Replies to post #205442 on Zeev's Turnips Patch-No Politics (ZEEV)

[lee kramer]

Zeev: I know little of this, but isn't cold fusion an answer? If so, has progress been made? Do you think it will eventually happen?

[phill]

Zeev, I absolutely agree with your take on fuel cells not resolving the source of energy problem. My understanding, however is that there is a net savings in available/usable energy post-conversion from gasoline or ethanol to hydrogen. In the case of gasoline, the gov't claims 100% increase in energy benefit (http://www.fueleconomy.gov/feg/fcv_benefits.shtml). disclaimer: I claim no expertise whatever in the chemistry of this stuff.

And, of course, I have no idea how to measure the potential re-tooling of the delivery structure. For one thing, this appears to be an area where the technology is not at all resolved. Perhaps we are more likely to see on-vehicle conversion and the same old filling stations? At any rate, this will all be decided by corporations for which successive short-term bottom line results will continue to be the greater determining factor, no?

phill

[FinnTroll]

I basically agree Zeev. Hydrogen for FC's is not a 'cheap' fuel. I think the main attraction, however, is that it can be derived from far more sources than gasoline. From sea water using electricity from any source such as hydro, tidal, nuclear, solar, wind, coal, oil, etc. From ethanol, oil or natural gas etc. in stationary units better equipped to control pollution. As the supply of crude oil diminishes the cost of producing H with renewable energy sources may become competitive. Later of course we can always send tankers to Jupiter to pick it up for free.

[ajtj99]

There is also the safe storage and transport problem. The high pressure required to store hydrogen is enough to make anyone with a brain think twice about this as a viable alternative to internal combustion.

It would make for nice car explosions in movies, however.

[tantal]

Zeev, the hydrogen economy rests on yet-to-be-invented technologies. They include high-energy density hydrogen storage materials and high efficiency, non-silicon photovoltaic devices. To hope for a practical hydrogen "fuel tank" to put into an automobile, you need a material which can completely reversibly release and uptake nearly 10% of its total weight in hydrogen. These materials are extremely difficult to come by, since this weight requirement can be met by only the simplest of compounds containing the lightest elements. The best current material is LiAlH4, which can reversibly provide two of those hydrogen atoms stoichiometrically at relatively mild operating temperatures, but the last one is extremely difficult to remove while retaining the reversibility. There aren't many candidates which are close to this material.

On the subject of photovoltaics, for them to be truly sources of energy from the sun, the devices must produce more energy in their life cycles than is required to manufacture them, and this means that they must be made of some fairly cheap materials - plastics for the most part. Silicon solar cells are the highest efficiency available today, and I think the best ones have about 20 % efficiency. Their cost to produce and lifetime together make them a poor prospect for a renewable energy economy. The technical challenges with the so-called organic photovoltaic devices are many; not the least of which is that far too many researchers in the field are trying to improve the "Graetzel cell," an overhyped demonstration of principals with the very best efficiencies achieved of less than about 10 %, and highly irreproducible at that. The greatest challenge in PV devices is the extreme difficulty in matching of electromotive potentials; the light-harvester must be as close as possible in oxidizing power to the electron-donating material's oxidation potential, etc, and at each electron-transfer interface, you have an efficiency loss. This coupled with internal losses in the materials, which are far from optimal in properties, presents a great challenge.

My apologies for being so long-winded, but note that materials challenges are the crucial technical barriers to both hydrogen storage and photovoltaics (among other hot topics). We need some brilliant inventions in these areas to make either happen. I would think, agreeing with you, that there will be no hydrogen economy without organic photovoltaics, the greater need. I believe that we could live with relatively inefficient hydrogen storage for some time if only we had high efficiency PV devices.

I'd love to see a good deal of the funding in your 1000 crazy ideas NSF program go toward materials development. Is is damn hard work.