Effect Of Alkali Metal Cations Research Articles

Effects of Alkali Metal and Organic Cations on the Hydrogen Oxidation Reaction in Alkaline Electrolytes

Spectator ionic species in electrolyte solutions affect the rate and mechanism of electro-catalytic reactions. For example, it is well known that many anions, including (bi)sulfate and organic sulfonate can specifically adsorb to a platinum electrode at high potentials and affect the rate of the oxygen reduction reaction, important to fuel cell performance. If organic anions can specifically adsorb at high potentials and effect reaction rates, it should be determined if the organic cations proposed for use in new anion exchange membrane (AEM) fuel cells could specifically adsorb to platinum at low potentials and affect the rate of the hydrogen oxidation reaction. Recent evidence has shown that alkali metal cations can affect a variety of electro-catalytic reactions on platinum, including methanol oxidation, hydrogen oxidation, and oxygen reduction, but direct experimental evidence for their specific adsorption is lacking. Previously, we have used density functional theory (DFT), an ab initio quantum mechanics based technique to show that alkali metal cations can specifically adsorb to platinum and palladium electrodes at low potentials and compete with hydrogen adsorption in high pH electrolytes. We have found experimentally that the rate of the hydrogen oxidation reaction is dependent on the cation present in an alkaline electrolyte solution. We proposed and evaluated a mechanism for this effect using DFT to show alkali metal cations can specifically adsorb to the most active low index platinum facet for hydrogen oxidation, Pt(110), and can promote the adsorption of hydroxide, an important reaction intermediate. We have extended both our computational and experimental work to find that quaternary ammonium cations can also specifically adsorb to low index platinum electrode surfaces. The development of the mechanism for the effect of alkali metal cations on the rate of the hydrogen oxidation reaction and the DFT methods for simulating alkali metal cation and organic cation specific adsorption will be discussed.

Non-covalent interactions in water electrolysis: influence on the activity of Pt(111) and iridium oxide catalysts in acidic media.

Electrolyte components, which are typically not considered to be directly involved in catalytic processes at solid-liquid electrified interfaces, often demonstrate a significant or even drastic influence on the activity, stability and selectivity of electrocatalysts. While there has been certain progress in the understanding of these electrolyte effects, lack of experimental data for various important systems frequently complicates the rational design of new active materials. Modern proton-exchange membrane (PEM) electrolyzers utilize Pt- and Ir-based electrocatalysts, which are among the very few materials that are both active and stable under the extreme conditions of water splitting. We use model Pt(111) and Ir-oxide films grown on Ir(111) electrodes and explore the effect of alkali metal cations and sulfate-anions on the hydrogen evolution and the oxygen evolution reactions in acidic media. We demonstrate that sulfate anions decrease the activity of Ir-oxide towards the oxygen evolution reaction while Rb(+) drastically promotes hydrogen evolution reaction at the Pt(111) electrodes as compared to the reference HClO4 electrolytes. Issues related to the activity benchmarking for these catalysts are discussed.

ChemInform Abstract: (MMgBO3)n (n = 1, M: Li, Na, K, Rb and n = 4, M: Cs): An Investigation on the Structure Transition and Optical Properties.

AbstractA force‐equilibrium model is established to discuss the size effects of alkali metal cations on structural transitions in the title compounds.

Electrochemical impedance of platinum in concentrated chloride solutions under potentiodynamic anodic polarization: Effect of alkali metal cations

Potentiodynamic electrochemical impedance spectroscopy has been applied to examine cation specific effects in anodic behaviour of platinum in 3M aqueous solutions of LiCl, NaCl, KCl and CsCl. Double layer capacitance was slowly varying with potential between “double layer” region and platinum anodic dissolution and chlorine evolution, and this provided a convenient background for examination of the complementary part of the potentiodynamic ac response which disclosed strong cation effect in the variation with potential of charge transfer resistance and parameters of equivalent circuit that represented interactions beyond the double layer.

Direct nucleophilic trifluoromethylation using fluoroform: a theoretical mechanistic investigation and insight into the effect of alkali metal cations

Prakash and co-workers recently reported a direct trifluoromethylation of Si, B, S, and C centers using fluoroform (CF3H) and dramatic effects of alkali metal salts of hexamethyldisilazane in this reaction (Science, 2012, 338, 1324). Herein, the detailed mechanisms of trifluoromethylation of Si and C centers in the presence of (Me3Si)2NK as a base have been studied using the DFT method. It has been found that the origin of the dramatic effect of the alkali metals is the stability of an intermediate MCF3. More interestingly, a linear relationship has been found between the chemical hardness of M+ (M = Li, Na, K, Rb, Cs) and the difference between the values of ΔGdec and ΔGtfm (ΔGdec, decomposition energy of the key intermediate MCF3; ΔGtfm, relative energy barrier for the formation of a Si–CF3 or C–CF3 bond). These results may help to both theoretically and experimentally search for better bases to develop more atom-economic and environmentally benign protocols to achieve trifluoromethylation using CF3H.

Adsorption of Carbon Dioxide on Sodium and Potassium Forms of STI Zeolite

AbstractSodium and potassium forms of STI zeolite synthesized with Si/Al ratios 15, 25, and 35 were characterized using X‐ray powder diffraction and nitrogen adsorption at 77 K. To obtain detailed information on the effect of alkali metal cations on CO2 adsorption, the temperature dependence of CO2 isotherms was investigated in the temperature range from 273 to 333 K. Based on these data, isosteric heats of adsorption of CO2 were determined. It was found that the isosteric heat of CO2 adsorption attains the highest values on the sodium form of STI zeolite with a Si/Al ratio of 15. The lowest values were found with both sodium and potassium forms of STI zeolite having a Si/Al ratio of 35. Heats of adsorption of CO2 obtained for STI zeolites were discussed in detail and compared with those of FER, MFI, MEL, TUN, and IMF structural types. This comparison revealed that isosteric heats of adsorption of CO2 on STI zeolites are lower by approximately 8 kJ mol−1 compared with heats of adsorption for FER, MFI, MEL, TUN, and IMF zeolites composed of the eight‐ or/and ten‐ring channel systems as well as STI zeolites. This effect was explained on the basis of stronger interaction of alkali metal cations with oxygen atoms of the zeolitic framework.

Structure of the electrical double layer on Ag(100): Promotive effect of cationic species on Br adlayer formation

We revealed the promotive effect of alkali metal cations on Br adlayer formation on an Ag(100) electrode by in-situ measurement of the x-ray specular rod. Alkali metal cations in the electrical double layer affect the onset potential of Br adsorption and the order-disorder transition. We determined the Cs structure in the electrical double layer during Br adlayer formation and found that (1) the Cs structure depends on the coverage of adsorbed Br, and (2) the amount of Cs increases at the initial stage of Br adlayer formation. Structural analysis suggests that hydrated Cs is localized in the area around adsorbed Br via noncovalent interactions. Formation of a Cs-Br complex promotes Br adsorption.

Electrochemistry of Pt (100) in alkaline media: A voltammetric study

Pt (100) is one of the fcc metal surface planes that reconstruct upon annealing at high temperatures. The state of the surface is important in electrochemistry, in order to correlate catalytic behavior with surface structure. Therefore, the behavior of single crystalline Pt (100) in alkaline media was investigated, with particular attention paid to surface long-range order. It was found that, in line with previous results, the manner of cooling the crystal after annealing influenced the state of surface significantly, with a profound effect on blank cyclic voltammetry as well as on carbon monoxide oxidation. Different ratios of inert and reductive gases were used to see if an optimal mixture could be obtained. Using air, argon, hydrogen, CO, and combinations of these gases gave rise to different states of the surface, with clear observable differences in blank voltammetric behavior and CO stripping. Also, the effect of alkali-metal cations and bromide on the blank and CO stripping voltammetry was investigated. Our main conclusion is that cooling in a carbon monoxide containing gas gives a clean, almost defect-free surface with long-range 1 × 1 symmetry. A similar surface can also be prepared with a hydrogen-containing cooling gas, but the content of hydrogen in that stream is critical.

Effect of alkali cations on heterogeneous photo-Fenton process mediated by Prussian blue colloids

This article evaluates Prussian blue (iron hexacyanoferrate) colloids as a heterogeneous photo-Fenton catalyst for the degradation of Rhodamine B. The emphasis is laid on the effects of alkali metal cations on the photo-Fenton process. The facts show that alkali cations strongly affect the degradation rate of organic species. The degradation rates of Rhodamine B, Malachite Green, and Methyl Orange in the presence of KCl, KNO 3, and K 2SO 4, respectively, are faster than their degradation rates in the presence of the corresponding sodium salts. The average degradation rates of Rhodamine B in 0.2 M KCl, NaCl, RbCl, and CsCl solution, decline in sequence, and the rate in KCl solution is greater than that without any salt added deliberately. Thus, potassium ions accelerate the degradation rate, but sodium, rubidium, and cesium ions slow the rate. The order of the rates is R K > R > R Na > R Rb > R Cs, which is consistent with that of the voltammetric oxidation currents of Prussian blue in the corresponding cation solutions. This phenomenon is attributed to the molecular recognition of the microstructure in Prussian blue nanoparticles to the alkali cations. The reaction mechanism of the photo-Fenton process has also been explored.

Spectroscopic (FT‐IR, FT‐Raman, UV, 1H, and 13C NMR) and theoretical studies of m‐anisic acid and lithium, sodium, potassium, rubidium, and caesium m‐anisates

AbstractIn order to understand the nature of the interactions of biologically important ligands, it is necessary to carry out the physico‐chemical studies of these compounds with their biological targets (e.g., receptors in the cell or important cell components). Results of this study make it possible to predict some properties of a molecule, such as its reactivity, durability of complex compounds, and kinship to enzymes. In this paper the effect of alkali metal cations (Li, Na, K, Rb, and Cs) on the electronic structure of m‐methoxybenzoic acid (m‐anisic acid) was studied. The experimental IR (in solid state and solution), Raman, UV (in solid state and solution), 1H, and 13C NMR spectra of m‐methoxybenzoic acid, and its salts were registered, assigned, and analyzed. Some of the obtained results were compared with published data for o‐anisic acid and o‐anisates. The structures of anisic acid and Li, Na, and K m‐anisates were optimized at the B3LYP/6‐311++G** level. The IR, 1H, and 13C NMR spectra and NPA, ChelpG, and MK atomic charges were calculated. The change of metal along with the series: Li → Na → K → Rb → Cs caused: (1) the change in the electronic charge distribution in anisate anion that is seen via the occurrence of the systematic shifts of several bands in the experimental and theoretical IR and Raman spectra of anisates; (2) systematic 1H and 13C NMR chemical shifts; (3) hypsochromic shifts in UV spectra of salts as compared to ligands. Copyright © 2009 John Wiley & Sons, Ltd.

Effect of alkali metal cations on the synthesis of 4,5,6,7-tetrahydroindole and its vinyl derivative from cyclohexanone oxime and acetylene in MOH-DMSO systems

273 In recent years, the synthesis of 4,5,6,7-tetrahydroindole (THI) and N -vinyl-4,5,6,7-tetrahydroindole (VTHI) from cyclohexanone oxime (CHO) and acetylene in MOH–DMSO superbasic media (M is Li, Na, K, Cs; DMSO is dimethyl sulfoxide), an example of pyrrole synthesis by the Trofimov reaction [1–4], has attracted the attention of synthetic chemists [5–8] and chemical engineers [9, 10] as a simple and efficient route to indole and its derivatives (Scheme 1).

Effects of alkali metal cations on the structures, physico-chemical properties and catalytic behaviors of silica-supported vanadium oxide catalysts for the selective oxidation of ethane and the complete oxidation of diesel soot

A comparative study on the effects of alkali metal on the structures, physico-chemical properties and catalytic behaviors of silica-supported vanadium catalysts for the selective oxidation of ethane and the complete oxidation of diesel soot was reported.

Amperometric determination of bovine insulin based on synergic action of carbon nanotubes and cobalt hexacyanoferrate nanoparticles stabilized by EDTA

A simple approach is proposed for the synthesis of cobalt hexacyanoferrate nanoparticles (CoNPs) with uniform shape and size controlled by ethylene diamine tetraacetic acid (EDTA) as a stabilizer. A sensitive amperometric biosensor for insulin has been prepared using glassy carbon electrodes by solubilization of carbon nanotubes (CNTs) in chitosan (CHIT) together with CoNPs synthesized by the new methodology. The CoNP-CNT-CHIT organic-inorganic system exerts a synergistic effect, resulting in the remarkably enhanced insulin currents owing to the superior electron-transfer ability of CNTs and the excellent reversible redox centers of CoNPs. High-resolution transmission electron microscopy (HRTEM) was used to provide closer inspection of the CoNPs. The effects of alkali metal cations and the concentrations of CNTs and CoNPs on the voltammetric behavior of the film-modified electrode were also investigated. In pH 6.98 phosphate buffer (PB) at +0.7 V (vs. SCE) the insulin biosensor exhibits a linear response range of 0.1-3 microM with a correlation coefficient of 0.98, and the detection limit (S/N=3) is determined to be 40 nM, the stability of the biosensor was tested and found satisfactory. There is great promise for in vivo measurements of this important hormone.

The spectroscopic (FT-IR, FT-Raman, UV and 1H, 13C NMR) and theoretical studies of alkali metal o-methoxybenzoates

The effect of alkali metal cations (Li→Na→K→Rb→Cs) on the electronic structure of o-methoxybenzoic acid was studied. The experimental IR, Raman, UV and 1H, 13C NMR spectra of o-methoxybenzoic acid and its salts were registered, assigned and studied. The structure of studied compounds were optimised in the B3LYP/6-311++G** level. The IR, 1H and 13C NMR spectra, and Mulliken atomic charges were calculated. The change of metal along with the series: Li→Na→K→Rb→Cs caused: 1) the change of electronic charge distribution in o-methoxybenzoate anion what is seen via the occurrence of the systematic shifts of several bands in the experimental and theoretical IR and Raman spectra of o-methoxybenzoates, 2) systematic chemical shifts for protons 1H and 13C nuclei, 3) hipsochromic shifts in UV spectra of salts as compared to ligand.

Effect of Alkali Metal Cation on the Anaerobic Hydrolysis and Acidogenesis of Vegetable Waste

Five batch testing scenarios were designed to evaluate the effects of alkali metal cations on anaerobic hydrolysis and acidogenesis. These scenarios were A (c=0 g l−1), B (cNa+ =25 g l−1), C (cNa+ =50 g l−1), D (cK+ =25 g l−1), and E (cK+ =50 g l−1, pH 7.0). A solution pH of 7.0 or above favored protein hydrolysis, higher proteinase activity and higher ammonia production. However, such a pH suppressed carbohydrate hydrolysis, as indicated by low α-amylase activity. Cation interference at pH 5.0–6.0 seemed not to affect carbohydrate hydrolysis, as showed by the unimpaired α-amylase activity at 50 g l−1 K+. Acidogenesis was more sensitive to alkali metal cations, so acid production and the drop in pH were lowest in a 25–50 g l−1 Na+, acidic environment (pH 4.0–6.0). It was insensitive to cations when the pH was maintained at 7.0–8.0. When the pH was uncontrolled and decreased freely to acidic values, 25 g l&minus1 of cation inhibited the action of the microbes, which rapidly acclimated, as presented by the slow transformation of soluble polymers to soluble metabolites. However, acidogenetic microbes could not easily recover from inhibition by 50 g l−1 of cation. When the pH was maintained at over 7.0, the microbes were not inhibited by cation (50 g l−1) as indicated by the more active acidogenesis. The metabolic pathways to lactate, acetate and alcohols were not fully coupled.

Ion flotation of zinc(II) and cadmium(II) with proton-ionizable lariat ethers—Effect of cavity size

Competitive flotation of Zn(II) and Cd(II) ions from dilute aqueous solutions ( c Me = 1 × 10 −5 M), by a series of lipophilic proton-ionizable lariat ethers varying ring sizes in the presence of nonylphenol(nonylethylene glycol) ether as the nonionic foaming agent is reported. The influence of the rings size variations from DB-13-C-4 through DB-16-C-5 to DB-19-C-6 on separation of zinc and cadmium ions is discussed. The influences of structural variation within the lariat ether, concentration of the macrocycle, and pH of the aqueous solution is presented. An effect of alkali metal cations, i.e. Li +, Na + and K +, on Zn(II) and Cd(II) ion flotation removal is also reported. It was shown, that the removal of Zn 2+ and Cd 2+ increases with increase of pH value and decreases with alkali metal cations concentration increase in aqueous solutions.

Synthesis, structure, and complexation properties of tetraamide derivatives of thiacalix[4]arene in different conformations

The interaction of p-tert-butylthiacalix[4]arene with N,N-diethylchloroacetamide was studied in the presence of alkali metal carbonates in acetone. Three stereoisomers, viz., cone, partial cone, and 1,3-alternate, of the tetraamide derivative of thiacalixarene substituted at the lower rim were synthesized selectively using the template effect of alkali metal cations, as well as a complex of the 1,3-alternate stereoisomer with potassium chloride. The structures of the compounds synthesized were studied by 2D NMR spectroscopy. A high extraction ability of the compounds toward alkali metal cations was demonstrated.

Effect of alkali metal cations on adsorption of guar gum onto quartz

The effect of cesium, potassium, sodium, and lithium cations on the adsorption of natural guar gum onto quartz was investigated. The role of these ions was analyzed in terms of their water structure-making or -breaking capabilities. In the presence of structure makers (Na +, Li +) the polymer adsorption density did not change compared to the adsorption levels observed in distilled water. However, in dilute solutions (0.01 N) of structure-breaking cations (Cs +, K +) the adsorption density of guar gum significantly increased, with potassium and cesium producing the same adsorption densities of the polymer. The resulting colloidal aggregation/dispersion equilibria in the quartz–guar gum system were discussed and mechanisms of guar gum–quartz interactions were also suggested. Assuming hydrogen bonding to be the driving adsorption mechanism, it was proposed that guar gum molecules compete with water for silanol surface sites. Structure-breaking cations disturb the interfacial water structure around the quartz particles thus allowing the polymer to more closely approach the quartz surface and interact with the surface groups.

The effect of alkali metals on the formation of geopolymeric gels from alkali-feldspars

Abstract The effect of alkali metal cations in alkaline solutions and alkali metals structured in alkali-feldspars on the formation of gel phase and the formed geopolymers has been investigated by using ICP, PAS-FT-IR, Raman, 29Si MAS NMR and SEM/EDX techniques. In a concentrated alkaline solution, the dissolution of alkali-feldspars is found to be inhibited, which is partly due to the reversible dissolution and precipitation reactions. DSC results indicate that K contained in the gel phase, either derived from KOH solution or from the dissolution of K-feldspar, is observed to increase the extent of disorder of the gel phase as well as the mechanical strength of the formed geopolymers. The reason for this effect is determined by 29Si MAS NMR analysis as being the higher polymerising activity between silicate species and between silicate and aluminosilicate species caused by the presence of K. The elemental analysis of gel phase using SEM/EDX shows that when the molar ratio of Na/K ranges from 3.5 to 85.6, the geopolymers synthesised from alkali-feldspar/kaolinite matrices demonstrate a high compressive strength. This study also reveals that a higher dissolution tendency as well as the involvement of K can increase the compressive strength of the geopolymers synthesised from alkali-feldspar/kaolinite matrices in alkaline solutions.

Ion Flotation of Zinc(II) and Cadmium(II) in the Presence of Side-Armed Diphosphaza-16-Crown-6 Ethers

Competitive flotation of zinc(II) and cadmium(II) ions from dilute aqueous solutions by side-armed lariat ether-type derivatives of diphosphaza-16-crown-6 ethers in the presence of nonylphenol nonylethylene glycol ether as the non-ionic foaming agent has been investigated. The influence of the type of group attached to the PNP-lariat ether molecule on the selectivity and efficiency of Zn(II) and Cd(II) ion flotation is studied. An effect of alkali metal cations, i.e., Li+ and Na+, on Cd(II) ion-flotation removal is also reported. It was shown that the removal of Cd2+ increases with increase of pH values and decreases with alkali metal cations concentration increase in aqueous solutions. The correlation between selectivity coefficients of Cd(II)/Zn(II) and pH of aqueous solution as well as molar intrinsic volume and hydrophilic–lipophilic balance of studied ethers was found.