Supporting electrolyte

Abstract: The effects of changes in ionic strength on the adsorption behavior of selenite (SeO32−) and selenate (SeO42−) on goethite and hydrous ferric oxide have been modeled using a generalized version of the triple-layer surface complexation model. Selenite adsorption, which is relatively unaffected by changes in ionic strength, is best modeled assuming that selenite forms an inner-sphere (surface coordination) complex; selenate adsorption, which is markedly reduced by increasing ionic strength, is best modeled assuming that selenate forms an outer-sphere (ion-pair) surface complex. The modeling results suggest that it is possible to distinguish between inner-sphere and outer-sphere anion surface complexes by studying the effects of ionic strength on anion partitioning.

Abstract: A limited number of IR optically transparent thin-layer electrochemical (OTTLE) cell constructions containing a three-electrode system inside the thin-layer chamber has been reported having the electrodes usually sandwiched between Teflon® spacers. This design feature, however, does not prevent completely the leakage of oxygen and/or supporting electrolyte. In this paper an alternative construction of the sandwich-type IR OTTLE cell is presented. The working Au- or Pt-mesh, twinned Ag-wire reference and Pt-mesh auxiliary electrodes are melt-sealed into a polyethylene spacer. This IR OTTLE cell design permits; (i) rapid electrolyses of highly air-sensitive compounds without the necessity of surrounding the cell with an inert atmosphere, (ii) ready variation of the electrode and window materials and (iii) ready alignment of the cell in various types of IR, UV-Vis and resonance Raman spectrometers.

Abstract: A fundamental study of the influence of solvents on the oxygen reduction reaction (ORR) in nonaqueous electrolytes has been carried out for elucidating the mechanism of the oxygen electrode processes in the rechargeable Li−air battery. Using either tetrabutylammonium hexafluorophosphate (TBAPF6) or lithium hexafluorophosphate (LiPF6) electrolyte solutions in four different solvents, namely, dimethyl sulfoxide (DMSO), acetonitrile (MeCN), dimethoxyethane (DME), and tetraethylene glycol dimethyl ether (TEGDME), possessing a range of donor numbers (DN), we have determined that the solvent and the supporting electrolyte cations in the solution act in concert to influence the nature of reduction products and their rechargeability. In solutions containing TBA+, O2 reduction is a highly reversible one-electron process involving the O2/O2− couple. On the other hand, in Li+-containing electrolytes relevant to the Li−air battery, O2 reduction proceeds in a stepwise fashion to form O2−, O22−, and O2− as products. Th...

Abstract: The site-binding model for the electrical double layer of hydrous oxides reported in a previous paper is applied to adsorption of anions from dilute solution. Generally, more than one stoichiometric surface reaction is needed to describe the adsorption behavior of divalent weak acid anions. If mass law equations for surface reactions are corrected for effects of the electrostatic field at the interface, the calculated adsorption density depends upon the type of surface species formed. It is shown that calculations which consider formation of surface complexes by protonated anionic forms, e.g., HCrO 4 − , HSeO 4 − , HSO 4 − , are more consistent with experimental adsorption data than complexation by bidentate surface sites. Modeling results predict that adsorbed anions are more easily protonated than those in bulk water, and a qualitative explanation for this phenomenon is presented. The model applies over a wide range of solute concentrations and accounts for effects of changes in composition of the supporting electrolyte. In addition calculated results for a shift in pH PZC upon specific adsorption of sulfate are in reasonable agreement with other experimental studies.

Abstract: Voltammetry combined with single-potential alteration infrared spectroscopy (SPAIRS) were used to study the extent of adsorbed CO produced at Pt, Ru and Pt-Ru alloy electrodes during methanol and formic acid oxidation in acidic supporting electrolyte. The addition of even small atomic fractions of Ru to Pt surfaces caused a decrease in the quasi-steady-state level of CO on the surface for both reactions. This result is consistent with the bifunctional mechanism proposed previously: Ru sites nucleate oxygen containing species at ≈0.2-0.3 V lower potential than on the pure Pt surface; the adsorption of methanol occurs on Pt ensembles producing adsorbed CO; in the case of formic acid, adsorption is equally facile at Pt-Pt, Pt-Ru and Ru-Ru sites, with dehydration producing adsorbed CO; the further electro-oxidation of CO is catalyzed by oxygen-containing species nucleated onto nearby by Ru atoms. The improved efficiency of the alloy surfaces for oxidation of adsorbed CO at low potential shifts the rate limiting step to the adsorption step, which results in very low coverages of the surfaces by adsorbed CO.