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Posted: Sat Mar 06, 2010 8:59 am
Posted: Sat Mar 06, 2010 9:32 am
The underlying theory appears to be summarised here;
http://web.mit.edu/chemistry/dgn/www/re ... pcet2.html
There are a few efforts around the world to "do" articifical photosynthesis and it really is one of the good ROI bets!
It seems so 'do-able'; the energy in a visible-wavelength photon is higher than that needed to liberate H from O in water that it strikes me as a problem waiting for some good chemistry/nano-technology to solve.
I'm against hydrogen as an energy vector due to the difficulties of handling, storage and the risk of unrecoverable atmospheric damage from industrial-scale leakage, but if artificial photosynthesis can be made to work [more efficiently than just growing-and-burning stuff!] then it will likely be worth the challenge of running a hydrogen infrastructure.
Posted: Sat Mar 06, 2010 9:43 am
What problems would leakage of hydrogen cause?
I would assume that it would just bind with an oxygen atom to form H20? Or maybe H2O2 under some circumstances?
Posted: Sat Mar 06, 2010 9:50 am
ozone depletion and earth and sea acidification.
There is around 500ppb elemental H in the atmosphere and there is almost no understanding of where it comes from and where it goes. Upset that balance [of something you just don't understand] and you'll get what you deserve!
Lots of CO2 has been seen before on earth, and life evolved from it. Lots of H2 has never been seen before - care to guess what'd happen, then, if you upset that balance?... 'cos it would be a guess....
Posted: Sat Mar 06, 2010 11:31 am
Posted: Sat Mar 06, 2010 11:45 am
Posted: Sat Mar 06, 2010 11:51 am
Posted: Sat Mar 06, 2010 12:07 pm
You are correct on both counts. When you ask the on site hydrogen generator mfgs what their energy efficiency is they clam up. The best number I ever got was in the range of 50%.
On top of that the safety rqmts for hydrogen are some of the most stringent. The ignition energy is very low. Sparks that would not ignite gasoline will set off hydrogen (if the concentration is right). I'd have to go back and look at the intrinsic safety charts to get numbers.
Now maybe a sealed system could work. Except that hydrogen is very hard to seal. It leaks through everything. Mechanical (bolting) joints esp. So you need a lot of monitoring. And regular inspections of the system.
The one thing it has going for it is that it dissipates rapidly (lighter than air) and doesn't pool.
And there is also the detonation velocity. Very high.
Oh. Yeah. Sufficiently high intensity UV can set it off.
Any way. We know what to do. Can it be done economically? Remains to be seen.
Posted: Sat Mar 06, 2010 12:21 pm
Posted: Sat Mar 06, 2010 2:17 pm
Posted: Sat Mar 06, 2010 3:21 pm
Posted: Sat Mar 06, 2010 5:40 pm
Posted: Sat Mar 06, 2010 6:05 pm
Posted: Sat Mar 06, 2010 6:23 pm
Posted: Sat Mar 06, 2010 6:47 pm