Cyclic voltammetry and dynamic and steady state polarization measurements have been used to examine the electrocatalytic activity of glassy carbon, GC, bearing a layer of adsorbed hemin, Hm, Hm | GC, toward hydroxylamine, NH2OH, in neutral aqueous solutions. The results obtained have provided ample evidence that Hm | GC promotes the reduction and oxidation of NH2OH, as well as its disproportionation. Also presented is a mechanistic model that accounts quantitatively for steady state polarization data for the reduction of NH2OH recorded with a Hm | GC rotating disk electrode, RDE. This model predicts that a very large fraction of the current is attributed to the reduction of a Hm species axially coordinated by a NH2OH molecule on one side and a nitrosyl group on the other at lower overpotentials and NH2OH on either side at higher overpotentials.

A method is herein described that allows for solution phase superoxide generated via the reduction of dioxygen in neutral aqueous solutions at a rotating disk electrode to be oxidized at a concentric Au ring electrode bearing a covalently linked monolayer of 3-mercapto-1-propanol, a modified surface that blocks the oxidation of solution phase of hydrogen peroxide. Experiments were performed in which the potential of a glassy carbon disk electrode was linearly scanned in the oxygen reduction region and the ring voltage was poised at a value at which superoxide oxidation ensued yielded bell-shaped ring currents. This behavior is consistent with changes in the relative rates constant for the processes involved in the mechanism of oxygen reduction on this carbonaceous material induced by the applied potential which so far had remained undetected using other techniques.

A theoretical model is herein proposed to account for changes in the normalized differential reflectance, ΔR/R, of well-defined single crystal Pt(111) surfaces|aqueous electrolyte interfaces. It assumes that ΔR/R 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, E. 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).

The oxidation dynamics of the well-defined (2 × 2)-3CO (θCO = 0.75) and √19 × √19R23.4°-13CO (θCO = 0.68) CO adlayer phases on quasi-perfect Pt(111) facets have been examined in CO-saturated 0.1 M H2SO4 aqueous solutions via a combination of simultaneous, in situ, time-resolved, second harmonic generation (SHG, λinc = 590 nm), normalized differential reflectance spectroscopy (ΔR/R, λinc = 633 nm), and potential step techniques. For both of these phases, the onset of oxidation of COads was found to be delayed with respect to the time at which the potential was stepped to values positive enough, Eox, to promote oxidation of the entire CO adlayers. This induction time, τind, was much longer for the (2 × 2)-3CO (few tens of milliseconds) compared to the √19 × √19R23.4°-13CO phase (few milliseconds) and decreased monotonically for both of the phases as Eox was increased. Furthermore, for a fixed Eox, the oxidation rates, as measured by the optical techniques, were higher for the √19 × √19R23.4°-13CO compared to the (2 × 2)-3CO phase. In the case of the (2 × 2)-3CO phase, the transient in situ optical data collected for Eox = 0.98 V vs RHE could be quantitatively accounted for by a model that assumes all sites on the surface are occupied either by CO or bisulfate. In fact, excellent statistical fits to the θCO transients for this latter phase derived from the SHG data could be obtained using Avrami’s nucleation and growth model. On this basis, the oxidation of the fully assembled (2 × 2)-3CO phase occurs at the edge of the domain and propagates through the entire island until the entire process is completed. Similar experiments involving CO adlayers on Pt(111) facets below saturation coverages (i.e., θCO < 0.75) formed by oxidative stripping of the fully assembled (2 × 2)-3CO phase yielded much longer τind values than surfaces with similar θCO prepared by dosing the otherwise bare Pt(111) surfaces. These findings strongly suggest that the rates of oxidation of COads increase with the number of non-CO-covered neighboring sites on the surface.