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Files:
Vertex CV interactive .EXP
Vertex CV interactive 01I.CRV
Abstract
Platinum (Pt) is known as an "inert" metal with
a strong catalytic activity for many electrochemical reactions.
Many components can be adsorbed on Pt surfaces and the adsorption
of hydrogen is a well known phenomenon in electrochemistry. This
experiment concerns two fundamental mechanisms which occur on a
Pt electrode polarised in a strong acid media, H2SO4 [1].
* Cathodic area: Hydrogen adsorption / desorption (from - 250 mV
to + 200 mV versus Calomel)
* Anodic area: Platinum "oxides" formation and reduction (from +
200 mV to 1300 mV versus Calomel)
This extract from a CV interactive establishes the correlation between
the anodic excursion which generates Pt oxides (from 0.6 V) and
their cathodic reduction [1].
Sample
Solution: H2SO4 0.5 M
WORK: Platinised platinum
Plate ± 5X5 mm
(CDC641T conductivity cell)
REF: Calomel electrode (XR100)
AUX: Platinum wire (XM100)
CP06 cell at room temperature (22°C) without nitrogen bubbling
Settings – Experimental
Scan rate 50 mV/s (5 mV potential steps).
A Chrono amperometry starts the sequence. It polarises the WORK
at -300 mV /REF to stabilise the WORK interface and to saturate
the solution with H2 in the vicinity of the WORK.
Curve examination
1) Display:
Type = Normal X = Potential Y1 = Current Y2 = No
The peak magnitude and the peak position
depends upon the anodic potential vertex
2) Display:
Type = Normal X = Time Y1 = Current Y2 = Potential
The anodic potential vertex has been
adjusted during the experiment.
3) Display:
Type = Normal X = Time Y1 = Current Y2 = Quantity (C)
To evaluate the reversibility of the
anodic reaction it is also possible to display Q (charge) versus
potential since Q is recorded along with current during the experiment.
As an alternative, a Peak analysis will evaluate if the charge of
the anodic peak equals the charge of the cathodic peak, for instance
within the 3rd cycle.
Reversibility with Peak analysis
Determine the peak and integrate the peak with user selected base
line
03-02-1999, 16:20:35
DATA
Base line Mode : No
Point 1: 190.109 sec.
Point 2: 226.06 sec.
Equation: y = 0
RESULTS
Integration Point 1 : 190.109 sec. Point 2 : 226.06 sec.
Total : 5.003 mC/cm²
Positive : 63.77 mC/cm²
Negative : -58.7 mC/cm²
Peak
Position : 219.958 sec.
Height : -11.559 mA/cm²
Width : 14.346 sec.
The excess in positive charge calculated with peak analysis with
a manual base line can be interpreted as oxygen gas evolution. This
value is in good accordance with the values "Quantity (C)".
Conclusion
The
interactive cyclic voltammetry establishes the correlation between
the anodic excursion which generates Pt oxides (from 0.6 V) and
their cathodic reduction [1]. The more anodic the potential limit,
the bigger the peak: the peak magnitude and the peak position are
correlated with the anodic potential vertex.
References
[1]
P.A. Christensen and A. Hamnett in "Techniques
and Mechanisms in Electrochemistry", p228 Blackie A&P (Imprint
of Chapman&Hall, Glasgow, 1994)
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