Peter Marchand

Highly pseudocapacitive Nb-doped TiO2 high power anodes for lithium-ion batteries

Nb-doped TiO2 (anatase) nanoparticles were synthesized using a continuous hydrothermal flow synthesis reactor using a supercritical water flow as a reagent and crystallizing medium. The as-prepared nano-powders with ca. 25 at% Nb5+ (<6 nm diameter) were used as possible anodes for lithium-ion batteries without any further heat-treatment. Cyclic voltammetry and galvanostatic charge/discharge cycling tests were performed in the range of 1.2 to 3.0 V vs. Li/Li+. The Nb-doped TiO2 samples showed superior capacity retention at high current rates compared to the corresponding undoped nano-TiO2. The superior performance of the doped samples (at specific currents up to 15 A g−1) was attributed to higher electronic conductivity and a greater charge storage contribution from surface effects like pseudocapacitance (Faradaic processes) as well as Helmholtz double layer charge storage.

High-Throughput Synthesis, Screening, and Scale-Up of Optimized Conducting Indium Tin Oxides

A high-throughput optimization and subsequent scale-up methodology has been used for the synthesis of conductive tin-doped indium oxide (known as ITO) nanoparticles. ITO nanoparticles with up to 12 at % Sn were synthesized using a laboratory scale (15 g/hour by dry mass) continuous hydrothermal synthesis process, and the as-synthesized powders were characterized by powder X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray analysis, and X-ray photoelectron spectroscopy. Under standard synthetic conditions, either the cubic In2O3 phase, or a mixture of InO(OH) and In2O3 phases were observed in the as-synthesized materials. These materials were pressed into compacts and heat-treated in an inert atmosphere, and their electrical resistivities were then measured using the Van der Pauw method. Sn doping yielded resistivities of ∼ 10(-2) Ω cm for most samples with the lowest resistivity of 6.0 × 10(-3) Ω cm (exceptionally conductive for such pressed nanopowders) at a Sn concentration of 10 at %. Thereafter, the optimized lab-scale composition was scaled-up using a pilot-scale continuous hydrothermal synthesis process (at a rate of 100 g/hour by dry mass), and a comparable resistivity of 9.4 × 10(-3) Ω cm was obtained. The use of the synthesized TCO nanomaterials for thin film fabrication was finally demonstrated by deposition of a transparent, conductive film using a simple spin-coating process.

Synthesis and characterisation of novel aluminium and gallium precursors for chemical vapour deposition

The β-ketoimine ligand [(Me)CN(H){iPr}–CHC(Me)O] (L1H) and the bis(β-ketoimine) ligands [(CH2)2{N(H)C(Me)–CHC(R)O}2] (L2H2, R = Me; L3H2, R = C6H5) linked by ethylene bridges have been used to form aluminium and gallium complexes: [Al(L1)Et2] (1), [Ga(L1)2Cl] (2), [AlL2(OiPr)] (3) and [GaL3Me] (4). The complexes were characterised by NMR spectroscopy, mass spectroscopy, and single crystal X-ray diffraction, with the exception of 1 which was isolated as an oil. Compounds 1–4 have been used for the first time as single source precursors for the deposition of Al2O3 (1, 3) and Ga2O3 (2, 4) respectively. Thin films were deposited via aerosol assisted (AA)CVD with toluene as the solvent.

Conducting Al and Ga-doped zinc oxides; rapid optimisation and scale-up

A high-throughput synthesis, screening and subsequent scale-up approach was utilised for the optimisation of conductive aluminium and gallium-doped zinc oxide (AZO and GZO, respectively) nanoparticles. AZO and GZO nanoparticles with up to 6 at% dopant (with respect to Zn) were directly synthesised using a laboratory scale continuous hydrothermal process at a rate of 60 g per hour. The resistivities were determined by Hall effect measurements on pressed, heat-treated discs. Both Al- and Ga-doping yielded resistivities of the order of 1 × 10−2 Ω cm for most samples; the lowest resistivity of AZO was 7.0 × 10−3 Ω cm (at 2.5 at% Al doping), and the lowest resistivity of GZO was 9.1 × 10−3 Ω cm (at 3.5 at% Ga doping), which are considered exceptionally conductive for pressed nanopowders. Synthesis of the optimised lab-scale compositions was scaled-up using a pilot-scale continuous hydrothermal process at a production rate of 8 kg per day (by dry mass); results obtained from these nanopowders generally retained resistivity trends observed for the lab-scale analogues.

Synthesis and Structural Characterization of β‐Ketoiminate‐Stabilized Gallium Hydrides for Chemical Vapor Deposition Applications

Bis-β-ketoimine ligands of the form [(CH2 )n {N(H)C(Me)CHC(Me)O}2 ] (L(n) H2 , n=2, 3 and 4) were employed in the formation of a range of gallium complexes [Ga(L(n) )X] (X=Cl, Me, H), which were characterised by NMR spectroscopy, mass spectrometry and single-crystal X-ray diffraction analysis. The β-ketoimine ligands have also been used for the stabilisation of rare gallium hydride species [Ga(L(n) )H] (n=2 (7); n=3 (8)), which have been structurally characterised for the first time, confirming the formation of five-coordinate, monomeric species. The stability of these hydrides has been probed through thermal analysis, revealing stability at temperatures in excess of 200 °C. The efficacy of all the gallium β-ketoiminate complexes as molecular precursors for the deposition of gallium oxide thin films by chemical vapour deposition (CVD) has been investigated through thermogravimetric analysis and deposition studies, with the best results being found for a bimetallic gallium methyl complex [L(3) {GaMe2 }2 ] (5) and the hydride [Ga(L(3) )H] (8). The resulting films (F5 and F8, respectively) were amorphous as-deposited and thus were characterised primarily by XPS, EDXA and SEM techniques, which showed the formation of stoichiometric (F5) and oxygen-deficient (F8) Ga2 O3 thin films.

High-Throughput Continuous Hydrothermal Synthesis of Transparent Conducting Aluminum and Gallium Co-doped Zinc Oxides

High-throughput continuous hydrothermal flow synthesis was used to generate a library of aluminum and gallium-codoped zinc oxide nanoparticles of specific atomic ratios. Resistivities of the materials were determined by Hall Effect measurements on heat-treated pressed discs and the results collated into a conductivity-composition map. Optimal resistivities of ∼9 × 10-3 Ω cm were reproducibly achieved for several samples, for example, codoped ZnO with 2 at% Ga and 1 at% Al. The optimum sample on balance of performance and cost was deemed to be ZnO codoped with 3 at% Al and 1 at% Ga.

Aerosol-assisted fabrication of tin-doped indium oxide ceramic thin films from nanoparticle suspensions

Sn-doped In2O3 (ITO) thin films were fabricated on float glass substrates from a nanoparticle suspension using a new and inexpensive aerosol-assisted chemical transport (AACT) process. The influence of the solvent type, loading level and film deposition time on the structural, electrical and optical properties of the deposited thin films was investigated. In addition, the effect of the post-deposition heat-treatment of ITO films on the film resistivity and transparency was investigated using microwave radiation and compared with more conventional radiant heat-treated films. The SEM images of the films prepared using a 30 min deposition time with 0.20% (wt/vol%) methanolic ITO suspension provided better surface coverage compared to the other deposition times investigated. The optimised ITO films were heat-treated after deposition by either conventional radiant or microwave assisted heating methods in order to improve the inter-particle connections and film adherence. The films heat-treated after deposition by microwave annealing exhibited an average transmittance of >85% in the visible region with a resistivity of 12 Ω cm and a carrier concentration of −3.7 × 1016 cm3, which were superior to films that were heat-treated using more conventional thermal processing (despite the shorter processing time for the microwave process). The resistivity of ITO films was further decreased to 6.0 × 10−2 Ω cm with an increased carrier concentration of −8.0 × 1018 cm3 when ethyl cellulose was added to the ITO suspension prior to the AACT deposition. The enhanced conductivity of this film is due to the improved particle–particle and particle–substrate connections as observed by SEM imaging.

Si-doped zinc oxide transparent conducting oxides; nanoparticle optimisation, scale-up and thin film deposition

Silicon-doped zinc oxide, Zn1−xSixOy, transparent conducting oxide nanoparticles were prepared using a laboratory scale (production rate of 60 g h−1) continuous hydrothermal flow synthesis (CHFS) process in the dopant range 0.25 to 3.0 at% Si. The resistivity of the materials was assessed as pressed heat-treated pellets, revealing that the sample with the lowest resistivity (3.5 × 10−2 Ω cm) was the 0.25 at% Si doped ZnO sample. The synthesis of this optimum composition was then scaled up to 350 g h−1 using a larger pilot plant CHFS process. Spin coating of a slurry of the resulting nanopowder made on the pilot plant, followed by an appropriate heat-treatment, produced a thin film with an optical transmission >80% and a low resistivity of 2.4 × 10−3 Ω cm, with a carrier concentration of 1.02 × 1020 cm−3 and a mobility of 11 cm2 V−1 s−1. This is a factor of almost twenty times improvement in the resistivity versus the analogous pressed, heat-treated pellet.