Connect two different metals in series with the frog's leg and make Battery
Alessandro Giuseppe Antonio Anastasio Volta (February 18, 1745 – March 5, 1827) was a Lombard physicist known especially for the development of the first electric cell in 1800.
Around 1791 Alessandro Volta began to study the "animal electricity" noted by Galvani when two different metals were connected in series with the frog's leg and to one another. He realized that the frog's leg served as both a conductor of electricity (we would now call it an electrolyte) and as a detector of electricity. He replaced the frog's leg by brine-soaked paper, and detected the flow of electricity by other means familiar to him from his previous studies of electricity. In this way he discovered the electrochemical series, and the law that the electromotive force (emf) of a galvanic cell, consisting of a pair of metal electrodes separated by electrolyte, is the difference of their two electrode potentials. This may be called Volta's Law of the electrochemical series.
In 1800, as the result of a professional disagreement over the galvanic response advocated by Luigi Galvani, he invented the voltaic pile, an early electric battery, which produced a steady electric current. Volta had determined that the most effective pair of dissimilar metals to produce electricity was zinc and silver. Initially he experimented with individual cells in series, each cell being a wine goblet filled with brine into which the two dissimilar electrodes were dipped. The electric pile replaced the goblets with cardboard soaked in brine.
The dangerous Voltaic battery of Alessandro Volta
The battery made by Volta is credited as the first electrochemical cell. It consists of two electrodes: one made of zinc, the other of copper. The electrolyte is sulphuric acid or a brine mixture of salt and water. The electrolyte exists in the form 2H+ and SO4 2-. The zinc, which is higher than both copper and hydrogen in the electrochemical series, reacts with the negatively charged sulphate. (SO4)The positively charged hydrogen bubbles start depositing around the copper and take away some of its electrons. This makes the zinc rod the negative electrode and the copper rod the positive electrode. We now have 2 terminals, and the current will flow if we connect them. The copper does not react, functioning as an electrode for the reaction
However, this cell also has some disadvantages. It is unsafe to handle, as sulfuric acid, even if dilute, is dangerous. Also, the power of the cell diminishes over time because the hydrogen gas is not released, accumulating instead on the surface of the electrode and forming a barrier between the metal and the electrolyte solution.