Effect of monocationic ionic liquids as electrolyte additives on the electrochemical and thermal properties of Li-ion batteries

The conventional electrolyte system has been compared with the ionic liquid (IL) additive containing electrolyte system at room temperature as well as elevated temperature. In this work, two types of monocationic ILs such as 1-butyl-3-methylpyrrolidinium hexafluorophosphate (Pyr IL) and 1-ethyl-3-methylimidazolium hexafluorophosphate (IMI IL) are added as an additive at two different weight ratios in 1.15 M LiPF₆ (EC/EMC = 3/7 v/v) electrolyte solution, the structural, electrochemical and thermal characteristics of LiNi_0.80Co_0.15Al_0.05O₂ (NCA)/carbon full-cell in different electrolyte formulations have been reconnoitered. X-ray diffraction (XRD) studies have proved that IL as an electrolyte additive does not alter the structural stability of cathode materials after cycling. Under room temperature, Pyr IL additives at 1 wt% and 3 wt% deliver better cycleability than others, with the retention ratios of 93.62% and 92.8%, respectively. At elevated temperature, only 1 wt% Pyr IL additive is giving stable capacity retention ratio of 80.74%. Ionic conductivity and self-extinguishing time (SET) values are increasing with respect to the amount of additive added to the electrolyte. Thermal studies reveal that 3 wt% Pyr IL is favorable regarding the safety of the battery as it shows shifting of peak to higher temperature of 272.10 °C. Among the IL additives evaluated in this study, addition of 1 wt% Pyr IL is the most desirable additive for achieving the best cycling performance as well as thermal behavior of Li-ion batteries.     

Effect of In3+ ions on the electrochemical performance of the positive electrolyte for vanadium redox flow batteries

Influence of In³⁺ ions on electrochemical performance of positive electrolyte for vanadium redox flow battery was investigated in this paper. The electrochemical activity and kinetics of V(IV)/V(V) redox couple can be enhanced by the addition of In³⁺ ions, and the optimal concentration of In³⁺ ions was found at 10 mM. At this condition, the oxidation peak current with 10 mM In³⁺ ions is 46.6 mA at a scan rate of 20 mV s^?1, larger than that of pristine electrolyte (41.8 mA), and the standard rate constant is 6.53?×?10^?5 cm s^?1, 42 % larger than that of the pristine electrolyte (4.58?×?10^?5 cm s^?1). The cell using electrolyte with 10 mM In³⁺ ions was assembled, and the charge–discharge performance was evaluated, and the average energy efficiency increases by 1.9 % compared with the pristine cell. The improved electrochemical performance may be ascribed to that In³⁺ ions change the hydration state of vanadium ions in electrolyte and promote charge transfer process.     

Evaluation of solid electrolyte cells with a versatile electrochemical technique

Voltage losses in fuel cells and other solid electrolyte systems are due to several mass transport and kinetics processes at the electrode/electrolyte interface as well as to ohmic contributions from the electrolyte, electrodes, current collectors and contact resistances. Electrochemical impedance spectroscopy (EIS) has been in use for several decades in fuel cell research and is quite effective in determining the contribution of individual electrode and electrolyte processes. However, data acquisition and analysis can be time-consuming and the technique has many limitations whilst cell performance and operating conditions are varying rapidly with time especially when the cells are under current load. The galvanostatic current interruption (GCI) technique is fast and can be used under a wide range of operating as well as for rapidly varying loads and cell performance conditions. In this paper a totally new and very simple way of adapting commercially available equipment has been described to perform high quality, reliable and fast GCI measurements over a range of different currents in one sequence without having to use an electronic switch or a solid state relay or a separate fast data logging system. Its versatility has been demonstrated with a number of standard RC circuits simulating slow electrode and fast electrolyte processes and by evaluating a number of solid oxide fuel cell materials. The GCI technique has been shown to be able to determine the composition of all standard test circuits within ±1 % of those determined from the EIS technique and actual values of circuit components. The technique has been applied to investigating solid electrolyte cells and produced excellent results.     

Non-faradaic electrochemical modification of catalytic activity in solid electrolyte cells

The catalytic activity and selectivity of metal catalysts used as electrodes in high temperature solid electrolyte cells can be altered dramatically and in a reversible manner. This is accomplished by electrochemically supplying oxygen anions onto catalytic surfaces via polarized metal-solid electrolyte interfaces. Oxygen anions, forced electrochemically to adsorb on the metal catalyst surface, alter the catalyst work function in a predictable way and lead to reaction rate increases as high as 4000%. Changes in catalytic rates typically exceed the rate of O^2– transport to or from the catalyst surface by 10²-3 · 10⁵. Significant changes in product selectivity have been also observed. The case of several catalytic reactions in which this new phenomenon has been observed is presented and the origin of the phenomenon is discussed.     

Influence of ultrasound on the kinetic parameters of electrochemical redox reactions

The aim of this work is to determine the Tafel parameters with and without ultrasound. The total overvoltage has been corrected for diffusion by using rotating disk technique and potentiostatic extrapolation to infinite rotating speed. Three well known redox systems have been selected regardless to their different electrochemical behaviour: the quinone-hydroquinone, the Fe(II)Fe(III) chlorides and Fe(II)-Fe(III) cyanide systems. This work shows that the reversibility is higher with ultrasound only in the case of the quinone-hydroquinone system.     

The origin of luminescence accompanying electrochemical reduction or chemical decomposition of peroxydisulfates

The spectral features of the electrochemiluminescence occurring during the reduction of peroxydisulfate anions at magnesium, silver or platinum electrodes (ecl), the luminescence following their decomposition on a magnesium surface (mcl), and the chemiluminescence accompanying the thermal decomposition of peroxydisulfates in acidic media (tcl), were thoroughly examined in order to discover the origin of the light emission. The intensity of emission followed the order ecl>mcl?tcl and depended on the method of its generation and other experimental conditions. Probable pathways of the reactions leading to the formation of light-emitting species were examined at the density functional theory level. The theoretical studies and experimental findings seem to indicate that the luminescence originates from ¹O₂, ¹(O₂)₂ and ³(O₂)₂, the precursors of which are SO₄^•−, HO^•, HOO^•, HOOH and O₃ formed in the primary and secondary processes following electrochemical reduction or thermal decomposition of peroxydisulfates. Supplementary experiments demonstrated the participation of HOOH in the generation of light emitting entities.     

Multiple UV-blue luminescence emissions in electrochemical anodic etched n-type silicon wafer

This very paper is focusing on the preparation of porous nanostructures in n-type silicon (1 1 1) wafer by chemical etching technique in alkaline aqueous solutions of 5 M NaOH, 5 M K₂CO₃ and 5 M K₃PO₄, and particularly, on its ultraviolet-blue photoluminescence emission. The anodic chemical etched silicon wafer has been characterized by means of optical microscopy, scanning electron microscopy, fluorescence spectroscopy, atomic force microscopy and Fourier transform infrared spectroscopy. This very surface morphology characterization has been clearly shown - the effect of anodic-chemical-etching procedure processed in K₂CO₃ or K₃PO₄ was much vigorous than that processed in NaOH. The FTIR spectra indicate that the silicon oxide was formed on the surface of electrochemical etched n-Si (1 1 1) wafers, yet not on that of the pure chemical etched ones anyhow. And an intense ultraviolet-blue photoluminescence emission is observed, which then differs well from the silicon specimen etched in alkaline solution with no anodic potential applied. The proper photoluminescence mechanism is discussed, and hence there may be a belief that the intense ultraviolet-blue photoluminescence emission would be attributed to the silicon oxide coating formed on silicon wafer in anodic-chemical-etching process.     

Structural characterization,luminescence and electrochemical properties of the Schiff base ligands

In this study, we prepared two Schiff base ligands N-(4-hydroxy phenyl)-2,4-di-methoxy benzaldimine (TS¹) and N-(4-hydroxy phenyl)-2,5-di-methoxybenzaldimine (TS²) which were characterized by structural, spectroscopic and analytical methods. The ligands TS¹ and TS² were obtained as single crystals from ethanol solution. X-ray diffraction data for two compounds showed that the bond lengths are within the normal ranges. The electrochemical properties of the Schiff base ligands were studied in different solvents and at various scan rates. The luminescence properties of the ligands TS¹ and TS² in different solvents and at different pH values have been investigated. The results show that the ligands exhibit more efficient luminescence properties in CH₃CN and n-butanol.     

The influence of pH electrolyte on the electrochemical deposition and properties of nickel thin films

Ni thin films were electrodeposited on gold substrate from chloride solution with different pH at room temperature. The effect of electrolyte pH on Ni coatings was studied by using the cyclic voltammetry, the scanning electron microscopy (SEM), x-ray diffraction, and alternating gradient force magnetometer measurements. From electrochemical measurements, the onset potential for reduction of Ni was gradually shifted towards more cathodic scan with increase in pH; this is due to the protons in the case of low pH values and to the hydroxide ions in the case of higher pH values. The SEM study showed that a granular and compact structure of the electrodeposited Ni layers and the variation of film morphology with bath pH are established. The x-ray diffraction spectra revealed the formation of fcc structure Ni thin films with a preferential orientation along the Ni(111). The size of the deposited crystals in both the cases has been found to be in the range of 49–153 nm. Magnetic properties such as coercivity and saturation magnetization showed strong dependence on the electrolyte solution pH and consequently the crystallite size. Coercivity higher than 130–160 Oe was achieved for a pH value of 4 to 5. The differences observed in the magnetic properties were attributed to the structural changes caused by the electrolyte pH.     

Preparation and electrochemical characterisation of supporting SOFC–Ni–YZT anodes

Symmetrical cells consisting of Ni–Y_0.20Ti_0.18Zr_0.62O_1.90 (Ni–YZT) cermet electrodes on a Ni–YSZ support have been investigated with respect to the hydrogen/water partial pressures. Impedance spectra at open circuit potential were obtained as function of temperature and analysed in terms of a fractal finite length Gerischer Impedance. For fine and coarse microstructures of the Ni–YZT electrodes, a consistent set of model parameters could be obtained. The results indicate that surface diffusion rather than bulk diffusion plays a role in the hydrogen/water reaction but also that a fine-grained fraction in the mixed conducting YZT phase is advantageous for the overall electrode performance and the surface exchange reaction.     

Influence of S incorporation on the luminescence property of ZnO nanowires by electrochemical deposition

Sulfur-doped zinc oxide (ZnO) nanowires have been successfully synthesized by an electric field-assisted electrochemical deposition in porous anodized aluminum oxide template at room temperature. X-ray diffraction and the selected area electron diffraction results show that the as-synthesized nanowires are single crystalline and have a highly preferential orientation. Transmission electron microscopy observations indicate that the nanowires are uniform with an average diameter of 120 nm and length up to several tens of micrometers. Room-temperature photoluminescence is observed in the doped ZnO nanowires, which exhibits a violet emission and blue emissions besides the typical photoluminescence spectrum of a single crystal ZnO.     

Exactly solvable quantum model for electrochemical electron-transfer reactions

We consider electron exchange between a metal electrode and a solvated reactant coupled to a harmonic oscillator bath. In the wide-band approximation the time development of the occupation probability for the reactant orbital can be calculated explicitly. From the behavior at long times we derive an expression for the reaction rate that is valid for all strengths of the electronic interaction between the metal and the reactant. The rate constant is related to the scattering matrix for electron exchange between a metal substrate and a scanning tunneling microscope via an electroactive adsorbate.     

Nanofiber membrane based on ionic liquids as high-performance polymer electrolyte for sodium electrochemical device

Composite nanofibrous electrolyte membranes (CFEM) of poly(vinylidene fluoride-hexafluoropropylene) P(VdF-HFP)-1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF₄) and its NaSCN are electrospun as nanofibrous membranes. Scanning electron microscope (SEM) images clearly inform that electrospun CFEM and CFEM–NaSCN with average fiber diameters of 50–200 nm have interconnected multifibrous layers with ultrafine porous structures. They exhibited a high uptake of the electrolyte solution (370–880 %). The polymer electrolytes have decreased crystalline, which is advantage to the increase in ionic conductivity. In addition, polymer electrolytes also are prepared by swelling nanofibre into blend of sodium salt and BMIMBF₄. CFEM obtained 15 % BMIMBF₄ exhibited higher ionic conductivity maximum of 5.6?×?10^?5 S cm^?1 at room temperature, and the conductive model of CFEM–NaSCN electrolyte answer for Arrhenius function. CFEM–NaSCN electrolyte showed a high electrochemical window of above 4.5 V, which is higher than electrospun pure P(VdF-HFP) without BMIMBF₄ or BMIMBF₄–NaSCN. With these improved performance characteristics, CFEM electrolyte and CFEM–NaSCN electrolyte will be found its suitability as polymer electrolyte for high-performance rechargeable batteries and super capacitor.     

Effect of photonic bandgap on luminescence from silicon nanocrystals

The modification of the luminescence of silicon nanocrystals experiencing the effect of a photonic bandgap in a 2D photonic crystal was investigated. The time-integrated photoluminescence spectra detected in the plane of the photonic crystal revealed a dip in the light emission corresponding to the wavelength of the bandgap, whose position changes according to the geometry of the prepatterned pillar array. The calculated emission pattern for a pointlike dipole placed in such a structure suggests an inhibition of the spontaneous emission rate at certain directions as a physical reason for the observed modification of luminescence.     

氮对金刚石缺陷发光的影响

利用低温显微荧光光谱研究了IIa型、Ib型、Ia型金刚石的缺陷发光性质. 研究发现, 随着氮含量增加, 间隙原子及空位逐渐被氮原子所束缚, 从而使得GR1中心、533.5 nm及580 nm中心等本征缺陷发光减弱, 而氮-空位复合缺陷(NV中心)及523.7 nm中心等氮相关缺陷发光增强. 高温退火后, 间隙原子与空位可以自由移动, IIa型金刚石中出现了NV⁰中心, Ib型金刚石中只剩下了NV中心, Ia型金刚石中氮原子之间发生团聚, 出现了H3中心及N3中心. 另外, 氮作为施主原子, 有利于负电荷缺陷的形成, 如3H 中心、NV^- 中心.     

Potentialities of ionic liquids as new electrolyte media in advanced electrochemical devices

This paper reviews the various classes of ionic liquids (ILs) in view of their established and expected applications in advanced electrochemical devices, such as lithium batteries, fuel cells, and supercapacitors. In this respect, particular attention is devoted to aprotic and protic ILs, with a related discussion in terms of their thermal and transport properties. In addition, the role in the electrochemical technology of a new class of ILs having cation and anion tethered in an intramolecular form is stressed. Due to their emerging importance, IL-based polymers are finally reported and discussed. A conclusion, where the expected evolution of the ILs research and development is evaluated, is also included.