Benchmarking electrodes modified with bi-doped polypyrrole for sensing applications

Polypyrrole-modified electrodes bi-doped with salicylate and perchlorate anions were synthetized, characterized, and benchmarked according to their ability to meet a set of performance criteria, with the aim of obtaining the best potential candidate for the development of electrochemical sensors. Bi-doped PPy films (PPy-DA) were assessed as compared to those resulting from electropolymerization in solutions providing a single doping anion, namely salicylate (PPy-Sa) or perchlorate (PPy-ClO4-) solutions. Morphological and spectroscopic characteristics of the different polymer films were determined by means of SEM and XPS and Raman spectroscopies. The electrochemical response and electrocatalytic activity of PPy-DA electrodes were characterized by chronoamperometric, voltammetric and electrochemical impedance spectroscopy (EIS) measurements. EIS appeared as a singular tool for determining the conditions where electrochemical response is either dictated by the redox process of the polymer film or governed by a redox couple in solution, and for comparing the electrocatalytic activity of the films without the requirement of knowing the real active electrode area. Comparison was also made among PPy-DA films synthesized by varying dopant concentration in the polymerization bath and electropolymerization time. The presence of salicylate ions favored the formation of films with a three-dimensional tubular structure whereas perchlorate ions contribute to increase their conductivity and electrocatalytic activity. The tubular three-dimensional structure of the electrode surface exhibits an open extended-area pattern that is highly suitable for the electrodeposition of gold nanoparticles (AuNPs), offering new possibilities for developing electrodes for voltammetric sensing. Accordingly, electrodes modified with PPy-DA films decorated with AuNPs were successfully tested for hydrazine determination.