Confocal Raman microscopy is being applied to quantify chemical composition at electrode-solution interfaces and within electrode-supported films under the control of a potentiostat. Experimental strategies (i.e., cell designs and data acquisition and processing techniques) that are enabling sensitive in-situ spectral measurements will be discussed with focus on redox transformations at electrode-solution interfaces and within electrode-supported polymer membranes and thin films. Emphasis will be on the ability to investigate mass transport and measure dimensional (e.g., swelling/de-swelling) changes within operating catalytic membranes.<br/>     The microscope system being utilized employs a high numerical aperture oil immersion objective to achieve (i) diffraction-limited focusing and probe volume characteristics and (ii) high efficiency in collecting Raman scattered radiation from molecules of interest. With the objective mounted to an inverted microscope frame, the electrochemical cell is positioned above the objective on the microscope stage. A glass microscope coverslip attached to the bottom of the electrochemical cell serves as the optical window. One electrochemical cell platform has been constructed around an optically transparent indium tin oxide (ITO) coated coverslip that serves as both the cell working electrode and optical window. The objective brings excitation radiation through the coverslip and to a focus a few micrometers above the ITO surface. Species diffusing into the confocal probe volume region are detected and quantified based on their Raman spectral band frequencies and intensities. A second electrochemical cell platform has a thin layer design and enables use of conventional disk working electrodes. The performance of this cell in conjunction with a spectral difference technique that allows detection of transformations within redox active films and polymer membranes supported on carbon electrodes will be presented.

Adapting confocal Raman microscopy for in-situ studies of electrode-supported films

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