Microbial Fuel Cells (MFCs) harness the power of microorganisms to convert organic matter into electricity while treating wastewater. By utilizing various biomass sources like wood, food waste, and sewage sludge, MFCs offer a sustainable solution for renewable energy production without competing with food sources. Originally conceptualized in 1911 by Potter, MFC technology has evolved, utilizing catalysts like Escherichia coli and Saccharomyces cerevisiae, and electrodes such as platinum. Over time, advancements have led to the elimination of artificial mediators, with bacteria directly transferring electrons to electrodes. MFCs stand as a promising avenue for clean energy generation, aligning with the imperative to mitigate climate change and reduce reliance on fossil fuels.

1. Catalyst Development of
Microbial Fuel Cells for
Renewable-Energy
Production
By-Piyush Kumar Pandey

2. INTRODUCTION
 The use of fossil fuels has the potential to spark a global energy crisis and
increase global warming.
 Alternative sources of energy are desirable to replace oil and carbon.
 Microbial fuel cells can treat wastewater at the same time for reuse and power
generation.
 By generating electricity from what would otherwise be considered garbage,
microbial fuel cell technology provides a new source of sustainable energy.

3.  without the problem of by-products and multiple operations, electricity can be
directly obtained from the devices.
 Use of biomass waste as fuel, no food competition will occur.
 There are various types of biomass, e.g.,
 Sustainably harvested wood,
 Waste paper,
 Food waste,
 Sewage sludge, and
 various wastewaters.
 Considering wood-based biomass as a fuel, in biofuel cells, although
electricity is generated from the sugar obtained from the biomass, other
components in the wood, such as lignin, can be used for purposes other than
power generation.

4.  Potter conceived and reported on the notion of employing microbes to generate
power in 1911.
 Catalysts
 Escherichia coli and Saccharomyces cerevisiae
 Electrode
 Platinum
History

5.  Cohen demonstrated in 1931 that connecting a series of tiny fuel cells produced
2 mA of electricity at a voltage of over 35 V.
 Early MFCs used an artificial mediator, e.g., thionine, methyl viologen, and
humic acid.
 By 1976 Suzuki had resolved the problem of unstable nature of hydrogen
production studied by DelDuca.

6.  Then, in 1990s, several bacteria were discovered to be able to get electrons
from the electrode via a self-mediator without addition of artificial mediator.
 Moreover, they used electrons for their growth; for example, a ferric-iron-
reducing bacterium Shewanella putrefaciens grew on lactate by obtaining
electrons from the electrode .
 It was discovered in the early 2000s, that bacteria carried electrons directly
from electrodes directly to cell surface.

7. Performance of MFCs
The maximum power per anode electrode area (power density per area) or the
maximum power per cell volume (power density per volume).

8. General principles of MFCs
Mechanism of electron generation in microbial cells
 MFCs utilize the decomposition energy of organic matters by the organisms to produce ATP.
 Example : Glucose decomposition in Saccharomyces cerevisiae .
 Glucose taken into the microbial cells by cell membrane enzymes is oxidized and
decomposed to pyruvic acid by various enzymes.
 Pyruvic acid becomes carbon dioxide and water when it is completely oxidized via the TCA
cycle.
 The electrons then collected in the mitochondrial inner membrane in eukaryotes, and in
prokaryotes, they were accumulated in the cell membrane via NADH and FADH2.

9.  Quinone compounds and cytochrome proteins are also included along with the
complex that help in the flow of electron in these membranes.
 ATP is synthesized by the membrane enzyme.
 A mediator transports a portion of the electrons produced by the microbes to an
electrode outside the cell.

10. Calculation of the energy obtained from
glucose
 The reaction that occurs in the anode tank having potential −0.42 V is E1.
C6H12O6 + 6H2O → 6CO2 + 24H+ +24e− E1
 In the cathode tank, the reduction reaction having potential 0.82 V is expressed by E2
6O2 + 24H+ + 24e− → 12H2O E2
 Theoretically, the voltage exceeds 1 V, but in most cases, it has never reached that value.
 Assuming that 24 electrons are obtained from 1 glucose molecule in 1 h, the quantity of
electricity (Ah) obtained from the glucose (1 kg) can be calculated using the Faraday
constant (96,485 C/mol).

11. Basic components of dual-chambered
MFCs using a mediator
 Cation Exchange Membrane (CEM)
 Electrodes
 Buffer solution
 Fuel
 Mediator
 Cathode solution

12. Cation Exchange Membrane (CEM)
 A dual-chambered fuel cell consisting of an anode tank and a cathode tank.
 They are separated by a cation exchange membrane (CEM)
 To create a potential difference between the two tanks .
 Prevents mixing of each content.
 Allows the protons generated in the anode to migrate to the cathode.
 Regulates the movement of the protons responsible for the pH reduction at the
anode affecting the activity of microorganisms and the delivery of electrons to the
oxygen at the cathode.
 Factors to consider, such as durability and cost, are important for selecting CEM.
 Nafion is popular.

13.  Carbon materials, e.g., carbon rod, carbon fiber, carbon felt, and carbon cloth
 Noncorrosive
 High electrical conductivity and chemical stability.
 For its selection important factors are :
 Biocompatibility,
 specific surface area,
 electrical conductivity,
 and cost.
 The high specific surface area, electrical conductivity, and biocompatibility of
graphene have attracted much attention Since its discovery in 2004.
Electrodes

14.  Already used in lithium-ion batteries.
 The development of graphene-modified materials to increase the power density
has progressed actively.
 Metals are also used as the electrodes.
 Conductivities are higher than those of carbon materials.
 Prone to corrosion in the anode solution.
 Except for stainless and titanium and using graphite in which metals are
incorporated.

15. Buffer solution
 A Phosphate buffer or bicarbonate buffer solution is often used for the anode
electrode solution to achieve high performance.
 pH of the solution effects
 The activity of microorganisms
 The transfer of hydrogen ions used from the anode to the cathode when the
electrons are transferred to oxygen at the cathode.
 In solution Microorganisms serves as catalyst, organic matter as the fuel, and
mediators as the electron carrier in the solution.
 Performance of MFCs was improved by adding NaCl to increase the ionic
strength

16. Fuel
 Generally, the fermentable substrate of microorganisms is used to generate
electricity more efficiently.
 According to trend
 Glucose is used when using S. cerevisiae,
 Lactic acid when using S. oneidensis, and
 acetate when using G. sulfurreducens in the experiments.
 Depending on the metabolic pathways , each substrate generates a different
number of electrons.

17. Mediator
 Why do we need mediator?
In many cases, microorganisms cannot carry the electrons, or the performance is
low even if carried.
 Solution
Artificial mediator that can pass through the cell membrane is added to the anode
solution were developed.
 How they work?
The oxidized mediators came into contact with the microbial cells, and were
reduced by accepting electrons, and they were then separated from the microbial
cells. They diffused and made contact with the electrode's surface, releasing
electrons before being reoxidized.

18.  compounds for artificial mediators are
 neutral red,
 methylene blue,
 thionine, benzyl viologen
 2-hydroxy-1,4-naphthoquinone (HNQ),
 various phenazines.
 and 2,6-dichlorophenolindophenol,
 Depending on the type of mediator, the electrons may be taken directly from
NADH or obtained from the electron transfer system of the cell membrane.
 The level of use is necessary to be controlled due to its toxicity effect .

19. cathode solution
 The electrons generated at the anode are carried
to the cathode, where the reduction reaction takes place.
 Aeration is necessary because
oxygen(electron acceptor)has low solubility (about 8 mg/L DO).
 In the reaction at the cathode, H2O is produced by oxygen.

20. Types
Mediated
 Electron transfer from microbial cells to the electrode is facilitated by mediators.
Mediator-free
 use electrochemically active bacteria such as Shewanella putrefaciens and
Aeromonas hydrophila.
Microbial electrolysis
 by the bacterial decomposition of organic compounds in water.
Soil-based
 soil acts as the nutrient-rich anodic media.
 the inoculum and the proton exchange membrane

21. Applications of MFC
 Waste water treatment
 To harvest energy utilizing anaerobic digestion.
 Power generation
 Only low power.
 Where replacing batteries may be impractical
 Secondary fuel production
 Bio-Sensors
 MFCs can measure the solute concentration of wastewater.

22. Advantages of MFC
 Generation of energy out of biowaste / organic matter
 Direct conversion of substrate energy to electricity
 Omission of gas treatment
 Aeration
 Bioremediation of toxic compounds

23. Limitations of MFC
 Low power density
 High initial cost
 Activation losses
 Ohmic losses
 Bacterial metabolic losses

24. Conclusion
 MFCs have not reached the desirable level because of the problems such as
scaling-up.
 MFCs have the potential to serve as power sources in areas with poor
infrastructure, such as portable power sources that generate electricity when
water is added.
 Regarding microbial catalysts, it is also known that various microorganisms can
generate power, and if the excellent power generation function of these
microorganisms can be incorporated into microbial cells using a recently
developed synthetic biological process, the microbial catalyst will The ability will
improve dramatically.
 Its power generation ability could be greatly improved in combination with the
progress of other constituents.

25. References
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suitable electrode and bioengineered organisms: A review. Bioengineered. 2017;8(5):471-487. DOI: 10.1080/21655979.2016.1267883.
 Stoll ZA, Dolfing J, Xu P. Minimum performance requirements for microbial fuel cells to achieve energy-neutral wastewater treatment.
Water. 2018;10(3):243. DOI: 10.3390/w10030243
 Bennetto HP, Delaney GR, Rason JR, Roller SD, Stirling JL, Thurston CF. The sucrose fuel cell: Efficient biomass conversion using a
microbial catalyst. Biotechnology Letters. 1985;7(10):699-704. DOI: 10.1007/BF01032279
 Zhou T, Han H, Liu P, Xiong J, Tian F, Li X. Microbial fuels cell-based biosensor for toxicity retection: A review. Sensors.
2017;17(10):2230. DOI: 10.3390/s17102230
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