1. Cells & Batteries

2. Cells & Batteries Primary Cells
these cells cannot be easily re-charged; once they die… they stay dead.

3. Primary Cells I. Regular Carbon – Zinc Dry Cell Zinc Case (Anode)‏
Carbon Rod (Cathode)‏
ZnCl2, MnO2, & NH4Cl in paste
Zn(s) --> Zn2+(aq) e-
(Anode Rxn)‏
2 NH4+(aq) MnO2(s) e- --> Mn2O3(s) NH3(aq) + H2O(l)
(Cathode Rxn)‏
Overall reaction:
Zn(s) NH4+(aq) MnO2(s) --> Zn2+(aq) + Mn2O3(s) NH3(aq) + H2O(l)‏ E = 1.5 V

4. Primary Cells II. Alkaline Cells
More efficient; better in high load situations

5. Primary Cells Zn – KOH anode paste Steel (Fe) Case
MnO2 Cathode mixture
KOH electrolyte
Brass current collector
Zn(s) + 2 OH-(aq) --> ZnO(s) + H2O(l) + 2e
Anode Rxn (oxidation)‏
MnO2(s) H2O(l) + 2 e- --> Mn(OH)2(s) OH-(aq) + H2O(l)
Cathode Rxn (Reduction)‏
Overall Rxn:
Zn(s) + MnO2(s) + H2O(l) --> ZnO(s) + Mn(OH)2(s) E =1.5V

6. Primary Cells III. Mercury Battery
– smaller; used to power hearing aids & calculators
Zn(s) OH-(aq) --> ZnO(s) + H2O(l) + 2 e-
Anode Rxn (Oxidaion)
HgO(s) + H2O(l) + 2 e > Hg(l) + 2 OH-(aq)‏
Cathode Rxn (Reduction)‏
Overall Rxn:
Zn(s) HgO(s) --> ZnO(s) + Hg(l) E = 1.35 V‏

7. Secondary Cells IV. Ni-Cad
These cells can be re-charged by running a current backwards through them.
IV. Ni-Cad
The first practical rechargeable “drycell”.
Ni-Cad Demo

8. Secondary Cells
Cd(s) OH-(aq) --> Cd(OH)2(s) + 2 e- anode rxn (oxidation)‏
NiO(OH)(s) + H2O(l) + 2 e > Ni(OH)2(s) + OH cathode rxn (reduction)
Overall Rxn:
Cd(s) + OH-(aq) + NiO(OH)(s) + H2O(l) ↔ Cd(OH)2(s) + Ni(OH)2(s) E =1.2V‏
These reactions can be reversed. The cell can be re-charged many times over (about 1000 x). The cells are more expensive to manufacture but last much longer. The reactions are not 100% reversible and eventually the cells can not be made to “hold” a charge and must be replaced. These are being replaced by the new Li-Metal hydride cells.)‏

9. Secondary Cells V. Lead Acid Storage Battery
the first practical re-chargeable battery; still used in cars, motorcycles, boats etc.
This is the first true “battery” made up of 6 separate cells. It is a good choice for motor vehicles because it provides a large initial supply of energy to start the engine, has a long shelf life, and is reliable at low temperatures. The downside is the weight of the batteries (they contain lead after all) and the environmental problems of lead.

10. Secondary Cells
Pb(s) + SO42-(aq) --> PbSO4(s) + 2 e- anode rxn (oxidation)‏
PbO2(s) H+(aq) + SO42-(aq) + 2 e- --> PbSO4(s) +2 H2O(l) cathode)‏
Overall Rxn:
Pb(s) + PbO2(s)+ 4 H+(aq) + 2 SO42-(aq) -->2 Pb(SO4)(s) + 2 H2O(l) E =12V

11. Secondary Cells VI. Lithium Metal
an alternative to the Lead-Acid battery; a much higher power to mass ratio than the lead-acid; better for use in electric cars, small electric devises such as cameras
A cross section of the newer Li-Metal hydride rechargeable cell.

12. Secondary Cells Li(s) --> Li+(aq) + 2 e- (oxidation @ anode)‏
Zn(s) NH4+(aq) MnO2(s) --> Zn2+(aq) + Mn2O3(s) NH3(aq) + H2O(l) cathode)‏
These cells output almost 3.0 V compared to the 1.5 V of regular carbon – zinc cells.

13. Newer Technologies VII. Fuel Cells
combining hydrogen gas with oxygen gas without “burning” but with the production of electricity.
The electricity is then used to power an electric motor.
A clean re-newable type of power source.
Fuel Cell demo

14. Fuel Cells The reaction occurs in two half cells as follows:
2 H2(g) OH-(aq) > 4 H2O(l) + 4e- Anode Rxn (oxidation)‏
2 O2(g) H2O(l) e- --> 4 OH-(aq) Cathode Rxn (reduction)‏
Overall Rxn:
2 H2(g) + O2(g) > 2 H2O(l)‏
(same as “burning hydrogen gas with oxygen!!)‏

15. Fuel Cells Advantages:
The great thing about fuel cells is that they are very low polluters. The only product is water. The fuel sources are atmospheric oxygen and breaking down water can generate hydrogen. Large solar cells using the sun energy could be used to do this.
Disadvantages:
Still need a source of H2 gas (they use fossil fuels for this now). Storage capacity for H2 gas is still a problem (Capacity and dangers from the gaseous H2). The fuel cell still has problems with reliability.

16. The End!