Wednesday, 2 September 2015

Hybrid Artificial Photosynthesis - Generating Natural Gas from Sunlight and Carbon Di-Oxide

Scientists at Berkeley National Laboratory have demonstrated the conversion of CO2 to natural gas methane (CH4) using energy from sunlight with help from nano-technology and a well known bacteria.  http://newscenter.lbl.gov/2015/08/24/another-milestone-in-hybrid-artificial-photosynthesis/

Currently natural gas, a major energy source, is a fossil fuel which was produced from decaying vegetation buried underground million of years ago. Burning methane releases CO2 a green-house gas (GHG) implicated in globalwarming leading to climate change.
Hybrid artificial photosynthesis is carbon neutral as it recycles CO2 present in the environment.
The study http://www.pnas.org/content/early/2015/08/18/1508075112
is a beautiful example of application of nanotechnology to improve what nature can do.  Nature, over billion of years has fine-tuned its processes to perfection.  By using the new technologies and hybrid systems which combine inorganic and organic components, we can even improve on what nature has achieved!
The Berkeley team has developed a hybrid system that produces renewable molecular hydrogen and uses it to synthesize CO2 into CH4, the primary constituent of natural gas.
A membrane of semiconductor nanowires that can harness solar energy is populated with a bacterium that can feed off this energy and uses it to produce CH4.
The membrane consists of indium phosphide photo-cathodes and titanium dioxide photo-anodes. Solar energy is absorbed by the membrane to generate hydrogen from water via the hydrogen evolution reaction (HER).  Nickel sulphide nanoparticles are used as catalysts for HER.  Nickel is a relatively cheap and abundant element and the catalyst operates efficiently at biologically compatible conditions.  The team used anaerobic microbe Methanosarcina barkeri https://en.wikipedia.org/wiki/Methanosarcina  that reduces carbon dioxide to methane using hydrogen.

Michelle Chang of the Berkeley team says “Using hydrogen as the energy carrier rather than electrons makes for a much more efficient process as molecular hydrogen, through its chemical bonds, has a much higher density for storing and transporting energy”

Hydrogen for fixing CO2 can be produced from renewable energy sources like solar (in this case) and wind or even nuclear energy.  Also, other microbes and synthetic biology can be used to manufacture a range of value-added chemical products. 



The demonstration of methane production in the laboratory is very impressive.  It will be good to see if the system can be scaled up to produce large amounts of natural gas that can fire up our industries in a carbon neutral fashion.  

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