Hydrogen Product By Photovoltaic Electolytic Cell

[Turtle]

That would be your cathode then. Your cathode really shouldn't oxidize like that - nor form a sludge. That is odd. Let me think on this...

 

You weren't getting any oxygen right? I'm guessing the chlorine ion was being oxidized to chlorine gas that was then immediately redissolved. So, the side with no gas would have to be the positive anode - which would confirm your terminals but make the sludge an oddity.

 

Ok, still thinking...

 

Correct; no Oxygen, or more properly no gas bubbles, accumulated in the vessel over the Positive terminal. I read in your link about the Chlorine gas at the Anode in a Sodium Chloride electrolyte, but then puzzled about where it went. I'll stay tuned.

 

Oh, there was that Yellow Prussiate(sp) or some such a matter that was added as an anti-caking agent to the salt I used. I don't recall if it was this thread I mentioned it in or another. Edit: post #29 has that reference.

[modest]

Ok Turtle,

 

I just read closer over your very excellent thread and think I have a better idea of what happened now. Sorry I was probably confusing last night as I was most tired.

 

Next, and somewhat puzzling, is the positive terminal is not bubbling that I can tell and the amount of collected Oxygen looks pretty much the same to me as yesterday. I may be losing the gas out through the electrolyte soaked lead wire I mentioned last post. :(

 

There is no real way to know if you collected oxygen or chlorine that first day or two. It depends on how much salt you had in the mix. However, with this setup it would not have been unexpected to have produced neither oxygen nor chlorine (or indeed any gas) at the anode. The reason for this:

 

Chlorine and hydroxide are not the only anions fighting to give electrons to the positive side of the cell. There is another player in the form of copper. Even if your electrolyte has no solution of copper, it can strip the anode itself to use as a substance for oxidation. It dissolves as it gives up electrons - copper is known as a soluble anode in this situation.

 

You can see that copper wants to give its electrons to the system more than the other anions by looking at this list:

 

Standard electrode potential (data page) - Wikipedia, the free encyclopedia

 

where you will see the half-reaction for copper (+0.340) is smaller or more negative than hydroxide or chlorine (at about .4 and 1.4) meaning it wants to be oxidized more than the other anions. So copper is starting to dissolve and as it does so, less oxygen and really no oxygen is produced.

 

Looking around a bit, I found that the positive electrode was completely gone, electrolyzed away. I'm using #12 or #14 braided copper wire, so I see already that's not the best choice. Anyway, I just stripped back more wire on the lead and set it going again. On the negative side, the electrode on the other hand is growing.

 

Yep, Yep. The copper gives up its electrons at the anode, goes into solution, moves to the cathode where it accepts an electron. Electroplating it is.

 

It sounds like, however, the electroplating is not proceeding perfectly. For whatever reason (funky copper alloy most likely) not all the electricity is going toward reducing the copper-II that's in solution and binding it to the cathode. Some electricity is clearly reducing hydrogen.

 

If both your electrodes were pure copper (most importantly, your negative) and your electrolyte were good and proper (I don't mean this as a critique) then you would expect little to no bubbles. I've heard people complain about hydrogen bubbles ruining what they're electroplating, so it is obviously something that can happen even with an intentional plating setup.

 

Update Dusk: Activity is falling off as night sets. Even after stripping new wire, I saw no bubblage in the positive electrode Oxygen producing side. The bubblage that is in that bottle may be at least 1/2 accounted for by air trapped when I originally filled it. :hihi: Hmmm... Could be either it's leaking out the conductor, or I have too little voltage and/or amperage.

 

At this point the water is filling faster with copper ions in solution than it is bonding to the negative cathode. So, the solution is becoming more and more metallic. The copper is probably starting to oxidize and come out of solution where it can.

 

After disturbing the electrodes, the negative electrode shed a bunch of fine brownish-yellow-orange particles so that the entire electrolyte in the bottle is now distinctly ooky, and the electrolyte in the main cell is becoming ookier by the time-step.

 

Indeed, it sounds like it became over saturated with copper that was not able to properly bond to the cathode which oxidized, came out of solution, and became yucky.

 

Update Day 4, Noon: I replaced the positive electrode with a copper rivet and hot-melt glued the edge where the insulation stops/begins. Still little to no Oxygen collecting, but the Hydrogen side is bubbling away and the bottle has collected a wonderful amount of ooky goo. I wonder if it still tastes salty?

 

So it surely sounds like that's what happened. I probably once again haven't explained very well at all. Feel free to poke holes in my theory.

 

 

Which makes me wonder, are you planing on doing this setup again? I love the idea of the photo-voltaic and I think everything would work perfectly if you used electrodes made of any conductive material that is below hydrogen (or negative) on this list:

 

Standard electrode potential (data page) - Wikipedia, the free encyclopedia

 

And wikipedia says this about an appropriate electrolyte:

 

The following cations have lower electrode potential than H+ and are therefore suitable for use as electrolyte cations: Li+, Rb+, K+, Cs+, Ba2+, Sr2+, Ca2+, Na+, and Mg2+. Sodium and lithium are frequently used, as they form inexpensive, soluble salts.

 

Electrolysis of water - Wikipedia, the free encyclopedia

 

Come to think of it, I think I have an extra solar... humm...

[freeztar]

Good post Modest!

 

Na as an electrode?!

How does that work? (without reacting with the water)

[Moontanman]

Have you considered that the sludge might be sodium hydroxide or am I missing something. I have run an experiment to electrolyze salty water but I used a high voltage high amperage DC current. I got a huge amount of chlorine in just twelve hours but my energy input was no doubt many times higher than yours using photvoltaic cells. I used some where around 200 volts DC, I don't remember the amps now but it was just below the point at which a huge spark would jump the 36" between the electrodes in the brine and boil the water.

 

(Why is it called tourist season if can't I shoot them?)

[Pyrotex]

Day 2: Noon - Everything is gray and not a patch of clear sky to be had, but the panel is happily providing a steady 15 Volts. As we might expect, there is more accumulated Hydrogen than Oxygen...nearly twice as much it looks like...hat's all I got. :eek: :confused:

Since the formula for water is H2O, you should expect twice as much volume of hydrogen as for oxygen.

 

The gas in the bottles will be at normal (standard) pressure. This is because several inches of water doesn't generate enough water pressure. If you do this under about 16 feet of water (from memory here), you would have the gases at double standard pressure. The volumes would be halved.

 

To pressurize your gases, you will need a pump. And I wouldn't use glass bottles! :) :)

[modest]

Good post Modest! :eek:

 

Na as an electrode?!

How does that work? (without reacting with the water)

 

Good eye! I should have added the qualification that it isn't corrosive or explosive :confused:

 

//EDIT, this site is better for comparing metals to use as electrodes

Electrochemical Series (Corrosion Reactions) for Common Metals

//edit

 

Have you considered that the sludge might be sodium hydroxide or am I missing something.

 

Since no chlorine was liberated, we would expect no great amount of NaOH. The sodium would rather bond with chlorine, so if a precipitate had to form, I'd reckon it would be NaCl.

 

 

I have run an experiment to electrolyze salty water but I used a high voltage high amperage DC current. I got a huge amount of chlorine in just twelve hours but my energy input was no doubt many times higher than yours using photvoltaic cells. I used some where around 200 volts DC, I don't remember the amps now but it was just below the point at which a huge spark would jump the 36" between the electrodes in the brine and boil the water.

 

Cool. Isn't it hard to imagine (it is for me at least) that navy subs and even the ISS use this process for life support? I wonder how much energy is needed per human life to support in this manner.

 

-modest