lecture’#1’ ’to’electrochemistry’ - unige...

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


Polarography (mercury electrode)


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

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

lecture’#1’ ’to’electrochemistry’ - unige...

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