Hello,
I have built a redox flow (fuel) cell that uses K3[Fe(CN)6] as oxidant instead of MnO2 because of its higher reduction voltage. When MnO2 is reduced, it is easily regenerable by air (oxygen). What is about the potassium ferrocyanide? Can it also be oxidized by air as a regenerable catalyat? Or is the redox potential of oxygen too low to oxidize it back to ferricyanide?
Thanks very much,
regards,
André Leonhardt
Dear André Leonhardt
The answer to your question can be easily found in the literature. You need to learn basics of chemical thermodynamics. If I did not know that you are a high school student, I would use tough wording to answer.
In general, MnO2 is much stronger oxidant than K3[Fe(CN)6] and can't be regenerated by O2. K4[Fe(CN)6] is slowly oxidized by O2 in water.
Thanks for your answer, but one thing confuses me: if MnO2 is not regenerable by O2, why then is it used as catalyst in metal-air batteries, it may not be able to be oxidized by air alone, but I think it is oxidized in presence of OH-, though. I know, that MnO2 is the better oxidant, but I wonder, why it does not give an OCV (open circuit voltage) as high as the K3[Fe(CN)6] in my fuel cell? Thermodynamics is a very big subject and not easily learnable by a 15yr old person, but I always try my best.
Thanks a lot,
regards,
André
Reaction rates (current in a fuel cell) are studied by chemical kinetics, one more area you need to know well. MnO2 exists in different forms. The properties of K3[Fe(CN)6] depend on pH an [K+]
so you say, that f.e. alpha/beta-MnO2 will react differently? Then why does bulk (non crystalline) MnO2 work as catalyst? I mean, the reaction entropy should stay the same, right, I mean there isn't any reason the entropy itself changes eith different morphologies, doesn't this just depend on the particle size?
Yeah, I know the reaction needs K+, this is the reason why my overall ph is alkaline rather than acidic. I use -.5M KOH, but I think NaOH should work as well, too, the fact I am using an anion membrane makes even the alkaline metal ion impossible to permeate through the membrane
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