Many students have seen the the lemon cell
(a Galvanic cell)when they were studying
science in junior secondary.
The lemon cell consists of two dissimilar metals
(copper and zinc) pushed into a lemon
and joined by an external wire.
This cell does not make a good battery as:
there are no copper ions for the half reaction:
Cu2+ + 2e¯Cu
to occur at the positive electrode.
The reaction at the positive electrode is probably:
2H+ + 2e¯ H2
While the reaction: ZnZn2+ + 2e¯,
could occur at the zinc electrode,
the acid of the lemon could also react directly with the zinc:
Zn + 2H+Zn 2+ + H2
Thus both electrodes become covered with hydrogen bubbles
and the cell quickly loses its potential.