Papers by Author: Shuo Jen Lee

Abstract: Micro-arc oxidation (MAO) is known as a novel technique to use for the modifying the surface of valve metal, which improve mechanical and corrosion resistance properties. In this study, MAO coatings are fabricated on ALZ magnesium lithium alloy to protect the substrate from corrosion using environmentally friendly electrolytes under a high voltage power supply. The Taguchi method is used to identify the effects of current density, coating time and electrical frequency on the thickest coating uniformity. The optimum coating properties are characterized by coating thickness measurement, Scanning electron microscopy (SEM), Potentiodynamic polarization analysis. It was found that the processing time is the main factor affecting the thickest coating uniformity (t_u). Coatings fabricated under optimum conditions are in close agreement with the predicted values of Taguchi analysis. The corrosion resistance of MAO coated on ALZ magnesium lithium alloy are greatly improved compare to the bare alloy in corrosive environments.

Abstract: In recent years, the development of fuel cells has proceeded rapidly, and so the reforming of methanol to produce hydrogen has become a serious problem. Supplying hydrogen from a micro methanol reformer to fuel cells is an important topic. The structure of a micro flow channel must support the transfer of external heat to the reform reaction, facilitating the diffusion of methanol vapor into the catalyst layer, increasing the rate of transfer of hydrogen. In this investigation, the micro-electro-mechanical systems (MEMS) technique is utilized to fabricate micro pressure, temperature and flow sensors. Polyimide film (PI) exhibits high temperature resistance and stress corrosion resistance, and is adopted herein as a flexible substrate. In future work, such micro sensors will be embedded in a micro methanol reformer for in-situ diagnosis.

Abstract: A lot of flow channels should be processed on stainless steel bipolar plates of fuel cell. In order to increase contact area of gas with electrode and ensure the gas flowing smoothly, the flow channels will be multichannel maze. It is difficult to be machined by conventional methods, because the width and depth of the flow channels are very small (about 300μm). When using micro electrochemical machining, flow channels with low surface roughness and good machining accuracy could be produced efficiently. The machining cathode tool, fixture, μ-second grade pulse power supply and machining parameters are introduced. Using microsecond pulse current processing, the maze-shaped flow channel on bipolar plates of fuel cell can be processed seccessfully, with high efficiency and good quality. Thus graphite bipolar plates may be replaced by metal bipolar plates. It may promote the technology advancing for fuel cell, and reducing its cost. Key factors for influencing electrochemical machining process of flow Channels on bipolar plates include the design of cathode and fixture , microsecond pulse current, and suited technical parameters

Abstract: In this study, the parametric effects of the EMM process were studied by both numerical simulation and experimental tests. The numerical simulation was performed using commercial software, FEMLAB, to establish a multi-physics model which consists of electrical field, convection and diffusion phenomena to simulate the parametric effects of pulse rate, pulse duty, electrode gap and inflow velocity. From the simulated results, the relationship between parameters and the distribution of metal removal could be established. Proper process variables were also chosen to conduct the EMM experiments. After the experiments, the profile of the processed rectangular slot was measured by a Keyence digital microscope. Comparing profile of the processed rectangular slot with the profile of the cathode, the machining accuracy of EMM process could be determined. It could also verify the efficacy of the multi-physics model for predicting machining accuracy. From this study, the effects of parameters such as pulse rate, pulse duty, electrode gap and inflow velocity are better understood. The simulation model could be employed as a predictive tool to provide optimal parameters for better machining accuracy and process stability of the EMM process.

Abstract: Due to lack of desirable mechanical properties of silicon substrate; the current trend of micro-fabrication technology is towards metallic materials. In this study, the electrochemical micromachining (EMM) technology is developed to fabricate micro-scale flow channels on thin metallic 316L stainless steel plate. The cathode electrode, the tool, is the mirror image of flow channels. It was produced by the MEMS and UV-LIGA technology and the size is 200μm in width and 500μm in height for the intension to fabricate a serpentine flow channel of 200μm in both depth and width. Because of the electrode size, the process control parameters and geometrical features surpassed conventional and CMOS methods. The flow channels on 0.6mm thick SS 316L plates were fabricated by EMM process within 30 seconds with effective area of 625mm2. The dimensions of flow channel were varying from 1504m to 5004m in width and about 2004m in depth. The results demonstrate the EMM technology produces good quality metallic flow channels efficiently.

Abstract: The fuel cell has the potential to become an indispensable source of electric power. However, some problems have not yet been resolved. Measuring the temperature and humidity inside the fuel cells is currently difficult. Accordingly, in this study, micro sensors were fabricated within the fuel cell, in which the temperature and humidity distributions were measured. The substrate of the fuel cell was made of stainless steel (SS-304) and etching was employed to fabricate the channel on the stainless steel substrate. Then micro-electro-mechanical-systems (MEMS) technology was used to fabricate the array micro temperature and humidity sensors on the rib of channel of stainless steel. The advantages of array micro temperature sensors are their small volume, their high accuracy, their short response time, the simplicity of their fabrication, their mass production and their ability to measure the temperature at a precise location more effectively than the traditional thermocouple. The micro humidity sensors were made from gold and titanium as down and up electrodes in the channel. The performance curve of the single cell was operating at 41.54 °C and gas flow rates of H2/O2 at 200/200ml/min. The max power density of the bipolar with micro sensor was 56 mW/cm2.

Abstract: The temperature and humidity conditions of a membrane electrode assembly (MEA) determine the performance of fuel cells. The volume of traditional temperature and humidity sensors is too large to allow them to be used to measure the distribution of temperature and humidity in the MEA of fuel cells. Measurements cannot necessarily be made where required. They measure only the temperature and humidity distribution outside the fuel cells and yield results with errors that exceed those of measurements made in MEA. Therefore, in this study, micro-electro-mechanical-systems (MEMS) fabrication technology was employed to fabricate an array of micro sensors to monitor in situ the temperature and humidity distributions within the MEA of fuel cells. In this investigation, an array of micro temperature and humidity sensors was made from gold on the MEA. The advantages of array micro gold temperature and humidity sensors are their small volume, which enable them to be placed on MEA and their high sensitivity and accuracy. The dimensions of the temperature and humidity sensors are 180μm × 180μm and 180μm × 220μm, respectively. The experiment involves temperatures from 30 to 100 °C. The resistance varied from 23.084 to 28.196 /. The experimental results reveal that the temperature is almost linearly related to the resistance and the accuracy and sensitivity are less than 0.3 °C and 3.2×10-3/°C, respectively. The humidity sensor showed that the capacitance changed from 15.76 to 17.95 pF, the relative humidity from 20 to 95 %RH, and the accuracy and sensitivity were less than 0.25 %RH and 0.03 pF/%RH.

Abstract: This investigation utilizes porous silicon as the gas diffusion layer (GDL) in a micro fuel cell. Pt catalyst is deposited on the surface of, and inside the porous silicon, to improve the performance of a fuel cell, and the Pt metal that remains on the rib is used to form a micro thermal sensor in a single lithographic process. Porous silicon with Pt catalyst replaces traditional GDL, and the relationships between porosity and pore diameter, and the performance of the fuel cell are discussed. In this work, electrochemical etching technology is employed to form porous silicon to replace the gas diffusion layer of a fuel cell. This work focuses on porous silicon with dimensions of tens of micrometers. Porous silicon was applied to the gas diffusion layer of a micro fuel cell. Boron-doped 20 '-cm n-type (100)-oriented doubly polished silicon wafer was used on both sides. The process is performed to etch a fuel channel on one side of a silicon wafer, and then electrochemical etching was adopted to form porous silicon on the other side to fabricate one silicon wafer that combines porous silicon with a fuel channel on a silicon wafer to minimize a fuel cell. The principles on which the method is based, the details of fabrication flows, the set-up and the experimental results are all presented.

Abstract: With advances in micro fuel cell development, the production of hydrogen for micro reformer has become increasingly important. However, some problems regarding the micro reformer are yet to be resolved. These include reducing the size, reducing the quantity of CO and combining the fuel cell, among others. Accordingly, in this investigation, a micro temperature sensor and a heater are combined inside a stainless steel-based micro reformer to measure and control the temperature and thus improve performance and minimize the concentration of CO. In this work, micro-electro-mechanical-systems (MEMS) of the micro channel type are fabricated on a stainless steel substrate to enhance the methanol conversion ratio. The micro temperature sensor and heater are made of gold and placed inside the micro reformer. Although the micro temperature sensor and heater have already been used to measure and control temperature in numerous fields, they have not been employed in micro reformer and commercial products. Therefore, this study presents a new approach for integrating a micro temperature sensor and heater in a stainless steel-based micro reformer to minimize the size and improve performance.

Abstract: With advances in micro fuel cell development, the production of hydrogen for micro reformer has become increasingly important. However, some problems regarding the micro reformer are yet to be resolved. These include reducing the size, reducing the quantity of CO and combining the fuel cell, among others. Accordingly, in this investigation, array micro temperature sensors and heaters were combined within a silicon-based micro reformer to measure and control the temperature and thus improve performance and minimize the concentration of CO. In this work, micro-electro-mechanical-systems (MEMS) of the micro channel type were fabricated on a silicon substrate to enhance the methanol conversion ratio. Array micro temperature sensors and heaters were made of platinum and placed inside the micro reformer. Although the micro temperature sensor and heater have already been used to measure and control temperature in numerous fields, they have not been employed in micro reformer and commercial products. Therefore, this study presents a new approach for combining array micro temperature sensors and heaters within a silicon-based micro reformer to minimize the size and improve performance.