Electric Propulsion uses an electric field (grid) to accelerate plasma to a very high velocity resulting in thrust. Often cesium or xenon is the element that is used to generate the plasma. These engines are usually of the ion variety. Deep Space 1, flown by JPL to an asteroid, used a xenon ion engine. (Bragging now) When I was in High School, I built a working copper ion rocket engine for a science fair project. All you need is an ion that can be electrically accelerated to produce thrust.
Unfortunately, electric propulsion produces an extremely low thrust compared to others. However, you can run it (accelerate) for a very long time, slowly increasing the velocity far beyond what a short burn chemical rocket can obtain. (The chemical rocket runs out of fuel rather rapidly compared to an ion engine)
LOL, now why doesn't that surprise me.