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Berkeley Lab researchers advance hybrid bioinorganic approach to solar-to~chemicals conversion; 50% electrical-to-chemical, 10% solar-to-chemical efficiencies

A team of researchers at the US Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) have hit a new milestone in their development of a hybrid bioinorganic system for solar-to-chemical energy conversion. (Earlier post.) The system first generates renewable hydrogen from water splitting using sustainable electrical and/or solar input and biocompatible inorganic catalysts. The hydrogen is then used by living cells as a source of reducing equivalents for conversion of CO2 to the value-added chemical product methane.

The system can achieve an electrical-to-chemical efficiency of better than 50% and a solar-to-chemical energy conversion efficiency of 10% if the system is coupled with state-of-art solar panel and electrolyzer, said Peidong Yang, a chemist with Berkeley Lab’s Materials Sciences Division and one of the leaders of this study. A paper on their work is published in Proceedings of the National Academy of Sciences (PNAS).


Yang, who also holds appointments with UC Berkeley and the Kavli Energy NanoScience Institute (Kavli-ENSI) at Berkeley, is one of three corresponding authors of the paper. The other corresponding authors are Michelle Chang and Christopher Chang. Both also hold joint appointments with Berkeley Lab and UC Berkeley. In addition, Chris Chang is a Howard Hughes Medical Institute (HHMI) investigator.

Photosynthesis is the process by which nature harvests the energy in sunlight and uses it to synthesize carbohydrates from carbon dioxide and water. Carbohydrates are biomolecules that store the chemical energy used by living cells. In an earlier hybrid artificial photosynthesis system developed by the Berkeley Lab team, an array of silicon and titanium oxide nanowires collected solar energy and delivered electrons to microbes which used them to reduce carbon dioxide into a variety of value-added chemical products.

In the new system, solar energy is used to split the water molecule into molecular oxygen and hydrogen. The hydrogen is then transported to microbes that use it to reduce carbon dioxide into one specific chemical product, methane.

In our latest work, we’ve demonstrated two key advances. 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.

—Chris Chang

The concept in the two 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 first 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 carbon dioxide using hydrogen 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.

—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). The HER is 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.

We selected methane as an initial target owing to the ease of product separation, the potential for integration into existing infrastructures for the delivery and use of natural gas, and the fact that direct conversion of carbon dioxide to methane with synthetic catalysts has proven to be a formidable challenge. 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.

—Chris Chang

In addition to the corresponding authors, other co-authors of the PNAS paper describing this research were Eva Nichols, Joseph Gallagher, Chong Liu, Yude Su, Joaquin Resasco, Yi Yu and Yujie Sung.

This research was primarily funded by the DOE Office of Science.


  • Eva M. Nichols, Joseph J. Gallagher, Chong Liu, Yude Su, Joaquin Resasco, Yi Yu, Yujie Sun, Peidong Yang, Michelle C. Y. Chang, and Christopher J. Chang (2015) “Hybrid bioinorganic approach to solar-to-chemical conversion” PNAS doi: 10.1073/pnas.1508075112



Solar to chemical at 10% efficiency is game-changer level.

Combined with waste CO2 from industrial processes you have methane/methanol etc, highly transportable and storable in liquid form.

Is it as efficient as direct solar to a BEV?
Of course not, but nothing which actually, really, truly deals with the problems of intermittency and annual variance is.

It is probably 'good enough' though from an efficiency POV, and it now all depends on how the costs can be reduced.


This seems to use CO2 from the atmosphere and does not need concentrated CO2.
Even better, as it would be able to operate wherever there is plenty of sun and water, and not need to be sited near to industrial CO2 generating places.

william g irwin

If that H2O scheme allows filtered saltwater, this can be set up in locations that do not use up precious fresh water supplies (coastal regions like California etc.). This makes so much more sense than carbon sequestration. This is good news, and I hope to see a commercial prototype demonstration soon.


The water needed is not a lot compared to agriculture etc, and is anyway released again although in a different location when the fuel is burnt or used in a fuel cell.


Using natural gas to make nitrogen fertilizer has its obvious limits.
They may need to use solar/wind hydrogen, which will increase costs.


CO2, particularly in abundant calcium carbonate in seawater, is far more concentrated source material than the atmosphere. The pressure and chill of seawater only add to the enthalpy of hydrogen synthesis and CO2 recovery. Any amount of waste heat from the electricity will provide whatever heat the bacteria need ( no idea from the article whether these bacteria are cryophilic or thermophilic)

The capstone will be if valuable ocean materials like magnesium, phosphorus, silicic acid and lithium can be coproduced.


In addition to fuels, they can make proteins, starches, lipids for animal or human food or feeding fishfarms at very high efficience and close to the end-user.
One 3MW windmill close to a fish farm with an average continuous output of 1MW produces 1x60x60×24=86400MJ/day
=20571428 kCal / day
=6857 kg of fish per day !

1MJ = 4200 kCal
Fish is around 1kCal/gram
Fish convert food to "meat" with efficiencies around 75%

If Solazyme-like micro-organisms (also with 50% efficiency) are used, one 3MW windmill can produce 2571 kg wheat per day = 938.6 tons/year !
(Average wheat yield in the USA is 2.3 tons/hectare/year)

Or my small solar roof of 4MWh/ year would produce 428kg of wheat/year.

Wheat = 400 kcal/100g


Converting our surplus Hydro electricity into liquid fuels, to replace (100% in our case) imported Oil, instead of selling electricity for under $0.05/kWh to USA may be a better deal even at 50% efficiency?

Surplus electricity exist about 18 hours/day during 30 cold days in winter time and 24 hours/days during the other 335 days of the year.

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