The galvanic cell is a device consisting of two different metals connected by means of a salt bridge or a porous disk located between each half cell. It receives its name in honor to Luigi Galvani.
The voltaic cell, invented in 1800 by Alessandro Volta is similar to the galvanic cell. These discoveries paved the way for electric batteries.
The metal of a galvanic cell dissolves in the electrolyte at two different speeds. The metals become positive ions in dissolving and the electrons remain in the undissolved part. As a result, the metal acquires a net negative charge as the electrolyte becomes positively charged. Each metal is subjected to half of a redox reaction, with different dissolution rates giving different reduction potentials between the electrolyte and each metal. If an electrical connection, such as a wire or other direct contact between the two electrodes, an electric current appears to the metal. At the same time, an equal electric current of positive ions appears in the electrolyte. The ions of the more active metal, which forms the anode, are transferred to the electrolyte. The dissolved ions are also transferred to the less active metal, the cathode, and are deposited on their surface, coating it. In this way the anode is consumed or corroded, when the material of the anode has been totally consumed, the potential of the cell falls and the current stops. The metal can be considered as the fuel that provides the energy to the widget. A similar process is to use electrolysis. The electric current in the electrolyte is equal to the current of the external circuit, that is to say, the complete electric circuit is formed both by external path, that run through the electrons, and by the part of the electrolyte, which run through the positive ions.
There is a flow of electrons from the anode, the oxidized ions, towards the cathode, the reduced atoms (which capture electrons). This flow produced by an oxidation-reduction (redox) reaction is what constitutes the electric current produced by the cell.
Electrical potential of a galvanic cell
The standard reduction potential (electron withdrawal) of a cell can be easily determined using a potential table. A potential oxidation table can also be used, but it is much more common to use the reduction board. The first step is to identify the two metals that react to the cell. Then you have to look at the value of the Eo column, in volts, for each of the two half reactions. The potential of the cell will be equal to the most positive value of E or minus the least negative value of Eo.
Galvanic corrosion is a process that degrades metals electrochemically. This corrosion occurs when two different metals are brought into contact in the presence of an electrolyte, such as brine, forming a galvanic cell. The cell would also form if a single metal were exposed to two different concentrations of electrolyte. The resulting electrochemical potential produces an electric current that electrolytically dissolves the less noble metal.
History of the galvanic cell
In 1780, Luigi Galvani discovered that when two different metals (eg copper and zinc) are connected and then both simultaneously touch two different parts of a nerve of a frog leg, then the leg contracts. He called it "animal electricity." The voltaic cell, invented by Alessandro Volta in the 1800s, consists of a pile of cells similar to the galvanic cell. However, Volta built it entirely from non-biological material to challenge Galvani's (and the later experimenter Leopoldo Nobili's) animal power theory in favor of his own metal-metal contact electricity theory. Carlo Matteucci in turn built a battery entirely of biological material in response to Volta. These discoveries paved the way for electric batteries; The Volta cell was named a landmark of the IEEE in 1999.
It was suggested by Wilhelm König in 1940 that the object known as the battery of Baghdad could represent the galvanic cell technology of the ancient Parthia. Replicas filled with citric acid or grape juice have been shown to produce a voltage. However, it is far from certain that this was their purpose-other scholars have pointed out that it is very similar to containers known to have been used to store scrolls.
Type of galvanic cell
Of types of galvanic cells we distinguish three:
- Concentration cell
- Electrolytic cell
- Electrochemical cell