Science Buddies: "Ask an Expert"

Hi,

I'm interested in doing this mud thing to be processed in the microbial fuel cell that has two chambers and is connected by a salt bridge (made up of water, agar, and salt). I'm going to have at least 3 tests for each MFC (I have 3 MFC. 1 control and 2 experimental). So, my question is, can I use the same salt bridge of each MFC throughout the whole experimentation? Or I will create another salt bridge again for each test?

-Maries

Hi Maries,

I would definitely recommend using a new salt bridge each time you perform the experiment. Firstly, this greatly reduces the chances of contamination between trials, which could skew your results. Secondly, salt bridges gradually lose their ions every time they are used. If you want to control for this, you must use a fresh salt bridge each time you conduct a trial. Lastly, if you only used one salt bridge, any errors that may have occurred in making that bridge would affect your results for all three trials. You wouldn't even be able to detect these errors in your data because there wouldn't be any anomalies.

Hope this helped! If you have further questions, feel free to ask!

-Karen

Hi Karen!

How about the electrodes? Do I need to change them also after each trial?
By the way, thank you very much for the advice.

-Maries

Yes, you should switch the electrodes for the same reasons as the salt bridge. Think of this as a battery (which it technically is). If you were doing an experiment with a battery, you'd want to switch to a fresh one each time to make sure you're starting out with the same amount of potential energy. Doing this will also help you weed out any faulty batteries, since they'll behave very differently from the others you've tested.

-Karen

Oh, I see. Thank you! One last question, can I use carbon paper instead of a carbon cloth?

-Maries

I am assuming you are doing this experiment: https://www.sciencebuddies.org/science- ... ml#summary

I don't see carbon cloth anywhere in the materials or procedure. What are you planning on using it for?

-Karen

(Waste Not, Want Not: Use the Microbial Fuel Cell to Create Electricity from Waste) this is the one that I'm doing. But, carbon cloth isn't available here in my locality. I've read from the other articles that you'll be needing a carbon cloth in the electrodes to allow protons to pass through the PEM (salt bridges). And I've also read that using a carbon paper should do as a substitute for a carbon cloth.

-Maries

In that case, yes I believe you should be able to substitute carbon paper for carbon cloth. I recommend that you test it first however, by performing step 5 of "Making the Electrodes."

-Karen

I've already finished conducting my experimentation and it was awesome. The mud did produce electricity. Thank you so much Karen for helping me throughout my experimentation my only problem now is that I don't know how to read an analogue multi-meter hahaha anyways, thank you again for your advice.

-Maries

No problem! I'm glad your experiment worked!

-Karen

P.S. If you still need help with the multimeter, wikiHow is going to be your friend: http://www.wikihow.com/Read-a-Multimeter

Perhaps I am missing something, but are you supposed to leave the air pump running 24/7? The whole point of alternative energy is to reduce our dependency upon coal production, which is needed to power the air pump. Ultimately, I guess I am asking if the reaction can occur without the increased levels of oxygen provided by the pump. Thanks in advance.

Yes, in this experiment the air pumps should be running at all times to provide a constant supply of oxygen (which the fuel cell needs to work). However, the carbon footprint of the pump is negated when you consider the amount of energy that is produced by the microbial fuel cell. Overall, you are still conserving fossil fuels.

Some fuel cells that are used in industry have pumps with oxygen sensors, so the pump only activates when oxygen levels are low. Other pumps are designed to be energy efficient.

-Karen

Thanks for the help and the prompt reply. You are a lifesaver.