The voltammetry of micro- and nano-particle modified electrodes and other electrodes of partially covered and non-planar geometry is investigated by simulation. Building on existing theory, it is demonstrated that for a simple one-electron process (assuming that the diffusion fields of neighbouring electroactive regions strongly overlap such that diffusion to the entire surface is linear), the apparent electrochemical rate constant of the reaction, k app , is equal to the product of the true rate constant, k 0 , and the ratio, Ψ, of the total electroactive surface area to the geometric surface area of the substrate. It is demonstrated that for a given value of Ψ, the voltammetry is independent of the surface geometry; surfaces covered by, for example, long thin bands of electroactive material, or electroactive hemispherical or spherical particles, show the same voltammetry if they have the same surface area of electroactive material per area of substrate. Distributions of, most importantly, electroactive nanoparticles, with Ψ > 1 , will display an apparent catalytic effect compared to the bulk material which can be solely due to the geometry of the surface and not necessarily related to changes in kinetics at the nanoscale, for example by altered structural or electronic properties. Further, if an electrode surface is modified by a fixed mass of nanocatalyst per unit area, then the response will reflect the size and shape of the modified particles.