Dear M. Bogdahn,

Do you really need to insert H2 in your biological reactor? If the reason you want to insert a fuel cell in your experimental chamber is to remove O2, it's not necessary. To do that, oxygen sensors and pumps made out of zirconia already exists, and commercially. You can also build one yourself (link) with zirconia, platinium, a voltage generator and measurement device. The voltage imposed is directly bound to the O2 concentration in the chamber through the Nernst equation.

When handling with precise atmospheres, the only advices i could give you is to be absolutely sure that your setup is hermetic and to add a lot of sensors. The gas pipes and every connector should also be stainless steel ones. For example from the swagelok brand. This way your conclusions can be more strongly backed.

I hope I undestood your problem,

Léonard

http://jes.ecsdl.org/content/116/5/594.abstract

Dear Mr. Thommy,

Thanks for your answer.

Yes, I need H2 as electron donor for the cultivation of lithoautotrophic bacteria. So, the device dealing with O2 should not produce any heat. I cannot access your linked article due to a paywall, but it seems it requires high temperatures to work well.

This is a private / independent proof-of-concept experiment in an early stage, which does not yet require high precision. If it grows, it's good, if it doesn't, I have to improve the setup. I have not yet found an affordable commercial product that removes and detects O2. Most of then are for dissolved O2 (aquariums etc). You happen to know a specfic affordable product?

Even if it turns out to be too hard to calibrate, too unprecise or unsuitable for other reasons, I'm still curious whether the approach itself would be valid: can I support and accelerate O2-removal by an H2-FC even for low ppO2, by applying a voltage? And (how) would that voltage correlate with the O2-concentration?

thanks again

Dear Mr Bogdahn,

Now I understand better, and you're right, operating with a zirconia sensor or pump would need to heat it , and would heat you setup. It was just a device I knew that was affordable and self-buildable. It seems also possible to me to lessen oxygen concentration in a chamber by applying a voltage or a current to a fuel cell (an alkaline one or with a polymer membrane), which would not strongly heat your chamber. This would also obey to Nernst equation, so you should be able to calculate your O2 concentration, but you would need to take into account electrode polarization and concentration gradients. I don't know to what extent you would be able to deplete O2 from you atmosphere though. In the electrode polarization formula, there is a concentration polarization term that could hinder what you're trying to do.

It seemed to me that it would be more complicated to insert a fuel cell and to manage and monitor it than to buy or fabricate sensors and pumps, which are meant for the kind of application you need, but i'm ignorant of such ambient temperature working devices, sorry for that.

Anyway, I wish you good luck with your interesting experiment,

Léonard

Hello Léonard,

Thank you very much for your answer. I'm glad to hear that the concept should work in theory - I liked the idea and wanted to know. However, you are right, it makes things complicated and still does not give me good guarantees. Controlling things like electrode polarization and concentration gradients is clearly beyond my skillset, and diverts me from my actual problems.

I'll probably use argon to displace the atmosphere. Because argon sinks down, being a heavy gas, it should be easy to displace the atmosphere and also to get rid of it in the end. It is also reasonably affordable. 

thank you

best regards,

Ingvar