INTRODUCTION TO
ELECTROCHEMICAL
CELLS AND BASIC
ELECTROANALYTICAL
MEASUREMENTS
Sunny Holmberg
January 19th 2016
1
Topics in Lecture
• Fundamentals of Electrochemistry
– Two electrode systems
– Reference electrodes
– Three electrode systems
• Fundamental Kinetics
– Types of Mass Transport
• Basic Electrochemical IV Characterization
• C-MEMS IDEAS Basics
2
Topics in Lecture
• Fundamentals of Electrochemistry
– Two electrode systems
– Reference electrodes
– Three electrode systems
• Fundamental Kinetics
– Types of Mass Transport
• Basic Electrochemical IV Characterization
• C-MEMS IDEAS Basics
3
Basic Electrochemical Cells
• Electrochemistry is the
analysis of redox
reactions that occurs
between an electrode
and a liquid medium
• The characteristics of
which are measured
based on Voltages
and Currents
4
Basic Electrochemical Cells
• Voltage – the electrical potential between
two distinct “nodes”
– Voltage is therefore is always a measurement
between two points
– Consequences of this implication is that the
minimum number of electrodes in a basic
electrochemical cell must be two
• Electric potential of the solution cannot be directly
discerned and only indirectly measured with
electrodes.
5
Basic Electrochemical Cells
• Voltage is a characteristic parameter of an
electrochemical (redox) reaction.
– This means that each electrochemical (redox)
potential has (redox) potential associated with
it
– This redox potential could be partially
interpreted as the minimum energy (condition)
needed for a (redox) electrochemical reaction
to occur
– This potential is also its equilibrium potential,
6
i.e. when net current of reaction is zero
Basic Electrochemical Cells
• Current – The number of electrons
traveling between two “nodes” per unit of
time
– Two types of current faradaic and charging
– Faradaic current – current generated by the
single electron exchange between two
medium due to an electrochemical reaction
– Capacitive current – current generated by the
alignment of surface charges in an attempt to
offset the applied potential and reach
7
thermodynamic equilibrium
Basic Electrochemical Cells
• Current is a quantitative measurements.
– The absolute current measured is the
superposition of all the current within the
system
• Therefore careful planning of experiments is need
to decouple the individual current contributing
reactions (i.e. faradaic vs capacitive)
• Current Magnitudes are relatively meaningless
without a baseline for comparison
8
Basic Electrochemical Cells
• Capacitive Current
(baseline current)
– Result of charge
(ions) migrations
– Ions form a
capacitive layer at
interface of solution
and electrodes
– These layers act to
counterbalance the
electrical potential
"EDLC-simplified-principle" by Elcap - Own
work. Licensed under CC0 via Commons https://commons.wikimedia.org/wiki/File:EDL
C-simplified-principle.png#/media/File:EDLC9
simplified-principle.png
Basic Electrochemical Cells
• Two electrode
systems:
– The simplest
electrochemical setup
– Capable of measuring
the voltage and
current change
between two
electrodes in a
solution
10
Basic Electrochemical Cells
• Reference Electrodes
– A reference point to relate all electrochemical
reactions together
– Need a constant fixed potential during
electrochemical reaction that does not change
during experiment (difficult)
11
Basic Electrochemical Cells
• Reference Electrodes
12
Basic Electrochemical Cells
• Reference Electrodes
– Ag/AgCl
• +0.191 V vs SHE
– Calomel
• +0.241 V vs SHE
– CSE (Copper/Copper
sulfate)
• +0.314 V vs SHE
13
Basic Electrochemical Cells
• 3 Electrode Electrochemical Setup
– Needed to measure the behavior of
electrochemical setup over a range of voltage
– Voltage measured between working electrode
and Reference electrode
– Voltage is applied between counter and
working electrode (using a feedback vs
reference)
– Current is measured between working
electrode and counter electrode
14
Basic Electrochemical Cells
• 3 Electrode Electrochemical Setup
15
Topics in Lectrue
• Fundamentals of Electrochemistry
– Two electrode systems
– Reference electrodes
– Three electrode systems
• Fundamental Kinetics
– Types of Mass Transport
• Basic Electrochemical IV Characterization
• C-MEMS IDEAS Basics
16
Fundamental Kinetics
• Mass Transport in Solution
1.
2.
3.
4.
5.
6.
7.
Diffusion to surface
Adsorption to surface
Migration of reactant to reaction site
Electrochemical reaction
Migration of product on surface
Desorption of Product from Surface
Diffusion of Product away from Surface
17
Fundamental Kinetics
• Types of Mass Transport
– Diffusion – transport due to
concentration gradient
– Migration – Transport due to
Electric Potential gradient
– Convection – Transport due
to Pressure Gradient
18
Topics in Lecture
• Fundamentals of Electrochemistry
– Two electrode systems
– Reference electrodes
– Three electrode systems
• Fundamental Kinetics
– Types of Mass Transport
• Basic Electrochemical IV Characterization
• C-MEMS IDEAS Basics
19
Basic Electrochemical IV
Characterization
• Linear Sweep Voltammetry
– Potential is sweeped linearly across a range
E-
t
20
Basic Electrochemical IV
Characterization
• Cyclic Voltammetry
– Potential is sweeped linearly across a range
E-
t
Randles-Sevcik
equation: 3
1


I p  2.69 105 n 2 ACD 2 v
1
2
21
Topics in Lecture
• Fundamentals of Electrochemistry
– Two electrode systems
– Reference electrodes
– Three electrode systems
• Fundamental Kinetics
– Types of Mass Transport
• Basic Electrochemical IV Characterization
• C-MEMS IDEAS Basics
22
Redox Cycling through Inter Digitated electrodes
Arrays(IDA)
•
•
•
•
Two Working electrodes :Generator (Anode)
and Collector (Cathode) electrodes in close
proximity such that the adjacent regions with
concentration gradients overlap
The redox couple may redox cycle multiple
times before they diffuse out into the bulk
solution.
This behavior results in an amplified signal
thereby lowering the lower limit of detection
(LOD) significantly (upto pM)
.c
•Single mode: Cyclic Potential sweep across Generator, Collector not
connected.
•Dual Mode: Constant reduction potential applied across collector while
potential is swept linearly across generator
Redox Cycling as electrode width and gap
Redox Cycling as electrode height
23
Redox Cycling through Inter Digitated
electrodes Arrays(IDA)
•Two Working electrodes :Generator (Anode)
and Collector (Cathode) electrodes in close
proximity such that the adjacent regions with
concentration gradients overlap
•The redox couple may redox cycle multiple
times before they diffuse out into the bulk
solution.
•This behavior results in an amplified signal
thereby lowering the lower limit of detection
(LOD) significantly (upto pM)
•Single.cmode: Cyclic Potential sweep across Generator, Collector not
connected.
•Dual Mode: Constant reduction potential applied across collector while
potential is swept linearly across generator
Redox Cycling as electrode width and gap
Redox Cycling as electrode height