Sciencemadness Discussion Board

What about "glassy" carbon as an anode material in a chlorate or perchlorate cell?

jpsmith123 - 3-9-2005 at 22:10

I haven't seen this material discussed here before for this potential usage.

According to the abstract of US patent #4,802,959:

"Peroxydisulfuric acid and its salts are produced electrochemically from an aqueous acid sulfate solution using a glassy carbon anode in the presence of fluoride ions dissolved in the anolyte. A low cost alternative to platinum is provided and high current efficiencies are obtained".

Apparently the inventors feel it is an improvement over lead dioxide (at least for making persulfates):

"Attempts have been made to use cheaper materials to substitute for the expensive platinum anodes. Beta-lead dioxide and various dimensionally-stable anodes have been tested but none exhibited standtime under the extreme conditions of persulfate electrosynthesis".

The question is, what about for making chlorates and or perchlorates...has anyone tried it?

Esplosivo - 3-9-2005 at 23:13

My question may sound stupid, but what is 'glassy' carbon?

Glassy carbon

MadHatter - 3-9-2005 at 23:46

Found this using google:

"Glassy carbon is a composite consisting of amorphous carbon
and one or more additional materials that possesses unique
properties and chracteristics. Glassy carbon is formed
by carbonizing phenolic resins which are made by reacting
phenols with cellulosics, aldehydes and ketones (that is
special organic carbons).
It is a kind of synthetic polymer of carbon. that can substitute
graphite as an electrode.
Different electrodes have different usages, that define the
applications. Some glassy carbon electrodes have gold and platinum
deposits, combining both types."

The_Davster - 3-9-2005 at 23:56

So essentially making Bakelite in the shape you want your electrode, then going at it with a blowtorch until it is all carbon? Sounds too easy...:P

Yet Another Related Idea

jpsmith123 - 4-9-2005 at 05:43

Supposedly electrolysis of methanol using high voltage can produce a marginal quality diamond-like carbon film on an immersed substrate. If I remember correctly, the films are "defective" enough that they conduct electricity.

I wonder what effect, if any, such a thin DLC coating would have on a carbon anode in a chlorate cell? Maybe it would last longer?

Attached is a paper re electrolysis of methanolbject, in case anyone is interested in this.

Attachment: Electrolysis of Methanol.pdf (132kB)
This file has been downloaded 1442 times

Cyrus - 4-9-2005 at 15:35

Rogue Chemist, as far as I know, phenolic resins are pretty much bakelite. I searched for a long time for phenolic resins used for high temperature crucibles, but didn't find much, only that there are 2 kinds; resols and novolacs. The difference has to do with whether an alkaline or acidic catalyst is used, and each has different curing properties, but that's all I remember.

If anyone can figure out a OTC way to produce these resins, I'd be really happy, because glassy carbon is VERY useful for refractory compositions, crucibles, and other high temperature stuff. Apparently glassy carbon used to be made from pitch or tar, but the yields were lower than phenolic resin, only 15% or so of the carbon in the pitch remains, as opposed to 30% in phenolic resins, IIRC.

I'm not sure where to obtain pitch. But in any case you would definitely want to heat it in a neutral or reducing atmosphere to prevent it oxidizing away from nothing.

BTW, I recently fired all those lead dioxide ceramic substrates, and got some nitric acid for free, so I'll begin testing lead dioxide anodes soon.

Cyrus

jpsmith123 - 4-9-2005 at 15:53

BTW I found a usenet discussion where someone stated that glassy carbon can be used for ClO4 production:

http://groups.google.com/group/rec.pyrotechnics/browse_frm/t...

Now my question is, where can glassy carbon rods or plates be gotten cheaply?

Cyrus - 6-9-2005 at 16:04

As I hinted at above, you may want to try heating tar in a reducing atmosphere until it decomposes completely.

jpsmith123 - 6-9-2005 at 20:14

For right now I would just like to buy a glassy carbon rod to experiment with. (Especially since I don't have access to a vacuum or controlled atmosphere furnace). Unfortunately though, it seems glassy carbon products are hard to find and very expensive.

Twospoons - 6-9-2005 at 23:19

I was thinking a boron / nitrogen doped diamond film could be good for perchlorate. I remember reading somewhere that the oxygen overpotential is higher than platinum. Diamond film production in the garage looks do-able - its only a mix of hydrogen, methane, sometimes CO2 or H2O, at moderate pressures with a tungsten filament.

jpsmith123 - 7-9-2005 at 08:23

Hello Twospoons,

From what I've been reading, conductive diamond film coated electrodes would really be the "cat's ass", so-to-speak.

As I mentioned in an earlier post, it seems possible to coat conductors with a diamond-like film by high voltage electrolysis of methanol.

I wonder if adding a little boric acid to the methanol might incorporate some boron into the film? (If only I had a place to work, I would try it today).

Anyway, I'm attaching another paper on the subject.

Attachment: Electrolysis of Methanol_2.pdf (531kB)
This file has been downloaded 1440 times

10fingers2eyes - 2-7-2016 at 15:35

Thought I'd add this link to this paper as it is related. Someone electroplating DLC from Acetonitrile.
http://www.sciencedirect.com/science/article/pii/S0169433212...

ficolas - 3-7-2016 at 02:34

Quote: Originally posted by Cyrus  

If anyone can figure out a OTC way to produce these resins, I'd be really happy, because glassy carbon is VERY useful for refractory compositions, crucibles, and other high temperature stuff. Apparently glassy carbon used to be made from pitch or tar, but the yields were lower than phenolic resin, only 15% or so of the carbon in the pitch remains, as opposed to 30% in phenolic resins, IIRC.

I'm not sure where to obtain pitch. But in any case you would definitely want to heat it in a neutral or reducing atmosphere to prevent it oxidizing away from nothing
Cyrus


This may be a dumb question but... why don't you just use an old something (like cuterly) made out of bakelite, cut it the way you need it and then blowtorch it? Would it not be pure enough?
Its definitelly easier than getting phenol and formaldehide, and less messy.

For the pitch, maybe you can get some big cans and a good fire, and try to perform a dry distillation of wood to get it?

wg48 - 3-7-2016 at 06:57

Quote: Originally posted by jpsmith123  
Hello Twospoons,

From what I've been reading, conductive diamond film coated electrodes would really be the "cat's ass", so-to-speak.

As I mentioned in an earlier post, it seems possible to coat conductors with a diamond-like film by high voltage electrolysis of methanol.

I wonder if adding a little boric acid to the methanol might incorporate some boron into the film? (If only I had a place to work, I would try it today).

Anyway, I'm attaching another paper on the subject.


Wow I surprised methanol can be electrolysed and even more surprised it deposits carbon. Perhaps with 1.5kV surprising things happen though I suspect that's required to get the current thru the methanol. I will try it today.

wg48 - 3-7-2016 at 12:48

So I have given the electrolysis methanol a crude try.

Two nickel plated sheet steel electrodes approximately 20mm x 10mm area in the methanol separated by approximately 10mm.
Voltage estimated at 1.4kV from the half wave rectified output of a mot ballasted by a similar mot.

The crude arrangement is shown below.



Approximately 1mA passed between the electrodes and after 5 minutes the container was hot to the touch and the methanol had a light yellow color. No gas bubbles were noticble and both electrodes appeared unchanged. A few minutes after that bubbles rose from one corner of the anode and a condensation edge was see above the methanol. I assume the methanol was boiling.

The methanol is supposed to be 99.95% I need to check how dry it was. To allow a longer test I will need cooling or reflux.
The light bulb is a fuse and visual current monitor because its in series with the diode its rms current is much higher than the dc flowing between the electrodes .



[Edited on 3-7-2016 by wg48]

[Edited on 3-7-2016 by wg48]

WP_20160703_20_53_08_Pro.jpg - 1.5MB

macckone - 4-7-2016 at 07:14

If your methanol isn't dry you can electrolyze it at a much lower voltage until current goes to close to zero then swap out the electrodes for you desired substrate. Water is easier to electrolyze than methanol. This method can also be used to dry ethanol.

jpsmith123 - 30-8-2016 at 15:03

Here's a paper describing the electrodeposition of both nitrogen-doped and boron-doped DLC (the latter from a methanol-camphor-boric acid solution).

Attachment: AMPC_2013032716565756.pdf (950kB)
This file has been downloaded 636 times

Twospoons - 30-8-2016 at 17:08

Great find! Thanks for posting that paper.

wg48 - 31-8-2016 at 05:28

Yes thats an interesting paper. In particular how a none conductive substrate can be coated.

It gives more details of the set up than the previous paper such as the voltage and current. Unfortunately it does not give any details on how dry the methanol needs to be.

I am suspicious about the current.for example 500mA at 1000V would dissipate 500W in the set up and almost certainly boil one liter of electrolyte (its mostly methanol) vigorously in minutes. Given that the duration of each experiment was 40 minutes I would assume cooling would be required, but that is not mentioned in the procedure. At least reflux would be required to avoid loss of the methanol. The 350K (76.9C) for all experiments looks odd as methanol boils at 64.7C.

The deposition rate is slow 1um/40 minutes compared to even electroless nickel which is in the 20um/h range.

I will have to try this with a glass slide. It may be a simple method of putting a conductive coating on glass.

Her is a link to a paper from the same authors on depositing carbon nitride using methanol and urea.

https://www.researchgate.net/publication/260553071_Synthesis...

[Edited on 31-8-2016 by wg48]

jpsmith123 - 31-8-2016 at 06:02

Just thinking out loud, one of my ideas was to use the method described in this paper (possibly with greater boron doping than what the authors used) to put a conductive DLC layer over platinum, for example. Maybe a conductive-DLC coated platinum anode could be used to go directly from chloride to perchlorate without touching the platinum surface.
On its face this process seems simple and inexpensive enough that you could treat the anode to another coating after every couple of runs if need be.

yobbo II - 31-8-2016 at 14:54


The paper gives values of conductivity for films that range from about -10 to -22 of the In of conductivity (-10 to -22 the natural log of conductivity) which is about 4.5 x 10^-5 and 2.8 x 10^-10.
But it does not state what are the units of this conductivity. Are they Ohm cm or Ohm meters or or mho's per meter or what? Conductivity is usually quoted in Siemens per meter.

What do the values equate to in resistivity values. You would like something in the region of 5 x 10^-3 Ohm cm (less would do) for a nice low voltage drop across the coating.

wg48 - 1-9-2016 at 01:48

Quote: Originally posted by yobbo II  

The paper gives values of conductivity for films that range from about -10 to -22 of the In of conductivity (-10 to -22 the natural log of conductivity) which is about 4.5 x 10^-5 and 2.8 x 10^-10.
But it does not state what are the units of this conductivity. Are they Ohm cm or Ohm meters or or mho's per meter or what? Conductivity is usually quoted in Siemens per meter.

What do the values equate to in resistivity values. You would like something in the region of 5 x 10^-3 Ohm cm (less would do) for a nice low voltage drop across the coating.



The paper on the doped films in its abstract states this "Electrical resistivity at room
temperature was reduced by the doping effect, from 109 Ω-cm for undoped films to 107 Ω-cm for nitrogen doped films
and 108 Ω-cm for boron doped films"

The numbers after the ten are powers of the ten.

[Edited on 1-9-2016 by wg48]

Thinking about that level of resistivity for the undoped film its an insulator, not a very good one. So I guess it is more like diamond than graphite.

Even at 1um thickness the resistivity of the doped film would limited its usfullness as an electrode coating.

[Edited on 1-9-2016 by wg48]

jpsmith123 - 1-9-2016 at 05:11

I would think that the conductivity of the DLC coating could be increased - to a certain extent at least - by simply adding some more boric acid to the solution. And then maybe by watching the current vs time (during the electrodeposition process) you can get an idea if it's working.

Twospoons - 1-9-2016 at 19:21

10^7 Ω-cm isn't disastrous. A 10cm^2 electrode with a 1um coating is just 10 ohms additional resistance in the circuit. It really just means making larger area electrodes.

wg48 - 2-9-2016 at 02:45

Quote: Originally posted by Twospoons  
10^7 Ω-cm isn't disastrous. A 10cm^2 electrode with a 1um coating is just 10 ohms additional resistance in the circuit. It really just means making larger area electrodes.


I was thinking that a minimum of several A/cm^2 was used. However I did find one reference for chlorate production that suggested a minimum of 0.05A/cm (5A/decimeter) so your correct for a 1um coating.

Now if the attrition rate was such that only a 1um coating was required.



jpsmith123 - 2-9-2016 at 05:07

The authors used only 75 mg of boric acid per liter. I see that as a starting point. Maybe they didn't go any higher because along with methyl borate, adding more boric acid would've also made more water.

So what about upping the boric acid to 0.5 grams per liter, but then drying the methanol with zeolite or something?

wg48 - 3-9-2016 at 11:41

Apparently it works from ethanol, methanol and glycol water solutions and also acetic acid and water (not from the this reference)

From: ELECTRODEPOSITION OF DIAMOND-LIKE CARBON FILMS, Minhua Chen, B.S.


"In 1992, Namba [11] first employed electrochemical methods to deposit DLC films. In
his study, diamond phase carbon films had been grown on silicon substrates at
temperatures of less than 70 ºC by using ethanol solution. The potential applied to silicon
substrates was changed from 0 to -1.2 KV and the current density from 0 to 5 mA/cm2
. By
changing the electrolyte into a water-ethylene glycol solution, Suzuki et al. [12] soon
successfully deposited carbon films on the silicon substrate. After that, this electrolysis
method had been successfully employed to deposit DLC films from a variety of organic
solution including methanol, acetonitrile, N, N-dimethylformamide, nitromethane,
nitroethane, ethanol and acrylonitrile [14-26]. Both DC power and pulse-modulated power
7
were used as energy sources in these attempts. In 1996, Suzuki et al. [13] reported a new
approach to deposit carbon films from organic solutions by electrolytic heating of a water ethanol
solution. This method consisted of discharge-heating a tungsten cathode in a water ethanol
electrolyte under a high DC voltage. At high voltages, glassy carbon and disordered
graphitic carbon were deposited on the tungsten wire. Very similarly, Wang et al. [27] has
employed a thin tungsten wire as anode under high potential and successfully deposited
DLC films on silicon substrates. All of the above electrochemical methods have
demonstrated some obvious advantages over traditional PVD and CVD in terms of low
processing temperature, simple setup and low cost. However, all of them involved the use
of high potential, which greatly increases the difficulty to control the deposition process
and study the mechanism. In 1996, V. P. Novikov et al. [28] proposed a new
electrochemical method to deposit DLC films. They used a solution of acetylene in liquid
ammonia as electrolyte and carried out the electrolysis at a low voltage of 2.5 to 5 V as
well as low temperature -55 oC"

yobbo II - 3-9-2016 at 15:31

Paper here (if anyone can get it) where the voltages are more manageable.

http://ieeexplore.ieee.org/document/7131998/

wg48 - 4-9-2016 at 06:24

Quote: Originally posted by yobbo II  
Paper here (if anyone can get it) where the voltages are more manageable.

http://ieeexplore.ieee.org/document/7131998/


The abstract from the above paper:

"This paper presents electrodeposition of diamond-like carbon (DLC) thin film deposits on indium tin oxide (ITO) glass substrate under voltage 2.1V~120V with mixing varying acetic acids' portions with deionized water, forming 0.2~0.8% electrolytic solutions. The result shows that at deposition temperature 30°~65°, voltage 50V and 0.8% electrolytic solution concentration of DLC thin films, the reflection index reduced to 60%, and theoretical matching refractive index became 1.32. This finding is applicable on various optoelectronic device like protective or window layer of solar cell."

The abstract does provide the main details. Compared to dry methanol and kvoltages its a much more convenient method as it uses safe voltages and dilute acetic acid water solution.

I would think the current would be in the amps range per cm^2 for a dilute solution of an acid at 50V. Perhaps they used a pulsed supply to reduce the power dissipation in the solution. More details of their set would be very nice.




jpsmith123 - 4-9-2016 at 06:40

It seems that DLC films have been made (using various processes; CVD, PVD, eletrolysis, sputtering, etc.) from almost anything containing carbon.

IMO, the question is: which method is relatively simple to do at home which will give a reasonably "high quality" (e.g., adherent, relatively pinhole-free, boron-doped film) with a reasonable conductivity?

After reading everything I can find on the subject, it seems that in the case of processes using liquid and vapor phase precursors, methanol generally gives the best results.

Anyway, as I see it, for the purpose of making a perchlorate-capable anode for hobby purposes, we don't necessarily need a super high quality film, because if the process is simple enough, it shouldn't be too much trouble to re-coat the anode after a few runs.

One thing I'd like to know is: How much if at all does perchlorate production at a BDD surface depend on current density? (From what I've read, electrodeposited BDD films have lower conductivity than CVD-produced films, so they are not as good for high current applications, but if there is no lower limit on current density then this may not be a show-stopper but merely an inconvenience).

Edit: Here's a paper I just found: "Electrodeposition of DLC films on carbon steel from acetic acid solutions"
http://www.tandfonline.com/doi/pdf/10.1179/0020296714Z.00000...




[Edited on 4-9-2016 by jpsmith123]

wg48 - 4-9-2016 at 07:53

Quote: Originally posted by jpsmith123  
It seems that DLC films have been made (using various processes; CVD, PVD, eletrolysis, sputtering, etc.) from almost anything containing carbon.

IMO, the question is: which method is relatively simple to do at home which will give a reasonably "high quality" (e.g., adherent, relatively pinhole-free, boron-doped film) with a reasonable conductivity?

After reading everything I can find on the subject, it seems that in the case of processes using liquid and vapor phase precursors, methanol generally gives the best results.

Anyway, as I see it, for the purpose of making a perchlorate-capable anode for hobby purposes, we don't necessarily need a super high quality film, because if the process is simple enough, it shouldn't be too much trouble to re-coat the anode after a few runs.

One thing I'd like to know is: How much if at all does perchlorate production at a BDD surface depend on current density? (From what I've read, electrodeposited BDD films have lower conductivity than CVD-produced films, so they are not as good for high current applications, but if there is no lower limit on current density then this may not be a show-stopper but merely an inconvenience).

Edit: Here's a paper I just found: "Electrodeposition of DLC films on carbon steel from acetic acid solutions"
http://www.tandfonline.com/doi/pdf/10.1179/0020296714Z.00000...

[Edited on 4-9-2016 by jpsmith123]


Great find thanks.

The paper suggests a mechanism:

"According to Roy et al.,
14 acetic acid in water
ionises and is transported in the electrolyte under high
electric field, according to reaction (1):
CH3COOH = CH3 + CO + OH- (edited to display correctly)
The positively charged methyl groups are attracted to
the cathode to form diamond-like carbon films through
reaction (2).14
2 CHz
3 z2e{?2Cz3H2 (2)
The negatively charged hydroxyl groups, in contrast,
migrate towards the anode, where they undergo reaction
(3).18
2OH{?O2zH2Oz4e{"

That does not make sense to me. Acetic acid ionising to produce Ch3+, CO and OH- ??? that would be an alkali.

I would believe that an acetic acid ion is neutralized and decomposes into CO2 and a methyl radical.

Presumably the coating can be doped with boron via boric acid or nitrogen via urea to increase its conduction.



jpsmith123 - 5-9-2016 at 18:14

Nowadays, BDD nanopowder is available from places like www.us-nano.com (5 grams for $65). So another possible way to a BDD coated anode might be electrophoretic deposition of BDD powder onto a substrate.

BTW IIRC in one of Beer's MMO patents, he created a MMO coating on an anode by contacting the surface of the substrate with the powdered oxide material and then applying mechanical pressure. (The anode substrate may have been a graphite rod that was just rolled over the powdered MMO on a flat surface or something like that).