1. BASIC PRINCIPLES OF ELECTRODE PROCESSES Heterogeneous kinetics

2. - - - - - - - - Charged interfaces - - - - - -
Ions and dipoles in the volume element :
solutions (random distribution, isotropic) (charge Q = O)
charged interface: electrode/electrolyte (anisotropic) (Q  O)
Metal - +
Electrolyte -
Electric (electrode) double layer (EDL):
metals/electrolytes (Ag/Ag+) ; (Hg/NaF) ; (Hg/KI)
non-metallic elements/ electrolyte (gas, glass, polymers, membranes, colloides…)
liquid I/liquid II - - + + + - - + + + - - - + - - + + - - - + +

3. Potential creation on interface
Heterogeneous system 
solid conductive phase – interface – liquid conductive phase
 
1. Ag (Ag+ ) Ag+ NO3-
2. Pt ( Pt-Ir, graphite) Fe2+ , Fe3+ ( SO4 2- )
spontaneous ion crossing 1. or electron transfer 2.
 spontaneous interface charging:
1. Ag e  Ag
2. Fe e  Fe2+
0x z e  Red

4. Chemical potential: i = io + RT ln ai
i * = i + zF = in balance
i = /z/ F 
 = potential difference between solid phase and solution
 inner (Galvani) potential, immeasurable!
balance stabilization  electrochemical potential equality of ion i in both phases:
i *(l) = i* (s)
i *(l) = i zF 
chemical work
electrical work

5. Measurable  cell potential EMN , made from 2 hemi-cells:
standard hydrogen electrode SHE Eo = 0 V measured electrode E = b +  b = constant
EMN = E = E
Nernst : 1. 2.
That was a balance

6. From within entered potential on electrode:
charge goes through an interface
impossible of charging 
impolarizedable interface (impolarizedable electrode, Ag / Ag+ )
charge doesn´t go through an interface
possible of charging
polarizedable interface
(polarizedable electrode, Pt, graphite, Hg, without Hgz+ in solution)

7. ELECTRODE DOUBLE LAYER (EDL)

8. ELECTRODE DOUBLE LAYER (EDL)
electrostatic potential  charge density σ surface tension g capacity C adsorption G
Electrode
Solution
Electrode
Electrode -
+σS G
+ - - - + φ + -
-σM +
Solution -
+ -
Solution
+ - + - - -
+ - + - - -
+ -

9. a) capillary elevation b) stalagmometr (also DME)
surface tension g 2r  F Fg
b) stalagmometr (also DME) h

10. differential capacity Cd
charge density σ
Lippman equation
capacity C
differential capacity Cd
integral capacity Ci
adsorption G
Langmuir isotherm
fraction of coverage
surface or maximum surface excess ,
adsorption coefficient
activity of species i in bulk solution

11. Temkin isotherm Frumkin isotherm Esin-Markov effect
g …. parameter treating the interaction energy between the adsorbed species
Frumkin isotherm
Esin-Markov effect
The degree of specific adsorption should vary with electrolyte concentration, just as there should be a change in the point of zero charge

12. ELECTRODE DOUBLE LAYER STRUCTURE ON INTERFACE ELECTRODE - ELECTROLYTE
electrostatic
models
ELECTRODE DOUBLE LAYER STRUCTURE ON INTERFACE ELECTRODE - ELECTROLYTE
charges - points +
history
Electrolyte - + φ M φs x xH Cd E
 = 5-7
Electrode
(metal)
about F/cm2 xH
Helmholtz Model (1879)

13. - c1 > c2 + c2 c1 Gouy-Chapman Model (1910-1913) diffuse layer φ φM
ELECTRODE DOUBLE LAYER STRUCTURE ON INTERFACE ELECTRODE - ELECTROLYTE
diffuse layer
Electrolyte - +
c1 > c2 φ φM x xH Cd c2
Electrode
(metal) c1 φs E EZ
Gouy-Chapman Model ( )

14. Gouy-Chapman Model (1910-1913)
distribution of species with distance from electrode
(xDL = distance characteristic of the diffuse layer)
Bolztmann´s law
Poisson´s equation

15. diffuse layer thickness
Poisson-Bolztmann equation
xDL = distance characteristic of the diffuse layer
diffuse layer thickness
xDL for water at 298 K is 3.04*10-8 z-1c-1/2 cm
if c = 1M and z = 1, then xDL is 0.3 nm.

16. ELECTRODE DOUBLE LAYER STRUCTURE ON INTERFACE ELECTRODE - ELECTROLYTE
Compact Layer
Electrolyte - + φ φM
Diffuse Layer
Electrode
(metal) φs xH x
OHP Cd
Stern Model (1924) EZ E

17. far from EZ, CH  CGC and so Cd ~ CH
Stern Model (1924)
close to EZ, CH >> CGC and so Cd ~ CGC
far from EZ, CH  CGC and so Cd ~ CH
separation plane between the two zones is called the outer Helmholtz plane (OHP)

18. ELECTRODE DOUBLE LAYER STRUCTURE ON INTERFACE ELECTRODE - ELECTROLYTE
IHP - Inner Helmholtz Plane
IHP
OHP - Outer Helmholtz Plane
OHP
OHP φ
IHP
Diffuse Layer + - +
E > EZ - - - - +
E = EZ + +
Electrode
(metal)
Electrolyte - - +
E < EZ - + x - + - xH + - Cd - - + + - - - - + + EZ -E
Grahame Model (1947)

19. - - - - - - - - - - - - - OHP IHP + + - + - + - + - + + - + - + - + -
ELECTRODE DOUBLE LAYER STRUCTURE ON INTERFACE ELECTRODE - ELECTROLYTE
OHP +
+ -
IHP +
+ - -
+ - -
+ - +
+ -
+ -
Electrolyte - - -
+ - +
+ -
Electrode
(metal) -
+ - - + -
+ - +
+ - - - - -
+ - -
+ - +
+ -
+ - - - -
+ -
+ - -
Layer of oriented molecules of supporting electrolytes or solvents
+ -
BDM Model
Bockris, Devanathan, Müller Model (1963)

20. CHARACTERISTIC OF ELECTRODE POTENTIAL IN DOUBLE LAYER
OHP  2 x2
 x x2 2 
 x
OHP
adsorption

21. Chemical Model (Damaskin and Frumkin) (Trasatti) (Parsons)
ELECTRODE DOUBLE LAYER STRUCTURE ON INTERFACE ELECTRODE - ELECTROLYTE
Chemical Models - the electronic distribution of the atoms in the electrode
( not only electrostatic forces)
- difference between (sp) metals and transition (d)metals
- IHP as an electronic molecular capacitor
- jellium model
Classical representation φM φM
The jellium model φs φs
Variation of the electrostatic potentials with distance from a metallic electrode
Chemical Model (Damaskin and Frumkin)
(Trasatti)
(Parsons)

22. ELECTRODE DOUBLE LAYER STRUCTURE ON INTERFACE ELECTRODE - ELECTROLYTE
Electron spill-over at the surface of a metal according to the Jellium model.