Introduction to electrochemical systems

Sähkökemian peruseetKE-31.4100

Tanja Kalliotanja.kallio@aalto.fiC213

CH 1

Introduction to electrochemistry

Electrochemical cell

load

electrically charged species medium+ = electrolyte

ions

complex ionsmolecules

waterorganic solvent

ceramics

molten saltsionic liquids

membranes

electrodes

external circuitload or measuring equipment

Electrochemical reaction

electrode

e-electrochemical reaction = heterogeneous redox reaction

The rate of an electrochemical reaction depends on the potential of the electrode

Redox-reactions in the cell

load

PtPt

acidic aqueous electrolyteH2SO4, HClO4, …

AnodeH2 2H+ + 2e-

Eo = 0.00 V

Cathode O2 + 4H+ + 4e- 2H2OEo = 1.23 V

reaction of interest = working electrode

counter electrodereference electrodeauxillary electrode

I = nFr Q = It = nzFnF

GE

Metal bonding, Fermi level and work function

Fermi Dirac distribution

Fermi level P(E) = 1/2

Potential and voltage

f inner or galva potential

outer or voltapotential surface potential

faasi a

charge invacuum

nFGE

Electrode potential, potential difference and voltage

electrode

probability for finding an electron

solution

Ef

elec

trod

pote

ntia

l

+

- electrode

occupiedstates

unoccupie

d

occupied states

unoccupie

d

0.50 1

Ef’

0.50 1

solutionen

ergy

nFGE

kTEEeEP

/)( f1

1)(

Electron transfer on the electrode

Ef

electrode

occupiedstates

unoccupied

Ef’

ener

gy

HOMO

LUMOe-

HOMO

LUMOe-

electrode

a molecule in a solvent

a molecule in a solvent

Ag+(aq) + e- Ag Ag+(aq) + e- Ag

Potential window

polarizability

ideally nonpolarizable

ideally polarizable

reaction rate ~

reaction rate ~ 0

Li4Ti5O7 electrode for lithiun ion battery

ultra capacitor