Slashdot Mirror
Micromotors Race About By Turning Water Into Hydrogen Gas
MTorrice writes "Microscopic particles of aluminum and gallium rocket around using water as their fuel. The particles, which are 20 micrometers in diameter, are asymmetric: A chemical reaction on the back side of the particle forms hydrogen gas bubbles that propel the motor forward. Over the past several years, bioengineers have built micro- and nanosized rockets that zip through liquids, fueled by chemical reactions between the materials that make up the rockets and their environments. The engineers hope someday these tiny motors could help deliver cargo, such as drugs, in people. Unfortunately, many of these motors require toxic hydrogen peroxide as fuel source, limiting their use in the body. To overcome that constraint, the new micromotors harness a well-known reaction between aluminum and water to produce hydrogen gas."
Aluminum oxide byproduct.
I've been familiar with this reaction for awhile. You can see youtube videos of it. Gallium is expensive but can be recycled from the waste making the process a fairly reasonable method of transporting energy in a lightweight, and compact way.
This is a clever application and I will keep it in mind as a "gas generator", rocket, or source of pneumatic pressure.
argh, again this kind of misleading headline that makes the people who only read the headline think a perpetual machine is finally invented.
The energy comes from aluminium, aluminium "burning" into aluminium-oxide.
Putting the "converting water into hydrogen" into headline is misleading reporting.
There's no such thing as a free lunch. Any energy you hope to get out of burning hydrogen as a fuel has to have been put into it first. The key concept you're looking for is Gibbs Free Energy - a measure of the chemical energy potential of a mole of molecules. H2 and O2 have fairly high Gibbs free energies, while water is very low. So combining H2 and O2 to make H2O releases a lot of energy. But converting H2O back into H2 and O2 requires just as much energy as was released (more in fact, due to inefficiencies). There's no shortcut, as that would violate conservation of energy.
The only way to cheaply make H2 for fuel is to use substances which start off with high Gibbs free energies. You're probably familiar with many of them - methane, propane, various petroleum products, as well as alcohols and sugars/wood. Converting these substances to H2 for fuel is pretty much the same as burning them in an internal combustion engine, except with additional intermediate steps and huge storage, transportation,and delivery complications. There's an advantage in that there's no pesky carbon, nitrogen, and sulfur in the second step (hydrogen -> water) so we don't get CO2, nitrous oxides, and sulfides as byproducts. But you still need to deal with those byproducts in the first step (fuel -> hydrogen). So it's questionable whether the tradeoff is worth it.
Incidentally, this is why many people refer to hydrogen as a battery, not a fuel. Raw hydrogen gas is pretty much non-existent on this planet. So you're not getting free energy from the hydrogen. You're taking energy from other sources (burning coal or petroleum, nuclear, hydro, wind, solar) and storing it by converting something into hydrogen gas, then releasing that energy when you burn the hydrogen (well, releasing what's left after efficiency losses). Any energy calculation of the hydrogen economy has to take into account the efficiency losses due to this multi-step conversion process. It's almost bad enough to knock a hydrogen fuel cell car's efficiency down to the efficiency of an ICE gasoline car. (60% efficient fuel cell * 60% efficient hydrolysis = 36% efficiency. Modern ICEs are close to 30% efficient.)
In TFA's case, the energy used to convert aluminum oxide into metallic aluminum is used to liberate the H2 from the H2O (the Al being converted to Al2O3 by the extra oxygen in the process). So it's almost certainly wasting more energy than if you just did straight electrolysis on the water. The only benefit is that aluminum is very compact and easy to handle as a fuel source, much more so than hydrogen or storing electricity in a battery.