Transcript Batteries and Fuel Cells

Pgs 655 - 658
BATTERIES AND FUEL CELLS
How can we use galvanic
cells in everyday life?
 BATTERIES!!
 Take galvanic cells and make them easier to carry
around and use!
All batteries require
electrical potential:
 What is electrical potential:
 The “pressure” on electrons to flow
from one electrode to the other in a
redox reaction
 Depends on the difference between
the atoms being oxidized and reduced
on the activity series
 Measured in volts
Li
Rb
K
Cs
Ba
Sr
Ca
Na
Mg
Al
Zn
Cr
Fe
Ni
Sn
Pb
Cu
Hg
Least reactive Ag
Au
Most reactive
Types of Batteries
Lead Storage Batteries
Dry Cell Batteries
Dry Cell Batteries
 Advantage of this type of battery:
 Small, efficient at producing energy, don’t
contain a liquid
 Anode = Zinc case
 Solid Zn is oxidized at anode:
 Zn (s)  Zn2+ + 2e-
 Cathode = Graphite rod
 NH4+ and MnO2 is reduced
 Used in calculators, watches, flashlights
 What makes an alkaline battery
different?
 Last longer because the Zn doesn’t corrode
as quickly in the basic environment!
How does our lab from Friday
link to corrosion?
 Corrosion is the process of returning metals
to their natural state
 It’s a REDOX reaction!!
Fe (s) + O2 (g)  Fe2O3 (s)
 LOTS of metals corrode, but not all of them
corrode to the same extent:
 Ex  Aluminum!!
 Aluminum will be oxidized by the air
 Al (s) + O2 (g)  Al2O3 (s)
 A thin layer of Al2O3 will cover the metal and
protect it from further corrosion
How can we protect these
metals from corrosion?
 The Mg will react instead of the iron…but
why???
Lead Storage Batteries
 Advantages of this type of battery:
 Can work for several years in extreme
temperatures
 Provides a lot of voltage (12 V) for its size
 RECHARGE themselves!!
 Where do we use lead storage batteries?
 IN CARS!!!
Lead Storage Batteries
 Anode = metal lead
 Cathode = lead (IV) oxide coated onto lead
grids
 Solution = H2SO4
 Anode and cathode
are separated, so the
e- move through a wire
that provides an
electric current to run
the car
So what about hydrogen fuel
cells?
 Fuel cells: galvanic cells in which a fuel
substance undergoes oxidation which creates
energy
 Don’t have to be re-charged
 Can be created so that no air pollutants are
produced
 Used to run the Apollo missions
 Trying to find a way to use them in cars!
Hydrogen Fuel Cells
• Cathode compartment has oxygen gas
• Anode compartment has hydrogen gas
• Middle compartment a membrane that
allows H+ to move to O2
• Oxidation: 2H2 (g) +  4H+ + 4e• Reduction: O2 (g) + 4H+ +4e-  2H2O (l)
• Overall: 2H2 (g) + O2 (g)  2H2O (l)
Hydrogen Fuel Cells and Cars
http://www.chevrolet.com/fuelcell/
Show fuel cell Nova science now video