Monitoring of Silver Electrodeposition onto HOPG Electrodes in the Presence of Picolinic Acid by in Situ Surface-Enhanced Raman Spectra Measurements

Abstract

In situ surface-enhanced Raman spectra (SERS) have been recorded during silver potentiodynamic electrodeposition onto HOPG electrodes from solutions containing silver perchlorate and picolinic acid (PA). Modification of the composition and pH of the electrolyte has allowed us to achieve an adequate control of the electroactive species distribution in solution. The adsorption behavior of different PA species on silver growing crystallites has been studied by using the potential dependence of SERS signals. Analysis of the vibrational bands from additive molecules has allowed us to establish that at pH > 3.0 the PA anion is the most stable species on the electrode surface, whereas the predominant species in solution is the zwitterion. At pH 0.3, adsorption of zwitterion and anion species onto the silver surface, even though the PA cation is predominant in the solution, has been evidenced. For all the SERS spectra it was possible to infer the adsorption geometry and the ClO4– ion coadsorption. Detection of intensified signals of the adsorbed additive is facilitated by the morphological characteristics of the particles (globular flower-like structures), which results to be a good active SERS substrate on the HOPG electrodes. Spectroelectrochemical experiments are correlated with the SEM micrographs of the silver crystallites.