Thus, at E F < E F (Ag
+
/Ag) one can perform STM imaging and at E F > E F (Ag
+
/
Ag)—electrochemical measurements of the reaction kinetics.
Same discussion applies to the other half-cell reaction i.e.:
I 2 þ 2e
À
Ð 2I
À
ð3Þ
Applying a sufficiently positive voltage to the tip will result in oxidation of I
- ions
with formation of iodine.
Thus, the general condition for STM imaging without inducing electrochemical
reactions is given by:
E F I 2 =2I
À
ð
Þ< E F < E F Ag
þ
=Ag
ð
Þ
ð 4Þ
For higher, respectively lower Fermi levels electrochemical reactions of reduction
of Ag
+ or oxidation of I
- will be induced at the bare surface.
The Atomic Switch approach combined with scanning tunnelling spectroscopy
(STS) and current-displacement (I-z) spectroscopy and imaging provides a unique
opportunity for studying site-invariant electrochemical processes with highest possible resolution. It also allows to observe in situ or ex situ the stability and the
dynamics of the formed atomic clusters and relate them to the electrochemical
characteristics.
4.1.2 Using Time as a Kinetic Parameter
The methods used for studying kinetics of electrochemical electrode processes can
be formally divided into stationary (or steady-state), dynamical and quasi-stationary
(e.g. impedance spectroscopy) methods. To evaluate the reaction kinetics a precise
knowledge on the partial ionic current is essential. Determining the partial ionic
current (or the ionic transference number) is often a main challenge in electrochemistry. This especially applies to nanoscale systems. At small dimensions, structure
and properties deviate from the expected macroscopically defined quantities and
effects such as field assisted migration, leakage electronic currents and possibility for
electron tunnelling through the electrolyte should be taken into account. In fact, the
main contribution to the total current is the electronic partial current. Additionally, in
case of field assisted migration (exponential dependence of the ion velocity from
electric field and particle charge) the transference number can vary depending on the
magnitude of the applied voltage. Thus, in these systems there is a principle
difficulty to determine the ionic transference number and therefore to evaluate the
Faraday reaction kinetics. One possible solution of this problem is using the Atomic
Switch approach and introducing time (instead of current) as critical kinetic parameter. As an example can be considered the Butler-Volmer equation, describing the
Nanoscale Electrochemical Studies: How Can We Use the Atomic Switch
79
+
/Ag) one can perform STM imaging and at E F > E F (Ag
+
/
Ag)—electrochemical measurements of the reaction kinetics.
Same discussion applies to the other half-cell reaction i.e.:
I 2 þ 2e
À
Ð 2I
À
ð3Þ
Applying a sufficiently positive voltage to the tip will result in oxidation of I
- ions
with formation of iodine.
Thus, the general condition for STM imaging without inducing electrochemical
reactions is given by:
E F I 2 =2I
À
ð
Þ< E F < E F Ag
þ
=Ag
ð
Þ
ð 4Þ
For higher, respectively lower Fermi levels electrochemical reactions of reduction
of Ag
+ or oxidation of I
- will be induced at the bare surface.
The Atomic Switch approach combined with scanning tunnelling spectroscopy
(STS) and current-displacement (I-z) spectroscopy and imaging provides a unique
opportunity for studying site-invariant electrochemical processes with highest possible resolution. It also allows to observe in situ or ex situ the stability and the
dynamics of the formed atomic clusters and relate them to the electrochemical
characteristics.
4.1.2 Using Time as a Kinetic Parameter
The methods used for studying kinetics of electrochemical electrode processes can
be formally divided into stationary (or steady-state), dynamical and quasi-stationary
(e.g. impedance spectroscopy) methods. To evaluate the reaction kinetics a precise
knowledge on the partial ionic current is essential. Determining the partial ionic
current (or the ionic transference number) is often a main challenge in electrochemistry. This especially applies to nanoscale systems. At small dimensions, structure
and properties deviate from the expected macroscopically defined quantities and
effects such as field assisted migration, leakage electronic currents and possibility for
electron tunnelling through the electrolyte should be taken into account. In fact, the
main contribution to the total current is the electronic partial current. Additionally, in
case of field assisted migration (exponential dependence of the ion velocity from
electric field and particle charge) the transference number can vary depending on the
magnitude of the applied voltage. Thus, in these systems there is a principle
difficulty to determine the ionic transference number and therefore to evaluate the
Faraday reaction kinetics. One possible solution of this problem is using the Atomic
Switch approach and introducing time (instead of current) as critical kinetic parameter. As an example can be considered the Butler-Volmer equation, describing the
Nanoscale Electrochemical Studies: How Can We Use the Atomic Switch
79