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Commercial Voltaic Cells
 A voltaic cell can be a convenient, portable source
of electricity.
 We know them as batteries.
 Batteries have been in use for over 100 years in
various forms.
 The technology of batteries remained fairly
stagnant until about 1990. Why???
Lead-Acid Battery
 This type of cell has been around for over 80 years.
 It uses lead as the anode and lead(IV) oxide as the
cathode.
 Highly caustic H2SO4 is also involved in the overall
reaction.
 The reaction produces a reliable 2.0 V.
Lead-Acid Battery
Lead-Acid Battery
 The half-reactions are:
Pb(s) + HSO4-(aq)  PbSO4(s) + H+(aq) + 2e (anode)
PbO2(s) + 3H+(aq) + HSO4-(aq) + 2e 
PbSO4(s) + 2H2O(l) (cathode)
 Overall reaction is:
PbO2(s) + Pb(s) + 2H+(aq) + 2HSO4-(aq)  2PbSO4(s) + 2H2O(l) During
recharging, water is consumed. This used to require that water
occasionally was added to the battery.
 The new batteries use Pb/Ca alloy as the anode which resists the
consumption of water. This has led to the “maintenance-free”
batteries.
Lead-Acid Battery
 Advantages: produces steady voltage, very high
current, many recharges, relatively low cost.
 Disadvantages: environmental concerns, massive,
reverse reaction can produce H2.
Zinc-Carbon Dry Cell
 Known also as the LeLanche cell (for its inventor), uses
a zinc can as the anode and a graphite rod as the
cathode.
 A paste containing NH4Cl and MnO2 separates the two
electrodes.
Zinc-Carbon Dry Cell
 The anode and cathode reactions are:
 Zn(s)  Zn+2(aq) + 2e- (anode)
 2 NH4+(aq) + 2 MnO2(s) + 2e- 
Mn2O3(s) + H2O(l) + 2 NH3(aq (cathode)
 Advantages: inexpensive, produces a reliable 1.5 V.
 Disadvantages: performs poorly under high demand,
poor in cold weather, prone to leak when it gets old,
environmental (disposal).
The Zinc-Carbon Dry Cell
Alkaline Dry Cell
 Similar, but uses KOH as the paste between the
electrodes. The reactions are:
 Zn(s) + 2OH-(aq)  Zn(OH)2(s) + 2e (anode)
 2MnO2(s) + H2O(l) + 2e  Mn2O3(s) + 2 OH-(aq) (cathode)
 Advantages: better under high demand, better in
cold weather.
 Disadvantages: higher cost, environmental
(disposal).
Alkaline Dry Cell
NiCad Cell
 Nickel-Cadmium (Nicad) batteries were some of the first widely
used rechargeable batteries.
 The reactions are:
Cd(s) + 2OH-(aq)  Cd(OH)2(s) + 2e (anode)
NiOOH(s) + H2O(l) + e  Ni(OH)2(s) + OH-(aq) (cathode)
 Advantages: easy to recharge, many recharge cycles, good current
supply.
 Disadvantages: longer recharge times, cost, weight, toxicity of Cd,
and “memory loss.”
NiMH Cell
 Newer version is the Nickel-Metal hydride
(NiMH) battery that has longer life and
eliminates the Cadmium which is replaced
with a ZrNi2 metal alloy. This alloy absorbs
Hydrogen anions that are oxidized.
 Most hybrid automobiles use these type of
batteries.
 Advantages: Have a very long-life and can
last for up to eight years.
 Disadvantage: Replacement costs in an auto
can be upwards of $8,000.
Lithium-Iodine Cell
 A “true” dry cell.
 The anode is lithium metal and the cathode is an I2
crystal.
 Current is carried by diffusion of Li+ ions.
 This battery is used in pacemakers as well as the BIOS
in computers.
Lithium-Iodine Cell
 The anode and cathode reactions are:
Li(s)  Li+(aq) + 1e
(anode)
I2(s) + 2e  2 I-(aq)
(cathode)
 Advantages: environmentally friendly, produces a
large voltage (3.0 V), long life, rechargeable, large
power to mass ratio.
 Disadvantages: produces low current, cost.
Lithium-Ion Cell
 A newer version of the previous type.
 Graphite serves as one electrode with LiCoO2 as the other
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electrode.
During charging, the Li+ ions migrate to the anode
(graphite) and the Cobalt is oxidized.
During discharge, the Li+ migrate spontaneously to the
cathode.
These are the batteries of choice for most portable
computers and PDA’s.
Can be recharged many times for up to two years.
Lithium-Ion Cell
Lithium-Ion Cell
 Advantages: Store more energy per gram of weight, hold
their charge of long periods, and each cell has a large
voltage (3.6V).
 Disadvantages: Degrade even without use, last two to three
years, cannot be completely discharged, and may catch fire
if they fail.
Cell Voltages / Currents
 Most devices require
voltages of 3.0, 6.0, or
even 12.0V as well as
high currents.
 To produce these
values, cells are placed
in both series as well
as in parallel.
Fuel Cells
 Energy choice of the future.
 Not a true battery as it requires a constant supply
of reactants.
 Used by NASA on space vehicles to generate
electricity.
 May soon be mass produced for automobile
propulsion.
 Smaller versions could power laptops and cell
phones.
Fuel Cells
 The overall reaction converts H2 and O2 into H2O.
2 H2(g) + 4 OH-(aq)  4 H2O(l) + 4e (anode)
O2(g) + 2 H2O(l) + 4e  4 OH-(aq) (cathode)
Overall Reaction is:
2 H2(g) + O2(g)  2 H2O(l)
Fuel Cells
Fuel Cells
 Fuel Cell Organization
 www.fuelcells.org
 Fuel Cell Producer / Researcher
 www.ballard.com
Fuel Cells
 Advantages: best for the environment - produces
water!, relatively low mass, much more efficient
than the internal combustion engine, greatly
simplify car design.
 Disadvantages: cost, storage / use of hydrogen,
mass production, acceptance.
Corrosion
 Electrochemical process of corrosion is essentially
a mini voltaic cell.
 When a drop of water comes into contact with
iron, the corrosion process begins.
 At the center of the drop, iron metal is oxidized:
Fe  Fe+2 + 2e.
 At the edges, oxygen is reduced:
O2 + 4H+ + 4e  2H2O
Corrosion
Corrosion
 Corrosion of iron is more favored when:
 Moisture is present
 Concentrations of electrolytes (salt) is present
 Lower pH’s
 Prevention of corrosion can be achieved by:
 Paint – prevents oxygen and water from interacting with the iron
 Use of a sacrificial metal – any more active metal in contact with
the iron will be oxidized in preference to the iron. This is
sometimes called cathodic protection.
Cathodic Protection
Cathodic Protection