The one electron reduction of Cr3+ in aqueous solution is studied at silver nanoparticle modified electrodes of differing nanoparticle coverages and, for comparison, at a silver macroelectrode. The shape and size of the measured voltammograms were found to be extremely sensitive to the nanoparticle coverage and to reflect the transition from convergent to planar diffusion with increased coverage. Parameters inferred from the reduction studied at the macroelectrode were successfully used to model the nanoparticle modified electrodes data and to confirm the expected coverage and geometry dependence of the diffusion to and from the electrode surface. (c) 2010 Elsevier B.V. All rights reserved.