There may be, but for most of us who only do a few motors a year, plain water will give you acceptable results. If you're getting "ratty" looking comms, my guess is that you used too high a voltage or you let the water get too dirty before changing it.

I usually run the motors at 2v and use a container of water that holds at least 1/2 gallon of water. The practice of using a container like a cup from a fast food place is okay, but you have to change the water too often. Even with the large container I use, the water needs to be changed at least once and the motor should be finished in clean water at 2v.

I've never done this so don't know if it will work, but you could try this. Clean the comm with a metal polish, then water dip for a few minutes at low voltage. This probably won't work with a dirty comm for obvious reasons. I'm talking about reclaiming a motor with a rough comm after water dipping.