BATTERY BASICS

    As electrical applications continue to gain popularity in the search for alternative energy, battery technology has been receiving much attention.  The goal is to develop a battery that lasts long yet delivers high voltage.

LEAD BATTERIES
   In a lead battery, the anodes are plates of lead while the cathode is coated with PbO₂.  The electrolyte used is sulfuric acid.  This leads to the following reactions:
   PbO₂ (s) + 4H⁺ (aq) + SO₄^2- (aq) + 2e^- ---> PbSO₄ (s) + 2H₂O (on cathode)
    Pb (s) + SO₄^2- (aq) ---> PbSO₄ (s) + 2e^- (on anode)
produces a net reaction of:
    PbO₂ (s) + Pb (s) + 4H⁺ (aq) + 2SO₄^2- (aq) ---> 2PbSO₄ (s) + 2H₂O
    As the cell discharges energy, the concentration of sulfuric acid decreases.  When it becomes significantly low, the battery is considered "dead".  This leads to the major advantage of lead batteries.  These batteries can be recharged by applying a voltage to the battery from an external source (battery chargers).  This causes the following electrolysis reaction, thus recharging the battery.
    2PbSO₄ (s) + 2H₂O ---> PbO₂ (s) + Pb (s) + 4H⁺ (aq) + 2SO₄^2- (aq)
Lead batteries are the type used to start your conventional, combustion engine automobile.

NICKEL-CADMIUM BATTERIES
   The nickel-cadmium battery (better known simply as the "rechargeable battery") utilizes the following reactions:
    Cd (s) + 2OH^- (aq) ---> Cd(OH)₂ (s) + 2e^- (on anode)
    NiO₂ (s) + 2H₂O + 2e^- ---> Ni(OH)₂ (s) + 2OH^- (aq)  (on cathode)
Ni-Cd batteries utilize MnO₂ and KOH as electrolytes.

FUEL CELLS
   The primary advantage of fuel cells is their high efficiencies (around 75%).  Many cells use nickel and carbon electrodes, and potassium hydroxide as an electrolyte.  Hydrogen and oxygen (or other gases) provide the fuel in the following type of reactions:
    O₂ (g) + 2H₂O + 4e^- ---> 4OH^- (aq)   (on cathode)
    H₂ (g) + 2OH^- (aq) ---> 2H₂O + 2e^-    (on anode)
    2H₂ (g) + O₂ (g) ---> 2H₂O    (net reaction)

The disadvantages to a fuel cell of this type are its large size and high costs.  This type of cell is used to produce power and drinking water on spacecrafters.  For more information on fuel cells, see the related article, Sunlight in a Bottle, here at The Chemical Engineers' Resource Page.