molecules, but has to be able to allow the protons that are needed for the reaction with oxygen to pass through:
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As with the DMFC, so-called unwanted cross-over effects occur during this proton exchange: part of the ethanol does penetrate the membrane at the cathode and can thus no longer be used for the reaction. The Fraunhofer Institute's goal is now to develop special anorganic components in the membrane that will block the ethanol, without stopping the flow of the necessary protons. New catalysts that are adapted to the properties of ethanol are the main focus of the research. The design of the DAFC cell must also ensure that these new catalysts and membranes function optimally under the high temperatures that arise during the reaction.

So why the choice for an alcohol-fuel cell? "Ethanol is a much versatile and better energy carrier [than both hydrogen and methanol]", says Krausa and adds that the concept of ethanol fuel cells holds tremendous potential. Ethanol has a higher energy density than methanol and is already widely used and accepted in numerous industries and by the public at large. In contrast to methanol, it is also non-toxic. Ethanol is being produced more and more from biomass, with the industry becoming a global market. DAFCs can be used as mobile energy systems or in decentralised concepts.

More information:

Fraunhofer-Institute: Fraunhofer-Forscher entwickeln Ethanol-Brennstoffzelle - Oct. 10, 2006