KARPEN PILE

[pomodoro]

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    (http://www.overunity.com/Themes/default/images/post/xx.gif)   Re: KARPEN PILE  « Reply #440 on: August 12, 2014, 05:31:54 AM »  Quote
  BTW Im not going to do any tests if they require electrolysis,  these will of course show hydrogen overpotentials!
I cant modify the original message, so I'll keep pasting the original, with additions.


-----------------------------------------
Air Karpen    Pd black on Pt vs Glassy Carbon  in 1N Sulfuric Acid.


I've just unshorted the cell, after 18 hours  and will report hourly emf of cell.  I'll keep modifying this post rather than creating new one, so keep coming back here for the updates.

negative value  means C is more negative than the Pd/Pt

Time   EMF
0 -    0mV
1hr    -1mV
2hrs   -8mV
3hrs   -12mV

Voltage does change very slowly. Decided to end experiment here, now passing UHP hydrogen through exacltly same setup.  Cell is shorted out

-------------------------------------------------

Hydrogen Karpen, same setup as above, but flushed with constant UHP quality hydrogen

Notes:   Pd/Pt  electrode in 1N H2SO4 now becomes essentially the well known NHE electrode.  Normal hydrogen electrode found in all text books.  Very fast response / kinetics. Large exchange current . In other words, any stray oxygen gas has very little effect on its voltage as it is swamped by the fast hydrogen/proton reaction.  We need to focus on the other electrode to explain strange behavior. Forget about this electrode!

As soon as hydrogen was introduced, the voltage immediately rose to a healthy +800mV.  The carbon becoming the cathode, with reduction occuring at its surface.   This is very easily explained by remembering that any residual oxygen has little effect on the Pt electrode but will  give rise to a mixed potential at the  Carbon.  The hydrogen/proton kinetics are very slow at the carbon, so its potential will be a mixture of the oxygen redox and the hydrogen redox potentials,  the onw with faster kinetics will dominate the reading. 
Anyone repeating these experiments must remember that oxygen, or oxides on the surface  will fool you into believing you have a huge potential.

After a few hours of shorting out the terminals, to reduce  any oxygen reaching the Carbon, the short was removed and the voltage monitored, here are the results as measured with a 10^12 ohm electrochemistry style voltmeter.

Time         mV
30 secs    +26
1 min       +40
5 Min        +96
10 min     +118
40min      +137
70 min      +147

This is much slower than when the cell is shorted immediately after the hydrogen is first passed, an then unshorted.  In this case the voltage rose to +800mV in 15 seconds!

eighteen hours of shorting out later, and here are the results

Time       mV
30s        +8mV
1 min     13 mV
12 mins   +70mV
50 min     +122
1hr 50m   134
2h:50 min   141
4h:20 min   146
5hrs            +146

Conclusion,  after equilibrating, cell seems to show a potential difference of 146mV, with the carbon electrode taking on a positive voltage. 

Unless the cell is sealed completely, it is impossible to know if a trace of oxygen from the hydrogen which is being constantly bubbled through the cell has any influence on this voltage.

less than 0.1uA flows when shorted.

I then deliberately use a 6v cell and placed it across the electrodes for 3 seconds ,  visibly producing hydrogen at he carbon and oxygen at the Pt.

The voltages across the electrodes are now -1200mV, I'm planning to see its recovery

[MarkE]

Yes, this forum locks out changes after awhile.  I think it is about a day.

0.1uA is a pretty small short circuit current.

[profitis]

Excellent result @pomodoro. Proves a dead-stable 0.146v.it sounds about right for carbon systems.the chinese only got about 0.07 v for a different type of graphite vs Pt not Pd.you see now clearly the importance of shorting,then relaxing, before getting its real voltage

[profitis]

The one thing I don't like about carbons are that they tend to cling to gases quite long after a rest period.van der waals forces hold onto gas quite stubbornly,I wonder what diamond would do.

[profitis]

You should retry your industrial hydrogen vs uhp in the same setup,same waiting period and see if it differs.you should also try with an electrolyte additive that wets surfaces like ammonium sulfate