Quantitative Correlations between the Normal Incidence Differential Reflectance and the Coverage of Adsorbed Bromide on a Polycrystalline Platinum Rotating Disk Electrode

Normal incidence reflectance spectra (λ = 635 nm) data were acquired from a Pt disk of a rotating Pt|Pt ring-disk electrode in 0.1 M HClO₄ solutions containing bromide in the μM range, while scanning the disk potential linearly and measuring the diffusion limited bromide oxidation current at the ring. Analysis of the results obtained made it possible to correlate quantitatively the relative intensity of the reflected light, R, with the bromide coverage, i.e. the fraction of the surface covered by bromide, assuming the remaining areas of the Pt disk are covered by adsorbed hydrogen, using empirical functions to account for the potential dependence of the optical signals for each of the two surface regions. This technique opens new prospects for monitoring in real time the coverage of bromide and perhaps other adsorbed species during the course of a faradaic process under well-defined conditions of mass transport control.