Electrolyte Solution, Anionic Species

Such an enhancement of HER is attributed to lower pH value at the electrode/ electrolyte interface, as mentioned in Section 

l(//7). The pH would rise locally at the interface due to OH generation in cathodic reactions in aqueous media. Nevertheless, the buffer action of HPO4 neutralizes the OH keeping the pH at a 

Faradaic Efficiencies of Products from the Electroreduction of CO2 at a Cu Electrode at 5 mA cm in Various Solutions at 19°C. Reference 19-Reproduced by permission of The Royal 

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An aqueous electrolyte solution consists of a variety of charged and uncharged species, e.g. cations, anions, water dipoles, organic molecules, trace impurities, etc. which under equilibrium conditions are randomly oriented so that within the solution there is no net preferentially directed field. However, under the influence of a potential difference, the charge will be transported through the solution by cations and anions that migrate to... 

First, when a large excess of inert electrolyte is present, the electric field will be small and migration can be neglected for minor ionic components Eq. (20-16) then applies to these minor components, where D is the ionic-diffusion coefficient. Second, Eq. (20-16) applies when the solution contains only one cationic and one anionic species. The electric field can be eliminated by means of the electroneutrality relation. 

In the most recent method described by Hu et al. [239] for the direct determination of ultraviolet-absorbing inorganic anions in saline matrixes, an octadecylsilica column modified with a zwitterionic surfactant [3-(N,N-di-methylmyristylammoniojpropanesulfate] is used as the stationary phase, and an electrolytic solution is used as the eluent. Under these conditions, the matrix species (such as chloride and sulfate) are only retained weakly and show little or no interference. It is proposed that a binary electrical double layer is established by retention of the eluent cations on the negatively charged (sulfonate) functional groups of the zwitterionic surfactant, forming a cation-binary electrical double layer. 

In nonalkaline and nonfluoride aqueous solutions, silicon substrates behave as essentially inert electrodes due to the presence of a thin oxide film. Even in alkaline solutions, silicon is passivated by an oxide film at anodic potentials beyond the passivation peak. Very small current can pass through the passivated silicon surface of n- or p-type materials in the dark or under illumination. Depending on the pH of the electrolyte, oxidized surface sites Si—OH are more or less ionized into anionic species Si—0 owing to the acido-basic properties of such radicals so that the passivation current can vary in a wide range from a few... 

Some attention has also been paid to the simultaneous adsorption of sulfate anions and organic compounds. Futamata [44] has detected coadsorption of water molecules and sulfate species with uracil on polycrystalline gold electrode, applying attenuated total reflection-infrared spectroscopy. The adsorbed sulfate species appeared either as S04 or HS04, depending on the pH of the electrolyte solution. Skoluda... 

The electrical transport properties of alkali metals dissolved in ammonia and primary amines in many ways resemble the properties of simple electrolytes except that the anionic species is apparently the solvated electron. The electrical conductance, the transference number, the temperature coefficient of conductance, and the thermoelectric effect all reflect the presence of the solvated electron species. Whenever possible the detailed nature of the interactions of the solvated electrons with solvent and solute species is interpreted by mass action expressions. 

Charges of anionic species of phosphorus oxoacids were determined by an ion-exchange equilibrium method. For this purpose distribution ratios, D, of phosphorus oxoacid between an anion-exchange resin Dowex 1x4 phase and an aqueous solution phase containing tetramethylammonium chloride as a supporting electrolyte were obtained from the absorbancies of phosphorus oxoacid in the aqueous solution phase before and after equilibration. D was defined as the ratio of the concentration of phosphorus in the resin phase to the concentration of phosphorus in the solution phase. 

Doubts as to which component of the electrolyte solution is the electroactive species seem to arise predominantly in anodic reactions this is quite natural in view of the range of useful anions, spanning a range of oxidation potentials between 0 and 3-5 V, available for... 

As can be seen, the measurement of the conductivity of an electrolyte solution is not species selective. Individual ionic conductivities can be calculated only if the conductivity (or mobility) of one ion is known this in the case of a simple salt solution containing one cation and one anion. If various ions are present, calculation is correspondingly more difficult. Additionally, individual ionic conductivities can vary with solution composition and concentration. 

At higher ionic strength values, an additional dependence on [i] is often required to fit the observed solubility data. Alternatively, the Pitzer model can be used with a high degree of accuracy to describe the short-range binary (neutral-neutral, neutral-cation, neutral-anion) and ternary (neutral-neutral-neutral, neutral-cation-anion) interactions between ions and neutral species in single and mixed electrolyte solutions. ... 

If charged species, dissolved or suspended in an electrolyte solution, are subjected to a uniform potential gradient, they rapidly assume a constant rate of migration. As in conventional electrolysis cations migrate towards the cathode (negative electrode) and anions to the anode (positive electrode). The rate of migration reaches a constant value when(,the attractive force... 

The theories proposed to explain the formation of passivation film are salt-film mechanism and acceptor mechanism [21]. In the salt-film mechanism, the assumption is that during the active dissolution regime, the concentration of metal ions (in this case, copper) in solution exceeds the solubility limit and this results in the precipitation of a salt film on the surface of copper. The formation of the salt film drives the reaction forward, where copper ions diffuse through the salt film into electrolyte solution and the removal rate is determined by the transport rate of ions away from the surface. As the salt-film thickness increases, the removal rate decreases. In the acceptor mechanism, it is assumed that the metal-ion products remain adsorbed onto the electrode surface until they are complexed by an acceptor species like water or anions. The rate-limiting step is therefore the mass transfer of the acceptor to the surface. Recent studies confirmed that water may act as an acceptor species for dissolving copper ions [22]. 

It was in 1990 that Kratschmer et al. [217,218] reported the first macroscopic preparation of in gram quantities by contact-arc vaporization of a graphite rod in a 100 Torr atmosphere of helium, followed by extraction of the resultant soot with toluene. Fullerene ions could also be detected by mass spectrometry in low-pressure hydrocarbon flames [219]. The door was opened by, Kratschmer and co-workers preparative success to extensive studies of the electrochemical behavior of the new materials. Cyclic voltammetry of molecular solutions of Ceo in aprotic electrolytes, e.g., methylene chloride/quatemary ammonium salts, revealed the reversible cathodic formation of anionic species, the radical anion, the dianion, etc. (cf. [220,221]). Finally, an uptake of six electrons in the potential range of 1-3.3 V vs. SHE in MeCN/toluene at — 10°C to form the hexavalent anion was reported by Xie et al. [222]. This was in full accordance with MO calculations. A parametric study of the electroreduction of Cgo in aprotic solvents was performed [223]. No reversible oxidation of C o was possible, not even to the radical cation. However, the stability of di- and trications with special counterions, in the Li/PEO/C 3 MoFf cell, was claimed later [224]. 

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