Microbial Fuel Cells: Recent Trends

REVIEW

Microbial Fuel Cells: Recent Trends

Jatin Khera • Amreesh Chandra

Received: 14 January 2011 / Accepted: 8 April 2011 / Published online: 27 January 2012

� The National Academy of Sciences, India 2012

Abstract Microbial fuel cell (MFC) is one of the most

promising technologies in the area of small scale electricity

generation from waste water, industrial sludge or biode-

gradable wastes. The fabrication of MFCs brings together

the knowledge of physics, electrochemistry, biotechnology,

chemical engineering and environmental sciences. This

review gives a brief description of the evolution, present

state and application of the MFC technology with a focus

on the individual components which are used in MFCs

along with the challenges faced in tailoring these compo-

nents. The final part of the review also describes the

characterization techniques and methods used to evaluate

the performance of MFCs. The future of this technology is

also outlined.

Keywords Fuel cell � Microbial fuel cell

Introduction

The increasing awareness towards the need of cleaner and

renewable sources of energy has brought a major shift in the

area of energy research. This increased activity in area of

alternative energy sources can also be attributed to the

realization of the fact of fast depleting reserves of fossil fuel.

Such alternative energy technologies are expected to have

low carbon foot print whereby contributing in controlling the

green house effects and global warming. Different proposed

solutions in search of renewable sources are based on solar,

wind, tidal, bio, piezo-harvester and fuel cells [1, 2]. For a

country like India, solar and bio-energy are expected to play

a dominant role in achieving the desired energy targets to be

obtained using renewable sources. Biomass and bio-related

waste which are available in abundance promises an eco-

friendly solution to increasing demand of sustainable alter-

native energy source. Biomass is renewable and its use is

often regarded as carbon neutral. Two main biomass types

which are used as energy sources are (a) those that are pro-

duced for energy generating purposes (e.g., corn, jatropha)

and (b) those that are present in waste materials (e.g.,

wastewater from food industries, sludge from sewerage,

drain from breweries, etc.) [3, 4]. It is also important to

mention that the major limitation for such technologies is

their intrinsic intermittent nature. Therefore, alternative

methods/technologies/devices for energy storage may also

be required in the long run.

The idea of obtaining biowaste from waste water and

applying it for useful application can have a major implication

for India. Although lot of effort is being put in by the gov-

ernment in setting up of water treatment plants, this is failing

to answer the problem of waste water treatment. The main

reasons for failure are the high cost of installation, mainte-

nance and energy requirements. Therefore, technologies

which can concurrently answer both the problems namely,

(a) energy generation and (b) waste water treatment will be

ideal for Indian scenario [5, 6]. Such technologies may actu-

ally be small scale generation units but with low maintenance

costs. One of the technologies which is attaining prominence

and seemingly has the capacity to answer the above men-

tioned needs simultaneously is ‘‘Biological Fuel Cells’’

(BFCs). This technology is based on the concept of electricity

generation from biomass using bacteria or enzymes. Such

cells are renewable and capable of using naturally available

biomass as fuel and therefore are excellent alternatives

to conventional fuel cells and batteries. The basic working

J. Khera � A. Chandra (&)

Department of Physics and Meteorology, Indian Institute of

Technology Kharagpur, Kharagpur 721302, West Bengal, India

e-mail: [email protected]

123

Proc. Natl. Acad. Sci. Sect. A Phys. Sci. (January–March 2012) 82(1):31–41

DOI 10.1007/s40010-012-0003-2

principle of BFCs are same as that of the chemical fuel cells.

But, unlike conventional fuel cells which need periodic

refueling, BFCs cells continue to produce electricity as long as

the biological host is alive. Few other advantages include:

high efficiency due to the direct conversion of the fuel energy

into electricity, operation capability at room temperature,

lower cost and, most importantly, it does not produce toxic

byproducts [7, 8]. The present day research in the area of BFC

is focusing on development of new electrode assembly,

charge transfer agents, electron mediators, efficient bacterial

consortium, better ion-conducting membrane/separators,

compact design and increased power output. This review

focuses on one type of Biological Fuel Cells i.e., the

‘‘Microbial Fuel Cells’’.

Microbial Fuel Cells

Biological Fuel cells (BFCs) are based on the catalytic

activities of the bio-molecules such as enzymes or living

organisms (microbes) which oxidize biomass-based mate-

rials resulting in the generation of free electrons which

when pass through external circuit yield electrical energy

[9–11]. The biocatalysts catalytically oxidize the fuel at the

anode and reduce the ensuing oxidant at the cathode.

Depending upon the biocatalyst used the biofuel cells are

divided into two classes namely: (a) Enzymatic Fuel Cells

(use enzymes) and (b) Microbial Fuel Cells (uses bacteria).

A microbial fuel cell (MFC) is a bio electrochemical

device capable of continuously converting chemical energy

into electrical energy for as long as substrate and oxidant is

available [12–16]. Schematic of MFC is shown in Fig. 1

along with the operational steps involved in electricity

generation [17–19].

MFCs can generate electricity by the decomposition of

biodegradable waste through some specific bacteria.

The working of microbial fuel cell (MFC) is based upon

the principle of generation of electrical current by electrons

produced during microbial metabolism which involve the

steps of oxidation–reduction (redox) reaction. In MFCs,

living catalysts i.e. bacteria are used to convert organic

substrates into electricity. MFCs contain anodic and

cathodic chambers, separated by a proton exchange mem-

brane. In the anode chamber, protons and electrons are

produced by anaerobic oxidation of microbial substrates

(such as acetate) by bacteria.

The electrons passes through an electron transport

chain (ETC) and protons are translocated across the cell

membrane to generate energy in the form of adenosine

triphosphate (ATP). These electrons and protons exiting

through ETC. pass to electron acceptor such as oxygen,

nitrate, or Fe(III) [20–22]. However, in the absence of such

acceptors in an MFC, some microorganisms pass the

electrons (exoelectrogens) onto the anode surface. In an

MFC, the electrochemical redox potential difference of the

anode (electron donor) and cathode (electron acceptor)

determines how much energy is available to the microor-

ganisms for metabolic processes.

External electrical circuit is completed by the flow of

electrons from the anode to the cathode and internal circuit

is completed by the diffusion of protons from the anode to

the cathode through a proton exchange membrane (see

Figs. 2, 3).

The electrical power (measured in watts) produced by an

MFC is based on the rate of electrons moving through the

circuit (current, measured in amps) and electrochemical

potential difference (volts) across the electrodes. At the

cathode, the electrons and protons combine to reduce the

terminal electron acceptor, which in many applications is

oxygen.

In the absence of oxygen, micro-organisms consume a

substrate such as sugar/Glucose in aerobic conditions,

there-by producing carbon dioxide and water as given in

the following equation [23]:

C12H22O11 þ 13H2O! 12CO2 þ 48Hþ þ 48e� :

The release of the electrons also means that the mediator

returns to its original oxidized state ready to repeat the process.

It is important to note that this can only happen under

anaerobic conditions because in the presence of oxygen,

microorganism collect all the electrons as it has greater electro

negativity than the mediator. A number of mediators have

been suggested for use in microbial fuel cells. These include

natural red, methylene blue, thionine or resorfuin [24–26].

As the oxygen acts as the terminal electron acceptor, the

Fig. 1 Schematic of MFC showing the operational steps: a Oxidation

of Fuel, b Transfer of electrons to electrodes through microbes,

c Diffusion of protons to the cathodic chamber, d Reaction in

Cathodic chamber, e Diffusion of Oxygen

32 Proc. Natl. Acad. Sci. Sect. A Phys. Sci. (January–March 2012) 82(1):31–41

123

microbial activity is strongly dependent on the redox potential

of the anode. The cathode in the cathodic chamber has the

capacity to receive the electrons which are released in the

anodic chamber. Therefore, when the two electrodes are

connected via an external load, the free electrons pass through

it and produce current. The free ions, on the other hand, pass

through the ion-exchange membrane. On reaching the

cathodic chamber, these ions take the electrons available

because of the presence of oxidizing agent and attain a state of

charge neutrality [27, 28].

Current production in the MFCs is affected by many

factors such as substrate concentration, nature of elec-

trodes, membrane type, bacterial substrate oxidation rate,

presence of alternative electron acceptors, and microbial

growth. Electrochemical potential, on the other hand,

depends on the potential difference between the bacterial

respiratory enzyme or electron carrier and the potential at

the anode and the terminal electron acceptor.

Bacteria transfer electrons to anodes either directly or via

mediated mechanisms. In direct electron transfer, bacteria

require physical contact with the electrode for current

production. The contact point between the bacteria and the

anode surface requires outer membrane-bound cytochromes

or putatively conductive pili called nanowires. Although

direct contact of an outer membrane cytochrome to an

anodic surface would require microorganisms to be situated

upon the electrode itself, direct electron transfer mecha-

nisms are not limited to short-range interactions, as nano-

wires produced by Geobacter sulfurreducens have been

implicated in electron conduction through anode biofilms

more than 50 lm thick [17]. In mediated electron transfer

mechanisms, bacteria either produce or take advantage of

indigenous soluble redox compounds such as quinones and

flavones to shuttle electrons between the terminal respira-

tory enzyme and the anode surface.

Microbial research on MFCs has revealed an expansive

diversity of bacteria that transfer electrons onto external

electron acceptors. Until recently, knowledge of electricity-

generating bacteria was limited to bacteria that transfer

electrons to solid metals. However, culture-independent

studies of MFC anode biofilms indicate that the diversity of

such microbial communities far exceeds that of the avail-

able electricity-producing isolates, suggesting that many

organisms with this capability are yet to be discovered.

This knowledge has spurred interest in using a variety of

alternative inoculums sources, operating conditions, and

isolation methods to increase the known diversity of elec-

trode-reducing organisms.

Brief History of Microbial Fuel Cells

The idea of using microbial fuel cells to produce electricity

was first conceived way back in 1911 when Potter showed

that it is possible to generate electricity from cultures of the

bacterium Escherichia coli [29]. Significant knowledge

addition in the area of MFC was made in 1931 by Cohen

[30] when he reported the creation of an assembly of

microbial half fuel cells stack connected in series capable

of producing over 35 V but the current generated through

this stack was only 2 mA. More work on the subject came

with a study by DelDuca who used hydrogen produced by

the fermentation of glucose by Clostridium butyricum as

the reactant at the anode of a hydrogen and air fuel cell.

Unfortunately, though the cell functioned, it was found to

be unstable due to the fluctuating nature of the hydrogen

Fig. 2 Electron transfer mechanism in MFC and production of

electricity

Fig. 3 Polymeric structure of nafion

Proc. Natl. Acad. Sci. Sect. A Phys. Sci. (January–March 2012) 82(1):31–41 33

123

production from the micro-organisms. In 1976, Suzuki

resolved the issues regarding hydrogen production by C.

butyricum, and presented a new concept for MFC design

that is still used today [11, 31].

Major boost in the area of MFC research was received by

the pioneering work of M. J. Allen and H. Peter Bennetto in

early 1980s when they published a series of paper

explaining the functioning of fuel cells and the various

aspects related with the improvement of the MFC [32]. The

major hurdle faced by the authors in improving the power

density was the use of chemical mediators (or electron

shuttles for transferring electrons from inside the cell to

exogenous electrodes) which meant that the fuel cell would

only function till the mediators were present. In early 1990s,

Kim et. al [33]. showed that the Fe(III)-reducing bacterium,

Shewanella oneidensis (formerly Shewanella putrefaciens)

was electrochemically active: i.e., it could generate elec-

tricity in a microbial fuel cell without any added electron

mediators. Kim et. al [34]. also reported, through a series of

papers, that a fuel cell-type electrochemical device can be

fabricated by using electrochemically active microbes that

oxidize various organic materials. Since then electro-

chemical activity has been observed in many different

bacteria, and several of fuel cell designs have been tested

using pure cultures as well as enriched mixed cultures.

Quite a few explanations have been given for the electron

transfer using electrochemically active bacteria but the most

accepted is that the electron transfer occurs as a conse-

quence of electron metabolism through cytochromes in

cytoplasmic membrane, periplasm and outer membrane

[17]. Most recently, MFCs containing various mediators

have been designed where the mediators in an oxidized state

can easily be reduced by capturing the electrons from within

the membrane [13]. The mediators then move across the

membrane and release the electrons to the anode and

become oxidized again in the bulk solution in the anodic

chamber. This cyclic process accelerates the electron

transfer rate and thus increases the power output.

The activities in the area of MFCs over the last few

decades have been led by the pioneering work of the group

of Bruce E. Logan in Pennsylvania State University, USA

[12, 13, 18, 21, 22, 26, 27, 35–37]. These workers have

proposed a large number of reactor designs which can be

made as per the requirement of the application. Along with

this, Logan et al. have also proposed few theoretical

models to explain the electron transfer from bio-organism

to the anode material. Some details of the work of Logan

et. al is discussed in later section of this review. Few other

groups which have been making significant contributions in

the area of MFCs are: Lovely [17, 23, 24, 38–42], Rabaey

[16, 43–47], Schroder [12, 28, 48–50] etc.

The power densities of such devices continue to remain

low but they can still be used to power quite a few

electronic gadgets such as biosensors, mobile chargers and

even laptop chargers [51–53]. One of the proposed niche

areas of application is energy generation in space. Bio-

logical systems may offer a high power-to-weight ratio;

convenient fuel storage and many of them make useful

byproducts like molecular oxygen. But the ultimate

promise is that they might be grown on demand as per the

requirement of the astronauts. The innovation in designs

promises portability and sources for providing reusable

water especially in the remote areas of the developing

nations. Although scaling up microbial fuel cells to help

power large facilities/communities is a long-term goal,

their capacity to clean waste water and deliver clean

drinking water while simultaneously generating electricity,

would allow developing countries towards sustainable

water treatment. For making MFCs economically and

socially viable, major emphasis of research is on increasing

the power density and reducing the cost. In the following

sections, we briefly outline the recent trends in the design

and development of individual components of MFCs which

are being proposed to increase the overall performance of

the fuel cells [54].

Components of MFCs

The performance determining components of MFC are:

(a) electrodes (both anode and cathode)

(b) anolytes and catholytes in anodic and cathodic

chambers

(c) ion (Proton) exchange membrane

(d) electrode catalyst

(e) oxidizing fuel and reducing agents

(f) external load and circuit design

Electrode Material

(a) Anode: Anode materials used in MFCs must exhibit

the following properties:

• high electronic conductivity

• biocompatibility

• chemical stability

• high specific surface area

• high porosity

Metallic electrode is mostly used but electrodes based on

various forms of carbon are also being tried. The electrodes

which are being tried are based on noncorrosive stainless

steel mesh, compact graphite plates/rods/granules, fibrous

material based on carbon such as felt, cloth, paper, fibers,

foam and amorphous carbon (4). The simplest materials for


123

anode electrodes are graphite plates or rods as they are

relatively inexpensive, easy to handle, and have a defined

surface area. Much larger surface areas are achieved with

graphite felt electrodes which can have high surface areas.

It has been shown that current increases with overall

internal surface area.

To increase the anode performance, different chemical

and physical strategies have been followed e.g. incorpo-

ration of Mn(IV) and Fe(III) and use of covalently linked

neutral red/methylene blue to mediate the electron transfer

to the anode [55, 56]. Electro catalytic materials such as

polyanilines/Pt composites have also been shown to

improve the current generation through assisting the direct

oxidation of microbial metabolites [57].

(b) Cathode: In cathode we can use all those materials

which are used as anode and described in earlier

section. Mostly following materials are used as

cathode in MFC:

• Carbon coated with platinum catalyst.

• Carbon without platinum catalyst.

• Plain carbon.

• Metals other than platinum.

• Bio cathodes.

Chemical reaction occurring at the cathode is a triphase

reaction as the electrons, protons and oxygen all meet at a

catalyst. Catalyst must be exposed to air and water so that

electrons and protons in these different phases reach the

same point with no time lag.

Catholyte and Anolyte

K3[Fe(CN)6] is catholyte which is commonly used as an

electron acceptor in microbial fuel cells. The greatest

advantage of ferricyanide is the low over potential in the

case of plain carbon cathode, resulting in the cathode

working potential close to its open circuit potential. The

disadvantage, however, is the insufficient reoxidation by

oxygen because of which the electrolyte has to be regularly

replaced. Further, the long term performance of the system

can be affected by diffusion of ferricyanide across the

separator and into the anodic chamber.

Biological phenomenon of MFC is mainly concerned

with the anodic chamber. Various kind of anolytes are used

in MFC which contain different exoelectrogens of pure

culture or mixed culture. Studies on MFC also reveal the

use of bio film electrodes and different substrates which

together interact with each other to increase the perfor-

mance i.e. current density or power density. Varieties of

substrates used in MFCs are: (i) glucose (ii) acetate (iii)

lactate (iv) sodium formate (v) starch (vi) urban wastewater

(vii) artificial wastewater etc. These substrates when inter-

act with suitable microorganisms (inoculums) decompose

the substrate to produce protons and electrons. The addition

of electron shuttling compounds such as neutral red, thio-

nin, methyl viologen, and phenazine ethosulfate are effec-

tive in electron transfer from microorganism to electrode.

These electron shuttles accept electrons from intracellular

and membrane-bound redox proteins and transfer the elec-

trons to the electrode surface, with the regeneration of the

oxidized form of the shuttle.

The overall fuel cell efficiency depends upon the Redox

reaction occurring in cathodic and anodic chambers which

can be improved by the use of catalysts.

Some of the important catalysts used in MFCs are: Pt,

MnO2, CNT, TiO2 [54, 58, 59].

Ion Exchange Membrane

Most of the MFC designs require the separation of the

anode and the cathode compartments by an Ion exchange

membrane (IEM) or salt bridge. The use of IEM is similar

to that in conventional fuel cells. When an IEM is used in

an MFC, it is important to recognize that it may be per-

meable to chemicals such as oxygen, ferricyanide, other

ions, or organic matter used as the substrate [35].

The major requirements for a membrane to be used in

MFCs are:

(a) excellent thermal, chemical and mechanical stability.

(b) high ionic conductivity.

(c) low cost.

(d) low degradation.

The selection of a membrane, separating anode and

cathode, represents a choice between two opposing

interests:

(i) High selectivity: the higher the selectivity for protons,

the better the biofuel cell will operate and the lower

will be the resistance of the membrane;

(ii) High stability: membranes need to be robust in a

colloidal and nutrient rich environment.

Large numbers of separator membranes are being

investigated upon the application of MFCs. Some of

membranes which are being tried are: Ralex, Ultrex,

Fumatech, PEO, PEG, etc. [60–62].

One of the most used membranes in MFCs is Nafion

which is a proprietary item of Du Pont. Nafion is made

of a per-fluorinated sulfonic acid polymer(pSAP) consist-

ing of a continuous skeleton of –(CF2)n—groups to which

a certain number of hydrophilic segments containing

sulfonic acid group —SO3H are attached (17). Its super


123

acidity is attributed to the electron-withdrawing effect of

the per fluorocarbon chain acting on the sulfonic acid

group. Nafion is able to catalyze various reactions, such as

alkylation, disproportionation, and esterification.

Various Design of MFC’s

The MFC’s design should be such that it is not only able to

produce high power density and columbic efficiencies, but

one that is also economical for mass production. Some

typical designs of MFCs are shown in Fig. 4 viz.

(a) Cube reactor design [18] (Fig. 4a): This design run in

batch mode and mainly concerned for the research

purpose. The main limitation is increasing the size of

the reactor without inflating the overall cost.

(b) Air cathode two chamber MFC (Fig. 4b): The design

is much simpler as compared to the cube reactor. In

this case, oxygen is used as the catholyte and can be

easily used for the long run time applications.

(c) Bottle reactor design [37] (Fig. 4c): In such designs,

anode and cathode chambers are separated by salt

bridge or by IEM to block the diffusion of oxygen

into the anodic chamber. Such designs can be used for

larger fuel cells when power densities required by the

application is the main criteria.

(d) Single chamber design [18] (Fig. 4d): To scale-up

two chamber MFCs is quite difficult due to their

complex design and cost.

Therefore, single chamber MFC was the answer to

resolve these problems. Such designs are basically

used to characterize the performance of anodic(or

cathodic) chamber separately and is therefore mostly

of research use.

(e) Flat Plate type MFC [63] (Fig. 4e): Logan group has

designed a Flat plate MFC in 2004 and its basic

structure is like of a chemical fuel cell. They have

used hot pressed method to make a layer of carbon

cloth on Nafion to form electrode/IEM assembly. The

authors have proposed that higher power densities can

be obtained from such cells.

(f) U-Tube type MFC [64] (Fig. 4f): Such kind of MFCs

is used in laboratories for the research purpose and the

main purpose of these designs to generate hydrogen

gas by using electrolysis process. Such cells may find

large scale application in the field of bio-hydrogen.

A simple design for efficient and low cost MFC is the air

breathing MFC [4]. This cell can be used both in batch as

well as continuous mode. Constructional steps are shown in

Fig. 5.

PMMA (acrylic) sheets are used to cut the anodic

chamber. Fig. 5a shows the isometric view of ABMFC

without the rubber gasket. To prevent leakage, rubber

gasket is placed in the careful fabricated/cut groove in the

acrylic sheet. (see Fig. 5b) The separator/membrane is

placed on one side of the anode chamber followed by

perforated acrylic sheet for enabling oxygen/air breathing.

Upper view of the final ABMFC design is shown in

Fig. 5c. Final isometric is illustrated in this figure with a

single hole shown in front which is for inlet of anolyte in

MFC and the three holes in the side view are for the

electrodes. Suitable holes are made for fixing the electrodes

and reference electrodes (see Fig. 5d).

Characterization Techniques for MFCs

Electrode Potential

The potential of an electrode (anode or cathode) can only

be determined by measuring the voltage against an elec-

trode with a known potential, i.e., a reference electrode.

The most popular reference electrode in MFC experiments

is the silver–silver chloride (Ag/AgCl) reference electrode,

because of its simplicity, stability, and nontoxicity. In a

saturated potassium chloride solution at 25�C the Ag/AgCl

reference electrode develops a potential of ?0.197 V

against the NHE (normal hydrogen electrode).

Power

The overall performance of an MFC is evaluated in many

ways, but principally through power output and Coulombic

efficiency. Power is calculated by measuring voltage and

current. Voltage is measured across a fixed external resistor

(Rext), while the current is calculated from Ohm’s law as

P = Ecell 9 I This is the direct measure of the electric

power. The maximum power is calculated from the

polarization curve.

P ¼ E2cell=Rext

Power Density

The power density (PAn, W/m2) is therefore calculated on

the basis of the area of the anode (AAn).

Polarization Curves

Polarization curves represent a powerful tool for the anal-

ysis and characterization of fuel cells. A polarization curve

represents the voltage as a function of the current (density).

Polarization curves can be recorded for the anode, the

cathode, or for the whole MFC using a Potentiostat. The

polarization curve should be recorded both up and down


123

(i.e., from high to low external resistance) and vice versa.

When a variable external resistance is used to obtain a

polarization curve, the current and potential values need to

be taken only when pseudo-steady-state conditions have

been established. Power density in Microbial fuel cell

depends on the following factors:

Fig. 4 a Cube reactor design b Air Cathode two chamber design c Bottle Reactor design d Single chamber MFC e Flat Plate Type MFC f U-

Tube MFC


123

a) nature of substrate

b) mediator type

c) type of exoelectrogens

d) reactor configuration

e) nature of anode material and cathode material

f) physical condition like temperature, pH value etc.

Electrochemical Characterization

Cyclic Voltammetry

For electrochemical characterization, generally either the

potential or current of the electrode is varied and the

complimentary electrical parameter (current or potential

respectively) is monitored in order to study the electro-

chemical response of the electrode at that specific condi-

tion. The potentiostat is typically operated in a three-

electrode-setup consisting of a working electrode (anode or

cathode), a reference electrode, and a counter electrode. In

MFC experiments, the potentiostatic mode of this instru-

ment is often used for voltammetry tests in which the

potential of the working electrode (anode or cathode) is

varied at a certain scan rate (expressed in Vs-1) [65]. In the

case where a scan only goes in one direction the method is

referred to as linear sweep voltammetry (LSV); if the scan

is also continued in the reverse direction and comes back to

the start potential the method is cyclic voltammetry. Vol-

tammetry can be used for assessing the electrochemical

activity of microbial strains or consortia, determining the

standard redox potentials of redox active components and

testing the performance of novel cathode materials. Cyclic

voltammetry (CV) offers a rapid and proven method to

discern whether bacteria use mobile redox shuttles to

transfer their electrons, or pass the electrons ‘‘directly’’

through membrane associated compounds [42, 46, 48]. For

CV, a reference electrode is placed in the anode chamber of

the MFC close to the anode (working electrode); the

counter electrode (e.g., platinum wire) is preferably placed

in the cathode chamber, but can also be placed in the

anode chamber. A potentiostat is used to obtain a scan

of potential. For bacterial suspensions, a scan rate of

25 mVs-1 appears to be reasonable based on the work of

several researchers. For the analysis of mediators in bio-

films, however, this scan rate needs to be decreased, pos-

sibly to 10 mV s-1 and lower. A potentiostat can also be

operated in a two-electrode setup to obtain polarization

curves or to determine the ohmic resistances using the

current interrupt technique. In the two electrode setup, the

working electrode connector is connected to the cathode

(positive terminal) and both the counter electrode and

reference electrode connectors are connected to the anode.

Fig. 5 Different views of Air Breathing MFC: a. Side upper view without Gasket, b. Side upper view with Gasket, c. Upper view, d. Tilted view


123

Electrochemical Impedance Spectroscopy

More advanced measurements can be done when the

potentiostat is equipped with a frequency response ana-

lyzer (FRA), allowing electrochemical impedance spec-

troscopy measurements (EIS). In EIS, a sinusoidal signal

with small amplitude is superimposed on the applied

potential of the working electrode. By varying the fre-

quency of the sinusoidal signal over a wide range (typi-

cally 10-4–106 Hz) and plotting the measured electrode

impedance, detailed information can be obtained about

the electrochemical system. EIS can also be used to

measure the ohmic and internal resistance of an MFC

[65–67].

Performance Limiting Factors

• Rate of fuel oxidation

• Proton mass transfer

• Oxygen reduction by cathode

• Activation overpotential

• Ohmic overpotential

• Concentration polarization

The detailed descriptions of these limiting factors are not

being discussed in this review. For details, the references

[47, 50, 68–70] can be consulted by interested readers.

Application of Microbial Fuel Cell

Hydrogen Production

In the conventional fuel cell, hydrogen gas is produced in

the anodic chamber as there is formation of protons and

electrons through the degradation of organic substrate by

bacterial catalyst. In the cathodic chamber, protons which

diffuse from proton exchange membrane combines with

electrons to produce water [49, 71, 72]. More hydrogen

can be produced when the electricity generated by MFC

is fed into the same cell or any other microbial electrol-

ysis cell. Biohydrogen can also be produced when

microbial electrolysis is connected with solar power

energy source. MFC-MEC coupled system produce

hydrogen by using acetate as substrate. Following reac-

tions take place while production of biohydrogen in

cathodic chamber.

Anode:

C2H4O2 þ 2H2 ! 2CO2 þ 8e� þ 8Hþ

Cathode:

8Hþ þ 8e� ! 4H2

Waste Water Treatment

This is the broad area in which MFC is playing a dominant.

Various bacteria which are using in MFC have capability

to reduce the toxic chemicals and reagents present in

waste water. As the wastewater contain plenty of organic

substrate which can act as a source of fuel for MFC

[73–75]. Therefore, MFC can perform two important func-

tions simultaneously, namely, (a) Electricity generation,

(b) Waste water treatment.

Biochemical Oxygen Demand (BOD) Sensor

As the current from a MFC is proportional to the concen-

tration of available organic contaminants, this microbial

device can also be used as a biochemical oxygen demand

sensor.

Conclusion and Future Prospects

Microbial fuel cells are evolving as a simple and robust

technology holding promise towards sustainable energy

generation in the near future. Many bottlenecks still exist,

which pose a challenge that will take a multidisciplinary

approach and intensive research. Analyses of the literature

show that the performance of MFCs is limited by their

internal resistance derived from proton mass transfer and

poor oxygen reduction kinetics at the cathode. As proton

transfer through the aqueous phase is slow, the depth of

proton transfer should be minimized to reduce internal

resistance through improvement of proton mass transfer

from the anode to the cathode. This might be possible

through the use of hollow fiber-type reactors. Inorganic

compounds added to the anodic compartment as nutrients

result in high cation concentrations that can inhibit proton

transfer through the cation-specific membrane. Develop-

ment of a proton-specific membrane may be a means of

solving this problem. Biological redox materials including

aerobic bacterial cells have a much higher affinity for

oxygen than any of the known abiotic cathode materials

used in fuel cells. Several papers have reported improved

fuel cell performance using a cathode with aerobic bacte-

ria, including those that develop as a corroding biofilm.

It is expected that a properly enriched cathode microbial

consortium could further improve oxygen reduction

kinetics [76–78].

Certainly in the field of wastewater treatment, middle

term application can be foreseen at market value prices.

However, to increase the power output towards a stable

1 kW per m3 of reactor, many technological improvements

are needed. This technology might qualify as a new core


123

technology for conversion of suitable organic material to

electricity in years to come, provided the biological

understanding increases, the electrochemical technology

advances and the overall electrode prices decrease.

Acknowledgements We would like to thank Mr. Mayur Rastogi

and Mr. Parth Gattani for their help for completing this review article.

References

1. Joel M, Pernick R and Wilder C (2009) Clean energy trends;

clean edge

2. Tsuneo H (2001) Research and development of international

clean energy network using hydrogen energy. Int J Hydrogen

Energy 27:115–129

3. Tim P (2009) The next big biofuel ; time magazine

4. Zhao F, Rahunen N, Varcoe JR, Chandra A, Rossa CA, Thumser

AE, Slade RCT (2008) Activated carbon cloth as anode for

sulfate removal in a microbial fuel cell. Environ Sci Technol

42(13):4971–4976

5. Casado J, Fornaguera J, Galan MI (2005) Mineralization of

aromatics in water by sunlight-assisted electro-fenton technology

in a pilot reactor. Environ Sci Technol 39(6):1843–1847

6. Shukla AK, Suresh P, Berchmans S, Rajendran A (2004) Bio-

logical fuel cells and their application. Curr Sci 87:455–468

7. Sisler FD (1971) Biochemical fuel cells. Prog Ind Microbiol

9:1–11

8. Williams KR (1966) An introduction to fuel cells. Elsevier,

Amsterdam

9. Barton SC, Gallaway J, Atanassov P (2004) Enzymatic biofuel

cells for implantable and microscale devices. Chem Rev 104:

4867–4886

10. Habermann W, Pommer EH (1991) Biological fuel cells with

Sulphide storage capacity. Appl Microbiol Biotechnol 35:128–133

11. Rao JR, Richter GJ, Von Sturm F, Weidlich E (1976) The per-

formance of glucose electrodes and the characteristics of different

biofuel cell constructions. Bioelectrochem Bioenerg 3:139–150

12. Logan BE, Hamelers B, Rozendal R, Schroder U, Keller J, Fre-

guia S (2006) Microbial fuel cells: methodology and technology.

Environ Sci Technol 40:5181–5192

13. Logan BE, (2008) Microbial fuel cell. Wiley Publication, ISBN

978-0-470-23948-3

14. Pant D, Bogaert GV, Diels L, Vanbroekhoven K (2010) A review

of the substrates used in microbial fuel cells (MFCs) for sus-

tainable energy production. Bioresource Technol 101:1533–1543

15. Bennetto HP (1984) Microbial fuel cells. Life Chem Rep 2:

363–453

16. Rabaey K, Verstraete W (2005) Microbial fuel cells: novel bio-

technology for energy generation. Trends Biotechnol 23:291–298

17. Bond DR, Lovley DR (2003) Electricity production by Geobactersulfurreducens attached to electrodes. Appl Environ Microbiol

69:1548–1555

18. Liu H, Ramnarayanan R, Logan BE (2004) Production of elec-

tricity during wastewater treatment using a single chamber

microbial fuel cell. Environ Sci Technol 38:2281–2285

19. He Z, Minteer SD, Angenent LT (2005) Electricity generation

from artificial wastewater using an upflow microbial fuel cell.


20. Delaney GM, Bennetto HP, Mason JR, Roller SD, Stirling JL,

Thurston CF (1984) Electron-transfer coupling in microbial fuel

cells. 2. Performance of fuel cells containing selected microor-

ganism-mediator substrate combinations. J Chem Tech Biotech-

nol 34B:13–27

21. Logan BE (2009) Exoelectrogenic bacteria that power microbial

fuel cells. Nat Rev Microbiol 7:375–381

22. Logan BE, Regan JM (2006) Electricity-producing bacterial

communities in microbial fuel cells. Trends Microbiol 14:512–518

23. Chaudhuri SK, Lovley DR (2003) Electricity generation by direct

oxidation of glucose in mediatorless microbial fuel cells. Nat

Biotechnol 21:1229–1232

24. Gregory KB, Bond DR, Lovley DR (2004) Graphite electrodes as

electron donors for anaerobic respiration. Environ Microbiol

6:596–604

25. Park DH, Zeikus JG (2000) Electricity generation in microbial

fuel cells using neutral red as an electronophore. Appl Environ

Microb 66:1292–1297

26. Oh S, Min B, Logan BE (2004) Cathode performance as a factor

in electricity generation in microbial fuel cells. Environ Sci

Technol 38:4900–4904

27. Oh SE, Logan BE (2006) Proton exchange membrane and elec-

trode surface areas as factors that affect power generation in

microbial fuel cells. Appl Microbiol Biotechnol 70:162–169

28. Schroder U, Nieben J, Scholz F (2003) A generation of microbial

fuel cells with current outputs boosted by more than one order of

magnitude. Angew Chem Int Ed 42:2880–2883

29. Potter MC (1911) Electrical effects accompanying the decom-

position of organic compounds. Proc R Soc London Ser B

84:260–276

30. Cohen B (1931) The bacterial culture as an electrical half-cell.

J Bacteriol 21:18–19

31. Suzuki S, Karube I, Matsunaga T (1978) Application of a bio-

chemical fuel cell to wastewater. Biotechnol Bioeng Symp 8:

501–511

32. Kim BH, Kim HJ, Hyun MS, Park DH (1999) Direct electrode

reaction of Fe(III)-reducing bacterium, Shewanella putrifaciens.

J Microbiol Biotechnol 9:127–131

33. Allen RM, Bennetto HP (1993) Microbial fuel-cells: electricity

production from carbohydrates. Appl Biochem Biotechnol

39/40:27–40

34. Kim HJ, Park HS, Hyun MS, Chang IS, Kim M, Kim BH (2002)

A mediator-less microbial fuel cell using a metal reducing bac-

terium, Shewanella putrefaciens. Enzyme Microb Technol 30:

145–152

35. Min B, Cheng S, Logan BE (2005) Electricity generation using

membrane and salt bridge microbial fuel cells. Water Res

39:1675–1686

36. Logan BE (2004) Extracting hydrogen and electricity from

renewable resources. Environ Sci Technol 38:160a–167a

37. Logan BE, Murano C, Scott K, Gray ND, Head IM (2005)

Electricity generation from Cysteine in a microbial fuel cell.

Water Res 39:942–952

38. Lovely DR (2008) Extracellular electron transfer: wires, capaci-

tors, iron lungs, and more. Geobiology 6:225–231

39. Lovley DR, Coates JD, Blunt-Harris EL, Phillips EJP, Woodward

JC (1996) Humic substances as electron acceptors for microbial

respiration. Nature 382:445–448

40. Bond DR, Holmes DE, Tender LM, Lovley DR (2002) Electrode

reducing microorganisms that harvest energy from marine sedi-

ments. Science 295:483–485

41. Lovely DR (2006) Microbial fuel cells: novel microbial physiologies

and engineering approaches. Curr Opin Biotechnol 17:327–332

42. Richter H, Nevin KP, Jia H, Lowy DA, Lovley DR, Tender LM

(2009) Cyclic voltammetry of biofilms of wild type and mutant

Geobacter sulfurreducens on fuel cell anodes indicates possible

roles of OmcB, OmcZ, type IV pili, and protons in extracellular

electron transfer. Energy Environ Sci 2:506–516

43. Rabaey K, Lissens G, Siciliano SD, Verstraete W (2003) A

microbial fuel cell capable of converting glucose to electricity at

high rate and efficiency. Biotechnol Lett 25:1531–1535


123

44. Rabaey K, Boon N, Siciliano SD, Verhaege M, Verstraete W

(2004) Biofuel cells select for microbial consortia that self-

mediate electron transfer. Appl Environ Microb 70:5373–5382

45. Rabaey K, Boon N, Hofte M, Verstraete W (2005) Microbial

phenazine production enhances electron transfer in biofuel cells.


46. Aelterman P, Freguia S, Keller J, Verstraete W, Rabaey K (2008)

The anode potential regulates bacterial activity in microbial fuel

cells. Appl Microbiol Biotechnol 78:409–418

47. Aelterman P, Rabaey K, Pham TH, Boon N, Verstraete W (2006)

Continuous electricity generation at high voltages and currents

using stacked microbial fuel cells. Environ Sci Technol 40:

3388–3394

48. Fricke K, Harnisch F, Schroder U (2008) On the use of cyclic

voltammetry for the study of anodic electron transfer in microbial

fuel cells. Energy Environ Sci 1:144–147

49. Schroder U (2008) From wastewater to hydrogen: biorefineries

based on microbial fuel cell technology. Chem Sus Chem 1:

281–282

50. Zhao F, Harnisch F, Schroder U, Scholz F, Bogdanoff P, Herr-

mann I (2005) Application of pyrolysed iron(II) phthalocyanine

and CoTMPP based oxygen reduction catalysts as cathode

materials in microbial fuel cells. Electrochem Commun 7:

1405–1410

51. Chang IS, Moon H, Jang JK, Kim BH (2005) Improvement of a

microbial fuel cell performance as a BOD sensor using respira-

tory inhibitors. Biosens Bioelectron 20:1856–1859

52. Kim BH, Chang IS, Gil GC, Park HS, Kim HJ (2003) Novel BOD

(biological oxygen demand) sensor using mediator-less microbial

fuel cell. Biotechnol Lett 25:541–545

53. Source: http://www.lebone.org/

54. Jang JK, Pham TH, Chang IS, Kang KH, Moon H, Cho KS

(2004) Construction and operation of a novel mediator-and

membraneless microbial fuel cell. Process Biochem 39:

1007–1012

55. Park HS, Kim BH, Kim HS, Kim HJ, Kim GT, Kim M (2001) A

novel electrochemically active and Fe(III)-reducing bacterium

phylogenetically related to Clostridium butyricum isolated from a

microbial fuel cell. Anaerobe 7:297–306

56. Lovley DR, Holmes DE, Nevin KP (2004) Dissimilatory Fe(III)

and Mn(IV) reduction. Adv Microb Physiol 49:219–286

57. Cheng S, Liu H, Logan BE (2006) Increased power generation in

a continuous Flow MFC with advective flow through the porous

anode and reduced electrode spacing. Environ Sci Technol 40:

2426–2432

58. Sharma T, Reddy ALM, Chandra TS, Ramaprabhu S (2008)

Development of carbon nanotubes and nanofluids based micro-

bial fuel cell. Int J Hydrogen Energy 33:6749–6754

59. Cheng S, Liu H, Logan BE (2006) Power densities using different

cathode catalyst (Pt and CoTMPP) and polymer binders (Nafion

and PTFE) in single chamber microbial fuel cells. Environ Sci

Technol 40:364–369

60. Mo YH, Liang P, Huang X, Wang H, Cao X (2009) Enhancing

the stability of power generation of single-chamber microbial fuel

cells using an anion exchange membrane. J Chem Technol Bio-

technol 84:1767–1772

61. Mohan SV, Raghavulu SV, Sarma PN (2008) Biochemical

evaluation of bioelectricity production process from anaerobic

wastewater treatment in a single chambered microbial fuel cell

(MFC) employing glass wool membrane. Biosens Bioelectron

23:1326–1332

62. Zuo Y, Cheng S, Call D, Logan BE (2008) Ion exchange mem-

brane cathodes for scalable microbial fuel cells. Environ Sci

Technol 42:6967–6972

63. Min B, Logan BE (2004) Continuous electricity generation

from domestic wastewater and organic substrates in a flat plate

microbial fuel cell. Environ Sci Technol 38:5809–5814

64. Zuo Y, Xing D, Regan JM, Logan BE (2008) Isolation of the

exoelectrogenic bacterium Ochrobactrum anthropi. Appl Environ

Microbiol 74:3130–3137

65. Liang P, Huang X, Fan MZ, Cao XX, Wang C (2007) Compo-

sition and distribution of internal resistance in three types of

microbial fuel cells. Appl Microbiol Biotechnol 77:551–558

66. He Z, Mansfeld F (2009) Exploring the use of electrochemical

impedance spectroscopy (EIS) in microbial fuel cell studies.

Energy Environ Sci 2:215–219

67. Fan Y, Sharbrough E, Liu H (2008) Quantification of the internal

resistance distribution of microbial fuel cells. Environ Sci

Technol 42:8101–8107

68. Gil GC, Chang IS, Kim BH, Kim M, Jang JK, Park HS, Kim HJ

(2003) Operational parameters affecting the performance of a

mediator-less microbial fuel cell. Biosens Bioelectron 18:

327–334

69. Liu H, Logan BE (2004) Electricity generation using an air-

cathode single chamber microbial fuel cell in the presence and

absence of a proton exchange membrane. Environ Sci Technol

38:4040–4046

70. Rozendal RA, Hamelers HVM, Euverink GJW, Metz SJ, Buis-

man CJN (2006) Principle and perspectives of hydrogen pro-

duction through biocatalyzed electrolysis. Int J Hydrogen Energy

31:1632–1640

71. Watanabe K (2008) Recent developments in microbial fuel cell

technologies for sustainable bioenergy. J Biosci Bioeng 106:

528–536

72. Ieropoulos I, Greenman J, Melhuish C, Hart J (2005) Energy

accumulation and improved performance in microbial fuel cells.

J Power Sources 145:253–256

73. Walker AL, Walker CW Jr (2006) Biological fuel cell and an

application as a reserve power source. J Power Sources 160:

123–129

74. Zhuwei Du, Li Haoran, Tingyue Gu (2007) A state of the art

review on microbial fuel cells: a promising technology for

wastewater treatment and bioenergy. Biotechnol Adv 25:464–482

75. Tayhas G, Palmore R (2004) Bioelectric power generation.

Trends Biotechnol 22:99–100

76. Larminie J, Dicks A (2000) Fuel cell systems explained. Wiley,

Chichester

77. Bard AJ, Faulkner LR (2001) Electrochemical methods: funda-

mentals and applications, 2nd edn. Wiley, New York

78. Manohar AK, Bretschger O, Nealson KH, Mansfeld F (2008)

The polarization behavior of the anode in a microbial fuel cell.

Electrochim Acta 53:3508–3513


123

http://www.lebone.org/

Documents

Microbial Fuel Cells: Recent Trends