Direct ethanol fuel cell

The direct ethanol fuel cell (Engl. Direct Ethanol Fuel Cell , DEFCs ) is a type of fuel cell , the ethanol as a fuel ( " fuel use"). Like all fuel cells, it converts the chemical energy of the fuel into electrical energy . Ethanol, the best-known representative of the alcohol group , is relatively inexpensive, comparatively non-toxic and environmentally friendly, e.g. B. when it is obtained through biological processes, such as bioethanol from bio-waste .

Applications for which direct ethanol fuel cells have been considered as power sources range from cell phones and laptops to electric cars . However, in contrast to direct methanol fuel cells , the development of the direct ethanol fuel cell is still at an early stage despite years of research, since a sufficient service life must be ensured before such cells can be marketed. Initial attempts to bring a salable power source onto the market have ultimately not been successful. Ethanol is less reactive than methanol and must therefore be converted at higher temperatures (above 90 ° C). Therefore, a gaseous ethanol-water mixture is usually used as fuel. The fuel cell is usually supplied with air as the cathodic oxidizing agent , in special cases pure oxygen . The cell parts (cathode and anode compartment) are separated by a special ion-permeable polymer membrane, the proton exchange membrane (PEM) .

Reaction equations

Complete conversion of the ethanol C ₂ H ₅ OH to the end product carbon dioxide CO _{2 is} desired for optimal fuel utilization . Then the reaction equations are:

	equation
Anode negative pole	${\displaystyle \mathrm {H_{3}CCH_{2}OH+3\ H_{2}O\to 12\ H^{+}+12\ e^{-}+2\ CO_{2}} }$ Oxidation / electron donation
Cathode positive pole	${\displaystyle \mathrm {3\ O_{2}+12\ H^{+}+12\ e^{-}\to 6\ H_{2}O} }$ Reduction / electron uptake
Overall response	${\displaystyle \mathrm {H_{3}CCH_{2}OH+3\ O_{2}\to 3\ H_{2}O+2\ CO_{2}} }$ Redox reaction / cell reaction

The above full conversion requires cleavage of the C – C bond and is difficult to achieve. In many cases, therefore, an incomplete reaction does not take place up to CO ₂ , but only up to the level of acetic acid CH ₃ COOH:

	equation
Anode negative pole	${\displaystyle \mathrm {H_{3}C\!-\!CH_{2}OH+H_{2}O\to 4\ H^{+}+4\ e^{-}+H_{3}C\!-\!COOH} }$ Oxidation / electron donation
Cathode positive pole	${\displaystyle \mathrm {O_{2}+4\ H^{+}+4\ e^{-}\to 2\ H_{2}O} }$ Reduction / electron uptake
Overall response	${\displaystyle \mathrm {H_{3}C\!-\!CH_{2}OH+O_{2}\to H_{2}O+H_{3}C\!-\!COOH} }$ Redox reaction / cell reaction

The energy obtained from the ethanol with these reactions is significantly lower than with complete conversion. Since this incomplete implementation is much easier to achieve, an attempt was made to sell fuel cells that exploit this. Units with outputs of 3 W , 25 W and 250 W were planned.

Advantages and disadvantages

The energy density of ethanol is 7.5 kWh / kg or 5.9 kWh / l, which is higher than that of methanol (5.6 kWh / kg or 4.4 kWh / l). However, bioethanol is more expensive than methanol.

Demonstration applications

Employees at the Offenburg University of Applied Sciences built a vehicle that was powered by direct ethanol fuel cells and that took part in the Shell Eco-Marathon in southern France in 2007 .

Individual evidence

1. ↑ Kevin Bullis: Efficient Ethanol Fuel Cells. Sustainable Energy. In: MIT Technology Review. MMCD NEW MEDIA GmbH, May 6, 2007, accessed on May 31, 2018 .  
2. ^ ^{A b} Andrew Tarantola: Monster Machines: The Fuel Cell That Runs On Corn Husks And Old Bullets. In: Gizmodo. Allure Media, June 14, 2013, accessed May 31, 2018 .  
3. ↑ ^{a b c} Portable Power. In: Products & Services> Consumers. nanoMaterials Discovery Corporation NDCPower, 2011, accessed May 31, 2018 .  
4. ↑ Peter Kurzweil: fuel cell technology . Basics, components, systems, applications. 2nd Edition. Springer Vieweg Fachmedien, Wiesbaden 2013, ISBN 978-3-658-00084-4 , p. 230 , doi : 10.1007 / 978-3-658-00085-1 ( springer.com [accessed May 31, 2018]).
5. ^ Costs of bioethanol. In: Research Information System> Energy, Environment and Climate> Energy and Energy Carriers. Federal Ministry of Transport and Digital Infrastructure (BMVI), April 25, 2016, accessed on May 31, 2018 .  
6. ↑ Electricity from alcohol. In: innovations-report> Subjects> News & Reports> Energy and Electrical Engineering. IDEA TV, June 4, 2007, accessed May 31, 2018 .  
7. ↑ Electricity from alcohol. First direct ethanol fuel cell built. In: scinexx.de. MMCD NEW MEDIA GmbH, May 6, 2007, accessed on May 31, 2018 .