Physical and mathematical models are proposed which describe the electrochemical transformation of compounds diffusing from the solution to an ensemble of nanoparticles (i.e., nanoelectrodes), located on a solid bulk electrode surface. Electrochemical oxidation of ascorbic acid at solid electrodes (glassy carbon, Graphite Ultra Trace and gold) unmodified and modified with gold nanoparticles (Au_nano-ensemble of nanoelectrodes) was experimentally studied. Nanoeffects and diffusion limiting current were observed in the investigation of ascorbic acid oxidation on Au_nano electrodes. Nanoeffects manifested themselves in a shift of the oxidation potential towards negative values with decreasing size of the nanoparticles. Agreement between theoretical and experimental results was demonstrated. The shift of the peak potential or half-peak potential can be used to estimate the size of nanoparticles and Gibbs free surface energy and contribution of nanoeffects to the kinetics of the electrode process.