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The Galvanic cell, named after Luigi Galvani, consists of two different metals connected by a salt bridge or a porous disk between the individual half-cells. It is also known as a voltaic cell and an electrochemical cell.

Contents 1 History 2 Description 3 Electric potential of a Galvanic cell 4 Galvanic corrosion 5 Cell types 6 See also 7 External links

In 1780, Luigi Galvani discovered that when two different metals (copper and zinc for example) were connected together and then both touched to different parts of a nerve of a frog leg at the same time, they made the leg contract. He called this "animal electricity". The Voltaic pile, invented by Alessandro Volta in the 1800s, is similar to the galvanic cell. These discoveries paved the way for all electrical batteries.

The Galvanic cell's metals dissolve in the electrolyte at two different rates. Metals become positive ions upon dissolving, and leave electrons behind. As a result, the metal acquires a negative net charge while the electrolyte becomes equally positive. Each metal undergoes a different half-reaction, giving different dissolving rates, which builds up different electrode potentials between the electrolyte and each metal. If an electrical connection, such as a wire or direct contact, is formed between the two electrodes, an electric current appears in the metal. At the same time, an equal electric current composed of positive ions appears in the electrolyte. Ions of the more active metal which forms the anode are transferred to the electrolyte. Dissolved ions are also transferred to the less active metal, the cathode, and deposited there as a plating. In this way the anode is consumed or corroded. When the anode material corrodes entirely away, the cell's potential drops and the current halts. The metal may be regarded as the fuel which powers the device. A similar process is used in electroplating. The electric current in the electrolyte is equal to the current in the external circuit, so a complete circuit is formed with a path through the electrolyte.

There is a flow of electrons from the oxidized ion at the anode to the reduced atom (formerly an ion) at the cathode. It is this flow, due to this redox reaction which constitutes the current.

The electrode potential of a cell can be easily determined by use of a standard potential table. An oxidation potential table could also be used, but the reduction table is more common. The first step is to identify the two metals reacting in the cell. Then one looks up the E^o (standard electrode potential, in volts) for each of the two half reactions. The electric potential for the cell is equal to the more positive E^o value minus the more negative E^o value.

For example, in the picture above the solutions are CuSO₄ and ZnSO₄. Each solution has a corresponding metal strip in it, and a salt bridge or porous disk connecting the two solutions and allowing SO₄²⁻ ions to flow freely between the copper and zinc solutions. In order to calculate the electric potential one looks up copper and zinc's half reactions and finds that:

Cu²⁺ + 2e⁻ → Cu (E = +0.34 V)

Zn²⁺ + 2e⁻ → Zn (E = −0.76 V)

Thus the reaction that is going on is really

Cu²⁺ + Zn → Cu + Zn²⁺

The electric potential is then +0.34 V −(−0.76 V) = 1.10 V

If the cell is operated under non-standard conditions, the potentials must be adapted using the Nernst equation.

Main article: Galvanic corrosion

Galvanic corrosion is a process that degrades metals electrochemically. This corrosion occurs when two dissimilar metals are placed in contact with each other in the presence of an electrolyte, such as salt water, forming a galvanic cell. A cell can also be formed if the same metal is exposed to two different concentrations of electrolyte. The resulting electrochemical potential then develops an electric current that electrolytically dissolves the less noble material.

• Concentration cell
• Electrolytic cell
• Electrochemical cell

• Electrode potential
• Galvanic series
• Alessandro Volta
• Voltaic pile
• Volt
• Battery (electricity)
• Electrosynthesis

• "Galvanic (Voltaic) Cells and Electrode Potential". Chemistry 115B, Sonoma.edu.
• "Making and testing a simple galvanic cell". Woodrow Wilson Leadership Program in Chemistry, The Woodrow Wilson National Fellowship Foundation.
• "Galvanic Cell" Good Animation