Chemical source of electric current a galvanic cell is a device in which the energy of a chemical reaction is converted into electric energy (electric current).
In case of usual redox reactions, the oxidizer and the reducer typically have contact with usually touch each other and can exchange electrons. In chemical current sources electrochemical cells, oxidizers and reducers are spatially separated, creating a possibility for the generation of electric current in a wire that connects the electrodes. Electrons flowing through the conductive wires enables to power electric consumers loads connected to the same circuit.
Several current sources are known, such as primary and secondary batteries and fuel cells. Their practical importance is extremely high.
The simplest battery-galvanic cell consists of two metal electrodes, immersed into corresponding salt solutions. In the well-known Jakob-Daniell cell, (+)electrode is copper in copper salt solution and (-)electrode is zinc in zinc salt solution.
A "lemon battery" is the simplest current source that can be prepared using household materials. A lemon (you can also use potatoes, apples, oranges …etc) and two different metal pairs were used in this experiment:
Metal sheets were pressed separately into a lemon.
In Zn/Cu and Zn/Fe elements, zink atoms oxidized (release of electrons) and formed Zn2+-ions that were dissolved in lemon juice:
1) On (-) electrode (or Zn anode), release of electrons:
Zn(s) → Zn2+(aq) + 2e-,
giving an excess of electrons on to the zinc surface.
By closing the circuit, these electrons moved through the external wire to the copper (iron) electrode, thus. This, creatinges the electrical current. On copper (iron) surface, the electrons join with the hydrogen ions in from the lemon juice:
2) On (+) electrode (or Cu cathode), consumption of electrons
2H+(aq) + 2e- → H2(g)
In our Zn/Cu and Zn/Fe galvanic elements (cells), the voltage was ~0.9 V ja and ~0.46 V, respectively.
The larger the difference between the acitivities of the used metal pairs used, the higher the resulting output voltage of the galvanic cellelement gives.