o2 sensor o2?
 

Has anyone tried increase the atmospheric O2 concentration at the O2 sensor by using tank or electrolysis?

i have not tried that one, never heard of it before either.
can you explain it a bit further, whats the purpose, what is it supposed to do ...

Are you talking about doing this in the exhaust stream, or on the cold side of the o2 sensor?
A few people have put tin foil around their o2 sensor, on the outside of it, because it's using the o2 in the outside air as a reference point, if you restrict that air flow it will make the engine run leaner and a difficult to control manner.