Electrochemistry and batteries

Galvanic cell, Nernst equation, Calomel electrode, Quinhydrone electrode, Glass electrode, Dry cell, Lead Acid battery, Li ion cell, Methanol oxygen fuel cell

1. MATRUSRI ENGINEERING COLLEGE
DEPARTMENT OF SCIENCES AND HUMANITIES
SUBJECT NAME: CHEMISTRY
FACULTY NAME: VISHNU THUMMA
MATRUSRI
ENGINEERING COLLEGE
TOPIC: ELECTROCHEMISTRY AND BATTERIES

2. CHEMISTRY
COURSEOBJECTIVES:
➢Correlatethepropertiesofmaterialswiththeirinternalstructureanduse
theforEngineeringapplications
➢Applytheprinciplesofelectrochemistryinstorageofelectricalenergyin
batteries.
➢Gainsknowledgeincausesofcorrosionanditsprevention.
➢Attainsknowledgeaboutthedisadvantagesofhardwaterfordomestic
andindustrialpurposes.
➢Alsolearnsthetechniquesofsofteningofhardwaterandtreatmentof
waterfordrinkingpurpose.
➢Exposedtoqualitativeandquantitativeparametersofchemicalfuels.
➢Awareeco-friendlymaterialsandprocesses.
MATRUSRI
ENGINEERING COLLEGE
2

3. CHEMISTRY
COURSEOUTCOMES:Aftercompletionofcoursestudentswillbeableto
➢Analyzeandapplyknowledgeofelectrodicsincalculationofcell
potentialsofbatteries.
➢Identifythedifferenttypesofhardnessandalkalinitiesinwaterand
makeuseofsofteningmethods,analyzeandapplytheknowledgeof
corrosionforitsprevention.
➢Discussdifferenttypesofpolymersbasedontheirendonuseandthe
needtoreplacetheconventionalpolymerswithpolymersofengineering
applications.
➢Identifyandanalyzedifferenttypesofchemicalfuelsfordomesticand
automobileapplications.
➢Outlinetheprinciplesofgreenchemistryforsustainableenvironment
andpreparationofbiodieselfromrenewablesources.
MATRUSRI
ENGINEERING COLLEGE
3

4. 4
Course Title Chemistry
Course Code BS105CH
Programme Common for all branches
Semester I (CSE, EEE) II (ECE,MECH, IT)
Course Type Basic Sciences
Regulation AICTE Model curriculum
Course Structure
Theory Practical
LecturesTutorialsCreditsLaboratoryCredits
3 1 4 3 1.5
MarksDistribution
CIE SEE - CIE SEE
30 70 - 25 50
COURSE DESCRIPTION
MATRUSRI
ENGINEERING COLLEGE

5. UNIT-I ELECTROCHEMISTRY AND BATTERIES
MATRUSRI
ENGINEERING COLLEGE
INTRODUCTION:
•Theelectrochemistryisthesubjectwhichdealswiththeapplicationofelectricitywith
chemicalspecies.
•Itisthebranchofphysicalchemistrywhichdealswithconversionofelectricalenergy
intochemicalenergyorviceversa.
•Inelectrolyticcellstheconversionofelectricalenergytochemicalenergytakesplace;
whereasthechemicalenergyisconvertedtoelectricalenergyinagalvaniccell.
5
OUTCOMES:Aftercompletionofcoursestudentswillbeabletoanalyzeandapplyknowledge
ofelectrodicsincalculationofcellpotentialsofbatteries.

6. MATRUSRI
ENGINEERING COLLEGEELECTRIC CONDUCTOR:
Any substance which allows the passage of electrical current through it is called an
electric conductor.
Metallic conductors
•Involvetheflowofcurrentwith
whichdoesnotundergoany
chemicalchange.
•Theflowofcurrentintheformof
flowofelectrons,hencetheyare
alsocalledaselectronic
conductors.
•Passageofelectricitydoesnot
causeanychangeexceptasmall
riseintemperature.
•TheyobeyOhm’slawbutnot
Faraday’slaw.
Eg:Cu,Aletc.
Electrolytic conductors
•Involve the flow of current followed
by a chemical change.
•In solutions the current flows in
the form of movement of ions.
•Passage of electricity causes the
transfer of matter, and rise in
temperature increases the rate of
dissociation of electrolyte, thus,
conductance increases.
•Ex: solutions of acids, bases and
salts.
6

7. CONTENTS: ELECTROLYTE –ELECTROLYSIS -ELECTROLYTIC CELL
MODULE-1: ELECTROLYTIC CELL
MATRUSRI
ENGINEERING COLLEGE
7
Electrolysis:Theprocessofchemical
decompositionofanelectrolytebythepassageof
electricitythroughitsmoltenordissolvedstate.
Electrolyte: A substance that produces an electrically conducting solution
when dissolved in a polar solvent, such as water.
Itsplitsupintochargedparticlescalledions.
Thepositivelychargedionsarecalledcationswhilethenegativelycharged
ionsarecalledanions.
Electrolyticcell:Thedeviceinwhichthe
processofelectrolysisiscarriedout.

8. MATRUSRI
ENGINEERING COLLEGE
8
Electrolytic cell
Thecellcontainsaqueoussolutionofanelectrolyte,inwhichtwometallicrods
(electrodes)aredippedwhichareconnectedtoabattery.
ANODE(+):Positiveelectrode.
Currententersthecell.
CATHODE(-):Negativeelectrode
Currentleavesthecell.
Whenelectriccurrentispassedthroughthesolution,the
ionsrespondtotheappliedpotentialdifferenceandtheir
movementisdirectedtowardsoppositelycharged
electrodes.
Thecationsmovetowardsthenegativelycharged
electrodewhileanionsmovetowardsthepositively
chargedelectrode.
Productsareformedattherespectiveelectrodestakesplace
duetooxidationattheanodeandreductionatthecathode.`

9. ELECTRICAL ENERGY IS CONVERTED INTO CHEMICAL ENERGY
A CHEMICAL CHANGE IS BROUGHT UP BY PASSING ELECTRICITY.
In a Electrolytic cell:
MATRUSRI
ENGINEERING COLLEGE
9
OR
HCl
(l)
→H
+
+ Cl
-
Anode: Cl
-
→½ Cl
2
+ e
-
(Oxidation)
Cathode: ½ H
+
+ e
-
→H
2
(Reduction)

10. 1. Electrolytic cell converts _________ energy into _______ energy.
Quiz
MATRUSRI
ENGINEERING COLLEGE
10
a.chemical, electrical
b.electrical, chemical
c. electrical, mechanical
d. mechanical, electrical
2. Electrolytic conductioninvolves
a.Chemical change
b.Migration of ions
c. Mobility of ions
d. All the above
3. At anode ________ reaction occurs.
a.reduction
b.oxidation
c. redox
d. All the above
4. Reduction reaction occursat __________
a.anode
b.cathode
c. Both a&b
d. None

11. A redoxreaction is utilized to get electrical energy.
CONTENTS: GALVANIC CELL –CONSTRUCTION -CELL REACTION –SALT BRIDGE –EMFOF CELL
MODULE-2: GALVANIC CELL
MATRUSRI
ENGINEERING COLLEGE
11
Chemical energyis converted into electrical energy.
Itconsistsoftwohalfcellsconnectedthrough
anexternalwireandareseparatedwithasalt
bridge.
Eachhalfcellconsistsofanelectrodewhich
isdippedinasuitableelectrolyticsolution.

12. MATRUSRI
ENGINEERING COLLEGE
12
DANIEL CELL
Itconsistsoftwoelectrodes.
ZnroddippedinZincSulphatesolution.(Anode)
CuroddippedinCopperSulphatesolution.
(Cathode)
Boththesolutionsareseparatedwithasemi
permeablemembraneorsaltbridge.
Saltbridgepreventsthediffusionofthetwoliquids
butallowsthepassageofionsthroughit,whenthe
flowofelectriccurrenttakesplace.
Whenthecircuitiscompletetheflowofelectric
currenttakesplace.
At anode (-): Zn →Zn
2+
+ 2e
-
(Oxidation) (Metal dissolved)
At cathode (+): Cu
2+
+ 2e
-
→Cu (Reduction) (Metal deposited)

13. MATRUSRI
ENGINEERING COLLEGE
13
Themovementofelectronsfromzinctocopperproducesacurrentinthecircuit.
Thenetchemicalchangeisdescribedasthecellreaction.
AtAnode(-):Zn→Zn
2+
+2e
-
(Oxidationhalfcellreaction)
AtCathode(+):Cu
2+
+2e
-
→Cu(Reductionhalfcellreaction)
Cellreactions:Zn+Cu
2+
→Zn
2+
+Cu(Redoxreaction)
SaltBridge:Itisaninverted‘U’shapetubeopenatboththeends,it
containsinertelectrolytessuchasKCl,KNO
3
,NH
4
NO
3
etc.,mixed
withagar-agargeltomakeitassemisolidpaste.
Role of salt bridge:
•It connects the two solutions and prevents their intermixing.
•It prevents the accumulation of charges around the electrode.
•Itallowsthemovementofanionsfromcathodicsolutiontoanodic
solution.
•Itmaintainselectricalneutralityofsolutionandthiscompletesthe
circuit.

14. Thenegativeelectrodeiswrittenontheextremeleftandthepositiveelectrodeis
ontheextremeright.
Cell Notation (Representation):
MATRUSRI
ENGINEERING COLLEGE
14
Thesingleverticallineindicatestheelectrode-electrolyteinterface.
Thedoubleverticallinesbetweenthetwoliquidssignifiesthesaltbridgeorsemi
permeablemembraneseparatingthetwohalfcells.
The emfof the cell is written on extreme right.
Zn ZnSO
4(1.0 M)
CuSO
4(1.0 M)
Cu 1.1V
An inert electrode is indicated in ( ).
(Pt) Q,QH
2
/H
+
(Pt) H
2
/H
+(Pt) Hg, Hg
2Cl
2(s)/KCl

15. EMF OF THE CELL:
MATRUSRI
ENGINEERING COLLEGE
15
It is equal to the sum of oxidation potential and reduction potential.
E
cell
= E
Ox
+ E
Red
= E
0
Zn/Zn
2+
(SOP)
+ E
0
Cu/Cu
2+
(SRP)
= +0.76 + 0.34 = +1.10 V
When Standard reduction potentials (SRP) are taken into account
E
cell
= E
cathode
-E
anode
When emfof cell is positive then the cell reaction is feasible
Since, ΔG = -nFE

16. MATRUSRI
ENGINEERING COLLEGE
16
1. Which of the following is not related to galvanic cell
Quiz
MATRUSRI
ENGINEERING COLLEGE
16
a.Chemical energy is converted to electrical energy
b.It requires source of electrical energy
c.Flow electrons takes place from anode to cathode
d.As salt bridge is required
2. The purpose of saltbridge in galvanic cell is
a.Prevents accumulation of charge.
b.Provide a path for mobility of electrons
c.Prevents electrical neutrality.
d.All the above
3. Standard reduction potentialof copper is
a. -0.76 V b. +0.76 Vc. +0.34 V d. -0.34V
4. For spontaneous cell reactionemfof cell should be
a. positive b. negative c. 0.0Vd. none

17. CONTENTS: NERNST EQUATION –DERIVATION –APPLICATIONS –NUMERICALPROBLEMS
MODULE-3: NERNST EQUATION
MATRUSRI
ENGINEERING COLLEGE
17
Let us consider a galvanic cell whose cell reaction is written as:
aA+ bB→cC+ dD
Nernstequationestablishestherelationshipbetweenconcentrationsoractivities
ofelectrolytesolutionswithcellemf.
The equilibrium constant for above equation:
= Activity coefficient = Q

18. MATRUSRI
ENGINEERING COLLEGE
18
Nernst equation can be derived from VantHoff’s isotherm:
From the thermodynamics:
By substituting ∆G and ∆G
0
values in equation (1), we get
By dividing the equation (2) with -nFon both sides
ΔG=∆G
0
+RTlnQ----------(1)
∆G = -nFEand∆G
0
= -nFE
0
-nFE=-nFE
0
+RTlnQ----------(2)
E =E
0-
RT
nF
lnQ
E =E
0-
2.303RT
nF
log
[C]
c
[D]
d
[A]
a
[B]
b
E =E
0-
2.303RT
nF
log
[Products]
[Reactants]

19. MATRUSRI
ENGINEERING COLLEGE
19
R = Gas constant = 8.314 J K
-1
mol
-1
T = Temperature in Kelvins(at 25
0
C = 298 K)
F = Faraday = 96500 C
n = number of electrons (Faradays)
At 25
0
C, by substitutingthe R, T & F values,
Nernst equation canbe simplified as:
Thestandardcellemfisequaltothecellemfwhentheactivitiesofboth
reactantsandproductsareequaltounity.

20. MATRUSRI
ENGINEERING COLLEGE
20
For Redoxreaction:Ex: Zn + Cu
2+
→Zn
2+
+ Cu
Since, [Zn] and [Cu] are unity.
For a reduction reaction:M
n+
→M + ne
-
At 25
0
C,
Since, [M] = 1

21. MATRUSRI
ENGINEERING COLLEGE
21
Applications of Nernst Equation:
It is used to:
Study the effect of electrolyte concentration on electrode potential.
To calculate single electrode potential of a half cell.
Used for calculation of cell potential under non standard conditions.
pH of a solution can be calculated. (Ecell= E°cell–0.0592 pH)
Helpful to determine the unknown concentration of one of the ionic species
of cell if E
0
cell and concentration of other species is known.
Used for finding the valence of number of e
-
involved in a reaction.

22. MATRUSRI
ENGINEERING COLLEGE
22
Q:CalculatetheemfofacellinwhichironisincontactwithFeSO
4(0.1M)electrolyteand
CuwhichisplacedinCuSO
4(0.01M)solution.TheSRPsofFeandCuare-0.44Vand
+0.34Vrespectively.
Numerical Problems
Cell Notation:Fe FeSO
4
CuSO
4
Cu
Cell reactions:
At anode: Fe →Fe
+2
+ 2e
-
(Oxidation)
At cathode: Cu
2+
+ 2e
-
→Cu ( Reduction)
Cell reaction: Fe + Cu
2+
→Fe
2+
+ Cu
E
0
cell
= E
0
cathode
-E
0
anode
= 0.34 –(-0.44) V = 0.78v
= 0.78 V
At 25
0
C,

23. Questions
MATRUSRI
ENGINEERING COLLEGE
23
1.Derive Nernst equation? Write its applications?
2.Calculate the single electrode potential of Cu dipped in 0.01M CuSO
4
Solution, the given E
0
Cu
2+
/Cu= 0.34 V.
3.Write the cell reaction and calculate the emfof the following cell at 25
0
C:
Zn
(s)l Zn
2+
(0.001M) llAg
+
(0.0001M) l Ag
(s)
Given E
0
Zn
2+
/Zn= -0.76 V and E
0
Ag
+
/Ag = 0.80 V.

24. MODULE-4: CALOMEL ELECTRODE
MATRUSRI
ENGINEERING COLLEGE
24
It is a secondary reference electrode consisting of mercury-mercurouschloride (Hg-Hg
2Cl
2)
paste in contact with KClsolution.
Itconsistsofaplugatthebottomofwhicha
smallamountofHgisplaced.
Hgiscoveredwithapasteofsolidmercury-
mercurouschloride(calomelpaste).
ThesolutionofKClisplacedoverthepaste.
Aplatinumwireisemployedforelectricalcontact.
The potential of calomel electrode depends
on KClsolution.
It is represented as: Pt | Hg, Hg
2
Cl
2
| KCl

25. MATRUSRI
ENGINEERING COLLEGE
25
Electrode reaction: Hg
2
Cl
2
+ 2e
-
2Hg + 2Cl
-
Electrode potential:
The calomel electrode is reversible to Cl
-
ion concentration.
The standard reduction potential of calomel electrode at 25
0
C is
0.1M KCll Hg
2
Cl
2(s)
l Hg, Pt 0.3338V DecinormalCalomel Electrode(DNCE)
1.0M KCll Hg
2
Cl
2(s)
l Hg, Pt 0.2800V Normal Calomel Electrode (NCE)
Sat. KCll Hg
2
Cl
2(s)
l Hg, Pt 0.2415V Saturated Calomel Electrode (SCE)

26. MATRUSRI
ENGINEERING COLLEGE
26
QUIZ
1.Calomelelectrodeisreversibleto_____ions
a)K+ b)Cl- c)Hg d)Hg2Cl2
2.Calomelisapasteof
a)Hg2Cl2 b)Hg c)KCl d)all
3.Thereductionreactionofcalomelelectrodeis
a) Hg
2
Cl
2
+ 2e
-
2Hg + 2Cl
-
b) 2Hg + 2Cl
-
Hg
2
Cl
2
+ 2e
-
c) Pt/Hg,Hg2Cl2/KCl
d) none

27. MATRUSRI
ENGINEERING COLLEGE
27
MODULE-5: QUINHYDRONE ELECTRODE
Quinhydroneisa1:1equimolarmixtureofquinoneandhydroquinonewhich
existinequilibriuminpresenceofH
+
ions.O
O
2H 2e
OH
OH
Quinone (Q) Hydroquinone (QH
2
)
+
+
+
-
QuinhydroneelectrodeissetupbyaddingapinchofQuinhydronetothesolutionwhose
pHistobemeasured.APtelectrodeisplacedinittoacquirepotential.
Electrode representation: Pt |Q, QH
2
| H
+
(unknown)

28. MATRUSRI
ENGINEERING COLLEGE
28
ThepotentialdevelopedonaPtelectrodeimmersedinthissystemisgivenbyNernst
equationas:
EQHE=E°QHE
_ 2.303RT
2F
log
[QH2]
[Q][H]
+ 2
at 25
0
C the equation may written as
EQHE=E°QHE+
0.0592
2
log
[QH2]
[Q][H]
+ 2
Since,Quinhydroneissparinglysolublesalt,concentrationterms[Q]and[QH
2]are
termedasunity.
Hence, E
QHE
= E
0
QHE
+ 0.0592 log [H
+
]
Since, pH = -log [H
+
]
E
QHE= E
0
QHE–0.0592pH ORE
QHE= 0.6996 –0.0592pH
Thus, the potential of Quinhydroneelectrode depends on the pH of the solution with
which it is in contact. Therefore it can be used for the measurement of pH.

29. MATRUSRI
ENGINEERING COLLEGE
29
DeterminationofpHusingQuinhydroneelectrode:
ThepotentialofQuinhydroneelectrode(QHE)isdeterminedbyconnectingitwitha
saturatedcalomelelectrode(SCE)
Pt |Hg, Hg
2
Cl
2(s)
|KCl
(saturated)
||H
+
(unknown)
|Q, QH
2
|Pt
The emfof the cell E
cell= E
QHE-E
SCE
E
cell
= (0.6996 –0.0592pH) –0.242 V
pH=
0.4576 -Ecell
0.0592

30. MATRUSRI
ENGINEERING COLLEGE
30
Advantages:
•TheQuinhydroneelectrodeissimpletosetupandneedsnoremovalofair.
•Thereversibilityequilibriumisachievedfasterthanhydrogengaselectrodethereby
allowingaquickmeasurement.
•pHvaluesofsolutionscontainingreduciblesubstanceslikeCu
2+
,Cd
2+
,unsaturated
acids,NO
3
-
etc.,andcatalyticpoisonscanbemeasuredusingQuinhydroneelectrode,
wherehydrogenelectrodecannotbeused.
Limitations:
TheQuinhydroneelectrodecannotbeusedwhenpHofthesolutionismorethan8.
Because,atthispHhydroquinonedissociatesandundergoesoxidationbythe
atmosphericoxygen.Thisalterstheequilibriumbetweenquinoneandhydroquinone.

31. MATRUSRI
ENGINEERING COLLEGEQUIZ
1.Whatisquinhydrone?
a)1:1mixtureofquinoneandhydroquinone
b)1:2mixtureofquinoneandhydroquinone
c)2:1mixtureofquinoneandhydroquinone
d)none
2.Quinhydroneelectrodeissensitiveto
a)pH b)quinone
c)hydroquinone d)none
3.Thestandardpotentialofquinhydroneelectrodeis
a)0.6996V b)0.2419V
c)-0.6996V d)-0.2419V

32. MATRUSRI
ENGINEERING COLLEGE
MODULE-6: GLASS ELECTRODE
Glasselectrodeconsistsofthinwalledglassbulb
containingPtwireofAgClcoated,dippedin0.1NHCl
solution.
Theglassmembraneactsasanionexchangeresinwhich
ishighlypHsensitive.
Glassbulb,whenincontactwithacidtestsolutionfurnishes
aconstantH
+
ionconcentrationonbothsideswhichis
responsibleforpotentialdifference.
ThispotentialdifferenceisdirectlyproportionaltothepH
differencebetweensolutionsonbothsidesofglass.
Itisrepresentedas:
Pt|Ag,AgCl|0.1NHCl|Glassmembrane

33. MATRUSRI
ENGINEERING COLLEGE
MEASUREMENT OF pH USING GLASS ELECTRODE
Theglasselectrodeiscoupledwithasaturatedcalomelelectrodesoastoconstructa
galvaniccell.
Pt |Ag, AgCl
(s)|0.1NHCl |Glass membrane |H
+
(unknown) |Sat.KCl|Hg
2
Cl
2
,Hg Pt
The emfof the cell E
cell= E
SCE–E
Glass
E
cell
= 0.242 -(E
0
glass
-0.0592 pH)
Electrode Reaction: AgCl+ e
-
AgCl
E
glass
= E
0
glass
-0.0592 pH

34. QUIZ
34
MATRUSRI
ENGINEERING COLLEGE
1.Glass electrode is a type of
a) inert electrode b) ion selective electrode
c) gas electrode d) metal insoluble electrode
2. The bulb in glass electrode is filled with
a) 0.1N HCl b) 1.0N HCl
c) 0.1 AgCl d) 1.0N AgCl
3. In glass electrode the semi permeable membrane is sensitive to
a) pH b) Ag ions
c) Chloride ions d) solvent
4. The standard potential of glass electrode depends on
a) nature of glass membrane
b) nature of electrolyte
c) nature of solvent
d) all the above

35. MODULE-8: THERMODYNAMICS OF EMF OF CELL
35
MATRUSRI
ENGINEERING COLLEGE
Enthalpy and EMF:
From thermodynamics∆G = ∆H -T∆S
According to Gibbs-Helmholtz equation:
∆�=∆�+�
??????∆�
??????�
??????
Since, ∆G = -nFE
−??????��=∆�+�
??????−??????��
??????�
??????
−??????��=∆�−??????��
??????�
??????�
??????
∆�=−??????��+??????��
??????�
??????�
??????
Here,the
??????E
??????T
P
iscalled
TemperatureCoefficientofthe
cell.
If
??????E
??????T
P
=0,thenElectrical
energyisequaltoEnthalpyof
thecellreaction.EMFofthecell
increaseswithtemperature.

36. MODULE-8: THERMODYNAMICS OF EMF OF CELL
MATRUSRI
ENGINEERING COLLEGE
Entropy and EMF:
From thermodynamics∆G = ∆H -T∆S --1
Since,
∆�=−??????��+??????��
??????�
??????�
??????
and
∆G = -nFE
Thenequation(1)canbewrittenas
−??????��=−??????��+??????��
??????�
??????�
??????
−�∆�
Then,
�∆�=??????��
??????�
??????�
??????
And
∆�=??????�
??????�
??????�
??????

37. MODULE-8: BATTERY CHEMISTRY
Batteryisanelectrochemicalcelloroftenseveralelectrochemical
cellsconnectedinseriesthatcanbeusedasasourceofdirect
electriccurrentatconstantvoltages.
Batteryisacommercialelectrochemicalcell.
Classification:
PrimaryCells.Eg.:Drycell
SecondaryCells.Eg.:Leadacidcell.
37
MATRUSRI
ENGINEERING COLLEGE

38. Primary Cells
Produceelectricityfromchemicalsthataresealedintoit.
Electricalenergycanbeobtainedattheexpenseofchemicalenergy
onlyaslongastheactivematerialsarestillpresent.
Cannotberechargedasthecellreactioncannotbereversed
efficientlybyrecharging.
Thecellmustbediscardedafterdischarging.
Ex:Zinc–Carbonbattery(Drycell)
Zinc–Mercuricoxidecell.
Zinc–Silveroxidecell
38
MATRUSRI
ENGINEERING COLLEGE

39. Secondary Cells
Generationofelectricenergy,thatcanberestoredtoitsoriginal
chargedconditionafteritsdischargebypassingcurrentflowingin
theoppositedirection.
Thesecellshavealargenumberofcyclesofdischargingandcharging.
Theyareknownasrechargeablecells,storagecells,oraccumulators.
Ex:Leadstoragecell.
Nickel-cadmiumcell.
Lithium-ionbatteries.
39
MATRUSRI
ENGINEERING COLLEGE

40. Differences
Primary Batteries
➢Cell reaction is irreversible.
➢Must be discarded after use.
➢Have relatively short shelf life.
➢Function only as galvanic cell.
➢They cannot be used as storage devices.
➢They cannot be recharged.
Ex:Dry cell.
Li-MnO
2battery.
Secondary Batteries
➢Cell reaction is reversible.
➢May be recharged
➢Have long shelf life.
➢Functions both as galvanic & electrolytic
cell.
➢They can be used as energy storage
devices. Ex: solar/ thermal energy
converted to electrical energy
➢They can be recharged.
Ex: Lead acid,
Ni-Cdbattery.
40
MATRUSRI
ENGINEERING COLLEGE

41. Anode:Zinc metal container.
Cathode:MnO
2+ Carbon (powdered graphite)
Electrolyte:Aqueous paste of NH
4Cl and ZnCl
2
Cell Notation:
Zn
(s)| ZnCl
2(aq),NH
4Cl
(aq)|MnO
2(s) |Mn
2O
3(s)|C
Output voltage = 1.5 V
41
DRY CELL(LECLANCHE CELL)
MATRUSRI
ENGINEERING COLLEGE

42. DRY CELL(LECLANCHE CELL)
42
MATRUSRI
ENGINEERING COLLEGE

43. Working:
Primary Electrode Reactions:
Anode: Zn
(s)→Zn
2+
(aq)+ 2e
-
Cathode:2MnO
2(s)+H
2O
(l)+ 2e
-
→ Mn
2O
3(s)+ 2OH
-
(aq)
Net Reaction: Zn
(s)+2MnO
2(s)+ H
2O
(l)→ Zn
2+
(aq)+Mn
2O
3(s)+2OH
-
(aq)
43
Secondary Reactions:
2NH
4
+
(aq)+2OH
-
(aq)→ 2NH
3(g)+2H
2O
(l)
Zn
2+
(aq)+2NH
3(s)+2Cl
-
→ [Zn(NH
3)
2Cl
2]
Over all reaction:
Zn + 2MnO
2+ 2NH
4Cl → [Zn(NH
3)
2Cl
2] + H
2O + Mn
2O
3
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44. Applications:
❖ In small portable appliances where small amount of
current is needed.
❖ In consumer electronic devices –flash lights, clocks,
remote controllers, walkman etc.
44
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45. Advantages:
❖Dry cell is cheap.
❖Normally works without leaking (leak proof cells).
❖Has a high energy density.
❖It is not toxic
❖It contains no liquid electrolytes.
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46. Disadvantages:
❖Voltagedropsduetobuildupofreactionproductsaroundthe
electrodeswhencurrentisdrawnrapidlyfromit.
❖Ithaslimitedshelflifebecausethezinciscorrodedbythe
faintlyacid,ammoniumchloride.
❖Theshelflifeofdrycellis6-8months.
❖Theycannotbeusedoncetheygetdischarged.
❖Itsemfdecreasesduringuseasthematerialisconsumed.
46
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47. QUIZ
1.Which of the following sentence is incorrect?
a) primary battery should be discarded after single use.
b) secondary battery should be discarded after single use.
c) battery is a portable source of electrical energy.
d) battery operate as galvanic cell during discharging.
2. Dry cell cannot be recharged because of
a) secondary reactions are not reversible.
b) primary reactions are not reversible.
c) battery dries after discharging.
d) battery leaks if connected to external source of emf.
3. The inert electrode in dry cell is
a) Zn b) Graphite c) MnO2 d) NH4Cl
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48. Anode: Spongy lead on lead grid.
Cathode: Porous PbO
2.
Electrolyte: H
2SO
4(aq)( 20 %)
(density 1.21-1.30g/ml)
Cell Notation:
Pb/PbSO
4;H
2SO
4(aq);PbSO
4;PbO
2/Pb
Voltage = 2V
48
MODULE-9: Lead-Acid Battery
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49. 49
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50. Discharging (as voltaic cell):
Anode: Pb
(s)→ Pb
2+
(aq)+ 2e
-
Pb
2+
(aq)+ SO
4
2-
(aq)→ PbSO
4(s)
Pb
(s)+ SO
4
2-
(aq)→ PbSO
4(aq)+ 2e
-
Cathode: PbO
2(s)+ 4H
+
(aq)+2e
-
→Pb
2+
(aq)+ 2H
2O
(l)
Pb
2+
(aq)+SO
4
2-
(aq)→PbSO
4(s)
PbO
2(s)+4H
+
(aq)+SO
4
2-
(aq)+2e-→ PbSO
4(s)+ 2H
2O
(l)
Overall:
Pb
(s)+PbO
2(s)+4H
+
(aq)+ 2SO
4
2-
(aq)→2PbSO
4(s) + 2H
2O
(l)+ Energy
(2H
2SO
4)
50
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51. Charging (as electrolytic cell)
Cathode:
PbSO
4(s)+2H
2O
(l)→PbO
2(s)+ SO
4
2-
(aq)+4H
+
(aq)+2e-
Anode :
PbSO
4(s)+ 2e
-
→ Pb
(s)+ SO
4
2-
(aq)
Net reaction:
2PbSO
4 (s)+ 2H
2O
(aq)→ Pb
(s)+ PbO
2(s)+2H
2SO
4
51
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52. A lead storage battery is highly efficient.
Voltage efficiency = average voltage during discharge
average voltage during charge
The voltage efficiency of the lead –acid cell is about 80 %.
A lead –acid battery provides a good service for several years. Its larger
versions can last 20 to 30 years, if carefully attended.
(i.e. longer design life)
It can be recharged. The number of recharges possible range from 300 to
1500, depending on the battery’s design and conditions.
52
ADVANTAGES
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53. ✓The battery’s own internal self –discharging is low.
✓The length of time that is generally required for recharging process is
less.
✓Low environmental impact of constituent materials is an added
advantage.
✓It has sensitivity to rough handling and good safety characteristics.
✓Ease of servicing as indicated by several local battery service points.
✓It is a low-cost battery with facilities for manufacture throughout the
world using cheap materials.
53
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54. Limitations
Self discharge:They are subject to self discharge with H
2evolution at negative
plates and O
2evolution at positive plates.
Pb+H
2SO
4→PbSO
4+ H
2
PbO
2+ H
2SO
4→PbSO
4+H
2O +1/2 O
2
SO
4
2-
+2 H
+
(From dissociation of water) → H
2SO
4
H
2O →H
+
+OH
-
Loss of Water:Due to evaporation, self discharge and electrolysis of water
while charging. Hence water content must be regularly checked and distilled
water must be added.
54
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55. CorrosionofGrid:Canoccurduetooverchargingwhengridmetal
getsexposedtotheelectrolytewhichweakensthegridand
increasestheinternalresistanceofthebattery.
Effectiveness of batteryis reduced at low temperature due to
increase in the viscosity of electrolyte.
55
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56. Applications:
•To start Automotive engines.
•Standby/Back-up/Emergency power for electrical
in hospitals, industries, households etc.
•Submarines.
•UPS (Uninterruptible Power Supplies).
•Lighting
•High current drain applications like trains.
56
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57. QUIZ
1.Which of the following is incorrect in lead acid battery
a) anode is spongy lead b) cathode is PbO2
c) H2SO4is the electrolyted) none
2. During discharging the change in oxidation number of Pbat cathode is
a) Pb(II) to Pb(IV) b) Pb(IV) to Pb(II)
c) Pbto Pb(II) d) none
3. During charging the lead acid battery acts as
a) voltaic cell b) galvanic cell
c) electrolytic cell d) all the above
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58. MODULE-10: Lithium Ion Battery
•Itconsistsofagraphiteanodeandlithiumoxidecathode.
•Cathodeconsistsofalayeredcrystalintowhichthelithiumis
intercalated.
•ExperimentalcellshavealsousedlithiatedmetaloxidesuchasLiCoO
2,
NiNi
0.3Co
0.7O
2,LiNiO
2,LiV
2O
5,LiV
6O
13,LiMn
4O
9,LiMn
2O
4,LiNiO
0.2CoO
2.
•ElectrolytesareusuallyLiPF
6althoughthishasaproblemwithaluminum
corrosion,andsoalternativesarebeingsoughtonesuchisLiBF
4.
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59. •CellreactionsinLithiumionbatteryinvolvemigrationoflithiumions
betweenthepositiveandnegativeelectrode.
•Nochemicalchangesareobservedatthetwoelectrodesorinthe
electrolyte.
•Lithium-Graphiteintercalationcanbechargedanddischarged
reversiblywherelithiumdopingischargingreactionandun-dopingis
dischargingreaction.
59
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Lithium Ion Battery

60. Duringdischarginglithiumionsareextractedfrom
anodebyelectrochemicaloxidationandinserted
intothecathodebyelectrochemicalreduction.
Thiscellproducesanemfof3.7V.
60
Lithium Ion Battery
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61. Duringchargingoflithiumionbatteries,Lithium
ionsareextractedbyoxidationfromLiCoO
2
cathodeandtheextractedlithiumionsare
dopedbyelectrochemicalreductionintocarbon
anodetoformLi-GIC.
61
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Lithium Ion Battery

62. Advantages
•The high energy density.
•Low self-discharge.
•They do not require and maintenance to ensure their
performance.
•The voltage produced by each lithium ion cell is about 3.7
volts.
•Variety of types of lithium ion cell available.
62
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63. Disadvantages
•They require protection from being over charged and discharged too
far.
•They need to have the current maintained within safe limits.
•Ageing.
•Transportation: Any lithium ion batteries carried separately must be
protected against short circuits by protective covers, etc.
•Cost: They are around 40% more costly to manufacture than Nickel
cadmium cells.
63
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64. Applications
•Theseareusedinmobilephonesandsmartphones,laptopsand
tablets,digitalcameras,electroniccigarettes,handheldgame
consolesandtorchesetc.
•Electricvehicles.
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65. QUIZ
1.Which of the following is correct sentence incase of lithium ion battery
a) lithium ions move between the electrodes during operation
d) Li ion battery consists of graphite anode and lithium oxide cathode
c) Electrolytes are usually LiPF
6or LiBF
4 in Li ion battery.
d) all the above
2. During discharging in Li ion battery
a) Li ions are extracted from anode
b) Li ions are extracted from cathode
c) Li ions are inserted to anode
d) none
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66. MODULE-11: Fuel Cells
A fuel cell is a galvanic cell in which chemical energy of a fuel –oxidant
system is converted directly into electrical energy in a continuous
electrochemical process.
•Cell Schematic Representation:
Fuel/electrode/electrolyte/electrode/oxidant.
e.g. H
2-O
2; CH
3OH-O
2
66
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67. Thereactants(i.e.fuel+oxidant)areconstantlysuppliedfromoutside
andtheproductsareremovedatthesamerateastheyareformed.
Anode:
Fuel+oxygen→Oxidationproducts+ne
-
Cathode:
Oxidant+ne
-
→Reductionproducts.
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68. Requirements Of Fuel Cell.
Electrodes:Mustbestable,porousandgoodconductor.
Catalyst:Porous electrode must be impregnated with catalyst like Pt, Pd,
Ag or Ni, to enhance otherwise slow electrochemical reactions.
Temperature: Optimum.
Electrolyte:Fairly concentrated.
68
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69. CH
3OH-O
2Fuel Cell
Both electrodes: Made of porous nickel plates impregnated with finely-
divided Platinum.
Fuel:Methyl alcohol.
Oxidant:Pure oxygen / air.
Electrolyte:Conc.Phosphoricacid/Aq.KOH
Operating Temperature: 150-200
o
C.
69
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70. CH
3OH-O
2Fuel Cell
70
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71. The emfof the cell is 1.20 V at 25
o
C.
CH3OH is one of the most electro active organic fuels in the low
temperature range as
*It has a low carbon content
*It possesses a readily oxidizableOH group
*It is miscible in all proportions in aqueous electrolytes.
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72. At anode:
CH
3OH + 6OH
-
→CO
2+ 5H
2O + 6e
-
•At cathode:
3/2 O
2+3H
2O + 6e
-
→6OH
-
Net Reaction:
CH
3OH +3/2O
2→CO
2+ 2H
2O.
It is used in military applications as doesn't produce much noise &
gives high efficiency of energy conversion with a high long life
and in large scale power production. It has been used to power
television relay stations.
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73. Advantages Of Fuel Cells.
•High efficiency of the energy conversion process.
•Silent operation.
•No moving parts and so elimination of wear and tear.
•Absence of harmful waste products.
•No need of charging.
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74. Limitations Of Fuel Cells.
•Cost of power is high as a result of the cost of electrodes.
•Fuels in the form of gases and O
2need to be stored in tanks under
high pressure.
•Power output is moderate.
•They are sensitive to fuel contaminants such as CO,H
2S, NH
3&
halides, depending on the type of fuel cell.
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75. QUIZ
1.In which of the following cell the reactants are not stored?
a) Lead-acid battery b) Ni-Cdbattery
c) Methanol-oxygen fuel cell d) Dry cell
2. The products of the methanol-oxygen fuel cell are
a) CO2, CH3OH b) CO2, H2O
c) CH3OH, H2O d) H2O, KOH
3. Advantages of the methanol-oxygen fuel cell are
a) silent operation b) no harmful products
c) high efficiency d) all the above
4. Which of the following is not correct with respect to methanol-oxygen fuel cell
a) anode is fed with CH3OHb) cathode is fed with O2
c) KOH is the electrolyted) electrodes are not filled with catalyst
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