Pot. Linear V with RCB200 (position B) Autoranging performances

Files:
Bipotentiostat.EXP
Bipotentiostat005.CRV
Bipotentiostat011.CRV

A +244 mV offset has been automatically applied to the experimental files in order to obtain their potential quoted versus SHE. The half potential calomel electrode used as reference is +244 mV/SHE [2]

A 10 mV/s linear voltammetry is operated on the disc electrode from +400mV down to -600mV (versus the reference electrode) while the potential on the ring electrode is set at +400mV (versus the same reference electrode) in order to detect Cu(I).

Working Electrode:Rotating Ring and Disc electrode Pt/Pt type EAD
Rotation speed:2500rpm
Reference Electrode:XR110
Auxiliary Electrode:XM110
Solution:CuCl2 0.01M KCl 0.5M

Working electrode 1 = Platinum Disc (production)
Working electrode 2 = Platinum Ring (detection)
Auxiliary electrode = Platinum wire
Reference electrode = Calomel

Two PGZ are operated simultaneously and the potentiostat which drives the ring records the ring current and the disc current, thanks to the A/D IN additional input channel.

WORK Cell Disc
AUXShort circuited with the PGZ One REF
REFShort circuited with the PGZ One AUX

PGZ One settings (Disc)

WORKCell ring
AUXCell AUX
REFCell REF

PGZ Two settings (Ring)

1) Linear Voltammetry (EAD_Copper005.CRV)

Display: Type = Normal X = Time Y1 = Current Y2 = Iring

Y1 represents the disc current and Y2 represents the ring current.

1-a) Disc and ring
According to [1], two waves are detected on the disc which correspond to the reaction (1) and then (2) while the ring exhibits a signal which increases during the first disc wave and then decreases. This reaction correspond to the reaction (1). When the disc reaches a potential which corresponds to the second wave, the reaction which is taking place on the disc is cooper deposition; there is no more Cu(+) which can be captured by the ring. As a consequence, the ring current falls to zero.

(1) [Cu(2+)] <==> [Cu(+)] e° = +0.16 V / SHE
(2) [Cu(2+)] <==> [Cu(0)] e° = +0.34 V/SHE

(a) [Cu(0)] + [Cu(2+)] --> [Cu(+)]

2) Open circuit potential (EAD_Copper011.CRV

Display: Type = Normal X = Time Y1 = Potential Y2 = Iring

Once the voltammetry is finished, the disc electrode regulation is opened but the regulation on the ring electrode continues. The Ring potential which is measured corresponds to the open circuit potential of the ring. At the beginning, the ring is covered with copper [which results from the Cu(2+) deposition operated during the voltammetry]. One can say that the disc is a cooper disc. Since a spontaneous chemical oxidation of this cooper layer takes place (a), it takes less than one minute to dissolve the cooper and obtain a platinum disc again. The variation of the potential correspond to that phenomenon. Since that chemical oxidation generates [Cu(+)], this [Cu(+)] can be detected on the ring. The current recorded in the meanwhile on the ring is Iring. During the chemical dissolution of the cooper, a significant current is recorded which correspond to the fact that Cu(+) are available and can be oxidised onto the ring. Once the cooper layer is completely dissolved, there are no more Cu(+) ions in solution and thus the ring current goes back to zero.

It is convenient and simple to achieve bipotentiostatic experiment with VoltaLab.

[1] Simultaneous and independant Potentiostatic control of two indicator electrodes - D.T. Napp, DC Jonhson, and Stanley Bruckenstein. Analytical chemistry Vol 39, No4 april 1967.

[2] Standard potentials in aqueous solution, ed. A.J. Bard, R. Parsons, and J. Jordan, Dekker, New York, 1985.