[crassman22]

If I good understand, we put in the metal to solution of his own ions that a stable state has been established. And then we can appointment electrochemical potential between the metal and solution.

My question is. Why we have to put in the metal to solution of his own ions? All after if we put in the metal in clear water, the ions of metal also will be go to water, and after some time, the stable state also has been established bewteen metal and solution of his own ions.

Maybe the solution is used only for faster observation of the phenomenon?

[Arkcon]

That's pretty much it.  Also, not every metal will for a solution of ions just by putting in water.  If you want to understand this sort of half-cell, its just clearer in a solution of its own ion.  But you can look up and see, almost no batteries are made in that way.

[crassman22]

Yes, I know that type of galvanic cell is impractical, but Im interested in mechanism of action of galvanic cells.
Now, i can try understand cells build from the same electrodes.

When we connect zinc electrode and copper electrode by conductor, we will be see current flow (both electrodes are put in solution of his own ions). Ions of zinc will be oxidized, and electrons will be flow by cundoctor to copper electrode, where there will be reduced by ions of copper.

But, we can also build electrods from the same metal, for example from platinum. Then we have to put in solutions both half-cells. There solution for cathode can be Sn2+ and Sn4+, and for anode Fe2+ and Fe3+. I can't understand why solution of Sn2+ are oxidizes to Sn4+, and Ions of Fe3+ are reduced to Fe2+?