In situ solution-phase Raman spectroscopy under forced convection

In situ Raman spectra of solution-phase electrogenerated species have been recorded in a channel-type electrochemical cell incorporating a flat optically transparent window placed parallel to the channel plane that contains the embedded working electrode. A microscope objective with its main axis (Z) aligned normal to the direction of flow was used to focus the excitation laser beam (λ_exc = 532 nm) in the solution and also to collect the Raman scattered light from species present therein. Judicious adjustment of the cell position along Z allowed the depth of focus to overlap the diffusion boundary layer to achieve maximum detection sensitivity. Measurements were performed using a Au working electrode in iron hexacyanoferrate(II), [Fe(CN)₆]^4-, and nitrite, NO₂ ^-, containing aqueous solutions as a function of the applied potential, E. Linear correlations were found between both the gain and the loss of the integrated Raman intensity, I_R, of bands, attributed to [Fe(CN) ₆]^3- and [Fe(CN)₆]^4-, respectively, recorded downstream from the edge of the working electrode, and the current measured at the Au electrode as a function of E. The same overall trend was found for the gain in the I_R of the NO₃ ^- band in the nitrite solution. Also included in this work is a ray trace analysis of the optical system.