The Voltaic battery has the following structure, with a zinc (Zn) negative electrode and a copper (Cu) positive electrode immersed in a hydrogen sulfide (H2SO4) electrolyte.
The mechanism is as follows.
First, ① Zn has a higher tendency to ionize than Cu, so it dissolves into the aqueous solution as Z2+ ions. ②The surplus electrons then move to the positive electrode through the circuit.
This means that a current is generated. ③The electrons that reach the positive electrode combine with H in the aqueous solution to become H2 and are released into the atmosphere.
＜Electromotive force＞
The electromotive force can be determined from standard electrode batteries of Zn and Cu.
Using these values, Zn is -0.76V and Cu is 0.34V, so the difference between the two, 1.1V will be the electromotive force.
＜Disadvantage＞
As the current flows, H gradually attaches to the Cu surface, making it impossible for new electrons to combine with H, and the current stops flowing. This is called polarization.
■Daniel batteries
Daniel batteries have a structure that does not cause polarization, which is a drawback of voltaic batteries.
The negative electrode is still Zn and the positive electrode is Cu, but the electrolyte is different. Electrons released from Zn combine with Cu ions in the aqueous solution at the positive electrode.
Since Cu is the material of the positive electrode, there is no problem even if Cu is newly attached.
Furthermore, the electromotive force of the Daniel battery is the same as that of the Voltaic battery, which is 1.1V.
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