Principles of Chemistry
Principles of Chemistry CHEM 135
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Popular in Chemistry
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Date Created: 10/13/15
Fuel Cells Fuel Cell Descriptions tnrougn an rnt U r tnrt as lrl a hall n are suoolled Contlnuoualy as n an englne Because electncal energy ls generated Stand polrlt Attractlvefuel Cell Characterlstlcs lrlclude nlgn energy conyerslon errlclency rnodulardesl n yery low cnernlcal and acoustlcal oollutlon ruel flexlblllty cogeneratlon caoaolllty raold load response n electnc current Fuel cells conslst or an electrolyte rnatenal Wnlcn ls sandwrcned ln between Wotth electrodes porous anode and catnode Tne lnoutruel passes oyer oyer a and electrons Tne electrons go tnrougn an external clrcult to serve an electnc load At tne electrode lons cornolne to create byrproductsy onrnanly Water and co2 l l TyM Hm Typa of Fuel Cells There are tour prrrhary types ot tuet ceus whrch are based oh the etectrotyte erhptoyeo Phospho c acrd fue CeH Mo ten Carbonate fue CeH Sohd oxrde fue CeH Proton exchange membranefue CeH A corhparrsoh ot the fue ceH types rs surhrharrzeo petow mo hm Isorc pmrc Hummus llaltzncmaamte cam puma u l OPERATING 375 F 12qu mm I7S F TEMPERATURE 1 9D CJ t55n c mnn cj Em PE iELECTROLYTE u Jkamre Tw E s Hydmgzn I 2 o t 2 R Reform Refarm at W39 Exmm W IxtemaJlnlemal oxTDANT 0 An ConOzAu WAR ESTER c monoa monoa SEES w Fuet ceus are typrcahy grouped rhto three sectrohs uet Processor 2 Power Sectroh fue ceH stack 3 PowerCondmoner uwmu warm mm mam me Fun m mwat unm unwsn mm mam 53mm mm m m thetuet processor atuet such as haturat gas rs retorrheo to poostthe cohcehtratroh ot hydro eh The hydro enr ch tuet and oxygen arr theh teed rhto the power sectroh to produce DC etectrrcrty aho reusapte heat The power sectroh mdudes a tuet ceH stack whrch rs a serres ot etectrooe ptates tnterconnected to produce a set ouanttty ot electrtcal power Tne output DC electrtctty ts tnen converted to AC electrtctty tn tne power condtttontng sectton Wnere tt also reduces yoltage sptxes and narrnontc dtstorttons Phosphoric Acid Fuel Cells Tne Pnospnortc Actd Fuel Cell PAFC ts tne rnost rnature tuel cell tecnnology tn terrns ot systern development and cornrnerctaltzatton acttytttes lt nas been under u tptn tttt ttttt tttan tn tne deyeloprnent and dernonstratton ottnetecnnology tn excess ot 500 rntllton t at ago because ot tne peltet that arnong tne low ternperature tuel cells ltWaS tne only t tttt t gy could naye WtdeSpread appltcaotltty tn tne nearterrn PAFC Design and Operation contatned tn aTe on bonded stltcone carotde rnatrtx Tne srnall pore structure ottnts rnatrtx preterenttally xeeps tne actd tn place tnrougn captllary actton Some ac d any nours ot operatton Plattnurn catalyzed porous carbon electrodes are used on ootn tne tuel anode and oxtdant catnode stdes ot tne electrolyte parallel grooyestorrned tnto carbon or carbonrcomposlte plates Tnese plates are tne adtacent cell in rnost est n the plates are otpolar tn tnat tney naye grooyes on ootn stdes 7 one stde suppltes tuel to tne anode of one cell Wntle tne otner stde suppltes atr or oxygen to tne catnode of tne adtacent cell Tne oyproduct Water ts rernoyed as stearn on tne catnode atr or oxygen stde of eacn cell by owing excess oxtdant past tne packs of tne electrodes Tnts water rernoyal procedure requtres tnat tne systern be operated at ternperatures around 375 F 190 C At lowertemperaluresy tne productwaterwtll dtssolye tn tne electrolyte and not be rernoyed as stearn At approxtrnately 4mquot 210 C tne pnospnortc actd oegtns to decornpose contatntng cooltng cnannels evenfew cells Ettner atror a ltoutd coolant sucn as Watery can be passed tnrougn tnese cnannelsto rernoye excess neat The PAFC reactions that occur are Amch tt32trn 39 cittuut I o i t Zc39vl 120 At the anode hydrogen ts spttt tnto two hydrogen tons H t Whtch pass through the pass through etectrtc toad to the cathode At the cathode the hydrogen etectrons and oxygen cornotneto torrn Water Thts ts shown oetow e Load when Deptaad 0mg he mg gt and mm 5155 H 10 cut rua tr Oman tr Anode etlrolyle Cathode The standard ernt or the ceH can be catcutated trorn the standard reductton potenttats ttts eouat to 123 y Thusthe ceH reactton ts spontaneous under r u u H m L tthe yandmey atorntc spectes prtorto etectron transter They are eectrncaIaysts Metats such as ptattnum ntchet and rhod urn are good etectrocatatysts tn addttton to the H20 System a number or other ruet cetts have been deyetoped Anode C3HE9 6H20 gt 3c029 20H39aq 2oe ath de so 20H a 20e gt10H o Oyeratt C3HE9 5029 e 3c029 tr 1200 The oyeratt reactton ts tdenttcat to the ourntng or propane tn oxygen PAFC Performance Characteristics h r p t 42 The htgher errtctency destgns operate wtth pressurtzed reactants The htgher errtctency pressurtzed destgn reoutres rnore cornponents and tthety htgher cost PAFC power ptants suppty usaote therrnat energy at an etttctency or 37 to 41 A portton otthetherrnat energy can be supptted atternperatures ot250 quotFlo 3oo quotF Howevery the rnatortty or the therrnat energy ts supptted attso quotF The PAFC has a power derlslty of M30 to l75 Wattsft2 of actlve Cell area Molten Carbonate Fuel Cells The Molterl Carbonate Fuel Cell MCFC evolved from Work lrl he l960 5 alrned at on coal seerns less llkely today operatlon on coaldenyedruel gases ornatural gas ls ylable MCFC Design and Operation a rnolten carbonate salt rnlxture as lts electrolyte The cornposltlon or the electrolyte yanes but usually conslsts or llthlurn carbonate and potasslurn b nate At the operatlng temperature or about 0 quotF 650 C the salt mlxture The electrol r lnsulatlng and chernlcally lnert ceramlc LlAlOZ matrlx The MCFC reactlons that occur are H2 203239 gt H20 co 2e 0 203239 e2coa 2e Cathode reactlon 02 2C024e39 gt 2coaz39 Arlode reactlorl The anode process lnyolyes a reactlon between hydrogen and carbonate lons c031 orn the electrolyte Whlch produces Water and carbon dloxlde cog whlle releaslng electronsto the anode The cathode process cornblnes oxygen and co2 rornt the electrolyte The need ror co2 lrl the oxldarlt strearn requlres a systern ror collectlng Drum new mm mat H gt IndVln lmG K 39 lhzmout 02 e a 20 5 4 a2 02 Wle 4 ommln 1 was army Emma l r a lu Cell decreases arld Wlth ll he rnagtltlrnurn theoretlcal fuel efflclerlcy Orl the other hand increasing the operating temperature increases the rate of the electrochemical reaction and thus the current which can be obtained at a given voltage The net effect forthe MCFC is that the real operating voltage is higherthan the operating voltage for the PAFC at the same current density The higher operating voltage of the MCFC means that more power is available at a higher fuel efficiency from a MCFC than from a PAFC of the same electrode area As size and cost scale roughly with electrode area this suggests that a MCFC should be smaller and less expensive than a quotcomparablequot PAFC The MCFC also produces excess heat at a temperature which is high enough to yield high pressure steam which may be fed to a turbine to generate additional electricity ln combined cycle operation electrical efficiencies in excess of 60 have been suggested for mature MCFC systems The MCFC operates at between 1110 F 600 C and 1200 F 650 C which is necessary to achieve suf cient conductivity ofthe electrolyte To maintain this operating temperature a higher volume of air is passed through the cathode for cooling purposes As mentioned above the high operating temperature ofthe MCFC offers the possibility that it could operate directly on gaseous hydrocarbon fuels such as natural gas The natural gas would be reformed to produce hydrogen within the fuel cell itself The need for C02 in the oxidant stream requires that C02 from the spent anode gas be collected and mixed with the incoming air stream Before this can be done any residual hydrogen in the spent fuel stream must be burned Future systems may incorporate membrane separators to remove the hydrogen for recirculation back to the fuel stream At cell operating temperatures of 1200 F 650 C noble metal catalysts are not required The anode is a highly porous sintered nickel powder alloyed with chromium to prevent agglomeration and creep at operating temperatures The cathode is a porous nickel oxide material doped with lithium Signi cant technology has been developed to provide electrode structures which position the electrolyte with respect to the electrodes and maintain that position while allowing for some electrolyte boiloff during operation The electrolyte boiloff has an insigni cant impact on cell stack life A more signi cant factor of life expectancy has to do with corrosion of the cathode The cell performance is sensitive to operating temperature A change in cell temperature from 1200 F 650 C to 1110 F 600 C results in a drop in cell voltage of almost 15 The reduction in cell voltage is due to increased ionic and electrical resistance and a reduction in electrode kinetics Solid Oxide Fuel Cells reduces corrostoh cohstoerattohs aho ettrhthates the etectrotyte rhahagerheht cohoucttytty th such a Ceramtcy howevery the system must operate at about 1830 quotF 1000 quotFt oosstbte and the Waste heat trorh such a oeytce wouto be eastty uttttzeo by SOFC naign and Operation The SOFC ts based upon the use ot a sotto cerarhtc as the etectrotyte The oreterreo materta t oehse yttrtastabtttzeo ztrcohta ts ah exceHent cohouctor ot hegattyety devtces thh The atr ot the tube A tayer ot etectrotyte ts theh depostteo oh the outstoe ot the cathode and tthatty a tayer ot ahooe ts depostteo oyer the etectrotyte A number ot cetts are cortrtected together by htgh temperature serhtcortductor corttacts th Operguon hydrogen or carbon monoxtde c0 th thetuet strearh reacts wtth oxtde tons to or the anode The etectrohs bass outstoe the tuet ceH through the toad and back to the co as WeH as hydrogen as tts otrect tuet The SOFC reacttohsthat occur thctuoe man to o e ttzo V 2 out o39 co t 2 ch m39 4 ago t co t 35 Clmndareamnn 12 T 20 nutmeg mama mass m out 7 i gt End mm szs 39 thot out mt tn Uxmnn tn v A s any EtKuDMr emu n t about 232 Aft2 Ltfettrnes tn excess of 30000 nours for stng e CeHs nave been demonstrated as nave a number of neatCoot Cydes Present y avanabte Argonne Nattonat Laboratones suggests tnat pressurtzed systerns coutd ytetd ruet etttctenctes ot 00 t o quotF 1000 quot3 ts acnteyed tnrougn rnatntenance ot proper yoturne ottne atr strearn tnto tne ceH rnperature ot posstotttty ot tnternat retorrntng As tn tne MCFC co does not act as a potson and as atuet tu t ceH type to sutrur tt can toterate seyerat orders ot rnagnttude rnore sutrurtnan otnerruet ceHs Tne anode Conststs of rnetaHtc Nt and Yzoystabthzed ZrOz sketeton wntcn expanston Coef ctent Comparab e to tnose of tne otner CeH rnatena s Tne anode reactant and product gases Tne Sredoped tantnanurn rnangantte tatpSrXMnoa y o tn conductor Strnttar to tne anodet tne catnode ts a porous structure tnat rnust perrntt raptd rnass transport of reactant and product gases Tne t u r1000 starteup ttrne Tne ceH performance ts yery senstttye to operattng ternperature A t a oxygen torts yst andto retatn neat wntte sucn reoutrernents are acceptaote tn a uttttty apphcatton they are not consistent with the demands of most transportation applications nor do they lend themselves to small portable or transportable applications Proton Exchange Membrane Fuel Cells The Proton Exchange Membrane Fuel Cell PEFC offers an order of magnitude higher power density than any other fuel cell system with the exception of the advanced aerospace alkaline fuel cell which has comparable performance The PEFC can operate on reformed hydrocarbon fuels with pretreatment and on air The use of a solid polymer electrolyte eliminates the corrosion and safety concerns associated with liquid electrolyte fuel cells lts low operating temperature provides instant startup and requires no thermal shielding to protect personnel Recent advances in performance and design offer the possibility of lower cost than any other fuel cell system PEFC Design and Operation The PEFC uses as its electrolyte a polymer membrane This membrane is an electronic insulator but an excellent conductor of hydrogen ions The materials used to date consist ofa fluorocarbon polymer backbone similar to Teflon to which are attached sulfonic acid groups Nafion The acid molecules are fixed to the polymer and cannot quotleakquot out but the protons on these acid groups are free to migrate through the membrane With the solid polymer electrolyte electrolyte loss is not an issue with regard to stack life The electrolyte membrane looks rather like a thick sheet of food wrap and can be handled easily and safely The anode and cathode are prepared by applying a small amount of platinum black to one surface ofa thin sheet of porous graphitized paper which has previously been wetproofed with Te on The electrolyte is then sandwiched between the anode and cathode and the three components are sealed together under heat and pressure to produce a single quotmembraneelectrode assemblyquot MEA This assembly which is the heart of the fuel cell is less than a millimeter thick The anode and cathode are contacted on the back side by flow eld plates made of graphite in which channels have been formed The ridges between the channels make electrical contact with the backs ofthe electrodes and conduct the current to the external circuit The channels supply fuel to the anode and oxidant to the cathode The electrode reactions in the PEFC are analogous to those in the PAFC Hydrogen from the fuel gas stream is consumed at the anode yielding electrons to the anode and producing hydrogen ions which enter the electrolyte At the cathode oxygen combines with electrons from the cathode and hydrogen ions from the electrolyte to produce water The water does not dissolve in the electrolyte and is instead rejected from the back ofthe cathode into the oxidant gas stream As the PEFC operates at about 175 quotF 80 ct tne water ts produced as ttoutd water and ts arrted out ot tne tuet ceH by excess oxtdant ttow muutcuut Ni V m V m Calhndnv tart 02 s 0H Ou39 znzo meta otptm Oman m but H 4 in Vm uile S 39 Hzmom H7 4 gt1 rt ruwn 4 ownmm 2 Am awn emu 850 Am2 are acnteyed at 0 7 ycett on nydrogen and oxygen at 05 psta and oyer 500 Am2 ts obtatned on atr at tne same pressure Earty tn 1987 Battard Power Systems recetyed an expertmenta membrane wnen ptaced tn t new Dow membrane produced 4000 Mt2 at 0 5 ycett on nydrogen and owgen at 05 sta Tnat re resents a power denstty ot 2000 Mt2 At0 7 ycett tne BattardDow expertmenta tecnnotogy produced 2000 Am on hydrogenoxygen at 05 psta and oyer 1000 Am2 on nydrogenatr at 05 psta Tne power denstty descrtbed aboye ts rougnty a tactor ot 10 greater tnan tnat obsetyed tortne otner tuet ceH systems Tnts represents a potenttat tor a stgntttcant reductton tn stackstze and cost oyertnat posstbte tor otner systems n productton tuet ceH stacks Battard ts acnteytng 0 7 y at 050 Am2 on nydrogen on atr at psta e stack dtmenstons are x x1 7 my ytetdtng a stackromy power denstty ot oyer 5 4 WW3 Power denstttes approacntng 14 2 kWt are certatnty teastbte A nearrterm SySIem tnctudtng tuet and owdant controts coottng and product water remoyat wntcn operates on nydrogen and atr at 45 pstawttt proytde t 25 kW 3 and Wtb tne tuet ceH ts operated T nus a PAFC and MCFC or a PEFC operattng at 0 7 tnat at a gtyen stack etttctency ceH vottage tne PEFC wttt dettyer more current and 10 thus more power for a given size fuel cell Equivalently the PEFC can provide the same power at a given stack efficiency from a smaller less costly stack When hydrocarbon fuels are to be used or air is to be used as the oxidant higher temperature fuel cells the MCFC the SOFC and to some extent the PAFC have an ef ciency advantage overthe PEFC at the system level The highertemperature waste heat of these systems can be used to drive air compressors to assist in the reforming of hydrocarbon fuels and in the case ofthe MCFC and SOFC to produce steam for thermal electric generation or other thermal load The PEFC can be operated using either air or liquid cooling For those applications requiring a compact power generator liquid cooling will be the method of choice This will also be the case ifthe excess heat is to be used for space or hot water heating in residential or utility cogeneration applications In addition to pure hydrogen the PEFC can also operate on reformed hydrocarbon fuels without removal or recirculation ofthe byproduct C02 The traces of CO produced during the reforming process must be converted to C02 by a selective oxidation process before the fuel gas enters the fuel cell This is a simple catalytic process which can easily be integrated into a fuel supply system The PEFC can operate on air As is true with all fuel cells performance is improved by pressurizing the air In any application there will be a tradeoff between the energy and nancial cost associated with compressing air to higher pressures and the improved performance Pressures above 45 psia are not likely to be advantageous for most applications Because the PEFC uses a solid electrolyte a signi cant pressure differential can be maintained across the electrolyte This allows the operation of the PEFC with low pressure fuel and higher pressure air if desired to optimize performance The PEFC uses platinum at both the anode and cathode At the end of the NASA program typical platinum loadings were about 0001 ozin2 for each electrode At the cell performance then being obtained this represented a very significant cost penalty as compared with the PAFC With the present performance ofthe PEFC production units even at 0001 ozin2 platinum requirements would be about 060 ozkW for operation on hydrogen and air Signi cant reductions in platinum loading are possible Work at Los Alamos National Laboratory and Texas AampM University has demonstrated techniques to reduce the platinum loading to about 000007 ozin2 while maintaining performance This represents a requirement ofabout 0042 ozkW on air or about 0021 ozkW on oxygen Further reductions in platinum loading and further improvements in PEFC performance can reasonably be expected to reduce platinum requirements to 0035 ozkW or about 2kW Because the PEFC operates at low temperatures and does not contain a liquid electrolyte catalyst migration and recrystallization are not problems Cell operating lifetimes in excess of 50000 hours were demonstrated for the PEFC during the NASA program The PEFC typically operates at 160 F 70 C to 185 F 85 C About 50 of maximum power is available immediately at room temperature Full operating power is available within about 3 minutes under normal conditions The low temperature of operation also reduces or eliminates the need forthermal insulation to protect personnel or other equipment The excess heat can be used for space heating or for residential hot water but is not hot enough for generating steam for fuel reforming or for utility bottoming cycles In addition to the four major types of fuel cells discussed above the following fuel cells have also been developed Alkaline Fuel Cells Long used by NASA on space missions these cells can achieve power generating ef ciencies of up to 70 percent They were used on the Apollo spacecraft to provide both electricity and drinking water Their operating temperature is 150 to 200 OC about 300 to 400 OF They use an aqueous solution ofalkaline potassium hydroxide soaked in a matrix as the electrolyte This is advantageous because the cathode reaction is faster in the alkaline electrolyte which means higher performance Until recently they were too costly for commercial applications but several companies are examining ways to reduce costs and improve operating flexibility They typically have a cell output from 300 watts to 5 kW Anode H2g 20H39aq gt 2H20I 2e39 Cathode 1202g H20I 2e39 gt 20H39aq Cell H2g 1202g gt H20I Direct Methanol Fuel Cells DMFC These cells are similar to the PEFC cells in that they both use a polymer membrane as the electrolyte However in the DMFC the anode catalyst itself draws the hydrogen from the liquid methanol eliminating the need for a fuel reformer Efficiencies ofabout 40 are expected with this type of fuel cell which would typically operate at a temperature between 120190 0F or 50 100 0C This is a relatively low range making this fuel cell attractive for tiny to midsized applications to power cellular phones and laptops Higher efficiencies are achieved at higher temperatures A major problem however is fuel crossing over from the anode to the 12 cathode without producing electricity Many companies have said they solved this problem however They are working on DMFC prototypes used by the military for powering electronic equipment in the field Anode CH30Haq H20I gt 0029 6Haq 6e39 Cathode 6Haq 6e39 g02g gt 3H20I Cell CH30Haq 02g gt 0029 2H20I Regenerative Fuel Cells Still a very young member of the fuel cell family regenerative fuel cells would be attractive as a closedloop form of power generation Water is separated into hydrogen and oxygen by a solarpowered electrolyzer The hydrogen and oxygen are fed into the fuel cell which generates electricity heat and water The water is then recirculated back to the solarpowered electrolyzer and the process begins again These types of fuel cells are currently being researched by NASA and others worldwide ZincAir Fuel Cells ZAFC In a typical zincair fuel cell there is a gas diffusion electrode GDE a zinc anode separated by electrolyte and some form of mechanical separators The GDE is a permeable membrane that allows atmospheric oxygen to pass through After the oxygen has converted into hydroxide ions and water the hydroxide ions will travel through an electrolyte and reach the zinc anode Here they react with the zinc and form zinc oxide This process creates an electrical potential when a set of ZAFC cells are connected the combined electrical potential ofthese cells can be used as a source of electric power This electrochemical process is very similar to that of a PEFC fuel cell but the refueling is very different and shares characteristics with batteries Metallic Power is working on ZAFCs containing a zinc quotfuel tankquot and a zinc refrigerator that automatically and silently regenerates the fuel In this closed loop system electricity is created as zinc and oxygen are mixed in the presence of an electrolyte like a PEFC creating zinc oxide Once fuel is used up the system is connected to the grid and the process is reversed leaving once again pure zinc fuel pellets The key is that this reversing process takes only about 5 minutes to complete so the battery recharging time hang up is not an issue The chief advantage zincair technology has over other battery technologies is its high specific energy which is a key factor that determines the running duration ofa battery relative to its weight When ZAFCs are used to power EVs they have proven to deliver longer driving distances between refuels than any other EV batteries of similar weight Moreover due to the abundance of zinc on earth the material costs 13 for ZAFCs and zincair batteries are low Hence zincair technology has a potential wide range of applications ranging from EVs consumer electronics to military Powerzinc in southern California is currently commercializing their zincair technology for a number of different applications Problems with Fuel Cells We learned in the last section that a fuel cell uses oxygen and hydrogen to produce electricity The oxygen required for a fuel cell comes from the air In fact in the PEM fuel cell ordinary air is pumped into the cathode The hydrogen is not so readily available however Hydrogen has some limitationsthat make it impractical for use in most applications For instance you don39t have a hydrogen pipeline coming to your house and you can39t pull up to a hydrogen pump at your local gas station Hydrogen is difficult to store and distribute so it would be much more convenient if fuel cells could use fuels that are more readily available This problem is addressed by a device called a reformer A reformer turns hydrocarbon or alcohol fuels into hydrogen which is then fed to the fuel cell Unfortunately reformers are not perfect They generate heat and produce other gases besides hydrogen They use various devices to try to clean up the hydrogen but even so the hydrogen that comes out of them is not pure and this lowers the ef ciency of the fuel cell Some of the more promising fuels are natural gas propane and methanol Many people have naturalgas lines or propane tanks at their house already so these fuels are the most likely to be used for home fuel cells Methanol is a liquid fuel that has similar properties to gasoline It is just as easy to transport and distribute so methanol may be a likely candidate to power fuelcell cars Bene ts of Fuel Cells Pollution reduction is one ofthe primary goals ofthe fuel cell By comparing a fuel cellpowered car to a gasolineengine powered car and an electric car you can see how fuel cells might improve the efficiency of cars today FuelCeIIPowered Electric Car lfthe fuel cell is powered with pure hydrogen it has the potential to be up to 80 percent efficient That is it converts 80 percent of the energy content of the hydrogen into electrical energy But as we learned in the previous section hydrogen is dif cult to store in a car When we add a reformer to convert methanol to hydrogen the overall efficiency drops to about 30 to 40 percent We still need to convert the electrical energy into mechanical work This is accomplished by the electric motor and inverter A reasonable number for the ef ciency ofthe motorinverter is about 80 percent 80 we have 30 to 40percent ef ciency at converting methanol to electricity and 80percent efficiency converting electricity to mechanical power That gives an overall ef ciency of about 24 to 32 percent GasolinePowered Car The ef ciency of a gasolinepowered car is surprisingly low All ofthe heat that comes out as exhaust or goes into the radiator is wasted energy The engine also uses a lot of energy turning the various pumps fans and generators that keep it going So the overall ef ciency of an automotive gas engine is about 20 percent That is only about 20 percent of the thermalenergy content ofthe gasoline is converted into mechanical work BatteryPowered Electric Car This type of car has a fairly high efficiency The battery is about 90percent efficient most batteries generate some heat or require heating and the electric motorinverter is about 80percent efficient This gives an overall ef ciency ofabout 72 percent But that is not the whole story The electricity used to power the car had to be generated somewhere If it was generated at a power plant that used a combustion process rather than nuclear hydroelectric solar or wind then only about 40 percent of the fuel required by the power plant was converted into electricity The process of charging the car requires the conversion ofalternating current AC power to direct current DC power This process has an efficiency of about 90 percent 80 if we look at the whole cycle the efficiency of an electric car is 72 percent for the car 40 percent for the power plant and 90 percent for charging the car That gives an overall efficiency of 26 percent The overall ef ciency varies considerably depending on what sort of power plant is used lfthe electricity for the car is generated by a hydroelectric plant for instance then it is basically free we didn39t burn any fuel to generate it and the efficiency of the electric car is about 65 percent Maybe you are surprised by how close these three technologies are This exercise points out the importance of considering the whole system not just the car We could even go a step further and ask what the efficiency of producing gasoline methanol or coal is Efficiency is not the only consideration however People will not drive a car just because it is the most ef cient if it makes them change their behavior They are concerned about many other issues as well They want to know o Is the car quick and easy to refuel o Can it travel a good distance before refueling o Is it as fast as the other cars on the road o How much pollution does it produce This list of course goes on and on In the end the technology that dominates will be a compromise between efficiency and practicality Energy Security US energy dependence is higher today than it was during the quotoil shockquot ofthe 1970s and oil imports are projected to increase Passenger vehicles alone consume 6 million barrels of oil every single day equivalent to 85 percent of oil imports lfjust 20 percent of cars used fuel cells we could cut oil imports by 15 million barrels every day Security of Supply Because they are ef cient modular and fuel exible fuel cells can enable a transition to a secure renewable energy future based on the use of hydrogen A fuel cell system that includes a quotfuel reformerquot can utilize the hydrogen from any hydrocarbon or alcohol fuel natural gas ethanol methanol propane and even gasoline or diesel Hydrogen can also be produced from electricity from conventional nuclear or renewable sources Hydrogen can be extracted from novel feed stocks such as landfill gas or anaerobic digester gas from wastewater treatment plants from biomass technologies or from hydrogen compounds containing no carbon such as ammonia or borohydride Electrolysis uses an electric current to extract hydrogen from water Fuel cells in combination with solar or wind power or any renewable source ofelectricity offer the promise of a totally zeroemission energy system that requires no fossil fuel and is not limited by variations in sunlight or wind ow This hydrogen can supply energy for power needs and for transportation Physical Security Because of their distributed nature fuel cells allow the country to move away from reliance on central station power generation and longdistance high voltage power grids which are the most likely terrorist targets in any attempt to cripple our energy infrastructure High Reliability Fuel cells can be configured to provide backup power to a grid connected customer should the grid fail They can be configured to provide completely gridindependent power Or they can use the grid as the backup system Modular installation the installation of several identical units to provide a desired quantity of electricity provides extremely high reliability in specialized applications fuel cells can achieve up to 999999 reliability less than one minute of down time in a six year period High Quality Power Fuel cells offer high quality power crucial to an economy that depends on increasingly sensitive computers medical equipment and machines High Efficiency Because they make energy electrochemically and do not burn fuel fuel cells are fundamentally more efficient than combustion systems Power generation Fuel cell power generation systems in operation today achieve 40 percent fueltoelectricity ef ciency utilizing hydrocarbon fuels Systems fueled by hydrogen consistently provide 50 percent ef ciency Even more ef cient systems are under development In combination with a turbine electrical efficiencies can exceed 60 percent When waste heat is put to use for heating and cooling overall system ef ciencies exceed 85 percent Transportation According to the Energy Information Administration net oil imports surpassed 10 million barrels per day in 2000 We burned 825 million barrels per day in our cars and trucks US drivers consumed 155 billion gallons of motor fuel in 1998 o Fuel cells can help the United States move away from the current dependence on petroleum by providing more ef cient vehicles in the short term and ultimately by allowing a transition to renewable energy Fuel cell passenger vehicles are expected to be up to three times more ef cient than internal combustion engines Environmental Benefits Air pollution continues to be a primary health concern in America Exposure to ozone particulate or airborne toxic chemicals has substantial health consequences Scientists are now directly linking air pollution to heart disease asthma and cancer Recent health studies suggest polluted urban air is a comparable health threat to passive smoking Fuel cells can reduce pollution today and offer the promise of eliminating pollution tomorrow Power Generation Fuel cells offer excellent environmental performance compared to power generation technologies that rely on combustion o Based on measured data a fuel cell power plant may create less than one ounce of pollution per 1000 kilowatthours ofelectricity produced compared to the 25 pounds of pollutants for conventional combustion generating systems Fuel cell power plants are so low in emissions that some areas of the United States have exempted them from air permit requirements As we move toward use of renewable fuels in fuel cells producing electricity will become a zero emission process Motor Vehicles Fuel cell vehicles are the least polluting of all vehicles that consume fuel directly o Fuel cell vehicles operating on hydrogen stored onboard the vehicles produce zero pollution in the conventional sense Neither conventional pollutants nor green house gases are emitted The only byproducts are water and heat o Systems that rely on a reformer on board to convert a liquid fuel to hydrogen produce small amounts of emissions but would still reduce smogforming pollution by up to 90 percent compared to traditional combustion engines depending on the choice of fuel o The simple reaction that takes place inside the fuel cell is highly ef cient Even ifthe hydrogen is produced from fossil fuels fuelcell vehicles can reduce emissions of carbon dioxide a global warming concern by more than half o Tests performed on a fuel cell bus fueled by methanol showed zero emissions of particulate matter and hydrocarbons and nearzero emissions of carbon monoxide and nitrous oxides levels far below the 1998 emission standard for buses Fuel cells used as auxiliary power units APUs to power air conditioners and accessories in overtheroad trucks could reduce emissions by up to 45 from long haul vehicles and deliver economic benefits to the truck owner in lower fuel use and less wear and tear According to DOE fuel cell APUs in Class 8 trucks can save 670 million gallons ofdiesel fuel per year and 464 million tons of 002 per year International Benefits Fuel cells are entering the market at a time when countries face growing pressure to adopt alternative energy technologies on a large scale The challenge for the fuel cell industry is to ensure that it is ready with competitively priced performanceproven products as demand grows o More nations are focused on sustainable energy strategies Fuel cells offer an opportunity for countries to move toward greater sustainability in resource consumption Fuel cell efficiencies yield substantial reductions in emissions of climate change gases and promise an end to the exclusive reliance on carbon fuels for energy Portable Power Power generation Portable power applications cover a wide range of market segments including small generators and battery replacements Fuel cells are an excellent source of power for emergency and recreational uses where access to the electric grid is not available Domestic generatortype products are currently nearing commercialization Portable devices offer great potential as backup power supplies Battery replacementalternative Fuel cell power sources are also being developed for portable electronic devices In these applications the fuel cell would provide a much longer operating life than a battery would in a package of lighter or equal weight per unit of power output The fuel cell would not require quotrechargingquot a liquid solid or gaseous fuel canister could be replaced in a moment Fuel cells also have an environmental advantage over batteries since certain kinds of batteries require special disposal treatment Fuel cells provide a much higher power density packing more power in a smaller space The engineering and materials challenges related to micro fuel cell applications are substantial and will require innovative solutions to bring them to commercialization If these technologies can be commercialized then the portable and micro application market could be the fastest to develop There is a huge potential market Portable fuel cells carry environmental benefits comparable to fuel cells in other applications to the extent they replace combustion systems in homes in business or in recreation o Productivity Fuel cells carry productivity benefits in an increasingly mobile economy o Allied Business lntelligence39s report on quotPortable Fuel Cell Marketsquot says portable fuel cells are being developed to respond to the quotpoor performance of rechargeable batteries by quadrupling the run time before refueling is necessaryquot o Developers expect a fuel cell powered cell phone to have up to 200hours of talk time Recharging fuel cell powered electronic devices could be as simple as inserting a small methanol fuel cartridge or hydrogen container Military Applications Fuel cells help the military reduce the cost of battle eld logistics provide a source of energy forthe modern soldier save money and reduce pollution at military installations and on board ships and terrestrial vehicles and most importantly save lives and materiel by reducing telltale heat and noise A recent Defense Science Board report entitled quotMore Capable War ghting Through Reduced Fuel Burdenquot concluded quotover 70 percent of the tonnage required to position today39s US Army into battle is fuelquot The report also found that significant warfighting logistics and cost benefits occur when weapons systems are made more fuelefficient Stationary fuel cells are helping the military to address their peak electric power needs while complying with the presidential directive to reduce energy use at Federal facilities by 20 Stationary fuel cells for military applications can provide back up or standby power for special operations and activities and can provide power in remote areas Fuel cells may provide lifesaving power for the soldier of the future who will be carrying enough electronic equipment to require one kilowatt or more of electric power Fuel cells could be used in a number ofapplications Each proposed use raises its own issues and challenges Let39s take a look at the various applications starting with automobiles
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