Panasonic develops highly efficient artificial photosynthesis system with gallium nitride semiconductor for conversion of CO2 to formic acid
30 July 2012
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| Schematic view of artificial photosynthesis system. Click to enlarge. |
Panasonic has developed an artificial photosynthesis system using a gallium nitride photoelectrode and a metal catalyst which uses sunlight to convert CO2 mainly to formic acid (an important intermediate in chemical synthesis) at an efficiency (solar energy to chemical energy) of 0.2%—a comparable level to that of plants.
The reaction rate is completely proportional to the light power due to the low energy loss with the simple structure; in other words, the system can respond to focused light. This will make it possible to realize a simple and compact system for capturing and converting wasted carbon dioxide from incinerators and electric generation plants, according to Panasonic. Panasonic partially presented the technology on 30 July at the 19th International Conference on the Conversion and Storage of Solar Energy (IPS-19) in Pasadena.
Previous approaches to developing artificial photosynthetic systems for the direct conversion of CO2 have used complex structures such as organic complexes or plural photo-electrodes, which made it difficult to improve their efficiency in response to the light, according to the company. Panasonic’s artificial photosynthesis system has a simple structure with highly efficient CO2 conversion, which can utilize direct sunlight or focused light.
Gallium nitride semiconductors have attracted attention for their potential applications in highly efficient optical and power devices for energy saving. Panasonic determined that they can also be used as photo-electrodes for CO2 reduction; a nitride semiconductor has the capability to excite the electrons with enough high energy for the CO2 reduction reaction.
The CO2 reduction takes place on a metal catalyst at the opposite side of nitride semiconductor photo-electrode. The metal catalyst plays an important role in selecting and accelerating the reaction. Panasonic notes that the system comprises only inorganic materials, which can reduce the CO2 with low energy loss. Because of this, the amount of reaction products is exactly proportional to the light power.
This is one of the merits in such an all-inorganic system while some conventional systems cannot follow the light power in general because of their internal or external rate-limiting processes in the complex structures, Panasonic says.
Panasonic holds 18 domestic patents and 11 overseas patents, including pending applications, on the technology.
Also at the IPS-19 conference, a team from Toyota Central research reported on a method for the selective conversion of CO2 to formate (a salt of formic acid) using semiconductor/complex hybrid photocatalysts. The conversion efficiency of solar energy to chemical energy was 0.03-0.04%.
Resources
Hiroshi Hashiba et al. (2012) Highly Efficient CO2 Reduction in AlGaN/GaN - In Artificial Photosynthesis System (IPS-19, Nº 5711, oral plus poster)
Yotsuhashi, Satoshi; Deguchi, Masahiro; Hashiba, Hiroshi; Zenitani, Yuji; Hinogami, Reiko; Yamada, Yuka; Ohkawa, Kazuhiro (2012) Enhanced CO2 reduction capability in an AlGaN/GaN photoelectrode. Applied Physics Letters, Volume 100, Issue 24, id. 243904 doi: 10.1063/1.4729298
Shunsuke Sato, Takeo Arai, Takeshi Morikawa, Keiko Uemura, Tomiko M. Suzuki, Hiromitsu Tanaka, and Tsutomu Kajino (2011) Selective CO2 Conversion to Formate Conjugated with H2O Oxidation Utilizing Semiconductor/Complex Hybrid Photocatalysts. Journal of the American Chemical Society 133 (39), 15240-15243 doi: 10.1021/ja204881d
Our current gas guzzlers could pull a one to two tonnes trailer equipped with converters/generators to capture and convert the CO2 coming out of the tail pipes?
Posted by: HarveyD | 30 July 2012 at 07:47 AM
Help me understand this. This could be valuable. However, why wouldn't you just use the light source and the gallium arsenide and silicon (and all the other resources) to make PV chips, generate electricity at a 25% versus 0.2% efficiency rate, and simply avoid generating the CO2 in the first place?
Posted by: Dollared | 30 July 2012 at 08:43 AM
Interresting but what do they do with the formic acids, do they transform that formic acids in fuels ?
Posted by: A D | 30 July 2012 at 08:50 AM
"In the late 60s, Akira Fujishima discovered photocatalytic properties in titanium dioxide, the so-called Honda-Fujishima effect, which could be used for hydrolysis.[13]" wiki
These articles are a dime a dozen and surely would have amounted to something major during forty years if valid
Posted by: kelly | 30 July 2012 at 11:17 AM
Dollared - think of it as catalytic reduction equipment for carbon emitters. Putting a solar field next to a coal plant doesn't negate its nighttime emissions. Sized correctly a solar field could offset the day's CO2 at a fossil plant.
Posted by: Morris Meyer | 30 July 2012 at 11:19 AM
AD
"Interresting but what do they do with the formic acids, do they transform that formic acids in fuels ?"
There are fuel cells that can use Formic acid directly or formic acid can be reformed as a hydrogen source.
Posted by: Bill | 30 July 2012 at 12:08 PM
So recirculate back this hydrogen at the input of the co2 emitting station.
Posted by: A D | 30 July 2012 at 01:22 PM
Conversion efficiency is typically proportional to the cost of production for a given product, but not always. Maybe it's too early, (or maybe they don't want to say) but, what they should do is a projection of cost of production of the product assuming some adequate or appropriate scale. Solar is unlike fuels in that what falls on the ground wasted or unconverted was going to go there anyway. It is the cost of the electron or molecule that counts, not the specific efficiency.
Posted by: Brotherkenny4 | 30 July 2012 at 01:37 PM
Ah, there's the press release I couldn't find yesterday.
I agree that 0.2% is ridiculously low; the electron efficiency of the archaea-mediated conversion of CO2 to methane is 80% (divide by the overpotential fraction to get energy efficiency). That should be able to beat 15% efficiency from sunlight to fuel. However, it doesn't make a liquid fuel. If formate-based processes can get higher efficiencies, they could be good options.
CO2 is available from a number of sources. Imagine a bio-refinery piping its effluent to a process like this, or a potassium carbonate system grabbing CO2 out of the atmosphere. Electrolysis of the resulting KHCO3 yields some hydrogen, but far from enough to reduce all the CO2 that's also liberated; the excess CO2 can go to another process like this.
Posted by: Engineer-Poet | 30 July 2012 at 01:57 PM
The University of Toronto has developed a 70% efficient solar panel.
The two technologies could do a great job to convert CO2 and sunlight into useful form of energy.
By the way, a roof covered with 70% efficient solar panels could generate more than enough e-energy for the house and 2 to 3 BEVs. That could reduce CO2 emission per household.
Posted by: HarveyD | 31 July 2012 at 07:37 AM
@Harvey:
I do wish you would reference claims you make.
70% of what? All radiation, including infrared?
Not only is this way more than I have seen, even in experimental set-ups, but if so the house seems likely to get seriously cold!
Is this concentrated solar, or what are you talking about?
Posted by: Davemart | 31 July 2012 at 10:16 AM
@Davemart:
Try: http://www.lbl.gov/Science-Articles/Archive/MSD-full-spectrum-solar-cell.html
http://www.futurity.org/science-technology/full-spectrum-boosts-solar-cell-power/
http://www.tgdaily.com/trendwatch-features/39807-new-solar-cell-material-achieves-almost-100-efficiency-could-solve-world-w
None of them are commercial yet, but there is research.
Posted by: JMartin | 31 July 2012 at 11:18 AM
DM....you are close. The Toronto U panels convert most of the light spectrum into electricity, i.e. close to 37% more than current best panels (70% instead of 33%) The news became public yesterday.
Posted by: HarveyD | 31 July 2012 at 02:05 PM
And it doesn't even use quantum dots to turn "hot" electrons into additional carrier pairs.
Posted by: Engineer-Poet | 31 July 2012 at 04:07 PM
E-P...I think it does that (or similar) too...?
Posted by: HarveyD | 01 August 2012 at 09:23 AM
@HarveryD:
The Toronto work achieved 7.0% efficiency, not 70%. Seven percent is high efficiency for CQD solar cells, but other technologies achieve much higher efficiency.
Posted by: MQ | 02 August 2012 at 10:24 AM