OK on page two or three we find this: "So is the idea then to couple this to a photovoltaic and also couple it to a hydrogenproducing catalyst?
Interviewee - Daniel Nocera
Right. So here's how you would think about it. You take water plus these catalysts and
light from the photovoltaic and you make hydrogen and oxygen."
Is this gibberish clear to your? Now I ask , since when does a photovoltaic produce light? And that light goes to their catalysts? What? Did he say that?
I'm sorry but this makes zero sense.
I think they mean that it takes electricity from the photovoltaic, to produce the oxygen with their catalysts. Hydrogen is produced elsewhere, which I also don't understand.
In any case why is this not electrolysis? and their device an electrolyser?
It seems that even the so called science guys don't know what to ask or how to make it clear.
Isn't it incredible what the news people and science people will buy as "scientific breakthrough"
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Sure. He misspoke. Or was misquoted. He meant apply PV output to his electrolysis cell, and make gasses.
IOW, take an already inefficient source, toss away perhaps
2/3rds of that output to make something that you'll later burn, tossing away yet another 50-60%.
12% x .5 x .5 = 3%. I'd be pleasantly surprised if the thing's overall efficiency exceeded 2%.
Not only do thay ignore the hydrogen storage problem, they seem to think you can hop on over to Ace Hardware and pick up a convenient fuel cell system.
Whether that is accurate or not, it misses the main point, which is the question of how you use solar energy when then sun goes down (or the equivalent: how you use wind energy when the wind stops blowing). Solar and wind will remain minor contributors to our energy supply until we have an inexpensive means of addressing that issue. Storing some of the energy for later use is one obvious approach. Efficiency is only one factor in the expense of storing energy. The lower the capital and operating costs are (as well as the environmental impact, if you include that as a "cost"), the less efficiency is required in order to be economically feasible. Whether the MIT discovery will eventually lead to a cost effective solution is unknown at this point, but its potential contribution appears to be the lowering of capital costs more than any increase in efficiency. I don't have access to the Nature paper, however, so it is a bit difficult to tell from the (as others have noted) rather poorly written press releases.
Is this not the same school that discovered Resonate Energy Tunneling (Marin Soljacic from the Massachusetts Institute of Technology). Big hat, no cattle! Harry
Photovoltaic systems (including inverters, installation, wiring, battery, backup, etc.) aren't economic to the consumer above about $3/watt, or about $1.50-2.00/watt for the panels all by themselves. That's about 1/3rd the current price.
With this new-fangled innovation you'd have to quadruple your PV array, plus buy and maintain storage and generation-from-gas facilities to make up for the storage losses. These increase your system cost perhaps 6- to
10-fold. More for a fuel cell.
If you're going to use a very expensive power source, you can't afford to waste 3/4 of it.
No, FORTUNATELY that is not the case. To directly split water to H2 gas and O2 gas would make an explosive gas mixture at the active site. With separated electrodes, one can collect H2 gas bubbling from one electrode, and collect (or discard) the O2 gas from the other electrode.
The 'use' of the catalyst doesn't use it up, so expense is low. Mainly, efficiency of the electrolysis is higher than with untreated electrodes, which is important if you want to scale the process up. It's extremely important if you want to scale the process 'way up'
It's disadvantageous, however, to form small bubbles (the surface tension makes a high back-pressure which translates to gas generation inefficiency). It would be good to find some way around that step entirely.
Then the vanadium redox flow battery seems to be a better way of storing electric energy. Energy density is low, so those batteries are useless for powering vehicles, but since they can be built very large, they seem ideally suited for fields of wind generators, solar panels and such.
Quoting the Wikipedia,
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: Currently installed vanadium batteries include: : : * A 1.5MW UPS system in a semiconductor fabrication plant in Japan : : * A 275 kW output balancer in use on a wind power project in the Tomari Wind Hills of Hokkaido : : * A 200 kW, 800kWh output leveler in use at the Huxley Hill Wind Farm on King Island, Tasmania : : * A 250 kW, 2MWh load leveler in use at Castle Valley, Utah : : * A 12 MWh flow battery is also to be installed at the Sorne Hill wind farm, Donegal, Ireland
This is proven technology, currently in use (except for the projected last one). I think the numbers above speak for themselves.
As clear as mud. However, a quick search of patents filed did reveal some other interesting (but I would guess still rather unstable real photosynthetic mimics that can crack water using light). It seems the state of the art ones last about 4 hours in sunlight at present.
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That is a real system with photons in hydrogen out. And they do reference Nocera's work indirectly. I could not find anything relating to this recent paper.
It certainly looks that way. I asked my tame electrochemist (non-industrial) to attempt a translation of the gibberish MIT press release. Their comments were as follows:
Benign reaction conditions and neutral pH would be cute if it was coupled with high efficiency and high current capacity.
It is possible that they have found something that works better and has lower cell overpotential (less waste heat, better efficiency).
The invention/discovery relates to the oxygen electrode and electrolyte allowing it to be made from a much cheaper material without corroding.
It looks like electrolysis and still seems to use platinum for the hydrogen electrode.
They also said that the Henry Drefus Professor of Energy at MIT might reasonably be expected to know what he was talking about and that something has gone horribly wrong in the press office. The paper was after all published in Science and presumably survived peer review. I haven't had a chance to chase down a copy yet.
Be fair lets assume his convertion is at least as good as present state of the art and a decent fuel cell for the reverse process.
12% x 0.7 x 0.7 = 6% which is about as good as the best photosynthesis (although at a combined cost of at least $5000 / per installed kW excluding the cost of the electrolysis kit, gas compressor and storage). It would be even better efficiency with one of the fuel cells that heat domestic hot water with its waste heat.
Incidentally the "humble" lead acid battery would also manage about 70% storage efficiency.
I have removed sci.electronics.basics and added sci.chem to the cross posting list in the hope that a few of the regulars there will chime in. A contribution from someone working on state of the art industrial electrolysis cells would be most welcome.
The MIT press release that requires translation out of gibberish is at:
Following up my own post is bad form, but I have just found the least garbled summary of their invention so far online at EE Times:
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The claimed efficiency is "almost 100%" (sic). I'd be much happier if they actually gave a number. I thought thermodynamics set a limit somewhat lower than that. Have I missed something?
Incorrect, 100% of the current goes into the reaction.. Electrons/Ions still accomplish work on a 1 to 1 basis.
Power efficiency would be 95% @ the stated current density. Voltage loss would increase as current denisty increases, but that would still be a linear relationship.
I don't think you can make that assumption immediately. Below 1.23 V, NONE of the electrons can cause ionization, so I think it is premature to assume that 100% of the electrons cause ionization at 1.29 V. I used 95% based on Nocera's "almost 100%" claim.
I doubt that. It's probably safer to say that with 60 mV overpotential, that the power efficiency must be BELOW 95%. I think it's close to 90% overall.
AFAIK, it's the other way around : as Voltage (overpotential) increases, the current density increases. Unfortunately, overpotential is by definition a loss, so you want to keep that as low as possible. Also, the increased current density that would result from increased overpotential could further reduce efficiency if the electrodes 'saturate' (due to bubble forming etc).
Long story short : Nocera should at least report current density at 60 mV overpotential, and preferably a graph showing efficiency of production of H2/O2 w.r.t. current density and overpotential.
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