Ionizers use a voltage multiplier consisting of high voltage diodes and capacitors. You need a fairly high voltage to feed it to be practical. If you're starting from battery voltage, you will need an inverter and transformer. Look for "high voltage voltage multiplier" on any search engine and you should find plenty of examples. They're all pretty similar.
The first thing to understand is that high voltage diodes are not only a bit slow to switch on/off, but they can be damaged by high speed voltage changes across their terminals. Thus only low frequencies, not square waves (due to high speed voltage changes), are generally used.