The positive standard reduction potential of ${\mathrm{Cu}}^{2+}/\mathrm{Cu}$ electrode is due to

The positive reduction potential of copper means that copper has the ability to accept two electrons and get reduced to form copper metal. The high energy of atomisation for d-block elements is due to the ability to make many metallic bonds due to half-filled electron d-orbitals, but it seems here that copper has no free d-orbitals yet has a high enthalpy of atomisation.

Since the copper transit from +1 ion state to +2 ion state requires, a large amount of energy which is not compensated by the hydration energy hence the hydration energy is low.

Therefore, the positive standard reduction potential of ${\mathrm{Cu}}^{2+}/\mathrm{Cu}$ electrode is due to the high heat of atomization and low heat of hydration.