David,

Yes, you could do that. However, you would then have electrical current traveling between the electrodes. If you were to shield the configuration so no fish could swim in between, or place it in another water container, it could the be answer to put more O2 in the water than H2.

The greater the distance between the electrodes, the greater the voltage for the same current. Although, there is something called ohms per square, and in this case ohms per cube. It suggests that regardless of distance on the surface of a conductor, such as a sheet of copper (ohms per square), that the resistance doesn't change with distance. Maybe with three dimensions, as in a tank of conductive water, the resistance would actually decrease with distance, requiring less voltage the further apart the electrodes. Just a thought.

Good idea, though,

Oliver