Researchers have created a new artificial photosynthesis system using semi-conducting nanowires and bacteria that can produce hydrogen and use it for methane production from carbon dioxide.
The hybrid system, developed by a team from the US Department of Energy (DOE)'s Lawrence Berkeley National Laboratory, could be used for the production of natural gas, of which methane is the primary component.
"This study represents another key breakthrough in solar-to-chemical energy conversion efficiency and artificial photosynthesis," said Peidong Yang, a chemist with Berkeley Lab's Materials Sciences Division and one of the leaders of the study.
"By generating renewable hydrogen and feeding it to microbes for the production of methane, we can now expect an electrical-to-chemical efficiency of better than 50 per cent and a solar-to-chemical energy conversion efficiency of 10 per cent if our system is coupled with a state-of-art solar panel and electrolyser."
The system uses an array of silicon and titanium oxide nanowires that collects solar energy and splits the water molecule into molecular oxygen and hydrogen. The hydrogen is then transported to microbes that use it to reduce carbon dioxide to one specific chemical product, methane.
"In our latest work, we've demonstrated two key advances," said Chris Chang. "First, our use of renewable hydrogen for carbon dioxide fixation opens up the possibility of using hydrogen that comes from any sustainable energy source, including wind, hydrothermal and nuclear. Second, having demonstrated one promising organism for using renewable hydrogen, we can now, through synthetic biology, expand to other organisms and other value-added chemical products."
The researchers have previously created a similar system converting carbon dioxide into acetate. In the earlier system, solar energy was used to deliver electrons to microbes, which were subsequently breaking down the carbon dioxide.
"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," says Michelle Chang, a member of the team.
Photosynthesis is the process by which nature harvests the energy in sunlight and uses it to synthesise carbohydrates from carbon dioxide and water. Carbohyrates are biomolecules that store the chemical energy used by living cells.
The method was described in an article published in the latest issue of the journal Proceedings of the National Academy of Sciences.