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1. Energy Resources And Environment:
ASSIGNMENT:
NAEM=HALEEMULLAHM.SHAFIQ
ROLLNO=D-19-EE-04
SUBJECT=ENERGYRESOURCES ANDENVIRONMENT
DEPT=ENERGYANDENVIRONMENTENGINEERING
Subject TEACHER=DRHUBDARALIMAITLO

2. Energy Resources And Environment:
Q no 1
Fuel cell:
A fuel cell isanelectrochemical cell thatconvertsthe chemical energyof afuel (oftenhydrogen) andan
oxidizingagent(oftenoxygen) intoelectricitythroughapairof redox reactions.[2] Fuelcellsare
differentfrommostbatteriesinrequiringacontinuoussource of fuel andoxygen(usuallyfromair) to
sustainthe chemical reaction,whereasinabatterythe chemical energyusuallycomesfrommetalsand
theirionsor oxides[3] thatare commonlyalreadypresentinthe battery,exceptinflow batteries.Fuel
cellscan produce electricitycontinuouslyforaslongas fuel andoxygenare supplied.
Working:
There are manytypesof fuel cells,buttheyall consistof ananode,a cathode,andan electrolyte that
allowsions,oftenpositivelychargedhydrogen ions(protons),tomove betweenthe twosidesof the fuel
cell.Atthe anode a catalyst causesthe fuel toundergooxidationreactionsthatgenerate ions(often
positivelychargedhydrogenions) andelectrons.The ionsmove fromthe anode tothe cathode through
the electrolyte.Atthe same time,electronsflow fromthe anode tothe cathode throughan external
circuit,producingdirectcurrentelectricity.Atthe cathode,anothercatalystcausesions,electrons,and
oxygentoreact,formingwaterand possiblyotherproducts.Fuel cellsare classifiedbythe type of
electrolytetheyuse andbythe differenceinstartuptime rangingfrom1 secondforproton exchange
membrane fuel cells(PEMfuel cells,orPEMFC) to10 minutesforsolidoxide fuel cells(SOFC). A related
technologyisflowbatteries,inwhichthe fuelcanbe regeneratedbyrecharging.Individual fuel cells
produce relativelysmall electrical potentials,about0.7volts,socellsare "stacked",or placedinseries,
to create sufficientvoltage to meetanapplication'srequirements.Inadditiontoelectricity,fuelcells
produce water,heatand,dependingonthe fuel source,verysmall amountsof nitrogendioxide and
otheremissions.The energyefficiencyof afuel cell isgenerallybetween40–60%; however,if waste
heatis capturedina cogenerationscheme,efficienciesof upto85% can be obtained.
Types Of Fuel Cell:
There are many type of fuel cell some of them enlist below.
I. Hydrogen Fuel Cell
II. Microbial Fuel Cell
III. Polymer Membrane Fuel Cell
IV. Direct Methanol Fuel Cell
V. Alkaline fuel Cell
VI. Solid Oxide Fuel Cell
VII. Reversible Fuel Cell

3. Energy Resources And Environment:
Q no 2
Hydrogen Fuel Cell:
A PEM(ProtonExchange Membrane) cell useshydrogengas(H2) and oxygengas(O2) as fuel.The
productsof the reactioninthe cell are water, electricity,andheat.
Working Principle:
The anode,the negative postof the fuel cell,hasseveral jobs.Itconductsthe electronsthatare freed
fromthe hydrogenmoleculessothattheycan be usedinan external circuit.Ithaschannelsetchedinto
it thatdisperse the hydrogengasequallyoverthe surface of the catalyst.
The cathode,the positive postof the fuel cell,haschannelsetchedintoitthatdistribute the oxygento
the surface of the catalyst.It alsoconductsthe electronsbackfromthe external circuittothe catalyst,
where theycanrecombine withthe hydrogenionsandoxygentoformwater.
The electrolyte isthe protonexchange membrane.Thisspeciallytreatedmaterial,whichlooks
somethinglikeordinarykitchenplasticwrap,onlyconductspositivelychargedions.The membrane
blockselectrons.ForaPEMFC, the membrane mustbe hydratedinordertofunctionandremainstable.
The catalyst isa special material thatfacilitatesthe reactionof oxygenandhydrogen.Itisusuallymade
of platinumnanoparticlesverythinlycoatedontocarbonpaperorcloth.The catalystisrough and
porousso that the maximumsurface areaof the platinumcan be exposedtothe hydrogenoroxygen.
The platinum-coatedsideof the catalystfacesthe PEM.
As the name implies,the heartof the cell isthe protonexchange membrane.Itallowsprotonstopass
throughit virtuallyunimpeded,while electronsare blocked.So,whenthe H2hitsthe catalystandsplits
intoprotonsand electrons(remember,aprotonisthe same as an H+ ion) the protonsgo directly
throughto the cathode side,while the electronsare forcedtotravel throughanexternal circuit.Along
the way theyperformuseful work,like lightingabulbor drivingamotor,before combiningwiththe
protonsand O2 on the otherside to produce water.
How doesitwork?Pressurizedhydrogengas(H2) enteringthe fuel cell onthe anode side.Thisgasi-s
forcedthroughthe catalystby the pressure.WhenanH2 molecule comesincontactwiththe platinum

4. Energy Resources And Environment:
on the catalyst,itsplitsintotwoH+ ionsandtwo electrons(e-).The electronsare conductedthrough
the anode,where theymake theirwaythroughthe external circuit(doinguseful worksuchasturninga
motor) and returnto the cathode side of the fuel cell.
Meanwhile,onthe cathode side of the fuel cell,oxygengas(O2) isbeingforcedthroughthe catalyst,
where itformstwooxygenatoms.Each of these atomshas a strong negative charge.Thisnegative
charge attracts the twoH+ ionsthroughthe membrane,where theycombinewithanoxygenatomand
twoof the electronsfromthe external circuittoforma watermolecule (H2O).
All these reactionoccursina so calledcell stack.The expertisethenalsoinvolvesthe setupof a
complete systemaroundcore componentthatisthe cell stack.
The stack will be embeddedinamodule includingfuel,waterandairmanagement,coolantcontrol
hardware and software.Thismodule willthenbe integratedinacomplete systemtobe usedindifferent
applications.
Due to the highenergeticcontentof hydrogenandhighefficiencyof fuel cells(55%),thisgreat
technologycanbe usedinmany applicationslike transport(cars,buses,forklifts,etc) andbackuppower
to produce electricityduringafailure of the electricitygrid.
Diagram:

5. Energy Resources And Environment:
Q no 3
Microbial Fuel Cell:
A microbial fuel cell(MFC),ormicrobial desalinationcell,is abio-electrochemical system thatdrivesan
electriccurrentbyusingbacteriaand mimickingbacterialinteractionsfoundinnature.MFCscan be
groupedintotwogeneral categories:mediatedandunmediated.
Working Principle:
A microbial fuel cell(MFC) isa device thatconvertschemical energytoelectrical energybythe actionof
microorganisms. These electrochemical cellsare constructedusingeitherabioanode and/ora
biocathode.MostMFCs containa membrane toseparate the compartmentsof the anode (where
oxidationtakesplace) andthe cathode (where reductiontakesplace).The electronsproducedduring
oxidationare transferreddirectlytoanelectrode or,toa redox mediatorspecies.The electronflux is
movedtothe cathode.The charge balance of the systemiscompensatedbyionicmovementinsidethe
cell,usuallyacrossanionicmembrane.MostMFCs use an organicelectrondonorthatis oxidizedto
produce CO2, protons,andelectrons.Otherelectrondonorshave beenreported,suchassulfur
compoundsorhydrogen. The cathode reactionusesa varietyof electronacceptorsthatincludesthe
reductionof oxygenasthe moststudiedprocess.However,otherelectronacceptorshave beenstudied,
includingmetal recoverybyreduction,watertohydrogen, nitratereduction,andsulfate reduction.
Diagram:

6. Energy Resources And Environment:
Q no 4
Polymer Electrolyte Membrane Fuel Cell:
The proton exchange membranefuel cell(PEMFC) usesawater-based,acidicpolymermembraneas its
electrolyte,withplatinum-basedelectrodes....The protonspassthroughthe membrane tothe cathode
side of the cell while the electronstravel inanexternal circuit,generatingthe electrical outputof the
cell.
Working Principle:
PEMFC cellsoperate atrelativelylowtemperatures(below 100 degreesCelsius) andcantailorelectrical
outputto meetdynamicpowerrequirements.Due tothe relativelylow temperaturesandthe use of
preciousmetal-basedelectrodes,these cellsmustoperate onpure hydrogen.PEMFCcellsare currently
the leadingtechnologyforlightdutyvehiclesandmaterialshandlingvehicles,andtoa lesserextentfor
stationaryandotherapplications.The PEMFCfuel cell isalsosometimescalledapolymerelectrolyte
membrane fuel cell (alsoPEMFC).

7. Energy Resources And Environment:
Hydrogenfuel isprocessedatthe anode where electronsare separatedfromprotonsonthe surface of a
platinum-basedcatalyst.The protonspassthroughthe membrane tothe cathode side of the cell while
the electronstravel inanexternal circuit,generatingthe electrical outputof the cell.Onthe cathode
side,anotherpreciousmetal electrode combinesthe protonsandelectronswithoxygentoproduce
water,whichisexpelledasthe onlywaste product;oxygencanbe providedinapurifiedform, or
extractedatthe electrode directlyfromthe air.
A variantof the PEMFC whichoperatesatelevatedtemperaturesisknownasthe hightemperature
PEMFC (HT PEMFC). By changingthe electrolyte frombeingwater-basedtoamineral acid-basedsystem,
HT PEMFCs can operate upto 200 degreesCelsius.Thisovercomessome of the currentlimitationswith
regardto fuel puritywithHT PEMFCs able toprocessreformate containingsmall quantitiesof Carbon
Monoxide (CO).The balance of plantcanalsobe simplifiedthrougheliminationof the humidifier.
HT PEMFCs are not superiortolowtemperature PEMFCs;bothtechnologiesfindnichesinwhere their
benefitsare preferable.The table belowsummarisesdifferencesbetweenthe twoPEMFCvariants:

8. Energy Resources And Environment:
Diagram:

9. Energy Resources And Environment:
Q no 5
DIRECT METHONAL FUEL CELL:
Direct-methanolfuelcellsorDMFCsare a subcategoryof proton-exchangefuelcellsinwhichmethanol
isusedas the fuel.
Working Principle:
DMFCs use a methanol solution(usuallyaround1M, i.e.about3% inmass) to carry the reactantintothe
cell;commonoperatingtemperaturesare inthe range 50–120 °C,where hightemperaturesare usually
pressurized.DMFCsthemselvesare more efficientathightemperaturesandpressures,butthese
conditionsendupcausingsomanylossesinthe complete systemthatthe advantage islost.therefore,
atmospheric-pressure configurationsare currentlypreferred.
Because of the methanol cross-over,aphenomenonbywhichmethanoldiffusesthroughthe membrane
withoutreacting,methanolisfedasa weaksolution:thisdecreasesefficiencysignificantly,since
crossed-overmethanol,afterreachingthe airside (the cathode),immediatelyreactswithair;though
the exactkineticsare debated,the endresultisareductionof the cell voltage.Cross-overremainsa
majorfactor in inefficiencies,andoftenhalf of the methanolislosttocross-over.Methanol cross-over
and/orits effectscanbe alleviatedby(a) developingalternativemembranes(b) improvingthe electro-
oxidationprocessinthe catalystlayerandimprovingthe structure of the catalystandgas diffusion
layersand(c) optimizingthe designof the flow fieldandthe membrane electrode assembly(MEA) which
can be achievedbystudyingthe currentdensitydistributions
Otherissues include the managementof carbondioxide createdatthe anode,the sluggishdynamic
behavior,andthe abilitytomaintainthe solutionwater.
The onlywaste productswiththese typesof fuel cellsare carbondioxideandwater.
Reaction:
The DMFC reliesuponthe oxidationof methanolona catalystlayertoform carbon dioxide.Wateris
consumedatthe anode andis producedatthe cathode.Protons(H+) are transportedacrossthe proton
exchange membrane - oftenmade fromNafion - tothe cathode where theyreactwithoxygento
produce water.Electronsare transportedthroughan external circuitfromanode tocathode,providing
powerto connecteddevices.

10. Energy Resources And Environment:
Advantages:
CurrentDMFCs are limitedinthe powertheycanproduce,butcan still store ahighenergy contentina
small space.Thismeanstheycan produce a small amountof powerovera longperiodof time.This
makesthemill-suitedforpoweringlarge vehicles(atleastdirectly),butideal forsmallervehiclessuchas
forkliftsandtuggers [6] andconsumergoodssuch as mobile phones,digitalcamerasorlaptops.Military
applicationsof DMFCsare an emergingapplicationsince theyhave low noiseandthermal signatures
and no toxiceffluent.Theseapplicationsincludepowerforman-portable tactical equipment,battery
chargers,and autonomouspowerfortestandtraininginstrumentation.Unitsare available withpower
outputsbetween25wattsand 5 kilowattswithdurationsupto100 hoursbetweenrefuelings.

11. Energy Resources And Environment:
Diagram:

12. Energy Resources And Environment:
Q no 6
Alkaline Fuel Cell:
In fuel cell:Alkaline fuel cells.These are devicesthat,bydefinition,have anaqueoussolutionof sodium
hydroxide orpotassiumhydroxide asthe electrolyte.The fuelisalmostalwayshydrogengas,with
oxygen(oroxygeninair) asthe oxidizer.
Working Principle:
The fuel cell producespowerthrougharedox reactionbetweenhydrogenandoxygen.Atthe anode,
hydrogenisoxidizedaccordingtothe reaction producingwaterandreleasingelectrons.The electrons
flowthroughan external circuitandreturntothe cathode, reducingoxygeninthe reaction producing
hydroxide ions.The netreactionconsumesone oxygenmoleculeandtwohydrogenmoleculesinthe
productionof twowatermolecules.Electricityandheatare formedasby-productsof thisreaction.
The two electrodesare separatedbyaporousmatrix saturatedwithanaqueousalkaline solution,such
as potassiumhydroxide (KOH).Aqueousalkalinesolutionsdonotrejectcarbondioxide(CO2) sothe fuel
cell can become "poisoned"throughthe conversionof KOHto potassiumcarbonate (K2CO3).Because of
this,alkaline fuel cellstypicallyoperateonpure oxygen,oratleastpurifiedairandwouldincorporate a
'scrubber'intothe designtocleanoutas much of the carbon dioxide asispossible.Becausethe
generationandstorage requirementsof oxygenmake pure-oxygenAFCsexpensive,there are few
companiesengagedinactive developmentof the technology.There is,however,some debateinthe
researchcommunityoverwhetherthe poisoningispermanentorreversible.The mainmechanismsof
poisoningare blockingof the poresinthe cathode withK2CO3,whichisnot reversible,andreductionin
the ionicconductivityof the electrolyte,whichmaybe reversiblebyreturningthe KOHtoits original
concentration.Analternate methodinvolvessimplyreplacingthe KOHwhichreturnsthe cell backto its
original output.
Whencarbon dioxide reactswiththe electrolyte carbonatesare formed.The carbonatescould
precipitate onthe poresof electrodesthateventuallyblockthem.IthasbeenfoundthatAFCsoperating
at highertemperature donotshowa reductioninperformance,whereasataroundroomtemperature,
a significantdropinperformance hasbeenshown.The carbonate poisoningatambienttemperatureis
thoughtto be a resultof the lowsolubilityof K2CO3aroundroom temperature,whichleadsto
precipitationof K2CO3that blocksthe electrode pores.Also,these precipitantsgraduallydecrease the
hydrophobicityof the electrode backinglayerleadingtostructural degradation andelectrode flooding.
On the otherhand,the charge-carryinghydroxyl ionsinthe electrolytecanreactwithcarbon dioxide
fromorganic fuel oxidation(i.e.methanol,formicacid) orair toform carbonate species Carbonate
formationdepleteshydroxylionsfromthe electrolyte,whichreduceselectrolyte conductivityand
consequentlycell performance.Aswell asthese bulkeffects,the effectonwatermanagementdue toa
change in vaporpressure and/ora change inelectrolyte volume canbe detrimental as well.
Diagram:

13. Energy Resources And Environment:

14. Energy Resources And Environment:
Q no 7
Solid Oxide Fuel Cell:
A solidoxide fuel cell (orSOFC) isanelectrochemical conversiondevice thatproduceselectricitydirectly
fromoxidizingafuel.Fuel cellsare characterizedbytheirelectrolyte material;the SOFChasa solidoxide
or ceramicelectrolyte.
Working Principle:
A solidoxide fuel cell ismade upof fourlayers,three of whichare ceramics(hence the name).A single
cell consistingof these fourlayersstackedtogetheristypicallyonlyafew millimetersthick.Hundredsof
these cellsare thenconnectedinseriestoformwhatmostpeople refertoasan "SOFCstack". The
ceramicsusedinSOFCsdo not become electricallyandionicallyactive until theyreachveryhigh
temperature andasa consequence, the stackshave torun at temperaturesrangingfrom500 to 1,000
°C. Reductionof oxygenintooxygenionsoccursatthe cathode.These ionscanthendiffuse throughthe
solidoxide electrolyte tothe anode where theycanelectrochemicallyoxidize the fuel. Inthisreaction,a
waterbyproductisgivenoff as well astwoelectrons.These electronsthenflow throughanexternal
circuitwhere theycan dowork.The cycle thenrepeatsasthose electronsenterthe cathode material
again. Most of the downtime of a SOFC stemsfromthe mechanical balance of plant, the airpreheater,
prereformerafterburner,waterheatexchanger,anode tail gasoxidizer,andelectrical balance of plant,
powerelectronics,hydrogensulfide sensorandfans.Internal reformingleadstoa large decrease inthe
balance of plantcosts indesigningafull system.
Electrolyte
The electrolyte isadense layerof ceramicthatconducts oxygenions.Itselectronicconductivitymustbe
keptas lowas possible topreventlossesfromleakagecurrents. The highoperatingtemperaturesof
SOFCsallowthe kineticsof oxygeniontransporttobe sufficientforgoodperformance.However,asthe
operatingtemperature approachesthe lowerlimitforSOFCsataround600 °C, the electrolytebeginsto
have large ionictransportresistancesandaffectthe performance.Popularelectrolyte materialsinclude
yttria-stabilizedzirconia(YSZ) (oftenthe 8% form8YSZ),scandiastabilizedzirconia(ScSZ) (usually9
mol%Sc2O3 – 9ScSZ) and gadoliniumdopedceria(GDC).[8] The electrolyte material hascrucial
influenceonthe cell performances.[9] Detrimental reactionsbetweenYSZelectrolytesandmodern
cathodessuchas lanthanumstrontiumcobaltferrite (LSCF) have beenfound,andcanbe preventedby
thin(<100 nm) ceriadiffusionbarriers.[10]
If the conductivityforoxygenionsinSOFCcanremainhighevenatlowertemperatures(currenttarget
inresearch~500 °C),material choicesforSOFCwill broadenandmanyexistingproblemscanpotentially
be solved.Certainprocessingtechniquessuchasthinfilmdepositioncanhelpsolve thisproblemwith
existingmaterialsby:
reducingthe travelingdistance of oxygenionsandelectrolyteresistance asresistance isproportional to
conductorlength;

15. Energy Resources And Environment:
producinggrainstructuresthat are lessresistive suchascolumnargrainstructure;
controllingthe microstructural nano-crystalline fine grainstoachieve "fine-tuning"of electrical
properties;
buildingcomposite possessinglarge interfacial areasasinterfaceshave beenshownto have
extraordinaryelectrical properties.
Cathode
Anode
The ceramic anode layermustbe veryporousto allow the fuel toflow towardsthe electrolyte.
Consequently,granularmatterisoftenselectedforanode fabricationproceduresLike the cathode,it
mustconduct electrons,withionicconductivityadefinite asset.The mostcommonmaterial usedisa
cermetmade up of nickel mixedwiththe ceramicmaterialthatisusedforthe electrolyte inthat
particularcell,typicallyYSZ(yttriastabilizedzirconia) nanomaterial-basedcatalysts,thisYSZparthelps
stopthe graingrowthof nickel.Largergrainsof nickel wouldreduce the contactareathat ionscan be
conductedthrough,whichwouldlowerthe cellsefficiency.The anode iscommonlythe thickestand
strongestlayerineachindividualcell,because ithasthe smallestpolarizationlosses,andisoftenthe
layerthat providesthe mechanicalsupport.Electrochemicallyspeaking,the anode’sjobistouse the
oxygenionsthatdiffuse throughthe electrolyte to oxidize the hydrogenfuel.The oxidationreaction
betweenthe oxygenionsandthe hydrogenproducesheataswell aswaterandelectricity.If the fuel isa
lighthydrocarbon,forexample,methane,anotherfunctionof the anode istoact as a catalystfor steam
reformingthe fuel intohydrogen.Thisprovidesanotheroperational benefittothe fuel cell stack
because the reformingreactionisendothermic,whichcoolsthe stackinternally.Perovskitematerials
(mixedionic/electronicconductingceramics) have beenshowntoproduce apowerdensityof 0.6
W/cm2 at 0.7 V at 800 °C whichispossible because theyhave the abilitytoovercome alargeractivation
energy.
Cathode
Cathode materialsmustbe,ata minimum, electricallyconductive.Currently,lanthanumstrontium
manganite (LSM) isthe cathode material of choice forcommercial use because of itscompatibilitywith
dopedzirconiaelectrolytes.Mechanically,ithasasimilarcoefficientof thermal expansiontoYSZand
thuslimitsstressbuildupbecause of CTE mismatch.Also,LSMhas low levelsof chemical reactivitywith
YSZ whichextendsthe lifetime of the materials.Unfortunately,LSMisa poorionicconductor,and sothe
electrochemicallyactive reactionislimitedtothe triple phase boundary(TPB) where the electrolyte,air
and electrode meet.LSMworkswell asa cathode at hightemperatures,butitsperformance quicklyfalls
as the operatingtemperature isloweredbelow 800°C. In orderto increase the reactionzone beyond
the TPB, a potential cathode material mustbe able toconductbothelectronsandoxygenions.
Composite cathodesconsistingof LSMYSZ have beenusedtoincrease thistriple phase boundarylength.
Mixedionic/electronicconducting(MIEC) ceramics,suchas perovskiteLSCF,are alsobeing researched
for use inintermediatetemperature SOFCsastheyare more active andcan make up for the increase in
the activationenergyof the reaction.

16. Energy Resources And Environment:
Diagram:

17. Energy Resources And Environment:
Q no 8
Reversible Fuel Cell:
A regenerative fuelcell orreverse fuel cell (RFC)isafuel cell runinreverse mode,whichconsumes
electricityandchemical Btoproduce chemical A.By definition,the processof anyfuel cell couldbe
reversed.
Working Principle:
A hydrogenfueledprotonexchangemembranefuelcell,forexample,useshydrogen gas(H2) and
oxygen(O2) toproduce electricityandwater(H2O);a regenerativehydrogenfuelcell useselectricity
and waterto produce hydrogenandoxygen.
Whenthe fuel cell isoperatedinregenerativemode,the anode forthe electricityproductionmode (fuel
cell mode) becomesthe cathode inthe hydrogengenerationmode (reversefuelcell mode),andvice
versa.Whenan external voltage isapplied,wateratthe cathode side will undergoelectrolysistoform
hydrogenandoxide ions;oxideionswill be transportedthroughthe electrolyte toanode where itcan
be oxidizedtoformoxygen.Inthisreverse mode,the polarityof the cell isopposite tothatforthe fuel
cell mode.The followingreactionsdescribethe chemical processinthe hydrogengeneration mode:
At cathode: H2O + 2e− → H2 + O2−
At anode:O2− → 1/2O2 + 2e−
Overall:H2O→ 1/2O2 + H2
Diagram:

18. Energy Resources And Environment: