Joanne M. Elliott

Nanostructured tin for use as a negative electrode material in Li-ion batteries

A series of mesoporous tin samples have been prepared by means of a liquid crystal templating method. TEM images and X-ray diffraction data show the mesoporosity and the scale of the repeat structure. The lithium insertion and extraction behaviour of liquid crystal templated films were compared with those obtained from non-templating electrolytes. It was found that the templated films showed higher extraction capacities, which were attributed to the ability of mesoporous tin to expand and contract with less structural degradation than nonporous tin.

Electrodeposition and properties of nanostructured platinum films studied by quartz crystal impedance measurements at 10 MHz

The electrodeposition of platinum films from aqueous solutions and lyotropic liquid crystalline mixtures of the non-ionic surfactant octaethyleneglycol monohexadecyl ether, water, and hexachloroplatinic acid (HCPA) has been studied by rapid in-situ measurements of the quartz crystal electroacoustic impedance with an electrochemical quartz crystal microbalance (EQCM). For solutions and liquid crystalline template mixtures of high HCPA content large changes of the damping resistance, R have been observed at the initial stages and the end of the plating process as a result of composition changes in the depletion layer. They were corrected forte yield accurate in-situ mass data for the electroplating process. For the measured film thicknesses (< 200 nm) the faradayic efficiency depends inversely on the concentration of HCPA in the aqueous solutions and the template mixtures. This was attributed mainly to migrational transport of the intermediate [PtCl4](2-) anion away from the electrode and to the concentration dependence of the disproportionation/comproportionation reaction in the depletion layer between the Pt(0), Pt(II), and Pt(IV) species involved in the electrode reaction. A 65% increase in specific surface area was measured for the template deposited material compared to Pt deposits from aqueous solutions. This difference can be regarded as a minimum value for the thin films studied and becomes much larger for thicker films. Transmission electron microscopy (TEM) analysis of the former show the films to be mesoporous with a hexagonal nanostructure identical to that produced by template depositions onto non-oscillating substrates. The high specific surface area of the Pt films from lyotropic liquid crystalline templates results in a sensitivity enhancement of the in-situ electroacoustic impedance EQCM technique. It could hence be applied to mono- and sub-monolayer adsorption studies for polycrystalline Pt in sulfuric acid. An increase in damping resistance was found when stepping the potential from the double layer region into the hydrogen adsorption region and attributed to a higher degree of acoustic shear wave coupling to the bulk liquid. It is believed that the adsorbed hydrogen forms hydronium species, which others have observed earlier by IR spectroscopy.

Electrochemical impedance characterisation of a nanostructured (mesoporous) platinum film

Nanostructured platinum films with an hexagonal array of uniform, regularly-sized pores were grown on platinum substrates by electrochemical plating from a liquid crystalline electrolyte. The films were characterised as models for nanoporous electrodes, first by cyclic voltammetry in dilute sulfuric acid, showing enhanced currents due to the internal area of the pore structure. Complex impedance spectroscopy was then used to determine the access time of the capacitance and pseudocapacitance in the double layer and hydrogen adsorption regions, respectively. The results were analysed in terms of a transmission line model, showing capacitance at low frequencies and diffusive behaviour above 1 kHz. Capacitance values were as expected from the internal surface area and in agreement with the cyclic voltammetry results. The pore resistance was higher than predicted from a straight pore model, and showed apparent tortuosity factors of about 10. Nevertheless, the nanostructured material gave a very impressive performance as a supercapacitor, with a volumetric capacitance of 110 F cm−3 and an effective diffusion coefficient of 5 × 10−5 cm2 s−1 in the double layer region.

Facile Production of Ordered 3D Platinum Nanowire Networks with “Single Diamond” Bicontinuous Cubic Morphology

Direct electrochemical templating is carried out using a thin layer of a self-assembled diamond phase (QIID) of phytantriol to create a platinum film with a novel nanostructure. Small-angle X-ray scattering shows that the nanostructured platinum films are asymmetrically templated and exhibit “single diamond” morphology with Fd3m symmetry.

Molecular recognition between functionalized gold nanoparticles and healable, supramolecular polymer blends – a route to property enhancement

A new, healable, supramolecular nanocomposite material has been developed and evaluated. The material comprises a blend of three components: a pyrene-functionalized polyamide, a polydiimide and pyrene-functionalized gold nanoparticles (P-AuNPs). The polymeric components interact by forming well-defined π–π stacked complexes between π-electron rich pyrenyl residues and π-electron deficient polydiimide residues. Solution studies in the mixed solvent chloroform–hexafluoroisopropanol (6 : 1, v/v) show that mixing the three components (each of which is soluble in isolation), results in the precipitation of a supramolecular, polymer nanocomposite network. The precipitate thus formed can be re-dissolved on heating, with the thermoreversible dissolution/precipitation procedure repeatable over at least 5 cycles. Robust, self-supporting composite films containing up to 15 wt% P-AuNPs could be cast from 2,2,2-trichloroethanol. Addition of as little as 1.25 wt% P-AuNPs resulted in significantly enhanced mechanical properties compared to the supramolecular blend without nanoparticles. The nanocomposites showed a linear increase in both tensile moduli and ultimate tensile strength with increasing P-AuNP content. All compositions up to 10 wt% P-AuNPs exhibited essentially quantitative healing efficiencies. Control experiments on an analogous nanocomposite material containing dodecylamine-functionalized AuNPs (5 wt%) exhibited a tensile modulus approximately half that of the corresponding nanocomposite that incorporated 5 wt% pyrene functionalized-AuNPs, clearly demonstrating the importance of the designed interactions between the gold filler and the supramolecular polymer matrix.

Nanostructured materials for batteries

Nanostnuctured metals can aid fast battery cycling by providing continuous paths for electron and ion transport. The novel fabrication method of liquid crystal templating has been used to make nanostructured platinum and tin as monolithic films containing hexagonal pore structures with controllable lattice parameters of about 5 nm. The pore structure leads to a surface area enhancement in platinum giving a double layer capacitance of 0.05 Fcm(-2) and a series resistance of less than 0.005 Ohm.cm(2) in a 3 micron film. A similar nanostructure in tin has been shown to withstand the expansion and contraction strains during lithium cycling.

Electrochemical reduction of oxygen on mesoporous platinum microelectrodes

The electrochemical reduction of oxygen is studied using electrochemically deposited mesoporous platinum microelectrodes, which exhibit efficient mass transfer of material to the electrode surface and accelerated reduction kinetics when compared to polished microelectrodes.

Electrodeposition of mesoporous tin films

Mesoporous metallic tin has been electrodeposited, from the homogeneous hexagonal mesophase of a series of amphiphilic non-ionic surfactants, with a controllable repeat structure in the range of 5–10 nm.

Predicting the Orientation of Lipid Cubic Phase Films

Lipid cubic phase films are of increasingly widespread importance, both in the analysis of the cubic phases themselves by techniques including microscopy and X-ray scattering, and in their applications, especially as electrode coatings for electrochemical sensors and for templates for the electrodeposition of nanostructured metal. In this work we demonstrate that the crystallographic orientation adopted by these films is governed by minimization of interfacial energy. This is shown by the agreement between experimental data obtained using grazing-incidence small-angle X-ray scattering (GI-SAXS), and the predicted lowest energy orientation determined using a theoretical approach we have recently developed. GI-SAXS data show a high degree of orientation for films of both the double diamond phase and the gyroid phase, with the [111] and [110] directions respectively perpendicular to the planar substrate. In each case, this matches the lowest energy facet calculated for that particular phase.

Pyrene-Modified Quartz Crystal Microbalance for the Detection of Polynitroaromatic Compounds

The synthesis of a dithiol-functionalized pyrene derivative is reported, together with studies of interactions between this receptor (and other related pyrenes) and nitroaromatic compounds (NACs), in both solution and in the solid state. Spectroscopic analysis in solution and X-ray crystallographic analysis of cocrystals of pyrene and NACs in the solid state indicate that supramolecular interactions lead to the formation of defined π-π stacked complexes. The dithiol-functionalized pyrene derivative can be used to modify the surface of a gold quartz crystal microbalance (QCM) to create a unique π-electron rich surface, which is able to interact with electron poor aromatic compounds. For example, exposure of the modified QCM surface to the nitroaromatic compound 2,4-dinitrotoluene (DNT) in solution results in a reduction in the resonant frequency of the QCM as a result of supramolecular interactions between the electron-rich pyrenyl surface layer and the electron-poor DNT molecules. These results suggest the potential use of such modified QCM surfaces for the detection of explosive NACs.