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 Ba eries
Fuel cells Corrosion
Electropla ng of metals
Protein purifica on (Electrophoresis) 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
Diabetes Glucose sensor The leading cause for death in the world
Normal range 4.4 – 6.6 mM Dreams me.com How does it work?
biocataly c reac on Flavin adenine Glucose oxidase (GOx) dinucleo de (FAD)
electrode
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 Jaroslav Heyrovský Arne Wilhelm Kaurin Tiselius Latvia (1853-1932) Check republic (1890-1967) Sweden (1902-1971)
Nobel Prize in Chemistry Nobel Prize in Chemistry Nobel Prize in Chemistry in 1909 in 1959 in 1948 Catalysis, chemical Polarography (mercury electrophoresis equilibria, reac on electrode) veloci es What will happen when we put an electrode under aqueous solu on?
Pt, Ag etc. Ideal polarized electrode + V
No charge transfer (electrons do not move from solu on to the metal)
q H+ + E
OH-
OH- H+ Electrical double layer
Stern layer
h p://en.wikipedia.org/wiki/File:EDLC-Poten aldistribu on.png 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 V e-
There is charge transfer A + e- à B e-
- C à D + e + H R C E
OH-
H+
- OH Lecture 3: Impedance spectroscopy Electrode reac on rate V e-
There is charge transfer A + e- à B e-
C à D + e- Per unit me H+
- OH Per unit area
H+ OH- 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?
I V A
… Is this really RS? à NO! Two electrode measurements
Contact resistance RS (resistance at the interface) r r
I V A Four electrode measurements
VS V Contact resistance RS (resistance at the interface) r r
I Do not use this value! V A What if you are interested in one of the contact resistance r?
RS r r
I V A Three electrode measurements
VS V
RS r r
I V A In electrochemistry I V A
R1 R2
RSolu on
C1 C2
V R = = R + R + R I Solution 1 2 If you are interested only in one interface I V A VS Reference electrode V R1 R2
RSolu on
C1 C2
Working electrode Counter electrode (the electrode of interest)
V R = S = R + R I Solution 1 The standard three electrode setup in electrochemistry Three electrode cell Poten ostat Poten ostat
Counter electrode Pt V 1 Reference electrode AgCl
I A V V2
Au V Working electrode R = 2 I 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.
solu on
polymer
Au electrode
K. Sugihara, et al., The Journal of Physical Chemistry B, 2010, 114, 13982-13987. We want to study the polymer resistance.
solu on polymer 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. Alterna ve tricks to perform “4 electrode measurements” with 2 electrodes
I V A
R1 R2
RSolu on
C1 C2
V R = = R + R + R I Solution 1 2 Alterna ve tricks to perform “4 electrode measurements” with 2 electrodes
I V A
R1 R2
RSolu on
C1 C2
V R = = R + R + R I Solution 1 2 Ag/AgCl electrode (≠ AgCl electrode)
AgCl wire (solid)
KCl + AgCl solu on (Cl-, Ag+) Porous plug (salt bridge)
AgCl (s) + e- à Ag (s) + Cl- (aq)
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