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Electrical energy produced by microbes via breakdown of organic matter are augmented with a small additional current to facilitate proton reduction forming hydrogen gas.



Technology

What is it?

Electrical energy produced by microbes via breakdown of organic matter are augmented with a small additional current to facilitate proton reduction forming, hydrogen gas. A microbial electrolysis cell (MEC) can have a membrane or be membraneless and operates under anaerobic conditions.

Why is it important?

Microbial electrolysis presents the opportunity to use breakdown or organic matter to reduce the electrical input required for hydrogen production in an electrochemical cell.

Characteristics

  • Inputs: Water, organic matter; electricity; a suitable source of electrochemically active microbes
  • By-products: Carbon dioxide; valuable chemicals (depending on the type of substrates and the biodegradation pathways taking place)
  • Operating temperature: Near ambient, up to 40°C commonly tested

Benefits

  • Hydrogenase enzymes function with high catalytic rates at thermodynamic equilibrium.
  • Could be used in wastewater or water which cannot be used for drinking or agriculture
  • No light required for process to occur
  • Reduced electrical input required compared to electrolytic methods
  • Glucose or glucose-rich substrates such as cellulose can also be converted into hydrogen
  • Rates of hydrogen production and organic waste destruction/ conversion can be controlled and monitored via electrical means
  • Australia has plentiful supply of renewable energy in the form of wind and solar radiation. Microbial electrolysis can potentially be a platform technology for converting surplus electrical energy generated from the established wind-turbines and photovoltaic technologies into a storable energy form as hydrogen, while also accomplishing waste treatment

Limitations

  • Expensive precious metal cathodes required (Pt)
  • Energy losses at several point during MECs process
  • Process efficiencies may vary, depending on the microbial activities
  • The use of membrane separating the anode and the cathode in a MEC may result in pH splitting problems
  • Effective management of pH condition within the MEC may be required to ensure stable microbial activity

RD&D priorities

  • Develop inexpensive cathodes such as Nickel and stainless steel
  • Engineer cells with lower internal resistance
  • Improve anode geometry, eliminating ‘short circuit’ metabolic reactions (H2 cycling)
  • Improve production rates and yields
  • Increase current densities
  • Develop effective measures to prevent further conversion of hydrogen into other compounds such as methane gas

Known active organisations

  • CSIRO
  • Queensland University of Technology
  • The University of Queensland

Other opportunities like this

  • Microorganisms such as green algae and blue-green algae (cyanobacteria) split water into hydrogen and oxygen via direct or indirect bio-photolysis.

  • In the absence of light, microorganisms such as bacteria break down organic matter to produce hydrogen gas through dark fermentation. Bacteria can be engineered in order to increase metabolic activity for a higher hydrogen production rate.

  • Photosynthetic microbes use sunlight to break down organic matter via fermentation.

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