9
$\begingroup$

What is highest water pressure at which electrolysis can be performed to derive hydrogen and oxygen? Does the dielectric constant of water, which which lowers as pressure increases, have an effect on this?

$\endgroup$

2 Answers 2

2
$\begingroup$

A high-pressure environment tends to favor liquids over gases, insofar as liquids have higher density. So the higher pressure it is, the higher voltage you need to apply to make the reaction H2O --> H2+O2 occur.

But, with a high enough voltage, it should always be possible. ANY electrolytic reaction will eventually occur if you crank up the voltage high enough. Electrolysis only becomes impossible (in practice) (impossible at any voltage), if competing reactions are favored. I'm not sure what the competing reactions would be for electrolyzing pure water in a high-pressure environment. For example, presumably, H2O --> H2 + O3 (ozone gas) would be favored over H2O --> H2 + O2 at high enough pressure.

It's impossible to be quantitative here, because the catalyst and reaction mechanism also make a huge difference to favor one reaction over another. It's not enough to JUST calculate free energies.

$\endgroup$
2
  • $\begingroup$ Why that speculations on competing reactions? Do those make electrolysis impossible? -1 $\endgroup$
    – Georg
    Nov 4, 2011 at 18:47
  • 1
    $\begingroup$ @Georg -- You're asking "Why do competing reactions make electrolysis impossible?"? If you are trying to create a certain reaction A -->B at your electrodes, but a different reaction A-->C is going at a trillion times the rate of A-->B, then you'll obviously get a negligible amount of B. $\endgroup$ Nov 5, 2011 at 12:41
-2
$\begingroup$

for each gas there is the maximum compressibility factor (Q); and since we have two products hydrogen and oxygen we go by the lowest (Q) which is for oxygen therefore in case of water electrolysis under high pressure you expect your reaction to stop when the pressure inside reaches (Q) . now to find (Q). how we do that? for a gas you need to see how much is its density when it`s liquid ( liter per kg as example) then the fifth of that should be the maximum density you can get by any given pressure because after that pressure you would cause the atoms to fuse which means potentially releasing the Energy MC^2

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.