If you strip the electrons off some atoms and use just the electrons[0] as reaction mass, you will eventually get a large enough electric charge you can no longer throw the electrons away from you. Electric forces behave similarity to gravity, so while it wouldn’t normally be phrased like this, you could say your engine exhaust will eventually no longer have escape velocity from your ship.

For this reason, ion drives do things to neutralise the net charge.

(If you meant using them as a power source rather than reaction mass, it’s technically possible but that’s called a capacitor and they have very low energy density).

[0] or, by symmetry, just the nucleus.