Slashdot Mirror

← Back to Stories (view on slashdot.org)

Photocatalyst Cracks Water with Sunlight

Posted by michael on from the catalytic-cracking dept.

lonenut writes: "With fuel cell laptop batteries in the news lately, I thought this article on water-cracking photocatalysts would be good reading. A bit short on details, but apparently Zhigang Zou of the NIAIST in Tsukuba, Japan is working on a promising catalyst which creates hydrogen and oxygen from water and sunlight. I look forward to someday watering my laptop just like the houseplants."

13 of 43 comments (clear)

  1. We know it works by adamy · · Score: 2, Interesting

    Look at all the biological systems on the planet that convert sunlight into energy. I guess it is no surprise that we can get this to work in the lab...

    Yeah, I know, we've been using solar panels for years.

    From what I've read, storing energy as hydrogen is one of the most effecient ways to do so. I wonder why all thos windmills on Route 580 out outside Pleasonton, CA don't use this as opposed to just turning off. I heard that it was because there was not effecient way to store the energy. Couldn't they just generate electriticiy, split water into it's componenets, and store the Hydrogen?

    Forget for laptops, I want this for my house...no more rolling blackouts. Course My h2o will be sky high.

    --
    Open Source Identity Management: FreeIPA.org
    1. Re:We know it works by Alpha+State · · Score: 2

      From what I've read, storing energy as hydrogen is one of the most effecient ways to do so. I wonder why all thos windmills on Route 580 out outside Pleasonton, CA don't use this as opposed to just turning off. I heard that it was because there was not effecient way to store the energy. Couldn't they just generate electriticiy, split water into it's componenets, and store the Hydrogen?

      Conversion between different forms of energy results in a low efficiency. Converting from electricity to hydrogen and back would have an efficiency of about 50% (at a guess), not including transport of the hydrogen. The electricity grid has an efficiency of about 75% (again an educated guess), and is very convenient.

      Of course, if you are going to generate hydrogen directly it would be great for transport use. this sounds like a great new form of solar power if it works well.

    2. Re:We know it works by Pogue+Mahone · · Score: 3, Informative
      Course My h2o will be sky high.


      Why? When you "burn" the hydrogen to recover the
      energy, guess what you get back?

      --
      Every bloody emperor has his hand up history's skirt [Peter Hammill/VdGG]
    3. Re:We know it works by hairyian · · Score: 3, Interesting

      Conversion between different forms of energy results in a low efficiency. Converting from electricity to hydrogen and back would have an efficiency of about 50% (at a guess), not including transport of the hydrogen. The electricity grid has an efficiency of about 75% (again an educated guess), and is very convenient.

      This is indeed true: the processes which convert energy from one form to another are rarely efficient. There is one thing which has struck me about this: we don't need to be efficient. What we need it lots of energy which we can waste.

      On a day to day basis we waste more energy than could be imagined. The great fiery fusion reactor in the sky emits it whether we use it or not. Lot's of it. More energy than even a Californian household could use! In a sense, sitting on a rock and collecting what comes out way isn't very efficient. I doubt we get more than a hundred billionth of the energy that we could get. It's just difficult to it!

      Imagine a process of generating hydrogen using sunlight which was commercially viable but was only 1% efficient. Is this a problem? Not if you can collect 100 times more of the free energy which is being lost from the great fusion reactor in the sky. To put it in context, use a reflector 10 times the size.

      This is entirely an engineering problem, and with current technology it's solvable but expensive. The end result though, is enough energy for rock and roll for as long as the fusion reactor in the sky is pumping it out. All we have to do is enough work to collect some of what's wasted!

      (yes, I know. Ultimately, you want an elipse with a collector at one focus and the sun at the other so we don't waste any of it. Dyson sphere anyone? ;)

      Ian Woods

  2. Just defers the problem... by Hard_Code · · Score: 2

    ..so now the problem becomes the laborious chore of mining finite resources out of the earth?

    What is wrong with a solar-powered electric generator used to split water? Is that not efficient enough? At least you wouldn't be lugging around all these minerals to replenish the water splitter.

    --

    It's 10 PM. Do you know if you're un-American?
    1. Re:Just defers the problem... by belg4mit · · Score: 3, Informative

      No it doesn't

      a) catalyssts are by definition resuable
      b) there are other source of minerals than just the Earth. (There aren't any other useful sources of hydrocarbons on the other hand).

      --
      Were that I say, pancakes?
    2. Re:Just defers the problem... by AntipodesTroll · · Score: 3, Interesting

      How do you convert the sunlight to electricity?

      Electricity producing silicon solar-cells actually take more energy and generate more pollution during manufacture, than they will ever generate. The uninformed non-tech green set never seems to understand this point.

      This leaves using an intermediary like water or sodium, to be heated by sunlight, and to generate electricity mechanically. This is highly inefficient, and/or dangerous.

      The fact is, sunlight is too diffuse to be a practical large-scale energy supply without a hell of a lot of energy being put into it, by traditional means. Unless you count photosynthesis, which I give more creedence to than solar cells, the energy is just in a completely different form.

      The nice thing about conversion directly to hydrogen, is that it is definetly an easier way to concentrate the energy.

      --
      Anyone who considers arithmetical methods of producing random numbers is, of course, in a state of sin.-John von Neumann
    3. Re:Just defers the problem... by stevelinton · · Score: 3, Informative
      Electricity producing silicon solar-cells actually take more energy and generate more pollution during manufacture, than they will ever generate. The
      uninformed non-tech green set never seems to understand this point.


      I believe that this is no longer true. The latest generations of cells are much thinner and lighter (less silicon to refine and melt so less energy) and more efficient than earlier generations.
    4. Re:Just defers the problem... by Mandelbrute · · Score: 2
      Electricity producing silicon solar-cells actually take more energy and generate more pollution during manufacture, than they will ever generate.
      Some numbers to back this up would be nice - I hope it's not the trick of paying for the entire factory (which will outlive individual cells) plus all of the vehicles used to transport the products (which are also used for other things).

      Most people seem to forget that the oil they use doesn't grow in the pump, and the coal has to be dug up - getting those energy sources takes energy too.

      Anyway, the argument is fairly pointless, since the solar cells are used in applications where it is impractical to use power from the grid (eg. boats, pumps, telecommunication towers, navigation lights or hand held calculators)

      This leaves using an intermediary like water or sodium, to be heated by sunlight, and to generate electricity mechanically. This is highly inefficient, and/or dangerous.
      Why is it dangerous? Dangerous relative to what? More dangerous than the Hydrofluoric Acid used in oil refining (which of course is only nasty if it gets out)? Your garage is probably full of much more dangerous chemicals than small amounts of hydrogen.
      The fact is, sunlight is too diffuse to be a practical large-scale energy supply
      KiloWatts per square metre sound like serious amounts of energy to me. Even if you can only get 5 percent of that you are still getting a fair bit of energy.
  3. The problem is efficiency. by Bob_Robertson · · Score: 3, Informative

    Building the solar pannel requiers more energy than you get out of it. Same as a battery. It's only "efficient" for the end user.

    Petrolium is efficient because we are just harvesting millions of years of sunlight-and-plant stored energy. In real terms, it's not efficient at all. Ethanol is more efficient, brewing burnable liquid fuel out of sugar, or using lye and methanol to crack vegetable oil into "diesel" fuel. Or just burn the veggie oil directly, like Heir Diesel did in his original engines.

    All of these convert sunlight into fuel, with various efficiencies and usefulness. I think the direct use of veggie oil to be the best myself, but one still has to press the oil out!

    The answer, I believe, is to use them all. Bio-diesel, veggie oil, ethanol, hydrogen, tide and wave forces, wind, sunlight, petrolium.

    The "scarce resource" idea is a myth. 150 years ago, whale oil was an important strategic national resource. Silica is as common as sand, and more valuable than gold when formed into a computer chip.

    Bob-

    --
    The Ludwig von Mises Institute. The reasoning individuals economics
  4. Re:change? by hairyian · · Score: 2, Informative

    You still need to recharge your laptop with Hydrogen, and it will polute just as much as batteries do today(very little)

    There is a funamental difference between the use of hydrogen for power in a fuel cell and the use of a normal cell.

    You 'make' a cell. It's made of some pretty nasty things. There are around 70 million mobile phones in the UK, each of which has around 100 grammes of heavy metal in their rechargable (but not infinitely so) cells. In a few years each of these cells will need to be replaced. By my calculation that's 7 million kilogrammes, or 7000 tonnes of heavy metals that needs to be processed and/or recycled (or, thrown away). That's a hell of a lot of material for a place the size of the UK.

    A hydrogen fuel cell does not contain such nastiness and, baring wear and tear and failure, would last at least as long. Additionally, the oxidation of hydrogen (which is ultimately where the energy comes from) produces water. Not slightly nasty water, but pure water. The kind of thing which tastes awful ;)

    I think you'd find that a hydrogen fuel cell industry would be far better for the environment and cheaper to do (lower displosal, recycling, replacement cost) than any other chemical storage power supply.

    The part of the equation which is missing is an efficient (read, cheap) way of producing hydrogen. Sunlight is clean and free - if we don't use it then it's wasted. The sun emits quite a lot of it continuously. Using a million times more of it than we necessarilly need is still a hell of a lot cheaper and better than drilling for crushed and fermented vegetation below rock strata. If it can be made commercially viable, I for one am all for the use of H2 for power. The advantages are clear: the only thing missing is a cheap and plentiful supply of H2.

    Ian Woods

  5. Economic payback isn't hell by Spamalamadingdong · · Score: 2
    Electricity producing silicon solar-cells actually take more energy and generate more pollution during manufacture, than they will ever generate.
    The figures I read say that the panels pay back their energy of construction in 2-4 years. Lifetime of a typical panel is at least 20 years, possibly upwards of 30 years.
    The nice thing about conversion directly to hydrogen, is that it is definetly an easier way to concentrate the energy.
    Conversion directly to hydrogen eliminates a bunch of intermediate steps. If you're making hydrogen from sunlight anyway, you might as well do it in the way which is simplest and cheapest.

    I personally think that hydrogen isn't as easily transported as e.g. aluminum metal (you won't have any NOx emissions from aluminum-air batteries, and the fuel doesn't leak either), but the popular consciousness among the ecology-minded doesn't seem to be able to grasp conservation of energy, let alone economic payback and leveraging techniques.

    --
    Scientists restrict study to entire physical universe; creationist
  6. Water and light in, gas mix and heat out by Spamalamadingdong · · Score: 2
    You get a mixture of hydrogen and oxygen out of such a beast. You can separate them using well-understood techniques, such as allowing the hydrogen to diffuse through palladium leaving the oxygen behind. I seem to recall that there are cells which can use an H2/O2 mix directly, but I'd be leery about having very much of such a gas mix in any one place.

    The idea which occurs to me about this is that a collector could perhaps be used to harvest part of the energy as H2/O2 and the remainder as heat. If you did this with distilled water and catalyst, and allowed the mix to heat up until you had low-pressure steam with "contaminants" (diluted with water vapor to below the flammability limit), you could harvest energy in two useful forms and make productive use of the waste heat from the catalytic decomposition process.

    --
    Scientists restrict study to entire physical universe; creationist