Naked Science Forum
Non Life Sciences => Technology => Topic started by: McKay on 13/03/2014 07:23:24
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Water and some other molecules have a property called autoionization. That means they spontaneously ionize themselves just to recombine a picosecond later. The point is -the energy for this to happen is taken from the ambient heat (which is not perfectly uniform -some molecules have more speed than others). Could this phenomenon be utilized to generate electric current from these vibrations in matter that we know as temperature? Perhaps somehow similar as in photovoltaic cells -as soon as an electron-hole pair is created by a photon they are separated and forced to go through the p-n junction. In this case, though, there would be ions created, not free electrons, but still-could it somehow be harnessed?
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You need extremely high temperatures to dissociate water into hydrogen and oxygen, if that's what you're after.
Autoionization with no substantial separation of charge will result in recombination. One can put energy into the system by applying an electric field and separating the ions somewhat, but this won't store much energy, and is not a convenient way to do that anyway. With enough of an applied potential, and suitable electrode materials, redox reactions can be performed on the ions, producing hydrogen and oxygen, which store a lot of energy (splitting one liter of water stores almost 16 MJ or 4.5 kWh, optimally).
Thermal energy input is useful here too, though. The hotter the water is, the less electronic energy needs to be applied. Though this has more to do with the large increase in entropy that occurs when hydrogen and oxygen are produced from liquid water than with the change in autoionization of water. Though the increased ionization at higher temperatures does also allow for greater reaction rates.
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You may look at thermoelectric generators. For example the Seebeck Effect (http://en.wikipedia.org/wiki/Seebeck_effect#Seebeck_effect). However, apparently it creates a current loop based on a magnetic field.
Of course, most useful power generation would require a current loop.
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Autoionization with no substantial separation of charge will result in recombination.
Well, yes, but doesnt the same apply to ordinary photo voltaic cells? I mean - the electron-hole pair is created and is immediately separated by the electric field from the p-n junction..
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I am generally interested in the thermal background energy (vibrations of particles).
I know thermodynamics don not allow energy generation from a source where there is no energy difference - matter at thermal equilibrium, in this case.
But the thing about temperature and internal molecular/ atomic vibration is that it is not really ever at thermal equilibrium - some particles are moving faster than others, arent they? What we measure as equal temperature is just the average of all the particle different vibration/ motion speeds..
Is there no way to take advantage of that?