Analytical Electrochemistry :
The Basic Concepts
Module Description
What’s this all about?
Goals and Objectives
Why take the time to look at this?
Fundamentals
What is analytical electrochemistry and
what makes it work?
Voltammetric Methods
What are they and what are they good for?
Experimental Hardware
What do I need to do electrochemistry?
Introduction
Electrochemistry is something that is seldom studied
and yet is all around us, including the control circuitry of
our body. We are familiar with lightning that
reverberates with thunder in a rainstorm, with batteries
that power flashlights and hybrid autos, and with sensor
devices such as smoke and carbon monoxide detectors
or glucose analyzers for monitoring diabetes. All rely on
or exhibit some basics of electrochemistry. To
understand electrochemical phenomenon, we need to
have an understanding of some basic concepts and the
language that conveys these concepts. It is the goal of
this module to get you started – so that you can explore
further as you wish. Web-links and hardcopy references
are provided to assist you in that process. Good luck!
Experiments
Ready to give it a try?
References and Links
Tell me more!
Richard S. Kelly
Department of Chemistry, East Stroudsburg University,
East Stroudsburg, PA 18301
This work is licensed under a
Creative Commons Attribution-Noncommercial-Share Alike 2.5 License
Analytical Electrochemistry :
The Basic Concepts
Back to Introduction
Goals and Objectives
Why take the time to look at this?
Fundamentals
What is analytical electrochemistry and
what makes it work?
Voltammetric Methods
What are they and what are they good for?
Experimental Hardware
What do I need to do electrochemistry?
Experiments
Ready to give it a try?
References and Links
Tell me more!
Module Description
This module gently introduces a topic whose mere
mention often strikes fear in the hearts of students and
teachers alike. Whether because of some intimidating
mathematical aspects of the subject, or a lack of time to
provide an adequate basis for understanding, it is often
left off of course syllabi in analytical chemistry. This
learning module is designed as an introduction to the
underlying theory and general practice of several
common techniques in analytical electrochemistry. It is
intended to contain sufficient background material so
that educators or new practitioners in the field can use
the material in a “stand-alone” way. References and
links are provided so that users who so desire can
pursue a more extensive study of each topic presented.
Sufficient coverage is provided such that the module
could serve as a two- to three-week segment of a course
in analytical chemistry or instrumental methods.
2
Analytical Electrochemistry :
The Basic Concepts
Back to Introduction
Module Description
What’s this all about?
Fundamentals
What is analytical electrochemistry and
what makes it work?
Voltammetric Methods
What are they and what are they good for?
Experimental Hardware
Goals and Objectives
Each part of this module describes certain aspects of the
experience that is analytical electrochemistry.
The goal is to include enough information that you can
understand and use electrochemical techniques
effectively without getting bogged down in theory (or lost
in the double layer).
After study of this module, you should be able to:
What do I need to do electrochemistry?
Experiments
Ready to give it a try?
References and Links
Tell me more!
Discuss the physical basis underlying voltammetric
methods.
Describe an electrochemical cell and its contents.
Visualize how a potentiostat works.
No longer cringe at the mention of electrochemistry!
3
Analytical Electrochemistry :
The Basic Concepts
Back to Introduction
I. Fundamentals of Electrochemistry
Goals and Objectives
Why take the time to look at this?
Module Description
What’s this all about?
Voltammetric Methods
A. Electrochemical thermodynamics – the
study of an interface
1. What is potential?
2. The double-layer and charging current
What are they and what are they good for?
Experimental Hardware
What do I need to do electrochemistry?
Experiments
Ready to give it a try?
References and Links
Tell me more!
B. The Electrode Process – moving electrons
around
1. Plotting Conventions
2. Reversibility – chemical and
electrochemical
3. Mass Transport – getting stuff to the
electrode surface
4
Analytical Electrochemistry :
The Basic Concepts
I. Fundamentals of Electrochemistry
A. Electrochemical thermodynamics –
the study of an interface
1. What is potential?
2. The double-layer and
charging current
B. The Electrode Process – moving
electrons around
1. Plotting Conventions
2. Reversibility – chemical and
electrochemical
3. Mass Transport – getting
stuff to the electrode surface
Back to Introduction
A. Electrochemical Thermodynamics
Electrochemistry can be defined as the study of
phenomena at electrified interfaces.1 As such, two
things are fundamental to electrochemical
measurements:
a) Interface: boundary between two distinct,
chemically different phases
b) Electric field: existing across the interface
Generally, the interface occurs between a metallic
conductor (the electrode) and a fluid, ionic
conductor (the solution). The electric field usually
results as a consequence of contact between a
solid electrode and the solution. In
electrochemistry, the electric field is most often one
that is under user control, for example by utilizing a
device called a potentiostat, which will be discussed
in a later section.
5
Analytical Electrochemistry :
The Basic Concepts
I. Fundamentals of Electrochemistry
A. Electrochemical thermodynamics –
the study of an interface
1. What is potential?
2. The double-layer and
charging current
B. The Electrode Process – moving
electrons around
1. Plotting Conventions
2. Reversibility – chemical and
electrochemical
3. Mass Transport – getting
stuff to the electrode surface
Back to Introduction
B. The Electrode Process
As you have probably realized, the fundamental basis for most
electrochemical techniques is the measurement of current or voltage
changes between two electrodes in solution. Given that basis, it
follows that analytical electrochemistry is broken down into two major
categories: 1) techniques that measure current following a change in
potential, and 2) techniques that measure potential under conditions
of no current flow.
Techniques of the first type are known as voltammetric methods, while those
in the second are referred to as potentiometric methods. We will
concern ourselves here with voltammetry, leaving a discussion of
potentiometry including measurement of pH for a separate learning
module.
Voltammetry is defined as the measurement of current which flows at an
electrode as a function of the potential applied to the electrode. 3
Current-potential curves are the electrochemical equivalent of
absorbance-wavelength curves recorded in spectrophotometric
experiments.
Once you gain an understanding of the voltammetric process (hopefully by
the time you finish this module), you will recognize that
voltammograms have the potential (no pun intended) to yield
qualitative, quantitative, thermodynamic, and kinetic information
about redox active species.
6
Analytical Electrochemistry :
The Basic Concepts
Back to Introduction
II. Voltammetric Methods
Goals and Objectives
Why take the time to look at this?
Module Description
What’s this all about?
Fundamentals
A. Basics of Voltammetry – applying a potential
and measuring a current
1. Potential Step Methods
What is analytical electrochemistry and
what makes it work?
Experimental Hardware
What do I need to do electrochemistry?
Experiments
Ready to give it a try?
a) Chronoamperometry – current as
a function of time and applied potential
b) Chronocoulometry – charge as a function
of time and applied potential
References and Links
Tell me more!
continued
7
Analytical Electrochemistry :
The Basic Concepts
Back to Introduction
II. Voltammetric Methods
Goals and Objectives
Why take the time to look at this?
2. Potential Sweep Methods
Module Description
What’s this all about?
Fundamentals
What is analytical electrochemistry and
what makes it work?
Experimental Hardware
a) Linear Sweep Voltammetry – current as a
function of time and applied potential
b) Cyclic Voltammetry – current as a function of
applied potential – sweep in two directions
What do I need to do electrochemistry?
Experiments
Ready to give it a try?
References and Links
c) Anodic Stripping Voltammetry – current as a
function of applied potential following deposition of
species of interest
Tell me more!
previous page
8
Analytical Electrochemistry :
The Basic Concepts
II. Voltammetric Methods
A. Basics of Voltammetry – applying a
potential and measuring a
current
1. Potential Step Methods
a) Chronoamperometry
b) Chronocoulometry
2. Potential Sweep Methods
a) Linear Sweep Voltammetry
b) Cyclic Voltammetry
c) Anodic Stripping
Voltammetry
A. Basics of Voltammetry
Electrochemical techniques in which current is
measured as a function of the applied
potential in an electrochemical cell are called
voltammetric methods. In previous sections
we have introduced the concepts underlying
electron transfer reactions which can occur at
the surface of solid electrodes as the potential
across the solution interface is changed. In
this section we will introduce a number of
electrochemical techniques that use the
controlled application of potential to
accomplish analytical objectives.
Back to Introduction
9
Analytical Electrochemistry :
The Basic Concepts
1. Potential Step Methods
1. Potential Step Methods
a) Chronoamperometry current as a function of time
and applied potential
b) Chronocoulometry charge as a function of time
and applied potential
Back to Introduction
Methods of this type involve stepping the electrode potential from
a value where little or no faradaic current is observed to
one sufficient to oxidize or reduce an electroactive species
in the vicinity of the electrode. Large amplitude step
methods described in this section involve a change in
potential capable of instantly converting essentially all of
the electroactive material at the electrode surface to its
redox partner. In contrast, small amplitude potential
methods, described elsewhere in this module, involve small
changes in surface redox concentrations as a function of
changing potential, with the concentrations of the members
of the redox pair described by the Nernst Equation.
We will include here two of the most frequently used large
amplitude potential step (potentiometric) methods,
chronoamperometry and chronocoulometry.
Chronoamperometry involves the measurement of current passing
in the electrochemical cell at a fixed potential as a function
of time (i vs. t).
Chronocoulometry is the measure of total charge (the integrated i-t
response, Q), also as a function of time.
10
Analytical Electrochemistry :
The Basic Concepts
2. Potential Sweep Methods
2. Potential Sweep Methods
Potential sweep methods are those utilizing an
applied potential that changes with time as the
excitation signal. The most common
waveform is that of a linear sweep, beginning
at a potential far removed from the E0’ for the
b) Cyclic Voltammtery –
species of interest and increasing in
current as a function applied
magnitude at a constant rate. The current
potential and scan rate –
passing at the working electrode is measured
sweep in two directions
as a function of the applied potential, with
electron transfer accomplished by scanning
c) Anodic Stripping Voltammetry –
the potential through the regions on either
current as a function of applied
side of the E0’. The most common potential
potential following deposition of
sweep methods are linear sweep voltammetry
species of interest
(LSV), cyclic voltammetry (CV), and anodic
stripping voltammetry (ASV).
a) Linear Sweep Voltammetry current as a function of applied
potential and scan rate
Back to Introduction
11
Analytical Electrochemistry :
The Basic Concepts
b. Cyclic Voltammetry
i) Introduction
ii) Important parameters in CV
1. Peak location
2. Current ratios
3. Scan rate dependence of
peak current
iii) Chemical reactions coupled to
electron transfer
1. ErCi
2. ErCr
3. ErCi’
4. CrEr
5. ErCiEr
iv) Additional considerations
1. Capacitive current
2. Solution resistance
Back to Introduction
b. Cyclic Voltammetry
Cyclic voltammetry is one of the most widely used
of electroanalytical techniques. Its popularity
results from the modest cost of the required
instrumentation, the abundance of
mechanistic information that it can deliver, and
the conceptual simplicity of the data display.
We saw in a previous section that the currentpotential profile for LSV was peak shaped for
an electroactive species undergoing electron
transfer. In cyclic voltammetry, the potential
scan is reversed at some point beyond the
peak, and scanned back in the direction of the
initial potential. In the simplest CV
experiment, the potential waveform is a
triangle, with the initial and final potentials
being the same.
12
Analytical Electrochemistry :
The Basic Concepts
III. Experimental Hardware
III. Experimental Hardware
A. Electrochemical cells
1. Defining the cell
2. Positioning the electrodes
3. Other considerations
B. Reference and auxiliary electrodes
1. Reference electrodes
a) Saturated calomel
b) Silver/Silver chloride
c) Non-aqueous reference
2. Auxiliary electrodes
C. Working electrodes
1. Electrode types
2. Advantages and limitations
D. Potentiostats
Back to Introduction
Most voltammetric measurements make use of a
device called a potentiostat, which is capable
of applying a controlled potential to a working
electrode and measuring the current that
passes as a result of electron transfer to
solution species of interest. The working
electrode, along with a reference electrode
and an auxiliary electrode are commonly
placed in an electrochemical cell, with a fill
solution containing an inert electrolyte and the
analyte. Cell designs can be quite simple to
quite complex, with solution volumes ranging
from a few microliters to many milliliters.
13