Direct-ethanol fuel cell

Direct-ethanol fuel cells or DEFCs are a subcategory of Proton-exchange fuel cells where, the fuel, ethanol, is not reformed, but fed directly to the fuel cell.

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Advantages

DEFC uses Ethanol in the fuel cell instead of the more toxic methanol. Ethanol is an attractive alternative to methanol because it comes with a supply chain that's already in place. Ethanol also remains the easier fuel to work with for widespread use by consumers.

Ethanol is a hydrogen-rich liquid and it has a higher energy density (8.0 kWh/kg) compared to methanol (6.1 kWh/kg). Ethanol can be obtained in great quantity from biomass through a fermentation process from renewable resources like from sugar cane, wheat, corn, or even straw. Bio-generated ethanol (or bio-ethanol) is thus attractive since growing crops for biofuels soaks up a fair amount of the carbon dioxide emitted into the atmosphere from fuel used to produce the biofuels, and from burning the biofuels themselves. This is in sharp contrast to the use of fossil fuels. The use of ethanol would also overcome both the storage and infrastructure challenge of hydrogen for fuel cell applications. In a fuel cell, the oxidation of any fuel requires the use of a catalyst in order to achieve the current densities required for commercially viable fuel cells, and platinum-based catalysts are some of the most efficient materials for the oxidation of small organic molecules.

Issues

Platinum-based catalysts are expensive, so practical exploitation of ethanol as fuel for a PEM fuel cells requires a new catalyst. New nanostructured electrocatalysts (HYPERMEC™ by ACTA SpA for example) have been developed, which are based on non-noble metals, preferentially mixtures of Fe, Co, Ni at the anode, and Ni, Fe or Co alone at the cathode. With ethanol, power densities as high as 140 mW/cm² at 0.5 V have been obtained at 25°C with self-breathing cells containing commercial anion-exchange membranes. This catalyst does not contain any precious metals. In practice tiny metal particles are fixed onto a substrate in such a way that they produce a very active catalyst.

A polymer acts as electrolyte. The charge is carried by the hydrogen ion (proton). The liquid ethanol (C₂H₅OH) is oxidized at the anode in the presence of water, generating CO₂, hydrogen ions and electrons. Hydrogen ions travel through the electrolyte. They react at the anode with oxygen from the air and the electrons from the external circuit forming water.

Bio-Ethanol based fuel cells may improve the well-to-wheel balance of this biofuel because of the increased conversion rate of the fuel cell compared to the internal combustion engine. But real world figures may be only achieved in some years since the development of direct methanol and ethanol fuel cells is lagging behind hydrogen powered fuel cells [1].

Present accomplishments

Technofil has produced a 1.5 W Direct Ethanol Fuel Cell prototype. The prototype consists of two monoplanar fuel cells giving an output voltage of 0.9 to 0.5 V depending on the load.

On 13th of May 2007 a team from the University of Applied Sciences in Offenburg did present world's first vehicle powered by a DEFC at Shell's Eco-marathon in France. The car "Schluckspecht" attended a successful test drive on Nogaro Circuit powered by a DEFC stack giving an output voltage of 20 to 45 V (depending on load).

The Team and the vehicle "Schluckspecht" (with the DEFC in the back) after the test drive on Nogaro Circuit /France.

See also

• Timeline of alcohol fuel

Sources

• Chemistry
• DEFC membrane
• producer
• ICCOM-CNR Institute
• ISTM-CNR
• Universities of Trieste and Pisa.
• "Schluckspecht" Team Homepage