Electrodeposition of 3D nanostructured materials using a lyotropic liquid crystal template

Abstract

This thesis explores the technique of electrodeposition of materials through liquid crystal templates. Electrodeposition through liquid crystal templates offers a promising technique which enables us to fabricate intricate and ordered nanomaterials which have enhanced catalytic performance and properties. The liquid crystal phase of interest is the double diamond phase formed by the non-ionic surfactant phytantriol and its derivates with the addition of Brij-56. The main objective of this work is to deposit cadmium telluride (CdTe), platinum (Pt) and palladium (Pd) through this soft-template, and the characterisation of the resulting nanostructured materials using a wide array of techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), electrochemistry and small-angle X-ray scattering (SAXS). Another goal for this work is to design and develop a 3D printable electrochemical cell which enables in-situ small angle scattering experiments that is capable of monitoring the templated electrodeposition process.
Utilising the phytantriol/Brij-56 as a scaffold, electrodeposition was employed to successfully fabricate stoichiometric mesoporous CdTe as revealed by EDX. TEM revealed that the resulting CdTe had a 3D mesoporous morphology with an average nanowire diameter of 5.3 ± 0.8 nm and an average pore width of 7.0 ± 1.2 nm. Reflectivity measurements were used to determine the band gap of the nanostructured CdTe, which was calculated to be 1.65 ± 0.06 eV, which is an increase from 1.45 eV for bulk CdTe showing how the resulting morphology of the material influences its properties.
By varying the amount of Brij-56 in the phytantriol we could electrodeposit Pd with a single diamond phase with control over the lattice size. By increasing the Brij-56 content in the template we saw an increase in lattice parameter and nanowire diameter of resulting Pd. By adding 20 weight percent (wt%) Brij-56 to the phytantriol we increased the lattice parameter and nanowire diameter of the Pd from 143.7 ± 1.6 Å and 2.9 ± 0.1 nm to 217.3 ± 6.9 Å and 5.9 ± 0.3 nm. The lattice parameter in this work refers to the distance between repeating unit cells in the nanostructure or liquid crystal. It was found that the electrocatalytic performance of the single diamond Pd was size dependent for the electrooxidation of formic acid. There was an increase in peak current density of 177 A g-1 for the Pd with larger lattice parameter produced from phytantriol with 20 wt% Brij-56. This work highlighted that by tuning the size of the resulting nanostructure we can alter the catalytic performance of the material.
For the first time the single diamond phase of Pt produced by electrodeposition through phytantriol was tested for its performance for the oxygen reduction reaction in alkaline conditions. The resulting Pt showed comparable performance to commercial Pt/C with a positive shift in half-wave potential of 30 mV. The single diamond phase Pt showed enhanced durability compared to Pt/C with a lower relative loss in electroactive surface area after potential cycling.
Custom-made electrochemical cells were successfully designed, and 3D printed which provided bespoke sample environments for in-situ small angle scattering experiments. These cells were used in collaborative experiments with the University of Bath and the University of Glasgow, enabling a wide range of experiments to be performed on the DL-SAXS and I22 beamline at the Diamond Light Source, LoQ and ZOOM at ISIS Neutron and Muon Source. The experiments performed in these cells ranged from monitoring the electrodeposition of metals and semiconductors through liquid crystal templates to monitoring the growth of electropolymerised gels.

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Identifiers

ORCID for Iris Nandhakumar: orcid.org/0000-0002-9668-9126

ORCID for Neil White: orcid.org/0000-0003-1532-6452

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