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WAYNEL183
science forum beginner

Joined: 20 Aug 2005
Posts: 26

Posted: Mon May 01, 2006 12:08 pm    Post subject: Rate of gas production at the electrodes

Is there a paper/example on the rate of gas production at the
electrodes of say a simple cell using water?
After running a number of experiments I found that the rate of gas
production at the electrodes did not rise in a linear manner.
At between 2-3v it seemed linear but at 4v it seemed to be twice that
of 3v and again doubling at 5v. Does the rate of the decomposition of
water happen at an expo rate?
If the rate of gas production is proportional to the current then V=IR
is correct. However, if my results are correct then there must be
another power factor needed.
Or should I be looking at energy used (joules)?

Cheers

WayneL
Dieter Britz
science forum beginner

Joined: 04 May 2005
Posts: 45

Posted: Tue May 02, 2006 10:08 am    Post subject: Re: Rate of gas production at the electrodes

WAYNEL wrote:

 Quote: Is there a paper/example on the rate of gas production at the electrodes of say a simple cell using water? After running a number of experiments I found that the rate of gas production at the electrodes did not rise in a linear manner. At between 2-3v it seemed linear but at 4v it seemed to be twice that of 3v and again doubling at 5v. Does the rate of the decomposition of water happen at an expo rate? If the rate of gas production is proportional to the current then V=IR is correct. However, if my results are correct then there must be another power factor needed. Or should I be looking at energy used (joules)?

I doubt that there is a paper on this, but it looks like
simple electrochemistry. If you have a single reaction pair
producing gases, such as oxygen at the anode, hydrogen at
the cathode, and you have very efficient stirring, then you
would in fact, from the Butler-Volmer equations, expect such
exponential gas production, because the current would go up
exponentially with voltage. So, what are the currents as a
function of voltage? I assume you measure these also. It could
also happen that as you increase the overvoltage, other
reactions kick in, whatever you have in your soup. If it is
plain water and inert electrolyte, the above would apply.
So check up on Butler-Volmer, or Tafel curves, for that matter.
It certainly does not have to do with Ohm's Law.

I mention stirring because if you do not stir, then the
current will plateau out due to transport limitation. If you
however are evolving gases, the bubbles themselves are a very
efficient stirrer, as found out by Ibl in the 70's.
--
Dieter Britz, Kemisk Institut, Aarhus Universitet
Peter Lowrie
science forum beginner

Joined: 14 Jun 2005
Posts: 17

Posted: Thu May 04, 2006 9:18 pm    Post subject: Re: Rate of gas production at the electrodes

Ohms Law breaks down during electrolysis to be replaced by the Wein Effect
at circa 75 degrees C and at 1.24 volts above cell electrode overvoltage. I
have prepared a paper on the subject it is far from finished but it still
has some interesting numbers in it. You may want to email me for a copy.

Here are links to other useful data:

http://www.egaspower.com/files/MSDS-oxygen.pdf
http://www.egaspower.com/files/MSDS-nitrogen1.pdf
http://www.egaspower.com/files/MSDS-hydrogen.pdf
http://www.egaspower.com/files/MSDS-helium.pdf
http://www.egaspower.com/files/MSDS_ELECTROLYTIC_GAS.pdf
http://www.egaspower.com/files/MizunoTexperiment.pdf
http://www.egaspower.com/files/MizunoTconfirmatib.pdf
http://www.egaspower.com/files/MizunoTconfirmatia.pdf
http://www.egaspower.com/files/5kW_RAPS.PDF
http://www.egaspower.com/files/TM-2003-212059.pdf
http://www.egaspower.com/files/naca-tn-133.pdf
http://www.egaspower.com/files/naca-rm-e56b27.pdf
http://www.egaspower.com/files/naca-report-1383.pdf
http://www.egaspower.com/files/MizunoTgeneration.pdf
http://www.egaspower.com/files/MizunoTgenerationa.pdf
http://www.egaspower.com/files/naca-tn-3935.pdf

Dieter Britz wrote:
 Quote: WAYNEL wrote: Is there a paper/example on the rate of gas production at the electrodes of say a simple cell using water? After running a number of experiments I found that the rate of gas production at the electrodes did not rise in a linear manner. At between 2-3v it seemed linear but at 4v it seemed to be twice that of 3v and again doubling at 5v. Does the rate of the decomposition of water happen at an expo rate? If the rate of gas production is proportional to the current then V=IR is correct. However, if my results are correct then there must be another power factor needed. Or should I be looking at energy used (joules)? I doubt that there is a paper on this, but it looks like simple electrochemistry. If you have a single reaction pair producing gases, such as oxygen at the anode, hydrogen at the cathode, and you have very efficient stirring, then you would in fact, from the Butler-Volmer equations, expect such exponential gas production, because the current would go up exponentially with voltage. So, what are the currents as a function of voltage? I assume you measure these also. It could also happen that as you increase the overvoltage, other reactions kick in, whatever you have in your soup. If it is plain water and inert electrolyte, the above would apply. So check up on Butler-Volmer, or Tafel curves, for that matter. It certainly does not have to do with Ohm's Law. I mention stirring because if you do not stir, then the current will plateau out due to transport limitation. If you however are evolving gases, the bubbles themselves are a very efficient stirrer, as found out by Ibl in the 70's.

--
Regards,
Peter.
http://www.pelicom.net.nz
John Savage

Joined: 24 Mar 2005
Posts: 63

Posted: Fri May 05, 2006 6:34 am    Post subject: Re: Rate of gas production at the electrodes

"WAYNEL" <home@wlawson.co.uk> writes:
 Quote: Is there a paper/example on the rate of gas production at the electrodes of say a simple cell using water?

The rate of gas production is directly proportional to the electric
current into the electrodes (assuming it is not reacting with the
electrode material or electrolyte).

 Quote: After running a number of experiments I found that the rate of gas production at the electrodes did not rise in a linear manner.

As gas is liberated around the electrodes it appears as a cloud of gas
bubbles lightly suspended in the water. The bubbles are non-conductive
so act as a cloud of insulators mixed in with the electrolyte and tending
to obstruct the electrical path between the electrodes. The greater the
rate of gas production, the greater this electrical resistance becomes.

Also, some of the bubbles adhere to the surface of the electrodes, each
effectively insulating a small area of the electrode from the electrolyte
until the bubble grows and bouyancy forces free it. If you switch off and
wait until the bubbles surface, resistance returns to its low value.

You'll probably notice that O2 is liberated in bubbles of a different
size than those of H2.
--
John Savage (my news address is not valid for email)
novost@gmail.com
science forum beginner

Joined: 05 May 2006
Posts: 1

Posted: Fri May 05, 2006 7:14 am    Post subject: Re: Rate of gas production at the electrodes

WAYNEL wrote:
 Quote: Is there a paper/example on the rate of gas production at the electrodes of say a simple cell using water? snip voltage stuff If the rate of gas production is proportional to the current then V=IR is correct.

That's as maybe - but what evidence do you have
that R is independent of current and voltage?

It's the electron transfer that's doing the job.

If you are interested in the gas production, why don't you
measure the current directly instead of measuring the

[For accurate measurements, you should also consider
the solubility of the gases in water at cell temperature.]

Then you should find your results are depressingly linear.
If you can do better than linear I'm sure you can find a
patent clerk who will be eager to take your money.

If you are still interested in the cell voltage after the current
experiments, measure V versus I and try to work out what
is happening in the vicinity of the electrodes.

 Quote: However, if my results are correct then there must be another power factor needed. Or should I be looking at energy used (joules)?

No, you should be reading a large book on electrolysis.
Come back when you have finished it ;-)

LenW
WayneL
science forum beginner

Joined: 03 May 2005
Posts: 33

Posted: Fri May 05, 2006 1:18 pm    Post subject: Re: Rate of gas production at the electrodes

I forgot to mention that I have measure the current and it take the form of
an expo curve and after some time it starts to flattening out but maintains
a continuous growth, although very gradual.

Cheers

WayneL

<novost@gmail.com> wrote in message
 Quote: WAYNEL wrote: Is there a paper/example on the rate of gas production at the electrodes of say a simple cell using water? snip voltage stuff If the rate of gas production is proportional to the current then V=IR is correct. That's as maybe - but what evidence do you have that R is independent of current and voltage? It's the electron transfer that's doing the job. If you are interested in the gas production, why don't you measure the current directly instead of measuring the voltage and then scratching your head and looking puzzled? [For accurate measurements, you should also consider the solubility of the gases in water at cell temperature.] Then you should find your results are depressingly linear. If you can do better than linear I'm sure you can find a patent clerk who will be eager to take your money. If you are still interested in the cell voltage after the current experiments, measure V versus I and try to work out what is happening in the vicinity of the electrodes. However, if my results are correct then there must be another power factor needed. Or should I be looking at energy used (joules)? No, you should be reading a large book on electrolysis. Come back when you have finished it ;-) LenW
Peter Lowrie
science forum beginner

Joined: 14 Jun 2005
Posts: 17

Posted: Fri May 05, 2006 10:50 pm    Post subject: Re: Rate of gas production at the electrodes

Have you got a clamp meter that can measure both AC and DC? I have one of
each.

WayneL wrote:
 Quote: I forgot to mention that I have measure the current and it take the form of an expo curve and after some time it starts to flattening out but maintains a continuous growth, although very gradual. Cheers WayneL novost@gmail.com> wrote in message news:1146813252.614043.178380@j73g2000cwa.googlegroups.com... WAYNEL wrote: Is there a paper/example on the rate of gas production at the electrodes of say a simple cell using water? snip voltage stuff If the rate of gas production is proportional to the current then V=IR is correct. That's as maybe - but what evidence do you have that R is independent of current and voltage? It's the electron transfer that's doing the job. If you are interested in the gas production, why don't you measure the current directly instead of measuring the voltage and then scratching your head and looking puzzled? [For accurate measurements, you should also consider the solubility of the gases in water at cell temperature.] Then you should find your results are depressingly linear. If you can do better than linear I'm sure you can find a patent clerk who will be eager to take your money. If you are still interested in the cell voltage after the current experiments, measure V versus I and try to work out what is happening in the vicinity of the electrodes. However, if my results are correct then there must be another power factor needed. Or should I be looking at energy used (joules)? No, you should be reading a large book on electrolysis. Come back when you have finished it ;-) LenW

--
Regards,
Peter.
http://www.pelicom.net.nz
WayneL
science forum beginner

Joined: 03 May 2005
Posts: 33

Posted: Sat May 06, 2006 8:40 am    Post subject: Re: Rate of gas production at the electrodes

I am using a Potentiostat..

WayneL

"Peter Lowrie" <peterlowrie@paradise.net.nz> wrote in message
news:1490602.mUKJ0bssau@xbox.pelnet.net...
 Quote: Have you got a clamp meter that can measure both AC and DC? I have one of each. WayneL wrote: I forgot to mention that I have measure the current and it take the form of an expo curve and after some time it starts to flattening out but maintains a continuous growth, although very gradual. Cheers WayneL novost@gmail.com> wrote in message news:1146813252.614043.178380@j73g2000cwa.googlegroups.com... WAYNEL wrote: Is there a paper/example on the rate of gas production at the electrodes of say a simple cell using water? snip voltage stuff If the rate of gas production is proportional to the current then V=IR is correct. That's as maybe - but what evidence do you have that R is independent of current and voltage? It's the electron transfer that's doing the job. If you are interested in the gas production, why don't you measure the current directly instead of measuring the voltage and then scratching your head and looking puzzled? [For accurate measurements, you should also consider the solubility of the gases in water at cell temperature.] Then you should find your results are depressingly linear. If you can do better than linear I'm sure you can find a patent clerk who will be eager to take your money. If you are still interested in the cell voltage after the current experiments, measure V versus I and try to work out what is happening in the vicinity of the electrodes. However, if my results are correct then there must be another power factor needed. Or should I be looking at energy used (joules)? No, you should be reading a large book on electrolysis. Come back when you have finished it ;-) LenW -- Regards, Peter. http://www.pelicom.net.nz
Dieter Britz
science forum beginner

Joined: 04 May 2005
Posts: 45

Posted: Mon May 08, 2006 7:15 am    Post subject: Re: Rate of gas production at the electrodes

WayneL wrote:

 Quote: I forgot to mention that I have measure the current and it take the form of an expo curve and after some time it starts to flattening out but maintains a continuous growth, although very gradual.

That fits with my picture of a mix of Butler-Volmer at each
electrode, insufficient stirring (i.e. some concentration
gradients limiting the current), plus some iR in the solution.
These would combine to produce a I vs E curve that lies below
the expected exponential Tafel shape, but you should always
get exactly the amount of gas that corresponds to the current
flowing. Exactly what corresponds to the current, however,
depends on exactly what is happening at the electrodes. If
you, e.g. use Cu as electrodes, you will dissolve Cu at the
anode, instead of evolving oxygen there.
--
Dieter Britz, Kemisk Institut, Aarhus Universitet

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