Influence of pre-grafted pyrrole-based silane on the electrodeposition and chemical properties of polypyrrole films

Abstract

The functionalization of fluorine-doped tin oxide (FTO) substrates by a pyrrole-based silane and subsequent electrodeposition of polypyrrole films on the modified substrates has been achieved. First, N-[3-(trimethoxysilyl)propyl]pyrrole (TMSP) was successfully grafted on FTO substrates as evidenced using X-ray Photoelectron spectroscopy and Glow Discharge Optical Emission Spectroscopy. Second, polypyrrole was electrochemically prepared onto silanized (PPy/TMSP/FTO) and non-silanized (PPy/FTO) substrates, using potentiostatic and potentiodynamic techniques, in order to study the effect of silanization on the polypyrrole growth. Cyclic voltammetry experiments indicated that the growth of the polypyrrole films and their electrochemical activity weren’t strongly affected by the presence of a silane layer. On the contrary, the morphology of the PPy films was very different with and without the layer of silane since PPy/TMSP/FTO films were strongly less rough and more uniform than PPy/FTO films. The morphology of these new films was also granular and composed of globules having a submicrometric size. The lower roughness of the PPy/TMSP/FTO films, compared to the PPy/FTO ones, affected their wettability leading to a lower surface energy and more hydrophobic behavior. The conductivity of the PPy films was proved to be higher on unmodified FTO substrates by using conductive AFM experiments. Finally, the improvement of the adhesion of the polypyrrole films onto the FTO substrate, thanks to the silanization, was evidenced by immersing the modified FTO substrates in water for several weeks.