KINETIC-THEORY OF PHASE-TRANSITIONS AT ELECTRODE SURFACES - THE VOLTAMMOGRAM

In recent papers we investigated the equilibrium statistical mechanics of phase transitions at electrode interfaces. We derived the adsorption isotherm theta = A(z, u)/[1 + A(z, u)]n which both z and u are functions of molecular parameters and the applied potential, which satisfies correct scaling to any desired accuracy. Implicit in our model is the approximation that each transition is treated as a single adsorbate onto a sublattice of the available adsorption sites. This form can be extended to include reaction and diffusion kinetics. We discuss the cases with diffusion (small bulk concentration) and without diffusion (large bulk concentration). For the latter our model is solved mathematically, and we obtain explicit formulae for the shifts of the peaks in terms of the overall kinetic reaction constants. Asymptotic formulae for slow scanning rates are given. We discuss the case of Cu/Au(111) underpotential deposition (UPD) which is treated as a sequence of three uncoupled phase transitions. Phenomenological rate constants are derived fitting the theory to the experiments of Kolb and coworkers.