Surface-Sensitive Spectro-electrochemistry Using Ultrafast 2D ATR IR Spectroscopy

A new method is presented for the combination of spectro-electrochemistry and femtosecond 2D IR spectroscopy. The key concept is based on ultrathin (similar to nm) conductive layers of noble metals and indium-tin oxide (ITO) as working electrodes on a single-reflection attenuated total reflectance (ATR) element in conjunction with ultrafast, multidimensional ATR spectroscopy. The ATR geometry offers prominent benefits in ultrafast spectro-electrochemistry, that is, surface sensitivity for studying electrochemical processes directly at the solvent-electrode interface as well as the application of strongly IR-absorbing solvents such as water due to a very short effective path length of the evanescent wave at the interface. We present a balanced comparison between usable electrode materials regarding their performance in the ultrafast ATR setup. The electrochemical performance is demonstrated by vibrational Stark-shift spectroscopy of carbon monoxide (CO) adsorbed to platinum-coated, ultrathin ITO electrodes. We furthermore measure vibrational relaxation and spectral diffusion of the stretching mode from surface-bound CO dependent on the applied potential to the working electrode and find a negligible impact of the electrode potential on ultrafast CO dynamics.