Microbial electrolysis cell
Encyclopedia
A microbial electrolysis cell (MEC) is a technology related to Microbial fuel cell
s (MFC). Whilst MFC's produce an electric current
from the microbial decomposition of organic compounds, MEC's partially reverse the process to generate hydrogen
or methane
from organic material by applying an electric current. The electric current would ideally be produced by a renewable source of power.
Microorganisms - are attached to the cathode. The identity of the microorganisms determines the products and efficiency of the MEC.
Materials - The anode material in a MFC can be the same as an MEC, such as carbon cloth, carbon paper, graphite felt, graphite granules or graphite brushes. Platinum can be used as a catalyst to reduce the overpotential
required for hydrogen production. The high cost of platinum is driving research into biocathodes as an alternative. Other materials include membranes (although some MECs are membraneless), and tubing and gas collection systems.
) release electrons and protons, creating an electrical potential
of up to 0.3 volts. In a conventional MFC, this voltage is used to generate electrical power. In a MEC, an additional voltage is supplied to the cell from an outside source. The combined voltage is sufficient to reduce protons, producing hydrogen gas. As part of the energy for this reduction is derived from bacterial activity, the total electrical energy that has to be supplied is less than for electrolysis of water
in the absence of microbes. Hydrogen production has reached up to 3.12 m3H2/m3d with an input voltage of 0.8 volts. The efficiency of hydrogen production depends on which organic substances are used. Lactic and acetic acid achieve 82% efficiency, while the values for unpretreated cellulose or glucose are close to 63%.
The efficiency of normal water electrolysis is 60 to 70 percent. As MEC’s convert unusable biomass into usable hydrogen, they can produce 144% more usable energy than they consume as electrical energy.
Depending on the organisms present at the cathode, MEC’s can also produce methane by a related mechanism.
Calculations
Overall hydrogen recovery was calculated as RH2 = CERCat. The Coulombic efficiency is CE=(nCE/nth), where nth is the moles of hydrogen that could be theoretically produced and nCE = CP/(2F) is the moles of hydrogen that could be produced from the measured current, CP is the total coulombs calculated by integrating the current over time, F is Faraday’s constant, and 2 is the moles of electrons per mole of hydrogen. The cathodic hydrogen recovery was calculated as RCat = nH2/nCE, where nH2 is the total moles of hydrogen produced. Hydrogen yield (YH2) was calculated as YH2 = nH2 /ns, where ns is substrate removal calculated on the basis of chemical oxygen demand (22).
Microbial fuel cell
A microbial fuel cell or biological fuel cell is a bio-electrochemical system that drives a current by mimicking bacterial interactions found in nature....
s (MFC). Whilst MFC's produce an electric current
Electric current
Electric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...
from the microbial decomposition of organic compounds, MEC's partially reverse the process to generate hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
or methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...
from organic material by applying an electric current. The electric current would ideally be produced by a renewable source of power.
Microbial electrolysis cells
MEC systems are based on a number of components:Microorganisms - are attached to the cathode. The identity of the microorganisms determines the products and efficiency of the MEC.
Materials - The anode material in a MFC can be the same as an MEC, such as carbon cloth, carbon paper, graphite felt, graphite granules or graphite brushes. Platinum can be used as a catalyst to reduce the overpotential
Overpotential
Overpotential is an electrochemical term which refers to the potential difference between a half-reaction's thermodynamically determined reduction potential and the potential at which the redox event is experimentally observed. The term is directly related to a cell's voltage efficiency...
required for hydrogen production. The high cost of platinum is driving research into biocathodes as an alternative. Other materials include membranes (although some MECs are membraneless), and tubing and gas collection systems.
Generating hydrogen
Electrogenic microorganisms consuming an energy source (such as acetic acidAcetic acid
Acetic acid is an organic compound with the chemical formula CH3CO2H . It is a colourless liquid that when undiluted is also called glacial acetic acid. Acetic acid is the main component of vinegar , and has a distinctive sour taste and pungent smell...
) release electrons and protons, creating an electrical potential
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
of up to 0.3 volts. In a conventional MFC, this voltage is used to generate electrical power. In a MEC, an additional voltage is supplied to the cell from an outside source. The combined voltage is sufficient to reduce protons, producing hydrogen gas. As part of the energy for this reduction is derived from bacterial activity, the total electrical energy that has to be supplied is less than for electrolysis of water
Electrolysis of water
Electrolysis of water is the decomposition of water into oxygen and hydrogen gas due to an electric current being passed through the water.-Principle:...
in the absence of microbes. Hydrogen production has reached up to 3.12 m3H2/m3d with an input voltage of 0.8 volts. The efficiency of hydrogen production depends on which organic substances are used. Lactic and acetic acid achieve 82% efficiency, while the values for unpretreated cellulose or glucose are close to 63%.
The efficiency of normal water electrolysis is 60 to 70 percent. As MEC’s convert unusable biomass into usable hydrogen, they can produce 144% more usable energy than they consume as electrical energy.
Depending on the organisms present at the cathode, MEC’s can also produce methane by a related mechanism.
Calculations
Overall hydrogen recovery was calculated as RH2 = CERCat. The Coulombic efficiency is CE=(nCE/nth), where nth is the moles of hydrogen that could be theoretically produced and nCE = CP/(2F) is the moles of hydrogen that could be produced from the measured current, CP is the total coulombs calculated by integrating the current over time, F is Faraday’s constant, and 2 is the moles of electrons per mole of hydrogen. The cathodic hydrogen recovery was calculated as RCat = nH2/nCE, where nH2 is the total moles of hydrogen produced. Hydrogen yield (YH2) was calculated as YH2 = nH2 /ns, where ns is substrate removal calculated on the basis of chemical oxygen demand (22).
Uses
Hydrogen and methane can both be used as alternatives to fossil fuels in internal combustion engines or for power generation. Like MFC’s or bioethanol production plants, MEC’s have the potential to convert waste organic matter into a valuable energy source. Hydrogen can also be combined with the nitrogen in the air to produce ammonia, which can be used to make ammonium fertilizer.See also
- Hydrogen technologiesHydrogen technologiesHydrogen technologies are technologies that relate to the production and use of hydrogen. Hydrogen technologies are applicable for many uses....
- Microbial Fuel Cells
- Microbial electrosynthesisMicrobial electrosynthesisMicrobial electrosynthesis is a form of microbial electrocatalysis in which electrons are supplied to living microorganisms via a cathode in an electrochemical cell by applying an electric current. The electrons are then used by the microorganisms to reduce carbon dioxide to yield industrially...