A potato battery is an electrochemical battery , otherwise known as an electrochemical cell. An electrochemical cell is a cell in which chemical energy is converted to electric energy by a spontaneous electron transfer. In the case of the potato, the zinc in the nail reacts with the copper wire. The potato acts as a sort of buffer between the zinc ions and the copper ions . The zinc and copper ions would still react if they touched within the potato but they would only generate heat . Since the potato keeps them apart, the electron transfer has to take place over the copper wires of the circuit, which channels the energy into the clock. Presto! You have potato power.