Perchloric Acid Solutions Research Articles

Durability Enhancement of Intermetallics Electrocatalysts via N-anchor Effect for Fuel Cells

Insufficient durability and catalytic activity of oxygen reduction reaction (ORR) electrocatalyst are key issues that have to be solved for the practical application of low temperature fuel cell. This paper introduces a new catalyst design strategy using N-anchor to promote the corrosion resistance of electrocatalyst. The as-synthesized N-Pt3Fe1/C shows a high electrocatalytic activity and a superior durability towards ORR. The kinetic current density of N-Pt3Fe1/C as normalized by ECSA is still as high as 0.145 mA cm−2 and only 7% loss after 20000 potential cycles from 0.6 to 1.2 V (vs. NHE) in O2-bubbling perchloric acid solution, whereas Pt3Fe1/C shows 49% loss under the same tests. The N-anchor approach offers novel opportunities for the development of ORR catalyst with excellent electrochemical properties.

Synthesis, transport, and ionophore properties of α,ω-biphosphorylated azapodands: VIII. Solvent extraction of the metal ions with N,N′-bis(dioctylphosphorylmethyl)-1,8-diamino-3,6-dioxaoctane

Liquid extraction from the aqueous solutions of perchloric acid with neutral azapodand extractant N,N′-bis(dioctylphosphorylmethyl)-1,8-diamino-3,6-dioxaoctane has been highly efficient in the cases of uranyl ions and some metals of groups II and III. To estimate the synergic effect of organophosphorus extractants, the neutral extractant was applied in the mixture with an acidic component, bis(pentadecyl)phosphoric acid. The synergic effect has exclusively been observed in the extraction of zinc and cadmium ions.

The Stability of Silver Nanoparticles in a Model of Pulmonary Surfactant

The growing use of silver nanoparticles (AgNPs) in consumer products has raised concerns about their potential impact on the environment and human health. Whether AgNPs dissolve and release Ag(+) ions, or coarsen to form large aggregates, is critical in determining their potential toxicity. In this work, the stability of AgNPs in dipalmitoylphosphatidylcholine (DPPC), the major component of pulmonary surfactant, was investigated as a function of pH. Spherical, citrate-capped AgNPs with average diameters of 14 ± 1.6 nm (n = 200) were prepared by a chemical bath reduction. The kinetics of Ag(+) ion release was strongly pH-dependent. After 14 days of incubation in sodium perchlorate (NaClO4) or perchloric acid (HClO4) solutions, the total fraction of AgNPs dissolved varied from ∼10% at pH 3, to ∼2% at pH 5, with negligible dissolution at pH 7. A decrease in pH from 7 to 3 also promoted particle aggregation and coarsening. DPPC (100 mg·L(-1)) delayed the release of Ag(+) ions, but did not significantly alter the total amount of Ag(+) released after two weeks. In addition, DPPC improved the dispersion of the AgNPs and inhibited aggregation and coarsening. TEM images revealed that the AgNPs were coated with a DPPC layer serving as a semipermeable layer. Hence, lung lining fluid, particularly DPPC, can modify the aggregation state and kinetics of Ag(+) ion release of inhaled AgNPs in the lung. These observations have important implications for predicting the potential reactivity of AgNPs in the lung and the environment.

A Validated Chiral HPLC Method for the Enantiomeric Separation of Melphalan HCl

A new and accurate chiral HPLC method was developed for the determination of Melphalan HCl, L-Phenylalanine, 4-bis (2-chloroethyl) amino hydrochloride an anti-cancer chemotherapy drug and its potential impurity namely D-Phenylalanine, 4-bis (2-chloroethyl) amino hydrochloride ( D-enantiomer) in bulk substance. HPLC separation was carried out by reverse phase chromatography on Crownpak CR (+) (5μm, 4.0x150mm) with a mobile phase composed of perchloric acid (pH 4.0): methanol in the ratio of 90:10. Melphalan and its potential impurities were baseline resolved in the optimized method. The pH of perchloric acid solution in the mobile phase has played a key role in achieving chromatographic resolution between the enantiomers and in enhancing chromatographic efficiency. The developed method was completely validated and proved to be robust. The validated method yielded good results regarding specificity, precision, linearity, accuracy, robustness, sensitivity. Melphalan HCl sample solution is found to be stable for at least 60hrs at room temperature. The proposed method was found to be suitable and accurate for quantitative determination of Melphalan HCl and its D-enantiomer in bulk substance.

Electrochemical Hydrogenation of Dimensional Carbon

The hydrogen adsorption and electrochemical properties of epitaxial graphene (EG) grown on silicon carbide (SiC) and bulk graphite in dilute sulfuric acid (H2SO4) and perchloric acid (HClO4) solutions were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). According to EIS, electrochemical activity is dependent on starting I(D)/I(G) ratio suggesting a dependence on point defects in the material for successful hydrogenation. Electrochemical hydrogen loading and unloading on epitaxial graphene was also demonstrated and confirmed by Raman spectroscopy and CV. These results show that hydrogenation of graphene is electrochemically reversible and history dependent impacting H loading. This process demonstrates a new pathway to hydrocarbon bond formation for synthesis of advanced organic/inorganic carbon-based compounds.

Electrochemical features of Pt(S)[n(110) × (100)] surfaces in acidic media

Experiments have been carried out in sulfuric and perchloric acid solutions on Pt(S)[n(110)×(100)] electrodes. The comparison between the two different electrolytic media reveals an important influence of the anion in the voltammetric features. Total charge curves have been obtained with the CO charge displacement method in combination with voltammetric measurements. From these curves, the dependence of the pztc with the step density and the strength of the anion adsorption have been analyzed. The problem of the so-called third peak is treated for a series of electrodes that contain (110) terraces, revealing the requirement of (110) domains for occurrence of this adsorption state.

Involvement of ·OH radicals in the mechanism of excitation of the uranyl ion in the chemiluminescent oxidation of U(IV) by atmospheric oxygen in aqueous solutions of perchloric acid

The chemiluminescence (CL) kinetics in U(IV) oxidation by atmospheric oxygen in aqueous HClO4 has been investigated. The CL quantum yield (ηCL, E/(mol U(IV))) in this reaction is 1.4 × 10−8. The elementary event generating the CL emitter, which is the electronically excited uranyl ion *(UO22+), is electron transfer from the uranyl ion UO2+ to the oxidizer (·OH radical). The Ag+ ion quenches CL, and the Cu2+ ion enhances CL.

The effect of rhodium nanoislands on the electrocatalytic activity of gold for oxygen reduction in perchloric acid solution

The effect of spontaneously deposited rhodium nanoislands on the electrocatalytic activity of polycrystalline gold, Au(poly), for oxygen reduction reaction (ORR) was studied using rotating disc electrode technique in 0.1M HClO4 solution. Surface topography atomic force microscopy (AFM) images of obtained Rh/Au(poly) surfaces revealed that both the size and coverage of rhodium nanoislands increase with the deposition time, for a given depositing conditions. The exact values of rhodium coverage ranging from 50% to the full coverage, and the qualitative changes in the surface chemical composition with respect to bare gold were estimated from phase AFM images. Deposited Rh was also identified by the changes in cyclic voltammetry (CV) profiles from which potential limits for ORR were determined. Obtained Rh/Au(poly) surfaces have shown a significant shift of the initial potential for ORR to the more positive potentials with respect to pure gold already for 50% Rh coverage, indicating that a pronounced electronic effect is responsible for the lowering of the activation energy for oxygen adsorption. The initial potential increases only slightly with the further increase of Rh coverage. Reaction pathway changes from 2e− reduction at lower overpotentials to a partial 4e− reduction at higher overpotentials. The later is attributed to the increased activity of obtained Rh/Au(poly) surfaces towards hydrogen peroxide reduction (HPRR), which appear as an intermediate during ORR. The fraction of 4e− reduction slightly increases with the increase of Rh coverage.

Redox transformations of adsorbed NO molecules on a Pt(100) electrode

The electrochemical behavior of adsorbed NO molecules on a Pt(100) electrode has been studied in perchloric acid solutions by means of cyclic voltammetry. According to the literature data, a saturated NO adlayer with a coverage of ∼0.5 monolayers (MLs) is formed under open circuit conditions in an acidic nitrite solution as a result of a disproportionation reaction. The saturated adlayer is stable in the potential range of 0.4–0.9 V vs. a reversible hydrogen electrode in 0.1 M HClO4. NO molecules are oxidized at 0.9–1.1 V with the formation of adsorbed nitrite anions, and they can be reduced to ammonia at potentials less than 0.4 V. In this paper it has been shown that the adlayer stability depends on the surface coverage and extent of ordering. An unsaturated NO adlayer demonstrates NO ↔ NH3 redox transformations at 0.5–0.8 V.

Micromesoporous VC and WC Derived Carbons Supported Catalysts as Cathodes for Polymer Electrolyte Membrane Fuel Cells in Sulfuric and Perchloric Acid Solutions

not Available.

Kinetics and mechanism of nitrate and nitrite electroreduction on Pt(100) electrodes modified by copper adatoms

Kinetics and mechanism of nitrate and nitrite reduction on Pt(100) electrode modified by Cu adatoms have been studied in solutions of sulfuric and perchloric acids by means of cyclic voltammetry and in situ IR-spectroscopy. It has been shown that the surface redox process with participation of ammonia or hydroxylamine at 0.5–0.9 V occurs only on the Cu-free platinum. The causes of this effect could be low adsorption energy of nitrate reduction products on copper or changes in the composition of the products (ammonia for Pt(100) and N2O for Pt(100)+Cu). Nitrate reduction on Pt(100)+Cu electrode is much faster in the perchloric acid solution (by several orders of magnitude) as compared with unmodified platinum as a result of induced adsorption of nitrate anions in the presence of partly charged Cu atoms. In the solutions of sulfuric acid the rate of nitrate reduction is considerably lower as copper adatoms facilitate adsorption of sulfate anions, which block the adsorption sites for the nitrate.

Direct STM Elucidation of the Effects of Atomic-Level Structure on Pt(111) Electrodes for Dissolved CO Oxidation

We sought to establish a new standard for direct comparison of electrocatalytic activity with surface structure using in situ scanning tunneling microscopy (STM) by examining the electrooxidation of CO in a CO-saturated solution on Pt(111) electrodes with steps, with combined electrochemical measurements, in situ STM, and density functional theory (DFT). On pristine Pt(111) surfaces with initially disordered (111) steps, CO oxidation commences at least 0.5 V lower than that for the main oxidation peak at ca. 0.8-1.0 V vs the reversible hydrogen electrode in aqueous perchloric acid solution. As the potential was cycled between 0.07 and 0.95 V, the CO oxidation activity gradually decreased until only the main oxidation peak remained. In situ STM showed that the steps became perfectly straight. A plausible reason for the preference for (111) steps in the presence of CO is suggested by DFT calculations. In contrast, on a pristine Pt(111) surface with rather straight (100) steps, the low-potential CO oxidation activity was less than that for the pristine, uncycled (111) steps. As the potential was cycled, the activity also decreased greatly. Interestingly, after cycling, in situ STM showed that (111) microsteps were introduced at the (100) steps. Thus, potential cycling in the presence of dissolved CO highly favors formation of (111) steps. The CO oxidation activity in the low-potential region decreased in the following order: disordered (111) steps > straight (100) steps > (100) steps with local (111) microsteps ≈ straight (111) steps.

In Situ Scanning Tunneling Microscopy Study of Interfacial Structures of Self-Assembled Monolayers of 3-(2-Pyridyldithio)Propionyl Hydrazide on Au(111)

Self-assembled monolayers of 3-(2-pyridyldithio) propionyl hydrazide (PDPH) on Au(111) in perchloric acid solution were studied by in situ scanning tunneling microscopy (STM). The two-component PDPH molecules adsorbed uniformly on the Au(111) surface without phase separation in the monolayer. The 2-pyridine and propionyl hydrazide moieties of PDPH appeared as distinct features in the STM image of the PDPH monolayer and were successfully imaged in solution.

A Method Developed for Getting Kinetic Information from Electrochemical Impedance Spectroscopy Measured for Anodized Ti in Fluoride

EIS has been acknowledged to be a powerful tool for investigating the kinetic mechanisms of charge transfer processes at electrode/solution interfaces. The method of using equivalent electrical circuits (EECs) has been most frequently used for interpreting measured EIS spectra. But the mechanistic information that this method can deliver is very limited. In this work, an alternative but innovative method, which combines the EECs and the mechanism analysis, is developed. With anodically polarized, oxide film covered titanium in NaF-containing perchloric acid solutions as an example, a detailed procedure is described and discussed for obtaining kinetic information (such as the rate constant, rate-determining step) from the results estimated by EECs. Two double-step mechanism models for anodized titanium are proposed and tested based on the strategy of the developing approach.

Changes of the interfacial stress with electrode potential in the Ru|0.1 M perchloric acid system

Electrochemical and mechanical properties of ruthenium films electrodeposited on gold have been investigated in aqueous perchloric acid solutions. Cyclic voltammograms recorded at slow sweep rates in rotating disk experiments were highly asymmetric with respect to the electrode potential axis, and a negative current could be observed even during the positive sweep. Changes of the interfacial stress were measured by the bending beam method as functions of the electrode potential and of the concentration of chloride ions. The results are consistent with the earlier observation that perchlorate ions can be electrochemically reduced to Cl− on ruthenium. The resulting chloride ions decrease the interfacial stress and exert an inhibiting effect on the reduction process indicating the role of competitive adsorption. The desorption rate of Cl− is significantly influenced by the hydrodynamic conditions, probably through desorption/diffusion coupling.

A comparative study of the adsorption and oxidation of L-alanine and L-serine on Au(1 0 0), Au(1 1 1) and gold thin film electrodes in acid media

The adsorption and oxidation of l-alanine and l-serine at Au(111) and Au(100) single crystal and evaporated thin-film electrodes with preferential (111) orientation was studied in perchloric acid solutions. For this purpose, cyclic voltammetry experiments were combined with external reflection infrared spectroscopy (gold single crystals) and surface-enhanced infrared reflection–absorption spectroscopy under attenuated total reflection conditions (ATR-SEIRAS) (gold thin films). In addition, theoretical harmonic vibrational frequencies, obtained from B3LYP/LANL2DZ, 6-31+G(d) calculations for the zwitterionic species adsorbed on Au clusters with (111) orientation, were used to interpret the experimental spectra. The optimized geometry obtained from DFT calculations for the corresponding zwitterion plus a water molecule, under the application of an external electric field of 0.01a.u. corresponds to a bidentate asymmetrical bridge adsorption configuration. The absence of an adsorbate band for the asymmetric OCO stretching in the experimental infrared spectra confirms the bidentate bonding of the adsorbed zwitterion through the oxygen atoms of the carboxylate group irrespective of the crystallographic orientation of the electrode surface, the adsorbate coverage and the electrode potential. In addition to typical interfacial water bands associated to perchlorate anions, which are co-adsorbed in order to compensate the positive charge of the ammonium group, the ATR-SEIRA spectra also show bands around 2950cm−1 that can be related to the formation of hydrogen bonds between interfacial water and the ammonium group of the adsorbed zwitterion. The voltammetric experiments have shown that, as in the case of platinum electrodes, l-serine oxidizes at lower potentials than l-alanine. Under these conditions, the in situ infrared experiments show the formation of carbon dioxide and adsorbed cyanide as oxidation products of l-serine. In the case of l-alanine, only carbon dioxide was detected.

Electroreduction of peroxodisulfate anion at platinum rotating disc electrode in the cyclic voltammetry mode

Electroreduction of peroxodisulfate anion at smooth polycrystalline and platinized (at different deposition potentials) platinum in perchloric acid and sulfuric acid solutions is studied by rotating disc electrode and cyclic voltammetry techniques. Dependences of the process rate on the electrode rotating velocity, the potential scan rate, the anodic limit of the scanning, the peroxodisulfate anion concentration in the solution and the platinizing conditions are found. The suggestion on the complications in the peroxodisulfate anion reduction caused by adsorbate formation is corroborated, at least, for certain potential region. The reaction structure sensitivity is evidenced, which makes it possible to use the reaction for characterization of the platinized Pt surface structure. The comparing of obtained results with literature data concerning smooth platinum and the single-crystal platinum basis faces allows concluding that the peroxodisulfate anion reduction maximal rate in sulfuric-acid solutions occurs at the potentials close to those observed for the (110) face. When the platinized Pt surface roughness factor exceeds ~30, the peroxodisulfate anion reduction reaction proceeds under the inner-diffusion limitation control. The platinized-Pt rotating disc electrode can serve as model tool in the studying of properties of disperse material microdeposits.

Effect of non-thermostated capillary inlet in affinity capillary electrophoresis: Uranyl-selenate system at variable temperatures

The influence of non-thermostated capillary inlet on accuracy of data obtained by affinity capillary electrophoresis is examined in the case of kinetically labile systems (with fast kinetics of equilibrium) at different temperatures. The system uranyl-selenate is studied in aqueous perchloric acid solutions (pH 2.5, ionic strength 0.05moll−1) in the temperature range from 15°C to 55°C. Moving of the sample through the non-thermostated inlet into the thermostated region of the capillary is used in order to avoid the influence of non efficiently thermostated short capillary inlet. The data on mobility values of uranyl and the values of stability constants obtained by this mode are compared with the data obtained in a traditionally used mode (injection in non-thermostated inlet region). The uranyl mobility values obtained by the two methods are different at temperature higher than 35°C. However, the difference between stability constants obtained by the two methods is not significant (ambient temperature is 20°C).

Electrochemical properties of titanium-based catalytically active electrodes in perchloric acid

The electrochemical behavior of the electrodes made of titanium powders and catalytically active materials based on titanium in solutions of perchloric acid is studied by the voltammetry methods. The influence of preliminary preparation of titanium on its electrochemical behavior is investigated with an aim to develop new modes of treatment of titanium used as the base material for the gas-diffusion electrodes of electrochemical sensors. It is shown that, titanium may play the role of conductive base for catalytically active materials in HClO4 solutions within the potential range 0.5–1.7 V. The accumulated results show that there exists a range of values of the working potentials of titanium-based electrodes attained in air within which the analyzed components can be detected with high resolution. Depending on the nature of catalytically active materials, the range of working potential lies between 100 mV for the Ti/MnO2 electrode and almost 400 mV for the Ti/Pt electrode inside the range of values of the stationary currentless potential of the working electrode determined in air.

Nanoporous α-Alumina Membrane with High Chemical Resistance Prepared by Anodizing

not Available.