Characteristic of hydrogen-saturated Pd-based alloys for the application in electrochemical capacitors

Hydrogen electrosorption was performed in thin electrodeposits of Pd alloys with Pt, Au, and Rh. The possibility of their application as phase charging–discharging systems was investigated. The values of specific pseudocapacitance, power, and energy were calculated for hydrogen-saturated Pd-rich electrodes for temperatures 283–313 K. The best working parameters are exhibited by Pd–Rh alloys with 85–95% Pd, and by Pd–Pt alloys with 90–95% Pd in the bulk. The maximum values of specific pseudocapacitance are ca. 4,500 F?g^?1, specific energy ca. 150 J?g^?1 and specific power up to 750 W?g^?1 (per the mass of the electroactive material). In the case of the alloy deposits on reticulated vitreous carbon, their characteristics related to the total mass of the electroactive material and the substrate are comparable with those for other supercapacitors utilizing various redox reactions.     

Polarographic investigation of the stability of tin(II) solutions in the presence of some stabilizing agents

The stability of acidic tin(II) solutions was investigated polarographically in the presence of substances with mild antioxidant properties. The best stabilizing action is exerted by pyrogallol, hydrazine or phenolsulphonic acid. In methanolic solutions containing perchloric acid, the stability improves whereas chloride ions hasten the oxidation of tin(II). It is shown that the enhanced stability is due neither to complexation of tin(II) nor to reduction of oxygen by the antioxidants used. The fact that some of the reagents tested exert a powerful stabilizing action even in very small concentrations supports an earlier suggestion that the reaction between tin(II) and oxygen is a chain reaction which is inhibited by the stabilizer.     

Electrochemical absorption and oxidation of hydrogen on palladium alloys with platinum, gold and rhodium

Thin layers of Pd and its alloys with Pt, Au and Rh were prepared by electrodeposition on a Au substrate. Hydrogen electrosorption by the obtained electrodes was studied in 0.5 M H(2)SO(4) solution using cyclic voltammetry and chronoamperometry. The influence of the alloying process on selected thermodynamic (the amount of absorbed hydrogen, the stability of the β-phase, the extent of the absorption/desorption hysteresis) and kinetic aspects (the rate of hydrogen absorption and absorbed hydrogen oxidation) of hydrogen absorption and desorption was examined. It was found that the addition of the non-absorbing elements to Pd results in faster kinetics of the hydrogen electrosorption process and a smaller absorption/desorption hysteresis.     

Resolution of anodic stripping voltammetry with thin-film mercury electrodes

The potentialities of the use of thin-film mercury electrodes (TFME) for the improvement of resolution of stripping voltammetry were discussed from a theoretical viewpoint. A set of current functions was computed numerically on the basis of the de Vries and van Dalen theory. The data obtained permitted the summing of current functions of two neighbouring dissolution processes and the estimation of the influence of the extent of overlap on the enhancement of the peak height and on the separation of peak potentials. The separation is governed mainly by the parameter b_1/2 (peak width at half height) which approaches the value 75.53/n mV at TFME compared to 203/n mV characteristic for HMDE. The variations in film thickness and in voltage scan rate may also improve the separation of two adjacent peaks, but only if different numbers of electrons are involved in both electrode reactions. The maximum separation obtained by changes in film thickness may attain 160 mV for two reactions with a value of n equal to 1 and 3 respectively.The experimental results obtained for the systems: Bi and Sb; Pb and Cd; Pb and Tl; Bi and Cu; Pb, Tl and Cd at TFME with silver or graphite substrate confirmed the theoretical predictions.     

New Cyclic Dimers of Cholic Acid

Two new cyclic dimers of cholic acid were obtained in the reaction of 3-O-acetyl methyl cholate with oxalyl chloride. The oxalates bound the cholate subunits side-to-side as a result of acylation of 7 and 12 OH groups in the substrate. The selective deprotection of hydroxy groups at C-3 and C-24 proved to be rather difficult and led to various products depending on the reaction conditions.     

Clinical Trials and Basic Research in Photodynamic Diagnostics and Therapies from the Center for Laser Diagnostics and Therapy in Poland

The purpose of this review is to present an overview of the development of photodiagnostic and photodynamic therapy (PDD and PDT) techniques in Poland. The paper discusses the principles of PDD, including fluorescent techniques in determining precancerous conditions and cancers of the skin, digestive tract, bladder and respiratory tract. Methods of PDT of cancer will be discussed and the current state of knowledge as well as future trends in the development of photodynamic techniques will be presented, including the possibility of using photodynamic antimicrobial therapy. Research pioneers in photodynamic medicine such as Thomas Dougherty are an inspiration for the development of methods of PDD and PDT in our Clinic. The Center for Laser Diagnostics and Therapy in Bytom, Poland, promotes the propagation of PDD and PDT through the training of clinicians and raising awareness among students in training and the general public. Physicians at the Center are engaged in photomedical research aimed at clinical implementation and exploration of new avenues in photomedicine while optimizing existing modalities. The Center promotes dissemination of clinical results from a wide range of topics in PDD and PDT and serving as representative authorities of photodynamic medicine in Poland and Europe.     

Solvent effects on acid-base behavior: Five uncharged acids in water-sulfolane solvents

An electrometric titration method utilizing glass electrodes and silver-silver bromide electrodes in a cell without liquid junction has been applied to a determination of the dissociation constants of five uncharged weak acids (HA) in four mixtures of water and sulfolane (tetramethylene sulfone) at 25°C. The acids studied were monochloroacetic, formic, benzoic, and acetic acids andp-nitrophenol, and the mole fractions (x ₂) of sulfolane in the mixed solvents were 0.2, 0.4, 0.6, and 0.8. All measurements were made at a constant ionic strength of 0.02 mole-kg^–1 in a solution containing NaBr at a molality of 0.01 mole-kg^–1. The cell was standardized by measurements of HClO₄ at molalities from 0.002 to 0.01 mole-kg^–1 and, in subsequent measurements, a solution of NaA was titrated with HClO₄. To obtain the thermodynamic pK, an activity correction derived from the Debye-Hückel theory was applied. The pK of all five acids was found to vary linearly withx ₂ in the range 0 to 0.8. By comparison of data for acetic acid in water-methanol, water-dioxane, and water-sulfolane solvents, it was shown that the results are consistent with the known properties of sulfolane (low acidity, basicity, and solvating power), but the linear variation of pK with solvent composition remains unexplained.On leave 1973–1975 from the University of Gdansk, Poland.     

Interfering influence of silver on the voltammetric behaviour of Cd2+ and Zn2+ ions on hmde in supporting electrolytes containing nitrates

A new kind of secondarily formed peaks was found in cyclic and stripping voltammetry in neutral sulphate, perchlorate and nitrate supporting electrolytes containing some divalent cations and a substance (for example O₂), the reduction of which gives as a by-product OH^? ions. The hydroxides deposited in the vicinity of the mercury electrode, in the course of a cathodic scan, react during the anodic scan according to the reaction Hg+Me(OH)₂=Hg(OH)₂+Me²⁺+2e forming a new, separate anodic peak.It was found that silver exerts a catalytic effect on the reduction of NO₃^? ions on the mercury electrode. In neutral nitrate supporting electrolyte containing Ag⁺ ions the hydroxides of some cations (Cd²⁺, Zn²⁺, Mn²⁺, Co²⁺ and Ni²⁺) were deposited during the cathodic scan or during the preelectrolysis. Afterwards, in the course of the anodic scan, a new peak, of the kind described above, was observed. The same effect was formerly interpreted, for Zn²⁺ and Cd²⁺, as evidence for the formation of intermetallic compounds, AgZn and AgCd.     

Direct or indirect influence of triphenyl‐lead on activity of Na+/K+‐ATPase

We have studied the effect of triphenyl‐lead chloride on the lipid phase of erythrocyte membranes, on lipid monomolecular layers and Na⁺/K⁺‐ATPase of the microsomal fraction of rat brain. It was found that the haemolytic effect induced by this compound occurs when its concentration exceeds 30 µM . The minimal lead concentration inducing measurable effects in monomolecular lecithin layers is about 1 µM . Inhibition of Na⁺/K⁺‐ATPase activity begins at a concentration exceeding 0.5 µM . Maximum inhibition is observed at around 40 µM —a concentration at which haemolysis also occurs. It can thus be thought that at very low lead concentrations the main (or exclusive) role in modifying membrane function is played by direct interaction between lead and the sulphydryl groups of ATPase, whereas at higher concentrations two effects seem to overlap: direct interaction between lead and enzymic proteins via their sulphydryl groups and as indirect influence on the proteins via changes in the organization of the lipid phase of the membrane. Copyright © 2000 John Wiley & Sons, Ltd.