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A microbial electrolysis cell (MEC) is a technology related to Microbial fuel cells (MFC). Whilst MFCs produce an
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, MECs can also produce methane by a related mechanism. Calculations
Overall hydrogen recovery was calculated as ''RH''2 = ''C''E''R''Cat. The Coulombic efficiency is ''C''E=(''n''CE/''n''th), where ''n''th is the moles of hydrogen that could be theoretically produced and ''n''CE = ''C''P/(2''F'') is the moles of hydrogen that could be produced from the measured current, ''C''P 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 ''R''Cat = ''n''H2/''n''CE, where ''n''H2 is the total moles of hydrogen produced. Hydrogen yield (''Y''H2) was calculated as ''Y''H2 = ''n''H2 /''n''s, where ''n''s is substrate removal calculated on the basis of chemical oxygen demand (22).
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A microbial electrolysis cell (MEC) is a technology related to Microbial fuel cells (MFC). Whilst MFCs produce an electric current
An electric current is a flow of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is defined as the net rate of flow of electric charge through a surface. The moving particles are called charge c ...
from the microbial decomposition of organic compounds, MECs partially reverse the process to generate hydrogen
Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...
or methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The abundance of methane on Earth makes ...
from organic material by applying an electric current. The electric current would ideally be produced by a renewable source of power. The hydrogen or methane produced can be used to produce electricity by means of an additional PEM fuel cell or internal combustion engine.
Microbial electrolysis cells
MEC systems are based on a number of components: Microorganisms – are attached to the anode. The identity of the microorganisms determines the products and efficiency of the MEC. Materials – The anode material in a MEC can be the same as an MFC, such as carbon cloth, carbon paper, graphite felt, graphite granules or graphite brushes. Platinum can be used as a catalyst to reduce theoverpotential
In electrochemistry, overpotential is the potential difference (voltage) between a half-reaction's thermodynamically determined reduction potential and the potential at which the redox event is experimentally observed. The term is directly r ...
required for hydrogen production
Hydrogen gas is produced by several industrial methods. Nearly all of the world's current supply of hydrogen is created from fossil fuels. Article in press. Most hydrogen is ''gray hydrogen'' made through steam methane reforming. In this process, ...
. The high cost of platinum is driving research into biocathodes as an alternative. Or as other alternative for catalyst, the stainless steel plates were used as cathode and anode materials. Other materials include membranes (although some MECs are membraneless), and tubing and gas collection systems.
Generating hydrogen
Electrogenic microorganisms consuming an energy source (such asacetic acid
Acetic acid , systematically named ethanoic acid , is an acidic, colourless liquid and organic compound with the chemical formula (also written as , , or ). Vinegar is at least 4% acetic acid by volume, making acetic acid the main compone ...
) release electrons and protons, creating an electrical potential
Electric potential (also called the ''electric field potential'', potential drop, the electrostatic potential) is defined as electric potential energy per unit of electric charge. More precisely, electric potential is the amount of work neede ...
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 is using electricity to Water splitting, split water into oxygen () and hydrogen () gas by electrolysis. Hydrogen gas released in this way can be used as hydrogen fuel, but must be kept apart from the oxygen as the mixture ...
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, MECs can also produce methane by a related mechanism. Calculations
Overall hydrogen recovery was calculated as ''RH''2 = ''C''E''R''Cat. The Coulombic efficiency is ''C''E=(''n''CE/''n''th), where ''n''th is the moles of hydrogen that could be theoretically produced and ''n''CE = ''C''P/(2''F'') is the moles of hydrogen that could be produced from the measured current, ''C''P 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 ''R''Cat = ''n''H2/''n''CE, where ''n''H2 is the total moles of hydrogen produced. Hydrogen yield (''Y''H2) was calculated as ''Y''H2 = ''n''H2 /''n''s, where ''n''s 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 ininternal combustion engines
An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal comb ...
or for power generation. Like MFCs or bioethanol production plants, MECs 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. Ammonia has been proposed as a practical alternative to fossil fuel for internal combustion engines.
See also
* Hydrogen technologies * Microbial electrosynthesis * Microbial fuel cells * Microbial electrolysis carbon captureReferences
* M.Y. Azwar, M.A. Hussain, A.K. Abdul-Wahab (2014). Development of biohydrogen production by photobiological, fermentation and electrochemical processes: A review. Renewable and Sustainable Energy Reviews.Volume 31, March 2014, Pages 158–173. Copyright 2017 Elsevier B.V. http://doi.org/10.1016/j.rser.2013.11.022External links
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