STEP-SCAN FT-IR EXTERNAL REFLECTION SPECTROMETRY OF THE ELECTRODE-ELECTROLYTE INTERFACE BY POTENTIAL MODULATION

The application of conventional rapid-scanning Fourier transform infrared (FT-IR) spectrometry for infrared spectroelectrochemical measurements involving potential modulation is limited by the cross talk between the Fourier frequencies and the frequency at which the potential is modulated. In this report we show the first demonstration of electrochemically modulated infrared spectrometry using a step-scanning phase-modulated interferometer. The wavenumber of the absorption band of CO adsorbed on polycrystalline Pt electrode was modulated through the electrochemical Stark effect, and the detector signal was demodulated using two lock-in amplifiers, one for the phase modulation and the other for the potential modulation. The optimal data collection parameters and data manipulation techniques are discussed. The dynamic information contained in the in-phase and quadrature spectra is found to provide the time lag of the absolute potential at the surface of the working electrode relative to the applied potential. This parameter is an important characteristic of an electrochemical cell that is not readily accessible by other means.