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Ping Shi, Iosif Fromondi

Normalized Differential Reflectance Spectroscopy at Polycrystalline Platinum Electrodes in Aqueous Acidic Electrolytes: Quantitative Aspects

Keywords: Reflectance Spectroscopy, In Situ Methods, Platinum, Adsorption, Oxide Formation

The intensity of monochromatic light (λ = 633nm) reflected off the surface of a polycrystalline Pt electrode, R, has been measured in situ as a function of potential, E, during continuous voltammetric cycles in the range -0.25 < E < 1.05V vs. SCE, both in 0.5M HClO₄ and 0.5M H₂SO₄ aqueous solutions. Plots of the normalized differential reflectance, Δ R/R = [R(E_sam) - R(E_ref)]/R(E_ref) vs. Q_n, where E_sam and E_ref refer to the sampling and reference potentials, respectively, and Q_n is the coulometrically determined relative oxide charge (in terms of e/Pt surface atom), were found to deviate from linearity in the PtOH formation region. Improved proportionality between Δ R/R and Q_n was achieved up to Q_n = 1, upon correcting Δ R/R for double layer effects using the method originally reported by Conway et al. [3]. In the case of 0.5M H₂SO₄, however, remaining discrepancies could only be resolved by accounting for the charge due to bisulfate desorption induced by PtOH formation on the surface. On the basis of these results, it has been concluded that for both types of electrolytes, Δ R/R is proportional to the PtOH coverage, θ, and independent of the applied potential for Q_n ≤ 1, opening new prospects for monitoring θ quantitatively during the course of faradaic reactions.

Zeitschrift für Physikalische Chemie, Oldenbourg Wissenschaftsverlag

Print ISSN: 0942-9352
Volume: 221, 09/2007
Pages: 1307 - 1318

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