July 29, 2008

Zinc just keeps coming up in my posts

Al Fin Energy has a great article on a Zinc/Bromine battery that purports 5 times the energy density of a Lithium ion battery of similar size. Even if they end up being the same energy density, it's still a great step. Zinc is dirt cheap and safe to mine. If we went whole-hog using it for transportation, though, we might finally have to ditch pennies.

As ever, listen to the "end is near" crowd only with a large grain of NaCl. Better electric/energy storage and an expanded electrical grid are coming, and a post-oil future with them. In the meanwhile, we should be drilling everywhere we can.

In the short term, we can burn our own oil and save some cash. In the medium term (after we don't need it), we can sell it to the OPEC nations after they run out. Cackling madly while we do this is, of course, optional.

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July 13, 2008

Pennies = power? (reposted from LJ)

Bare with me, because this is either the worst or best idea I've had this week. It definitely gave me giggles when I thought of it. Sadly, it was not quite mad scientist cackling. I'm saving that for something bigger.

US penny = Copper clad zinc ingot (97.5% Zn, 2.5% Cu).

The Zinc-air battery (or Fuel Cell) uses zinc and atmospheric oxygen as a fuel, generating current through the oxidation of zinc. It would require some amount of copper wire to create conducting leads at the anode and cathode.

Copper and zinc have different reactivities, and this difference could be exploited to remove the copper jacket from the zinc ingot. This link shows a method for using 6M HCl to dissolve the copper and recover the zinc, but doesn't suggest a good way to recover the copper. That will take some looking around, but it's not critical to the project.

How many pennies would it take to build a Zn-ZnO battery that equaled the power output of a AA battery? Is there any chance that it's fewer pennies than such a battery would cost? It's not likely, by any means, but this is government we're talking about. Even if it isn't cost-effective, I've got loads of pennies to try this with just as an experiment in fabricating a simple battery (it's not technically a fuel cell in this case unless you can reverse the Zn-ZnO reaction and store new energy).

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DCFC links and thoughts, reposted from my LJ

Warning: Science content.

Fuel Cell basics
Solid Oxide Fuel Cell (SOFC) basics
Molten Carbonate Fuel Cell (MCFC) basics
SARA DCFC research (MCFC approach)
CellTech DCFC research (SOFC with a twist)

In all cases, DCFCs operate at between 700 and 850 degrees centigrade (reaction temperature). A reasonably sized residential cell would be intended for combined heat and power (CHP). Because there's no thermal cycle, per se, just direct chemical conversion, you can pretty much sneer arrogantly at the Carnot limit. In all cases, theoretical efficiency is ~70% for the overall system (compare to conventional coal at ~25-40%). The input fuel can vary from graphite powder to carbon black to methanol (ground diamond could theoretically work). The waste product is CO2, but it's easily captured if you care about that (I don't). The listed temperature suggests that these might be excellent candidates for thermoelectric conversion if electricity is more greatly desired than heat, and partial thermoelectric conversion might improve the overall efficiency in any case. Most of the papers I've read were written prior to the recent revolution in thermoelectrics, so that's worth looking into. Further, I can easily envision a situation utilizing all the waste from such a cell to heat simultaneously heat a greenhouse and supply it with extra CO2 to stimulate plant growth -- nearly ideal for an arctic or antarctic enclosed farm. Or Michigan in Winter, say.

This sort of cell could be scaled for use in a car, but the high temperature might be a very serious issue, which is likely why Honda went with the methanol-reforming cells for their super-expensive fuel cell concept car. They run at a much lower operating temperature (250-300 degrees centigrade, comparable to an internal combustion engine), and the waste from them is H2O rather than CO2 (H2O is actually the stronger greenhouse gas, but it can be caught and condensed at some cost to efficiency). However, you have to carry around a cell full of methanol as a hydrogen source, and the efficiency of such cells is much lower (25-40%). This is another area where thermoelectric insulation could make a very serious difference in the utility of such a cell for this very desirable application.

I shall continue to ponder. Both the companies I listed above did literally start as garage shops. I'm not likely to beat them to commercialization, but it would be fun to build a cell as a project. Wouldn't mind heating my house with graphite or carbon black, for that matter.

Posted by: leoncaruthers at 07:40 AM | No Comments | Add Comment
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