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This discussion relates to Technology Review's article Sun + Water = Fuel.

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  Bruceahz
  

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  10/20/2008 10:39 AM

  What am I missing?

  Photosynthesis is not:
  (solar generated)Electricity + H2O = H2 + O2.
  It is:
  Sun(energy) + H2O+ CO2 = Hydrocarbon + O2.
  
  Can someone clue me in on a) why Nocera's process is even linked to artificial photosysthesis and b)in what way it is better than/different from (or has the potential to be better than) standard electrolysis - is the claim just higher efficiency?

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    Shoreliner11
    

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    10/20/2008 12:06 PM

    Re: What am I missing?

    I was thinking the same thing Bruceahz. You see the same reaction on the electrodes when doing dna electrophoresis do you not?

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      ArtInvent
      

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      10/20/2008 12:25 PM

      Re: What am I missing?

      Exactly. This is not photosynthesis, it's an improved form of good old electrolysis: using electric current to eloctrolyse hydrogen from water. This has nothing to do with sunlight, other than the fact that solar power is obviously one conceivable way to produce the electricity.
      
      A similar misleading article on the same subject appeared previously in TR.
      
      Unless the sunlight photons are striking the water or catalysts directly, I fail to see how this is compared to photosynthesis. There is some mention of how a dye might theoretically be used to achieve this, but little work seems to have been done in that direction.

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        Kevin Bullis
        

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        10/22/2008 09:52 AM

        Re: What am I missing?

        This was a very difficult piece to write, and I can see it wasn’t very successful in the end, because people still have a lot of questions, particularly about how this is different than electrolysis.  I can assure you, that the piece is not meant to mislead or hype, but rather to explain a very significant advance.
        
        I'll have another try at it here.
        
        The problem, I think, has to do with where people are coming from, what their starting point is. Nocera is coming out of this basic chemistry world, where he has been working to solve a really basic problem:  How do plants manage, under the ordinary conditions found in nature, to use sunlight to split water, and how can we do the same thing with inorganic materials that will last longer than the proteins plants use?
        
        Part of the reason he’s asking this question is just curiosity. To understand how things work. But ultimately the idea is that if you could split water under the same benign conditions as plants and with commonly available materials and using sunlight for energy, then you should be able to do it on the same scale plants can do it. In other words, you could make devices that are as ubiquitous as plants and split enormous amounts of water worldwide. What’s more, instead of doing what plants do, which is to split water to make plants, you could design the process so that the end product is hydrogen, or even some other chemical fuel. That could solve our energy problems.
        
        As he’s working on this problem, he’s faced with one really big challenge, one of the key steps in the process plants use is proving very hard to do with inorganic materials. The problem is extracting oxygen atoms from water, the first step in making oxygen and hydrogen. It’s a very difficult process chemically and so far had required a lot of energy, very harsh alkaline conditions, or very expensive catalysts. All of those things would make it impossible to split water on a very large scale. You certainly wouldn’t want devices with extremely corrosive liquids to be as ubiquitous as plants, right? And you can’t afford to use a lot of energy, and you’d simply run out of materials such as platinum.
        
        Then suddenly (and it was quite sudden), his postdoc discovers a catalyst that can produce oxygen from water, and can do it at room temperature, with cheap materials, in neutral water, and without using huge amounts of energy. In other words, he’s found a catalyst that can do one of the steps in photosynthesis the same way plants can do it. This was one of the biggest challenges chemists in the field had been facing, and he’d solved it.
        
        Now, of course other problems remain. Probably the biggest challenge is another step in the process, which is absorbing sunlight and using it to free the electrons needed to drive Nocera’s catalyst. And here Nocera may have gotten a little ahead of himself. He knew that you could simply use electricity to drive the reactions, and you could get that from solar panels. That, conceptually, is the same as what plants do, he contends.
        
        But others point out that there are key differences in the details. In plants, one structure absorbs light and frees electrons. Others nearby use freed electrons to extract oxygen. This is more efficient, they say, than using a solar panel and a electrolyzer. It’s better to absorb light and generate electrons right next to the catalyst, rather than to generate them in a separate device (the solar panel), then extract them from that device and send them through a wire to the catalyst, where each step wastes energy. To really do what plants do, they say, you need a system where the light absorption happens right next to the catalyst for extracting oxygen.  Only then can you have the dream of really large scale production of hydrogen from water and sunlight.
        
        But here’s the thing: Nocera’s catalyst is really ideal for just such a system, a system that would amount to an artificial leaf. Not only does it operate under the same conditions as plants, it can also be formed in a way that allows it to be easily incorporated into an artificial leaf. In a leaf, the  that structure absorbs light and frees electrons is close to the structure that uses freed electrons to extract oxygen. This close proximity is important. How do you build an artificial system so that these two different structures are physically close?  We’re talking about control at the molecular scale, not a small feat.  The answer, in the case of Nocera’s catalyst, is you can use the first structure to build the second. Dye molecules can absorb light and free electrons. Those freed electrons cause the formation of Nocera’s catalyst, right there at the location of the dye.
        
        So because of the conditions under which it operates and the way it can be made, Nocera’s catalyst could be used in artificial leaves. We’re significantly closer now to doing what plants do on very large scales.

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    Kevin Bullis
    

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    10/20/2008 01:03 PM

    Re: What am I missing?

    There are several reasons, and I refer you to the article for details. I'll mention two here:
    
    For one thing, it catalyzes one of the key reactions of natural photosynthesis under the same conditions of natural photosynthesis. This is important because it suggests that the catalyst could be implemented on a very large scale.
    
    Also, the peculiar way Nocera's catalyst is formed means it can easily incorporated into an artificial leaf (details can be found toward the end of the article).

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  gp011
  

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  10/20/2008 12:07 PM

  Another Use

  When I hear people dying of drowning just because they are stuck in car or plane or in any other circumstances, I think of carrying a handy tool which can save lives. How about using this technology to produce a vey tiny portable device (may be battery powered), so that people can use it to inhale while stuck inside water until the help arrives?

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  bbawn
  

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  10/20/2008 02:45 PM

  Compared to storage CSP thermal storage

  For large scale applications how does this sort of hydrogen production compare to thermal storage used with Concentrating Solar power? I think this would be an interesting comparison.

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    Kevin Bullis
    

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    10/20/2008 03:52 PM

    Re: Compared to storage CSP thermal storage

    That is a good comparison to make.
    
    Right now, it's much cheaper to store heat than to store electricity. So when it comes to storage, solar thermal systems (which use heat to generate electricity via steam turbines or Stirling engines) clearly have an edge compared to photovoltaics, which generate electricity directly.
    
    It's too early to say if artificial photosynthesis will provide a cheaper way to store solar energy. The hope is that it will be cheaper and more efficient.

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    • 
      hixxxxx
      

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      12/22/2008 03:55 AM

      Re: Compared to storage CSP thermal storage

      Well, at least, solar thermal systems are years ahead. While this article is about basic research, solar thermal storage is used in industrial-sized prototyp applications, e.g.:
      http://en.wikipedia.org/wiki/Andasol_1_solar_power_station
      
      In this sense, I don't know what's meant by: "one of the main obstacles preventing solar power from becoming a dominant source of electricity: there's no cost-effective way to store the energy collected by solar panels"

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  JoeReal
  

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  10/20/2008 07:04 PM

  Many great ideas within the article.

  I like the many ideas within this article. Especially using saltwater. For one, saltwater already has electrolytes in it, and one of the end products is pure freshwater. California's growing population is in dire need of both electricity and freshwater. Small bottles of freshwater can sometimes be costlier than gasoline, depending where you buy them, and EPA has concluded that some of these bottled fresh water has more contaminants than freshwater from the tap.  If you bottle this "solar" reformed pure water and market it as such, more profit can be had and the investment costs would even take quicker time to pay-off, the "solar pure water" marketing gimmick might work.
  
  There are other things that can be exploited by using saltwater as the intake. Aside from the freshwater and fuel (or peak demand electricity), the minerals in the saltwater become more concentrated. Aside from the ordinary sodium chloride salt, there would be increasing concentrations of other minerals, such as Lithium salts which can be used to make Lithium based batteries that are in-demand for today's advanced electric car markets.
  
  Perhaps a better title would have been:
  Sun + Seawater = Fuel + Freshwater + Minerals
  
  I agree that stationary storage of hyrdogen is cheaper, and is needed when solar power becomes a major component of our electricity needs. I hope more topics related this subject matter will be available in the future. Thanks to Kevin Bullis!
  

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