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When I see anything related to splitting water into hydrogen, I'm worried that we're going to use water for energy on top of using to hydrate people. Still tod

by molyss 9y ago

When I see anything related to splitting water into hydrogen, I'm worried that we're going to use water for energy on top of using to hydrate people. Still today, over 10% of the world population don't have access to clean water. I'm also curious on how clean the water needs to be to be used with this catalyst. AFAIK, most catalyst conversion need pretty pure water, in which case, we would not only use water, but use _clean_ water, which is even more scare than "dirty" water...

maxerickson 9y ago
That aspect of it is a big meh. Reverse osmosis uses a great deal less energy than hydrolysis, so if you have so much energy that you are using a meaningful amount of water you also have so much energy that you can just make clean water.
ThatGeoGuy 9y ago
Wouldn't that be a good thing in general though? If we use Hydrogen as our storage format, then you can do the following: Sea Water (H2O + sea junk) -> H2 Then later when generating electricity: 2 * (H2) + O2 -> H2O (fresh) + energy Naturally, the resultant H2O can be moved and recycled. I think a catalyst that splits water points towards a potential where we have more fresh water, not less.
stale2002 9y ago
Human consumption of water is miniscule compared to other uses of water. If you are worried about water shortages, the place to fight that is water intensive farming, on luxury crops.
- deleted 9y ago
  [deleted]
forgotpwagain 9y ago
You regenerate the water when H2 and O2 are recombined to produce electricity. Dan Nocera ( http://nocera.harvard.edu http://nocera.harvard.edu ) is very prominent in the water splitting field and has done a calculation in which a volume of an olympic sized pool would need to be split every second to replace all power sources on earth ( https://poptech.org/blog/daniel_nocera_on_personalized_energy https://poptech.org/blog/daniel_nocera_on_personalized_energ... ). It seems like a lot, but it would presumably be decentralized across many many locations. Additionally, you don't need 24 * 60 * 60 * olympic pool volumes -- you can cycle the same amount of water into/out of a fuel cell in a closed system.
- maxerickson 9y ago
  You are talking about several hundred billion liters. The inland reservoir here is 100 billion liters: https://www.google.com/maps/@43.8937611,-86.4337261,8900m/data=!3m1!1e3 https://www.google.com/maps/@43.8937611,-86.4337261,8900m/da... It's not very much water.
gizmo686 9y ago
Some (possibly wrong) chemistry: Hydrogen has a specific energy of 142 MJ/kg [0]. 1 water molecule has 2 Hydrogen molecules and 1 Oxygen molcule. Hydrogen has a molecular weight of 1, while Oxygen has a weight of 16 [1][2]. This means that, by weight, water is about 1/9th hydrogen. So 9kg of water should give us 142 MJ worth of Hyrdogen. Gasoline is about 46 MJ/kg [0], so 3kg of water should give us the equivelent of 1kg gasoline. Gas has a density of .77 kg/L [3], water has a density of 1kg/L [4]. So 3L of water, should be about 2.31L worth of Gas. Also, if we keep the water that results from burning hydrogen we may be able to avoid needing to re-purify it. [0] https://en.wikipedia.org/wiki/Energy_density https://en.wikipedia.org/wiki/Energy_density [1] https://www.google.com/search?q=water+molecular+weight&oq=water+molecular+weight&aqs=chrome.0.0l6.4825j0j7&client=ubuntu&sourceid=chrome&ie=UTF-8#q=oxygen+molecular+weight https://www.google.com/search?q=water+molecular+weight&oq=wa... [2] https://www.google.com/search?q=hyrdogen+molecular+weight&oq=hyrdogen+molecular+weight&aqs=chrome..69i57j0l5.6122j0j7&client=ubuntu&sourceid=chrome&ie=UTF-8 https://www.google.com/search?q=hyrdogen+molecular+weight&oq... [3] https://www.google.com/search?q=gasoline+density&oq=gasoline+density&aqs=chrome.0.0l6.2402j0j7&client=ubuntu&sourceid=chrome&ie=UTF-8 https://www.google.com/search?q=gasoline+density&oq=gasoline... [4]https://www.google.com/search?q=gasoline+density&oq=gasoline+density&aqs=chrome.0.0l6.2402j0j7&client=ubuntu&sourceid=chrome&ie=UTF-8#q=water+density+kg/L https://www.google.com/search?q=gasoline+density&oq=gasoline...

by molyss 9y ago

maxerickson 9y ago

That aspect of it is a big meh. Reverse osmosis uses a great deal less energy than hydrolysis, so if you have so much energy that you are using a meaningful amount of water you also have so much energy that you can just make clean water.

ThatGeoGuy 9y ago

Wouldn't that be a good thing in general though? If we use Hydrogen as our storage format, then you can do the following: Sea Water (H2O + sea junk) -> H2 Then later when generating electricity: 2 * (H2) + O2 -> H2O (fresh) + energy Naturally, the resultant H2O can be moved and recycled. I think a catalyst that splits water points towards a potential where we have more fresh water, not less.

stale2002 9y ago

Human consumption of water is miniscule compared to other uses of water. If you are worried about water shortages, the place to fight that is water intensive farming, on luxury crops.

deleted 9y ago
[deleted]

forgotpwagain 9y ago

You regenerate the water when H2 and O2 are recombined to produce electricity. Dan Nocera ( http://nocera.harvard.edu http://nocera.harvard.edu ) is very prominent in the water splitting field and has done a calculation in which a volume of an olympic sized pool would need to be split every second to replace all power sources on earth ( https://poptech.org/blog/daniel_nocera_on_personalized_energy https://poptech.org/blog/daniel_nocera_on_personalized_energ... ). It seems like a lot, but it would presumably be decentralized across many many locations. Additionally, you don't need 24 * 60 * 60 * olympic pool volumes -- you can cycle the same amount of water into/out of a fuel cell in a closed system.

maxerickson 9y ago
You are talking about several hundred billion liters. The inland reservoir here is 100 billion liters: https://www.google.com/maps/@43.8937611,-86.4337261,8900m/data=!3m1!1e3 https://www.google.com/maps/@43.8937611,-86.4337261,8900m/da... It's not very much water.

gizmo686 9y ago

Some (possibly wrong) chemistry: Hydrogen has a specific energy of 142 MJ/kg [0]. 1 water molecule has 2 Hydrogen molecules and 1 Oxygen molcule. Hydrogen has a molecular weight of 1, while Oxygen has a weight of 16 [1][2]. This means that, by weight, water is about 1/9th hydrogen. So 9kg of water should give us 142 MJ worth of Hyrdogen. Gasoline is about 46 MJ/kg [0], so 3kg of water should give us the equivelent of 1kg gasoline. Gas has a density of .77 kg/L [3], water has a density of 1kg/L [4]. So 3L of water, should be about 2.31L worth of Gas. Also, if we keep the water that results from burning hydrogen we may be able to avoid needing to re-purify it. [0] https://en.wikipedia.org/wiki/Energy_density https://en.wikipedia.org/wiki/Energy_density [1] https://www.google.com/search?q=water+molecular+weight&oq=water+molecular+weight&aqs=chrome.0.0l6.4825j0j7&client=ubuntu&sourceid=chrome&ie=UTF-8#q=oxygen+molecular+weight https://www.google.com/search?q=water+molecular+weight&oq=wa... [2] https://www.google.com/search?q=hyrdogen+molecular+weight&oq=hyrdogen+molecular+weight&aqs=chrome..69i57j0l5.6122j0j7&client=ubuntu&sourceid=chrome&ie=UTF-8 https://www.google.com/search?q=hyrdogen+molecular+weight&oq... [3] https://www.google.com/search?q=gasoline+density&oq=gasoline+density&aqs=chrome.0.0l6.2402j0j7&client=ubuntu&sourceid=chrome&ie=UTF-8 https://www.google.com/search?q=gasoline+density&oq=gasoline... [4]https://www.google.com/search?q=gasoline+density&oq=gasoline+density&aqs=chrome.0.0l6.2402j0j7&client=ubuntu&sourceid=chrome&ie=UTF-8#q=water+density+kg/L https://www.google.com/search?q=gasoline+density&oq=gasoline...