T. Fukuda et A. Aramata, THE KINETIC-STUDY OF SPECIFIC ADSORPTION OF PHOSPHATE SPECIES ON PT(111) IN ACIDIC SOLUTIONS, Journal of electroanalytical chemistry [1992], 440(1-2), 1997, pp. 153-161
The study of the adsorption/desorption mechanism of phosphate anions a
t Pt(111) in acidic solution of pH 4.3 and 0.8 was performed by the po
tential step method in order to reveal the kinetics of anion adsorptio
n. The current-time curve due to phosphate adsorption/desorption showe
d various decay features, being dependent on the potential region. The
rate of current decay depended on pH, being faster in a lower pH solu
tion. Specific adsorption processes were analyzed by the Langmuir and
Elovich adsorption equations and also in terms of a two-dimensional nu
cleation-growth mechanism in different adsorption/desorption regions.
In the case of adsorption in 0.3 M phosphate buffer solution of pH 4.3
, random adsorption without interaction following the Langmuir adsorpt
ion, takes place at low coverage, while random adsorption with repulsi
ve force was observed at high coverage. In the desorption process, ran
dom desorption with repulsive force takes place at high coverage, and
the repulsive force disappears where random adsorption without interac
tion takes place at medium coverage. When the surface coverage becomes
further lower, the desorption mechanism changes dramatically into a t
wo-dimensional nucleation-growth type, suggesting that an ordered adso
rbate structure is formed after a rapid discharge process of anion ads
orption. (C) 1997 Elsevier Science S.A.