Lecture #1 Introducon to electrochemistry

Kaori Sugihara

Email: [email protected] HP: hp://www.unige.ch/sciences/chifi/sugiharalab/ Lecture plan

§ Lecture 1: Introducon to electrochemistry § Lecture 2: Thermodynamics of electrochemical cells § Lecture 3: Impedance spectroscopy § Lecture 4: Cyclic voltammetry § Lecture 5: Electrophorec techniques + Electrophysiology § Lecture 6: Other state of art applicaons in electrochemistry

Exam: A wrien 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 applicaons Allen J. Bard Larry R. Faulkner

Program of today´s class

Goal of the lecture § To understand what kinds of applicaons electrochemistry has

§ To understand the characteriscs of ideal polarized electrodes

§ To understand two-, three-, and four-electrode measurement setup Electrochemistry Baeries

Fuel cells Corrosion

Electroplang of metals

Protein purificaon (Electrophoresis) History of electrochemistry

Luigi Galvani, Italy (1737-1798) Electrolysis of water

William Nicholson, English (1753-1815)

Johann Wilhelm Rier, Germany (1776-1810) The first baery

Alessandro Volta, Italy (1745-1827) The first mass produced baery

William Cruickshank, Scotland (-1811) Biosensors

Diabetes Glucose sensor The leading cause for death in the world

Normal range 4.4 – 6.6 mM Dreamsme.com How does it work?

biocatalyc reacon Flavin adenine Glucose oxidase (GOx) dinucleode (FAD)

electrode

J. Wang, Chem. Rev. 2008, 108, 814-825 Dye-sensized solar cell

New generaon 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, reacon electrode) velocies What will happen when we put an electrode under aqueous soluon?

Pt, Ag etc. Ideal polarized electrode + V

No charge transfer (electrons do not move from soluon to the metal)

q H+ + E

OH-

OH- H+ Electrical double layer

Stern layer

hp://en.wikipedia.org/wiki/File:EDLC-Potenaldistribuon.png Charging currents for a constant voltage

V Charging currents for a constant voltage

Solve this equaon for q(t)… E constant! In case of constant current

Solve this equaon for E(t)… i constant! In case of linear voltage sweep

Solve this equaon 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 reacon 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 quesons 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

RSoluon

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

RSoluon

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 Potenostat Potenostat

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 coang on an gold electrode.

soluon

polymer

Au electrode

K. Sugihara, et al., The Journal of Physical Chemistry B, 2010, 114, 13982-13987. We want to study the polymer resistance.

soluon 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 acvies of ion channels.

S. Demarche, et al., Analyst, 2011, 136. Alternave tricks to perform “4 electrode measurements” with 2 electrodes

I V A

R1 R2

RSoluon

C1 C2

V R = = R + R + R I Solution 1 2 Alternave tricks to perform “4 electrode measurements” with 2 electrodes

I V A

R1 R2

RSoluon

C1 C2

V R = = R + R + R I Solution 1 2 Ag/AgCl electrode (≠ AgCl electrode)

AgCl wire (solid)

KCl + AgCl soluon (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 Electrolyc Take home messages

• Electrochemistry is technologically very important for baeries, solar cells, biosensors etc.

• Ideal polarized electrodes and non-polarized electrodes have different characteriscs (real electrodes are most of the me in between).

• It is extremely important to select the right configuraon (2, 3 or 4 electrode setup) for electrochemical measurements. Today’s references

§ Allen J. Bard, Larry R. Faulkner, Electrochemical methods – fundamentals and applicaons

§ J. Wang, Chem. Rev. 2008, 108, 814-825

§ A. Hagfeldt, et al., Chem. Rev. 2010, 110, 6595–6663