[Mimic]

In an electrolytic cell, the potential difference to be applied to the two electrodes must be at least equal, in absolute value, to that which would have the spontaneous process. In reality the difference of potential must be slightly greater because in case we have a platinum electrode, as happens in the copper electrolysis, it is covered with native copper: so, is like having a copper electrode.
My question is: how the native copper covering the platinum electrode surface increases the value of the potential difference required for the electrolysis process?

Thanks in advance