Steady-state voltammetry for the reduction of hydrogen ion at a Pt mic
roelectrode was carried out in an aqueous suspension of a monodisperse
sulfonated polystyrene latex with hydrogen ion as counterion to the l
atex particles. The measured transport-limited current for the reducti
on of the hydrogen ion was related to the gradient-diffusion coefficie
nt of the hydrogen ion over a wide range of concentration of inert, 1:
1 electrolyte. The gradient-diffusion coefficient for hydrogen ion in
the deionized, ordered latex crystal was less than 1/40th of the value
found without the latex. Addition of a 100-fold excess of electrolyte
(with respect to hydrogen ion concentration) resulted in a value for
the gradient-diffusion coefficient close to that without the latex. A
neutral molecule, 4-hydroxy-TEMPO, oxidized anodically in the suspensi
on under these same conditions yielded transport-limited currents that
were little affected by changes in salt concentration. This suggests
that most of the hydrogen ions are electrostatically accumulated near
the particles. This observation can be described in terms of an effect
ive charge on the latex particles. The gradient-diffusion coefficient
of hydrogen ion was found to be insensitive to the transition from an
ordered crystalline phase of the latex to disorder upon the addition o
f electrolyte. The dependence of the gradient-diffusion coefficient on
the concentration of 1:1 electrolyte agrees with the self-diffusion c
oefficient values predicted from the cell model using the nonlinear Po
isson-Boltzmann equation and with that predicted by a simple, semiempi
rical model.