When doing 3-electrode measurements, it´s always said that the area of the counter electrode should be as high as possible. Which is the real problem of using a counter electrode with small area? Graphite rods are usually used in the literature and the area is really small. Will that make the counter electrode to work in a larger potential window to be able to bear the current passing (if the mass is also not too large) and that may cause unwanted reactions in the counter electrode if it´s polarized to extreme potentials?
For example, when using activated carbon as counter electrode, should we use areas and/or masses as high as possible so that it works in a very narrow potential window?
When you use a high area counter electrode, the potential applied on its surface is lower, so that the side reactions implied are less numerous and less disturbing. In addition you don't need a very powerful potentiostat.
Marta,
You can use a grafite rod for counter electrode with no problem. In my systems: GC electrode 5 mm diameter load with a Pt-based/C catalysts I have no problems at all.
Previously I used Pt sheet, Pt wire, or Au wire. Graphite rod is cheaper, but sometimes, not too many (depending of electrolyte) it degrades.
If the counter electrode is really small, the overvoltage at the counter electrode would be large. This may exceed the capacity of the potentiostat. Large overvoltages would also increase the number of possible side reactions.
That said, we routinely used 6 mm diameter graphite rods as counter electrodes, with no issues at all.
the real imporant thing is to use the working electrode area as small as possible, micro or ultramicroelectrodes,
Hi.
Overall the counter electrode must be of a noble material, gold, platinum and eventually graphite. we used a platinum wire 1 cm long and 500 um in diameter. In any case depends on the configuration of the potentiostat and under what conditions is used.
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