<p>Galvani postulated the existence of <i>animal electricity</i> in 1791 after observing that touching the nerves and muscles of a skinned frog with an arc made of two different metals (e.g. Ag and Zn) caused convulsive movement. Alessandro Volta attributed the generation of electricity to the potential difference that arises when different metals come into contact (<i>metallic electricity</i>, 1796). On the basis of this hypothesis, Volta built his pile by placing discs of zinc and silver, on top of each other, separated by discs of wet cardboard (1800). However, as early as 1793, the Florentine chemist and agronomist Giovanni Fabbroni observed that, when two dissimilar metals (e.g. silver and zinc) were in contact in an aqueous solution, the oxidation of zinc occurred. Fabbroni proposed that this chemical process was responsible for generating electricity (chemical interpretation of galvanism). Fabbroni’s observations were confirmed by numerous scientists throughout the nineteenth century. However, a complete interpretation of how galvanic cells work only became possible after the discovery of the electron (Thomson in 1897). Over the following years, chemists clarified that oxidation–reduction reactions involve the transfer of electrons from the reducing agent to the oxidising agent, and that a galvanic cell can be obtained from each redox reaction by keeping the oxidant and the reductant in two separate half-cells that are connected electrically.</p>