I for one
i for one wish to welcome our new green fingered power providing overlords....
A synthetic leaf has been created that mimics the photosynthesis process, converting sunlight and water into a source of electrical energy. Developed by a research team at MIT led by Dr Daniel Nocera, the leaf could be a significant step towards green energy becoming a sustainable reality. The device is shaped more like a …
"...It was us who darkened the skies."
Sounds like a solar cell generating electricity to actively split water molecules using a bit of chemical reaction. Likely this bucket of water would need to be under a clear plastic O2 and H2 catcher and have an apparatus that can filter the two-gas mixture into separate O2 and H2 and pressurize it into canisters. Likely the energy produces from the O2/H2 burns could provide more power than the system requires, depending on the amount of water/sunlight involved. Some actual numbers would be useful.
Shame we only have press release drivel of "he showed that an artificial leaf prototype could operate continuously for at least 45 hours without a drop in activity." and "Right now, Nocera's leaf is about 10 times more efficient at carrying out photosynthesis than a natural leaf. However, he is optimistic that he can boost the efficiency of the artificial leaf much higher in the future." We need proper numbers! Would be like saying "the new Sandy Bridge chips perform fairly faster than the older Pentium 4 model." Bleh.
It can't produce any more than the incident solar energy which it's already been pointed out is max. ~~1 kW / square metre of card area unless some mirror system etc is used.
To the ones worrying about the amount of water I'd guess a very thin layer over the card is all that's required. The major problem looks to be the explosive potential of the hydrogen/oxygen gas mix
Yeah, but how long does it need to stay in the water & sunlight in order to produce electricity for a day? An hour? A day? A month? And is that for a single "leaf", or for a whole tree? And what does "a house in a developing country" mean? There are developing countries and developing countries. In some of them, many houses don't even *have* electricity.
Hydrogen is great, but as a fuel, it's very low density. Going to sugars or other simple hydrocarbons would be better, and more compatible with existing fuel-requiring devices (think boilers, cookers, engines...). I think that the leaf from UCL could be very good for generating real green fuel.
...is if it could use sunlight to produce hydrocarbons, not difficult to separate and store gases like hydrogen and oxygen, and not messy to burn solids like carbohydrates. Imagine if you could use it to produce C6-C10 alkanes which could be used in existing technologies. After all, as energy storage, these are pretty much optimal for use in transport, etc.
Surely if you had something which could convert CO2 into sugars, you could later burn the sugars and release the energy (and get the CO2 back). That would be a lot easier than having to store hydrogen,
If somebody could figure out how to do that on a large scale, they might be on to a winner. Seems a bit of a tall order though.
Wow, it'll power something with an unstated power requirement for a whole day, after being exposed to sunlight for an unstated amount of time. Way to go, scientists!
Still, having read the linked article their claim of 10x the efficiency of actual leaves is interesting...
Which seems to be the current thinking for how we're going to power the new hydrogen cars that seem to be just over the horizon.
Question is - how much hydrogen to we get vs cost of production and expected life of the leaf?
Good on them though - hope this comes to fruition, as it were.
According to Google (usual caveats apply), "Current photosynthesis collects about 0.7 watts per square meter", so 10 times that efficiency would be about 7W/sqm. Maximum solar irradiation (noon at the equator) is about 1000 W/sqm, so the efficiency of a leaf is 0.07%, and efficiency of the artificial leaf is 0.7%. Top-end solar panels approach 20% efficiency.
However natural leafs have a couple of very neat tricks - leaves are translucent AND they still work pretty well with indirect sunlight, not just direct sunlight - so that trees can stack massive amounts of leaves over each other, and each layer will collect some energy all the way to the lowermost leaves. Effectively a tree has many hundreds of times of leaf suface area than the effective surface area at ground level. Or to put it another way, the W/sqm efficiency for the entire tree is massively more than for a single leaf.
On the other hand solar panels work at 20% efficiancy on one layer only, efficiency drops dramatically in the shade. For a tree the extremely low efficiency of each leaf is compensated by huge amounts of leaves, while solar panels cost WAY too much to use this approach.
So the key with these artificial leaves isn't so much the efficiency as the cost. If they can be produced cheaply enough that it's cost-effective to build entire 'trees' having a lot of articial leaves in a very small effective area, we could be on to a winner.
Final neat trick that leaves have for us to emulate - it not only does photosynthesis but also pipes in water and pipes out sugars without compromising size / surface area. How much extra space does the artificial leaf need for the equipment needed to capture the released H2?
enough power to power a home for a day? from a playing car device in a bucket of water? hmm i suspect the critical missing information here would be -how long- it takes to transform said bucket of water into a days worth of energy...
if, as the linked report states its 10x as efficient as a real leaf, that would mean trees get gigawatts of energy a day from their ample leaf supply.. somehow i doubt that.
however something like this really could be the future
Its the size of a playing card, 10 times as efficient as a leaf, how long would it take to harvest enough energy to power a third world home for a day?
Suns energy reaching the ground at noon on the equator ~1KW/m^2 = E (as far as I recall, can't be bothered to look it up now)
Typical efficiency of a leaf ~ 2% = e (http://en.wikipedia.org/wiki/Photosynthetic_efficiency)
Area of device = 0.005544 m2 = a (http://en.wikipedia.org/wiki/Playing_card)
So under perfect conditions this thing is producing a * e * 1000E = 0.01W.
Let's be mean and give our african family a mere 0.01KWh of power per day, which might give them light for a few hours if they use LEDs, then their daily energy consumption would require
10 / 0.01 = 1000 hours of noonday sun.
This is why trees tend not to do too much.
1) Life cycle cost. It uses Silicon. If that's single crystal *device* grade Silicon, rather than photovoltaic grade (currently chip industry leftovers) the *real* cost (including all the energy used to make it) might not be greater than the energy it produces over its life. So did they use Silicon because it's available as a prototype or can they use cheaper grades (poly or amorphous grown on a cheap substrate) or replace it altogether?
2)It splits water into Hydrogen and Oxygen. Whoopee. Just like a string of photocells with each terminal in a bucket of water and couple of funnels over them to collect the gas. If they can't beat *that* baseline (but see 1 above) this is not much of an improvement. Keeping the gases you just made well apart is also quite important given how keen they are to re-combine.
Not much tech in this hardware section.
i seen a standup do a skit a few years back can't remember who and he made the point of how amazed we all were when like, portable tape players came out, or when sky first arrived here..it was amazing!
And how nowadays kids get given what would be classed as a supercomputer 20 years ago in their pockets and they just want more..
They've created a bloody artificial leaf! How about a few "wow! that's pretty freaking clever!"'s before questioning its operatability (is that even a word).
I dunno i just think that's bloody fantastic, ignoring all it's claims and if they're viable..the very fact that they did this is just incredible.
And whilst we're collecting criticisms, the figure of 45 hours jumped out at me. Even leaving it going over the weekend would have offered a longer running time than that so I think we can assume that this guy has tried it and 45 hours is his best yet.
But still, it is proof of concept for a fundamentally different approach. It's a prototype. It's not ready for prime time yet, people. Please don't rush out and tell the customers that they can place their orders immediately. But please *do* remember that this technique has now been proven to work and maybe it can be turned into a real product.
The first H-bomb was a small industrial facility that took several weeks to assemble on site. I don't suppose the generals were impressed. But then it yielded about 10 megatons which is at least 200 times the poxy A-bombs they had been playing with up until then. OK, so it still wasn't something you could possibly deliver to Comrade Stalin, except as a self-assembly kit (which is an unlikely way to bomb anyone) but it changed the set of possibilities for the future.
A few years back the slither photovoltaic solar cell developed by the CSIRO was to revolutionise solar energy production, as power is still generated when more than 90% of the cell was shaded whereas a traditional cell cuts out after a small percentage is shaded. It was also flexible rather than rigid, used significantly less materials and therefore cheaper to produce, and could be coated onto almost any surface including the glass panels of high-rise buildings whilst still allowing significant light to pass through. The only hurdle at the time was the need to hand cut the slithers, which was to be achieved with large scale automation.
This would have proved to be hugely disruptive to the traditional power generation industry. Needless to say the technology, which was bought by a large coal burning power company in Australia, sank without a trace. The last reference to this technology is from 2006.
Cue large traditional power generating company with a promise to develop this technology to large scale deployment, and quick as a flash, this artificial leaf technology will also disappear without a trace.
Do you have to keep the face of the "card" pointed directly at the Sun as it moves across the sky? Is that power output only going to happen in clear skies in the Sahara on the hottest day of the year? How often do I need to clean the card and the bucket, and do I need to do so with chemical cleaners? Just on cleaning it alone, exactly how much precious water am I using per day to get optimum performance? And how long do the card and storage batteries work before they wear out?
And then there are three new problems related to the water part. Is that power output using distilled water - will it work with dirtier water as is common in places like Africa? Are we expected to distill that water first or filter it somehow? What about limescale in the water, will it build up on the card and render it useless over time? And what if we're in some place where water is not plentiful enough that you can afford to leave buckets of it sitting idle rather than using it for farming or even just drinking?
Nice tech, but I don't think it's the answer to all our ills.
These days, I think, a superacid conductive membrane ("nafion" ?) is used to separate the cathode/anode compartment so little or no mixing of hydrogen/oxygen. This would seem rather difficult to adapt as presumably the hydrogen/oxgen is being emitted all over the surface.
As for the ultimate feasibilty I and others have already commented on the max. output from a playing card sized device.
No, of course it's not photosynthesis
This is *very* roughly the equivalent of the first stage of photosynthesis where light energy is captured and used to generate high-energy chemical species that are then used to power a complex series of chemical transformations that result in carbohydrates.
This is just 2H20 + light > 2H2 + 02 mediated ( i.e. kinetics accelerated) by a catalyst
i would say alot of people are impressed with the ability.
But that was immediatley counteracted by bullshit. All respect for the scientist was lost when he didnt put any figures to what he had done. Part at fault are the thausands of quacks before who promise you something for it just to be a scam
Ah, but just think of all the possibilities for terrorism! A terrorist now only needs a bucket of water and an artificial leaf to make things go 'boom'. Just look at how fast the government will outlaw water (when water is outlawed, only outlaws can drink water)!
No boom today. Boom tomorrow. Always boom tomorrow...
If this technology was indeed that great, then the "large coal burning power company" would be now "the largest renewable power company in the world".
Why would they waste money buying something supposed to kill their business and let it rot instead of using it to generate gazillions of value for the shareholders?
"...the leaf could be a significant step towards green energy becoming a sustainable reality."
It's already a sustainable reality. Freiburg, Germany proves it.
Still, a very potentially cool discovery. A lot of important details are missing from the article, but there's a lot of promise there.
Given a standard leaf is typically 3-6% efficient, a 30-60% efficiency for this device would be staggering, if they can pull it off.
Generally though producing hydrogen cleanly is not seen as the biggest technological challenge. The biggest problem is storing and transporting it safely and efficiently, not to mention the required infrastructure. There seems to be a lot of claims that 'wow, we're making green hydrogen, we've solved the energy crisis!', without consideration of the other major issues. Still, if we had devices such as this, local generation in more sunny climes could be a much more viable option.
Peak sunlight flux is about 1 kW per square metre. 20% conversion efficiency would be good going (200 W). The sun shines half the day, and most of that not vertically downwards (50 W). A playing card is maybe 55 mm by 90 mm, so there are about 200 per square metre (50/200 W).
Average output power looks to be 1/4 W at best.
Has it ever occured to you people that if an oil company was *really* evil and wanted to screw the world for endless profits, its response to a disruptive technology would be to buy it and make it work, thereby putting every other energy company out of business and ending up with a global monopoly?
And the reason these "to good to be true" technologies get bought by oil companies is because they are smarter than you are and already realise this, even if you don't?
And, by inference, the reason you never hear anything more about them is because they turned out to be "too good to be true"?
Admittedly it was only a matter of time to find the right catalyst, but its great to see it has been achieved.
The key concept here is the same as the key concept of photosynthesis, whilst it does not have the exact same chemicals, the principle of a two stage, two photon absorbtion, to split water is exactly what photosynthesis is.
The energy required to split a water molecule is greater than the energy of one photon (otherwise water would be falling apart everywhere!) so a multiple stage process is required to convert the water in two stages using one photon for each stage, via an intermediate step using a suitable catalyst.
What I like about this is the fact that it can operate as a closed system, the water is split into 2xH2+O2 and a fuel cell will combine the two again returning pure water 2xH2O, there is no need for water refills, and no need for massive amounts of pure water to be available. maybe just some cooling?
I'd be inerested to know if this can work at high pressures, as compresing hydrogen is daft, the only way to effectivly make compressed hydrogen for storage is to pressurise the water before splitting it. So does this mean we need a suitible glass window that will withstand the pressure and allow in enough light... Or perhaps a two stage process, where a low pressure system running dependant on light, powers a second high pressure electroliser for splitting for the purpose of storage.
To split water into Hydrogen and Oxygen does NOT require a catalyst. To do the opposite and combine Hydrogen and Oxygen to make water and electricity does require a catalyst. I don't know where the notion that a catalyst is required to perform electrolysis of water came from, but it just is not required. No platinum, no nickel, no gold. Precious metals need not apply. Just get yourself a cathode, an anode, some water doped with an electrolyte (don't use salt unless you can breathe Chlorine gas) and apply current with sufficient voltage to do the job.
Electrolysis it doesn't require a catalyst but this isn't electrolysis.
If we're being pedantic a catalyst does NOT alter an equilibrium only the kinetics.
2H2 + O2 > 2H2O + energy : the equilibrium lies heavily to the right, a catalyst allows the reaction to proceed usefully at low temperatures rather than needing a match - the match will give rather a large increase in rate !!
Using electricity to split water into its two components is indeed electrolysis, and that is what the article claims the artificial leaf is doing.
"The key is Nocera's use of inexpensive catalysts, made from nickel and cobalt, which efficiently electrolyse the water in the presence of sunlight."
A catalyst is not required to electrolyse water. The reaction 2H2 + O2 > 2H2O + Heat is the overall reaction that takes place in a fuel cell, which is exactly the opposite of water electrolysis. Since we're being pedantic, the fuel cell reaction is
Anode Reaction: 2H2 => 4H+ + 4e-
Cathode Reaction: O2 + 4H+ + 4e- => 2H2O
Overall Cell Reaction: 2H2 + O2 => 2H2O (plus heat)
The fuel cell process is exothermic (gives off heat).
Electrolysis of water
Cathode (Reduction): 2H(aq) +2e > H2(g)
Anode (Oxidation): 2H2O(/) > O2(g) +4H(aq) +4E
Overall Reaction: 2H2O(/) > H2(g) + O2(g)
The half reactions are balanced with the electrolyte (usually an acid but it can also be a base).
Electrolysis of water is endothermic (requires heat).
A catalyst may help speed up the process of electrolysis of water, it is however not a requirement.
Shall we take that quote from the original source:
"The key to this breakthrough is Nocera's recent discovery of several powerful new, inexpensive catalysts, made of nickel and cobalt, that are capable of efficiently splitting water into its two components, hydrogen and oxygen, under simple conditions. Right now, Nocera's leaf is about 10 times more efficient at carrying out photosynthesis than a natural leaf. However, he is optimistic that he can boost the efficiency of the artificial leaf much higher in the future. "
Note the lack of the word electrolyse, since in this case it is wrong. The word that should have been used is 'Photolsye' since the energy is being provided in the form of photons not electrons. So this is NOT electrolysis, no matter what the article states.
The general reaction of photosynthetic photolysis can be given as:
[H2X] + [2 photons] --> [2e-] + [2H+] + [X]
The chemical nature of "X" depends on the type of reaction. Both H2O and H2S are photolysed in Nature.
Whilst you are correct that a catalyst is not required to electrolyse water, This is not electrolysis.
It is also true that with very high levels of photons you can get Photodissociation of water without a catalyst but you are talking about the levels of light produced by say a Carbon Dioxide Laser. where two photons may simultainiously enter a reaction (see http://en.wikipedia.org/wiki/Photodissociation#Multiple_photon_dissociation)
But where the level of light/photons is such that only one photon will enter the reaction at any time a catalyst MUST be used. And in this case a catalyst was used!
A catalyst is not inert in a reaction, it provides a middle phase of a reaction, in this case that middle phase is after one photon is absorbed, the second photon completes the reaction and returns the catalyst. Water dissociation is not possible with just one photon.
So going back to equations the overall excluding the catalyst should be as follows:
2[H2O] + 4[photons] --> [Photolysis Eq] --> 2[H2] + [O2] --> [Fuel Cell Eq] --> 2[H2O] + 4[e-]
Giving the key result: photons in electrons out.
And you can do the same with TiO2 actually.
No need for the silicon either. I know nothing at all about the relative efficiencies mind. But juswt good old TiO2 containing slag (of which there is a monstrous amount lying around) made into roof tiles can do he same.
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