The Glittering Eye alerts me to a post about nanomaterials that can use light to split water into hydrogen and oxygen. The original Sandia National Laboratories press release adds more details on how these nanoscale devices might be the key to the use of solar energy to produce hydrogen for energy.
Sunlight splitting water molecules to produce hydrogen by devices too small to be seen in a standard microscope. That’s a goal of a research team led by Sandian John Shelnutt (1116) that has captured the interest of chemists around the world who pursue this “Holy Grail of chemistry."
“The broad objective of the research is to design and fabricate new types of nanoscale devices,” John says. “This investigation is exciting because it promises to provide fundamental scientific breakthroughs in chemical synthesis, self-assembly, electron and energy transfer processes, and photocatalysis. Controlling these processes is necessary to build nanodevices for efficient water splitting, potentially enabling a solar hydrogen-based economy.”
The prospect of using sunlight to split water at the nanoscale grew out of John’s research into the development of hollow porphyrin nano-tubes (see “Porphyrin nanotubes versus carbon” on page 4). These light-active nanotubes can be engineered to have minute deposits of platinum and other metals and semiconductors on the outside or inside of the tube.
The key to making water-splitting nanodevices is the discovery by Zhongchun Wang (1116) of nanotubes composed entirely of porphyrins. Wang is a postdoctoral fellow at the University of Georgia working in John’s Sandia research group. The porphyrin nanotubes are micrometers in length and have diameters in the range of 50-70 nm with approximately 20-nm-thick walls. They are prepared by ionic self-assembly of two oppositely charged porphyrins — molecules that are closely related to chlorophyll, the active parts of photosynthetic proteins.
Photovoltaic devices that convert photonic energy into electricity are just one of several approaches for methods to convert solar energy into more useful energy forms. Devices that could use light to catalyse the splitting of water would generate hydrogen that could be burned in fuel cells to generate electricity or burned in more conventional engines to produce mechanical energy.
Another approach might be to copy nature which uses photonic energy in chlorophyll to drive the fixing of hydrogen from water and carbon from carbon dioxide to produce hydrocarbons. Most biomass energy approaches use the ability of plants to do this. However, entirely synthetic materials could be developed that have the ability to generate hydrocarbons and those materials have the potential to generate hydrocarbons more efficiently than plants can manage.
Shelnutt thinks hydrogen-generating nanodevices could absorb and use a very large portion of the light energy spectrum. This could make them more efficient than either plants or all currently produced photovoltaic cell designs.
“Laboratory-scale devices of this type have already been built by others,” John says. “All we are doing is reducing the size of the device to reap the benefits of the nanoscale architecture.”
John says the nanodevice could efficiently use the entire visible and ultraviolet parts of the solar spectrum absorbed by the tubes to produce hydrogen, one of the “Holy Grails of chemistry.”
These nanotube devices could be suspended in a solution and used for photocatalytic solar hydrogen production.
“Once we have functional nanodevices that operate with reasonable efficiency in solution, we will turn our attention to the development of nanodevice-based solar light-harvesting cells and the systems integration issues involved in their production,” John says. “There are many possible routes to the construction of functional solar cells based on the porphyrin nanodevices. For example, we may fabricate nanodevices in arrays on transparent surfaces, perhaps on a masked free-standing film. However, we have a lot of issues to resolve before we get to that point.”
If solar energy can be harnessed to produce pure hydrogen we will still be faced with the problems of how to store and transport the hydrogen. We need both better battery technologies and better hydrogen storage materials.
By Randall Parker at 2005 April 14 03:17 PM Energy Tech | TrackBackI continue to wonder aloud why nobody's looking into carboniferous fuel synthesis using atmospheric CO2. Octane (gasoline, roughly) has around three times the volumetric energy density of liquid H2. Maybe it's too difficult to reduce the CO2. But I do know there is some work going on CO2 reduction, but it's not aimed at this particular target. That's a shame, IMO.
I agree with Rob. A machine that turns sunlight and water into O2 and H2 is half a solution. A machine that turns sunlight, water and C02 into Octane is a complete solution. Methanol or Ethanol are 95% of a solution.
As mentioned this points back to the one thing seriously lacking in our technology, an ultrahigh capacity, light, small, rapid recharge and "cheap" battery. Even the attempts at creating the hydrogen economy are simply a left field attempt at filling this need. With such a device there would still be technological gaps that would be vexing but they would also be far easier to work around.
Anyone have any good links to theoretical battery developement?
The last thing I read about this was not on general designs but on Toshiba's new quick-charging battery. Energy density of batteries remains a big problem; Green Car Congress published a figure of about 250 Wh/l. That's almost two orders of magnitude less than octane.
Rob McMillin
Hmm well they're getting closer with power density. Re-charge cycles are improved also but still seem a bit short of acceptable assuming how expensive the batteries will be. If fuel cells work out as the only option then so be it. Still as mentioned there's the problem of transport. The recent work by a Korean scientist (and earlier by a New Zealand group) may have some application. Their concept would hold the hydrogen in a clathrate form (similare to methane hydrate). Not as vexing as compression or liquifiecation but still not ideal. At least it would be less dangerous than using ammonia (shudder). Even worse is the wholesale leg of hydrogen movement.
My ideal would be a system which could move a light truck equivalent (easier with small cars but I really don't like them, I've had friends die in sub-compacts that would have walked away if they'd be in something like a GMC Safari) with reasonable speed and acceleration, a range of at least 300+ miles and could be recharged/fueled in no more than 15 minutes.
It may turn out that a solar/wind/powergrid system producing hydrogen at myriads of small fueling stations will be the only solution. I do agree we should move on from the origional ICE. But if we go with a pure hydrogen FC system for transport it's going be be a pretty klutzy infrastructure for fueling. We really need a battery tech breakthrough. Dammit we have two space probes leaving the solar system and we still can't creat a really decent battery.
The company Hydrogen Solar has been attempting to develop technology to economically generate hydrogen from water and sunlight. It has received news coverage in Wired, Science News, and the BBC.
The company claims that it can convert sunlight energy into hydrogen with 8 percent efficiency using "tandem cells". These cells have a layer containing metal oxide particles and the company envisions installing them on rooftops of home garages. They are aiming to improve efficiency and state that "at the benchmark 10% performance level, a 7m x 7m Tandem Cell unit on a double garage roof is capable of producing enough hydrogen from sunlight to run a Mercedes A-Class vehicle 11,000 miles over a year in Los Angeles light conditions".
Battery energy density is not directly comparable to chemical fuel; the battery includes the conversion step and allows a much smaller and lighter system (electric motors have higher power/weight than piston engines).
Asking when batteries will equal the energy density of gasoline is like asking when a gasoline engine will equal the power/weight of a rocket motor. It doesn't matter. What matters is when batteries will be good enough to take over most of the job.
If you need 100 miles of fuel-free driving, you could do it with about 150 kg of li-ion batteries in something like a Prius. This volume of cells would fit into the car's floor pan without changing the design much. Such batteries have the functional necessities to do the job; the rest hinges on charge time, lifetime and price.
Valence Technology has a li-ion battery based on lithium iron phosphate, which gets rid of the expensive and thermally problematic cobalt oxide cathode. Toshiba and Altair have ultra-fine anode materials which show huge gains in charge/discharge rate and cycle lifetime. Stability and lifetime are done, the last element is cost; that will come with time and experience.
Would it bother you terribly if you could plug in your car at a rest area and have its empty batteries up to 90% in the time it took you to pee? That's what we're looking at.
Back to the porphyrins: The Sandia discovery depends on gold and platinum; they are clearly not going to be manufactured in volume. Exploitation is doing to depend on the use of much cheaper, more readily available materials.
Engineer-Poet
Yes I concure with the energy density statement you made. I realise that a comparable range requirement would require a hefty weight in batteries. While a 100 mile range Prius would be useable by many it would fall far short of adequacy for a large portion of the population (also were those range tests done under real world conditions? i.e air/heat full blast and stereo/wipers etc?). I'm on the extreme edge as an example. I periodically have to drive to an area with a 175 mile gap between filling stations.
Further, while I didn't elucidate it well earlier, better batteries would be an enabler for better use of renewables. Military uses of course would abound (I still have nightmares of older days humping 30+ lbs of batteries for my com/encryption gear, laser designater etc.). I recognize what has been mentioned here about battery improvement but I'm simply stating it's not practical yet, especially since it's still unproven if these new designs are useable or simply laboratory queens.
I periodically have to drive to an area with a 175 mile gap between filling stations.So you'd cover 100 miles on electricity and burn fuel in the sustainer for the other 75. You'd probably need a bathroom break at the far end anyway; good time to grab a quick charge.
Most people's daily driving is commuting and local trips, many of which could be fuel-free even with a very modest all-electric range. That's the beauty of the plug-in hybrid; you may only be electrifying 20 miles per trip or even per day, but "a lot of littles make a lot".
Anyway, back to porphyrins. Suppose that we find a way to make good solar converters out of them, say by coating cheap (doped) carbon nanotubes with porphyrins as the light converters. This combination splits water. If you can get the efficiency high enough, the combination of porphyrin photolytic system and fuel cell yields electricity with built-in possibilities for energy storage (metal hydrides work well). My money's on photovoltaics and batteries, but I'm not going to discount the possibilities of dark-horse technologies taking niches or even the main markets.
Engineer-poet
One question I have about the recharge possibilities of plug-in hybrids relates to the grid capacity. It would need to be expanded a great deal from current levels, especially if rapid recharge is to be viable.
[grid capacity] would need to be expanded a great deal from current levels...My numbers say otherwise, even given generous estimates of vehicle efficiency (leading to higher than realistic values of the power needed to replace petroleum). If you electrified everything overnight and spread its full demand over the hours of 7 PM to 7 AM, you'd add about 360 GW to the load. In contrast, total nameplate generating capacity in the US is about a terawatt.
especially if rapid recharge is to be viable.This is a point, but it assumes that other measures (such as vehicle-to-grid) aren't brought into play. People who want power right now could deal with people who have energy to spare and don't care if they make up the difference now or three hours from now. What happens when the guy who wants half a megawatt for the next sixty seconds is able to buy fifty kilowatts from each of the ten cars in the parking lot across the street?
If you assume widespread cogeneration things look easier too. Consider a shopping mall which is cooling with a combination of compression A/C and absorption chillers driven by the waste heat from microturbine generators. Someone hooks up and bids for half a megawatt for one minute and 30 kW for the next 4. The mall accepts the bid, shuts down 440 kW of chillers and fires up 60 kW of microturbines, then brings the compression A/C back on-line as the demand abates. Cooling demand is met timely enough that nobody notices, and the mall makes money on the arbitrage between long-term power prices and spot prices.
E-P,
There is another obvious point about car recharging: Cars could be connected to a plug which will feed them electricity only when electricity prices drop below some threshold. After all, if the car is parked for 12 hours it doesn't matter when during those 12 hours it gets recharged.
One could rig it so that if the car hasn't been recharged by, say, 5:30 AM the computer on your meter could be instructed to up the price it is willing to pay in order to recharge the car.
BTW, what do you mean by "total nameplate generating capacity"? You mean the big generation plants that power the grid?
Randall Parker said "Cars could be connected to a plug which will feed them electricity only when electricity prices drop below some threshold."
This is an excellent point, and the widespread deployment of plug-in hybrid vehicles would improve the practicality of intermittent power sources like wind and solar enormously. If a vehicle is plugged into the grid when it is at home and at work then it can be charged when power is available. It can use the energy from wind and solar systems when the wind is blowing and the sun is shining.
If there is a dynamic market price for energy then it would even be possible for vehicles to sell the energy that they have stored back into the grid when there is sufficient demand and the price increases. (This idea was suggested by Amory Lovins several years ago.)
BTW, what do you mean by "total nameplate generating capacity"? You mean the big generation plants that power the grid?That's the term used by the Department of Energy; here's their definition.
IIRC, the "base load" of the electric grid is about 40% of peak load. Suppose that peak load is about 900 GW (accounting for losses); adding another 360 GW to the base load of 360 GW ups capacity of the grid to about 80%. Losses scale roughly as load squared, so losses (heat dissipation in transformers, etc.) would be about 65% of peak. Doing this would require a different mix between base-load (coal, nuclear, combined-cycle gas) and peaking (simple-cycle gas) plants, but it could certainly be done and we wouldn't need to change much of the electrical infrastructure to do it.
Shifting from 33%-efficient simple-cycle gas plants to 55%-efficient combined-cycle gas plants would increase overall electric generation efficiency a great deal (more of the peak load would be met by more efficient plants); even if those new CC plants burned oil to help meet transport needs, the well-to-wheels efficiency would go way up and greenhouse emissions would go down.
All thie energy,stored and locked in matter,and we cannot get to it. What happened to the dream of mining helium 3 from the moon to give us limitless power from fusion reactors?
Everyone still has a problem with liquid Hydro distribution, but in fact , it can be solved by small scale (mom 'n pop)or neighborhood size generation run from methane production from your sewer lines. Has been shown that the bacteria will up production of methane if exposed to light, then darkness in a set amount. Also helps take care of a liquid waste problem, and may even help pull those nasty hormones and pharmacueticals out of the water table.