Inexpensive electrode material

[Joshua Siegel]

Hi everybody, I'm a bit new to seperating hydrogen/oxygen from water. I have an idea that I want to try with pipes of differing diameters, but I don't know what to use.

Here's what I've researched up to now, in terms of pipe material:
Aluminum - no go, the sodium hydroxide eats it away.
Steel - nope, rust forms and stops electrolysis.
Copper - produces chlorine gas, no.
Stainless steel - Works, eaten away slowly, but expensive for pipe. 304 stainless is $10 per foot and I need 40 feet. Plus, most places have a minimum order of 1,000 feet.
Brass - Unknown - this is one I'd like to find out a bit more about.
Conducive paint on PVC - Could work, but hard to coat, sensitive to scratches, and $100 a gallon.
Conductive plastics - Where can I find these? HDLP maybe, but that's expensive and I haven't seen it tested anywhere before.
Carbon pipes/high carbon steel - Should be ok, but hard to find and expensive.
Galvanized steel - no, rusts once the zinc is eaten away.

Has anyone had good results with a material I haven't listed? Has anyone tried brass? I'd like to get my electrolysis cells built this weekend, but finding 2.25/2.5" diameter pipes in a reasonable material at a fair price is more difficult than I imagined. No local scrap metal places sell scrap, they just recycle it. Muffler shops don't have stainless, and home depot only has galvanized. Does anybody know what fence posts are made from? I'd guess galvanized.

The other thing I was thinking of was the use of a different electrolyte, as the only reason the aluminum wouldn't work is because of the lye. I'd say salt, but that makes chlorine gas. Any help is appreciated, I'll keep you posted with my progress!

[Bob Boyce]

It looks like you've paid attention to posts about materials.

Brass is a copper alloy and behaves like copper when used as an electrode. Copper only produces chlorine when used in combination with a chlorine based compound. But copper and brass do erode very rapidly.

Carbon materials disintegrate pretty rapidly and produce both carbon monoxide to a very large degree, and carbon dioxide to a much lesser degree.

Most conductive plastics have conductive particles added into the mixture, and once the conductive particles are eroded away, the plastic becomes porous and is no longer conductive.

Aluminum erodes rapidly even if not exposed to NaOH.



The problem that you are trying to solve is basically resistance to electrodeposition (electroplating). Many materials that have good chemical resistance, such as gold, are also very good at being eroded from the anode and electrodeposited onto the cathode by current flow.

You are right in that it is not just the metal alone, but also a catalytic reaction of the metal in combination with the catalyst in the electrolyte.

Much materials research was done, more than almost any phase of the experiment. The goal was to find a workable lasting combination of metal and catalyst at the least cost. I know that stainless steel is expensive, but alternatives that will hold up to the electrochemical processes are more exotic and even more expensive.

I wish I had better news for you in this regard. If you are not going to be exposing your electrodes to chlorine based compounds, you can get pretty good operational performance out of lower grades of stainless steel, but that is the best advice I can offer.

Usually if you check around you can find a scrapyard that deals in alloys that will sell scrap stainless steel by weight. If it's anything like here you may have to drive 3 or 4 hours each way to go there.

Bob

[thrival]

Bob:

What about coating the electrodes with dielectric? Now you have (+), (-) capacitive plates.

--thrival

P.S. Please introduce me to your girlfriend!

[Bob Boyce]

Dielectric plated electrodes, hmmm. Sounds like it would behave much like a capacitor and stop current flow once charged. I'm not sure what would happen then because the electrochemical reaction I am familiar with requires a continuous current flow. Capacitive coupling would block the DC flow and only pass AC components. Could be worth a try I guess if you could find a dielectric material that can withstand the chemistry involved.

Bob

[Joshua Siegel]

Thanks for the replies, looks like I'll be best off calling a few more scrap metal places around here. There's a guy on ebay selling the tube (SS304) in large diameter for $9/foot and small diameter for $7/foot. The problem is that he's 90 minutes away, so it doesn't make sense to do a proof of concent and I'm not about to shell out $160 or something for an idea I dont know works. If worse comes to worse, I'll make him a low-ball offer for the 16 feet I need. Can SS tube be cut with just a hacksaw? Also, how will I 'sand' the inside, or is the coating conductive enough that its trivial?

[thrival]

Joshua:

Plumbing contractors often have pieces of stainless tubing laying around, that's where I found mine. It's a real b!tch to cut, might want to borrow a saw-zall.

Bob:

I understand about capacitive DC blocking current flow, but isn't it really about charge? One plate attracts hydrogen and the other oxygen. We're not trying to electroplate anything. What if the water/electrolyte was moving, flowing through the plates, as in dielectrically coated screens? Me thinks the flow would be constantly carrying the charge away, so the capacitive plates would need to be kept replenished with DC pulses. Screens might actually have more surface area than plates, as bubbles can form inside the little squares. The flow of water wouldn't let them stay there though.

[Bob Boyce]

[thrival]

[Bob Boyce]

[thrival]

[Bob Boyce]

[johnh]

[thrival]

[johnh]

[Bob Boyce]

JohnH

If I understand him right now, he's planning on passing water vapor through dielectric coated screens to see if pulsed HV DC electrostatic potential will rip apart the water molecules of the water vapor.

Bob