Izabela Stepniak

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.

Impedance studies on poly(acrylonitrile)-dimethylsulfoxide-AgX (x = Cl, Br, I) gel electrolytes

A series of poly(acrylonitrile)-dimethylsulfoxide-AgX (PAN-DMSO-AgX, where X5 Cl, Br, I) gel-type solid polymer 24 electrolytes was synthesised. The bulk conductance, obtained from the complex impedance spectra, is of the order of 10 21 21 - V cm . The temperature dependence of the conductivity is of the Arrhenius type: s 5 A exp(2E /RT ). The linear plots 21 21 ln s 5 f(T ) give the activation energy, which is of the order of 19 kJ mol for the PAN-DMSO-AgCl and 21 PAN-DMSO-AgBr systems and ca. 25 kJ mol for the PAN-DMSO-AgI system. The activation energies for the 21 corresponding solid electrolytes containing additionally NaX salt are somewhat higher (about 3 kJ mol ). PAN-DMSO- AgCl foils tend to decompose slowly with visible precipitation of metallic silver; the remaining foils are stable even if exposed to light.

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.