A new approach to electrode kinetics and dynamics by potential modulated Fourier transform infrared spectroscopy

In order to study very fast dynamic processes at the electrochemical interf ace that cannot be readily accessible by conventional electrochemical techn iques, we have developed a new dynamic infrared spectroscopy in which step- scan Fourier transform infrared (FT-IR) interferometry, surface-enhanced in frared absorption spectroscopy (SEIRAS), and attenuated-total-reflection (A TR) techniques were coupled. The principle of this technique is similar to that of ac voltammetry or impedance spectroscopy. The electrode potential i s sinusoidally modulated at a certain frequency, and in-phase and quadratur e spectra (real and imaginary components, respectively, of the infrared res ponse with respect to the potential modulation) are. measured with a lock-i n amplifier. From the analysis of the infrared data collected at several mo dulation frequencies, kinetic and dynamic information is obtained. The cros s talk between Fourier frequencies and the potential modulation was removed by using step-scan FT-IR interferometry. The response of the spectroelectr ochemical cell with respect to the externally applied potential modulation was improved by the use of the ATR technique instead of the so-called refle ction-absorption spectroscopy technique, which allows us to change the modu lation frequency up to 100 kHz, Furthermore, the high sensitivity of SEIRAS shortens the spectral acquisition time significantly. A self-assembled mon olayer of 4-mercaptopyridine on an Au electrode was used as a model sample. The spectrum of the monolayer changed with potential due to the charge-tra nsfer between the molecule and the electrode. The charge-transfer rate was estimated to be about 5 x 10(5) s(-1). (C) 1999 Elsevier Science S.A. All r ights reserved.