Electrolysis - Electrode Materials, Factors Affecting Rate...

[spamonkey8]

I'm looking into electrolysis (using table salt for the electrolyte) and I'm finding that the electrodes don't last very well and they, of course, oxidize very readily. I've tried copper, steel (many kinds available), brass, lead, and even gold plated copper, but none of them stand up. Can anyone think of something that would work better? I have access to a lot of things: tin, lead, steel, iron, copper, brass, alluminum, and more.

 

Also, I'm trying to find out what affects the rate of electrolysis the most, ie, shape of electrode or amount exposed, aspects of the power supply, temperature (warmer water allows more gas to dissolve, O2 is completely dissolved).

 

The one last thing I wanted to know was an estimate of efficiency: watt-hours per mole.

 

So many questions, really just to start an open discussion on improving the production of O2 and H2 gas. So far I've blown up a balloon with hydrogen, breathed some O2 and, of course, blown up a mixture of both.

 

Thanks everyone!

[5614]

Temperature: hot is generally better

 

Surface area: you want a bigger S.A

 

Power supply: Bigger is better (within reason!)

 

And as for reactive materials, well, just use a reactive material! Iron would rust, but that may be a bit slow, see what happens with a reactive metal as found in group 1 or 2 in the periodic table (well, group 1 wouldn't really survive long in water!)

[YT2095]

and don`t bother with house hold salt, you`ll not only make Chlorine gas but your electrodes wont last long either.

 

dillute sulphuric acid is much better

[spamonkey8]

What's the periodic table?

 

 

Had you there for a second. In the last four and a half hours, I've found out some things that have made my little interest jump a quantum leap.

 

Electrolyte & Electrodes: I found using sodium bicarbonate (simple baking soda) for the electrolyte and stainless steel for the electrodes can allow the process to proceed with no visible residue or deterioriation except that the cathode (negative/ground) gets what looks like carbon buildup (can't hurt at all). This is a major improvement from chlorine gas and chunks of oxidized metal falling off, haha! I figure if I coil the stainless steel and loop it, I can easily get the surface area I need. As far as acids, I don't know if the difference is that noticible, and I'd rather avoid them if possible. If the guys in vegas were giving odds for sodium bicarbonate vs. sulphuric acid, who would I pick?

 

Power: I've been using a computer's power supply (the 12V 10A works better than the 5V 25A to my surprise). I also used a 12VDC 200mA transformer, and though it got really hot in the use, it worked comparably well. I have a couple big-and-honkin heavy transformers from a 400w RMS stereo system that burned out and an old monitor that I can use to get some decent power. One of them is as big as the computer power supply itself, so that should be nice once I figure out what voltage it puts out.

 

Right now I'm running a test setup to make sure this pans out. The water's getting warm, but all that means is I can see less O2 bubbles and everything's happening quicker I assume. I stuck a little sketch on the back end of this post so you can see how I'd split up the gasses. I figure I can make the tubes from PVC pipe and put a valve in the tops and a little pressure gauge if I want. If one tube was 6" the other would have to be about 4.2". I would have a cap to fill it from the oxygen end so that as the H side overflowed with water, I could be sure that there was absolutely no air (read O2) in the H2 side from air left over. It wouldn't really matter in the O2 side. This ended up lots longer than I wanted it...sorry

[jdurg]

Actually, warmer water allows LESS gas to dissolve. Have you ever wondered why you keep a bottle of soda inside the fridge? It's because the colder water allows more gas to dissolve into the liquid and keeps it carbonated longer. When the temperature is warmer, the gas readily escapes the solution. (If gases dissolved more readily in warmer water, it would be damned near impossible to degas liquids).

[spamonkey8]

That sounded a little funny when I wrote it. Now what explains the less O2 production... Divine intervention always works!

 

The dissolution of the gasses really only impacts Oxygen, as it has a much higher saturation point.

 

I'm about to zip tie/tie with string/tape a baloon onto the mouth of a water bottle and see how it fills. For the electrodes, I'm poking stainless steel wire through near the bottom and using epoxy around the puncture hole. The biggest problem will be keeping the seal of the electrodes from leaking water under the pressure. All this is is really a dry run for looking for potential problems with dealing with the gasses pressurized. I might have to use 2 bottles joined so the gasses are separate and I don't blow my sweet bottom to kingdom come.

[drizzt]

use platinum for the electrodes you will get the best response.

 

and if your aying "yea right platinum i cant afford that"

well just fyi you can go down to the autoparts store and but some bosh platinum spark plugs carfully smash the cramic coating and pull out the platinum

 

i used this method to show my son electrolsis of cource if you want a bigger H production you can also use carbon rods out of batteries.

 

because platinum is too expensive

 

i usedthe ones from the sparkplugs on a small scale model but it worked great

[spamonkey8]

I have a big question! As I said before, I'm getting what looks like carbon buildup on the cathode (negative). But, with only water and sodium bicarbonate (NaHCO3), the only way to get soot like that would be with this:

 

NaHCO3 -> C + NaOH + O2

 

This is all a guess, but if the above formula is correct, I'm getting:

 

• Soot - If carbon rods will work, then a little carbon buildup can't hurt.

• Sodium hydroxide - Just fine as it is a good electrolyte as well assuming no glass or excess CO2. Plus if I add some aluminum, I get Hydrogen gas chemically. I can just make the cathode out of Al.

• Oxygen - Uh oh...

 

But wait, the cathode gives me Hydrogen gas and it's an explosive mixture to combine it with Oxygen!

[drizzt]

carbon rods will work but only if used in high pwer applications.

 

 

you should try the sulphuric acid like YT siad its a hella better electrolyte and it

would produce very good results

[akcapr]

Al will deteriorate pretty fast

[drizzt]

o and stainless steel will oxidize

so dont be fooled just cause it says stainless

[akcapr]

thats why its not called rustless steel

[Gregoriev]

ever think of using sodium hydroxide for the electrolyte? Some people recomended it to me in this forum.

 

also, i know copper will definatly dissolve away as it oxydizes, however, i hope it takes a long time to do that.

 

I would normally be happy to draw a diagram for you as far as full scale production is concerned, but alas...i am a little lazy to do that.

 

here are some hints though:

 

Use smaller PVC pipes within a larger 4" pipe. cut the little ones and cap them. These will be used to collect your hydrogen only, you should be able to cram about 40 of these into the 1 foot section of pipe. each little tube will only be 3-4 inches long. Insert cathodes and annodes into them, and be sure to drill holes in the caps and run separate pipes from them for hydrogen and oxygen. I am sure as you make it you will get good ideas as far as actual construction.

 

For something on this sale you would need about 4 PSUs, each preferably and older more rugged model of about 250-300 watts. connect the 12v and 5v lines in a roughly symetrical fasion to all the cathodes and annodes, being sure that having two electrodes of the same charge next to eachother is avoided as much as possible. Then power up this bad boy and watch the hydrgoe nform.

[calbiterol]

I have a big question! As I said before' date=' I'm getting what looks like carbon buildup on the cathode (negative). But, with only water and sodium bicarbonate (NaHCO3), the only way to get soot like that would be with this:

 

NaHCO3 -> C + NaOH + O2

[/quote']

 

I'm not sure if this is correct. It doesn't quite look right to me... I'd expect that to releace CO₂, not C + O₂. It's an aqueous solution, NaHCO_3(aq), A.K.A. Na+ _(aq) + H+ _(aq) + CO₃2- _(aq). So, technically, it's NaH₂CO₃OH. The electric current frees H₂, as you said. You said it was the same amount of hydrogen but less oxygen than before? Well, the way you have it would make it twice as much oxygen as with plain electrolysis. But I s'pose that wouldn't have to be at the electrode, would it? I can't really think of anything else though, so perhaps yours is right. Wow, I'm rambling.

 

Anyways, it's quite possible that everything I just said was wrong , 'cause I'm really too tired to put these things together right now...

 

[Edit: Perhaps this is involving the stainless steel electrodes as well? Isn't stainless an alloy of iron and chromium? Perhaps forming chromate and steel? (Chromate is sparingly soluble) Just a thought.]

 

[Edit #2: Iron(III) oxide (black rust) looks a lot like carbon. Another possibility...]

[spamonkey8]

o and stainless steel will oxidize

so dont be fooled just cause it says stainless

 

Actually the anode has remained remarkably clean over the course of a couple hours with just a slight amber color near the surface. Yes, it rusted slightly, but in that time if it were copper it would have burned away 10 times over.

[drizzt]

thats good, just wanted to make sure you knew SS oxidized

 

i have taught a few welding classes b4 and have had students swear up and down that SS will not rust......until i proved them wrong lol

[drizzt]

agian platinum would be the ideal source, i have seen a thread on here that linked to an ebay site that was selling platinum wire for cheap!

[spamonkey8]

stainless steel electrodes,Iron(III) oxide (black rust)...

It looked like carbon deposits, but it was tougher to scratch/rub off than I would guess. At this point, I'd guess the one with the chromate and steel, partially because Occam's razor points me to guess that there isn't a reaction going on that's making a base, producing O₂ gas, and blackening only one electrode. I doubt Iron III Oxide as this would be more likely to happen at the anode with Oxygen than with Hydrogen only.

 

I'm starting the balloon a-fillin... This is gonna take soooo long...

If anybody wants pictures or has anything to say, let me know

[spamonkey8]

Just a little side note. Even though the PSU I'm using can supply 25A at 5V and 10A at 12V, and 0.8A at -12V and everyone has said that current matters most, using the 12V and -12V leads gives the best results.

 

I attached a pinout for the ATX specification.

[raivo]

Just a little side note. Even though the PSU I'm using can supply 25A at 5V and 10A at 12V, and 0.8A at -12V and everyone has said that current matters most, using the 12V and -12V leads gives the best results.

 

Current depends on resistance and voltage (according to Ohms law). You have to lower resistance or increase voltege to get more current. 25A at 5V will flow through electrolyte if resistance is as low as 0.2 ohm. Resistance in your apparatus is probably much higher. If it is 100 ohms for example you get just 0.05A current when using 5V, and 0.24A when using +12V and -12V. -12V rail cant supply more than 0.5A. Something like that is probably max current you have got so far.

[spamonkey8]

So to decrease resistance, I can give the electrodes a larger surface area, place them closer together, and saturate the solution with the electrolyte (some are better than others).

 

I have another question, though. As the process goes on and I get a little rust floating around, how is the resistance affected? Also, does temperature affect the resistance?

 

I have to dig up my old multimeter.

 

Also, the contacts spark when I connect them to the power, so the resistance can't be terribly high.

[raivo]

Resistance decreases with heating and rust will not affect it much. If you use NaHCO3 as electrolyte you cant get very low resistance. Its good idea to heat this salt on hotplate half on hour so it decomposes to Na2CO3. Na2CO3 is more soluble and has lower resistance. NaOH is still better. You could also use H2SO4 but electrodes will be a problem.

 

Multimeter is great help but you have to check what are max currents it can measure. Stronger currents can destroy it.

[akcapr]

not if u use carbon

[spamonkey8]

What not if I use carbon?

 

Update: The balloon is 17 inches in circumference, the water level raised about 10mL, and it got reeeely hot.

[akcapr]

no electrode problem w/ h2so4 and carbon