文档介绍：Electroanalytical Chemistry
Lecture #2
An Interfacial Process
For: O + ne- = R
5 separate events must occur:
O must be essfully transported from bulk solution (mass transport)
O must adsorb transiently onto electrode surface (non-faradaic)
CT must occur between electrode and O (faradaic)
R must desorb from electrode surface (non-faradaic)
R must be transported away from electrode surface back into bulk solution (mass transport)
What is an Electrode?
Electrical double layer
Electrode Classification
Based on the nature and number of phases between which electron transfer occurs
3 Classes:
Electrodes of the First Kind
Electrodes of the Second Kind
Electrodes of the Third Kind
Electrode of the First Kind
Metal in contact with its cations or non-metal in contact with its anions
EXAMPLES:
Cu2+ /Cu(s)
Zn2+/Zn(s)
SHE
Ag+/Ag (nonaqueous reference electrode)
Cl-/Cl2(g)/Pt
Electrodes in Daniell cell
Electrode of the First Kind (cont’d)
Electrode response given by Nernst equation (Nernstian):
E = E0 + (RT/nF) ln a(M2+)
NOTE: Fe, Al, and W electrodes are NOT electrodes of the First Kind
these have relatively thick surface oxide coatings
Electrode of the Second Kind
Metal in contact with sparingly soluble salt of the mon name: anion electrodes
EXAMPLES:
Ag/AgCl(s)
Hg/Hg2Cl2(s)/Cl- (saturated calomel electrode; SCE)
Electrode of the Second Kind
Electrode response given by:
E = E0 - (RT/F) ln a(Cl-)
NOTES:
anion activity determines potential
make great reference electrodes because of low solubility of salt (potential very stable)
The Calomel Reference Electrode
Note: concentrations typically high concentrations small electrode doesn’t e polarized potential constant