Why not use hydroxides as the ion source in ion thrusters

[mconnelldouglas]

Why can't dissolved hydroxides (for example KOH) be used as ions in ion thrusters? (K+) and (OH-) ions do not require any energy to form from KOH unlike (Xe+) ions

 

[mfb]

If they are dissolved in water, how do you accelerate them? How do you have water exposed to the vacuum without it boiling anyway?

Separating them from each other and from the water will likely need more energy than creating xenon ions. Not that it matters - most of the energy goes into the acceleration, not the ion creation. Light ions are worse, you need more of them for the same thrust.