In Situ Rapid Scan Spectrophotometry of Solution-Phase Species Generated on the Surface of a Rotating Disk Electrode

A rapid scan spectrophotometer has been coupled to a rotating disk electrode (RDE) to enable acquisition of potential difference near normal incidence UV-visible reflection absorption spectra of electrogenerated species in the diffusion boundary layer. The (correlated) noise associated with the wobbling of the RDE and other imperfections could be eliminated by synchronizing the rotation angle of the disk, with respect to an arbitrary fixed point, and the initiation of each spectral scan. This strategy was implemented by employing a signal generated by an optical sensor coupled to the rotating shaft as a primary source to drive the grating/galvanometer unit of a Harrick rapid scan spectrophotometer. Quantitative agreement between theory and experiment could be obtained using the oxidation of ferrocyanide to ferricyanide ions on the surface of a Pt RDE in an aqueous electrolyte as a model system. Calculations based on the observed signal to noise ratios indicate that this in situ spectroscopic/forced convection method can resolve potential difference spectral features on the order of 0.005 absorbance unit.