Galvanic cell

A galvanic cell is a type of electrochemical cell that generates electricity through chemical reactions. The type of chemical reactions that occur in galvanic cells are known as spontaneous redox reactions, which are reduction-oxidation reactions that release energy. Galvanic cells usually contain two types of metal, which undergo reduction and oxidation reactions in separate chambers. A porous membrane or salt bridge joins the two metals, permitting electrons to flow as the redox reactions occur. The resultant electricity can then be harnessed to perform tasks and work that require external energy input. Batteries often contain one or more galvanic cells where their electricity is produced.

Galvanic cells are also known as voltaic cells. They are named after the two Italian scientists whose research into electricity and electrochemistry led to their invention: Luigi Galvani (1737–1798) and Alessandro Volta (1745–1827).

Background

Luigi Galvani was a physician and physicist who spent much of his career conducting experiments on electricity in animal tissues. In 1787, Galvani conducted a random experiment that involved attaching an iron wire to a deceased frog’s muscle and a copper wire to its nerve. He then connected each wire to electrodes of different metals, applying electricity and triggering muscle contractions in the frog. The research marked a watershed moment in the history of bioelectricity research, demonstrating that muscle movement had an electrical component and electricity took an indirect rather than direct action. In 1791, Galvani published his findings, claiming to have discovered a phenomenon he called “animal electricity.”

Alessandro Volta reviewed Galvani’s findings and came to believe that Galvani had been mistaken about the nature of the phenomenon he had observed. In 1792, Volta conducted his own experiments on frogs, concluding that Galvani’s identification of “animal electricity” was incorrect and Galvani had actually observed the effects of normal electricity. Volta’s research eventually proved that it was the electrified contact with two different metals that actually caused the muscle movements. He then tested various pairs of metals to see which released the largest amounts of energy, which he called “electromotive force.” Volta identified a list of nine metallic electricity conductors, listing them in descending order of the strength of their electromotive force: zinc, lead, tin, iron, copper, silver, gold, graphite, and manganese ore. Volta also showed that the electrical effects could occur independent of any animal subject, with the apparatus he created to demonstrate this fact entering scientific history as the first battery ever invented.

The combined results of Galvani and Volta’s research marked a major breakthrough in scientific understanding of electricity. After Volta demonstrated his battery for the first time, a wave of successive research led to further milestones. A few weeks later, English scientists William Nicholson (1753–1815) and Anthony Carlisle (1768–1840) used a battery to break down water into its constituent hydrogen and oxygen elements. Around the turn of the nineteenth century, the Cornish inventor Humphry Davy (1778–1829) used a high-powered battery to discover multiple new elements and identify the electrical nature of the chemical bonds that holds atomic elements together.

Overview

Contemporary batteries still use galvanic cells, with the same basic design created by Volta in the late eighteenth century. Researchers have since identified the exact underlying scientific principles in much greater detail and optimized their function to produce efficient batteries capable of generating significant amounts of electricity for extended periods of time.

Galvanic cells use spontaneous reduction-oxidation (“redox”) reactions to generate electricity. Redox reactions occur when electrons transfer from one chemical species to another. They are called “spontaneous” when these transfers involve the release of energy. The energy released by the spontaneous redox reactions in galvanic cells provides the battery’s electricity, which can then be used for any number of applications that require the application of electrical energy.

Structurally, galvanic cells usually consist of two half-cells, which are connected with a porous membrane or salt bridge. The half-cells also contain metallic electrodes, which are conductors that relay electrical energy, that are dipped in an ionized fluid or gel known as an electrolyte. Each of the two half-cells are also attached to a voltmeter, which measures electromotive force in units called volts (after Volta), and an external switch, which is connected to each half-cell with a conductive metal wire.

Galvanic cells also contain multiple other important components, including an anode, a cathode, an external circuit, and a load. Anodes are the electrodes where oxidation reactions occur, resulting in the loss of electrons in the attached chemical species. Cathodes are the opposite. They are the electrodes where reduction, or electron gain, occurs. The external circuit controls the flow of electrons between anodes and cathodes, while the load represents the circuit connection between the battery and the attached device that uses the electricity it generates. Reduction-oxidation reactions are kept separate within each half-cell, while the salt bridge completes the galvanic cell’s internal electrical circuit. When each of the two half-cells is dipped in the same electrolyte, the salt bridge is not needed and can be replaced with a porous membrane that permits circuit completion.

Basic galvanic cells contain one copper electrode and one zinc electrode, both of which are dipped in a diluted sulfuric acid solution (the electrolyte). The anode generates the negative charge within the cell, while the cathode generates the positive charge. When the anode and cathode are connected with an external wire capable of conducting electricity, the energy released by the spontaneous redox reactions generated within each half-cell flows throughout the circuit, delivering electricity when it is connected to a load.

Batteries can also use a different type of electrochemical cell known as an electrolytic cell. These cells generate nonspontaneous redox reactions but apply additional energy that generates a surplus electromotive force the battery can then deliver to a load. They are primarily found in rechargeable batteries, which are capable of alternating between galvanic and electrolytic cell functions depending on whether the battery is being used or charged.

Bibliography

“Alessandro Volta.” Famous Scientists, 2021, www.famousscientists.org/alessandro-volta/. Accessed 17 June 2021.

"Galvanic Cells." GeeksforGeeks, 17 Apr. 2024, www.geeksforgeeks.org/galvanic-cells/. Accessed 18 Nov. 2024.

“Galvanic Cells.” Libre Texts, 15 Apr. 2021, chem.libretexts.org/Bookshelves/General‗Chemistry/Chemistry (OpenSTAX)/17%3A‗Electrochemistry/17.2%3A‗Galvanic‗Cells. Accessed 17 June 2021.

Helmenstein, Anne Marie. “Electrochemical Cells.” ThoughtCo, 26 Jan. 2019, www.thoughtco.com/types-of-electrochemical-cells-606455. Accessed 17 June 2021.

Helmenstein, Anne Marie. “Galvanic Cell Definition (Voltaic Cell).” ThoughtCo, 6 Oct. 2019, www.thoughtco.com/galvanic-cell-definition-604080. Accessed 17 June 2021.

“Luigi Galvani.” Famous Scientists, 2021, www.famousscientists.org/luigi-galvani/. Accessed 17 June 2021.

Reger, Daniel L., Scott R. Goode, and David W. Ball. Chemistry: Principles and Practice. Cengage Learning, 2009, p. 792.

Saslow, Wayne M. Electricity, Magnetism, and Light. Elsevier, 2002, p. 312.

Stamell, Jim. Excel HSC Chemistry. Pascal Press, 2011, pp. 49–50.