Batteries

• A galvanic cell or a group of galvanic cells connected in series

• Source of portable power

• Several types of battery in use today; we’ll look at two

Electrochemistry

Batteries

Lead Storage Battery

Pb + HSO4- PbSO4 + H+ + 2e-

PbO2 + HSO4- + 3H+ + 2e-

PbSO4 + 2H2O

Car battery has six of these connected in series.

Each cell produces ~ 2 V so the battery has a 12 V potential.

Lead Storage Battery

• In a car the battery is continuously recharged by the alternator.

• If allowed to run down, PbSO4(s) builds up on the surface of the grids.

• Applying a current reverses the reaction and removes the PbSO4.

Dry Cell Battery

• Acid version:

Zn Zn2+ + 2e-

2NH4+ +2MnO2 +2e- Mn2O3 +2NH3 +H2O

• Alkaline version:

Zn + 2OH- ZnO + H2O + 2e-

2MnO2 + H2O + 2e- Mn2O3 + 2OH-

Dry Cell Battery

Alkaline version lasts longer since Zn corrodes less rapidly under basic conditions

All cells from AAA to D provide ~1.5 V.

Larger cells provide more current.

Other Types of Batteries• Mercury batteries can

be very small

• Lithium-iodide batteries are lightweight and long-lasting.

• Also Ni-Cd and Ni metal hydride types

BatteriesBatteriesFuel CellsFuel Cells

Fuel CellsGalvanic cell for which the

reactants are continuously supplied.

Primary reaction under study is:

2H2(g) + O2(g) 2H2O(l)

Fuels cells of this type used by NASA, but not practical for general use yet.