Abstract Model calculations for the electrochemical kinetics of outer sphere electron transfer between redox ions and semiconductor and metal solids show that reaction rates can be strongly influenced by surface morphology and the dimension of this surface roughness relative to the size of the reactant. Employing spheres of nanometer dimension to model surface roughness at these surfaces, the rates of electron transfer reactions are calculated using electron transfer theory based on the assumption of a dielectric continuum. It is shown that the magnitude of the image charge induced by the reactant is influenced by the geometry of the environment about it, which can accelerate or decelerate kinetics for electron transfer by orders of magnitude. This simple approach serves to identify specific surface morphologies that merit further study. Its limitations are examined and the extent to which it may be extended to inner sphere electron transfer reactions is discussed. The results of this work imply that evaluation of electrocatalytic effects at surfaces must include an analysis of morphological effects upon electrochemical kinetics.