Browsing by Author "Rodopoulos, T"

Now showing 1 - 6 of 6
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    Electrical double-layer capacitance in room temperature ionic liquids: ion-size and specific adsorption effects
    (American Chemical Society, 2010-09-02) Lauw, Y; Horne, MD; Rodopoulos, T; Nelson, A; Leermakers, FAM
    The electrical double-layer structure and capacitance in room temperature ionic liquids at electrified interfaces were systematically studied with use of the self-consistent mean-field theory. The capacitance curve departs from symmetry with respect to the point of zero charge when unequal ion-size is implemented or when specific adsorption of ions is introduced. For the case of unequal ion-size, the shape of the capacitance curve is strongly determined by the size of the counterion and only weakly influenced by the co-ion size. When present, specifically adsorbed ions would change the capacitance within a limited range of applied potential from the point of zero charge, which itself varies with the strength of specific adsorption. © 2010, American Chemical Society
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    Electrochemical cell for neutron reflectometry studies of the structure of ionic liquids at electrified interface
    (American Institute of Physics, 2010-07) Lauw, Y; Rodopoulos, T; Gross, M; Nelson, A; Gardner, R; Horne, MD
    We describe the design and use of a closed three-electrode electrochemical cell for neutron reflectometry studies of the structure of the electrical double-layer in ionic liquids. A transparent glass counter electrode was incorporated to allow easy monitoring of any gas bubbles trapped in the cell. A 100 mm diameter silicon wafer polished to 0.1 nm rms roughness coated with gold over a chromium adhesion layer was used as the working electrode. The utility of the cell was demonstrated during neutron reflectometry measurements of the ultrahigh purity ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([C4mpyr][NTf2]) at two different applied potentials. © 2010, American Institute of Physics
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    Room-temperature ionic liquids: excluded volume and ion polarizability effects in the electrical double-layer structure and capacitance
    (The American Physical Society, 2009-09-10) Lauw, Y; Horne, MD; Rodopoulos, T; Leermakers, FAM
    We study structures of room-temperature ionic liquids at electrified interfaces and the corresponding electrical double-layer capacities using a self-consistent mean-field theory. Ionic liquids are modeled as segmented dendrimers and the effective dielectric constant is calculated from the local distribution of ions to accommodate the excluded volume and the local dielectric screening effects. The resulting camel-shaped capacitance curve is further analyzed in terms of the thickness of alternating layers and the polarization of ions at electrified interfaces. © 2009 The American Physical Society.
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    Structure of [C(4)mpyr][NTf2] room-temperature ionic liquid at charged gold interfaces
    (American Chemical Society, 2012-05-15) Lauw, Y; Horne, MD; Rodopoulos, T; Lockett, V; Akgun, B; Hamilton, WA; Nelson, A
    The structure of 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([C4mpyr][NTf2]) room-temperature ionic liquid at an electrified gold interface was studied using neutron reflectometry, cyclic voltammetry, and differential capacitance measurements. Subtle differences were observed between the reflectivity data collected on a gold electrode at three different applied potentials. Detailed analysis of the fitted reflectivity data reveals an excess of [C4mpyr]+ at the interface, with the amount decreasing at increasingly positive potentials. A cation rich interface was found even at a positively charged electrode, which indicates a nonelectrostatic (specific) adsorption of [C4mpyr]+ onto the gold electrode. © 2012, American Chemical Society
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    Studying electrical double layers in ionic liquids using neutron and x-ray reflectometry
    (Australian Institute of Physics, 2010-02-05) Lauw, Y; Nelson, A; Horne, MD; Rodopoulos, T; Minofar, B; Webster, NAS; Hamilton, WA
    Ionic liquids are typically defined as salts that exist in a liquid state at, or near, room temperature. Due to their favourable properties (e.g., good thermal stability, low volatility, and wide electrochemical window), ionic liquids have potential use in many industrial applications, such as catalysis, lubrication, batteries, and metal electrodeposition. Despite recent advances in the field, ionic liquid research is still in its infancy. Additional fundamental studies are needed to explore the properties of ionic liquids and to allow the full potential of these properties in particular applications to be exploited. Electrical double layers (EDL) are well known in aqueous colloidal systems where the potential field from a charged surface affects many properties of the particle. The structure of the EDL at a conductive surface is of prime importance to electrochemistry because it strongly affects the transport of reactants and products within the region where electrochemical reactions take place. The understanding of the EDL in ionic liquids is not nearly as advanced as aqueous systems and even a description of how it responds to changes in the conductor potential is yet to be agreed. Here we present some recent results from simulation and Neutron/X-ray reflectometry measurements that explore the electrical double layer in ionic liquids at the air-liquid and solid-liquid interfaces. The effect of water impurities within the (EDL) of an ionic liquid is of particular interest since they are known to reduce the electrochemical window of ionic liquids, decrease their density and viscosity, and anomalously decrease their surface tension.
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    X-ray reflectometry studies on the effect of water on the surface structure of [C(4)mpyr][NTf2] ionic liquid
    (Royal Society of Chemistry, 2009-10-21) Lauw, Y; Horne, MD; Rodopoulos, T; Webster, NAS; Minofar, B; Nelson, A
    The effect of water on the surface structure of 1-butyl-1-methylpyrrolidinium trifluoromethylsulfonylimide [C(4)mpyr][NTf2] ionic liquid was investigated using X-ray reflectometry. The measured reflectivity data suggests a significant amount of water is adsorbed at the surface, with the first layer from the gas (nitrogen)-liquid phase boundary mainly occupied by a mixture of cations and water. Beyond the cation + water layer, the scattering length density increases towards the bulk value, indicating a decreasing amount of water and cations, and/or an increasing amount of anions. The orientation of the butyl chain of cation at the phase boundary and the population of water at the surface were described based on results from an independent molecular dynamics (MD) simulation. We show that the presence of water in the ionic liquid has a non-monotonic effect on the overall thickness of the surface. At low water content, the addition of water does not change the surface thickness since water is mainly present in the bulk. As the water content increases, the surface swells before eventually shrinking down close to the solubility limit of water. The non-monotonic surface thickness is used to explain the anomalous trend of surface tension in ionic liquid-water mixtures reported in the literature. © 2009, Royal Society of Chemistry