Surface and Volumetric Phenomena on Polyaniline Supported Electrocatalysts

Conducting polymers have been used as support for catalysts towards distinct electrocatalytic reactions. The overall activity of the modified interfaces critically depends on both the processes on the catalyst surface and of the charge compensation within the polymer matrix. Therefore, understand the coupling between surface and volumetric processes in such systems is of utmost importance. In this contribution we report on the experimental investigation of the interplay between surface and volumetric processes during the electro-oxidation of formic acid (and also formaldehyde) on platinum modified polyaniline electrodes. The study was performed through in situ nanogravimetry, with the Electrochemical Quartz Crystal Nanobalance (EQCN). We have explored the dynamics of charge and mass changes along several experimental conditions, including the self-organized potential oscillations. The systematic study included the analysis of several configurations: gold electrodes covered with a PANI film and dispersed platinum (Au/PANI/Pt); platinum electrodes covered with PANI (Pt/PANI); and bare platinum electrodes. The methodology introduced includes the detailed analysis of the charge compensation process and of the time-derivative of the mass variations. Typical results for the electro-oxidation of formic acid on PANI supported platinum indicate that the electrocatalysis itself is reflected in the current profile, whereas the charge compensation rules the gravimetric response. This general observation also holds for the oscillatory electro-oxidation of formic acid. The physicochemical description of the support/catalyst systems described here opens interesting perspectives for the investigation of parent systems.