[Edited on 7-24-2010 by IrC]aeacfm - 25-7-2010 at 00:08
but this is so specific
i mean general idea or it differ with different electrodes and dependent on concentration of hydrogen ion ? Nicodem - 25-7-2010 at 04:01
That is true, but then I wander why your question is so non specific. Surely you can't expect to get a specific answer to a non specific question?
Mercury electrodes generally have a very high hydrogen over potential - even so high that sodium cations reduce faster than protons at most current
densities, thus forming sodium amalgam. The hydrogen overvoltage of Hg is also relatively independent of the current density (for example, it is -1.1V
at 0.01 to 1A/cm^2, and only drops to -0.9V at 0.001A/cm^2). The drawback is in that they are liquid and that the surface tends to passivate with the
deposited junk (the metals that deposit or form amalgams, also change its electrode properties). In analytical chemistry all these problems are
circumvented by using the classical dropping mercury electrode (as for example in polarography).
In preparative electrochemistry, lead electrodes are commonly used for reductions as they have a high enough overvoltage to be useful in
electroreducing many types of substrates rather than causing the proton reduction side reaction (they have an hydrogen overpotential of -1.26V at
1A/cm^2, but this drops significantly at low current densities). They are also rather inert. A lead electrode with the surface impregnated with
mercury is more effective in some cases. Copper can also be used in some cases, depending on what is the substrate to be reduced. Other metals with
high hydrogen overvoltage include Sn, Bi, Zn and Ni (only at high current densities). Platinum electrodes have the lowest H overpotentials. But
obviously, the choice of the electrode depends on the specifics of the intended use - of which you give no information whatsoever.aeacfm - 25-7-2010 at 06:27
thank you sir too much
you remove a lot of ambiguity to me
so,when i want(cathode) carbon electrode of high hydrogen overpotential , do you have idea about the parameters or simply how to make it work like
that ?
many thanks again aeacfm - 25-7-2010 at 13:08
i found some thing about glassy carbon electrode
but unfortunately the intended is graphite cathode
