Artificial photosynthesis used to produce renewable molecular hydrogen for synthesizing carbon dioxide into methane. Credit: Berkeley Lab
Researchers using a bioinorganic hybrid approach to artificial photosynthesis have combined semiconducting nanowires with select microbes to create a system that produces renewable H2 and uses it to synthesize CO2 into methane, the primary constituent of natural gas.
“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% and a solar-to-chemical energy conversion efficiency of 10% if our system is coupled with state-of-art solar panel and electrolyzer.”
The concept in the 2 studies is essentially the same – a membrane of semiconductor nanowires that can harness solar energy is populated with bacterium that can feed off this energy and use it to produce a targeted carbon-based chemical. In the new study, the membrane consisted of indium phosphide photocathodes and titanium dioxide photoanodes.
Whereas in the 1st study, the team worked with Sporomusa ovata, an anaerobic bacterium that readily accepts electrons from the surrounding environment to reduce carbon dioxide, in the new study the team populated the membrane with Methanosarcina barkeri, an anaerobic archaeon that reduces CO2 using H rather than electrons. “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.
In the newest membrane reported by the Berkeley team, solar energy is absorbed and used to generate hydrogen from water via the hydrogen evolution reaction (HER) >> catalyzed by earth-abundant nickel sulfide nanoparticles that operate effectively under biologically compatible conditions. Hydrogen produced in the HER is directly utilized by the Methanosarcina barkeri archaeons in the membrane to produce methane.
“Since we still get the majority of our methane from natural gas, a fossil fuel, often from fracking, the ability to generate methane from a renewable hydrogen source is another important advance.” Adds Yang, “While we were inspired by the process of natural photosynthesis and continue to learn from it, by adding nanotechnology to help improve the efficiency of natural systems we are showing that sometimes we can do even better than nature.” http://newscenter.lbl.gov/2015/08/24/another-milestone-in-hybrid-artificial-photosynthesis/
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