Evolution of the Bromate Electrolyte Composition in the Course of Its Electroreduction inside a Membrane-Electrode Assembly with a Proton-Exchange Membrane.

The passage of cathodic current through the acidized aqueous bromate solution (catholyte) leads to a negative shift of the average oxidation degree of Br atoms. It means a distribution of Br-containing species in various oxidation states between -1 and +5, which are mutually transformed via numerous protonation/deprotonation, chemical, and redox/electrochemical steps. This process is also accompanied by the change in the proton (H+) concentration, both due to the participation of H+ ions in these steps and due to the H+ flux through the cation-exchange membrane separating the cathodic and anodic compartments. Variations of the composition of the catholyte concentrations of all these components has been analyzed for various initial concentrations of sulfuric acid, cA0 (0.015-0.3 M), and two values of the total concentrations of Br atoms inside the system, ctot (0.1 or 1.0 M of Br atoms), as functions of the average Br-atom oxidation degree, x, under the condition of the thermodynamic equilibrium of the above transformations. It is shown that during the exhaustion of the redox capacity of the catholyte (x pass from 5 to -1), the pH value passes through a maximum. Its height and the corresponding average oxidation state of bromine atoms depend on the initial bromate/acid ratio. The constructed algorithm can be used to select the initial acid content in the bromate catholyte, which is optimal from the point of view of preventing the formation of liquid bromine at the maximum content of electroactive compounds.

Hydrogen-Chlorate Electric Power Source: Feasibility of the Device, Discharge Characteristics and Modes of Operation.

A power source based on the current-generating reaction of aqueous chlorate-to-chloride reduction by molecular hydrogen would provide as much as 1150 Wh per 1 L of reagent storage (for a combination of 700 atm compressed hydrogen and saturated aqueous solution of lithium chlorate) at room temperature, but direct electroreduction of chlorate only proceeds with unacceptably high overvoltages, even for the most catalytically active electrodes. In the present study, we experimentally demonstrated that this process can be performed via redox-mediator catalysis by intermediate products of chlorate reduction, owing to their participation in homogeneous com- and disproportionation reactions. A series of current-voltage and discharge characteristics were measured for hydrogen-chlorate membrane-electrode assembly (MEA) cells at various concentrations of chlorate and sulfuric acid under operando spectrophotometric monitoring of the electrolyte composition during the discharge. We established that chlorine dioxide (ClO2) is the key intermediate product; its fraction in the electrolyte solution increases progressively, up to its maximum, equal to 0.4-0.6 of the initial amount of chlorate anions, whereas the ClO2 amount decreases gradually to a zero value in the later stage. In most discharge experiments, the Faradaic yield exceeded 90% (maximal value: 99%), providing approximately 48% chemical energy storage-to-electricity conversion efficiency at maximal power of the discharge (max value: 402 mW/cm2). These results support prospect of a hydrogen-chlorate flow current generator as a highly specific energy-capacity source for airless media.

Electrochemical Properties of Carbon Aerogel Electrodes: Dependence on Synthesis Temperature.

A series of carbon aerogels (C-AGs) were prepared by the pyrolysis of resorcinol-formaldehyde aerogels at 700-1100 °C as potential supercapacitor electrodes, and their texture and electrochemical properties were determined. The specific surface area of all C-AGs was in the range of 700-760 m2/g, their electron conductivity increased linearly from 0.4 to 4.46 S/cm with an increase of the pyrolysis temperature. The specific capacitance of electrode material based on C-AGs reached 100 F/g in sulfuric acid and could be realized at a 2 A/g charge-discharge current, which makes it possible to use carbon aerogels as electrode materials.

Cobalt Oxide Materials for Oxygen Evolution Catalysis via Single-Source Precursor Chemistry.

The utilization of metal alkoxides as single-source precursors for (mixed-)oxide materials offers remarkable benefits, such as the possibility to precisely control the metal ratio in the resulting material, highly homogeneous distribution of the elements in the film, and the low temperatures required for film processing. Herein we report on the isolation and characterization of the bimetallic Co-Mo alkoxide [Co3 Mo4 O10 (OCH3 )10 (dmf)4 ] (Co3 Mo4 ; dmf=N,N-dimethylformamide), which was prepared by the anion metathesis reaction of the corresponding metal chlorides. The Co-Mo alkoxide was explored as a well-defined precursor of cobalt oxide catalysts for the oxygen evolution reaction (OER) in alkaline electrolyte MOH. The catalysts demonstrated excellent activity in the OER, manifested in low onset potentials and Tafel slopes and superb stability under the operating conditions both in alkaline and nearly neutral media. It was observed that the nature of the metal cation of the alkaline electrolyte MOH (M+ =Li+ , Na+ , K+ , Cs+ ) greatly affected the catalytic performance of the material. We propose that the positive effect of larger metal cations on the film activity in the OER could be explained by the higher hydration enthalpies of larger ions and enhanced mass transport within a larger interlayer space between the [CoO2 ]δ-∞ sheets of the in situ formed binary oxides. It may be deduced that this trend is universal and may be extended to other types of metal oxides forming layered structures during the OER.

Electronic and steric effects controlling monomer-dimer self-assembly in 6H-1,4-diazepinoporphyrazines: an experimental and theoretical study.

A series of 5,7-disubstituted 1,4-diazepinoporphyrazinato magnesium(II) and nickel(II) complexes, including two novel compounds, were obtained by metal-templated macrocyclization. A combination of X-ray diffraction, 1H NMR, UV-vis, and electrochemical analyses allowed us to study their tendency towards H-type dimerization and trace the influence of structural and solvation factors on dimer stability. Based on the physicochemical and theoretical DFT calculation data, it was found that the main binding forces between 6H-1,4-diazepinoporphyrazine decks in the dimers were efficient π-π donor-acceptor interactions induced by the interdeck C-H⋯N hydrogen bonds. Furthermore, the metal-ligand (Pz2- â†’ M2+) electronic interactions have a key influence on the π-π stacking of the porphyrazine cores. It was shown that the displacement of the metal ion out of the macrocycle plane induced by coordinating agents can trigger the dissociation of the dimer, since the resulting enhancement of the donor-acceptor electronic interaction between the metal ion and the π-system of the ligand leads to a subsequent weakening of the π-π stacking of the porphyrazine cores. The TD-DFT calculations predicted the non-degeneracy of the HOMO-1 → LUMO and HOMO → LUMO+1 transitions in the 6H-1,4-diazepinoporphyrazine H-dimers, which explains the Q-band splitting in their UV-vis spectra.

Electrochemical Measurement of Interfacial Distribution and Diffusion Coefficients of Electroactive Species for Ion-Exchange Membranes: Application to Br2/Br- Redox Couple.

A novel method has been proposed for rapid determination of principal transmembrane transport parameters for solute electroactive co-ions/molecules, in relation to the crossover problem in power sources. It is based on direct measurements of current for the electrode, separated from solution by an ion-exchange membrane, under voltammetric and chronoamperometric regimes. An electroactive reagent is initially distributed within the membrane/solution space under equilibrium. Then, potential change induces its transformation into the product at the electrode under the diffusion-limited regime. For the chronoamperometric experiment, the electrode potential steps backward after the current stabilization, thus inducing an opposite redox transformation. Novel analytical solutions for nonstationary concentrations and current have been derived for such two-stage regime. The comparison of theoretical predictions with experimental data for the Br2/Br- redox couple (where only Br- is initially present) has provided the diffusion coefficients of the Br- and Br2 species inside the membrane, D(Br-) = (2.98 ± 0.27) 10-6 cm2/s and D(Br2) = (1.10 ± 0.07) 10-6 cm2/s, and the distribution coefficient of the Br- species at the membrane/solution boundary, K(Br-) = 0.190 ± 0.005, for various HBr additions (0.125-0.75 M) to aqueous 2 M H2SO4 solution. This possibility to determine transport characteristics of two electroactive species, the initial solute component and its redox product, within a single experiment, represents a unique feature of this study.

New Nanosized Systems Doxorubicin-Amphiphilic Copolymers of N-Vinylpyrrolidone and (Di)methacrylates with Antitumor Activity.

Nanosized systems of DOX with antitumor activity on the base of micelle-like particles of amphiphilic thermosensitive copolymers of N-vinylpyrrolidone (VP) with triethylene glycol dimethacrylate (TEGDM), and N-vinylpyrrolidone and methacrylic acid (MAA) with TEGDM were explored. They were investigated in aqueous solutions by electron absorption spectroscopy, dynamic light scattering and cyclic voltammetry. Experimental data and quantum-chemical modeling indicated the formation of a hydrogen bond between oxygen-containing groups of monomer units of the copolymers and H-atoms of OH and NH2 groups of DOX; the energies and H-bond lengths in the considered structures were calculated. A simulation of TDDFT spectra of DOX and its complexes with the VP and TEGDM units was carried out. Electrochemical studies in PBS have demonstrated that the oxidation of encapsulated DOX appeared to be easier than that of the free one, and its reduction was somewhat more difficult. The cytotoxicity of VP-TEGDM copolymer compositions containing 1, 5 and 15 wt% DOX was studied in vitro on HeLa cells, and the values of IC50 doses were determined at 24 and 72 h of exposure. The copolymer compositions containing 5 and 15 wt% DOX accumulated actively in cell nuclei and did not cause visual changes in cell morphology.

A Hydrogen-Bromate Flow Battery as a Rechargeable Chemical Power Source.

The hydrogen-bromate flow battery represents one of the promising variants for hybrid power sources. Its membrane-electrode assembly (MEA) combines a hydrogen gas diffusion anode and a porous flow-through cathode where bromate reduction takes place from its acidized aqueous solution: BrO3− + 6 H+ + 6 e− = Br− + 3 H2O (*). The process of electric current generation occurs on the basis of the overall reaction: 3 H2 + BrO3− = Br− + 3 H2O (**), which has been studied in previous publications. Until this work, it has been unknown whether this device is able to function as a rechargeable power source. This means that the bromide anion, Br−, should be electrooxidized into the bromate anion, BrO3−, in the course of the charging stage inside the same cell under strongly acidic conditions, while until now this process has only been carried out in neutral or alkaline solutions with specially designed anode materials. In this study, we have demonstrated that processes (*) and (**) can be performed in a cyclic manner, i.e., as a series of charge and discharge stages with the use of MEA: H2, Freidenberg H23C8 Pt-C/GP-IEM 103/Sigracet 39AA, HBr + H2SO4; square cross-section of 4 cm2 surface area, under an alternating galvanostatic mode at a current density of 75 mA/cm2. The coulombic, voltaic and energy efficiencies of the flow battery under a cyclic regime, as well as the absorption spectra of the catholyte, were measured during its operation. The total amount of Br-containing compounds penetrating through the membrane into the anode space was also determined.

Mesoporous Networks of N-Vinylpyrrolidone with (di)Methacrylates as Precursors of Ecological Molecular Imprinted Polymers.

Mesoporous polymer networks were prepared via the cross-linking radical copolymerization of non-toxic hydrophilic N-vinylpyrrolidone (VP) with triethylene glycol dimethacrylate (TEGDM) and poly(ethylene glycol) methyl ester methacrylate (PEGMMA) in bulk, using appropriate soluble and thermodynamically compatible macromolecular additives with a branched structure as porogens. The branched copolymers of various monomer compositions were obtained by radical copolymerization in toluene, controlled by 1-decanethiol, and these materials were characterized by a wide set of physical chemical methods. The specific surface areas and surface morphology of the polymer networks were determined by nitrogen low-temperature adsorption or Rose Bengal (RB) sorption, depending on the copolymer compositions and scanning electron microscopy. The electrochemical properties of RB before and after its encapsulation into a branched VP copolymer were studied on a glassy carbon electrode and the interaction between these substances was observed. Quantum chemical modeling of RB-VP or RB-copolymer complexes has been carried out and sufficiently strong hydrogen bonds were found in these systems. The experimental and modeling data demonstrate the high potency of such mesoporous polymer networks as precursors of molecularly imprinted polymers for the recognition of fluorescent dyes as nanomarkers for biomedical practice.

Synthesis and characterization of heteroleptic rare earth double-decker complexes involving tetradiazepinoporphyrazine and phthalocyanine macrocycles.

Reaction of (2,3,9,10,16,17,23,24-octabutylphthalocyaninato)lanthanide(iii) acetylacetonates (BuPcLn(acac), 1a-c, Ln = Lu (a), Eu (b), La (c)) with a tetrakis(5,7-bis(4-tert-butylphenyl)-6H-1,4-diazepino)[2,3-b,g,l,q]porphyrazine ligand (tBuPhDzPzH2, 2) produced sandwich compounds (tBuPhDzPz)Ln(BuPc) (3a-c), which represent the first heteroleptic double-deckers incorporating both Pc and DzPz decks. A combination of high-resolution mass spectrometry, UV-Vis/NIR, MCD, and 1H NMR spectroscopy, and square-wave voltammetry provided unambiguous characterization of target complexes 3 indicating that their spectral and electrochemical properties are generally intermediate with respect to their homoleptic relatives. Based on the data of solution-state 1H-1H NMR (COSY, NOESY) correlation spectroscopy supported by DFT calculations, a dimerization tendency of compounds 3 proportional to the Ln(iii) ion size was found. The spectroelectrochemical study of 3 and the corresponding homoleptic double-deckers revealed a pronounced tendency to aggregation of the one-electron oxidized forms of DzPz-containing double-decker complexes compared to homoleptic Pc2Ln compounds.

Dataset of a vanadium redox flow battery 10 membrane-electrode assembly stack.

This paper contains a vanadium redox flow battery stack with an electrode surface area 40 cm2 test data. The aim of the study was to characterize the performance of the stack of the original design. The dataset include three series of galvanostatic charge-discharge cycling in the potential region 8-16 V with current densities 75, 150 and 200 mA/cm2 for 100 cycles. Coulomb, voltaic, energy efficiencies and capacity utilization coefficient are also provided for all three series.

Electrolyte Flow Field Variation: A Cell for Testing and Optimization of Membrane Electrode Assembly for Vanadium Redox Flow Batteries.

A great deal of research has been dedicated to improving the performance of vanadium redox flow battery (VRFB). In this work, we propose the design of a cell for testing membrane electrode assembly of VRFB, which enables the optimization of the flow field, conditions of charge-discharge tests, and the nature of components (electrodes, membrane) with minimal time and material expenses. The essence of the proposed cell is that the system of channels distributing the electrolyte is made by cutting shaped holes in the sheets of graphite foil (GF). This manner allows easy modification of the flow field configurations. Polarization curves for serpentine, interdigitated, and flow-through systems were measured according to procedures used in such studies. Cell with GF plates being tested with vanadium-sulfuric acid electrolyte, outperforms the cell with conventional graphite plates with the same parameters of the flow field. It demonstrates 734 mW cm-2 of peak power density at SOC 50 and 84.3 % of energy efficiency at 84.5 % of electrolyte utilization under galvanostatic charge/discharge cycling with 75 mA cm-2 .

Electrochemical and spectral properties of ferrocene (Fc) in ionic liquid: 1-butyl-3-methylimidazolium triflimide, [BMIM][NTf(2)]. Concentration effects.

Several earlier studies of the electrochemical oxidation of ferrocene (Fc) in room-temperature ionic liquids revealed an essentially nonlinear dependence of the oxidation current on the Fc concentration in its relatively dilute solutions, with its formally calculated diffusion coefficient strongly increasing with the concentration. Since no plausible mechanism leading to this very unusual finding had been proposed, our study of Fc solutions in 1-butyl-3-methylimidazolium triflimide, [BMIM][NTf(2)], was performed to verify whether the above observation originated from an incorrect determination of the dissolved Fc concentration. Our observations have demonstrated that reliable control of the Fc concentration in solution is complicated by factors such as the low amount of Fc used to prepare small-volume solutions or the great difficulty to dissolve completely a solid powder in a solvent with an extremely high viscosity. An unexpected additional complication is related to a sufficiently high volatility of Fc which manifests itself even at room temperature and especially at elevated temperatures or/and in the course of vacuum treatment of its solutions or its solid powder. Parallel measurements of electrochemical responses and UV-visible spectra for several series of Fc solutions of various concentrations (prepared with the use of different procedures) have shown a perfect parallelism between the peak current and the intensity of the absorption band in the range of 360-550 nm, leading us to the conclusion of a linear relationship between the oxidation current and the molecularly dissolved Fc concentration. The relations of these measured characteristics with the estimated Fc concentration in these solutions have demonstrated a much greater dispersion (attributed to the difficulty of a precise measurement of the latter) but without a significant deviation from the linearity in general. This finding has allowed us to estimate the diffusion coefficient of this species: D = (1.7 +/- 0.2) x 10(-7) cm(2)/s. The extinction coefficients for the maximum of the absorption band (at 440 nm) of Fc have been compared for a series of solvents: [BMIM][NTf(2)], acetonitrile, THF, heptane, CH(2)Cl(2), ethanol, and toluene. A simple method to estimate reliably the concentration of solute Fc in ionic liquids based on spectroscopic measurements has been proposed, owing to the proximity of Fc absorption properties for a great variety of solvents.

Ni-based heterogeneous catalyst from a designed molecular precursor for the efficient electrochemical water oxidation.

Bimetallic Ni-Mo alkoxide was synthesized and exploited as the single-source precursor for the solution-processed deposition of the mixed-oxide layers on different conducting surfaces. Upon potential cycling in 1 M NaOH, these composites convert, in situ, into highly porous NiOx/NiOOH catalysts characterized by the high electrocatalytic activity for water oxidation under both basic (pH 13.6) and near neutral (pH 9.2) conditions.

Correction: Ni-based heterogeneous catalyst from a designed molecular precursor for the efficient electrochemical water oxidation.

Correction for 'Ni-based heterogeneous catalyst from a designed molecular precursor for the efficient electrochemical water oxidation' by Denis A. Kuznetsov et al., Chem. Commun., 2016, 52, 9255-9258.