Sciencemadness Discussion Board

How to make manganese dioxide electrodes

TriiodideFrog - 14-12-2020 at 20:57

Does anyone know how to make manganese dioxide electrodes from manganese dioxide? Thanks in advance:)

Sulaiman - 15-12-2020 at 00:28

You can search like this https://www.google.com/search?safe=active&sxsrf=ALeKk01n...

mysteriusbhoice - 16-12-2020 at 00:37

you need manganese nitrate which u can start all the way from MnO2 from batteries.
dissolve in HCl and filter.
then dry and bake at 400 Celsius so only MnCl2 survives
react with baking soda to make MnCO3 and then react that with nitric acid.

DraconicAcid - 16-12-2020 at 00:40

I sMnO2 really conductive enough to make electrodes out of it?

B(a)P - 16-12-2020 at 01:07

Quote: Originally posted by DraconicAcid  
I sMnO2 really conductive enough to make electrodes out of it?


I have tried it and it works, kind of. You wouldn't want to be making a kg of chlorate, but for very small scale and low amperage it does work. I gave up in frustration at the low rate of conversion from chloride to chlorate and the high erosion rate of the electrode. I also ended up with plenty of permanganate forming in the electrolyte. It was a fun experiment, but will not give you useful quantities of chlorate if that is what you are after in my experience. I have read that others have had success though so maybe it is just me. I pretty much followed this Nurdrage video exactly.
I didn't ever try it for HHO if that is what you are after. Best of luck!
https://www.youtube.com/watch?v=BjKYiu8eKa8

j_sum1 - 16-12-2020 at 04:30

Quote: Originally posted by mysteriusbhoice  
you need manganese nitrate which u can start all the way from MnO2 from batteries.


Just be aware that you will produce a lot of chlorine gas doing this. With HCl it is a great foaming mess frothing out of your beaker as well as giving off chlorine.
You don't want any surprises.

mysteriusbhoice - 16-12-2020 at 06:32

overall for chlorate vacuum epoxy resin impregnated graphite doesnt errode and is a good as EDM graphite and lasts really long!

yobbo II - 16-12-2020 at 19:19

See attached.

These anodes last a long time and will make kg of stuff

Wont make perchlorate

Yob

Attachment: MnO2 Anodes.pdf (121kB)
This file has been downloaded 414 times


MnO2 keeps flaking

BAV Chem - 29-5-2021 at 02:56

I have already attempted making a working MnO2 on Ti (Grade 5) electrode twice now. However the coating just comes off after something like a day of runtime at not even full current density (like 25mA/cm^2).
Is this because I'm using GR5 instead of the recommended GR1?
I've already tried drying the Mn(NO3)2 on the Ti surface before decomposing it but it didn't seem to make a difference.
My plating solution doesn't seem to be bad or anything as it looks pretty pure and the electrodes don't passivate, they just fall apart within a few days.

markx - 29-5-2021 at 13:56

Yup....GR5 is alloyed and no good for electrochemical applications under anodic potentials. I've had it develop pitting and dissolve into the perchlorate cell liqour, creating a rather spectacular mess of precipitate. I had made the anode stem from GR5 Ti and it was unstable under anodic conditions in chloride/chlorate bearing electrolyte. It seems the alloying elements prevent it from forming a tough enough oxide coat on the surface. Good for mechanical applications, but not under extremes of the positive side of a cell.
With GR1 zero problems...it passivates completely and is stable. So always use the GR1 (CP commercially pure) grade of titanium for electrochemical purposes. Not to mention GR1 is a breeze to machine and tap compared to the alloyed grades that tend to be tough as a coffin nail.

BAV Chem - 30-5-2021 at 00:49

Alright, thanks. I guess I'm gonna get some GR1 titanium and try again.

yobbo II - 2-6-2021 at 15:17


Grade one, two, three or four will be OK.

Grade 11 if you want to go as far from getto as possible.

Yob

Electrochemical etching of titanium using oxalic acid

BAV Chem - 1-8-2021 at 15:18

Normally Ti is etched using HCl before depositing the MnO2. However this method does use a lot of concentrated HCl and handles a lot of nasty boiling acid.
Now, there's a way of etching Ti, that does not use HCl. Instead the Ti is submerged in boiling oxalic acid solution (mine was about 15%) and connected up to the negative (yes, the negative) lead of a power supply (in this case 10V but that might not be optimal). The positive is connected to a graphite rod, also suspended in the solution.
The solution begins to bubble and boil vigorously at the relatively small anode while the titanium cathode starts producing hydrogen and the solution turns yellow:mad: on the surface of the titanium. After a while (like 2min in this case) electricity is disconnected and the titanium is boiled for another few minutes. Apparrently the cathodic conditions reduce the titanium's passivation layer and expose the bare metal, essentially activating it and allowing it to react with the acid.

I also tried hooking things up the other way round but that only resulted in some really gay looking rainbowy titanium (no offence intended).

Now, is this process any useful? It certainly is to me so I can conserve my HCl a bit and the etching bath is easier to store. Though I should add that this process produces an oxalic acid aerosol, which is a bit harsh to breathe, so it's still not ideal.

Note: In the picture(s) the copper wire is also in the solution and I got away with it but it's definitely something to avoid. You can see a bit of a redish deposition of copper (oops) on the etched Ti but that was easily wiped off and the electrode turned out fine.

setup.png - 642kB etching.png - 799kB etched.png - 937kB


[Edited on 1-8-2021 by BAV Chem]

mysteriusbhoice - 1-8-2021 at 22:22

Quote: Originally posted by BAV Chem  
Normally Ti is etched using HCl before depositing the MnO2. However this method does use a lot of concentrated HCl and handles a lot of nasty boiling acid.
Now, there's a way of etching Ti, that does not use HCl. Instead the Ti is submerged in boiling oxalic acid solution (mine was about 15%) and connected up to the negative (yes, the negative) lead of a power supply (in this case 10V but that might not be optimal). The positive is connected to a graphite rod, also suspended in the solution.
The solution begins to bubble and boil vigorously at the relatively small anode while the titanium cathode starts producing hydrogen and the solution turns yellow:mad: on the surface of the titanium. After a while (like 2min in this case) electricity is disconnected and the titanium is boiled for another few minutes. Apparrently the cathodic conditions reduce the titanium's passivation layer and expose the bare metal, essentially activating it and allowing it to react with the acid.

I also tried hooking things up the other way round but that only resulted in some really gay looking rainbowy titanium (no offence intended).

Now, is this process any useful? It certainly is to me so I can conserve my HCl a bit and the etching bath is easier to store. Though I should add that this process produces an oxalic acid aerosol, which is a bit harsh to breathe, so it's still not ideal.

Note: In the picture(s) the copper wire is also in the solution and I got away with it but it's definitely something to avoid. You can see a bit of a redish deposition of copper (oops) on the etched Ti but that was easily wiped off and the electrode turned out fine.




[Edited on 1-8-2021 by BAV Chem]





why the cathode is connected up to the Ti instead of it being used as the anode at lower voltages/current density.
isnt the goal to generate some oxide so the oxalic can attack it.

BAV Chem - 1-8-2021 at 23:16

That's exactly what I thought too but running any current through it with it as the anode only resulted in some pretty colors and even more passivation. Seems like the oxalic acid is really slow at dissolving Ti oxides. Even some papers state that the etching process in boiling oxalic acid (no electrolysis) takes something like 12h.

mysteriusbhoice - 2-8-2021 at 12:15

Quote: Originally posted by BAV Chem  
That's exactly what I thought too but running any current through it with it as the anode only resulted in some pretty colors and even more passivation. Seems like the oxalic acid is really slow at dissolving Ti oxides. Even some papers state that the etching process in boiling oxalic acid (no electrolysis) takes something like 12h.


thats what happens if you run at high overpotential you need to like anodically etch it at around 1.8 volts or something.

BAV Chem - 7-8-2021 at 08:15

Quote: Originally posted by mysteriusbhoice  


thats what happens if you run at high overpotential you need to like anodically etch it at around 1.8 volts or something.


I guess I'm gonna give that a go the next time i make an anode.