文档介绍：Electroanalytical Chemistry
Lecture #6
An Introduction to Electrochemical Methods (cont’d)
Q: What Experiment is This?
Name of experiment
type of excitation
Response
i ____
slope
Deficiency
Excitation
Response
time
time
E
I
to
to
t
What Experiment Is This?
Name of experiment
Type of excitation
Response
Q ____
intercept
slope
Excitation
Response
time
time
E
Q
to
to
t
Qdl
Q: What Is This Experiment?
Name of experiment
Excitation
Response
i ____
Ep ____ of
E’= _____________
Time, s
Eapp, V
Excitation
E1
E2
Eapp, V
I, A
Ep
E1
E2
Response
Eo
Eo
X
X
Cyclic Voltammetry (CV)
Important parameters:
Epa and Epc
ipc and iac
E’
DE = |Epa - Epc|
Time, s
Eapp, V
Excitation
E1
E2
Eapp, V
I, A
Epa
Epc
E1
E2
Response
forward
reverse
R - ne- = O
For Nernstian CV
DEp = |Epa - Epc| = 59/n mV at 250C
independent of n
Eo = (Epa + Epc)/2
Ipc/Ipa = 1
For Nernstian Process
Potential excitation controls [R]/[O] as in Nernst equation: Eapp = E0- log [R]/[O]
if Eapp > E0, [O] ___ [R] and ox occurs
if Eapp < E0, [O] ___ [R] and red occurs
., potential excitation CONTROLS [R]/[O]
Criteria for Nernstian Process
Ep independent of scan rate
ip 1/2 (diffusion controlled)
Ipc/Ipa = 1 (chemically reversible)
Quasi-reversible or Irreversible
Quasi-reversible:
Ep > 59 mV and Ep increases with increasing
iR can mascarade as QR system
Irreversible:
chemically - no return wave
slow ET - 2 waves do not overlap
EXAMPLE: Electrocatalytic Oxidation of Guanine in DNA
Top: non-faradaic contribution
Bottom: shape and magnitude of redox waves
; Anal. Chem. 2000, 72, 3764-70.