I don't think it's adhesion, just differences in Fermi levels.
Agreed.
A cube of gold will adhere to another cube of gold, rather
dramatically in fact.
In contrast, if you want to create static electricity,
rubbing gold on gold is not a good strategy. It would
work better with two /different/ substances.
Slight nitpick: I would have preferred to say differences
in _work functions_ rather than "Fermi levels" in this
situation. Of course the physics of work functions is
intimately tied to the physics of Fermi levels ... but
there's other stuff going on, too, and the zero-reference
for the work function is defined in more-or-less exactly
the right way for this application. The zero of the Fermi
levels is not so immediately relevant.