Spectroelectrochemical Assessment of Polypyrrole Formation Dynamics on Silane-Modified Surfaces and Application to pH Sensing

Abstract

Interfacial processes during the electrodeposition of conducting polymers critically dictate layer growth, adhesion, and charge transfer behavior. In this work, polypyrrole (PPy) layers were electrodeposited onto indium tin oxide (ITO) electrodes modified with triethoxymethylsilane (TEMS) or trimethoxyvinylsilane (TMVS) using a double potential step (DPS) method. The deposition was investigated using in situ light absorption spectroscopy (λ = 530 and 750 nm) coupled with chronoamperometry. The results showed that conducting polymer formation involves an initial growth stage, an accelerated polymerization, and a transition to stable growth. The oxidation-to-reduction charge ratio remained >1, indicating net layer growth during successive pulses. The choice of the silane precursor modulated the polymerization kinetics and the relative abundance of polaronic and bipolaronic species. The PPy layers exhibited pH-dependent changes in optical absorption, where the TMVS-modified electrode showed a broader sensing range. These findings demonstrate that in situ spectroelectrochemical monitoring is effective for elucidating polymer growth and that silane-modified ITO/PPy structures hold potential for optical sensing applications.