Electricity from the Chemical Bond
If you vigorously knead a lemon to free the juices and then stick a strip of zinc in one end and a copper strip in the other, you can measure a voltage across the strips. Electrons will flow through the load without the inconvenience of having to supply heat. You have made yourself a chemical battery.
The chemical battery was the first direct conversion device. Two hundred years ago it was the scientists’ only continuous source of electricity.
Since the chemical battery does not need heat for its operation, it is logical to ask what makes the current flow. Where does the energy come from?
The battery has no semiconductors, but, like the thermoelectric couple and the thermionic diode, it uses dissimilar materials for its electrodes. A conducting fluid or solid is also present to provide for the passage of current between the electrodes. In the example of the lemon, the copper and zinc are the dissimilar electrodes, and the lemon juice is the conducting fluid or electrolyte that supplies positive and negative ions. The battery derives its energy from its complement of chemical fuel. The voltage difference arises because of the different strengths of the chemical bonds. The chemical bond is basically an electrostatic one; some atoms have stronger electrical affinities than others.