Strengthening adhesion of polypyrrole films by electrografting of diazonium layers

It is crucial for conductive polymer thin films to adhere well to the substrate to ensure stability, durability, and optimal performance in a wide range of applications, from flexible electronics to sensors. In this work, electrografting of phenyl (Bz/FTO) and 4-(1 H-pyrrol-1-yl)phenyl (BzPy/FTO) monolayers on FTO surface was performed in aqueous solution of aniline and 4-(1 H-pyrrol-1-yl)aniline, respectively, using the diazonium electroreduction method. Electrochemical experiments were used to demonstrate the functionalization of the FTO surface by the electrografted layer and to estimate the surface blocking rate, which reached over 99 %. A polypyrrole film was then successfully electrodeposited onto electrografted phenyl (PPy/Bz/FTO) or 4-(1 H-pyrrol-1-yl)phenyl (PPy/BzPy/FTO). The morphology, conductivity, electroactivity and stiffness of these films were determined and compared with those of polypyrrole electrodeposited on bare FTO surfaces (PPy/FTO). The electroactivity was found to be fairly similar for each of these films, while the PPy films electrodeposited on electrografted FTO surfaces showed three times lower conductivity than those electrodeposited on bare FTO substrates but stronger adhesion (47–48 nN against 33 nN). The very strong adhesion of the PPy films on electrografted FTO was confirmed by water immersion and drying tests, as they did not delaminate, whereas PPy films grown on bare FTO substrate peeled off. Therefore, the use of electrografted layers makes it possible to obtain PPy films that are more adherent in water and therefore potentially more interesting for applications in aqueous media such as sensors, energy storage or soft robotics.