Due to their potential applications in the field of energy storage, nanostructured conductive polymers having very high specific surface area have attracted growing attention. Up to now, conductive polymer nanostructures were mainly obtained using ‘hard’ or ‘soft’ templates. In this presentation, it will be shown that the direct electrodeposition of either oriented nanowires or interconnected nanofiber networks of polypyrrole (PPy) or poly(3,4-ethylenedioxythiophene) (PEPOT) can be achieved without using any template. These nanostructures are synthesized using a one-step electrochemical route. Actually, in order to obtain such nanostructures, the electro-oxidation of the monomers should be performed in the presence of both a high concentration of weak-acid anions such as HPO₄^2- which confer to the monomer aqueous solution a basic pH and a low concentration of non-acid anions such as ClO₄^-. The growth mechanism of the polymer nanostructures will be discussed. Notably, it will be highlighted why the presence of weak-acid anions at the electrode-solution interface is essential. At the very beginning of the electrochemical process, water oxidation should take place, it occurs at a pH-dependent potential and leads to the formation of hydroxyl radicals and to O₂ evolution. It will be shown that the interfacial pH which varies during the monomer oxidation due to proton release is the key point of the electrochemical growth of nanostructured conductive polymer.