Use of ionic liquids as electrolytes in electromechanical actuator systems based on inherently conducting polymers

The use of ionic liquids (ILs) as electrolytes for electromechanical actuators based on polypyrroles (PPy's) is described. The composition of the electrolytes has a significant effect on the electrochemical properties of the PPy actuator and subsequently on actuator performance, improving cycle life and strain generated. The actuator performance in ionic liquid electrolytes is significantly better than that in traditional organic and aqueous electrolytes.

Conducting polymer electrochemistry in ionic liquids

Applications of polymers like polypyrrole and polythiophene often require interaction with an electrolyte consisting of solvent and dissolved salt. Ionic Liquids (ILs) are pure saits, fluid at room temperature, that form charged electrolytes. Pure l-Bu-3-Me-Imidazolium PF₆ (BMI PF₆) a hydrophobic IL that has a wide potential window, was used to investigate the electrochemistry ofpolypyrrole. Enhanced electrochemic~l stability of polypyrrole was obtained on repetitive redox cycling with respect to the equivalent propylene carbonate electrolyte with tetrabutylammonium hexaflurophosphate (TBA PF₆) electrolyte.

Conducting polymers with fibrillar morphology synthesized in a biphasic ionic liquid/water system

The synthesis of poly(pyrrole), poly(terthiophene), and poly(3,4-ethylenedioxythiophene) with unusual fibrillar morphologies has been achieved by chemical polymerization in a biphasic ionic liquid/water system. Use of aqueous gold chloride as the oxidant, with the monomers dissolved in a hydrophobic ionic liquid, allows the polymerization to occur at the ionic liquid/water interface. The resultant conducting polymer fibrils are, on average, 50−100 nm wide and can be thousands of nanometers long. The polymers produced in this ionic liquid system are compared to those synthesized in a biphasic chloroform/water system.

One-step synthesis of conducting polymer–noble metal nanoparticle composites using an ionic liquid

Conducting polymers containing incorporated gold or silver nanoparticles have been synthesized using ionic liquid solutions of gold chloride or silver nitrate. Use of the metal salts as the oxidant for monomers such as pyrrole and terthiophene allows the composites to be formed in one simple step, without the need for templates or capping agents. The incorporated metal nanoparticles are clearly visible by TEM, and the composites have been further analyzed by TGA, CV, UV-Vis, Raman, XPS and scanning TEM coupled with EDS analysis. Utilization of an ionic liquid allows the full oxidizing power of the gold chloride to be accessed, resulting in incorporation of metallic gold into the polymers.

A new class of proton-conducting ionic plastic crystals based on organic cations and dihydrogen phosphate

Choline dihydrogen phosphate ([N_1.1.1.2OH]DHP) and 1-butyl-3-methylimidazolium dihydrogen phosphate ([C₄mim]DHP) were synthesized as a new class of proton-conducting ionic plastic crystals. Both [N_1.1.1.2OH]DHP and [C₄mim]DHP showed solid–solid phase transition(s) and showed a final entropy of fusion lower than 20 J K⁻¹ mol⁻¹ which is consistent with Timmerman’s criterion for molecular plastic crystals. The ionic conductivity of [N_1.1.1.2OH]DHP was in the range of 10⁻⁶ S cm⁻¹–10⁻³ S cm⁻¹ in the plastic crystalline phase. On the other hand, the ionic conductivity of [C₄mim]DHP showed about 10⁻⁵ S cm⁻¹ in the plastic crystalline phase. [N_1.1.1.2OH]DHP showed one order of magnitude higher ionic conductivity than [C₄mim]DHP in the temperature range where the plastic phase is stable.

Structure effect on the oxygen permeation properties of barium bismuth iron oxide membranes

In this work, we investigated the oxygen permeation properties of barium bismuth iron oxide within the family of [Ba_2−3xBi_3x−1][Fe_2xBi_1−2x]O_2+3x/2 for x = 0.17–0.60. The structure changed progressively from cubic to tetragonal and then to hexagonal as function of x in accordance with the different relative amounts of bismuth on A-site and B-site of ABO_3−δ perovskite lattices. We found that the oxygen flux and electrical conductivity correlated strongly, and it was prevalent for the cubic structure (x = 0.33–0.40) which conferred the highest oxygen flux of 0.59 ml min⁻¹ cm⁻² at 950 °C for a disk membrane x = 0.33 with a thickness of 1.2 mm. By reducing the thickness of the disk membrane to 0.8 mm, the oxygen flux increased to 0.77 ml min⁻¹ cm⁻², suggesting both surface kinetics and ion diffusion controlled oxygen flux, though the former was more prominent at higher temperatures. For disk membranes x = 0.45–0.60, the perovskite structure changed to tetragonal and hexagonal, and the oxygen flux was insignificant below 900 °C, clearly indicating electron conduction properties only. However, for two compositions with relatively high bismuth content, e.g. x = 0.55 and 0.60, there was a sudden and significant rise of oxygen permeability above 900 °C, by more than one order of magnitude. These materials changed conduction behavior from metallic to semiconductor at around 900 °C. These results suggest the advent of mixed ionic electronic conducting properties caused by the structure transition as bismuth ions changed their valence states to compensate for the oxygen vacancies formed within the perovskite lattices.

Research progress and materials selection guidelines on mixed conducting perovskite-type ceramic membranes for oxygen production

Oxygen production by air separation is of great importance in both environmental and industrial processes as most large scale clean energy technologies require oxygen as feed gas. Currently the conventional cryogenic air separation unit is a major economic impediment to the deployment of these clean energy technologies with carbon capture (i.e. oxy-fuel combustion ). Dense ceramic perovskite membranes are envisaged to replace the cryogenics and reduce O2 production costs by 35% or more; which can significantly cut the energy penalty by 50% when integrated in oxy-fuel power plant for CO2 capture. This paper reviews the current progress in the development of dense ceramic membranes for oxygen production. The principles, advantages or disadvantages, and the crucial problems of all kinds of membranes are discussed. Materials development, optimisation guidelines and suggestions for future research direction are also included. Some areas already previously reviewed are treated with less attention.

NMR and Raman studies of a novel fast-ion-conducting polymer-in-salt electrolyte based on LiCF3SO3 and PAN

We report spectroscopic results from investigations of a novel solid polymeric fast-ion-conductor based on poly(acrylonitrile), (PAN, of repeat unit [CH₂CH(CN)]_n), and the salt LiCF₃SO3 . From NMR studies of the temperature and concentration dependencies of ⁷Li- and ^lH-NMR linewidths, we conclude that significant ionic motion occurs at temperatures close to the glass transition temperature of these polymer-in-salt electrolytes, in accordance with a recent report on the ionic conductivity. In the dilute salt-in-polymer regime, however, ionic motion appears mainly to be confined to local salt-rich domains, as determined from the dramatic composition dependence of the ionic conductivity. FT-Raman spectroscopy is used to directly probe the local chemical anionic environment, as well as the Li⁺–PAN interaction. The characteristic δ_s(CF₃) mode of the CF₃SO₃⁻ anion at _~750–780 cm^−l shows that the ionic substructure is highly complex. Notably, no spectroscopic evidence of free anions is found even at relatively salt-depleted compositions (e.g. N:Li_~60–10:1). A strong Li⁺–PAN interaction is manifested as a pronounced shift of the characteristic polymer C=N stretching mode, found at _~2244 cm^−l in pure PAN, to _~2275 cm^−l for Li⁺-coordinated C=N moieties. Our proton-NMR data suggest that upon complexation of PAN with LiCF3 SO₃, the glass transition occurs at progressively lower temperatures.

Lithium doped N-methyl-N-ethylpyrrolidiniumbis(trifluoromethanesulfonyl)amide fast-ion conducting plastic crystals

The incorporation of dopant levels of lithium ions (0.5 to 9.3% by mole) in the N-methyl-N-ethylpyrrolidinium bis(trifluoromethanesulfonyl)amide (P₁₂TFSA) plastic crystalline phase results in increases in the solid state ionic conductivity of more than 3 orders of magnitude at 298 K. Conductivities as high as 10^−-4 S cm⁻¹ at 323 K have been measured in these doped plastic crystal phases. These materials can therefore be classified as fast-ion conductors. Higher levels of Li only marginally increase the conductivity, up to around 33 mol%, followed by a slight decrease to 50 mol%. Thermal analysis behaviour has allowed the partial development of the binary phase diagram for the LiTFSA–P₁₂TFSA system between 0–50 mol% LiTFSA, which suggests the presence of a solid solution single phase at concentrations less than 9.3 mol% LiTFSA. There is also strong evidence of eutectic behaviour in this system with a eutectic transition temperature around 308 K at 33 mol% LiTFSA. A model relating ionic conduction to phase behaviour in this system is presented. The increased conductivity upon doping has been associated with lithium ion motion via⁷Li solid state NMR linewidth measurements.

NMR studies of modified nasicon-like, lithium conducting solid electrolytes*1

²⁷Al, ³¹P and ⁷Li NMR measurements have been performed on lithium conducting ceramics based on the LiTi₂(PO₄)₃ structure with Al, V and Nb metal ions substituted for either Ti or P within the framework NASICON structure. The ²⁷Al magic angle spinning NMR measurements have revealed that, although Al is intended to substitute for octahedral Ti sites, additional substitution into tetrahedral environments (presumably phosphorous sites) occurs with increasing amount of Al addition. This tetrahedral substitution appears to occur more readily in the presence of vanadium, in Li_1+xAl_xTi_2−x(PO₄)_2.9(VO₄)_0.1, whereas similar niobium additions (in place of vanadium) appear to stifle tetrahedral substitution. ⁷Li static NMR spectra reveal quadrupolar structure with C_q approximately 42 kHz, largely independent of substitution. Measurement of the ⁷Li central transition linewidth at room temperature reveals a relatively mobile lithium species (300–900 Hz) with linewidth tending to decrease with Al substitution and increase with increasing V or Nb. This new structural information is discussed in the context of ionic conduction in these ceramics.

Cycling performance of lithium metal polymer cells assembled with ionic liquid and poly(3-methyl thiophene)/carbon nanotube composite cathode

A poly(3-methylthiophene) (PMT)/multi-walled carbon nanotube (CNT) composite is synthesized by in situ chemical polymerization. The PMT/CNT composite is used as an active cathode material in lithium metal polymer cells assembled with ionic liquid (IL) electrolytes. The IL electrolyte consists of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4) and LiBF4. A small amount of vinylene carbonate is added to the IL electrolyte to prevent the reductive decomposition of the imidazolium cation in EMIBF4. A porous poly(vinylidene fluoride-co-hexafluoropropylene) (P(VdF-co-HFP)) film is used as a polymer membrane for assembling the cells. Electrochemical properties of the PMT/CNT composite electrode in the IL electrolyte are evaluated and the effect of vinylene carbonate on the cycling performance of the lithium metal polymer cells is investigated. The cells assembled with a non-flammable IL electrolyte and a PMT/CNT composite cathode are promising candidates for high-voltage–power sources with enhanced safety.