Yu-Ming Lee

The Surface Morphology Effects of a Metallic Bipolar Plate on the Interfacial Contact Resistance of a Proton Exchange Membrane Fuel Cell

This article presents a fundamental study of the surface morphology effects of a metallic bipolar plate on interfacial contact resistance using both finite element method (FEM) analysis and experimental tests. The surface texture of a metallic bipolar plate is treated both chemically and mechanically. Both these treatments are used to increase the surface roughness of the metallic bipolar plate. The results show that the interfacial contact resistance is strongly related to the interfacial variations in the contact area. The FEM analysis indicates that when the surface roughness is above 8 μm, the interfacial contact area is 2.5 times larger than in the cell with an untreated bipolar plate. In addition, the experimental tests show that the contact resistance reduces significantly by approximately 65% when the surface roughness is above 10 μm. The single cell performance tests show that the current density of the treated cell increases by 17% over that of the untreated cell. Furthermore, the ohmic losses of the treated cell are lower than those of the untreated cell. This shows that the mass transport losses of a cell can be reduced by the rough surface of the bipolar plate, especially in the rib area.

In situ monitoring of temperature using flexible micro temperature sensors inside polymer lithium-ion battery

Polymer lithium-ion batteries must rapidly charge and discharge, rapidly increasing their inner temperature. This heating raises a safety issue. Therefore, a flexible micro temperature sensor for the in-situ monitoring of temperature within a polymer lithium-ion battery must be developed. Traditional thermocouples are too large to be used to measure temperature inside polymer lithium-ion batteries. In this study, a novel method for the in situ monitoring of temperature inside a polymer lithium-ion battery involves flexible micro temperature sensors. Temperature is successfully measured in situ using flexible micro temperature sensor.

Local Area Water Removal Analysis of a Proton Exchange Membrane Fuel Cell under Gas Purge Conditions

In this study, local area water content distribution under various gas purging conditions are experimentally analyzed for the first time. The local high frequency resistance (HFR) is measured using novel micro sensors. The results reveal that the liquid water removal rate in a membrane electrode assembly (MEA) is non-uniform. In the under-the-channel area, the removal of liquid water is governed by both convective and diffusive flux of the through-plane drying. Thus, almost all of the liquid water is removed within 30 s of purging with gas. However, liquid water that is stored in the under-the-rib area is not easy to remove during 1 min of gas purging. Therefore, the re-hydration of the membrane by internal diffusive flux is faster than that in the under-the-channel area. Consequently, local fuel starvation and membrane degradation can degrade the performance of a fuel cell that is started from cold.

Integrated flexible micro pressure, temperature and flow sensors for use in pemfc

Temperature, flow and pressure are critical parameters that influence the performance of fuel cells, in terms of potential, current and power density, for example. Hence, the monitoring of non-uniform temperature/flow rate/pressure within a proton exchange membrane fuel cell (PEMFC) is crucial. To prevent degradation of the performance of a PEMFC, the size of sensors is reduced herein to a μm scale using micro-electro-mechanical systems (MEMS). Integrated flexible micro sensors were fabricated and embedded in a PEMFC to measure local pressure, temperature, and flow rate. The temperatures upstream and downstream of the PEMFC were respectively 64.8°C and 64.7°C at RH50% and 0.1 A/cm2, and 62.7°C and 64.3°C at RH100% and 0.1 A/cm2.

The Resistive Properties of Proton Exchange Membrane Fuel Cells With Stainless Steel Bipolar Plates

In this research, electrochemical impedance spectroscopy is employed to monitor the resistance of a fuel cell during operation with different operating conditions and different materials for the bipolar plates. The operating condition variables are cell humidity, pure oxygen or air as oxidizer, and current density. Three groups of single cells were tested: a graphite cell, a stainless steel cell (treated and original), and a thin, small, treated stainless steel cell. A treated cell here means using an electrochemical treatment to improve bipolar plate anticorrosion capability. From the results, the ohmic resistance of a fully humidified treated stainless steel fuel cell is 0.28 Ω cm 2 . Under the same operating conditions, the ohmic resistance of the graphite and the original fuel cell are each 0.1 Ω cm 2 and that of the small treated cell is 0.3 Ω cm 2 . Cell humidity has a greater influence on resistance than does the choice of oxidizer; furthermore, resistance variation due to humidity effects is more serious with air support. From the above results, fuel cells fundamental phenomenon such as ohmic resistance, charge transfer resistance, and mass transport resistance under different operating conditions could be evaluated.

Integration of micro temperature sensor and metal foil as gas diffusion layer for micro fuel cell

Fuel cells will be applied extensively in the future as renewable energy sources, explaining why a considerable amount of research has addressed this topic. However, among the various problems encountered in the mass production of fuel cells that have yet to be solved include those associated with the bipolar plate, flow channel, catalyst, membrane electrode assembly (MEA), gas diffusion layer (GDL) and components. Given the present non-uniformity of gas reactions and the difficulty of measuring the temperature in a fuel cell, this study employs micro-electro-mechanical-systems (MEMS) to integrate a micro temperature sensor and a stainless steel foil as a gas diffusion layer. Experimental results reveal that the micro temperature sensor had an accuracy and sensitivity of 0.5°C and 2.7×10−3/°C, respectively.

An Electrolyte Soaking And Thermal Shock Test Of Microtemperature And Voltage Sensors

The safety issue of lithium battery has gained importance in recent years. The micro-electro-mechanical systems (MEMS) technology is used to fabricate microsensors, which are embedded in lithium battery for in situ monitoring of temperature and voltage. This information in lithium battery is picked up to improve safety. Lithium batteries have a harsh internal environment, which makes measurement difficult. For example, electrolyte and heat can diminish accuracy in microsensors or even cause them to crash. This work used electrolyte soaking test and thermal shock test to simulate the inner environment of a lithium battery. The comparison of calibration curve before and after tests shows repeatability and a highly linear relationship, which proves the strength that the microsensor can sustain in harsh environment.

Surface Treated SS304 Stainless Steel Bipolar Plates: Its Properties and Single Cell Performance

In this paper, a thin SS304 stainless steel is chosen as metallic bipolar plate. In order to improve the surface qualities, such as anticorrosion capability, surface roughness, and clearness, the surface of bipolar plate is treated by an electropolishing technology. From the results of corrosion and potentionstatic tests, the corrosion rate and corrosion current of treated plate are much improved. The corrosion rate and corrosion current are reduced to 0.037 mmPY and 3.56 μA cm−2. The cell performance tests show the peak power of treated cell is lower than original cell. However, for the long term tests, the cell with treated plate has a more stable power output. The results show that the treated plate has a good potential for using in the fuel cell.

A Novel Method for Measuring the Temperature Distribution Within the Fuel Cell Using Array Micro Sensors

The fuel cell has the potential to become an important source of electric power. However, measuring the temperature inside the fuel cell is difficult. Hence, in this investigation, array of micro sensors are set up inside a fuel cell to measure the temperature distribution. The substrate of the bipolar plate in a fuel cell is made of stainless steel (SS-316) and the electroforming technique is implemented to fabricate channels in the stainless steel substrate. Then NEMS (Micro-Electro-Mechanical Systems) technologies are employed to fabricate the platinum temperature sensor on the rib of a channel of stainless steel. The major advantages of array micro platinum temperature sensors are their small volume, high accuracy, short response time, simplicity in their fabrication, their mass production and ability to measure the temperature precisely and more effectively than a traditional thermocouple. The stainless steel bipolar plate is a good conductor of electric and heat. It has high mechanical strength and is non-porous. The graphite bipolar plate does not have such extensive advantages. This work electroforms a channel on stainless steel and then fabricates an array of micro temperature sensors on the rib of the channel. It is used to measure the temperature distribution at all locations in a fuel cell with a metallic bipolar plate. In the experiment, the temperature- is measured from 31 to 80 degrees Celsius and its resistance range from 0.593 to 0.649 ohm. The experimental results demonstrate that the temperature was almost linearly related to the resistance and the accuracy and sensitivity are under 1 degrees Celsius and 1.85×10−3 over degrees Celsius, respectively.© 2006 ASME