Direct-ethanol fuel cells or DEFCs are a category of fuel cell in which

ethanol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an alcohol with the chemical formula . Its formula can be also written as or (an ethyl group linked to a ...

is fed directly into the cell. They have been used as a model to investigate a range of fuel cell concepts including the use of PEM.

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 Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an alcohol with the chemical formula . Its formula can be also written as or (an ethyl group linked to a ...

is a hydrogen-rich liquid and it has a high specific energy (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 Sugarcane or sugar cane is a species of (often hybrid) tall, perennial grass (in the genus '' Saccharum'', tribe Andropogoneae) that is used for sugar production. The plants are 2–6 m (6–20 ft) tall with stout, jointed, fibrous stalk ...

wheat Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeologi ...

, corn, or even straw. Bio-generated ethanol (or bio-ethanol) is thus attractive since growing crops for biofuels absorbs much of the

carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...

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 Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...

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

catalyst Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...

s are some of the most efficient materials for the oxidation of small organic molecules.

Reaction

The DEFC, similar to the

DMFC Direct-methanol fuel cells or DMFCs are a subcategory of proton-exchange fuel cells in which methanol is used as the fuel. Their main advantage is the ease of transport of methanol, an energy-dense yet reasonably stable liquid at all environmental ...

, relies upon the

on a

layer to form

. Water is consumed at the

anode An anode is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, an electrode of the device through which conventional current leaves the device. A common mnemonic ...

and is produced at the

cathode A cathode is the electrode from which a conventional current leaves a polarized electrical device. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. A conventional current describes the direction in wh ...

. Protons (H⁺) are transported across the proton exchange membrane to the cathode where they react with

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...

to produce water.

Electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no ...

s are transported through an external circuit from anode to cathode, providing power to connected devices. The

half-reaction A half reaction (or half-cell reaction) is either the oxidation or reduction reaction component of a redox reaction. A half reaction is obtained by considering the change in oxidation states of individual substances involved in the redox reaction. ...

s are:

Issues

Platinum-based catalysts are expensive, so practical exploitation of ethanol as fuel for a PEM fuel cell 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

, and Ni, Fe or Co alone at the

. 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 membrane An anion exchange membrane (AEM) is a semipermeable membrane generally made from ionomers and designed to conduct anions but reject gases such as oxygen or hydrogen. Applications Anion exchange membranes are used in electrolytic cells and fuel ...

s. This catalyst does not contain any

precious metals Precious metals are rare, naturally occurring metallic chemical elements of high economic value. Chemically, the precious metals tend to be less reactive than most elements (see noble metal). They are usually ductile and have a high lu ...

. In practice tiny metal particles are fixed onto a substrate in such a way that they produce a very active catalyst. A

polymer A polymer (; Greek '' poly-'', "many" + ''-mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...

acts as electrolyte. The charge is carried by the hydrogen

ion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...

( proton). The liquid ethanol (C₂H₅OH) is oxidized at the anode in the presence of water, generating CO₂, hydrogen ions and

electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no ...

s. Hydrogen ions travel through the electrolyte. They react at the cathode with

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.

Recent accomplishments

On 13 May 2007 a team from the University of Applied Sciences in Offenburg presented the world's first vehicle powered by a DEFC at Shell's Eco-marathon in France. The car "Schluckspecht" completed a successful test drive on Nogaro Circuit, powered by a DEFC stack giving an output voltage of 20 to 45 V (depending on load). Various prototypes of Direct Ethanol Fuel Cell Stack mobile phone chargers have been built featuring voltages from 2V to 7V and powers from 800 mW to 2W were built and tested.

Sources

Membranes for DEFC -Fraunhofer Institute for Interfacial Engineering and Biotechnology

DEFC membrane

Advantages

Reaction

Issues

Recent accomplishments

Sources

See also

References

Further reading