Elecrochemical cells with only one metal
Two metals are not always required to make a cell. As long as you have one reactive metal to give away electrons and another substance to accept the electrons then you can construct a cell. You also need an ion bridge to allow ions to move between the two solutions.
Some non-metallic substances are found in the Electrochemical series and the same rule applies - the metal, which gives away its electrons, has to be higher in the electrochemical series than the other substance for the cell to produce an electric current. The further apart the metal and the other substance are, the higher the voltage produced by the cell.
Such a cell can be made from nickel dipping into nickel(II) sulfate solution and a carbon rod dipping into a solution of iodine as shown in the diagram below.
In this reaction the nickel atoms give away electrons and change into nickel(II) ions:
\(Ni(s) \to Ni_{}^{2 + }(aq) + 2e_{}^ - \)
The iodine molecules accept these electrons and change into iodide ions.
\(I_2^{}(aq) + 2e_{}^ - \to 2I_{}^ - (aq)\)
The overall equation for the reaction is:
\(Ni(s) + I_2^{}(aq) \to NiI_2^{}(aq)\)
