I'm working on a single chamber microbial fuel cell with air-breathing.
Its voltage already reached approximately 400 mV under OCV conditions, but when I used a 1000 ohm external resistor the voltage immediately drops to zero.
I already used a 10K resistor but the voltage hardly reached 30 mV and it's very low.
I don't know what the problem is!
Dear Alireza:
Microbial fuel cells have emerged as a promising technology to mitigate environmental pollution; it provides a solution to wastewater treatment and the removal and/or recovery of heavy metals. They are bioelectrochemical systems that utilize the catalytic activity of microorganisms organized in biofilms to oxidize organic or inorganic compounds by producing electric current, thus providing a new opportunity for sustainable energy production and bioremediation.
But a number of challenges such as: low production rates and limited efficiencies make the application of this technology restricted to lab scale only.
I think you could benefit from this valuable article about your topic:
"Challenges of Microbial Fuel Cell Architecture on Heavy Metal Recovery and Removal". at URL:
https://www.frontiersin.org/articles/10.3389/fenrg.2019.00001/full.
I hope it will be helpful ....
Indeed the external resistance should be comparable to the internal resistance. However, during the starting stage, the internal resistance is supposed to gradually decrease due to the development of functional microbial film on electrodes. So there is no rule, and you may yield different MFCs when apply different resistors.
There are some advices: The internal resistance depends on the surface area of the electrodes and the distances between the electrodes. If the area is huge and the distance is close, choose a resistor less than 1 k ohm, If not, choose more than 1k ohm. If you have no idea, just use any resistor and monitor the CCV for several days. For a conventional MFC, the OCV varies from 0.5 to 0.8. The CCV will decrease dramatically when loaded and slowly recover. If not recover, use bigger resistor; if no significant decrease, use smaller resistor.
Also depends on the purpose. If you want to obtain the maximum power output, the external resistance should be similar to the internal resistance. If the objective is the maximum exolectrogenic biomass growth, the external resistance should be lower to avoid current limitations. Exoelectrogenic activity is proportional to the current intensity; if your intensity is low (higher external resistance), exoelectrogens growth will be limited. When the cell is working at OCV (infinite resistance), intensity is zero and no exoelectrogenic activity is possible.
So you could benefit from these two valuable articles:
First....
"Microbial Fuel Cells: Influence of External Resistors on Power, Current and Power Density".
By: Kamau JM, Mbui DN, Mwaniki JM, Mwaura FB and Kamau GN.
Abstract:
The effect of external resistance on voltage, current, power, power density and current density is investigated in a microbial fuel cells using cowdung is investigated. This involves use of varying resistance resistors. The fuel cells
were operated under anaerobic condition for 9 days. PVC pipe was used to make a salt bridge using lamp wicks and potassium chloride. The obtained results indicated that the maximum voltage was on day 7 with 0.153 V across 33 kΩ resistor. The power was in the range of 0.000001 to 0.01 mW, current density was in the 0.1 to 23.29 mA/m2 range while the power density was in 7.5 × 10-7 to 3.1036 mW/m2 range.
And this is the second article:
"The Influence of External Load on the Performance of Microbial Fuel Cells"
By: Szymon Potrykus , Luis Fernando León-Fernández , Janusz Niezna ´nski
, Dariusz Karkosi ´nski.and Francisco Jesus Fernandez-Morales.
Abstract:
In this work, the effect of the external load on the current and power generation, as well as on the pollutant removal by microbial fuel cells (MFCs), has been studied by step-wise modifying the
external load. The load changes included a direct scan, in which the external resistance was increased from 120 Ω to 3300 Ω, and a subsequent reverse scan, in which the external resistance was decreased back to 120 Ω. The reduction in the current, experienced when increasing the external resistance, was maintained even in the reverse scan when the external resistance was step-wise decreased.
Regarding the power exerted, when the external resistance was increased below the value of the internal resistance, an enhancement in the power exerted was observed. However, when operating
near the value of the internal resistance, a stable power exerted of about 1.6 µW was reached. These current and power responses can be explained by the change in population distribution, which shifts to a more fermentative than electrogenic culture, as was confirmed by the population analyses.
Regarding the pollutant removal, the effluent chemical oxygen demand (COD) decreased when the external resistance increased up to the internal resistance value. However, the effluent COD increased
when the external resistance was higher than the internal resistance. This behavior was maintained in the reverse scan, which confirmed the modification in the microbial population of the MFC.
I have attached the pdf files ....
I hope it will be helpful...
Hello, Dr. Hassan Nasser .your answer was absolutely amazing and it was very helpful. I really appreciate it.
thank you for your time
Dear @Alireza Mousavi
you are welcome, and I wish you progress and success ...
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