You first have to understand the reason why we have CO2.
As the formula sugests C = carbon, that's is the purpose of injecting CO2 into a tank as plants are made up of 80% of it!!
This device uses an electrolysis system to react against a carbon plate sandwiched between 2 stainless steel ones. This is a consumable & has to be replaced when depleted.
Sevenoks Tropical Marine have one of these in a show tank in their shop. They are having good results from it, however the plates get used up quite rapidly (roughly every 6weeks) so is quite an expensive way of producing carbon. They can even be controlled with a PH meter!!