Sciencemadness Discussion Board

Synthesis of H2SO4 via CuSO4 Electrolysis - Few Questions

Sniffity - 16-11-2015 at 13:44


I'm going to attempt a synthesis of H2SO4, by electrolysis of a saturated CuSO4 solution. This is actually my first synthesis via electrolysis, so I have a few questions which I couldn't find an answer to via research. D:

I've done my research through this forum, particularly on which anode to use. I've narrowed it down to three options: Platinum, MMO and Graphite.

Now, I've found this on ebay:

It's a platinized titanium electrode.

Three questions on this:
1-Does the price seem fair? So far it's the cheapest I've been able to find.
2-The sticky listed on this forum, on anodes for chlorate and perchlorate synthesis, says that the rate of corrosion for platinum electrodes is non neglibible. Is this also true for synthesis not involving chlorates/perchlorates? Will my electrode corrode?
3-Does it matter that it's not pure platinum, and instead is a platinum coated titanium electrode?

Now; on the possibility of using MMO.... Obviously, my CATHODE will be copper. I was planning on using some copper wire I have available, it's not too thin but not too wide either. MMO is usually sold as a mesh, which means my anode will be way, way bigger than my cathode..

Couple of questions here too:
4.- Should I have the mesh go all around the insides of the beaker?
5.- Or should I just cut a bit off the mesh and use that as my anode?
6.- Is there any problem if one of my electrodes is significantly bigger than the other?

As for graphite, I've heard that it corrodes horrendously, using contaminating everything you might want to recover...
7.- Is this enough to rule it out as my possible anode?

8.- What would you recommend as an anode for this synthesis?

j_sum1 - 16-11-2015 at 17:20

Graphite will erode. Quite quickly in many cases. You can put it in a cloth sleeve to contain the dust but mostly it is a pain.
MMO will die. I know this. I killed one.
Pt on Ti will work ok. It is expensive. If you damage the Pt in any way then the exposed Ti is worse than useless.

I use a strip of lead flashing of the kind that is used by roofers. It builds up a nice PbO2 layer and works like a charm. Occasionally at the start of a run you find that the resistance is high but it comes down after an hour or so.
I haven't really tried using high current density. I have a regulated power supply and run batches of 50-100g of CuSO4 at a time. The vessel I use is a plastic peanut butter jar and the cathode is a copper wire. I adjust the current so that a batch is done in 24 hours. It is slow, but works well.

My next adventure in this direction will be to use MnSO4 since I have found a suitable local supply. I am also looking at ways of recycling the MnO2 produced by bubbling SO2. That will give me a route from sulfur to sulfuric acid that will meet my needs.

Sniffity - 16-11-2015 at 17:32

I saw NurdRage's synthesis of H2SO4 and it was a real messy result at the end due to corrosion of the graphite electrode, as you point out. I'm looking as far away from graphite as I can.

How exactly did you kill your MMO? :o Do you use the whole mesh or cut off a piece? Why? Is there any problem if there's a diffferent size between cathode and anode?

Also, how do you handle Pb without the toxicity issue? I'm reluctant to use Pb due to the risk involved.

Giving CuSO4s solubility, I'm guessing if you use 100g you used way more than 1 litre, correct? Would there be any issue in me heating up the CuSO4 solution so I can dissolve more CuSO4? As in running an electrolysis in a beaker with my magnetic stirrer hotplate below, under constant heating, using a supersaturated CuSO4 solution?


j_sum1 - 16-11-2015 at 17:47

The jar is maybe 600mL. 100g dissolves with difficulty. If there are a few undissolved granules at the bottom that matters little. Often I add more CuSO4 to a batch already done. It dissolves fine and then there is less boiling down needed.

MMO will die when the concentration of H2SO4 gets too high. (And too high is not really that much in this case.) I am not sure whether it is a passive oxide layer or whether some of the coating is dissolved. I suspect the latter. My batches at this time had a green colour that I could not get rid of.

The copper cathode quickly builds up to a thick mass after a few runs. Making sure you have enough surface area when you start is probably a good idea. Otherwise you will drop a bit of copper powder and that can be annoying.

I have the lead flashing bent into a curve and wrapped around half the circumference of the jar. It is bigger than the cathode but that is ok.

Any lead that reacts forms the PbO2 which is pretty solid on the electrode. (And that is not much at all.) I haven't been worried about the toxicity. Gloves are probably a sensible precaution, but the advantage is that you are not generating soluble Pb compounds. If you are worried, then mix up a spray bottle of sodium carbonate and spray everything down. PbCO3 is highly insoluble and probably the safest form you can get it in. Wipe down with a paper towel and dispose in solid waste.

NedsHead - 16-11-2015 at 20:13

what are peoples opinion on this cheap platinized titanium electrode?

claims to have a 5.0 micrometre coating

j_sum1 - 16-11-2015 at 21:03

Quote: Originally posted by NedsHead  
what are peoples opinion on this cheap platinized titanium electrode?

claims to have a 5.0 micrometre coating

Hard to tell from a pic.
The fact that they specify conditions of use tells you something. It always helps to be patient and keep your current density low. But 1-2V is a bit restrictive. I'd be a bit suspicious. But then, what have you got to lose at that price?