Direct methanol fuel cell

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The direct methanol fuel cell ( English direct methanol fuel cell , DMFC ) is a low-temperature fuel cell with cell temperatures between 60 and 120 ° C. Like all fuel cells, it converts chemical energy into electrical energy . As an energy supplier, it uses methanol , the simplest representative from the group of alcohols , whereby the fuel is usually supplied as an aqueous methanol solution, less often as a gaseous methanol-water mixture. The fuel cell usually uses air as the cathodic oxidizing agent , in special cases it is purerOxygen , supplied. The cell parts (cathode and anode compartment) are separated by a special ion-permeable polymer membrane, the proton exchange membrane (PEM) .

The most important applications of direct methanol fuel cells are in the mobile or off-grid power supply of small electrical devices, e.g. B. when camping , for military equipment in the field or remote measuring stations . What is particularly advantageous about the DMFC is that, in combination with an inverter , it represents an almost silent and low-maintenance alternative for gasoline or diesel-powered power units .

The theoretical voltage of a single cell is 1.2 V. The actual voltage during operation is typically significantly lower, namely around 0.5 V. The efficiency is specified as 20 to 30%.

principle

Direct methanol fuel cell

In the DMFC, methanol (CH 3 OH, empirical formula : CH 4 O ) is used as fuel , which - unlike in the indirect methanol fuel cell without prior reforming - is fed to the anode together with water and oxidized there. This reaction produces H + ions , free electrons and, as exhaust gas, CO 2 . The oxidizing agent (air) oxygen is fed to the cathode , which then reacts with H + ions and absorbs electrons to form water.

The problem with DMFC is the fact that methanol migrates through the membrane from the anode to the cathode, which is known as "methanol cross-over". On the one hand, there is a loss of fuel, on the other hand, undesired methanol oxidation at the cathode reduces the electrical potential (mixed potential) and the cell efficiency drops. The reduction of this technical problem is the subject of current research. A newly developed composite membrane by the Fraunhofer Institute , using ethanol as fuel, can reduce the cross-over by a factor of one hundred (as of May 2009).

Reaction equations

equation
Anode
positive pole
Oxidation / electron donation
Cathode
negative pole
Reduction / electron uptake
Overall response
Redox reaction / cell reaction

The internal charge transport takes place through H + ions. The reaction requires water on the anode side and produces it on the cathode side. Complex water management is necessary to cover the water requirement on the anode side. The u. a. by back diffusion through the membrane and moistening of the educts .

Historical

The principle of the direct methanol cell (DMFC) was first proposed in 1951 by Karl Kordesch and A. Marko, who were then working at the University of Vienna. However, they also used other alcohols or aldehydes as possible fuels. They already used electrodes made of carbon with platinum as a catalyst. The actual research and testing of the DMFC began in the 1960s, especially by the oil companies Esso and Shell . Fuel cells became known to a wide audience through the Americans' Apollo space program. However, these worked directly with the frozen liquid hydrogen carried along as rocket fuel. DMFC research became more intensive in the 1980s when B. was funded by the EU, but also by Hitachi , who equipped a golf course vehicle with DMFCs. In the 1990s, the DMFC was intensively researched, particularly in the Los Alamos National Laboratory . Initially, work was also carried out on the use of direct methanol fuel cells in electric cars; In comparison to the indirect fuel cell, which requires a reformer, as it was used in 1997 in the Mercedes-Benz NECAR 3, the construction is simpler.

In the years from 2000 to 2010 many prototypes of small direct methanol fuel cells for applications in mobile electronics were demonstrated, e.g. B. to power laptops, MP3 players or cell phones or smartphones. Expectations for a broad market launch reached their peak in 2005 and 2006. Companies that announced such DMFC devices included Motorola, as well as Japanese electronics companies Sony , Toshiba , NEC and Fujitsu . Hardly any of these developments were actually marketed. Some, such as The charger from Toshiba, for example, which was available in 2009, was only available for a short time. One reason for the lack of success of the DMFC for mobile electronics is likely to be the falling price and increasing performance of lithium-ion batteries , which enable the construction of particularly compact portable electronics.

More successful than the attempts to use the DMFC for the electronics of the home user is the application of the DMFC away from the power grids: The company SFC Energy, founded in 2000 (from 2002 to July 22, 2010 as Smart Fuel Cell GmbH) sells DMFC power supplies e.g. B. for camping needs or for network-independent measuring devices. By May 2017, SFC Energy said it had sold 36,000 direct methanol fuel cells. Besides SFC, only Oorja Protonics, Inc. is an active company in the DMFC market.

Special forms of the direct methanol fuel cell

Instead of atmospheric oxygen, other oxidizing agents can also be used on the anode side, for example nitric acid or hydrogen peroxide . That could e.g. B. for applications under water, because there the oxygen is not available in the environment anyway.

See also

Individual evidence

  1. ↑ a b c Peter Kurzweil: Direct methanol fuel cell (DMFC) . In: fuel cell technology . Basics, components, systems, applications. 2nd Edition. Springer Vieweg Fachmedien Wiesbaden, 2013, ISBN 978-3-658-00084-4 , p. 125-142 , doi : 10.1007 / 978-3-658-00085-1_5 .
  2. ^ DMFC, Research Center Jülich
  3. ↑ Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB: Composite membrane for fuel cells  ( page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.@1@ 2Template: Toter Link / www.igb.fraunhofer.de  
  4. ↑ a b c DS Cameron, GA Hards, B. Harrison, RJ Potter: Direct Methanol Fuel Cells . Recent developments in the search for improved performance. In: Johnson Matthey Plc (Ed.): Platinum Metals Review . tape 31 , no. 4 , October 1987, p. 173–181 (English, homepage of the article [PDF; 562 kB ; retrieved on June 14, 2017] Summary of the history up to 1987): “Article is based largely upon a paper given at the CEC-Italian Fuel Cell Workshop in Taormina, Sicily, in June 1987.”
  5. ↑ Angelika Heinzel, Marcella Cappadonia, Ulrich Stimming, Karl V. Kordesch, Julio Cesar Tambasco De Oliveira: Fuel Cells . In: Ullmann's Encyclopedia of Industrial Chemistry . Wiley-VCH Verlag, 2010, doi : 10.1002 / 14356007.a12_055.pub2 (English).
  6. ↑ Xiaoming Ren, Piotr Zelenay, Sharon Thomas, John Davey, Shimshon Gottesfeld: Recent advances in direct methanol fuel cells at Los Alamos National Laboratory . In: Journal of Power Sources . tape 86 , no. 1 . Elsevier, March 1, 2000, pp. 111-116 , doi : 10.1016 / s0378-7753 (99) 00407-3 .
  7. ↑ Xiaoming Ren, Mahlon S. Wilson, Shimshon Gottesfeld: On direct and indirect methanol fuel cells for transportation applications . September 1, 1995 ( osti.gov [accessed June 20, 2017]).
  8. ↑ Birgit Niesing: Mini electricity supplier with methanol. What is the state of affairs with the methanol cells? In: Mini power plants for home and on the go. scinexx® MMCD NEW MEDIA GmbH, October 12, 2007, accessed on June 19, 2017 : "This cell type can be accommodated in the hinged lid of a laptop, for example."
  9. ^ Toshiba's methanol fuel cell. Digital Photography Review DPReview, June 24, 2004, accessed June 19, 2017 : "to power an MP3 music player for as long as 20 hours"
  10. ↑ Janko: MTI MicroFuel Cells Mobion - enough juice for ten cell phones. In: testberichte.de, Photo, Video & Optics ›Chargers› USB Chargers ›MTI MicroFuel Cells Mobion. Producto AG, December 11, 2008, accessed on June 20, 2017 : "should make it possible to charge a cell phone up to ten times in a row"
  11. ↑ mak: methanol drive for smartphones. Fuel cell technology. In: News> Network World> Gadgets> Toshiba. Spiegel Online GmbH, October 22, 2009, accessed on June 19, 2017 .
  12. ↑ a b c Kerry-Ann Adamson: Whatever Happened to Direct Methanol Fuel Cells? (No longer available online.) In: Navigant Research Blog. Navigant Consulting, Inc, June 13, 2012, archived from the original on October 12, 2015 ; Retrieved June 19, 2017 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.  @1@ 2Template: Webachiv / IABot / www.navigantresearch.com
  13. ↑ Xianglin Li, Amir Faghri: Review and advances of direct methanol fuel cells (DMFCs) part I: Design, fabrication, and testing with high concentration methanol solutions . In: Journal of Power Sources . tape 226 . Elsevier BV, 2013, 3. Advances in DMFC prototype designs and developments, 3.2. DMFC stack development using high concentration methanol, p. 223–240 , doi : 10.1016 / j.jpowsour.2012.10.061 (English, researchgate.net [PDF; accessed on November 11, 2016]): “The state-of-the-art DMFC prototypes and products are more competitive than rechargeable batteries, especially in applications such as military uses. "
  14. ^ Toshiba Launches Direct Methanol Fuel Cell in Japan as External Power Source for Mobile Electronic Devices. In: Toshiba Press Releases. Toshiba Corporation, October 22, 2009, accessed on June 14, 2017 (English): "Dynario ™, an external power source that delivers power to mobile digital consumer products [...] limited edition of 3,000 units only"
  15. ↑ SFC Energy AG: New company name: SFC Smart Fuel Cell AG becomes SFC Energy AG. DGAP - a service of EQS Group AG, July 22, 2010, accessed on June 14, 2017 .
  16. ↑ SFC Energy receives order from the German Armed Forces to expand its mobile micro-energy supply (MKEV). (No longer available online.) In: SFC press releases. SFC Energy AG, May 30, 2017, formerly in the original ; accessed on June 14, 2017 .  ( Page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. @1@ 2Template: Dead Link / www.sfc.com  
  17. ↑ Oorja Protonics, Inc. Direct Methanol Fuel Cells April 2016

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