# Direct-ethanol fuel cell

﻿
Direct-ethanol fuel cell

Direct-ethanol fuel cells or DEFCs are a subcategory of Proton-exchange fuel cells where the fuel, ethanol, is fed directly to the fuel cell.

## Contents

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.[citation needed] 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 absorbs much 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.

## Reaction

flowchart of the reaction in a DEFC

The DEFC, similar to the DMFC, relies upon the oxidation of ethanol on a catalyst layer to form carbon dioxide. Water is consumed at the anode and is produced at the cathode. Protons (H+) are transported across the proton exchange membrane to the cathode where they react with oxygen to produce water. Electrons are transported through an external circuit from anode to cathode, providing power to connected devices.

The half-reactions are:

Equation
Anode $\mathrm{C_2H_5OH + 3\ H_2O \to 12\ H^+ + 12\ e^- + 2\ CO_2}$
oxidation
Cathode $\mathrm{3\ O_2 + 12\ H^+ + 12\ e^- \to 6\ H_2O}$
reduction
Overall reaction $\mathrm{C_2H_5OH + 3\ O_2 \to 3\ H_2O + 2\ CO_2}$
redox reaction

## 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 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 cathode 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.[citation needed] The prototype consists of two monoplanar fuel cells giving an output voltage of 0.9 to 0.5 V depending on the load.

On 13 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).

Various prototypes of Direct Ethanol Fuel Cell Stack mobile phone chargers were built featuring voltages from 2V to 7V and powers from 800mW to 2W were built and tested.

## References

Wikimedia Foundation. 2010.

### Look at other dictionaries:

• Direct methanol fuel cell — 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… …   Wikipedia

• Direct borohydride fuel cell — Direct borohydride fuel cells (DBFCs) are a subcategory of alkaline fuel cells which are directly fed by sodium borohydride or potassium borohydride as a fuel and either air/oxygen[1] or hydrogen peroxide[2] as the oxidant. DBFCs are relatively… …   Wikipedia

• Direct carbon fuel cell — A Direct Carbon Fuel Cell (DCFC) is a fuel cell that uses a carbon rich material as a fuel. The cell produces energy by combining carbon and oxygen, which releases carbon dioxide as a by product. The total reaction of the cell is C + O2 → CO2.… …   Wikipedia

• Fuel cell — For other uses, see Fuel cell (disambiguation). Demonstration model of a direct methanol fuel cell. The actual fuel cell stack is the layered cube shape in the center of the image A fuel cell is a device that converts the chemical energy from a… …   Wikipedia

• Formic acid fuel cell — Direct formic acid fuel cells or DFAFCs are a subcategory of proton exchange membrane fuel cells where, the fuel, formic acid, is not reformed, but fed directly to the fuel cell. Their applications include small, portable electronics such as… …   Wikipedia

• Metal hydride fuel cell — Metal hydride fuel cells are a subclass of alkaline fuel cells that are currently in the research and development phase. A notable feature is their ability to chemically bond and store hydrogen within the cell. This feature is shared with direct… …   Wikipedia

• Electro-galvanic fuel cell — 3 electro galvanic fuel cells from a rebreather An electro galvanic fuel cell is an electrical device, one form of which is commonly used to measure the concentration of oxygen gas in scuba diving and medical equipment. A chemical reaction occurs …   Wikipedia

• Molten carbonate fuel cell — Scheme of a molten carbonate fuel cell Molten carbonate fuel cells (MCFCs) are high temperature fuel cells, that operate at temperatures of 600°C and above. Molten carbonate fuel cells (MCFCs) are currently being developed for natural gas, biogas …   Wikipedia

• Protonic ceramic fuel cell — The Protonic ceramic fuel cell or PCFC is a fuel cell based on a ceramic electrolyte material that exhibits high protonic conductivity at elevated temperatures. PCFCs share the thermal and kinetic advantages of high temperature operation at 700… …   Wikipedia

• Magnesium-air fuel cell — A Magnesium Air Fuel Cell (MAFC) is a type of fuel cell which uses a magnesium anode, oxygen from air as a cathode and a salt water electrolyte.[1] Research and commercialization of the technology by MagPower Systems has shown an efficiency of… …   Wikipedia