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

Quantitative Aspects of Normalized Differential Reflectance Spectroscopy: Pt(111) in Aqueous Electrolytes

A theoretical model is herein proposed to account for changes in the normalized differential reflectance, Δ<i>R</i>/<i>R</i>, of well-defined single crystal Pt(111) surfaces|aqueous electrolyte interfaces. It assumes that Δ<i>R</i>/<i>R</i> is proportional to the area of the electrode either bare or covered by neutral and/or nominally charged species and, for a specific type of site, is modulated by the applied potential, <i>E</i>. Correlations between the coverage of the various species and E were obtained from data reported in the literature or by coulometric analysis of linear voltammetric scans. Excellent agreement was found for the adsorption/desorption of hydrogen and that of bisulfate from acidic electrolytes both on bare, and cyanide-modified Pt(111). Also discussed are extensions of this technique in the transient mode involving the reduction of adsorbed nitric oxide, NO, on Pt(111)

An Implantable Biofuel Cell for a Live Insect

A biofuel cell incorporating a bienzymatic trehalase|glucose oxidase trehalose anode and a bilirubin oxidase dioxygen cathode using Os complexes grafted to a polymeric backbone as electron relays was designed and constructed. The specific power densities of the biofuel cell implanted in a female Blaberus discoidalis through incisions into its abdomen yielded maximum values of ca. 55 μW/cm² at 0.2 V that decreased by only ca. 5% after ca. 2.5 h of operation

Porous Teflon Ring-Solid Disk Electrode Arrangement for Differential Mass Spectrometry Measurements in the Presence of Convective Flow Generated by a Jet Impinging Electrode in the Wall-Jet Configuration

A porous Teflon ring|solid disk electrode is herein described specifically designed for acquiring online mass spectrometric measurements under well-defined forced convection created by liquid emerging from a circular nozzle impinging on the disk under wall-jet conditions. Measurements were performed for the oxidation of hydrazine, N₂H₄, in a deaerated phosphate buffer electrolyte (pH 7) on Au, a process known to yield dinitrogen as the product. The N₂⁺ ion currents, measured by the mass spectrometer, <i>i</i>(N₂⁺), as well as the corresponding polarization curves recorded simultaneously displayed very similar s-like shapes when plotted as a function of the potential applied to the Au disk. In fact, the limiting currents observed both electrochemically and spectrometrically were found to be proportional to [N₂H₄]. However, the limiting values of <i>i</i>(N₂⁺) did not increase monotonically with the flow rate, ν_f, reaching instead a maximum and then decreasing to values independent of ν_f. This behavior has been attributed in part to hindrances in the mass transport of gases through the porous materials