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Author Topic: Bringing the solar-hydrogen economy a step closer  (Read 6238 times)

Offline peppercorn

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Tiny porphyrin tubes developed by Sandia may lead to new nanodevices

www.sandia.gov/news-center/news-releases/2005/renew-energy-batt/nano.html

sunlight + water + catalyst = hydrogen.

Better than making electricity from sunlight, yes?

Make it at sea (if salt water can be used), pipe back on land.

As simple as it sounds?
« Last Edit: 18/10/2007 21:12:40 by peppercorn »


 

another_someone

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Bringing the solar-hydrogen economy a step closer
« Reply #1 on: 18/10/2007 21:47:40 »
Very frightening.

If this catalyst can just keep on catalysing water, and releasing hydrogen - you must expect some amount of these nanotubes to escape into the environment (maybe only a very very small percentage, but if the process becomes widely used, even a small percentage can be a large amount).  What will then stop these nanotubes from continuing to function, and continuing to catalyse seawater, and allowing all the hydrogen released by such to just escape out into space, until 300 years from now this planet starts suffering serious water shortages?

Even without the catalyst being released into the wild, the increased use of hydrogen will mean an increase in the amount of hydrogen leaked into space; but with the possibility that the catalyst could leak out into the wild, this risk is only magnified.
 

lyner

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Bringing the solar-hydrogen economy a step closer
« Reply #2 on: 18/10/2007 22:39:14 »
Quote
serious water shortages?
And what about the poisonous levels of oxygen in our atmosphere, as a result, and the mysterious hydrogen explosions everywhere?
 

another_someone

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Bringing the solar-hydrogen economy a step closer
« Reply #3 on: 18/10/2007 23:26:11 »
Quote
serious water shortages?
And what about the poisonous levels of oxygen in our atmosphere, as a result, and the mysterious hydrogen explosions everywhere?

I cannot see explosions being more of an issue than it is with methane - and probably less so (this is not to say they will not happen, but probably less frequently than with methane).

I am not convinced about the oxygen argument either.  It will need to be a very significant shift in O2 levels to actually cause any poisonous effects (I believe we need to move from the present 20% to around 50% before we have very serious problems).

What it may do is initially increase the level of forest fires (even a modest increase in O2 will do that), and that combined with reduced water levels could reduce the level of photosynthesis, thus increasing the levels of CO2 (and if so, then ultimately actually reducing the levels of O2 in the long run).
 

lyner

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Bringing the solar-hydrogen economy a step closer
« Reply #4 on: 18/10/2007 23:57:26 »
Sounds a scary scenario.
The mass of water in the oceans is pretty huge, compared with the mass of the atmosphere - 10m of water is equivalent to 1 atmosphere - so an equivalent mass. If we lost 10m of water - well, more because of the areas of land, that would about double the amount of oxygen.Twice that and we'd be near your 50% level for Oxygen poisoning.
It's just as well that most catalysts degrade in time, then!
 

Offline peppercorn

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Bringing the solar-hydrogen economy a step closer
« Reply #5 on: 19/10/2007 15:09:47 »
Blimely!
What a cynical bunch you lot are!  ;)

Couple of points immediately spring to mind:
1. No evil genius is likely to dump trillions of these things into the world's oceans.
2. They aren't self replicating - if a few (even millions) escape the impact would be negligible.
3. I'm fairly sure in reality nanotubes would be poisoned by salt (I suggested using salt water originally as a hypothesis).
4. Outside a 'controlled' environment - ie. a hydrogen farm, degradation would, indeed, be swift.
5. Providing the system remains a closed cycle no run-away production oxygen, hydrogen or other malevolent substance will occur - ie. hydrogen is just a method of moving the (in this case, solar) energy conveniently to where it can be put to use.


So, putting the slim chance of world oblivion to one side for a moment, does anyone consider this a potentially advantageous technology w.r.t. our current environmental issues?
 

lyner

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Bringing the solar-hydrogen economy a step closer
« Reply #6 on: 19/10/2007 16:22:27 »
Of course, plants do this sort of thing pretty well, already. Ethanol is not a bad fuel and a similar area of receptors would be needed for the proposed system as for the equivalent energy production with plants.
It might be very suitable for use in space craft - no disease worries, for instance.
The politicians / businessmen need to learn a few lessons about real costs before any system will  be truly worthwhile, though.
 

Offline peppercorn

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Bringing the solar-hydrogen economy a step closer
« Reply #7 on: 19/10/2007 19:45:47 »
Indeed plants and nature, in general, have a rather good headstart on human invention & there is much we can learn there.

I agree about ethanol (and, by inference, biodiesel more so - as there's no need for fermentation).  However ethanol only has about 60% the energy density of hydrogen by mass and the system efficiency drops further for ethanol when harvesting and processing is factored in.

Liquid biofuels currently have a big advantage in that they are more attuned to current vehicle engine technologies. I hope this will eventually be superseded.

For non-transport applications, especially micro-CHP (combined heat and power), hydrogen is ideal and can be piped like natural gas.

Using hydrogen as an energy-transport system is much better than HT electricity lines and with much lower losses.

I say the research community should forget photovoltaics and focus on photocatalytic technologies.
 

lyner

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« Reply #8 on: 19/10/2007 21:05:21 »
Quote
Using hydrogen as an energy-transport system is much better than HT electricity lines and with much lower losses.
Do you mean piping Hydrogen around the place, or carrying in tankers?
As a distribution system, electricity takes a lot of beating.
 

another_someone

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Bringing the solar-hydrogen economy a step closer
« Reply #9 on: 19/10/2007 21:31:57 »
I do agree that resistive losses in electrical distribution can be quite high.  Still not convinced about hydrogen though, and certainly liquid fuels are much easier to manage.

Not sure that energy density is that critical when you have factored in all the overheads of the complex (and probably energy consuming) storage mechanisms required for hydrogen (the same argument could be made for methane, but methane powered cars are still typically shorter range than their petrol/diesel counterparts).
 

lyner

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Bringing the solar-hydrogen economy a step closer
« Reply #10 on: 19/10/2007 22:10:56 »
Losses are in the region of 8% for electrical distribution in the UK.
That doesn't seem too bad, when you think of the longevity and reliability of fixed installations such as OH lines and transformer stations. Fit and forget (almost) for 20 or 30 years.
Another advantage is that electricity separates the  energy source from the consumer; you can change your energy resource and still use all the same equipment at the user end.
Of course, you have to 'use it as you make it' which is not always convenient.
Regarding the 'energy density' of fuels. The mass of a tank of petrol / butane etc is almost all fuel. I believe that Hydrogen needs to be stored in quite a large mass of something else  or r stored cryogenically -  not good for your average car. The press is full of new storage methods, however - if a suitable (cheap) one comes along then the situation could change.
 

Offline Bored chemist

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Bringing the solar-hydrogen economy a step closer
« Reply #11 on: 20/10/2007 19:43:38 »
"If this catalyst can just keep on catalysing water, and releasing hydrogen - you must expect some amount of these nanotubes to escape into the environment (maybe only a very very small percentage, but if the process becomes widely used, even a small percentage can be a large amount).  What will then stop these nanotubes from continuing to function, and continuing to catalyse seawater, and allowing all the hydrogen released by such to just escape out into space, until 300 years from now this planet starts suffering serious water shortages?"
For a start these things need sunlight. most of those that escaped would probably end up buried.
Then there's the scale of things, imagine that we decide to replace our entire energy supply with this new catalyst. In order to work it will have to produce hydrogen at a rate that's equivalent to our current use of fossil fuels (more or less). In doing so it will produce oxygen equivalent to that consumed by burning fossil fuels. Since mankind started to exploit oil and coal we have altered the CO2 concentration in the air by a few tens of  parts per million; presumably we have had a similar effect on  the O2 conc but that's more difficult to measure.
If we then accidentally set all this catalyst free it would continue to produce O2 and H2. If it were as well organised as it would be in a power plant it would make the gases at the same rate. So over the course of 300 years it would make a difference to the atmosphere that's too small to measure accurately.
OK, how much water would it use up; well that's the same question as was answered here
"The mass of water in the oceans is pretty huge, compared with the mass of the atmosphere - 10m of water is equivalent to 1 atmosphere - so an equivalent mass. If we lost 10m of water - well, more because of the areas of land, that would about double the amount of oxygen.Twice that and we'd be near your 50% level for Oxygen poisoning."
but looked at the other way round. Even if this catalyst turned half the atmosphere into oxygen and hydrogen it would only use up a small fraction of the water.

Then there's the question of what would really happen to the hydrogen and oxygen in the air- most of them would simply recombine to produce water.

So, if we made a huge amount of this stuff then spilled it all and it didn't degrade and none of it was in the shade and it all got optimally supplied with water and sunlight then over the course of 300 years, if the recombination of hydrogen and oxygen were somehow prevented, it would make a difference to O2 and H2 levels that would be hard to measure and cause a drop of sea levels by some tiny fraction of an inch.

Can we find something more important to worry about now?
Now we
 

lyner

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Bringing the solar-hydrogen economy a step closer
« Reply #12 on: 21/10/2007 00:29:42 »
So we can all sleep easy in our beds?
 

another_someone

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Bringing the solar-hydrogen economy a step closer
« Reply #13 on: 21/10/2007 00:54:58 »
For a start these things need sunlight. most of those that escaped would probably end up buried.

Depends on the context in which they are lost, but since they are inevitably used in a context where water is readily available, it is likely that a fair amount will be lost into water.

Then there's the scale of things, imagine that we decide to replace our entire energy supply with this new catalyst. In order to work it will have to produce hydrogen at a rate that's equivalent to our current use of fossil fuels (more or less). In doing so it will produce oxygen equivalent to that consumed by burning fossil fuels. Since mankind started to exploit oil and coal we have altered the CO2 concentration in the air by a few tens of  parts per million; presumably we have had a similar effect on  the O2 conc but that's more difficult to measure.

The reason why I am not so concerned about O2 is that it is part of the natural carbon cycle, and always has been, so an increase in either can easily be converted to an increase in the other.  The carbon/oxygen cycle has quite a bit of flexibility in it (it must have, because natural variations are anyway quite substantial).

As far as I am aware, there is no major natural hydrogen cycle, and hydrogen has a far greater capacity to leak out of the Earth's atmosphere into space, so be lost forever.

If we then accidentally set all this catalyst free it would continue to produce O2 and H2. If it were as well organised as it would be in a power plant it would make the gases at the same rate. So over the course of 300 years it would make a difference to the atmosphere that's too small to measure accurately.

Yes, but so long as we maintain a closed cycle of O2 and H2, the fact that we produce it, and then it recombines to form water, and is then disassociated again, there is no long term loss of anything.  The problem with H2 is that if it is released into the atmosphere, it can break out of the cycle.

OK, how much water would it use up; well that's the same question as was answered here
"The mass of water in the oceans is pretty huge, compared with the mass of the atmosphere - 10m of water is equivalent to 1 atmosphere - so an equivalent mass. If we lost 10m of water - well, more because of the areas of land, that would about double the amount of oxygen.Twice that and we'd be near your 50% level for Oxygen poisoning."
but looked at the other way round. Even if this catalyst turned half the atmosphere into oxygen and hydrogen it would only use up a small fraction of the water.

Yes, but the point is not the instantaneous amount of oxygen added to the atmosphere, but the cumulative loss of hydrogen over time, where no single year has a discernible effect, but year on year it is a one way traffic in hydrogen leaking out of the atmosphere.

Ofcourse, the other factor (whether we are talking about water being exhausted from hydrogen combustion in internal combustion engines, or whether water is created by leaked hydrogen recombining with free atmospheric oxygen) is that it will increase the level of water vapour in the atmosphere - and water vapour is a more potent greenhouse gas than CO2 - sounds like something of an own goal there.

The other factor that has not been addressed is where is this water coming from.  It has been mentioned to use seawater (which would have the potential of increasing the salinity of the sea - although we can debate by how much), but if we are restricted to fresh water supplies, there are many who consider that to already be a scarce resource in many parts of the world.

Then there's the question of what would really happen to the hydrogen and oxygen in the air- most of them would simply recombine to produce water.

How quickly does hydrogen recombine with oxygen in ordinary conditions.  Clearly, eventually it is inevitable that it would recombine, but in the meanwhile it is rising through the atmosphere, and the question is whether it will recombine before it rises to an altitude where it is at risk of loss?

« Last Edit: 21/10/2007 00:57:43 by another_someone »
 

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