Several technologies have been studied as alternatives to
petroleum-based fuels. Among these stands out the technology of
fuel cells due to their diverse field of application extends from
portable devices to generate stationary, including automotive use.
Although the high cost still prevents the application of such devices
on a large scale, reduced cost, weight and increase efficiency, will
provide a rapid growth in the use of fuel cells. The technology of fuel
cells is divided into two categories electrochemical fuel cells (also
called conventional) and biocells fuel (or fuel cell biological - MFC),
the latter having received extensive attention in the past three years.
For the production of electricity, the MFC operates with two sections
(one cathode-anode-aerobic and anaerobic), separated by an ion
selective membrane H. Micro-organisms are used to catalyze the
oxidation of organic matter, generating electricity by transfer of
electrons to an external circuit, introduced before the step of reducing
an electron acceptor. In the anaerobic compartment is the oxidation
of organic material, with formation of CO2, protons and electrons.
The generated protons migrate to the aerobic compartment (cathodic
chamber) permeating through the proton exchange membrane. The
produced electrons are transferred to the cathode through the
external circuit, and this surface is the reduction of oxygen to water.
This flow of electrons through the external circuit generates an
electrical current that can be measured and used to do work. The
overall cell reaction is the conversion of biodegradable organic
material to carbon dioxide and water, generating electricity in the
process. The electrodes can not colonized by a few species of
bacteria. Electroactive bacteria can transfer electrons to the
electrode surface without the need for redox mediators. Some of the
micro-organisms known more electrochemical active Shewanella
putrefaciens and Shewanella oneidensis, the Gamma-proteobacteria,
Geobacter sulfurreducens, Geobacter metallireducens and
Desulfuromonas acetoxidans all Deltaproteobacteria and Rhodoferax
ferrireducens the Betaproteobacteria. The MFCs form a promising
technology for sewage treatment, as a method of recovering energy
in the form of hydrogen or electricity. In 2004, there was a change in
the relationship between electricity production and sewage treatment,
when it was shown that wastewater can be treated at practical levels
parallel to power generation. The amount of energy generated in the
study, although low, can be considered high compared to previous
studies. Reimers, 2001, demonstrated that inorganic and organic
materials present in marine sediments could be used in a new type of
MFC, with the use of variety of substrates, new materials and
structural arrangements in the construction of the MFCs.
MFC CONSTRUCTION
Materials
• 4 PLATES ACRYLIC 120x120mm, 5mm thick
• 2 PLATES ACRYLIC 100X75mm, 5mm thick
• 2 PLATES 120X75mm, 5mm de thick
• 24 screw-nut M6
• 24 washer/bezant M6
• 6 tubes of 20g of cyanoacrylate (superglue)
• 6 connectors 1/4''
• Hose 1/8''
• Straight connectors 1/8''
• 3 valves d
• carbon fiber
• 10x10cm de NAFION®
Procedures
1) Machining of acrylic pieces.
The acrylic pieces were cut according to the specifications.
MEMBRANE117
Assembly
• Plates were united in order to form a rectangle with
cyanoacrylate based glue as shown below:
https://igem.org/File:8.png
Electrode:
Aluminum wire was wound and coated with a carbon fiber for
A heat sink aluminum was used as the counter electrode to the
SETUP OF MEASUREMENT DEVICE
The electrodes were connected to a resistor of 0.9620 KΩ, and
then connected to an Agilent U1252A multimeter. The potential was
measured at intervals of 15 minutes by 9hrs30min, and stored. From
the same may construct the table below, where the MFC produced
watts / hour.
This means that the MFC produced is necessary to feed our
own meter for approximately 5.6 minutes. The calculations below
demonstrate our conclusion:
Current battery power meter = 2.8mA = I.
Supply voltage meter = 7.38 V = V
Power generated by the MFC = 1930.085 μW
Power required by multimeter:
P = VXI = 7.38V x 0.0028 = nd = 0.020664W 20664μW
PMFC / Pmultimetro = 0.093405 h ≈ 5.6 minutes
The electricity generated is measured as follows:
The MFC electrodes are connected in parallel with the
multimeter, whose terminals are also placed in parallel with screw
terminals, so that there is overhang of the screws engaged in the
junction, in order to connect, also in parallel with a resistor (15 k) with
sole purpose of measuring its power.
The voltage produced by the full MFC suffers a fall due to
the consumption of the load. With a quarter of a period of time, it is
checked potential difference "up" resistor, so in the end of 8 hours of
perform the integration of the power to obtain energy.
Through the knowledge of Ohm's law, we know that the voltage
produced undergoes substantial decrease before the presence of the
load, which does not affect the efficiency of the system.
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