Aaron Dodd

Mechanochemical synthesis of nanocrystalline SnO2–ZnO photocatalysts

Mechanochemical processing of anhydrous chloride precursors with Na2CO3 has been investigated as a means of manufacturing nanocrystalline SnO2 doped ZnO photocatalysts. High-energy milling and heat-treatment of a 0.1SnCl2+0.9ZnCl2+Na2CO3+4NaCl reactant mixture was found to result in the formation of a composite powder consisting of oxide grains embedded within a matrix of NaCl. Subsequent washing with deionized water resulted in removal of the NaCl matrix phase and partial hydration of the oxide reaction product with the consequent formation of ZnSn(OH)6. The extent of this hydration reaction was found to decrease in a linear fashion with the temperature of the post-milling heat-treatment over the range of 400–700 °C. For a heat-treatment temperature of 700 °C, the SnO2 doped ZnO powder was found to exhibit significantly higher photocatalytic activity than either single-phase SnO2 or ZnO powders that were synthesized using similar processing conditions. The heightened photocatalytic activity of the SnO2 doped ZnO was attributed to its higher specific surface area and the enhanced charge separation arising from the coupling of ZnO with SnO2.

Triconstituent co-assembly synthesis of N,S-doped carbon–silica nanospheres with smooth and rough surfaces

Multifunctional porous nanospheres are desirable for many applications, but their synthesis involves multi-step procedures and their simplification still remains a challenge. Herein, we demonstrate a facile synthesis of polymer–silica nanospheres by using an extended Stober method via triconstituent co-assembly of 3-aminophenol, formaldehyde, and bis[3-(triethoxysilyl)propyl]tetrasulfide followed by copolymerization. N,S-doped carbon–silica nanospheres with either smooth or rough surface can be obtained by direct carbonization of the polymer–silica nanospheres. The carbon–silica spheres feature multifunctional properties and exhibit very good performance as adsorbents for CO2 capture (67 cm3 g−1 at 0 ± 1 °C and 1.0 bar) and as supercapacitor electrodes with high specific capacitance (221 F g−1). This strategy could pave the way for design of carbon nanostructures at molecular level for multi-purpose applications.

Nanocrystalline zirconia powders synthesised by mechanochemical processing

Mechanochemical processing of zirconium and yttrium chloride precursors with lithium hydroxide has been used to synthesise ultrafine powders of yttria-stabilised zirconia. The precursors reacted during milling to form a composite consisting of nanocrystalline oxide grains embedded within a matrix of lithium chloride. The ultrafine powder was recovered subsequently by removing the lithium chloride through washing with deionised water and methanol. The powders were characterised using X-ray diffraction (XRD), transmission electron microscopy (TEM), and BET gas adsorption. The sintering behaviour of cold pressed pellets was examined by dilatometry.

Chromium deposition and poisoning of La0.8Sr0.2MnO3 oxygen electrodes of solid oxide electrolysis cells

The effect of the presence of an Fe-Cr alloy metallic interconnect on the performance and stability of La(0.8)Sr(0.2)MnO3 (LSM) oxygen electrodes is studied for the first time under solid oxide electrolysis cell (SOEC) operating conditions at 800 °C. The presence of the Fe-Cr interconnect accelerates the degradation and delamination processes of the LSM oxygen electrodes. The disintegration of LSM particles and the formation of nanoparticles at the electrode/electrolyte interface are much faster as compared to that in the absence of the interconnect. Cr deposition occurs in the bulk of the LSM oxygen electrode with a high intensity on the YSZ electrolyte surface and on the LSM electrode inner surface close to the electrode/electrolyte interface. SIMS, GI-XRD, EDS and XPS analyses clearly identify the deposition and formation of chromium oxides and strontium chromate on both the electrolyte surface and electrode inner surface. The anodic polarization promotes the surface segregation of SrO and depresses the generation of manganese species such as Mn(2+). This is evidently supported by the observation of the deposition of SrCrO4, rather than (Cr,Mn)3O4 spinels as in the case under the operating conditions of solid oxide fuel cells. The present results demonstrate that the Cr deposition is essentially a chemical process, initiated by the nucleation and grain growth reaction between the gaseous Cr species and segregated SrO on LSM oxygen electrodes under SOEC operating conditions.

In situ assembled La0.8Sr0.2MnO3 cathodes on a Y2O3-ZrO2 electrolyte of solid oxide fuel cells-interface and electrochemical activity

Formation of an intimate electrode/electrolyte interface is essential for solid oxide fuel cells (SOFCs). In this study, a comparative investigation has been undertaken to study the interface formation between a La0.8Sr0.2MnO3 (LSM) cathode and Y2O3–ZrO2 (YSZ) electrolyte by high temperature sintering and by cathodic polarization using EIS, SEM, AFM and HAADF-STEM techniques. The electrode/electrolyte interface formed by the conventional pre-sintering process is characterized by the formation of distinctive convex contact rings on the YSZ surface and such convex contact rings are due to the cation interdiffusion such as manganese species between LSM and YSZ. Similar to the thermally induced interface, the electrode/electrolyte interface can also be formed by electrochemical polarization for the in situ assembled LSM cathode on YSZ as well as on Gd2O3–CeO2 (GDC) electrolytes without pre-sintering at high temperatures. The polarization induced interface has smaller contact marks due to the much finer grain size of the as-prepared LSM electrodes. Detailed electrochemical impedance studies indicate that both thermally and polarization induced LSM/YSZ interfaces show comparable electrocatalytic activity and behaviour for the oxygen reduction reaction with similar activation energies. The present study clearly demonstrates the formation of effective electrode/electrolyte interfaces in SOFCs under the influence of cathodic polarization without high temperature sintering steps.

Synthesis and Characterization of Doped ZnO Photocatalysts

Zinc oxide (ZnO) is a semiconductor material with a direct band-gap energy of approximately 3.2 eV. As a result, irradiation of ZnO with sufficiently energetic ultraviolet (UV) light results in the promotion of electrons to the conduction band and the consequent formation of holes in the valence band. These photogenerated charge carriers can subsequently migrate to the surface of the ZnO and initiate redox reactions with absorbed molecules in a process known as heterogeneous photocatalysis [1].

Synthesis of Nanocrystalline Yttrium Oxide Powders by Mechanochemical Processing

Mechanochemical processing of an yttrium carbonate hydrate precursor has been used to manufacture nanocrystalline powders of yttrium oxide. The first stage of processing involved high-energy ball milling of the precursor with sodium chloride, which resulted in the progressive disintegration of the carbonate particles and their dispersion into the salt matrix. Heat treatment of the as-milled powder was then used to decompose the yttrium carbonate particles to yttrium oxide. The sodium chloride matrix phase effectively separated the yttrium oxide powder particles during heat treatment, thus allowing retention of the nanocrystalline grain structure that was developed during milling. Subsequent washing with deionised water was then used to recover a nanocrystalline yttrium oxide powder by removing the sodium chloride salt matrix. The average particle and crystallite size of the final washed powder was found to decrease with milling time down to approximately 20 nm following 360 minutes of milling.

Synthesis and Photocatalytic Activity of Doped Zinc Oxide Nanoparticles

In this study, we have investigated the effect of doping with cobalt and manganese oxide on the photocatalytic activity of nanoparticulate zinc oxide. Zinc oxide powders with controlled particle size, minimal agglomeration, and controlled chemical composition were manufactured by mechanochemical processing. The photocatalytic activity of the powders was measured using the spin trapping technique with electron paramagnetic resonance spectroscopy. It was found that the addition of cobalt oxide decreased the yield of photogenerated hydroxyl radicals. In contrast, doping with manganese oxide was found to substantially increase the rate of radical production.