Density, conductivity, viscosity, and excess properties of (pyrrolidinium nitrate-based Protic Ionic Liquid + propylene carbonate) binary mixture

International audienceDensity, ρ, viscosity, η, and conductivity, σ, measurements of binary mixtures containing the pyrrolidinium nitrate Protic Ionic Liquid (PIL) and propylene carbonate (PC), are determined at the atmospheric pressure as a function of the temperature from (283.15 to 353.15) K and within the whole composition range. The temperature dependence of both the viscosity and conductivity of each mixture exhibits a non-Arrhenius behaviour, but is correctly fitted by using the Vogel–Tamman–Fulcher (VTF) equation. In each case, the best-fit parameters, such as the pseudo activation energy, and ideal glass transition temperature, T0 are then extracted. The excess molar volumes VE, and viscosity deviations from the ideality, Δη, of each investigated mixture were then deduced from the experimental results, as well as, their apparent molar volumes, Vϕ, thermal expansion coefficients αp, and excess Gibbs free energies (ΔG∗E) of activation of viscous flow. The VE, αpE, Δη values are negative over the whole composition range for each studied temperature therein. According to the Walden rule, the ionicity of each mixture was then evaluated as a function of the temperature from (283.15 to 353.15) K and of the composition. Results have been then discussed in terms of molecular interactions and molecular structures in this binary mixture

Eutectic mixture of Protic Ionic Liquids as an Electrolyte for Activated Carbon-Based Supercapacitors

International audienceOne of the drawbacks of ionic liquids is that some of them are solid or very viscous at room temperature; this prevents their use as electrolytes in energy storage systems. One solution consists of a binary mixture of pure, solid salts with the formation of a eutectic, allowing it to be used at room temperature. This work describes, for the first time, the formulation and use of a binary mixture of protic ionic liquids (PILs) based on the same H-bond donor, pyrrolidinium cation, with nitrate ([Pyrr][NO3]) and bis(trifluoromethanesulfonyl) imide ([Pyrr][TFSI]) anions as an electrolyte for carbon-based supercapacitors. The physico-chemical and thermal properties of mixtures as a function of composition and temperature were fully investigated and related to their electrochemical behavior as an electrolyte. The electrochemical characterization of some selected optimal compositions (x[Pyrr][NO3] = 0.64, 0.72, 0.80) shows, at first, good capacitive behavior (up to 148 F g−1) at a potential voltage of 2.0 V. Moreover, above 2.0 V, anion intercalation was observed, increasing the specific capacitance up to 209 F g−1. At 2.5 V during cycling, the characteristic peak of anion intercalation/deintercalation decreases, caused by saturation of the positive electrode by anions. Finally, accelerated aging tests showed good capacity retention (> 80%) at 2.0 V during 110 hours for x[Pyrr][NO3] = 0.72, at 25 °C. According to these results, the use of eutectic PIL binary mixtures is a promising way to design adapted electrolytes according to the material electrode for energy devices at room temperature

Deep eutectic solvent based on sodium cations as an electrolyte for supercapacitor application

International audienceThis study proposes a new deep eutectic solvent based on sodium nitrate and N-methylacetamide as an electrolyte for carbon-based supercapacitors at 80°C. The reversible intercalation of ions into the graphitized ultra-micropores of activated carbon, separately detected at negative and positive electrodes, permits high pseudo-capacitance (up to 302 F g−1). The SEM/EDX mapping and XRD profile show homogeneous distribution of Na in negative polarized electrodes indicating that sodium is well incorporated in the ultra-micropores of the carbon structure. The good capacitance obtained at 80 °C in two-electrode cells at an operating voltage up to 2.0 V remained stable after 1000 charge–discharge cycles. Based on its physicochemical properties, as well as its electrochemical performances and stabilities, the sodium based DES can be considered a promising electrolyte for supercapacitor applications

Physicochemical and electrochemical properties of a new series of protic ionic liquids with N-chloroalkyl functionalized cations

International audienceSix new protic ionic liquids (PILs) based on N-chloroalkyl functionalized morpholinium, piperidinium, pyrrolidinium and alkylammonium cations, with bis[(trifluoromethyl)sulfonyl]imide as counter-ion, were synthesized by a metathesis reaction. To understand the differences of structure, charge distribution and volume between the various investigated N-chloroalkyl functionalized cations, as well as between their non-chloro analogues, computational methods were used to generate the COSMO volume and the sigma profile of each ion. Physicochemical investigations showed lowered melting point of these PILs (−8.5 °C < Tm < 34.1 °C) as compared to their non-functionalized analogues and a high thermal stability with T5%onset in the range 280–337 °C. The alkylammonium and pyrrolidinium-based PILs display reasonable conductivity (1.23 mS cm−1 < σ < 1.71 mS cm−1), although their viscosity values are relatively high (0.0665 Pa s < η < 0.1093 Pa s). The effect of temperature on the transport properties of each PIL has then investigated by fitting the experimental data with the Arrhenius law and the Vogel–Tamman–Fulcher (VTF) equations, revealing the convergence of viscosity with the former model and conductivity with the latter one. The electrochemical stability of cations towards reduction is discussed in light of the frontier orbital theory. All N-chloroalkyl functionalized PILs display a wide electrochemical stability window (4.1–5.1 V), in the same range as the representative of non-chloro functionalized analogues, [HN222][TFSI], (4.3 V)