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A microbial electrolysis cell (MEC) is a technology related to
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 cell Microbial fuel cell (MFC) is a type of bioelectrochemical fuel cell system that
generates electric current by diverting electrons produced from the microbial oxidation of reduced compounds (also known as fuel or electron donor) on the anode to oxid ...
s (MFC). Whilst MFCs produce an electric current
An electric current is a stream of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is measured as the net rate of flow of electric charge through a surface or into a control volume. The moving pa ...
from the microbial decomposition of organic compounds, MECs partially reverse the process to generate hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...
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 relative abundance of methane on Eart ...
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 relat ...
required for hydrogen production. 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 component ...
) release electrons and protons, creating an electrical potential
The electric potential (also called the ''electric field potential'', potential drop, the electrostatic potential) is defined as the amount of work energy needed to move a unit of electric charge from a reference point to the specific point in ...
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
Reduction, reduced, or reduce may refer to:
Science and technology Chemistry
* Reduction (chemistry), part of a reduction-oxidation (redox) reaction in which atoms have their oxidation state changed.
** Organic redox reaction, a redox react ...
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, also known as electrochemical water splitting, is the process of using electricity to decompose water into oxygen and hydrogen gas by electrolysis. Hydrogen gas released in this way can be used as hydrogen fuel, or remi ...
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 combus ...
or for power generation. Like MFCs or bioethanol
Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an Alcohol (chemistry), alcohol with the chemical formula . Its formula can be also written as or (an ethyl ...
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
Hydrogen technologies are technologies that relate to the production and use of hydrogen as a part hydrogen economy. Hydrogen technologies are applicable for many uses.
Some hydrogen technologies are carbon neutral and could have a role in preven ...
*Microbial electrosynthesis Microbial electrosynthesis (MES) 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 microorgan ...
*Microbial fuel cell Microbial fuel cell (MFC) is a type of bioelectrochemical fuel cell system that
generates electric current by diverting electrons produced from the microbial oxidation of reduced compounds (also known as fuel or electron donor) on the anode to oxid ...
s
* Microbial electrolysis carbon capture
References
* 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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