Jinzhu Tan

Degradation Characteristics of Elastomeric Gasket Materials in a Simulated PEM Fuel Cell Environment

Polymer electrolyte membrane (PEM) fuel cell stack requires gaskets and seals in each cell to keep the reactant gases (hydrogen and oxygen) within their respective regions. The stability of the gaskets/seals is critical to the operating life as well as the electrochemical performance of the fuel cell. The time-dependant chemical and mechanical degradation of two commercially available silicones-based elastomeric gasket materials in a simulated fuel cell environment was investigated in this work. Two temperatures based on actual fuel cell operation were selected and used in this study. Using optical microscopy, the topographical damage on the sample surface due to the acidic environment was revealed. Atomic adsorption spectrometer analysis shows that silicon, calcium, and magnesium were leached from the materials into the soaking solution. Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) were employed to study the surface chemistry of the elastomeric gasket materials before and after exposure to the simulated fuel cell environment over time. The ATR-FTIR and XPS test results indicate that the surface chemistry changed significantly and the chemical degradation mechanism is de-crosslinking and chain scission in the backbone. The microindentation test results show that the mechanical properties of the silicone materials changed significantly after exposure to the simulated PEM fuel cell environment over time.

Microindentation Test for Assessing the Mechanical Properties of Silicone Rubber Exposed to a Simulated Polymer Electrolyte Membrane Fuel Cell Environment

The elastomeric materials used as seals and gaskets in polymer electrolyte membrane (PEM) fuel cells are exposed to acidic environment, humid air, and hydrogen, and subjected to mechanical compressive load. The long-term mechanical and chemical stability of these materials is critical to both sealing and the electrochemical performance of the fuel cell. In this paper, mechanical degradation of two elastomeric materials, Silicone S and Silicone G, which are potential gasket materials for PEM fuel cells, was investigated. Test samples were subjected to various compressive loads to simulate the actual loading in addition to soaking in a simulated PEM fuel cell environment. Two temperatures, 80°C and 60°C, were selected and used in this study. Mechanical properties of the samples before and after exposure to the environment were studied by microindentation. Indentation load, elastic modulus, and hardness were obtained from the loading and unloading curves. Indentation deformation was studied using Hertz contact model. Dynamic mechanical analysis was conducted to verify the elastic modulus obtained by Hertz contact model. It was found that the mechanical properties of the samples changed considerably after exposure to the simulated environment over time. The temperature and the applied compressive load play a significant role in the mechanical degradation. The microindentation method is proved to provide a simple and efficient way to evaluate the mechanical properties of gasket materials.

Degradation of Gasket Materials in a Simulated Fuel Cell Environment

A Polymer Electrolyte Membrane (PEM) fuel cell stack requires elastomeric gaskets in each cell to keep the reactant gases within their respective regions. If any gasket degrades or fails, the reactant gases (O2 and H2 ) can leak overboard or mix with each other directly during operation or during standby, and affect the overall operation and performance of the fuel cell. The degradation of four commercial gasket materials was investigated in a simulated fuel cell environment in this study. In an effort towards predicting lifetime of fuel cells, two solutions and two temperatures were used in the short-term, accelerated aging tests. Bend-strip environment crack resistance tests were performed on samples with various bend angles. Weight loss was monitored and surface structure changes were examined using optical microscopy on the samples exposed to the simulated fuel cell environment for selected periods of time. Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR) spectroscopy was employed to study surface chemistry of the gasket materials before and after exposure to the simulated fuel cell environment over time. Stress and strain analysis was conducted using finite element method (FEM) to quantify the stress/state in test samples. The test results reveal that two silicone materials were degraded significantly while the other two did not show much degradation up to 42 weeks exposure to the simulated fuel cell environment. Optical microscopy and ATR-FTIR spectroscopy analysis indicate that the surface chemistry altered gradually via mechanisms involving de-cross linking and chain scission in the backbone. From experimental and numerical results, it is concluded that there is an interaction between chemistry and stress that appears to accelerate the degradation of the gasket materials in fuel cell environment.Copyright

Performance of Proton Exchange Membrane in the Presence of Mg2

Proton exchange membrane (PEM) fuel cell is regarded as one of the potential renewable energy which may provide a possible long-term solution to reduce carbon dioxide emissions, reduce fossil fuel dependency and increase energy efficiency. Even though great progress has been made, long-term stability and durability is still an issue. The contamination ion plays an important role on the electrical performance of PEM fuel cell. This paper investigates the effect of Mg2+ contamination on PEM fuel cell performance as a function of Mg2+ concentration. Two levels of Mg2+ concentration was chose. From the experimental results, it can be obtained that a significant drop in fuel cell performance occurred when Mg2+ was injected into the anode fuel stream. The voltage and power density of fuel cell decreased larger and larger with increase of Mg2+ concentration over time. The Mg2+ mainly caused the concentration polarization loss from the anode catalyst to the membrane in fuel cell.

Dynamic Mechanical Properties of Polymeric Materials Aged in PEM Fuel Cell Conditions

Gaskets/seals in PEM fuel cells are exposed to acidic, humid air, mechanical compressive pressure and cyclic temperature environment. Chemical degradation of three elastomeric gasket materials in a simulated and an aggressive accelerated fuel cell solution at 80oC up to 63 weeks was investigated in this work using dynamic mechanical analysis (DMA) which assesses the change of dynamic mechanical properties of the three material samples as they aged. The three materials tested are copolymeric resin (CR), liquid silicone rubber (LSR), and fluorosilicone rubber (FSR).