lecture’#1’ ’to’electrochemistry’ - unige...
TRANSCRIPT
Lecture #1 Introduc.on to electrochemistry
Kaori Sugihara
Email: [email protected] HP: h@p://www.unige.ch/sciences/chifi/sugiharalab/
Lecture plan
§ Lecture 1: Introduc.on to electrochemistry § Lecture 2: Thermodynamics of electrochemical cells § Lecture 3: Impedance spectroscopy § Lecture 4: Cyclic voltammetry § Lecture 5: Electrophore.c techniques + Electrophysiology § Lecture 6: Other state of art applica.ons in electrochemistry
Exam: A wri@en exam for 2 h (the date to be fixed later) You are allowed to bring the printouts and a calculator. Reference: Electrochemical methods – fundamentals and applica.ons Allen J. Bard Larry R. Faulkner
Program of today´s class
Goal of the lecture § To understand what kinds of applica.ons electrochemistry has
§ To understand the characteris.cs of ideal polarized electrodes
§ To understand two-‐, three-‐, and four-‐electrode measurement setup
Electrochemistry
Protein purifica.on (Electrophoresis)
Corrosion
Ba@eries
Fuel cells
Electropla.ng of metals
History of electrochemistry
Luigi Galvani, Italy (1737-‐1798)
Electrolysis of water
William Nicholson, English (1753-‐1815)
Johann Wilhelm Ri@er, Germany (1776-‐1810)
The first ba@ery
Alessandro Volta, Italy (1745-‐1827)
The first mass produced ba@ery
William Cruickshank, Scotland (-‐1811)
Biosensors Glucose sensor
Diabetes The leading cause for death in the world
Dreams.me.com Normal range 4.4 – 6.6 mM
How does it work?
electrode
Glucose oxidase (GOx) Flavin adenine dinucleo.de (FAD)
biocataly.c reac.on
J. Wang, Chem. Rev. 2008, 108, 814-‐825
Dye-‐sensi.zed solar cell
New genera.on solar panel § Higher efficiency? § Lower cost?
A. Hagfeldt, et al., Chem. Rev. 2010, 110, 6595–6663
How does it work?
( fluorine-‐doped .n oxide)
A. Hagfeldt, et al., Chem. Rev. 2010, 110, 6595–6663
Nobel prize in electrochemistry
Wilhelm Ostwald Latvia (1853-‐1932)
Jaroslav Heyrovský Check republic (1890-‐1967)
Arne Wilhelm Kaurin Tiselius Sweden (1902-‐1971)
Nobel Prize in Chemistry in 1909
Catalysis, chemical equilibria, reac.on
veloci.es
Nobel Prize in Chemistry in 1959
Polarography (mercury electrode)
Nobel Prize in Chemistry in 1948
electrophoresis
What will happen when we put an electrode under aqueous solu.on?
Pt, Ag etc.
Ideal polarized electrode
H+
H+
OH-‐
OH-‐
No charge transfer (electrons do not move from solu.on to the metal)
V
E
q
+
+
Electrical double layer
h@p://en.wikipedia.org/wiki/File:EDLC-‐Poten.aldistribu.on.png
Stern layer
Charging currents for a constant voltage
V
Charging currents for a constant voltage
Solve this equa.on for q(t)… E constant!
In case of constant current
Solve this equa.on for E(t)… i constant!
In case of linear voltage sweep
Solve this equa.on for i(t)… E(t), i(t)
So far we learned ideal polarized electrodes. However, most of the .me, real electrodes are NOT ideal polarized electrodes!
Non-‐polarized electrodes
H+
H+
OH-‐
OH-‐
V
E
There is charge transfer
e-‐
R C
A + e-‐ à B
e-‐
C à D + e-‐
Lecture 3: Impedance spectroscopy
Electrode reac.on rate
H+
H+
OH-‐
OH-‐
V
There is charge transfer
e-‐ A + e-‐ à B
e-‐
C à D + e-‐ Per unit .me
Per unit area
polarized electrodes vs non-‐polarized electrodes
Pt
Au
AgCl
Number of the electrodes
This part is extremely important! This will be one of the ques.ons in the exam!!
Two electrode measurements What is the resistance of this sample RS?
A V
… Is this really RS? à NO!
I
Two electrode measurements
A V
RS r r
Contact resistance (resistance at the interface)
I
Four electrode measurements
A V
RS r r
Contact resistance (resistance at the interface)
V
VS
I Do not use this value!
What if you are interested in one of the contact resistance r?
A V
RS r r
I
A V
RS r r
V
VS
I
Three electrode measurements
In electrochemistry V
R1
C1
R2
C2
RSolu.on
A
I
R = VI= RSolution + R1 + R2
If you are interested only in one interface V
R1
C1
R2
C2
RSolu.on
A
I
R = VSI= RSolution + R1
Working electrode (the electrode of interest)
V
VS Reference electrode
Counter electrode
The standard three electrode setup in electrochemistry
Three electrode cell
Poten.ostat
Au
V1
I
Pt
A
Working electrode
Counter electrode
Poten.ostat
AgCl
V
Reference electrode
V2
R = V2I
Which technique do you have to use? Two, three or four electrode set up?
We want to study the effect of polymer coa.ng on an gold electrode.
Au electrode
polymer
solu.on
K. Sugihara, et al., The Journal of Physical Chemistry B, 2010, 114, 13982-‐13987.
We want to study the polymer resistance.
polymer
solu.on
Chip (insulator) with a pore
K. Sugihara, et al., The Journal of Physical Chemistry B, 2010, 114, 13982-‐13987.
We want to study the ac.vi.es of ion channels.
S. Demarche, et al., Analyst, 2011, 136.
V
R1
C1
R2
C2
RSolu.on
A
I
R = VI= RSolution + R1 + R2
Alterna.ve tricks to perform “4 electrode measurements” with 2 electrodes
V
R1
C1
R2
C2
RSolu.on
A
I
R = VI= RSolution + R1 + R2
Alterna.ve tricks to perform “4 electrode measurements” with 2 electrodes
Ag/AgCl electrode (≠ AgCl electrode)
AgCl (s) + e-‐ à Ag (s) + Cl-‐ (aq)
AgCl wire (solid)
KCl + AgCl solu.on (Cl-‐, Ag+) Porous plug (salt bridge)
Very small charge transfer resistance and capacitance à Perfect non-‐polarized electrode
Galvanic vs Electroly.c
Take home messages • Electrochemistry is technologically very important for ba@eries, solar cells, biosensors etc.
• Ideal polarized electrodes and non-‐polarized electrodes have different characteris.cs (real electrodes are most of the .me in between).
• It is extremely important to select the right configura.on (2, 3 or 4 electrode setup) for electrochemical measurements.
Today’s references § Allen J. Bard, Larry R. Faulkner, Electrochemical methods – fundamentals
and applica.ons
§ J. Wang, Chem. Rev. 2008, 108, 814-‐825
§ A. Hagfeldt, et al., Chem. Rev. 2010, 110, 6595–6663