ELECTROCHEMICAL METHODS Fundamentals and Applications - Allen.J.Bard

20 Chapter 1. Introduction and Overview of Electrode Processes
Electrode
variables
Material
Surface area (A)
Geometry
Surface condition
Mass transfer
variables
Mode (diffusion,
convection,...)
Surface concentrations
Adsorption
Figure 1.3.2
Solution variables
Bulk concentration of electroactive
species (C o, c R)
Concentrations of other species
(electrolyte, pH,...)
Solvent
External variables
Temperature (T)
Pressure {P)
Time (?)
Electrical variables
Potential (£)
Current (i)
Quantity of electricity (Q)
Variables affecting the rate of an electrode reaction.
Another way of visualizing an electrochemical experiment is in terms of the way in
which the system responds to a perturbation. The electrochemical cell is considered as a
"black box" to which a certain excitation function (e.g., a potential step) is applied, and a
certain response function (e.g., the resulting variation of current with time) is measured,
with all other system variables held constant (Figure 1.3.3). The aim of the experiment is
to obtain information (thermodynamic, kinetic, analytical, etc.) from observation of the
(a) General concept
Excitation System Response
(b) Spectrophotometric experiment
Lamp-Monochromator
(c) Electrochemical experiment
Optical cell
with sample
Phototube
Figure 1.3.3 (a) General principle of studying a system by application of an excitation (or
perturbation) and observation of response, (b) In a spectrophotometric experiment, the excitation
is light of different wavelengths (A), and the response is the absorbance (si) curve, (c) In an
electrochemical (potential step) experiment, the excitation is the application of a potential step,
and the response is the observed i-t curve.