Crazy if it works at scale

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Crazy if it works at scale

#1  Postby Macdoc » Jun 30, 2017 11:18 pm

Researchers have developed a solar paint that can absorb water vapour and split it to generate hydrogen -- the cleanest source of energy.

The paint contains a newly developed compound that acts like silica gel, which is used in sachets to absorb moisture and keep food, medicines and electronics fresh and dry.

But unlike silica gel, the new material, synthetic molybdenum-sulphide, also acts as a semi-conductor and catalyses the splitting of water molecules into hydrogen and oxygen.


https://www.sciencedaily.com/releases/2 ... 091833.htm

Can't quite figure how it can be a continuous process :scratch:
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Re: Crazy if it works at scale

#2  Postby DavidMcC » Jul 01, 2017 11:34 am

Macdoc wrote:...

Can't quite figure how it can be a continuous process :scratch:

The paint appears to be just a catalyst for the reaction, so it doesn't get used up, and the process can contnue as long as the gases continue to escape.
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Re: Crazy if it works at scale

#3  Postby DavidMcC » Jul 01, 2017 1:04 pm

Althpugh pure MoS2 would decompose in air, the paint also incorporates TiO2, which apparently prevents the Mo2 from decomposing:
https://www.sciencedaily.com/releases/2017/06/170614091830.htm

One of the biggest hurdles to the widespread use of hydrogen fuel is making hydrogen efficiently and cleanly. Now researchers report a new way to do just that. They incorporated a photocatalyst in a moisture-absorbing, semiconducting paint that can produce hydrogen from water in the air when exposed to sunlight. The development could enable hydrogen fuel production in almost any location.
...


EDIT: Obviously, as implied by the term, "photocatalyst", sunlight is also necessary for the process to work. I don't know how much, or at what wavelengths, but it may well need to be done near the equator. :dunno:
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Re: Crazy if it works at scale

#4  Postby DavidMcC » Jul 01, 2017 4:32 pm

Of course! Why didn't I think of it before? TiO2 is transparent to the whole visible spectrum, so it is presumably used to protect the MoS2 layer from the air, with which it would otherwise react, while letting light through. This probably means that the hydrogen would have to come out at the back of the MoS2 layer, however, and I'm not sure how that is arranged. :scratch:
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Re: Crazy if it works at scale

#5  Postby DavidMcC » Jul 01, 2017 4:47 pm

The problem is, how does the TIO2 layer prevent the MoS2 reacting with air, yet still allow the absorption of moisture from the air, and the photocatalysis? That's a puzzle!
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Re: Crazy if it works at scale

#6  Postby DavidMcC » Jul 01, 2017 7:41 pm

A possible solution to the conundrum is tbe possibility that MoS2 reacts with oxygen in the air, but very slowly. This is only a guess, though.
NB, the TiO2 would hold on to its own oxygen, and possibly steal some from any Mo oxide formed.
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Re: Crazy if it works at scale

#7  Postby DavidMcC » Jul 02, 2017 2:44 pm

My last shot at this is to suggest that a continuous flow cell is set up, containing water vapour, but not air, flowing over the MoS2. The exhaust gas from the cell should contain hydrogen (and, presumably, oxygen). The only scaling problem I would foresee would be prevention of fire/explosion due to large amounts of H2/O2 mixtures generated.
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Re: Crazy if it works at scale

#8  Postby DavidMcC » Jul 03, 2017 11:22 am

Sorry for making yet another "last shot", but I now realise that it would be best if the TiO2 was incompletely oxidized, ie, if it was TiOx, where x<2. This would have two effects: cause the Ti oxide to steal oxygen from any Mo oxide formed from O2 generated when water vapour is split into H2 and O2, and (unfortunately) to cause some absorption loss in the TiOx film before it gets fully oxidized. Even so, I suspect that this kind of hydrogen generator would not last indefinitely - it would need periodic replacement, as the TiOx gets fully oxidized, and is unable to reduce Mo oxides any more.
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Re: Crazy if it works at scale

#9  Postby DavidMcC » Jul 05, 2017 10:41 am

Possibly, my "rubber bible" (= the CRC Handoook of Chemistry and Physics, not a flexible version of the christian holy book!) was too vague when it said "d in air" (ie, decomposes in air), because it more likely meant "decomposes to the sesquisulphide, Mo2S3", rather than "oxidizes".

EDIT: Indeed, if it had meant "oxidizes in air", it would have said so. Therefore, I was wrong to assume it meant oxidation.
Decomposition to the sesquisulphide implies that the continuous flow cells would gradually get coated in sulphur on the inside, so they would have a limited useful lifetime. The question then is, how long would such cells last at any given temperature, and how easy would it be to restore them to the disulphide form?
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Re: Crazy if it works at scale

#10  Postby DavidMcC » Jul 05, 2017 10:57 am

As my rubber bible is over 40 years old, it is possible that a more up-to-date edition would say more on the topic, or that somewhere on the internet, there would be more detailed info.
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