The properties of polyaniline (PANI) films, grown electrochemically on Au using the potential sweep method to two different upper potential limits (type I and II) to various thicknesses in sulfuric acid solution, were studied systematically using cyclic voltammetry. ne impedance, and for the first time, by tracking die rate of the hydrogen evolution reaction (HER). The HER results show that hath films follow the nucleation and growth mechanism initially and that continuing growth occurs primarily at the outer PANI surface. Because type II PANI films are formed at a much more rapid rate than type I films, a greater amount of anodic degradation products are incorporated into type I films. Impedance and HER measurements show that type II films, compared for the first time in this work with type I films, have a more open PANI film/Au interfacial structure. A new observation is that the cyclic voltammograms for type I films show a prepeak which is absent for type II films, Furthermore, constant PANI redox peak potentials are observed for type I films, whereas these shift with film thickness for type II films. This unique observation implies that type II films undergo structural changes during their growth, while type I films remain more uniform.