The operating principles of a potato battery are very similar to those of the lemon battery (described in the experiment “Galvanic cell”).
1) On the iron anode (-), electrons are released:
Fe(s) → Fe2+(aq) + 2e-
2) On the copper cathode (+), electrons are consumed:
2H+(aq) + 2e- → H2(g) (i.e., hydrogen depolarization reaction)
If the concentration of hydrogen ions (H+ ions originating from the vinegar (CH3COOH)) is low, oxygen depolarization reaction is possible:
O2(g) + 2H2O(l) + 4e- → 4OH-(aq)
3) ELECTROCHEMISTRY: “Lithium-ion battery”