Diffusion Boundary Layer of a Rotating Disk Electrode As a Thin-Layer Spectroelectrochemical Cell

摘要

A UV-visible rapid scan spectrophotometer (RSS) was coupled to a Au rotating disk electrode (RDE) for monitoring at near-normal incidence the reflection-absorption spectrum of the diffusion boundary layer in [Fe(CN)_(6)]~(4-) aqueous solutions over a potential region in which [Fe(CN)_(6)]~(4-) oxidizes, generating highly absorbing [Fe-(CN)_(6)]~(3-) (λ_(max)=420 nm). Measurements were performed under steady-state conditions at rotation rates, ω, in the range 300≤ω≤2500 rpm, yielding well-defined spectra displaying characteristic features of [Fe(CN)_(6)]~(3-). In agreement with theoretical predictions, the absorbance A at λ_(max), using as a reference A(λ_(max)) for the spectrum recorded at a potential negative to the onset of [Fe(CN)_(6)]~(4-) oxidation, was found to be proportional both to the current and also to ω~(1/2) under conditions in which E was positive enough for the reaction to proceed under diffusion-limited control.