Electrochemical investigations of self-doped polyaniline nanofibers as a new electroactive material for high performance redox supercapacitor

Self-doped polyaniline (SDPA) nanofibers were deposited on platinum (Pt) electrode by reverse pulse voltammetric (RPV) method and their electrochemical performance was evaluated in an aqueous redox supercapacitor constituted as a two electrode cell in a weak acidic medium. Scanning electron micrographs clearly revealed the formation of nanofiber structures with diameters in range of 60–90 nm under optimum experimental conditions. Different electrochemical methods including galvanostatic charge–discharge (CD) experiments, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were carried out in order to investigate the applicability of the system as a redox supercapacitor. Based on the charge–discharge results obtained, the SDPA represented high specific capacitance, specific power and specific energy values of 480 F g⁻¹, 436 W kg⁻¹ and 9.40 Wh kg⁻¹, respectively, at a current density of 5 mA cm⁻². The present study introduces new nanofiber materials for electrochemical redox capacitors with advantages including low cost, long cycle-life and stable at low acidic solutions of pH 3.     

Comparative magnetic studies of (Sm, Nd) trichloroacetates and their heteronuclear CuLn2(CCl3COO)8·6H2O systems: structure and spectroscopy of a new type of Eu trichloroacetate

Two series of compounds: heteronuclear CuLn₂(CCl₃COO)₈·6H₂O (Ln = Nd and Sm) and their simple analogues Ln(CCl₃COO)₃·2H₂O (Ln = Eu, Nd, Sm) were synthesized. New Eu(III) trichloroacetate; Eu(CCl₃COO)₃·3H₂O·CH₃OH was obtained, its molecular structure was determined by X-ray diffraction and compared with the data of respective systems reported earlier. Magnetization was measured and the susceptibility was derived in the limit of low field. Magnetic susceptibilities were calculated and discussed for series of homo- and hetero-nuclear chloroacetates.

Untypical hysteresis was found (two loops) in samarium trichloroacetate. This phenomenon is most probably the effect of flops of spins in magnetic fields of 30,000 Oe and very weak (if any) interaction intermediated by weak hydrogen bonding between the chains. A similar magnetic behavior was observed in neodymium carboxylate where the magnetic ordering was observed as a result of Nd–Nd interaction at low temperature (1.6 K). For this system, the magnetic moment depends on magnitude of the magnetic field and ferromagnetic ordering appears at low temperatures. The strongest interactions of coupled ions and antiferromagnetic ordering with T_N=6.5 K were found in CuSm₂(CCl₃COO)₈·6H₂O single crystals.

Heisenberg model was applied in the calculations for three interacting ions located linearly. The following relation was derived:

and applied in calculations of the exchange integrals. Mechanism of the exchange interaction was discussed on the basis of the obtained results.     

Synthesis, crystal structure and properties of the new semiconductor (EVT)4·[Pt(CN)4]

A novel radical cation salt based on of the donor (4,5-ethylenedithio-4′,5′-vinylenedithio)tetrathiafulvalene (EVT) with the square planar anion Pt(CN)₄²⁻ has been synthesized: (EVT)₄·[Pt(CN)₄] (1). According to the X-ray analysis its crystal structure includes EVT cation layers alternating with anion layers along the a-axis of the unit cell. The radical cation layer is formed by EVT stacks with β-packing type, the donors in stacks are tetramerized. The EPR spectra of a plate-like crystal of (EVT)₄·[Pt(CN)₄] salt shows a very weak signal with typical parameters of TTF derivative. The room temperature conductivity of salt 1 is 8×10⁻² Ω⁻¹ cm⁻¹ and the temperature dependence of the conductivity exhibits semiconducting character.     

Recording of hydrogen evolution—a way for controlling the doping process of sodium alanate by ball milling

A simple equipment was developed which allows to monitor gas evolution or absorption occurring in the course of a ball milling process. The equipment has been applied to characterize via hydrogen evolution the reduction process of metal halides used as doping agents in the preparation of sodium alanate hydrogen storage materials. The gas flow curves resulting from the measurements (Fig. 2, Fig. 3 and Fig. 4) deliver useful informations concerning the rate, progress and completion of each of the involved reduction process, so that the stoichiometry of the underlying chemical reactions could be conceived or confirmed ( (3), (4), (5), (6) and (7)). In the preparation of sodium alanate hydrogen storage materials, the presented method can help to find out ball milling parameters necessary to produce an optimal catalytic activity of a dopant.     

Electrochemical deposition of cupric ions for the determination of mass transfer rates to a stepped rotating cylinder electrode

The stepped rotating cylinder electrode (SRCE) geometry has been developed as a simple aid to the practical study of the flow-enhanced corrosion and applied electrochemistry problems commonly observed under conditions of disturbed, turbulent flow. The electrodeposition of cupric ions from an acid sulphate plating bath has been used to characterise differential rates of mass transfer to the SRCE. The variation in thickness of electrodeposited copper films has allowed the mapping of local rates of mass transfer over the active surface of this geometry. Both optical and scanning electron microscopy were used for the examination of metallographic sections to provide a high resolution evaluation of the distribution of mass transfer coefficient. Results are also discussed using the convective-diffusion model in combination with the existing direct numerical flow simulation (DNS) data for this geometry.