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Electrolyte yields
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cjpeaceful Offline
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Post: #1
Electrolyte yields
Can someone direct me to where I might be able to find information on what types of electrolytes yield what percentages of gases? And/or the type of gases created during electrolysis (besides the hydrogen and oxygen)?

finallyME?

Anyone?
12-16-2008 01:26 PM
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cjpeaceful Offline
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RE: Electrolyte yields
Here's some more information which might better help you guys understand where I'm going with these questions.

This is a clip from another website showing you how basic electrolysis works and what is actually created. I never really thought much about the uses of various electrolytes until summer when I came across the article from MIT and their latest results using various electrolytes.

Quote:When you electrolyzed a NaCl solution, your ratio of H2/O2 was much higher than when you used a solution of - say - baking soda (NaHCO3). Suggest why the ratio of the NaCl experiment was higher than 2.

Quote:Note: There are reasons for using NaCl versus NaHCO3, and reasons for using different concentrations:

1. NaCl vs NaHCO3: The reactions in electrolysis are not usually as simple as they may seem. With NaCl as the electrolyte, you actually have these two reactions first:
* Na+ + ε- → Na°
* Cl- → Cl° + ε-

Instantly the Na° reacts with water to yield hydrogen gas: 2 Na° + H20 → 2 Na+ + H2 + 2 OH-
And 2 Cl° → Cl2, which dissolves into the water and disperses.
This explains why those of you who use NaCl as the electrolyte get large amounts of hydrogen and very little oxygen.

What you need to do is use an anion that is not readily oxidizable. While many will think of sulfate, this can be oxidized to persulfate, which is only very, very slowly unstable releasing oxygen gas. Hence, you should think of phosphate or carbonate. NaHCO3 and Na2CO3 have been chosen since they are readily available in the supermarket as baking powder and baking soda, respectively.
2. Using different concentrations: Because the ideal electrolysis reaction occurs in pure water, and because pure water is a very poor conductor of electricity, you must resort to an experiment that gives you data that approaches ideality. If 0.1M NaHCO3 gives you a proportion of H2/O2 = 4/1, you might find that 0.05 M NaHCO3 gives you 3/1, and 0.01 M gives you 2.5/1. As you can see, you are approaching the theoretical 2/1 as the concentration of electrolyte decreases. Yes, you could try 0.001 M and 0.0001 M, but those reactions would be much too slow for classroom demonstration.
12-16-2008 01:41 PM
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gtkco Offline
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RE: Electrolyte yields
I think you are on the right track CJ. I have notice that the introduction of various forms of alcohol have an affect on the gas output per amp. It doesn't just reduce the amp level of the elite. Even if I up the NaOH to get the amps back up to pre alcohol levels the output is less and significantly less is some cases. Clearly the differant molecular structure of the alcohol affect the electrolysis behavior. So I think you are right that different catalysts might do the same depending on how they cause the electrolysis. I wish I could help a little more but I am afraid that you, finallyme, and jjb are our local chemists. They are the only two guys on this forum that might be able to guide you. Good luck!
(This post was last modified: 12-16-2008 05:55 PM by gtkco.)
12-16-2008 05:53 PM
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cjpeaceful Offline
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RE: Electrolyte yields
Thanks gtkco.

It seems, depending on the electrolyte to water concentration, greatly dictates the amount of hydrogen and/or oxygen created. This is something a few people, myself included, have asked but have only been ridiculed to suggest anything different than a theoretical 2:1 hydrogen/oxygen ratios.

This may explain why some of those individuals who are still using an electrolyte other than KOH or NaOH maybe actually producing more hydrogen or oxygen per liter versus those who are using a strong base. They maybe producing more hydrogen per volume of gas. But, their trade off maybe frequent electrode changes.

Just something for everyone to ponder.
12-19-2008 10:43 AM
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Paulusgnome Offline
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RE: Electrolyte yields
CJ, there are no stupid questions, we need to ask questions in order to improve our understanding. The following is what I have picked up from this forum, elsewhere on the net(surprisingly unhelpful, actually), and reading through a chemistry textbook that was lying around home.

1) When an electrolyser is run, it splits water into its component parts, hydrogen and oxygen. Water is composed of two hydrogen atoms and one oxygen atom. So when they split you get the two gasses in a fixed 2:1 ratio.
2) The function of the electrolyte is to increase the electrical conductivity of the water because pure water is not that great a conductor. There are many substances which will do this, but some are better than others. Desirable characteristics are that it have a high solubility in water and that it not produce any undesirable by-products when electrolysed.
3) The purpose in adding alcohols (methanol, ethanol, isopropanol etc) is to depress the freezing point of the electrolyte so that it does not freeze in cold weather. These also reduce the electrical conductivity of the electrolyte, so reducing the current that the electrolyser takes.
4) Some of the electrolytes that people have tried :
  • Table Salt
  • Baking Soda
  • Vinegar
  • Citric Acid / Koolade
  • Hydrogen Peroxide
  • Sodium Hydroxide and/or Potassium Hydroxide

Table salt is sodium chloride, and in an electrolyser it splits into sodium and chlorine gas. The sodium recombines with water to form sodium hydroxide and hydrogen gas. The chlorine and hydrogen gas mix is then fed into the engine and burned, releasing some undoubtedly-nasty pollutants as the chlorine combines with the other combustion products. Chlorine will also attack aluminium alloy parts, corroding them. A bubbler filled with sodium hydroxide solution may help to cut the chlorine level a little but will not get rid of it all. IMHO a very bad choice for an electrolyte, as would be any other chlorides.

Baking soda is sodium bicarbonate, formula NaHCO3. In an electrolyser this decomposes into sodium hydroxide and CO2 gas. Whatever effect the added CO2 has on engine performance can only be detrimental. There are also legions of posts from people who have complained about baking soda rotting their 316 plates. IMHO another poor choice.

Vinegar is acetic acid. It appears to be stable under electrolysis but it has relatively poor electrical conductivity. If you can tolerate the need for larger plates to compensate for this then vinegar may be OK. Best to use white vinegar or try and get some pure acetic acid if possible.

Citric acid is the organic acid derived from citrus fruit, and I am reasonably sure that it is the citric acid in koolade that is mostly responsible fir its electrical conductivity. Like acetic acid, it appears to be stable under electrolysis but is also a poor electrical conductor. Koolade also contains other salts ('electrolytes'), some of which may pollute the gas stream.

Hydrogen peroxide decomposes under electrolysis into water and oxygen. It will go some way to fulfil CJ's wish to twiddle the hydrogen/oxygen ratio, but the hydrogen peroxide will be consumed in the process, so needing to be replenished steadily to maintain electrical conductivity and keep gas production and composition steady. IMHO fun, but ultimately a bit complicated.

Sodium hydroxide / Potassium Hydroxide. Not a lot to choose between them, both are very good and both have been industry standards for water electrolysis electrolyte for decades. Both are stable and do not produce any nasty by-products when electrolysed. Problems are that they are strongly corrosive and they do slowly erode stainless steel electrode plates. IMHO, the best choice.

There are a few others that I had thought may be worth trying out, but I have not been able to find out much about their properties in an electrolyser : sulphuric acid, nitric acid, phosphoric acid, sodium/potassium nitrates, suphates and phosphates, calcium hydroxide. I'm sure there are others too.

Note I've written the above off the top of my head from memory, but I am reasonably sure that I can find references for most of it, if anyone wants them.

Best of luck with your experimentation.
Mark aka Paulusgnome
12-19-2008 01:52 PM
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