Preparation and ionic conductivity of (100−x)(0.8Li2S·0.2P2S5)·xLiI glass–ceramic electrolytes

The glass–ceramic electrolytes of (100?x)(0.8Li₂S·0.2P₂S₅)·xLiI (in mole percent; x?=?0, 2, 5, 10, 15, 20, and 30) were prepared by mechanical milling and subsequent heat treatment. Crystalline phases analogous to the thio-LISICON region II or III in the Li₂S–GeS₂–P₂S₅ system were precipitated. The thio-LISICON III analog phase was mainly precipitated at the composition x?=?0, and the thio-LISICON II analog phase was precipitated in the composition range from x?=?2 to 15. The X-ray diffraction peaks of the thio-LISICON II analog phase shifted to the lower diffraction angle side with increasing the LiI content. High conductivities above 2?×?10^?3?S?cm^?1 at room temperature were observed in the glass–ceramics at the wide composition range from x?=?2 to 15. The glass–ceramic electrolyte at x?=?5 with the highest conductivity of 2.7?×?10^?3?S?cm^?1 showed a wide electrochemical window of about 10 V. The addition of LiI to the 80Li₂S·20P₂S₅ (in mole percent) glass was effective in crystallizing the thio-LISICON II analog phase with high conductivity from the glass.     

All-solid-state batteries with Li2O-Li2S-P2S5 glass electrolytes synthesized by two-step mechanical milling

Sulfide solid electrolytes, which show high ion conductivity, are anticipated for use as electrolyte materials for all-solid-state batteries. One drawback of sulfide solid electrolytes is their low chemical stability in air. They are hydrolyzed by moisture and generate H₂S gas. Substituting oxygen atoms for sulfur atoms in sulfide solid electrolytes is effective for suppression of H₂S gas generation in air. Especially, the xLi₂O·(75-x)Li₂S·25P₂S₅ (mol%) glasses hardly generated H₂S gas in air. However, substituting oxygen atoms for sulfur atoms caused a decrease in conductivity. The x?=?7 glass showed high chemical stability in air and maintained high conductivity of 2.5?×?10^?4 S cm^?1 at room temperature. Performance of cells using the 7Li₂O·68Li₂S·25P₂S₅ and the 75Li₂S·25P₂S₅ glasses as solid electrolytes were compared. All-solid-state C/LiCoO₂ cell using the 7Li₂O·68Li₂S·25P₂S₅ glass produced performance as good as that obtained using the 75Li₂S·25P₂S₅ glass. Capacity retention and change of interfacial resistance of the former cell were superior to those of the latter cell after storage at 4.0 V and 60 °C. The diffusion of oxygen element into the 7Li₂O·68Li₂S·25P₂S₅ glass was less than that into the 75Li₂S·25P₂S₅ glass after storage at the voltage of 4.0 V at 60 °C. Improvement of the stability of sulfide solid electrolytes to moisture was related to cell performance as well as an increase in conductivity.     

Electrochemical properties of sulfur adsorbed on gold electrodes

The electrochemical properties of sulfur adsorbed on gold electrodes were studied in 10^?5M solutions of S^2? in 1 M NaOH. In general, ∵_S is less than a monolayer. At E=0.05 V only, a monolayer will be formed after long times. The sulfur layer is stable in the potential range between ?0.6 and +0.4 V. At lower potentials, sulfur can be desorbed cathodically (charge Q_red), but at higher potentials, where layers of gold oxide are formed, the sulfur is oxidized anodically (charge Q_ox). From the ratio Q_red·6/Q_ox=γ, the electrosorption valency γ=?2 is obtained. This means, that the sulfide ions are almost completely discharged during adsorption. The same layer can be formed by adsorption from polysulfide solutions, which can be explained by a break of the sulfur bond and adsorption of single sulfur atoms. The double layer capacity decreases during adsorption of sulfur indicating the formation of an insulating sulfur layer with a dielectric constant of about 2. The anodic adsorption of sulfide ions is limited by diffusion only. For longer polarisation times, the coverage is independent of time, i.e. place exchange reactions between Au and S can be excluded. The cathodic desorption as well as the anodic oxidation of the adsorbed sulfur are potential dependent charge transfer processes, as can be concluded from potentiodynamic measurements with various sweep rates.     

Hydrogen diffusivity in the massive LaNi5 electrode using voltammetry technique

The Randles–Sev?ik relationship has been applied to evaluate atomic hydrogen diffusivity in massive LaNi₅ intermetallic compound. The electrode was cathodically hydrogenated in 6 M KOH solution (22 °C), and then voltammetry measurements were carried out at various, very slow potential scan rates (υ?=?0.01–0.1 mV?·?s^?1). At potentials more noble than the equilibrium potential of the H₂O/H₂ system, the anodic peaks were registered as a consequence of oxidation of hydrogen absorbed in cathodic range. The peak potentials linearly increase with the logarithm of the scan rate with a slope of 0.059 V. The slope testifies to a symmetric charge transfer process with symmetry factor α?=?½. The peak currents linearly increase with the square root of the potential scan rate, and the straight line runs through the origin of the coordinate system. The slope of the I _a ^(peak) ?=?f(υ ^1/2) straight line is a measure of the atomic hydrogen diffusion coefficient. Assuming the hydrogen concentration in the LaNi₅ material after cathodic exposure to be C _0,H?=?0.071 mol?·?cm^?3 (63 % of theoretical value), the hydrogen diffusion coefficient equals D _H?=?2.0?·?10^?9 cm²s^?1. Extrapolation of rectilinear segments of potentiodynamic polarization curves with Tafel slopes of 0.12 V and linear polarization dependencies from voltammetry tests allowed the exchange current densities of the H₂O/H₂ system on the tested material to be determined. The exchange current densities on initially hydrogenated LaNi₅ alloy are close to 1 mA?·?cm^?2, irrespective of the electrode potential scan rate.     

Influence of sulfide and cyanide ions on the electrochemical behavior of the Fe(II)/Fe(Hg) system in thiocyanate solutions at mercury electrodes

The reduction and reoxidation processes of the Fe(II)/Fe(Hg) system in thiocyanate solutions at stationary mercury electrodes have been investigated by cyclic voltammetric, anodic stripping and controlled potential electrolysis methods. In 0.1 M NaSCN and 0.4 M NaClO₄ solution containing 1×10^?3M Fe(II), the voltammogram on the first cycle at. 0.05 V s^?1 gives two consecutive cathodic peaks near ?1.2 and ?1.39 V with a hysteresis on the reversal, and an anodic wave with two large peaks near ?0.58 and ?0.05 V and two small peaks near ?0.52 and ?0.43 V, respectively. The multicyclic voltammogram under the same conditions in the potential region between 0.00 and ?1.50 V gives a cathodic wave with a principal peak near ?1.02 V and two small peaks near ?0.02 and ?0.53 V, respectively, and an anodic wave with a principal peak near ?0.72 V, three small peaks near ?0.64, ?0.52 and ?0.40 V, and with a shoulder near ?0.05 V, respectively. The variation of the shape of the voltammogram on the second and subsequent runs is due to the formation of S^2? and CN^? during the process of electroreduction of Fe(II). A mechanism is proposed which involves an initial reduction of Fe(II)?SCN^? produced in an activation step at a mercury electrode, followed by the chemical redox reaction of a part of Fe(0)?SCN^? in the species giving FeS and CN^?, and takes into account the influence of FeS and CN^? on the further reduction and reoxidation of iron. Both FeS and CN^? stimulate further reduction, and reoxidation of iron. The hysteresis of the cathodic wave on the first cycle arises from the fact that Fe(II) is reduced more easily at the mercury electrode covered with FeS than at a pure mercury electrode.     

Subspeciation of nickel disulfide by carbon paste electrode voltammetry catalyzed by Ni2+

In subspeciation of sulfidic nickel, carbon paste electrode voltammetry was developed for the specific determination of Ni₃S₂ or NiS, but NiS₂ was found to be unreactive. Ni²⁺ in pH 7.2 acetate solution was able to catalyze NiS₂ to undergo redox reactions. The cyclic voltammogram showed two anodic peaks at –0.3 and +0.7 V and a cathodic peak at –0.6 V. The first anodic peak at –0.3 V and the cathodic peak were common among the three nickel sulfides, but the second anodic peak at +0.7 V was unique to NiS₂. This peak current gave a linear dose response to NiS₂ from 40 to 610 μg, with a correlation coefficient of 0.994, and a detection limit of 40 μg.     

Influence of cyanide and sulphide ions on the reduction and reoxidation of cobalt(II) in thiocyanate solution at mercury electrodes

The process of reduction and reoxidation of cobalt(II) in thiocyanate solution at hanging mercury drop electrode has been investigated by cyclic voltammetric, chronoamperometric and anodic stripping methods. In 0.1 M NaSCN and 0.4 M NaClO₄ solution containing 1×10^?3M cobalt(II), the voltammogram on the first cycle at 0.05 V s^?1 gives a cathodic peak at ?1.06 V with hysteresis on reversal, and an anodic wave with a peak potential of ?0.28 V and with two shoulders near ?0.38 and ?0.45 V, respectively. Multicyclic voltammograms under the same conditions give a cathodic peak at ?0.90 V and an anodic peak at ?0.45 V. The reduction and reoxidation of cobalt(II) in thiocyanate solution is accelerated by the reduction products of thiocyanate ion, cyanide and sulphide ions, which are produced during the electroreduction of cobalt(II).A mechanism of reduction and reoxidation of cobalt(II) which involves a chemical reduction of thiocyanate ion by electroreduced metallic cobalt and takes into account cyanide and sulphide ions is proposed. The hysteresis on the cathodic wave is caused by the difference in reduction potentials of cobalt(II)-thiocyanate and-cyanide complexes. Cyclic voltammetric study of cobalt(II) in perchlorate solution containing trace amounts of cyanide and sulphide ions supports these conclusions.     

Interfacial Electrochemical Behavior of RuS2 Single Crystal Electrodes in Sulfuric Acid Medium

The electrochemical behavior of RuS₂ has been studied using cyclic voltammetry and Energy Dispersive X-ray Spectroscopy (EDX) techniques. Cyclic voltammograms reveal one major anodic peak and two major cathodic peaks on the reverse sweep; these peaks are attributed to the electroadsorption/desorption of OH^? groups on the electrode surface. It is proposed that the electroadsorption of the OH^? group on RuS₂ is due to the presence of Ru 4d electrons in the uppermost part of the valence band. Thus, OH^? is oxidized by holes on Ru 4d states in the first step. These groups are transferred to S₂^2?sites in the second step. EDX surface analysis reveals preferential release of S₂^2? from the pyrite lattice. A mechanism for the anodic dissolution of RuS₂ is proposed, according to which elemental sulfur is not a direct product, but rather the end product which forms from thiosulfate.     

Direct electrochemistry of myoglobin in a layer-by-layer film on an ionic liquid modified electrode containing CeO2 nanoparticles and hyaluronic acid

We describe an ionic liquid modified electrode (CPE-IL) for sensing hydrogen peroxide (HP) that was modified by the layer-by-layer technique with myoglobin (Mb). In addition, the surface of the electrode was modified with CeO₂ nanoparticles (nano-CeO₂) and hyaluronic acid. UV-vis and FTIR spectroscopy confirmed that Mb retains its native structure in the composite film. Scanning electron microscopy showed that the nano-CeO₂ closely interact with Mb to form an inhomogeneously distributed film. Cyclic voltammetry reveals a pair of quasi-reversible redox peaks of Mb, with the cathodic peak at ?0.357?V and the anodic peak at ?0.269?V. The peak separation (??E _p) and the formal potential (E ^0??) are 88?mV and ?0.313?V (vs. Ag/AgCl), respectively. The Mb immobilized in the modified electrode displays an excellent electrocatalytic activity towards HP in the 0.6 to 78.0???M concentration range. The limit of detection is 50?nM (S/N?=?3), and then the Michaelis-Menten constant is 71.8???M. We believe that such a composite film has potential to further investigate other redox proteins and in the fabrication of third-generation biosensors.

Direct current and differential pulse polarographic behaviour of benzylpenicilloic acid

The differential pulse and direct current polarographic behaviour of benzylpenicilloic acid (BPA) is discussed. In pH 9.2 borate buffer, the single anodic wave (E_{$\text{1}\text{2}$} = -0.25 V) obtained is diffusion-controlled at concentrations less than 2 × 10^-5 M but adsorptioncontrolled in 10^-4 M solution. Cyclic voltammetry at a hanging mercury drop electrode shows that the electrode reaction is reversible at pH 9.2. The differential pulse peak current is linearly related to concentration in the range 10^-6—2 × 10^-5 M. Penicillamine yields an anodic peak well separated from the BPA peak. Both substances may be determined in each other's presence. Intact penicillin decreases the BPA peak but the linearity between i_p and BPA concentration is maintained.     

Phase equilibrium and p s-T-x diagrams of the Ln2S3-LnS2 (Ln = La, Pr, Nd, Sm-Er) systems

A new methodology is proposed and the phase equilibrium is investigated in the Ln₂S₃-LnS₂ systems, in which the low-temperature behavior of nonstoichiometric phases is controlled by the kinetics of the ordering of defects. It is shown that, under equilibrium conditions, the phase equilibrium in the systems is represented not only by a polysulfide with a wide homogeneity region, but also by several (or one) phases of constant irrational compositions combined in the homologous series Ln_nS_2n?1 (n = 3, 4, 7, 8, and 10). The formation of sulfur vacancies and isolated [S₂]^2? ions (which compensate the charge) in the anionic S^2? layer is the basic mechanism of changing the composition of the members of the series. On the basis of structural data, the possible mechanisms of the ordering of defective LnS_2?x polysulfides are examined and it is shown that the formation of stable or metastable phases is a kinetics-controlled process. The role of p _s-T-x diagrams in the interpretations of complex structures of metastable phases from the point of view of attainment of the equilibrium state is discussed.     

Controllable Synthesis of Bandgap‐Tunable CuSxSe1−x Nanoplate Alloys

Composition engineering is an important approach for modulating the physical properties of alloyed semiconductors. In this work, ternary CuS_xSe_1?x nanoplates over the entire composition range of 0≤x≤1 have been controllably synthesized by means of a simple aqueous solution method at low temperature (90 °C). Reaction of Cu²⁺ cations with polysulfide/‐selenide ((S_nSe_m)^2?) anions rather than independent S_n^2? and Se_m^2? anions is responsible for the low‐temperature and rapid synthesis of CuS_xSe_1?x alloys, and leads to higher S/Se ratios in the alloys than that in reactants owing to different dissociation energies of the Se?Se and the S?S bonds. The lattice parameters ‘a’ and ‘c’ of the hexagonal CuS_xSe_1?x alloys decrease linearly, whereas the direct bandgaps increase quadratically along with the S content. Direct bandgaps of the alloys can be tuned over a wide range from 1.64 to 2.19 eV. Raman peaks of the S?Se stretching mode are observed, thus further confirming formation of the alloyed CuS_xSe_1?x phase.     

Electroanalytical studies of the pesticides menazon and its hydrolysis products

An electroanalytical study based on d.c. polarography, differential pulse polarography (d.p.p.) and coulometry is described for Menazon, S-[4, 6-diamino-1,3,5-triazin-2-yl)- methyl]-O,O-dimethylphosphorodithioate, and its alkaline hysdrolysis products in a (1 + 4) methanol/water medium. The responses of the different species are studied for analytical utility. Menazon itself produces two diffusion-controlled cathiodic waves or peaks at pH 4.78; the determination limit is 5.5 × 10^-7 M for the d.p. peak at about ?0.8 V vs. Ag/AgCl. The hydrolysis products obtained in 0.1 M sodium ydroxide give rise to four anodic waves. Acidification of the alkaline medium to pH 4.3 produces three well-defined waves; two cathodic and one anodic. The responses for the cathodic processes are linear with concentration over 2–2.5 orders of magnitude; the anodic wave is adsorption-controlled and provides linear response only at low concentrations. The detection limit for the hydrolysis products is 0.17 × 10^-6 M. Reaction mechanisms are proposed.     

Synthesis and characterization of PrBaCo2 − x Ni x O5 + δ cathodes for intermediate temperature SOFCs

Nickel-substituted layered perovskite PrBaCo_{2 ? x} Ni _x O_{5 + δ} (PBCN) powders with various proportions of nickel (x?=?0, 0.1, 0.2, and 0.3, abbreviated as PBCN-0, PBCN-1, PBCN-2, and PBCN-3, respectively) are investigated as potential cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs) based on the yttria-stabilized zirconia (YSZ) electrolyte. It is found that PBCN-1 has the highest electrical conductivity of 1,397 S cm^?1 at 400 °C. Substitution of Co by Ni decreases the thermal expansion coefficient (TEC) clearly. The average TEC at the temperature range of 35–900 °C decreases from 22.8?×?10^?6 K^?1 for PBCN-0 to 18.9?×?10^?6 K^?1 for PBCN-3. The polarization resistances of PBCN samples on YSZ electrolyte at 800 °C are 0.053, 0.048, 0.052, and 0.042 Ω cm² for PBCN-0, PBCN-1, PBCN-2, and PBCN-3, respectively. The single fuel cell with the configuration of PBCN-3/YSZ/Pt delivers the highest power densities of 100, 185, 360, 495, and 660 mW cm^?2 at 600, 650, 700, 750, and 800 °C, respectively.     

Zur Kenntnis des Natriumthioferrates(III)

The mixed valency compound Na₃Fe₂S₄, which is also formed in iron-sodium polysulfide melts, is oxidized and hydrated to NaFeS₂·H₂O (x ≈ 2) on air. It is shown by TGA that this hydrate loses the water reversibly between 80–140 °C. A crystal structure model for the water free phase NaFeS₂ is proposed (space group I 222,a=6.25 Å,b=10.83 Å,c=5.40 Å). The formation of NaFeS₂·xH₂O from Na₃Fe₂S₄ and the reversible phase transformation between NaFeS₂·xH₂O and NaFeS₂ are topotactic. Na⁺ ions in NaFeS₂·xH₂O are easily exchanged against K⁺, Rb⁺, Cs⁺, Tl⁺, Ca²⁺, Sr²⁺, and Ba²⁺. The high chemical reactivity of the sodium thioferrates is discussed and their crystal structures are compared with the other alkali metal thioferrate structures.     

The electrochemical behaviour of the V2O5+MoO3 system and the defect structure of (MoxV1-x)2O5 solid solution

The V₂O₅+MoO₃ system has been examined by a stripping voltammetry technique using a carbon paste electroactive electrode and EPR. The feasibility of establishing the phase composition and the capability oxygen chemisorption has been demonstrated. The processes of electrochemical transformations of the substances to be investigated and of chemisorbed oxygen appearing on their surface as a result of electrochemical water oxidation serve as sources of information. The cathodic signal spectrum of chemisorbed oxygen anables its energetic inhomogeneity to be estimated, while the difference in potentials of the corresponding cathodic and anodic currents, its lability. It has been established that in the system investigated the dominant role in processes of oxygen chemisorption is played by the V⁴⁺ surface centres. A model of defect formation in solid solution (Mo_xV_1-x)₂O₅ is discussed.     

Crystal growth kinetics of Sb2S3 in Ge–Sb–S amorphous thin films

Sb₂S₃ crystal growth kinetics in (GeS₂) _x (Sb₂S₃)_1?Cx thin films (x?=?0.4 and 0.5) have been investigated through this study by optical microscopy in the temperature range of 575?C623?K. Relative complex crystalline structures composed of submicrometer-thin Sb₂S₃ crystal fibers develop linearly with time. The data on temperature dependence of crystal growth rate exhibit an exponential behavior. Corresponding activation energies were found to be E _G?=?279?±?7?kJ?mol^?1 for x?=?0.4 and E _G?=?255?±?5?kJ?mol^?1 for x?=?0.5. These values are similar to activation energies of crystal growth in bulk glasses of the same compositions. The crystal growth is controlled by liquid?Ccrystal interface kinetics. It seems that the 2D surface-nucleated growth is operative in this particular case. The calculated crystal growth rate for this model is in good agreement with experimental data. The crystal growth kinetic characteristic is similar for both the bulk glass and thin film for x?=?0.4 composition. However, it differs considerably for x?=?0.5 composition. Thermodynamic and kinetic aspects of crystal growth are discussed in terms of Jackson??s theory of liquid?Ccrystal interface.     

Über Chalkogenolate. 198. Untersuchungen über Polythiocuprate (I) [Cu(Sx)]− 2. Hydrazinium- und Ethylendiammoniumpolythiocuprate(I)

On Chalcogenolates. 198. Studies on Polythiocuprates(I) [Cu(S_x)]^?. 2. Hydrazinium and Ethylenediammonium Polythiocuprates(I) The red polythiocuprates(I) 1–5 (formulae see ?Inhaltsübersicht”?) have been prepared by reaction of hydrazinium or ethylenediammonium polysulfides with copper(II) salts, dissolved in water, under variable conditions. Their properties are described. In aqueous alkaline media 1–5 decompose into CuS and S; in the presence of carbon disulfide CuS, S_x^2?, and CS₃^2? besides CS₄^2? and S₂CO^2? are formed. The existence of the discreet ion [Cu₂CS₇]^2?, described in literature, was not confirmed. The polythiocuprates(I) 1–5 , dissolved im dimethylformamide, decompose via the radical anion S₃^?. The decomposition of S₃^? has been studied kinetically by means of compound 5 . The half-life of decay of S₃^? is τ_1/2 = 71.5 h at 20°C. The pentathiocuprate(I) 3 reacts with n-butyl chloride to produce the substituted sulfanes (C₄H₉)₂S_x′ where x = 1, 2 and 3.     

Determination of lead,tin, tellurium,and some doping elements in PbxSn1−xTe

A single method, based on gravimetric and polarographic analysis, has been developed to determine, in the same sample, the fundamental constituents and some doping elements in the Pb_xSn_1?xTe system. First tellurium is separated by sulfur dioxide in an acid solution (5% in HCl). This medium is suitable both for the total tellurium separation and for the subsequent tin precipitation by phenylarsonic acid. Moreover, this analytical procedure allows determination in the same sample, the concentration of some doping elements such as copper, cadmium, and zinc which are necessary to vary some physical properties of the Pb_xSn_1?xTe semiconductor system. The trace elements were determined by stripping voltammetry after tellurium, tin, and lead separation. The residual solution contains a variable amount of phenylarsonic acid which makes difficult quantitative polarographic measurements, because the electrodissolution potentials are varied and peak heights are masked. However, polarographic measurements are not altered through a wide range of phenylarsonic acid concentration if the solution is previously neutralized.     

Linear-sweep polarographic determination of active chlorine in aqueous solutions containing phenylthiourea

The linear-sweep polarographic determination of active chlorine is based on its reaction with phenylthiourea in acidic phosphate buffer (pH 2.5) containing potassium chloride. The product, C,C-diphenyldithiodiformamidine, is strongly adsorbed and then reduced at a mercury electrode with two peaks at about ?0.35 V and ?0.87 V (vs. SCE). In the presence of 0.05 M potassium chloride, the potential of the first peak shifts positively to ?0.31 V. This peak provides high sensitivity and selectivity for the determination of traces of active chlorine. The linear range is 1×10^?7?2.5×10^?5 M and the detection limit is 5×10^?8 M (3.6 μg l^?1). The method is used for the direct determination of active chlorine in tap water. The mechanism of the reaction was studied by cyclic voltammetry, electrolysis and potentiometric titration. The first peak (?0.35 V) is ascribed to the reduction of a mercury (II) sulfide film produced by reaction of the adsorbed dithio product with mercury. In the presence of 0.05 M chloride, the formation of a mixed HgS·xHg₂Cl2 film shifts the peak to ?0.31 V.