How do sacrificial electrodes work?

[iScience]

i have brass metal in contact with ammonia(liq), could someone help me identify the oxidation reaction?

i thought the oxidation rxn was supposed to involve the ammonia and the copper, but that combination would lead to the copper being reduced, not oxidized. am i right?
how exactly is copper losing its electrons?

 

[Bystander]

http://en.wikipedia.org/wiki/Solvated_electron