Electrochemistry Principles and Battery Technologies

Electrochemistry and Electrolysis

Electrochemistry studies the transformation between electrical energy and chemical energy. Electrolysis is the decomposition of a substance by means of an electric current.

Classification of Conductors

A conductor is a substance that allows the passage of electric current. They are classified as follows:

• Conductors of the first kind: Metals are characterized by conducting electrical current without changing their structure.
• Second-class conductors: Compounds, either fused or in solution, conduct electric current; however, as the current passes, chemical bonds are broken and the substances are converted into other materials.
• Covalent compounds: These compounds have covalent bonds and do not conduct current.

Industrial Applications of Electrolysis

• Electroplating: This process is used to prevent the corrosion of metals by creating a thin film of a less corrodible metal on the surface.
• Electrometallurgy: A process used to separate pure metals from compounds using electrolysis. For example, in the electrolysis of sodium hydroxide, sodium is separated into pure sodium, pure oxygen, and water.
• Anodizing: This technique is used to protect metals from corrosion.
• Industrial Production: Electrolysis is used for the production of materials with multiple uses in industry, such as fuel for welding, etc.

Electrochemical Cells

The Daniell Cell

The Daniell cell is constructed with a copper plate and a zinc plate introduced into an aqueous solution of copper sulfate. Both plates, called electrodes, are joined by an electronic conductor (e.g., copper wire). In this situation, the oxidized zinc atoms lose electrons and pass into solution as positive ions. Simultaneously, the positive copper ions in the solution are reduced, gain electrons, and are deposited as metallic copper atoms on the copper electrode.

The Lead Battery

A lead battery consists of a container filled with a solution of sulfuric acid as the electrolyte, where two mesh plates made of thin lead are immersed. One plate is filled with lead oxide and the other with finely divided, spongy lead. The lead oxide plate serves as the positive terminal of the battery, and the spongy lead plate serves as the negative pole; between them, there is a nominal voltage of 2 volts.

Oxidation Potential and Corrosion

Oxidation Potential: This is the difference between a half-cell of a certain element and the normal half-cell of Hydrogen (M), measured with a voltmeter. The potential measures the tendency of the element to oxidize.

Electrolytic Series: A table showing the values of oxidation potential.

Corrosion: The deterioration of a material as a result of electrochemical attack by its environment.

Chemical Equations for Common Batteries

Dry Cell

Oxidation (anode): Zn → Zn²⁺ + 2e^-

Reduction (cathode): 2 MnO₂ + 2 NH₄⁺ + 2e^- → Mn₂O₃ + 2 NH₃ + H₂O

Alkaline Battery

Oxidation (anode): Zn → Zn²⁺ + 2e^-

Reduction (cathode): 2 MnO₂ + H₂O + 2e^- → Mn₂O₃ + 2 NH₃ + 2OH^-

Lithium Battery

Oxidation (anode): Li → Li⁺ + 1e^-

Reduction (cathode): Ti + 1e^- → Ti

Nickel-Cadmium Battery

Anode: Cd + 2OH^- → Cd(OH)₂ + 2e^-

Cathode: NiO(OH) + H₂O + e^- → Ni(OH)₂ + OH^-

Mercury Battery

Anode: Zn° + 2OH^- → ZnO + H₂O + 2e^-

Cathode: HgO + H₂O + 2e^- → Hg + 2OH^-

Lead Cell

Anode: Pb + SO₄^2- → PbSO₄ + 2e^-

Cathode: PbO₂ + SO₄^2- + 4H⁺ → PbSO₄ + H₂O

Fuel Cells

Anode: 2H₂ + 4OH^- → 4H₂O + 4e^-

Cathode: O₂ + 2H₂O + 4e^- → 4OH^-