Contents
Introduction
DMFC description
Concept of DMFC
Chemical reaction
Components of typical DFMC
Micro Fuel Cell Stack for cellular Telephone
Developments of micro fuel cell for cellular phones
Proposed design of micro fuel cell
Mentions
Introduction Introduction
As hi-tech multifunctional and illumination devices such as laptop computing machines, digital picture recording equipments, digital multimedia phones and PDAs go more widely used, new power beginnings need to be developed that have much longer run clip and stronger power than those that current power beginnings, viz. lithium batteries, provide. A fuel cell, which is a device that generates electricity by a chemical reaction, is considered the promising campaigner for replacing them. Among assorted fuel cells, direct methyl alcohol fuel cell ( DMFC ) is the most suited power beginning because it does non necessitate any fuel processing equipment and can be operated at low temperatures. Besides DMFC has advantages of easy transit and storage of the fuel, and decreased system weight and size [ 1, 2 ] . However, in order to develop a micro fuel cell needs much scrutiny due to a limited weight and size and a high public presentation, lastingness. To run into these demands, the MEA has to execute good and the stack design has to be really compact.
DMFC description DMFC description
Concept of DMFC Concept of DMFC
Direct-methanol fuel cells or DMFCs are a subcategory of proton-exchange fuel cells where the methyl alcohol fuel is non reformed as in the indirect methyl alcohol fuel cell, but fed straight to the fuel cell runing at a temperature. Because the methyl alcohol and H2O is fed straight into the fuel cell, steam reforming is non required. Storage of methyl alcohol is much easier than for H as it does non necessitate high force per unit areas or low temperatures, because methyl alcohol is a liquid from to. The energy denseness of methyl alcohol – the sum of energy contained in a given volume – is an order of magnitude greater than even extremely tight H. The waste merchandises with these types of fuel cells are carbon dioxide and H2O.
The efficiency of current direct-methanol fuel cells is low due to the high pervasion of methyl alcohol through the membrane stuffs used, which is known as methyl alcohol crossing over.
Presents DMFCs are limited in the power they can bring forth, but can still hive away a high energy content in a little infinite. This means they can bring forth a little sum of power over a long period of clip. This makes them soon ill-suited for powering vehicles ( at least straight ) , but ideal for consumer goods such as nomadic phones, digital cameras or laptops.
Methanol is toxic and flammable. However, the International Civil Aviation Organization ‘s ( ICAO ) Dangerous Goods Panel ( DGP ) voted in November 2005 to let riders to transport and utilize micro fuel cells and methyl alcohol fuel cartridges when aboard airplanes to power laptop computing machines and other consumer electronic devices. On September 24th, 2007, the US Department of Transportation issued a proposed rulemaking to let air hose riders to transport fuel cell cartridges on board. The Department of Transportation issued a concluding opinion on April 30, 2008, allowing riders and crew to transport an sanctioned fuel cell with an installed methyl alcohol cartridge and up to two extra spare cartridges. It is deserving observing that 200 milliliters maximal methanol cartridge volume allowed in the concluding opinion is dual the 100 milliliter bound on liquids allowed by the Transportation and Security Administration in carry-on bags.
Chemical reaction Chemical reaction
The DMFC relies upon the oxidization of methyl alcohol on a accelerator bed to organize C dioxide. Water is consumed at the anode and is produced at the cathode. Positive ions are transported across the proton exchange membrane & # 8211 ; frequently made from Nafion ( Nafion is a sulfonated tetrafluoroethylene copolymer discovered in the late sixtiess by Walther Grot of DuPont [ 3 ] . It is the first of a category of man-made polymers with ionic belongingss which are called ionomers ) & # 8211 ; to the cathode where they react with O to bring forth H2O. Electrons are transported through an external circuit from anode to cathode, supplying power to connected devices.
Figure 1. The overall reaction in a DMFC
The reactions are:
Anode:
Cathode:
Overall reaction:
Methanol and H2O are adsorbed on a accelerator normally made of Pt and Ru atoms, and lose protons until C dioxide is formed. As H2O is consumed at the anode in the reaction, pure methyl alcohol can non be used without proviso of H2O via either inactive conveyance such as back diffusion, or active conveyance such as pumping. The demand for H2O bounds the energy denseness of the fuel.
Presents, Pt is used as a accelerator for both half-reactions. This contributes to the loss of cell electromotive force potency, as any methyl alcohol that is present in the cathode chamber will oxidise. If another accelerator could be found for the decrease of O, the job of methyl alcohol crossing over would probably be significantly lessened. Furthermore, Pt is really expensive and contributes to the high cost per kW of these cells.
During the methanol oxidization reaction C monoxide is formed, which strongly adsorbs onto the Pt accelerator, cut downing the surface country and therefore the public presentation of the cell.
Components of typical DFMC Components of typical DFMC
DMFC by and large consists of membrane-electrode assembly ( MEA ) , gas diffusion bed ( GDL ) , bipolar home bases. MEA is comprised by a polymer electrolyte membrane and electrode accelerator beds and gas diffusion beds. Polymer electrolyte membrane has to hold two belongingss: carry oning ions from the anode to the cathode and supplying electrical insularity between the anode and the cathode to coerce the negatrons to travel from the anode to the cathode all the manner through an external circuit. A sulfonated tetrafluorethylene copolymer such as Nafion developed by Dupont is normally used as a polymer electrolyte membrane but late hydrocarbon series which improved a methyl alcohol crossing over get down to be applied [ 4 ] . The best accelerator for both the anode and the cathode is platinum. The Pt is prepared into really little atoms on the surface of C pulverizations to increase the reaction country and rate of the electrodes [ 5 ] . A C endorsing stuff such as C fabric or paper is normally called the gas diffusion bed. It provides the basic mechanical construction for the electrode and carries away reaction merchandises from the accelerator and reactants towards T
he accelerator. Besides it provides an electrical connexion between the accelerator and the bipolar home base. Bipolar home bases separate single cells in a fuel cell stack. Each bipolar home base distributes reactants over the cell surface through the system of channels and collects current produced by single cell and transports this current from one cell to another [ 6 ] . Machined black lead is traditionally used as the bipolar home bases due to a good conduction but metals and composite stuffs are under development to replace for it because of its high cost and larger volume. Gasket to forestall liquid and gas escape is PTFE and stop home bases are a unstained steel or a Cu coated by gold.
Figure 2.
Construction and chief constituents of DMFC.
Figure 2 shows building of direct methyl alcohol fuel cell, holding MEA and the modular constituents of anode and cathode. MEA is mounted within bipolar home bases dwelling of two electrically carry oning field home bases in which channels are fabricated, as shown in Figure 2. PTFE ( Teflon ) gaskets are fitted next to flux channels to move as efficient gas seals around the borders of the Nafion membrane [ 7, 8 ] .
Micro Fuel Cell Stack for cellular Phone Micro Fuel Cell Stack for cellular Telephone
Developments of micro fuel cell for cellular phones Developments of micro fuel cell for cellular phones
Many micro fuel cell designed for cellular phones were demonstrated by many Nipponese and Korean electronic companies such as Toshiba, Hitachi, Fujitsu and Samsung.
| Company | Size ( milliliter ) | Power ( W ) | Year of presentation |
| Toshiba | 200 | 0.3 | 2005 |
| Hitachi | 122 | 0.3 | 2005 |
| Fujitsu | 160 | 9 | 2005 |
| Samsung | 100 | 2 | 2006 |
Table 1. Features of the fuel cells for cellular phones
Fuel cells mentioned in Table 1 are based on DMFC engineering. They are compact between 100 and 200 milliliters and bring forth power between 0.3 and 9 W. The fuel cell for the cellular phone developed by Toshiba is a intercrossed type, which is combined at the dorsum of the French telephone with lithium ion battery. It can increase the battery tally clip 2.5 times longer with a individual refill. The fuel cell for the cellular phone developed by Hitachi is besides a intercrossed type but it is more compact. One characteristic is that whenever its methyl alcohol fuel becomes low, it can be easy refilled from a compact cartridge [ 9 ] . The fuel cell developed by Fujitsu enables eight hours of uninterrupted talk and improved the capacity by increasing the methyl alcohol concentration from 30 % to over 99 % and developing a method of recycling the generated H2O [ 10 ] . Samsung demonstrated the universe & # 8217 ; s smallest fuel cell nomadic device courser. It produces 2W is 5mm midst and weight 5.3 ounces. It includes user-replaceable methyl alcohol cartridges. It is designed to reload the battery system in a PDA, cell phone or digital camera [ 11 ] .
Proposed design of micro fuel cell Proposed design of micro fuel cell
Stack design is being suggested to be with five cells that have an electrode country about. It has the internal manifolds for supply of air and fuel. Its dimensions are 50 & # 215 ; 75 & # 215 ; 15 millimeter, this dimensions are common PDA phone sizes. Each cell of this DMFC stack has an active country about, such country is sensible for current cell size. Ballard Power Systems Inc. recommends Nafion based MEA with GDS22100 on the anode and P75T on the cathode. GDS22100 prevents methanol crossing over by commanding the methanol pervasion rate. Figure 3 shows I-V curves for the mentioned thought [ 12 ] .
Figure 3. Voltage versus current denseness for Ballard & # 8217 ; s MEA.
Graphite could be used as bipolar home bases with two flow waies.
It could be easy estimated that proposed fuel cell stack will give approximately 3W power, this power is adequate to bear down PDA phone battery.
Such fuel cell could be used like courser or even like constituent of mentioned intercrossed power beginning for nomadic devices, such system can supply longer lifetime than common Lithium battery, but the worse things of such system are increasing sizes and mass of PDA, so it is still necessary to happen some better stuffs and engineerings for DMFC.
Of class is should be noted that such & # 8220 ; design & # 8221 ; is merely proposal and in order to cipher end product power and other of import characteristics experimental work must be provided, otherwise it is merely treatment about theoretical possibility.
Mentions Mentions
1. M.S. Wilson and S. Gottesfeld, High Performance Catalyzed Membranes of Ultra-low Pt Loadings for Polymer Electrolyte Fuel Cells, Electrochem. Soc. , 139, L28 ( 1992 ) .
2. D.H. Jung, S.Y. Cho, D.H. Peck, D.R. Shin, and J.S. Kim, Preparation and public presentation of a Nafion/montmorillonite nanocomposite membrane for direct methyl alcohol fuel cell, J. Power Sources, 118, 205 & # 8211 ; 211 ( 2003 ) .
3. Church, Steven ( January 6, 2006 ) . “ Del. house installs fuel cell ” , The News Journal, p. B7.
4. C. Heitner-Wirguin, Recent advances in perfluorinated ionomer membranes: construction, belongingss and applications, J. Membr. Sci. , 120 1 & # 8211 ; 33 ( 1996 ) .
5. H. Liu, C. Song, L. Zhang, J. Zhang, H. Wang, and D.P. Wilkinson, A reappraisal of anode contact action in the direct methyl alcohol fuel cell, J. Power Sources, 155, 95 & # 8211 ; 110 ( 2006 ) .
6. A.A. Kulikovsky, Voltage loss in bipolar home bases in a fuel cell stack, J. Power Sources, 160, 431 & # 8211 ; 435 ( 2006 ) .
7. W. Vielstich, A. Lamm, and H.A. Gasteiger, Handbook of Fuel Cell, ( Wiley, Chichester, England, 2003 ) , pp. 306 & # 8211 ; 7.
8. M. Hogarth, P. Christensen, A. Hamnett, and A. Shukla, the design and building of high-performance direct methyl alcohol fuel cells. 1. Liquid-feed systems, J. Power Sources, 69, 113 & # 8211 ; 124 ( 1997 ) .
9. ( September 28, 2005 ) , hypertext transfer protocol: //www.embeddedstar.com, KDDI, Toshiba, Hitachi Showcase Mobile Phone Fuel Cells at CEATEC Japan.
10. ( July 6, 2005 ) hypertext transfer protocol: //www.nttdocomo.com, NTT DoCoMo Enhances Prototype Micro Fuel Cell for FOMA Handsets.
11. ( December 6th, 2006 ) hypertext transfer protocol: //www.techshout.com, Smallest Fuel Cell Mobile Charger developed by Samsung and SAIT Team.
12. hypertext transfer protocol: //www.ballard.com/Carbon_Fiber/Gas_Diffusion_Layer_Products/Specification_Sheets.htm, Paper-based Diffusion Layer for Direct Methanol Fuel Cells.
