W. Kautek et al., IN-SITU-MONITORING OF ELECTROCHEMICAL DOUBLE-LAYER STRUCTURE CHANGES AT GOLD WITH A PHASE-CONTROLLED QUARTZ MICROBALANCE, Berichte der Bunsengesellschaft fur Physikalische Chemie, 99(4), 1995, pp. 667-676
Citations number
87
Categorie Soggetti
Chemistry Physical
Journal title
Berichte der Bunsengesellschaft fur Physikalische Chemie
Continuum hydrodynamics and no-slip boundary conditions apply to Conti
nuum hydrodynamics and no-slip boundary conditions apply to electroche
mical quartz microbalances of the thickness shear mode type with gold
in aqueous contact. Electrochemical phase-stabilized quartz microbalan
ce measurements can give insight into ion adsorption, solvation, hydro
gen bonding, and water clustering at charged surfaces. Species in the
outer and inner Helmholtz layer can be treated as rigidly coupled mass
es. Frequency changes on polycrystalline gold electrodes in alkaline a
queous contact, and in the potential range from the hydrogen evolution
up to the bulk oxide formation, are primarily caused by ion solvation
and ion pair formation. Specifically adsorbed anions, like sulfate an
d hydroxide, are stripped of nearly half of their original solvation s
hell, and function as counter charge carriers analogously to completel
y solvated anions in the outer Helmholtz plane. Their saturation cover
age is limited by lateral electrostatic repulsion and steric crowding
by their solvation shells. Specifically adsorbed anions which form neu
tral ion pairs with alkali metal cations practically do not exhibit el
ectrostatic repulsion and solvation shell crowding. They contribute mu
ch stronger to the double layer loading than specifically adsorbed par
tially hydrated ions and non-specifically attracted species. In the ox
ide monolayer potential region, electrosorbed hydroxyl functions are d
eprotonated, and become neutralized by alkali metal ions at high pH. I
n a first order approximation, viscous fluid coupling and roughness ch
anges do not have to be invoked to explain the observed frequency data
.