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IEEE Spectrum has a story on research into graphene which shows protons can pass through the material. One of the key properties of graphene was that it was previously thought to be impermeable to gases and liquids:
But as Geim and his colleagues discovered, in research that was published in the journal Nature, monolayers of graphene and boron nitride are highly permeable to thermal protons under ambient conditions. So hydrogen atoms stripped of their electrons could pass right through the one-atom-thick materials.
This has significant applications in fuel cells, since proton exchange membrane fuel cells require a barrier that only passes protons, and this discovery could be used to improve the efficiency of existing designs. However in addition to this it could also allow the cells to extract hydrogen directly from humid air
It is conceivable, based on this research, that hydrogen production could be combined with the fuel cell itself to make what would amount to a mobile electric generator fueled simply by hydrogen present in air.
“When you know how it should work, it is a very simple setup,” said Marcelo Lozada-Hidalgo, a PhD student and corresponding author of this paper, in a press release. “You put a hydrogen-containing gas on one side, apply a small electric current, and collect pure hydrogen on the other side. This hydrogen can then be burned in a fuel cell.”
Additional detail is available at Science Daily and in the original press release from the University of Manchester.
(Score: 2) by Zinho on Friday December 12 2014, @06:28PM
... why does the purpose of the fuel cell HAVE to be to produce electricity?
The answer to this question is easy; that's what fuel cells [wikipedia.org] do. If it doesn't take in fuel and oxidizer and produce water + electricity then it's not a fuel cell.
I was pitting the efficiency of electrolysis plus an internal combustion engine against the efficiency of an electric motor
OK, that's reasonable. Bear with me for a bit.
The first big obstacle you'll run into is the very high efficiency of electric motors: good ones run up to 94% under the right conditions, and degrade to about 78% under poor conditions [1]. These are practical efficiency measurements, not theoretical; electric motors are really that good.
In contrast, an internal combustion engine (I.C.E.) running the Carnot cycle (impossible) with H2 and ambient air [wikipedia.org] as fuel/oxidizer will run at a theoretical maximum of ~91%; real engines use the Otto cycle [wikipedia.org] which is limited by the autoignition temperature [wikipedia.org] of the fuel, which puts a ceiling on compression ratio.[2] Gasoline engines are limited to about 60% efficiency due to this; a back-of-the-envelope calc based on H2 autoignition suggests we could increase compression by half[3] and boost ideal H2 Otto efficiency to 66%. These are again theoretical maximum values, in practice they will be lower (55% or less would not surprise me).
That gap between 90% and 66% is a lot to make up for. To beat the efficiency of running a motor off of the battery you would literally need to extract 36% more energy potential in H2 + O2 during your electrolysis stage than you spent on electricity to operate the separator (0.9 = 1.36 * 0.66); this is a definitive example of an "over unity" device [4]. You're not going to get efficiency greater than 1 on any process without extracting more energy from somewhere, even with an efficient catalyst (as pointed out to me in another part [soylentnews.org] of this thread). So no, regardless of how efficiently you perform electrolysis it will never catch up to just running an electric motor off of the battery.
Thermodynamics is a harsh mistress.
[1] source [energy.gov], PDF warning, see attachment C on page 13
[2] if you want to do your own math on this, remember that you need to convert to Absolute temperature scales; add 273.15 degrees to Celsius to get Kelvin. Any math for Thermodynamics that asks for temperature assumes you're on a temperature scale that starts at absolute zero instead of some phase transition of water.
[3] I used the Ideal Gas Law [wikipedia.org] as my base for this calculation, which makes assumptions about temperatures and pressures being around 20 C and 1 Atm. Given the high temperatures and pressures typical of the Otto cycle those assumptions may break down making my estimate incorrect, but it's probably close.
[4] Beating this dead horse some more: basically to make electrolysis even an option, you'd need to start with an I.C.E. more efficient than an electric motor. Carnot's theorem says you're going to fall short there when using Hydrogen, regardless of how good your engine is.
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