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11.4.1.1: The Voltaic Cell

  • Page ID
    84610
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    The invention of electrochemical cell is credited to Alessandro Volta, an italian scientist, who published it in 1799. Volta used copper and zinc electrodes. In his early cells they were immersed in brine (a water solution of ordinary salt) which served as electrolyte, and in later versions in acids.

    An experiment of little practical, but of really high educational value is to make the so-called “lemon battery”. Lemon juice, containing citric acid, is a good electrolyte. In order to make a cell, it’s enough to make two incisions in the lemon’s skin and insert a copper plate into one, and a zinc plate into the other (instead of plates, one can use nails, pieces of wire, etc.). By using several lemons and connecting the “cells” in series, one gets a battery with enough voltage to lit up a small LED. There are several videos in the YouTube worth watching, for instance, lemon battery, or another lemon battery.

    Furthermore, Volta invented the “Voltaic pile”. He made the electrodes in the form of discs, and put a put a cardboard or felt disc soaked with electrolyte in between each copper-zinc pair – and then, stacked them up into a pile, as shown in Web page. A single pair produced about one Volt, so by building high piles one could obtain a source of a really high voltage – the record was about 2000 elementary disc pairs. The Voltaiuc piles were essential for all research on electric currents until about 1870, when more powerful sources, electric dynamos, took over.

    We have not told what is the physical mechanism that forces the electrons to run from the anode to the cathode, and the ions in the electrolyte to take the charge back from the cathode to the anode. But here we will limit the explanation to a simplified “phenomenological” description – i.e., to one based primarily on empirical facts. Namely, there is a property characterizing electrode materials known as the Standard Electrode Potential (a Hyperphysics page) – in short, it’s the voltage supplied by a cell made of the given electrode material, and of a “standard electrode” – a widely acceptedone is the Standard Hydrogen Electrode. Tables listing the electrode potentials (denoted by the symbol E) of different electrode materials can be found in many Web pages, e.g., in a very extensive table presented by Wikipedia, or, in a more concise table in the Hyperphysics page linked above. In addition, in the Hyperphysics portal there is a useful tutorial on how to calculate the voltage supplied by a cell made of two different electrode materials.

    However, our natural curiosity clearly raises the question: “but what causes that a given material has just such a value of the E parameter? Yet, there is no way to answer this question in a concise way, covering no more than a few paragraphs in this chapter. A Reader who would like to learn more about the in-depth theory of electrode potential should be referred to an electrochemistry textbook at the academic level – it should be noted, however, that the material in question may constitute a significant part of such textbook. Articles devoted to this material can also be found in the Web, and they are definitely not something for “short reading” – here is one example. Another good tutorial worth recommending is a sequence of Chapter 1.1 1.8 in Unit 1: Electrochemistry in Chemistry LibreTexts, a Web publication from University of California Davis.

    The voltaic cells and batteries are all disposable, no rechargeable, so they cannot be used for energy storage. However, it is worth to start with them the discussion about batteries in general, because of their simplicity. This makes it easy to introduce a number of basic concepts that are important for all classes of electric batteries.


    11.4.1.1: The Voltaic Cell is shared under a CC BY 1.3 license and was authored, remixed, and/or curated by Tom Giebultowicz.

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