Blueprint for “artificial leaf” mimics Mother Nature

[OKIsItJustMe]

http://portal.acs.org/portal/PublicWebSite/pressroom/newsreleases/CNBP_024355

March 25, 2010

Blueprint for “artificial leaf” mimics Mother Nature

SAN FRANCISCO, March 25, 2010 — Scientists today presented a design strategy to produce the long-sought artificial leaf, which could harness Mother Nature’s ability to produce energy from sunlight and water in the process called photosynthesis. The new recipe, based on the chemistry and biology of natural leaves, could lead to working prototypes of an artificial leaf that capture solar energy and use it efficiently to change water into hydrogen fuel, they stated.

Their report was scheduled for the 239th National Meeting of the American Chemical Society (ACS), being held here this week. It was among more than 12,000 scientific reports scheduled for presentation at the meeting, one of the largest scientific gatherings of 2010.

“This concept may provide a new vista for the design of artificial photosynthetic systems based on biological paradigms and build a working prototype to exploit sustainable energy resources,” Tongxiang Fan, Ph.D. and colleagues Di Zhang, Ph.D. and Han Zhou, Ph.D., reported, They are with the State Key Lab of Matrix Composites at Shanghai Jiaotong University, Shanghai, China.

Fan pointed out that using sunlight to split water into its components, hydrogen and oxygen, is one of the most promising and sustainable tactics to escape current dependence on coal, oil, and other traditional fuels. When burned, those fuels release carbon dioxide, the main greenhouse gas. Combustion of hydrogen, in contrast, forms just water vapor. That appeal is central to the much-discussed “Hydrogen Economy,” and some auto companies, such as Toyota, have developed hydrogen-fueled cars. Lacking, however, is a cost-effective sustainable way to produce hydrogen.

With that in mind, Fan and co-workers decided to take a closer look at the leaf, nature’s photosynthetic system, with plans to use its structure as a blueprint for their next generation of artificial systems. Not too surprisingly, the structure of green leaves provides them an extremely high light-harvesting efficiency. Within their architecture are structures responsible focusing and guiding of solar energy into the light-harvesting sections of the leaf, and other functions.

The scientists decided to mimic that natural design in the development of a blueprint for artificial leaf-like structures. It led them to report their recipe for the “Artificial Inorganic Leaf” (AIL), based on the natural leaf and titanium dioxide (TiO2) — a chemical already recognized as a photocatalyst for hydrogen production.

The scientists first infiltrated the leaves of Anemone vitifolia - a plant native to China - with titanium dioxide in a two-step process. Using advanced spectroscopic techniques, the scientists were then able to confirm that the structural features in the leaf favorable for light harvesting were replicated in the new TiO2 structure. Excitingly, the AIL are eight times more active for hydrogen production than TiO2 that has not been “biotemplated” in that fashion. AILs also are more than three times as active as commercial photo-catalysts. Next, the scientists embedded nanoparticles of platinum into the leaf surface. Platinum, along with the nitrogen found naturally in the leaf, helps increase the activity of the artificial leaves by an additional factor of ten.

In his ACS presentation, Fan reported on various aspects of Artificial Inorganic Leaf production, their spectroscopic work to better understand the macro- and microstructure of the photocatalysts, and their comparison to previously reported systems. The activity of these new “leaves”, are significantly higher than those prepared with classic routes. Fan attributes these results to the hierarchical structures derived from natural leaves:

“Our results may represent an important first step towards the design of novel artificial solar energy transduction systems based on natural paradigms, particularly based on exploring and mimicking the structural design. Nature still has much to teach us, and human ingenuity can modify the principles of natural systems for enhanced utility.”

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[WhiteTara]

1. can you imagine the fanciful cars with palm leaf

decorations that turn the sunlight into hydrogen? They could be like Hollywood type machines.

[tama]

2. It's good to mimic

But you can't really improve living natural quantum computation:
http://www.newscientist.com/article/mg20527464.000-natures-hot-green-quantum-computers-revealed.html

[OKIsItJustMe]

3. Yeah, actually, you can

http://en.wikipedia.org/wiki/Photosynthesis#Efficiency

..

Efficiency

Plants usually convert light into chemical energy with a photosynthetic efficiency of 3-6%. Actual plants' photosynthetic efficiency varies with the frequency of the light being converted, light intensity, temperature and proportion of carbon dioxide in the atmosphere, and can vary from 0.1% to 8%. By comparison, solar panels convert light into electric energy at a photosynthetic efficiency of approximately 6-20% for mass-produced panels, and up to 41% in a research laboratory.

...

[Statistical]

4. his link was on quantum computing not solar efficiency.

Pretty cool stuff that for millions of years plants have done quantum computing at room temperature.

That far exceeds anything mankind has come close to achieving by a couple magnitudes.

[tama]

5. Apples and oranges

Photosynthesis stores entropic energy potential, ie. exergy, into chemical bonds with maximal efficiency (quantum computation). Chemical bonds are highly stable and can store exergy "negentropically" for millions of years naturally without human effort, including in most highly concentrated forms known (fossile fuels).

Exergy in form of electric current is dependent from vast infrastructure of technological matrix that is build with and dependent from exergy in chemical bonds (especially fossile exergy), cannot be stored efficiently and as a whole has negative EROEI.

It is strange that techno-utopians fail so constantly to understand even most basic physics - thermodynamics. For them it seems to be all about quantity without any understanding of quality except 'more numerically is better'.

[OKIsItJustMe]

6. Natural photosynthesis is a wonderful thing, however, it is not optimized

At noon, when the most energy is available for harvesting, plants shut down their photosynthesis. (See "http://en.wikipedia.org/wiki/Photoinhibition">photoinhibition".)

[tama]

7. I find no such mention

"Real plants (as opposed to laboratory test samples) have lots of redundant, randomly oriented leaves. This helps to keep the average illumination of each leaf well below the mid-day peak enabling the plant to achieve a result closer to the expected laboratory test results using limited illumination."
http://en.wikipedia.org/wiki/Photosynthetic_efficiency

"Quantum yield

Photosystem II is damaged by light irrespective of light intensity.<2> The apparent quantum yield of the damaging reaction in typical leaves of higher plants exposed to visible light,<19> as well as in isolated thylakoid membrane preparations,<23> is in the range of 10−8 to 10−7 and independent of the intensity of light.<19> Therefore, photoinhibition occurs at all light intensities and the rate constant of photoinhibition is directly proportional to light intensity. Some measurements suggest that dim light causes damage even more efficiently than strong light.<20>"
http://en.wikipedia.org/wiki/Photoinhibition


The ratio of 10% efficiency of PV versus 0,3% efficiency of PS looks very promising at first sight, but the qualitative systemic complexities are staggering. First of all, there is c. two thirds loss of electric exergy during transmission in the grid. Building and maintanenance of the whole technological matrix required to make the electricity exergetic, starting from mining and trasporting the minerals. Not to forget that we can't eat electricity, our metabolism is based on chemical energy.

I don't know about calculations about how many acres of PS (biofuels) would be required to build and maintain an acre of PV (electricity) sustainably and self-sufficiently, fully recycling the mineral and organic resources. But I'm willing to bet the ratio would be much worse than 100:3. Burning the biofuel directly to create the same amount of electric current would seem much more efficient than wasting it in PV technology.

[OKIsItJustMe]

8. Compare natural photosynthesis to artificial photosynthesis

http://www.treehugger.com/files/2010/03/breakthrough-producing-hydrogen-water-sunlight.php
http://www.uea.ac.uk/che/news/2-3-10nann_pickett
http://www3.interscience.wiley.com/journal/123275459/abstract

[tama]

9. Thanks, interesting

Gold and Indium (phosphide)? Hmm... sounds poetic. :)

Promising, but the systemic compexities still remain, and I have no idea how that compares to electricity directly from biomass. Which beats recycling exergy through ethanol: http://www.worldwatch.org/node/6109

[OKIsItJustMe]

10. Well, let's assume you burn that biomass to run a steam turbine

http://www.bios-bioenergy.at/en/electricity-from-biomass/steam-turbine.html

Description of the biomass CHP technology based on a steam turbine process

...

Relevant technical data and efficiencies of the steam turbine process

If only chemically untreated wood-like biomass is used, after present state of the art, live steam temperatures to approximately 540°C are achieved. Using waste wood the live steam temperatures must be lowered on approximately 450 °C to avoid increased deposition -und corrosion attack.

The attainable electric annual use efficiency (= annual electricity production / annual fuel input based on its net caloric value) depends on the live steam parameters (temperature, pressure) and on the other hand on the necessary temperature level for the process and/or district heat consumers. Electric annual use efficiencies are usually between 18 and 30 % for biomass CHP plants in the capacity range between 2 and 25 MW_el.

..