Electrooxidation Mechanism of Methanol at Pt-Ru Catalyst Modified GC Electrode in Electrolytes with Different pH Using Electrochemical and SERS Techniques

The electrochemical and in-situ surface-enhanced Raman spectroscopy （SERS） techniques were used to investigate the electrooxidation behavior of methanol in acidic, neutral and alkaline media at a Pt-Ru nanoparticle modified glassy carbon （Pt-Ru/GC） electrode. The results showed that methanol could be dissociated spontaneously at the Pt-Ru/GC electrode to produce a strongly adsorbed intermediate, CO. It was found that CO could be oxidized more easily in the alkaline medium than in the acidic and neutral media. The peak potential of methanol oxidation was shifted from 0.663 and 0.708 V in the acidic and neutral media to -0.030 V in the alkaline medium, which is due to that the adsorption strength of CO on the Pt surface in the alkaline medium is weaker than that in the acidic and neutral media. The final product of the methanol oxidation is CO2. However, in the alkaline medium, CO2 produced would form CO3^2- and HCO3^- resulting in the decrease in the alkaline concentration and then in the decrease in the performance of DMFC. Therefore, the performance of the alkaline DMFC is not Stable.     

The Role of Discrepant Reactive Intermediates on Ru-Ru2P Heterostructure for pH-Universal Hydrogen Oxidation Reaction

Developing highly efficient electrocatalysts for hydrogen oxidation reaction (HOR) under alkaline media is essential for the commercialization of alkaline exchange membrane fuel cell (AEMFC). However, the kinetics of HOR in alkaline media is complicated, resulting in orders of magnitude slower than that in acid, even for the state-of-the-art Pt/C. Here, we find that Ru-Ru₂P/C heterostructure shows HOR performance with a non-monotonous variation in a whole pH region. Unexpectedly, an inflection point located at pH≈7 is observed, showing an anomalous behavior that HOR activity under alkaline media surpasses acidic media. Combining experimental results and theoretical calculations, we propose the roles of discrepant reactive intermediates for pH-universal HOR, while H* and H₂O* adsorption strengths are responsible for acidic HOR, and OH* adsorption strength is essential for alkaline HOR. This work not only sheds light on fundamentally understanding the mechanism of HOR but also provides new designing principles for pH-targeted electrocatalysts.     

Thermodynamic calculation of the solubility of solid hydroxides of group IIIA elements in water and aqueous media

The effect of pH on the molar solubility of amorphous and crystalline hydroxides M(OH)₃ and metahydroxides MO(OH), where M is B, Al, Ga, In, or Tl, in aqueous alkaline and acidic media at 25°C was calculated thermodynamically taking into account the formation of hydroxo complexes.     

Calculation of Raman spectra and structure elucidation of guanine in the polycrystalline state and in aqueous solution

The frequencies and relative intensities of lines in the Raman spectra of the condensed states of guanine and its deutero substituted analog have been calculated. The effect of hydrogen bonding on the Raman spectrum has been studied. Guanine exists in different tautomeric forms (G-N₉H and G-N₇H) at different pH in aqueous solution (for acidic and alkaline media, respectively).     

Molecular mobility in micellar complexes of a nonionic surfactant and the poly(acrylic acid)-based hydrogel

The interaction between the polyelectrolyte gel of crosslinked poly(acrylic acid) (PAA) and nonionic surfactant Brij 58 based on poly(ethylene glycol) (C₁₆H₃₃(CH₂CH₂O)₂₀OH) is studied. It is established that poly(acrylic acid)-surfactant complexes are formed. Nondissociated carboxyl groups of poly(acrylic acid) and oxygen atoms of the surfactant are involved in the complexation. Surfactant micelles are a kind of bridge that connects polymer chains. The presence of the surfactant decreases the equilibrium swelling of the hydrogel. The spin probe method is employed to determine the local mobility of the hydrocarbon core of a micelle in the complex. It was shown that the local mobility is independent of the hydrogel crosslink density and is much lower in acidic than in alkaline media. In acidic media, much more surfactant molecules of micelles are involved in the complexation than in alkaline media. However, even in alkaline media, surfactant micelles cannot leave the hydrogel, while the spin probes located in micelles are at equilibrium with the spin probes present in the external aqueous medium. The prospects for applying the considered systems as carriers for controlled release drugs are discussed.     

Study of the reaction between styrene and electrogenerated superoxide ion in dimethylformamide

The oxidation of some hydroxamic acids (RCONHOH, R=CH₃, C₆H₅, C₆H₅CH₂) has been investigated on platinum electrodes in aqueous solution buffered at different pH values. The voltammetric data showed that in acid media the dissociation of the acids in the chemical reaction preceding the quasi-reversible charge transfer step, while in alkaline media a weak adsorption of the reagent is operative. The reaction mechanism proposed in alkaline medium involves the formation of transient radical-anions, evidentiated by cyclic voltammetry, which dimerize and, by intramolecular rearrangement, quantitatively give (N,O-diaceyl)hydroxylamines. In acid media a two-electron oxidation process leads to carboxylic acids as final products.     

The Structural,Molecular and Functional Properties of Lignin-Containing Beechwood Glucuronoxylan

The samples of 4-O-methyl-D-glucurono-D-xylan (GX) with different lignin and uronic acid (MeUA) contents were prepared from beechwood by various procedures. The re-dissolution process of the partially water-soluble GX-2 lyophilizate in aqueous medium depended on the content and distribution of MeUA. In contrast to the supernatant after ultracentrifugation, the sediment had a significantly lower MeUA content and showed mainly high-molecular mass components. A part of lignin degradation products is separable by repeated dissolution and precipitation of GX in acidic and alkaline 80% ethanolic media with assistance of ultrasound. Irradiation in acidic ethanol (GX-3/ac) showed no effect on the distribution of the UV₂₅₄-absorbing component. GX-3 sonicated in neutral and alkaline media (GX-3/ne, GX-3/alk) lost water solubility. The lignin-rich GX samples showed remarkable emulsifying efficiency and protein foam stabilization effect. In addition, the presence of phenolics provided antioxidant properties to these xylan preparations indicating their potential as polymeric radical scavengers.     

Methanol oxidative fuel cell: electrochemical synthesis and characterization of low-priced WO<Subscript>3</Subscript>-Pt anode material

Electroplating of WO₃-Pt has been carried out using a suitable plating bath solution and optimum working conditions. X-ray and SEM studies of the deposit reveal a smooth and uniform distribution of micro-particles on the surface. New phases of the plated material appear on heat treatment. The electrocatalytic activity of the WO₃-Pt co-deposit is considerably higher than for platinum alone. WO₃ in the WO₃-Pt co-deposit reduces the retardation effect of methanol oxidation by the reaction intermediate observed in the case of Pt alone. WO₃-Pt co-deposits exhibit low overpotential for methanol oxidation in both acidic and alkaline media at low temperature and have good corrosion resistance in electrolytic media. The electrochemical parameters for methanol oxidation of these co-deposits depend on trace amounts of the platinum, heat treatment and the microstructure of the coating.     

Sorption behavior of γ-irradiated α-Al2O3

Irradiation of α-Al₂O₃ (Corundum) was carried out in contact with acidic media and with different doses (100-to-2500 kGy) and dose-rates (0.9, 2.6 and 6.1 kGy·h⁻¹) of γ-rays. Simultaneously parallel experiments were carried out using the same procedure, but preheated at 150°C for two days and then irradiated without acidic media. The solid thus obtained was used to determine the effect of γ-irradiation on the sorption capacities of microamounts of fission products from strongly alkaline aqueous solutions of uranium. The results revealed that the effect of γ-irradiation of α-Al₂O₃ and the acidic media in which it is immersed, is associated with a stable matrix resistant to significant changes in the composition of the surface layer; whilst it seems that the effect of γ-irradiation of preheated α-Al₂O₃, is connected with changes of surface-OH groups strongly affected by heat treatment and irradiation dose.     

The Effect of Media Composition,pH, and Formulation Excipients on the In Vitro Lipolysis of Self-Emulsifying Drug Delivery Systems (SEDDS)

The objective of the present work was to investigate the effects of pH, ions, and excipients on the in vitro lipolysis of self-emulsifying drug delivery systems (SEDDS). Studies were performed in bio-relevant media using a pH stat autotitrator for analysis. The results demonstrated that alkaline media were essential for lipolysis, which was enhanced by divalent CaCl₂ ions and medium chain glycerides. Monovalent NaCl and the hydrophile-lipophile balance (HLB) of the surfactant had insignificant effect on lipolysis. Consequently, it was concluded that the activity of lipase, at an optimum pH of 6.5, is the predominant factors for digestion of SEDDS.     

Silver supported on Co3O4 modified carbon as electrocatalyst for oxygen reduction reaction in alkaline media

The electroreduction of oxygen was firstly studied on Ag/Co₃O₄–C in alkaline media prepared by depositing Ag on Co₃O₄ modified carbon (Co₃O₄–C). The Ag/Co₃O₄–C composite not only displayed relatively large electrochemical active surface area (ESA), high catalytic activity towards oxygen reduction reaction (ORR), but also exhibited good methanol tolerance and stability in alkaline media. Ag/Co₃O₄–C could be a valuable catalyst for ORR and be applied to alkaline fuel cells and metal–air batteries.     

Oligonucleotides and nucleotidylpeptides. XXXII. Synthesis and hydrolytic stability of amino acid derivatives of adenosine 5′-di(tri)phosphates

The synthesis has been effected of the ethyl esters of adenosine-5′-diphospho-(P_β→N)-and adenosine-5′-triphospho(P_γ→N)-alanine. It has been shown that under the conditions of synthesis the serine analogues of ATP and ADP decompose. An investigation of the hydrolytic stability of the compounds synthesized has shown that they are unstable in acid and alkaline media. In an acid medium the phosphoramide bond is cleaved more rapidly than the phosphoric anhydride bond (in the case of the ADP analogue), while in an alkaline medium the ester bond is saponified and the phosphoric anhydride bond is cleaved. The ATP analogue is more labile both in acid and in alkaline media.     

The formation of carbon dioxide during glycerol electrooxidation in alkaline media: First spectroscopic evidences

In this work we investigate the glycerol electrooxidation reaction on polycrystalline gold in alkaline media. By using in situ FTIR we demonstrate for the first time the unambiguous presence of CO₂ as electrooxidation product of glycerol in alkaline media. The estimation of OH^? consumption during the electrooxidation of glycerol allows us to explain the formation of CO₂ as a consequence of a sudden decrease of pH inside the thin layer, which forces glycerol (or their fragments) to react with water, thus forming CO₂.     

Heterocyclic analogs of pleiadiene

Electron-acceptor substituents (phenyl, benzyl, methoxymethyl, acetonyl, and phenacyl) in the 1 position of perimidine do not have an appreciable effect on the ease of opening of the perimidine ring under the influence of aroyl chlorides in the presence of mild bases. However, some of them (C₆H₅ and CH₃OCH₂) substantially hinder the step involving the cyclization of the pseudo bases to arylperimidines under the influence of alkalis. It was shown by kinetic measurements that substituents in the N-aroyl group of N-methyl-N-formyl-N-aroyl-1,8-naphthalenediamines have virtually no effect on the rate of cyclization in alkaline media. A mechanism for the alkaline and acidic cyclization of the pseudo bases is proposed on the basis of the regularities observed. 1,2-Diarylperimidines were synthesized for the first time.See [1] for communication XXXV.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1125–1131, August, 1978.     

Kinetics and mechanism of oxidation of some basic amino acids with bromamine-T

Kinetics of oxidative decarboxylation of arginine, glutamine, histidine and lysine by bromamine-T (BAT) was investigated in acid and alkaline media at 30° and 20° fespectively. The form of the rate law at low concentrations of HClO₄ has been worked out. Proton inventory studies in H₂O-D₂O mixtures with Arg as a probe have been made. The rate increases in the order: His > Lys > Arg > Glu - NH₂. In alkaline media, the rate shows a first order dependence on [BAT]₀ and is fractional in [S] and [OH].p-Toluene sulphonamide retards the rate. Mechanisms proposed are consistent with the experimental rate laws.     

Square wave voltammetry of nitrofurans in aqueous media using a carbon fiber microelectrode

The nitrofuran compounds exhibit a wide spectrum of biological action, and the understanding of their reduction mechanism can contribute to a better comprehension of their biological action. In this sense, the electrochemical reduction of nitrofurans has been studied through square wave voltammetry (SWV) in aqueous media, having a carbon fiber microelectrode as working electrode. One single cathodic peak in acidic media is registered for all studied drugs (nitrofurazone, nitrofurantoin, and furazolidone), being the hidroxylamine derivative formation linearly dependent on pH. In alkaline media, the peaks reduction is not pH-dependent, but a split of the original into two distinct peaks is observed. The evaluation of the results obtained in unprecedented form by SWV for different alkaline pH media, suggests that the charge transfer process for the R-NO₂ ^?? formation is followed by irreversible chemical reaction, which chacraterizes an EC mechanism.     

Corrosion properties of nickel coatings obtained from aqueous and nonaqueous electrolytes

Nickel was deposited on a copper substrate from aqueous and nonaqueous ethanol electrolytes. X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy and chronovoltametry, scanning electron microscopy, and atomic force microscopy were used to study the effect of the solvent on the surface and corrosion properties of the Ni coatings formed. Unifom and relatively smooth Ni films were obtained as measured with microscopy techniques. The formation of a passive film in acidic, alkaline, and neutral chloride-containing media was confirmed with X-ray photoelectron spectroscopy. The water-based nickel-plating electrolyte makes it possible to deposit coatings with higher corrosion resistance as compared with coatings deposited from ethanol electrolyte in NaOH and NaCl media. The proposed mechanism of corrosion in a 0.5 M H₂SO₄ solution involves cycles of active-passive surface behavior due to its passivation by corrosion products.     

Methanol and ethanol electrooxidation on Pt and Pd supported on carbon microspheres in alkaline media

Noble metal (Pt, Pd) electrocatalysts supported on carbon microspheres (CMS) are used for methanol and ethanol oxidation in alkaline media. The results show that noble metal electrocatalysts supported on carbon microspheres give better performance than that supported on carbon black. It is well known that palladium is not a good electrocatalyst for methanol oxidation, but it shows excellently higher activity and better steady-state electrolysis than Pt for ethanol electrooxidation in alkaline media. The results show a synergistic effect by the interaction between Pd and carbon microspheres. The Pd supported on carbon microspheres in this paper possesses excellent electrocatalytic properties and may be of great potential in direct ethanol fuel cells.     

An effective aza-Michael addition of aromatic amines to electron-deficient alkenes in alkaline Al2O3

Aza-Michael addition of aromatic or aliphatic amines with various electron-deficient alkenes was performed using alkaline Al₂O₃ as solid media at room temperature afforded the corresponding Michael addition products in good to excellent yields. The alkaline Al₂O₃ can be easily recovered and reused.     

Phase‐Junction Electrocatalysts towards Enhanced Hydrogen Evolution Reaction in Alkaline Media

To ensure sustainable hydrogen production by water electrolysis, robust, earth‐abundant, and high‐efficient electrocatalysts are required. Constructing a hybrid system could lead to further improvement in electrocatalytic activity. Interface engineering in composite catalysts is thus critical to determine the performance, and the phase‐junction interface should improve the catalytic activity. Here, we show that nickel diphosphide phase junction (c‐NiP₂/m‐NiP₂) is an effective electrocatalyst for hydrogen production in alkaline media. The overpotential (at 10 mA cm^?2) for NiP₂‐650 (c/m) in alkaline media could be significantly reduced by 26 % and 96 % compared with c‐NiP₂ and m‐NiP₂, respectively. The enhancement of catalytic activity should be attributed to the strong water dissociation ability and the rearrangement of electrons around the phase junction, which markedly improved the Volmer step and benefited the reduction process of adsorbed protons.