‘Electrochemical and optical techniques for the study and monitoring of metallic corrosion’

Abstract

Surface-enhanced infrared absorption spectroscopy (SEI-RAS) in attenuated total reflection (ATR) configuration has been extended to the Fe electrode/electrolyte interface in neutral and weakly acidic solutions for the first time. The SEIRA-active Fe film electrode was obtained through a potentiostatic electrodeposition of a virtually pinhole-free 40 nm-thick Fe overfilm onto a 60 nm-thick Au underfilm chemically predeposited on the reflecting plane of an ATR Si prism. The infrared absorption for CO adlayer at the Fe film electrode measured with ATR-SEIRAS was enhanced by a factor of larger than 34, as compared to that at a Fe bulk electrode with external infrared absorption spectroscopy in the literature. More importantly, the unipolar band shape enabled the reliable determination of the Stark tuning rates of CO adlayer at Fe electrode. In situ ATR-SEIRAS was also applied to study the elec-trosorption of a typical corrosion inhibitor benzotriazole (BTAH) on Fe electrode as a function of potential, providing additional spectral information at positive potentials in support of the formation of a polymer-like surface complex Fe II m (BTA) n as the corrosion-resistant layer. Iron is perhaps the most popular metal in the world with unique and technologically important chemical properties. On one hand, Fe is essential in many (electro)catalytic reactions; for example, Fe is the main catalyst in the synthesis of ammonia, and Fe-alloyed materials are developed as efficient CO-tolerant anode and cathode catalysts for proton-exchanged membrane fuel cells. 1,2 On the other hand, Fe is prone to corrosion due to its active property; intensive interests have been directed to the corrosion-inhibition on Fe. 3 Therefore, extension and application of high-sensitivity in situ molecular spectroscopies 4,5 are of great interest for probing the adsorption and reaction involved in the (electro)catalysis and corrosion-inhibition at the Fe electrode. Along this line, surface-enhanced Raman spectroscopy (SERS) has been reported to be the study of relevant topics by Tian's group; 6-8 it was found that the surface enhancement for a roughened Fe electrode was about 3 to 4 orders of magnitude as low as that for a typical SERS substrate of Ag, Au, or Cu. In contrast, the theory of surface-enhanced IR absorption spectros-copy (SEIRAS) predicts a comparable surface enhancement factor for nearly all appropriately structured metal nanoparticle films. As well as being demonstrated in previous reports, 9-23 electro-chemical SEIRAS in attenuated total reflection (ATR) configuration is a powerful analytical tool for the characterization of the adsorption and reaction at metal surfaces.