Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

<p>The main objective of this work it to produce membrane electrode assemblies (MEAs) that have improved performance over MEAs produced by the conventional manner, by producing highly efficient, electroactive, uniform catalyst layers with lower quantities of platinum electrocatalyst. The catalyst coated membrane (CCM) method was used to prepare the MEAs for the PEM fuel cell as it has been reported that this method of MEA fabrication can improve the performance of PEM fuel cells. The MEAs performances were evaluated using polarisation studies on a single cell. A comparison of polarisation curves between CCM MEAs and MEAs produced in the conventional manner illustrated that CCM MEAs have improved performance at high current densities (&gt / 800 mA/cm2).</p>

Galvanotaxis is the movement of cells in an applied electric field. The first steps to design a chip for observations of galvanotaxic behavior of cells were done in this work. The chip is a miniaturised system of previous larger galvanotaxis systems and uses materials which are thought to be biocompatible. The system was constructed on microscope slides with a channel in PDMS with adjacent polymer electrodes. The polymer electrodes were made from poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS), glycerol and Silquest A-187. The PEDOT:PSS electrodes were connected with either an evaporated metal electrode of titanium and gold or a gold net. Systems with PEDOT:PSS are neutralised when put in excessive amount of PBS (pH=7.4) for 24 hours. The final system had a channel with dimension length=14 mm, width=0.5 mm and height=0.25 mm. PEDOT:PSS worked as an electrode material and the achieved electric field through the channel was between 55 V/m and 160 V/m with an applied voltage of 1 V. The decrease of the electric field within the first hour was between 10 % and 30%.  Further development of this system could give an easy way to observe galvanotaxic behaviour of cells or an instrument that can distinguish between different cell types.

Thesis (M. Phil.)--University of Hong Kong, 1984.

In this study, the properties of nickel and antimony doped tin oxide (NATO) electrode materials were investigated in relation to the electrochemical generation of ozone. The performance of NATO materials was correlated to ·OH radical generation and oxygen adsorption properties. Long-time ozone generation results suggested that surface property changes, including surface morphology, chemical composition and electro-catalyst thickness, could lead to ozone production rate decreased from 137 to 0 mg·h-1 and the current efficiency declined from 18% to 0. The loss of Ni in the electrode was suggested for the decrease in ozone generation. Moreover, material characterization results indicated the presence of NiOOH and multiple oxidation states of Sb (+3 and +5), which were proposed as the critical sites for the electrochemical generation of ozone. In addition, NATO nanocrystals of 3.5 ~ 7.5 nm in size prepared by the hydrothermal method were used as an alternative route to fabricate electrodes. The highest current efficiency of 41% was achieved on NATO material of 6% Sb in the precursor, which led to the lowest resistivity of 2.38 ± 0.03 Ω·cm in the product NATO material. This further demonstrated the applicability of NATO materials used as electro-catalysts for the electrochemical generation of ozone. Hydroxyl free radicals (·OH) can be regarded as one of the most important intermediates for ozone generation. The presence of ·OH radicals was quantified by fluorescence spectroscopy with terephthalic acid as probes. Quantitative analysis results showed that Ni dopant could significantly enhance ·OH generation, while over-doping of Sb and Ni can decrease the generation of ·OH radicals. An oxygen chemisorption study on NATO materials showed that more active sites available for oxygen chemisorption lead to higher catalytic activity for ozone generation. The highest oxygen chemisorption capacity of 49.76 μmol·g-1 was achieved on NATO-5 (Sn:Sb:Ni=1000:16:2), which showed the highest current efficiency of 43%. In addition, temperature programmed oxygen adsorption and desorption showed different patterns on different NATO materials. This suggested that oxygen adsorption on NATO materials has a correlation to the electrochemical generation of ozone. In addition, oxygen adsorption was further investigated with near ambient oxygen adsorption. Oxygen adsorption isotherm results indicated that both physisorption and chemisorption can occur on the surface of SnO2 based material (NATO-5) with or without hydrogen pretreatment. When NATO-5 was treated with hydrogen, adsorption was mainly in the form of chemisorption. However, it was mainly in the form of physisorption without hydrogen pretreatment. By comparing NATO-6 (Sn:Sb:Ni=1000:16:0) with NATO-7 (Sn:Sb:Ni=1000:0:2), it was found that Sb was more important in the oxygen adsorption ability of NATO materials compared to Ni doping. Based on the findings in this study, two active sites (Sb and Ni sites) were proposed for ·OH generation and oxygen adsorption in order to explain the mechanism of ozone generation on NATO materials. Also, electrochemical generation of ozone was correlated with oxygen adsorption and ·OH generation. / published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Master / Master of Philosophy

No description available.

No description available.

<p>The main objective of this work it to produce membrane electrode assemblies (MEAs) that have improved performance over MEAs produced by the conventional manner, by producing highly efficient, electroactive, uniform catalyst layers with lower quantities of platinum electrocatalyst. The catalyst coated membrane (CCM) method was used to prepare the MEAs for the PEM fuel cell as it has been reported that this method of MEA fabrication can improve the performance of PEM fuel cells. The MEAs performances were evaluated using polarisation studies on a single cell. A comparison of polarisation curves between CCM MEAs and MEAs produced in the conventional manner illustrated that CCM MEAs have improved performance at high current densities (&gt / 800 mA/cm2).</p>

No description available.