A comprehensive physicochemical model for cobalt deposition onto a cobalt rotating disk electrode in sulfate-borate (pH 3) solutions is derived and statistically fit to experimental EIS spectra obtained over a range of CoSO4 concentrations, overpotentials and rotation speeds. The model accounts for H+ and water reduction, homogeneous reactions and mass transport within the boundary layer. Based on a thermodynamic analysis, the species CoSO4(aq). B(OH)(3(aq)), B3O3(OH)(4-),H+ and OH-and two homogeneous reactions (B(OH)3() hydrolysis and water dissociation) are included in the model. Kinetic and transport parameters are estimated by minimizing the sum-of-squares error between the model and experimental measurements using a simplex method. The electrode response is affected most strongly by parameters associated with the first step of Co(II) reduction, reflecting its control of the rate of Co deposition, and is moderately sensitive to the parameters for H+ reduction and the Co(II) diffusion coefficient. Water reduction is found not to occur to any significant extent under the conditions studied. These trends are consistent with that obtained by fitting equivalent electrical circuits to the experimental spectra. The simplest circuit that best fits the data consists of two RQ elements (resistor-constant phase element) in parallel or series with the solution resistance. (C) 2011 Elsevier Ltd. All rights reserved.