Secrets of the first practical artificial leaf

May 09, 2012
Secrets of the first practical artificial leaf

A detailed description of development of the first practical artificial leaf — a milestone in the drive for sustainable energy that mimics the process, photosynthesis, that green plants use to convert water and sunlight into energy — appears in the ACS journal Accounts of Chemical Research. The article notes that unlike earlier devices, which used costly ingredients, the new device is made from inexpensive materials and employs low-cost engineering and manufacturing processes.

Daniel G. Nocera points out that the artificial leaf responds to the vision of a famous Italian chemist who, in 1912, predicted that scientists one day would uncover the "guarded secret of plants." The most important of those, Nocera says, is the process that splits water into hydrogen and oxygen. The artificial leaf has a sunlight collector sandwiched between two films that generate oxygen and hydrogen gas. When dropped into a jar of water in the sunlight, it bubbles away, releasing hydrogen that can be used in fuel cells to make electricity. These self-contained units are attractive for making fuel for electricity in remote places and the developing world, but designs demonstrated thus far rely on metals like platinum and manufacturing processes that make them cost-prohibitive.

To make these devices more widely available, Nocera replaced the platinum catalyst that produces hydrogen gas with a less-expensive nickel-molybdenum-zinc compound. On the other side of the leaf, a cobalt film generates oxygen gas. Nocera notes that all of these materials are abundant on Earth, unlike the rare and expensive platinum, noble metal oxides and semiconducting materials others have used. "Considering that it is the 6 billion nonlegacy users that are driving the enormous increase in energy demand by midcentury, a research target of delivering solar energy to the poor with discoveries such as the provides global society its most direct path to a sustainable energy future," he says.

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More information: The Artificial Leaf, Acc. Chem. Res., Article ASAP. DOI: 10.1021/ar2003013

Abstract
To convert the energy of sunlight into chemical energy, the leaf splits water via the photosynthetic process to produce molecular oxygen and hydrogen, which is in a form of separated protons and electrons. The primary steps of natural photosynthesis involve the absorption of sunlight and its conversion into spatially separated electron–hole pairs. The holes of this wireless current are captured by the oxygen evolving complex (OEC) of photosystem II (PSII) to oxidize water to oxygen. The electrons and protons produced as a byproduct of the OEC reaction are captured by ferrodoxin of photosystem I. With the aid of ferrodoxin–NADP+ reductase, they are used to produce hydrogen in the form of NADPH. For a synthetic material to realize the solar energy conversion function of the leaf, the light-absorbing material must capture a solar photon to generate a wireless current that is harnessed by catalysts, which drive the four electron/hole fuel-forming water-splitting reaction under benign conditions and under 1 sun (100 mW/cm2) illumination.

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lonewolfmtnz
2.6 / 5 (9) May 09, 2012
"practical" bullshit (except for those cashing their 'research' checks).
Now, where did I put those "Money Tree" seeds?
Terriva
1.4 / 5 (9) May 09, 2012
"practical" bullshit (except for those cashing their 'research' checks).
I do fully agree with it. The energetic effectiveness of this "artificial leaf" is way lower, than the yield of solid state solar cells connected to classical electrolyzer - not to say about stability, complexity, environmental friendliness (presence of toxic salts of cobalt and rare metals) and installation cost. For me it's just a grant generator without any practical usage, whereas the research of cold fusion is ignored for years. Unfortunately in mainstream physics the "effective research" is considered the research, which can bring the another grants for physicists - not the practically applicable results.
Terriva
1 / 5 (4) May 09, 2012
The problem essentially is, the artificial leaf connects the functionality of sold state solar cell and electrolyzer into the single device. In general, it's not so easy to find an effective semiconductor junction with high quantum yield and it's not so easy to find an effective electrolyzer with low hydrogen and oxygen overvoltage, which is prone to the fotocorrosion. The probability, we can succeede with finding of both systems at the same device is the product of two low probabilities, i.e. the number even lower.

Even if we would succeed with it, then the high investment cost of large area fotoelectrolyser installation would lead us to the modularization of both processes into two separate devices anyway. It's not cheap to install the hollow heavy glass panels full of water solution with high hydrostatic pressure equipped with electrodes and membranes, cooling and circulation pipes and so on. The maintenance and installation cost of simple robust flat panel is way cheaper.
El_Nose
3.1 / 5 (7) May 09, 2012
really people ---

splitting water takes ALOT of energy. We have not had an efficient way of doing this ever. but splitting water is the best way to produce hydrogen planetside. as long as the longevity of the leaf offsets its production cost then this is pure gold. This is literally wine from water and gold from lead.

@terriva
why hollow glass tubing??? no one cares what the bottom of the container is made of -- and the top can be low grade plastic... as long as it can catch the gas being produced and transparent enough to allow enough sunlight to filter in.

the water unfortunately has to be darn near neutral so taht means it has been purified... but keeping a pool near full with modest evaporation rates is easy -- the question is the amount of water desynthesised ml / cm^2 / sec that will tell you everything you need to know to build a facility.

and give me a break condensation tubes are cheap... you over thought this one.
Origin
2.3 / 5 (3) May 10, 2012
The artificial leaf of Nocera has a power efficiency about four percents - whereas the power efficiency of top solar cells can be ten-times higher - and they don't require any complex infrastructure. I can appreciate the effort of Nocera's group - but you cannot beat these simple numbers. BTW Whole the hydrogen economy is a hoax, the only purpose of which is to get additional money of tax payers into account of research of real energy solutions, like the cold fusion (compare the PO article here, too).
stealthc
1 / 5 (2) May 10, 2012
100w/3.08m not practical. That's a poor performance rating since the solar panels coming out recently have hit 500w/m2 and some even as much as 1000w/m2. I wonder how this would work with nitrogen instead of zinc (another article posted today on platinum alternatives)
El_Nose
5 / 5 (2) May 11, 2012
this isn't about solar panels -- its about the cost to split water, why is no one addressing the real issue
Terriva
2.3 / 5 (3) May 11, 2012
First off, this is old news and Nocera is making the same bold claims each year in copy&paste way. Here's a press release from 2008.. In many sources Nocera sounds like showman. The popular science articles don't convey that his goal is to enable electricity generation for the poorest people in the world (every founder of global company claimed it at the very beginning, after all). However, I'm going to continue to roll my eyes when he describes his own work as the "holy grail of science" and "nirvana." Here's his upcoming New Yorker article. I particularly dislike grandiose quotes in these articles because it makes everyone who doesn't exaggerate look like a slacker. This is tabloid science and parasitic, unethical behavior.