galvanic element
Below you find a scheme of a simple voltaic cell with copper and zincum electrodes.
In this complex, we can discover a sufficiently strong oxydator (Cu2+) and also a reasonable strong reductor (Zn)
The spontaneous reactions that dominate the process, are:
Zn(s) 
Zn2+ + 2e-
and
Cu2+ + 2e- Cu(s)