Fabrication of high-performance supercapacitors based on transversely oriented carbon nanotubes

High-performance supercapacitors with organic electrolyte 1 M TEABF₄ (tetraethyl ammonium tetrafluoroborate) in PC (propylene carbonate) were fabricated and tested, based on multiwall carbon nanotubes (MWNTs) deposited by electrophoresis on three types of alternative substrates: aluminium foil, ITO (indium tin oxide) coated PET (polyethylene terephthalate) film and PET film. In all cases, SEM (scanning electron microscopy) and STEM (scanning transmission electron microscopy) micrographs demonstrated that protruding, transversely oriented MWNT structures were formed, which should increase the transverse conductivity of these MWNT electrodes. The best supercapacitor cell of MWNT electrodes deposited on aluminium foil displayed good transverse orientation of the MWNT structures as well as an in-plane MWNT network at the feet of the protruding structures, which ensured good in-plane conductivity. Capacitor cells with MWNT electrodes deposited either on ITO-coated PET film or on PET film demonstrated lower but still very good performance due to the high density of transversely oriented MWNT structures (good transverse conductivity) but some in-plane inhomogeneities. Capacitor cells with drop-printed MWNTs on aluminium foil, without any transverse orientation, had 16–30 times lower specific capacitance and 5–40 times lower power density than the capacitor cells with the electrophoretically deposited MWNT electrodes.     

Electrophoresis and orientation of multiple wall carbon nanotubes in polymer solution

This paper contains an in-depth analysis of the electrophoresis of multi-wall carbon nanotubes (MWNTs) in liquid epoxy where electrophoresis experiments under DC and AC fields were carried out for five different types of multi-wall carbon nanotubes (MWNTs). DC electrophoresis and particle image velocimetry were used to determine the electrophoretic particle mobility and zeta potential, where the MWNTs with the largest outer diameter and length led to the highest mobility values. The orientation and agglomeration of MWNTs into “striation” lines under AC electrophoresis were investigated by analysing the hue, saturation and intensity of the transmitted polarised light under microscope, following a schedule of step-wise applied voltage in the range of 0 to 100 V. Plots of hue and saturation as a function of the applied voltage were used to assess the degree of orientation and density of orientated MWNT structures, respectively, and to determine an optimum AC electric field value for the orientation of a specific MWNT type by electrophoresis.     

Flow Through a Two-Scale Porosity,Oriented Fibre Porous Medium

A model is described for the meso- and micro-flow through an array of oriented fibre tows with meso-channels between the tows. Axial Stokes's flow was considered in the meso-channels and Darcy's law was applied within the porous fibre tows, taking into account injection pressure and capillary pressures in both types of flow. Transverse flow transfer was modelled from the leading flow front to the lagging flow and a partial-slip boundary condition was applied at the permeable boundaries of meso-channels. Flow visualisation experiments and microstructural characterisation of laminates provided appropriate experimental data for model validation. In this, the predictions for the progress of the leading meso-flow were in excellent agreement with the experimental data. Parametric studies followed including the effects of injection pressure and meso-channel size.     

Contents of Volume 54

Volume Contents

Contents of Volume 54