Maciej Galinski

Ionic liquids as electrolytes

Salts having a low melting point are liquid at room temperature, or even below, and form a new class of liquids usually called room temperature ionic liquids (RTIL). Information about RTILs can be found in the literature with such key words as: room temperature molten salt, low-temperature molten salt, ambient-temperature molten salt, liquid organic salt or simply ionic liquid. Their physicochemical properties are the same as high temperature ionic liquids, but the practical aspects of their maintenance or handling are different enough to merit a distinction. The class of ionic liquids, based on tetraalkylammonium cation and chloroaluminate anion, has been extensively studied since late 1970s of the XX century, following the works of Osteryoung. Systematic research on the application of chloroaluminate ionic liquids as solvents was performed in 1980s. However, ionic liquids based on aluminium halides are moisture sensitive. During the last decade an increasing number of new ionic liquids have been prepared and used as solvents. The general aim of this paper was to review the physical and chemical properties of RTILs from the point of view of their possible application as electrolytes in electrochemical processes and devices. The following points are discussed: melting and freezing, conductivity, viscosity, temperature dependence of conductivity, transport and transference numbers, electrochemical stability, possible application in aluminium electroplating, lithium batteries and in electrochemical capacitors.

A novel chitosan/sponge chitin origin material as a membrane for supercapacitors – preparation and characterization

A new chitosan/sponge chitin – based membrane (CS/CH membrane) was prepared via the casting method for the first time. We used the demineralized skeleton of the marine demosponge Ianthella basta as a source for a chitinous network. The obtained membrane was immersed in 1 M LiOAc (lithium acetate) solution and tested in an Electric Double Layer Capacitor (EDLC) cell. For comparison, chitosan (CS) with LiOAc solution was also tested. The studies performed indicated good properties of the CS/CH membrane. Very good mechanical stability (for use in electrochemical capacitors) and electrochemical properties of the CS membrane were achieved by the addition of chitin isolated from the sponge to the polymer matrix. Their electrochemical performances were tested in EDLC cells by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge/discharge. The specific capacitances of the tested capacitor cells were found to be approximately 97 F g−1 and 88 F g−1 with CS/CH and CS membranes (in the voltage range 0–0.8 V), respectively.

Temperature coefficients of Ag/Ag+ and Ag/Ag+–cryptand 222 electrode potentials, thermodynamics of Ag+–cryptand 222 complex formation and molar transfer properties for Ag+ cations into aprotic media

Temperature coefficients of the stability constants, d log K(Ag+222)/dT, of Ag+ complexes with cryptand 222, Ag+222 cryptate (Ag+222) have been derived from potentiometric titrations at different temperatures in acetone (Ac), acetonitrile (AN), propanenitrile (PN), butanenitrile (BuN), benzonitrile (BN), N,N-dimethylacetamide (DMA), N,N-dimethylformamide (DMF), N-methyl-2-pyrrolidinone (NMP), dimethyl sulfoxide (DMSO), propylene carbonate (PC) and tetramethylene sulfone (sulfolane, TMS). The temperature coefficients of the standard electrode potentials, dE0/dT, for the Ag/Ag+ and Ag/Ag+222 couples have been derived from potentiometric measurements in a non-isothermal cell, where the reference electrode was kept at a constant temperature of 25 °C. It has been found that while the dE0/dT value for the Ag/Ag+ couple depends strongly upon the solvent, the corresponding temperature coefficient for the Ag/Ag+222 cryptate electrode is similar in all the solvents studied and can be approximated as dE0(Ag/Ag+222)/dT= 0.69 mV K–1 with a standard error of 0.03 mV K–1. Single-ion entropies of the Ag+ cation transfer from acetonitrile have been derived both from dE0(Ag/Ag+)/dT, applying the assumption of negligible thermal diffusion potential between cold and hot parts of the non-isothermal cell as well as from d log K(Ag+222)/dT, applying the ‘cryptate extrathermodynamic assumption’. Gibbs energies, enthalpies and entropies of silver(I) complexation by cryptand 222 agree well with literature data obtained employing different techniques.

Electrocapillary Curves for the Hg/Ionic Liquid Interface

Abstract Electrocapillary curves (surface tension γ as a function of the electrode potential E) for a series of room-temperature ionic liquids (RTILs) were measured using a mercury dropping electrode with the drop-weight (drop-volume) technique. The curves γ = f (E) for the Hg/RTIL interface have one maximum and may be approximated with a polynomial of sixth-order. There are no ‘humps’ in the curves. The interfacial tension of the Hg/RTIL system changes with potential E in a monotonic way. The second derivative of γ = f (E) leads to a polynomial of fourth order, indicating the capacitance of the Hg/RTIL interface. The potential of zero charge is within a relatively narrow range. The specific capacitance at the minimum is of the order 10 μF/cm2

Differential Capacity of the Double-Layer Formed at a Solid Electrode (Pt, Au)/Ionic Liquid Interface

The differential capacity at the electrode (Pt, Au)/ionic liquid interface of 18 ionic liquids (ILs), was measured applying chronoamperometry. The measurements were done by a two electrode system. The double layer capacity at the Pt/IL and Au/IL interface was 1 - 8 μF/cm2. The capacity, estimated from the impedance measurements, was approximately constant within a potential range of ca. 3 V.

Modification of chitin structure with tailored ionic liquids

Chitin, poly N-acetylglucosamine, has a great potential for use on an industrial scale as an enzyme carrier but it has an unfavorable particle structure that can be modified using ionic liquids (ILs). Several ionic liquids were investigated that have the same substituents on the ring (methyl- and propyl-) but differed in the type of cationic ring (pyrrolidinium, piperidinium, and piperazinium). Organic acid ions (acetic and lactic) were used as counter ions. 1-ethyl-3-methyl-imidazolium acetate and 1-ethyl-3-methyl-imidazolium lactate were used as a reference. The results confirm that the chitin particle structure or size, or both, simultaneously changes if chitin is dissolved in an IL and then precipitated. Organic acid anions and short substituents on the cationic ring of ILs influenced particle modification substantially, whereas the type of ring played a minor role. Additionally, the ionic liquids [MPpyrr][OAc], [MPpip][OAc] and [DMPpz][OAc] could be reused up to at least 4 times without losing their ability to dissolve chitin.