Fuel Cells - Green Power - Martin's Marine Engineering Page

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References:Bill McKibben, “A Special Moment inHistory.” The Atlantic Monthly,May, 1998.James J. MacKenzie, “Oil as a FiniteResource: When is GlobalProduction Likely to Peak?”World Resources Institute, March1996.Colin Campbell and Jean H. Laherrère“The End of Cheap Oil .” ScientificAmerican, March 1998.“Busting Through with Ballard.”Financial Times EnergyWorld. Number Five, Winter1998.Jacques Leslie. “The Dawn of theHydrogen Age.” Wired. October,1997.McGraw-Hill Dictionary of Scientificand Technical Terms. 1994.Motor Vehicle Facts and Figures.American AutomobileManufacturers Association. 1998.Resources:World Resources Institutehttp://www.wri.orgInternational Fuel Cellshttp://www.hamiltonstandard.com/ifc-onsiUnited Nations Framework Conventionon Climate Changehttp://www.unfccc.de/Linkages http://www.iisd.ca/linkages/Environmental Protection Agency,Alternative Fuelshttp:// www.epa.gov/omswwwU.S. Fuel Cell Councilhttp://www.usfcc.comFuel Cells 2000http://fuelcells.org– CF 2 – CF – CF 2 –lOlCF 2lCF – CF 3lOlCF 2lCF 2lSO 3 - H +Chemical structureof membranematerial;Nafion TM by DuPontDefinitions:Electrochemical reaction: A reactioninvolving the transfer ofelectrons from one chemicalsubstance to another.Fuel cell: An electrochemical devicethat continuously converts thechemical energy of externallysupplied fuel and oxidant directlyto electrical energy.Oxidant: A chemical, such as oxygen,that consumes electrons in anelectrochemical reaction.Electrolyte: A substance composed ofpositive and negative ions,Ion: An atom that has acquired anelectrical charge by the loss or gainof electrons.1 micron = 10 -6 m, 10 -4 cm, 10 -3 or0.001 mm = 1 mPolymer: A substance made of giantmolecules formed by the union ofsimple molecules (monomers).Thermal: Pertaining to heatStructure of Polymer Electrolyte MembranesThe polymer electrolyte membrane is a solid, organic polymer,usually poly[perfluorosulfonic] acid. A typical membrane material,such as Nafion TM , consists of three regions:(1) the Teflon-like, fluorocarbon backbone, hundreds of repeating– CF 2 – CF – CF 2 – units in length,(2) the side chains, –O– CF 2 – CF – O– CF 2 – CF 2 –, which connect themolecular backbone to the third region,(3) the ion clusters consisting of sulfonic acid ions, SO 3-The negative ions, SO 3 - , are permanently attached to the side chainand cannot move. However, when the membrane becomes hydratedby absorbing water, the hydrogen ions become mobile. Ion movementoccurs by protons, bonded to water molecules, hopping from SO 3 - siteto SO 3 - site within the membrane. Because of this mechanism, thesolid hydrated electrolyte is an excellent conductor of hydrogen ions.Future OpportunitiesPolymer electrolyte membrane fuel cells arelimited by the temperature range over whichwater is a liquid. The membrane must containwater so that the hydrogen ions can carry thecharge within the membrane. Operating polymerelectrolyte membrane fuel cells attemperatures exceeding 100˚C is possibleunder pressurized conditions, required to keepthe water in a liquid state, but shortens thelife of the cell. Currently, polymer electrolytemembranes cost about $100/square foot.Costs are expected to decrease significantlyas the consumer demand for polymer electrolytemembrane fuel cells increases.Remaining Challenges:H + .• producing membranes not limited by thetemperature range of liquid water,possibly based on another mechanism forprotonic conduction• reducing membrane cost by developingdifferent membrane chemistriesThis document, and more, is available for download at Martin's Marine Engineering Page - www.dieselduck.net
The Polymer Electrolyte Membrane Fuel CellAs little as 10 years ago, vehicles powered byfuel cells seemed more science fiction than fact.Today, development of fuel cell technology for transportationis made possible due to the polymer electrolytemembrane fuel cell. This type of fuel cell is also knownas the proton exchange membrane fuel cell, the solidpolymer electrolyte (SPE TM ) fuel cell and simply, polymerelectrolyte fuel cell. It is often referred to simply asthe “PEM” fuel cell. The center of the fuel cell is thepolymer electrolyte membrane. For all five families offuel cells, it is the electrolyte that defines the type of fuelcell, so the discussion of the polymer electrolyte membranefuel cell should logically begin with its electrolyte,the membrane.The Polymer Electrolyte MembraneAn ordinary electrolyte is a substance that dissociatesinto positively charged and negatively charged ions inthe presence of water, thereby making the water solutionelectrically conducting. The electrolyte in apolymer electrolyte membrane fuel cell is a type ofplastic, a polymer, and is usually referred to as a membrane.The appearance of the electrolyte variesdepending upon the manufacturer, but the most prevalentmembrane, Nafion TM produced by DuPont,resembles the plastic wrap used for sealing foods. Typically,the membrane material is more substantial thancommon plastic wrap, varying in thickness from 50 to175 microns. To put this in perspective, consider that apiece of normal writing paper has a thickness of about 25microns. Thus polymer electrolyte membranes havethicknesses comparable to that of 2 to 7 pieces of paper.In an operating fuel cell, the membrane is well humidifiedso that the electrolyte looks like a moist piece ofthick plastic wrap.to carry positive charge through the membrane. Inpolymer electrolyte membrane fuel cells these positiveions are hydrogen ions, or protons, hence the term –proton exchange membrane. Movement of the hydrogenions through the membrane, in one direction only,from anode to cathode, is essential to fuel cell operation.Without this movement of ionic charge within the fuelcell, the circuit defined by cell, wires, and load remainsopen, and no current would flow.Because their structure is based on a Teflon TM backbone,polymer electrolyte membranes are relatively strong,stable substances. Although thin, a polymer electrolytemembrane is an effective gas separator. It can keep thehydrogen fuel separate from the oxidant air, a featureessential to the efficient operation of a fuel cell. Althoughionic conductors, polymer electrolytemembranes do not conduct electrons. The organicnature of the polymer electrolyte membrane structuremakes them electronic insulators, another featureessential to fuel cell operation. As electrons cannotmove through the membrane, the electrons produced atone side of the cell must travel, through an externalwire, to the other side of the cell to complete the circuit.It is in their route through the circuitry external to thefuel cell that the electrons provide electrical power torun a car or a power plant.Polymer electrolyte membranes are somewhat unusualelectrolytes in that, in the presence of water, which themembrane readily absorbs, the negative ions are rigidlyheld within their structure. Only the positive ionscontained within the membrane are mobile and are freeThis document, and more, is available for download at Martin's Marine Engineering Page - www.dieselduck.net7
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Page 3 and 4: What’s InsideFuel Cells- Green Po
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Page 20 and 21: Regenerative Fuel CellA regenerativ
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Page 24 and 25: Other Fuel Cell TechnologiesThe ele
Page 26 and 27: Wood Coal OilNaturalGasHydrogenHydr
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Page 32 and 33: References:Jason Mark. “Zeroing o
Page 34 and 35: References:“Report to the Nation:
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