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From Nature magazine
Not all prototypes make it out of the laboratory, but the 'artificial leaf' is so elegant that its design seems to beg for commercial production. Described in Science last year by a team led by Dan Nocera at the Massachusetts Institute of Technology, the catalyst-coated wafer is a silicon version of a photosynthesizing leaf: it turns sunlight into storable fuel by splitting water into oxygen and hydrogen.
But Sun Catalytix, the company founded in Cambridge off the back of Nocera's work, says that it won’t be scaling up the prototype for field tests. The device offers few savings over other ways to make hydrogen from sunlight, the company says.
“We have to be focused on what will be durably better than conventional ways to make renewable hydrogen,” explains chief technology officer Tom Jarvi. Hydrogen from a solar panel and electrolysis unit can currently be made for about US$7 per kilogram, the firm estimates; the artificial leaf would come in at $6.50. (It costs just $1–2 to make a kilogram of hydrogen from fossil fuels).
With the prices of solar cells dropping all the time, the firm is not going to make a heavy investment that's unlikely to pay off. Instead, it is looking at cheaper designs — but these require yet-to-be-invented semiconductor materials. So for the moment, “the artificial leaf is in the fridge”, Sun Catalytix chemist Joep Pijpers says.
The solar hydrogen challenge
That decision is disappointing but not surprising. Both Sun Catalytix and a report commissioned by the US Department of Energy have found that the cost of systems to produce hydrogen from sunlight is dominated by the engineering costs of the photovoltaic (light-harvesting) infrastructure, mainly because of the sheer mass of material required, including frames, substrates and materials to protect the semiconducting silicon from damage.
That is also true for the artificial leaf, says Pijpers. The design improves on previous attempts to couple light-harvesting solar cells and water-splitting catalysts into one device because it uses cheap, abundant catalysts and does not require extremely acidic or alkaline solutions. It is not, however, very efficient, converting only about 2.5% of the energy it gets from sunlight into chemical bonds (although that's still an improvement on plant leaves, which average 1%).
The path to cheaper solar hydrogen probably lies in cutting down the expense of the light-harvesting part of the system. One solution may be to resculpt the silicon into flexible micrometre long wires; another could be to avoid silicon altogether, in favour of solar cells made from other kinds of semiconductors, or perhaps organic materials.
Sun Catalytix's current thinking is to keep the wireless design of the artificial leaf, but to reduce engineering costs by scattering a slurry of small particles through water, rather than having slabs of silicon. The snag is that simply cutting up the artificial leaf into small particles won’t work. One panel of silicon doesn't produce enough voltage to split water, so the leaf links up three panels to gain voltage in much the same way as batteries do when connected in series. But that’s not an option in a nanoparticle design. The firm is therefore looking to other light-harvesting materials, such as iron oxide. The advantage of such already-oxidized materials is that they need less protection from the oxygen produced during water-splitting, but it is also hard to get at the electric charges created when iron oxide absorbs photons.
Inspirational design
There are other ways to reduce costs, says Nocera. For example, a dye-impregnated plastic could be used to absorb the light, then pass the photons on to the silicon to generate the current for photo-catalysts. This would cut down on the amount of silicon needed. Jarvi agrees that the panel configuration could probably be made cheaper — another option is to concentrate the sunlight to cut down on the area over which the panels would have to be installed, he says. But for now, Sun Catalytix — which is backed by the multinational conglomerate Tata Group and has received a $4-million grant from the energy department’s Advanced Research Projects Agency-Energy (ARPA-E) — has decided not to focus on this approach.
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7 Comments
Add CommentSounds like your leaf needs to learn to multiply itself. Perhaps while shading like a normal tree does. Oh and becoming a WiFi point. :)
Reply | Report Abuse | Link to this"The device offers few savings over other ways to make hydrogen from sunlight, the company says."
Reply | Report Abuse | Link to thisIf I recall correctly, that was the primary issue raised concerning this 'elegant' electrolysis device - in these pages two years ago...
http://blogs.scientificamerican.com/observations/2010/03/03/shift-happens-will-artificial-photosynthesis-power-the-world/
I guess they successfully soaked the venture capitalists without a reasonable ROI justification - again.
Funny the headline doesn't say, "MIT's Artificial Leaf Fails' Headlines are always to quick to throw MIT into invention announcements, why the omission when the result is negative?
Reply | Report Abuse | Link to thisi think this research should start from a new premise .first solar has achieved many levels , but , still a disapointing level of efficiency . maybe if we looked at different fields of exploration then ,we could find some insights from their - glitch resolutions. photon transfers , perhaps a surficant ladened water supply , less encumbering energy transfer mechanism , etc. as stated this process was always used for low level , high dependability and for laptop augmentation this is okay and about the best . for nano then it must be enviromentally reactive only .
Reply | Report Abuse | Link to thisUS photovoltaic installations doubled in 2011 (value $8.4billion), and the growth in 2012 is projected at 35%. Comments about 'disappointing levels of efficiency' are antebellum. It works very very well - but the manufacturing glut is squeezing profit margins. That's the key to the leaf turning into a shelf ornament - it's a loser in the price-performance curve.
Reply | Report Abuse | Link to thishttp://www.reuters.com/article/2012/03/14/us-solar-us-idUSBRE82D08J20120314
Just curious - how do you know that the prototype "works very very well?" Thanks in advance.
Reply | Report Abuse | Link to thisOkay, but I'm not raking them up when they fall. Nope. Not me. Have you ever tried to burn a pile of these leaves?
Reply | Report Abuse | Link to thisWell, have you?