Michael Breedon

High-Temperature Anodized WO3 Nanoplatelet Films for Photosensitive Devices

Anodization at elevated temperatures in nitric acid has been used for the production of highly porous and thick tungsten trioxide nanostructured films for photosensitive device applications. The anodization process resulted in platelet crystals with thicknesses of 20-60 nm and lengths of 100-1000 nm. Maximum thicknesses of approximately 2.4 microm were obtained after 4 h of anodization at 20 V. X-ray diffraction analysis revealed that the as-prepared anodized samples contain predominantly hydrated tungstite phases depending on voltage, while films annealed at 400 degrees C for 4 h are predominantly orthorhombic WO3 phase. Photocurrent measurements revealed that the current density of the 2.4 microm nanostructured anodized film was 6 times larger than the nonanodized films. Dye-sensitized solar cells developed using these films produced 0.33 V and 0.65 mA/cm2 in open- and short-circuit conditions.

Electrowetting of superhydrophobic ZnO nanorods.

This paper reports the electrowetting properties of ZnO nanorods. These nanorods were grown on indium tin oxide (ITO) substrates using different liquid-phase deposition techniques and hydrophobized with sputtered Teflon. The surfaces display superhydrophobic properties. When the applied voltages are less than 35 V, the contact angle change is small and exhibits instant reversibility. For higher voltages, larger contact angle changes were observed. However, the surface was not reversible after removing the applied voltage and required mechanical agitation to return to its initial superhydrophobic state.

Towards chromate-free corrosion inhibitors: structure–property models for organic alternatives

Progressive restrictions on the use of toxic chromate-based corrosion inhibitors present serious technical challenges. The most critical of these is the lack of non-toxic ‘green’ alternatives that offer comparable performance, particularly on corrosion-prone aluminium alloys such as the 2000 and 7000 series. In this study we used computational modelling methods to investigate the properties of a range of small organic, potentially safer inhibitors and their interactions with technologically relevant alloy surfaces. We have generated robust and predictive computational models of corrosion inhibition for a structurally related data set of organic compounds from the literature. Our studies have correlated molecular features of the inhibitor molecules with inhibition and identified those features that have the greatest impact on experimentally determined corrosion inhibition. This information can be used to drive guided decision making for in silico or experimental screening of molecules for their corrosion inhibition efficiency, while considering more carefully their environmental consequences.

Sensing behavior of YSZ-based amperometric NO2 sensors consisting of Mn-based reference-electrode and In2O3 sensing-electrode

Yttria-stabilized zirconia (YSZ)-based amperometric NO(2) sensors comprised of an In(2)O(3) sensing-electrode (SE), a Pt counter-electrode (CE) and a Mn(2)O(3) reference-electrode (RE) in both tubular and rod geometries were fabricated and their sensing characteristics were examined. For comparative purposes, the performance of the In(2)O(3)-SE and Pt-CE were also examined against an internal Pt/air-RE. Experimental observations of tubular YSZ-based gas sensors revealed that a three-electrode system exhibited better electrical signal stability, when compared with a two-electrode system. Additionally, replacing the internal Pt/air-RE with an external Mn(2)O(3)-RE (exposed to the sample gas), was found to have a negligible effect on the gas sensing characteristics of the tubular sensor. This gas sensing equivalence indicates that Mn(2)O(3)-RE can successfully replace the Pt/air-RE in an amperometric gas sensor. Similarly, rod-type sensors utilizing an In(2)O(3)-SE and a Mn(2)O(3)-RE were observed to have almost identical NO(2) sensing characteristics to that of the tubular sensor. Furthermore, both sensors (tubular or rod geometry) exhibited a linear response to increasing NO(2) concentration in the range of 20-200 ppm at 550°C.

Construction of sensitive and selective zirconia-based CO sensors using ZnCr2O(4)-based sensing electrodes.

The carbon monoxide (CO) sensitivity of a mixed-potential-type yttria-stabilized zirconia (YSZ)-based tubular-type sensor utilizing a ZnCr(2)O(4) sensing electrode (SE) was tuned by the addition of different precious metal nanoparticles (Ag, Au, Ir, Pd, Pt, Ru and Rh; 1 wt % each) into the sensing layer. After measuring the electromotive force (emf) response of the fabricated SEs to 100 ppm of CO against a Pt/air-reference electrode (RE), the ZnCr(2)O(4)-Au nanoparticle composite electrode (ZnCr(2)O(4)(+Au)-SE) was found to give the highest response to CO. A linear dependence on the logarithm of CO concentration in the range of 20-800 ppm at an operational temperature of 550 °C under humid conditions (5 vol % water vapor) was observed. From the characterization of the ZnCr(2)O(4)(+Au)-SE, we can conclude that the engineered high response toward CO originated from the specific properties of submicrometer sized Au particles, formed via the coalescence of nanosized Au particles located on ZnCr(2)O(4) grains, during the calcining process at 1100 °C for 2 h. These particles augmented the catalytic activities of the gas-phase CO oxidation reaction in the SE layer, as well as to the anodic reaction of CO at the interface; while suppressing the cathodic reaction of O(2) at the interface. In addition, the response of the ZnCr(2)O(4)(+Au)-SE sensor toward 100 ppm of CO gradually increased throughout the 10 days of operation, and plateaued for the remainder of the month that the sensor was examined. Correlations between SEM observations and the CO sensing characteristics of the present sensor were suggestive that the sensitivity was mostly affected by the morphology of the Au particles and their catalytic activities, which were in close proximity to the ZnCr(2)O(4) grains. Furthermore, by measuring the potential difference (emf) between the ZnCr(2)O(4)(+Au) and a ZnCr(2)O(4) electrode, sensitivities to typical exhaust component gases other than CO were found to be negligible at 550 °C.

Improvement of Toluene Selectivity via the Application of an Ethanol Oxidizing Catalytic Cell Upstream of a YSZ-Based Sensor for Air Monitoring Applications

The sensing characteristics of a yttria-stabilized zirconia (YSZ)-based sensor utilizing a NiO sensing-electrode (SE) towards toluene (C7H8) and interfering gases (C3H6, H2, CO, NO2 and C2H5OH) were evaluated with a view to selective C7H8 monitoring in indoor atmospheres. The fabricated YSZ-based sensor showed preferential responses toward 480 ppb C2H5OH, rather than the target 50 ppb C7H8 at an operational temperature of 450 °C under humid conditions (RH ≃ 32%). To overcome this limitation, the catalytic activity of Cr2O3, SnO2, Fe2O3 and NiO powders were evaluated for their selective ethanol oxidation ability. Among these oxides, SnO2 was found to selectively oxidize C2H5OH, thus improving C7H8 selectivity. An inline pre-catalytic cell loaded with SnO2 powder was installed upstream of the YSZ-based sensor utilizing NiO-SE, which enabled the following excellent abilities by selectively catalyzing common interfering gases; sensitive ppb level detection of C7H8 lower than the established Japanese Guideline value; low interferences from 50 ppb C3H6, 500 ppb H2, 100 ppb CO, 40 ppb NO2, as well as 480 ppb C2H5OH. These operational characteristics are all indicative that the developed sensor may be suitable for real-time C7H8 concentration monitoring in indoor environments.

Insight into the Aging Effect on Enhancement of Hydrogen-Sensing Characteristics of a Zirconia-Based Sensor Utilizing a Zn–Ta–O-Based Sensing Electrode

A significant enhancement in the hydrogen (H2) sensitivity as well as selectivity after aging for more than 40 days has been observed for a mixed-potential-type sensor using ZnO (+84 wt % Ta2O5) as the sensing electrode (SE) and yttria-stabilized zirconia (YSZ) as the solid electrolyte. The effect of the aging process in enhancing the sensing characteristics of the sensor using ZnO (+84 wt % Ta2O5)-SE was studied here by investigating the changes in the morphology, crystal structure, chemical surface state, and catalytic properties of the SE material before and after aging at 500 °C for 80 days. X-ray diffraction measurements confirmed that the crystal structure of the SE material was found to be unaffected by aging, while the morphological change observed via scanning electron microscopy imaging indicated a decrease in the porosity and an increase in the particle size after aging. A significant change, particularly in the binding energy of Ta 4f, was also observed for the SE material after long-term aging. Although the catalytic activities toward the anodic reaction of H2 and the other examined gases were moderately stable after aging, a significant decrease in the heterogeneous catalytic activity of the gas-phase reaction (oxidation) of H2 was observed. Such a trend presumably resulted in a higher fraction of H2 reaching the triple-phase boundary, where the electrochemical reactions generate a sensing signal (mixed potential), resulting in high H2 sensitivity as well as high H2 selectivity after long-term aging of the present sensor.

Pt/MoO 3 nano-flower/SiC Schottky diode based hydrogen gas sensor

In this paper, we report the development of a novel Pt/MoO 3 nano-flower/SiC Schottky diode based device for hydrogen gas sensing applications. The MoO 3 nanostructured thin films were deposited on SiC substrates via thermal evaporation. Morphological characterization of the nanostructured MoO 3 by scanning electron microscopy revealed randomly orientated thin nanoplatelets in a densely packed formation of nano-flowers with dimensions ranging from 250 nm to 1 µm. Current-voltage characteristics of the sensor were measured at temperatures from 25°C to 250°C. The sensor showed greater sensitivity in a reverse bias condition than in forward bias. Dynamic response of the sensor was investigated towards different concentrations of hydrogen gas in a synthetic air mixture at 250°C and a large voltage shift of 5.7 V was recorded upon exposure to 1% hydrogen.

Hydrogen gas sensors based on thermally evaporated nanostructured MoO 3 Schottky diode: A comparative study

In this paper, a comparative study of Pt/nanostructured MoO3/SiC Schottky diode based hydrogen gas sensors is presented. MoO3 nanostructured films with three different morphologies (nanoplatelets, nanoplatelets-nanowires and nano-flowers) were deposited on SiC by thermal evaporation. We compare the current-voltage characteristics and the dynamic response of these sensors as they are exposed to hydrogen gas at temperatures up to 250°C. Results indicate that the sensor based on MoO3 nano-flowers exhibited the highest sensitivity (in terms of a 5.79V voltage shift) towards 1% hydrogen; while the sensor based on MoO3 nanoplatelets showed the quickest response (t90%-40s).

Molecular ionization and deprotonation energies as indicators of functional coating performance

The molecular ionization and deprotonation of small organic compounds are important molecular properties which are increasingly being calculated and considered in the mechanistic justification of functional coating performance. Often, only a few molecules are examined for any given set of systems, leading to potentially spurious correlations between calculated molecular properties, and experimentally observed trends. In this study the calculated molecular ionization potential, electron affinity, fundamental gap, and deprotonation energies of 28 small organic molecules will be investigated using ab initio methods, to explore the role that in silico simulation could have in predicting the performance of a functional coating. Results will be presented with respect to an experimentally determined measure of functional coating efficacy. It will be shown that there is no apparent correlation between the experimentally determined measure of the functional coating performance and the calculated molecular properties of small organic molecules investigated in this study. These findings cast aspersions on the popularised relationship between a single molecular property and the ultimate efficacy of a functional coating.