Certain aspects of the oxidation of bromide in acidic aqueous electrolytes have been investigated via a combination of rotating disk electrode (RDE) and in situ reflection absorption UV-visible spectroscopic techniques. Koutecky-Levich plots of polarization curves recorded with a Pt RDE in 5 mM KBr in 0.1M HClO 4 at rotation rates in the range 400 to 2000 rpm yielded for low overpotentials rates independent of the applied potential. This conclusion supports the reports of Conway et al. (J. Chem. Soc., Faraday Trans., 1995, 91, 283) which relied on the analysis of the results different type of experiments performed in more concentrated bromide solutions. Advantage was taken of the very high molar absorptivity of tribromide, i.e. ε(λ = 266 nm) = 4.09 × 10 7 cm 2 mol −1 , a solution phase species generated via the reaction of bromine and bromide, to monitor quantitatively its presence within the diffusion boundary layer and thus gain insights into the reaction mechanism. Numerical simulations of the electrochemical-chemical (EC) mechanism that take into account the dynamics of formation and dissociation of tribromide, yielded good agreement with both the optical and electrochemical data collected in this work under strict diffusion control. The development and optimization of efficient and economical means of storing energy from renewable and intermittent sources, including wind and solar, will have a pronounced impact toward mitigating problems derived from the depletion of oil reserves, as well as improve the way in which the electrical grid is currently managed. Although their capital costs per cycle are higher than those associated with pumped-storage hydroelectricity, the versatility of electrochemical energy storage devices, such as batteries, fuel cells and double layer capacitors may indeed hold the key to accomplishing these goals. Capacitors display very high power densities and sub-second response times and, as such, are suitable for power quality management. Batteries, on the other hand, including those of the flow redox type, and fuel cells, exhibit much higher specific energy densities than capacitors and therefore can meet the requirements of large-scale electrical energy storage.Whereas batteries store energy within, and, therefore, their energy and power densities are determined by the characteristics and size of its constituent electrodes, the redox active materials in a fuel cell (or redox flow battery) are stored externally; hence, their energy capacity is dictated by the size of the containers. The latter constitutes a great advantage, as in analogy to an internal combustion engine, the power and energy densities are governed, respectively, by the size of the engine and that of the fuel tank. In stark contrast, the energy of a battery of a specific chemistry can only be augmented by increasing the number of modules and thus of all its integral components, including among others, separators and current collectors. Yet another complicating factor relates to changes in the intrinsic structure, i...

Understanding nanoscopic bubble nucleation and growth is critical to reducing significant losses in efficiency during water electrolysis or photoelectrochemical hydrogen production. Herein, we demonstrate the controlled nucleation and growth of H2 nanobubbles at individual Pt nanoparticles (NPs) via the hydrogen evolution reaction (HER) using the dual-barrel mode of scanning electrochemical cell microscopy (SECCM). The NPs, with an average radius of 35 nm, were dispersed on highly oriented pyrolytic graphite (HOPG), an otherwise inert surface, with a spacing much greater than the radius of the probe, allowing for the voltammetric recordings of HER at individual Pt NPs. Finite-element simulations indicate that the concentration of electrogenerated H2 is highly nonuniform at the NP/solution interface, reaching a maximum at the three-phase HOPG/NP/solution boundary. Using finite-element modeling, we establish a correction factor to estimate the H2 surface concentration required for nucleation, as determined from the maximum current measured just prior to bubble formation. Furthermore, a drop in ionic current is measured between the two barrels of the SECCM nanopipette upon bubble formation, in agreement with simulations of local conductance when a nanobubble blocks the current path.

While investigating the influence of an alloying element on the corrosion properties of a metal, materials scientists and engineers typically fabricate an array of samples with increasing concentrations of the alloying element in order to build up a gradient of substrates suitable for corrosion testing. The resulting series of substrates can consist of many samples, which can be time consuming to test and hence slow to reveal the effects of the alloying element's concentration. In this work, we present a fast, simple, and reliable methodology on an ideal model system for monitoring the effect of one of the most commonly used alloying elements in Magnesium alloys, aluminum, on magnesium's corrosion behavior using a single Mg-Al diffusion couple sample and the scanning micropipette contact method. The use of ethylene glycol as the solvent was carried out to enhance the stability of the micro electrochemical setup. The corrosion potentials and currents of pure Mg and Al as well as the intermetallic regions were collected using micro polarization measurements without the influence of grain boundaries and inclusion size. Similar measurements performed across the interfacial region of Al diffusion into Mg revealed a threshold value of Al wt% on the corrosion potentials measured. Such methodology proved to be reproducible and therefore is a good way to measure the effects of various alloying elements for any metal in question.

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.

Changes in the electrocatalytic activity of Pt for the oxygen and hydrogen peroxide reduction reactions (ORR and HPRR, respectively) in an aqueous acidic electrolyte induced by the adsorption of bromide, as a model impurity, have been investigated using chronoamperometric techniques under forced convection. Experiments were carried out using a polycrystalline Pt|Pt rotating ring-disk electrode in O 2 -saturated 0.1 M HClO 4 containing 10 μM KBr (800 ppb). Potential steps were applied to the Pt disk from E o , at which Br − is fully desorbed, to more positive values, E step , at which Br − undergoes adsorption. During this period, the currents both at the disk, i disk , and at the ring, i ring , were monitored, with the ring polarized at a potential at which H 2 O 2 (aq) oxidation proceeds under diffusion-limited conditions. The results obtained, assuming the ORR does not interfere with Br − adsorption, made it possible to correlate i disk and i ring with the coverage of adsorbed Br − , θ Br − , and E step . As evidenced from the data collected, significant drops in the diffusion-limited currents for O 2 reduction induced by the presence of 10 μM KBr could only be observed for θ Br − > 0.25 regardless of E step . Similar measurements involving the same Pt(poly) rotating disk electrode performed in 1 mM H 2 O 2 in deaerated 0.1 M HClO 4 devoid of O 2 displayed a similar trend. This behavior was found to be consistent with a simple blockage of surface-active sites by adsorbed bromide, as predicted by the attenuation model proposed by Levart. shielded i ring using the method reported originally by Markovic et al. 1,7,16 This information made it possible to correlate the disk current, i disk and i ring , associated, respectively, with the ORR and the oxidation of H 2 O 2 (aq) under diffusion-limited conditions, with θ Br − in O 2 -saturated solutions. Also to be