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Published on March 8th, 2014 | by Tina Casey


New Bionic Leaf Could Solve Solar Energy Storage Problem

March 8th, 2014 by  

Researchers from Lawrence Berkeley National Laboratory are developing a new bionic leaf that can convert energy from sunlight into an energy-dense fuel, imitating the photosynthetic process of plants. We’ve covered the artificial leaf concept before but aside from using a cool new name (bionic leaf sounds much cooler than artificial leaf, right?) the Berkeley project represents a new twist on the technology that could lead to far greater efficiencies.

The Artificial Leaf Concept

Whether you call it an artificial leaf or a bionic leaf, the basic concept is relatively simple. Instead of using a photovoltaic cell to generate electricity directly from sunlight, you deploy a chemical reaction that stores solar energy in the form of hydrogen, which you can then use in a hydrogen fuel cell to generate electricity.

artificial leaf sustainable hydrogen from sunlight

Bionic leaf courtesy of Berkeley Lab.

That sunlight-to-hydrogen chain means you can store solar energy indefinitely, potentially in huge quantities, so think of it as a kind of battery and you’re on the right track. The fuel cell connection means that the intermittent nature of solar energy is not an issue, and neither is its resistance to mobility.

As for how you get there, you drop a photoelectrochemical cell in a bucket of water and let it go to work stripping out the hydrogen.

That’s a much more sustainable way to produce hydrogen than the current standard, which involves a good deal of fossil energy. With Toyota, GM and other auto manufacturers poised to deliver hydrogen fuel cell vehicles to the mass market, the race is on to develop solar powered hydrogen production at scale.

The Berkeley Lab Bionic Leaf

The trick behind the photoelectrochemical cell is to find the right combination of materials that give you a cost-effective reaction, otherwise your bionic leaf is going to sit in the lab and amuse visitors forever.

We’ve been following one solution, an actual leaf-sized artificial leaf that is being developed with a focus on low cost materials to serve households in underserved communities. The absolute efficiency of the cell is not as important as the overall cost, since in this market electricity consumption is almost negligible (in the latest development, the artificial leaf has been tweaked to function effectively in impure water).

The Berkeley team is also taking cost into consideration while moving along a tack that is focused on revving up the performance of the photocathode at the molecular level (the cathode is the part of the cell that generates an electrical current).

The team has been focusing on a hybrid photocathode of gallium phosphide (a semiconductor that absorbs visible light), and cobaloxime, a hydrogen-producing catalyst.

Both materials are relatively abundant and inexpensive compared to conventional precious metal catalysts like platinum.

So far, so good. The team just published its latest analysis of the photocathode in the journal Physical Chemistry Chemical Physics under the title “Energetics and efficiency analysis of a cobaloxime-modified semiconductor under simulated air mass 1.5 illumination,” which demonstrated that almost 90 percent of the electrons generated by the hybrid material were stored in the target hydrogen molecules.

The team has also found that the ability of the gallium phosphide to absorb solar energy is far outstripping the ability of the cobaloxime to catalyse a reaction. The result is that only 1.5 percent of the photons that hit the surface get converted into a photocurrent.

So, the search is on for a faster and more efficient catalyst.

Entering The Age Of The Bionic Leaf

The cathode is just one part of the equation, by the way. For example, a multinational research team has been working on a low cost, high efficiency electrode made from iron oxide (aka rust).

For a completely different angle on sustainable hydrogen production, you can also check out the thermochemical process under way at a municipal wastewater treatment facility in California.

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About the Author

specializes in military and corporate sustainability, advanced technology, emerging materials, biofuels, and water and wastewater issues. Tina’s articles are reposted frequently on Reuters, Scientific American, and many other sites. Views expressed are her own. Follow her on Twitter @TinaMCasey and Google+.

  • chuck

    IDK; maybe “surround” the Gallium P. molecule with an array of cobaloxime molecules like petals or benzene ring formation joined by a “speed” bridge like the “supersonic” one the others guys are working on.

  • Leonard Rusciani Jr

    Is this more efficient than just using the standard photovoltaic effect to generate electricity which can be used to hydrolyze water? It seems a “bionic’ leaf would require chemicals that may degrade over shorter time that a photovoltaic cell. Mass production and implementation may be more problematic also.

  • TCFlood

    In natural photosynthesis, sunlight is used to split water into dioxygen and one or two potent biological reducing agents – ATP and/or NADPH – which in turn are used to reduce CO2 to synthesize glucose. For at least 50 years chemists have been trying to use light to split water into an oxidation product – most preferably dioxygen – and our industrial equivalent of nature’s ATP, namely dihydrogen. While people like Dan Nocera (two of your linked articles are about his work) do a lot of interesting
    research, one of the things some of them do best is to over-hype the significance
    and novelty of their work to the public (and to funding agencies). This makes a joke of the volumes and decades of work done by their predecessors and peers that forms the basis of most of what they do. Hyping “synthetic leaves” IMO is a bit of a joke.

    Reported here is one recent tweak on the massive amount of work done on the photosplitting of water that couples a well-known cobalt complex (pyridine chlorocobaloxime) with a semiconductor that absorbs visible light. Organic dyes, for example, have been used previously to harvest visible light with similarly modest results. It is true that cobalt is dramatically cheaper than platinum, but the catalyst is
    also way too slow to be useful.

    It would be nice to read critical reporting of interesting results with less uncritical amplification of overblown hype.

  • JamesWimberley

    “With Toyota, GM and other auto manufacturers poised to deliver hydrogen fuel cell vehicles to the mass market ..”
    Tina must be using a different definition of “mass market” to me. A handful of $100,000 sedans will be pilots, not mass production. There are huge network effects in automotive technology: nobody will buy a hydrogen car until there is a dense network of hydrogen filling stations. The same holds of course for electric cars and chargers. The difference is that battery chargers are being rolled out today, and evs are being sold in the tens of thousands. By the time hydrogen fuel cell cars are affordable, battery evs will have cornered the market. Fuel cells may at best have a future in heavy trucks and ships.

    • sambar

      Sounds like the same kind of guffaws aimed at electric cars a few years ago.

      Another market might be residential fuel cells for electricity and heat production.

      • James Van Damme

        Well, it did take electric cars 100 years to catch up to ICE, not that they’re there yet.

        There are more problems to be overcome, like storage and distribution.

      • From the true experts in this field who I’ve spoken with, the only thing I’ve heard is: no time soon, if ever. Simply far more expensive and far larger infrastructure barriers… plus stronger competition now.

    • Rick Kargaard

      A early market may be the city bus and delivery truck segment. But as you mentioned heavy trucks and ships are a huge market if fueling options become available. As a form of solar it may become competative with electric.

    • lkwjr

      I would remind those who favor hydrogen fuel cells to remember the Hindenburg! H2 is explosive and cyrogenics is expensive. Graphene will win the day, I believe for collection and storage of solar energy. LKW

      • Robin Utley

        The damage caused by the Hindenburg was mostly due to the combustible marital it was made of. If you watch the film you will see the hydrogen burn right above the airship rather quickly as other materials continue to burn. The ignition of a hydrogen spill is safer than gasoline. Hydrogen will rise above the source exceedingly fast and ignition is rare after a relatively short time because the tendency of hydrogen to quickly disperse. Gasoline will track along the ground and can coat individuals and pool in a wreck it is also combustible for a longer period of time. It will track on water making it difficult to extinguish. The future of Graphene quite wonderfully KICK-ASS but we will always have a need for portable combustibles to use in non-stable non-civilized locations. We need a diversity of green energy solutions. The wonder of this “leaf” is that it also functions as water purification. Imagine a village with access to spoiled or brackish water given the ability to not only stop using charcoal/wood to heat/cook but also have pure water as a waste product. This would help eradicate newly established cholera from Haiti and help solve its massive deforestation problem.

    • Plus, battery-electrics can be charged at home.

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