Microbial Fuel Cells (MFC)

[khlor]

Recently I've been making some search on internet about fuel cells(I was expecting being able to make one) But I found something even more interesting(from my view point) that are the microbial fuel cells(http://en.wikipedia.org/wiki/Microbial_fuel_cell). and I'm about 3 or 4 days searching some informations about it, even thinking in making my own(once I saw many tutorials about) but questions appeared in my mind and I can't find the answer. I hope you guys help me out.

first is about the electrodes, there is no much about them I have no idea what kind material to use.

second is "am I making a fuel cell or a battery? since according with some of my sources some designs and tutorias they use reactive metals that oxidize and move electrons making electric current"

I think thats all.

[EdEarl]

See also flow battery. I suspect that microbial fuel cells may be used for microscopic applications and flow batteries for macroscopic applications, provided both are perfected, because a flow battery promises to let one to fill a tank with "liquid electricity" and run an electric motor without the anode and cathode of the battery being consumed. Although a microbial fuel cell has similar specifications, it seems unlikely the power density will be as high as flow batteries.

[khlor]

Interesting. I have more one doubt about the fuel cells.... (this one I forgot to mention) so, here it goes:

 

How do I define cathode from anode(positive pole and negative pole) in a fuel cell? since according with my searches both are made from the same material?

See also flow battery. I suspect that microbial fuel cells may be used for microscopic applications and flow batteries for macroscopic applications, provided both are perfected, because a flow battery promises to let one to fill a tank with "liquid electricity" and run an electric motor without the anode and cathode of the battery being consumed. Although a microbial fuel cell has similar specifications, it seems unlikely the power density will be as high as flow batteries.

Sounds interesting. remember when I was searching about some kind of batterie that the electrodes are not consumed by the reaction so I could just put more electrolyte and continue using it. this seach led me to this search about fuel cells. and on my search I found this:

 

so, according with the link about flow cell this would be the pratical thing, right?

Edited January 19, 2014 by khlor

[CharonY]

With regards to microbial fuel cells.

The material is usually graphite, however they are not simple to establish and maintain, if they are supposed to have any amount efficiency.

 

You have to maintain the bacteria in a an anaerobic chamber (the anode) which is not quite trivial. The material does not determine what the cathode is, but the direction of electron flow, which goes from the bacterium to the anode and then to the cathode where it has to have some kind of electron acceptor.

[khlor]

With regards to microbial fuel cells.

The material is usually graphite, however they are not simple to establish and maintain, if they are supposed to have any amount efficiency.

 

You have to maintain the bacteria in a an anaerobic chamber (the anode) which is not quite trivial. The material does not determine what the cathode is, but the direction of electron flow, which goes from the bacterium to the anode and then to the cathode where it has to have some kind of electron acceptor.

about the cathode I knew that(about definition) as english is not my native language I didn't found better word for that so I used definition. and so I was with some problems with understanding, because batteries works in a similar way and then if I use reactive metals I was fearing to make a common battery and not a microbial fuel cell. but anyway thanks, this clarification was very helpful. so, I carrying on my search and I found something that they call "mudwatt" made from an enterprise that calls "keegotech" I was wondering about it. please, take a look:

does this works this way? well I mean is this really a microbial fuel cell?

Edited January 23, 2014 by khlor

[CharonY]

Depends on the details. Assuming that the chamber is filled with a liquid, the main issue is that oxygen may permeate the chamber. In that case the bacteria would just utilize the oxygen instead of transferring to the anode. Also the medium most be low or devoid of alternative electron acceptors, or again have means to limit bacterial access to them. However, if there is a rich community in that thing and something that limits diffusion (e.g. densely packed particles and/or a slurry) it should work.

 

If a liquid medium is used I some kind of membrane is required to separate the electrodes (to limit diffusion).

Edited January 23, 2014 by CharonY

[khlor]

Depends on the details. Assuming that the chamber is filled with a liquid, the main issue is that oxygen may permeate the chamber. In that case the bacteria would just utilize the oxygen instead of transferring to the anode. Also the medium most be low or devoid of alternative electron acceptors, or again have means to limit bacterial access to them. However, if there is a rich community in that thing and something that limits diffusion (e.g. densely packed particles and/or a slurry) it should work.

 

If a liquid medium is used I some kind of membrane is required to separate the electrodes (to limit diffusion).

 

 

So, what could be used as electron acceptors by the bacteria? and is there any by product? I mean, anaerobic process ever leaves by products such as acids, alcohols or something else.

 

and about the "fuel" what is used to feed the bacteria? here is listed acetic acid, but some of my search says glucose and others even sucrose.

Edited January 26, 2014 by khlor

[CharonY]

 

 

So, what could be used as electron acceptors by the bacteria? and is there any by product? I mean, anaerobic process ever leaves by products such as acids, alcohols or something else

 

No, you are thinking of fermentation. While it is a means to regenerate NAD, it is not always done during anaerobic respiration. Obviously different bacteria utilize different electron acceptors including nitrate, fumarate, metals (Fe, Cr, U to name a few) and much more. The key is that the redox potential betwen NADH and the potential acceptor is sufficient to power proton extrusion.

However, in a MFC this point is moot as the electrode is acting as the acceptor (otherwise there would be no electricity).

 

As electron donors quite a lot of sources can be used, which are shuffled into the TCA cycle. However, many anaerobic bacteria are adapted to utilize small C bodies such as acetate and propionate as occur more frequently where they live (such as deep in soil).

Edited January 27, 2014 by CharonY