Papers by Keyword: Gas Diffusion Layer

Abstract: The gas diffusion layer (GDL) is a crucial component of Proton Exchange Membrane Fuel Cells (PEMFC), water flooding will occur during the operation of PEMFC, resulting in performance degradation, and its water management plays a significant role in PEMFC performance. To investigate the transport mechanism of liquid water in GDL, the lattice Boltzmann method to simulate the behavior of GDL droplets using the 'random reconstruction' method. The accuracy of this model by calculating the tortuosity and comparing it with reported results in literature. The effects of different GDL structural parameters on permeability were studied. Finally, the conductivity and thermal conductivity of the GDL in various directions were examined. The results indicate that the porosity error of the three-dimensional structure model of GDL is within 0.01, enabling a realistic simulation of the GDL structure. The average error between the calculated results and the Bruggeman equation is only 2.5362%, and the average error compared to the reference results is less than 6%, demonstrating the model's high accuracy. As the porosity and fiber diameter of the GDL three-dimensional structure model increase, the permeability also increases. Conversely, the permeability decreases with an increase in the thickness of the GDL three-dimensional structure model. Moreover, an increase in GDL porosity leads to a gradual decrease in electrical conductivity and thermal conductivity in both the thickness and plane directions, with a more pronounced effect on the thickness. This study uncovers the transport characteristics of liquid water in the gas diffusion layer, which can inform the optimization of GDL structure design and serve as a theoretical reference for enhancing water management in proton exchange membrane fuel cells. Future research directions will focus on further optimizing the three-dimensional structure of GDL to improve its transmission characteristics and overall performance.

Abstract: Gas diffusion media (GDM) is an integral part of all gas diffusion electrodes because it facilitates both the transport of reactants to the electrocatalyst surface and the removal of reaction products from the system. Proper reactant/product distribution is critical for high power operation in polymer electrolyte fuel cells (PEMFCs) because oxygen transport and water rejection determine the maximum current density that can be obtained from PEMFCs. This paper will discuss NRL’s research on how GDM morphology influences cell performance in both closed-cathode fuel cell and open-cathode fuel cell designs. The comprehensive study linking the influence of compression on the GDM micro and macro structure morphology will be presented using micro X-ray computed tomography (μ-CT), scanning electron microscopy (SEM), N₂ Physisorption (BET) and traditional electrochemical characterization techniques (CV, Pol. Curves, etc.). Optimal GDM selection for the challenge of open-cathode operation will be presented and related to water retention through rational morphology selection. The relationship between high power performance and water transport will be elucidated and the goals for future GDM properties will be proposed for use in unmanned systems

Abstract: Both assembly force and temperature play an important role in the proton exchange membrane (PEM) fuel cell performance. In this paper, contact pressure between bipolar plate and gas diffusion layer (GDL) in a PEM fuel cell under various assembly forces and at different temperatures was studied numerically. Considering the coupling effects of assembly force and operating temperature on contact pressure, a three-dimensional finite element model of the PEM fuel cell was established and the contact pressure between the GDL and the bipolar plate was studied using commercial code ABAQUS. In order to verify the simulated results, the experimental study was conducted to investigate the contact pressure distribution between the bipolar plate and the GDL. The experimental results are in good agreement with the finite element method (FEM) results. The simulated and experimental results reveal that the contact pressure increased with the increase of assembly force and temperature. It is found that the contact pressure distribution between the bipolar plate and the GDL had the best uniformity under the applied torque of 3.0N·m and at the operating temperature of 80 °C in this work.

Abstract: The performance of proton exchange membrane fuel cell is greatly influenced by the presence, distribution and transport of liquid water in the gas diffusion layer (GDL). In this study, air-water flow in a 3D GDL microstructure along the in-plane direction is studied numerically by using the volume of fluid (VOF) method. The GDL microstructure is considered initially filled with water, air flows into the structure under the driving force of a set pressure drop and the flow is supported by the capillary pressure due to the hydrophobic nature of the GDL structure. It is found that water removal can be accelerated by improving pressure drop. Pressure drop has little influence on the state-steady water volume fraction when the pressure drop is over a critical value.

Abstract: Assembly pressure plays an important role in the factors affecting the performance of a PEM fuel cell. An insufficient clamping pressure may cause large contact resistance and thus lower the cell performance. On the other hand, over-clamping may reduce the porosity and permeability of the gas diffusion layer (GDL) and also result in poor cell performance. Therefore, it is very important to determine the proper assembly pressure for obtaining optimal performance. In this study, we design a special test fixture to evaluate the effect of assembly pressure on the performance of a PEM fuel cell. Without disassembling the fuel cell, the clamping pressure can be adjusted in situ to measure the cell performance directly and precisely. The unique single cell design eliminates the influence of gasket around the membrane electrode assembly (MEA) and makes it possible to estimate the compression effect of GDL independently. Three different types of carbon paper are used in the experiments as the GDLs. The variations of water contact angle, gas permeability, and in-plane electrical resistivity with the assembly pressure are also measured to explore the effects of assembly pressure on these physical properties. The results show that an optimal assembly pressure is always observed in each case, indicating an adequate compression on GDL is quite necessary for fuel cells.

Abstract: The main compound of natural fibers is a hydrocarbon. The heating of hydrocarbon in inert gas produces charcoal or carbon. Carbon materials are widely used for several purposes depending on the physical and electric properties, for example for hydrogen storage, conductive or reinforced plastics, catalyst supports, batteries and fuel cells. The main raw material of Gas diffusion Layer (GDL) of the Proton Exchange Membrane Fuel Cell (PEMFC) is a carbon. The properties of GDL are porous and electron-conductive material, because of the function of GDL is to distribute the gas as fuel and electricity conductors. This study aims to analyze the carbon fibers made from coconut fibers for the application of GDL materials. The carbon fiber was made using pyrolysis process in the inert gas (nitrogen) at a certain temperature according to the analysis of Differential Thermal Analysis (DTA) 3000C, 4000C, 5000C, 6000C, and 9000C. The crystalstructure, carbon content, powder density and morphology of carbon fibers were observed using X-Ray Diffraction (XRD), fixed carbon according to ASTM D 1762-64, Archimedes method (BS 19202 Part 1A), and Scanning Electron Microscope (SEM), respectively. The results showed that the structure of carbon was amorphous, and content of 51% ̶ 71%, powder density of 0.42g/cm3 ̶ 0.71g/cm3. The morphology having many parallel hollows like a tube that are close to each other with diameters of 2m ̶ 10m, and in the wall of tube there are some porous with sizes around 1m. According to this analysis, the coconut carbon fiber enables to be applied as candidate for a basic material of GDL.

Abstract: Carbon fiber paper was modified by adding carbon nanotubes to make it reach the demand of gas diffusion layer (GDL) by the process of impregnation with phenolic resin solution dispersed with carbon nanotubes, molding, and carbonization. The properties of modified carbon fiber paper, thickness, density, porosity, gas permeability, specific resistance and tensile strength, were characterized. The results indicate that surface treatment is helpful to disperse carbon nanotubes in phenolic resin. Phenolic resin is used to bond the carbon fibers, and carbon nanotube could reduce the specific resistance of the carbon fiber paper. When carbon nanotube content is 5 %, modified carbon fiber paper is prepared with thickness of 0.30 mm, density of 0.43 g/cm3, porosity of 77 %, gas permeability of 2400 mL•mm/(cm2•h•mmAq), specific resistance of 0.020 Ω•cm and tensile strength of 15 MPa, which basically qualifies for the application requirement.

Abstract: Fuel cells, as devices for direct conversion of the chemical energy of a fuel into electricity by electrochemical reactions, are among the key enabling technologies for the transition to a hydrogen-based economy. Among the various types of fuel cells, polymer electrolyte membrane fuel cells (PEMFCs) are considered to be at the forefront for commercialization for portable and transportation applications because of their high energy conversion efficiency and low pollutant emission. Cost and durability of PEMFCs are the two major challenges that need to be addressed to facilitate their commercialization. The properties of the membrane electrode assembly (MEA) have a direct impact on both cost and durability of a PEMFC. An overview is presented on the key components of the PEMFC MEA. The success of the MEA and thereby PEMFC technology is believed to depend largely on two key materials: the membrane and the electro-catalyst. These two key materials are directly linked to the major challenges faced in PEMFC, namely, the performance, and cost. Concerted efforts are conducted globally for the past couple of decades to address these challenges. This chapter aims to provide the reader an overview of the major research findings to date on the key components of a PEMFC MEA.

Abstract: MEMS technology requires low cost techniques to permit large scale fabrication for production. Porous silicon (PS) can be used in different manner to replace standard expensive etching techniques like DRIE (Deep Reactive Ion Etching). To perform same process quality as the latter, one need to understand how different parameters can influence porous silicon properties. We investigate here local formation of macroporous silicon on 2D and 3D silicon substrates. The blank substrate is a low doped (26–33 Ω cm) n type 6 inches silicon wafer. Then, an in situ phosphorus-doped polycrystalline silicon (N+ Poly-Si) is deposited on a thermal oxide layer to delimit the regions to be etched. Porous silicon is obtained afterwards using electrochemical anodization in a hydrofluoric acid (HF) solution. The effect of the temperature process on Si-HF electrochemical system voltamperometric curves, macropores morphology and electrochemical etch rates is more specifically studied. Moreover, permeation of porous substrates to hydrogen is studied after various anodization post-treatments such as KOH and HF wet etching or after a thin gold layer deposition used as current collector in micro fuel cells.

Abstract: A Gas Diffusion Layer (GDL) is a sandwiched conductive and porous material interposed between the catalyst layer and the bipolar plates in a Proton Exchange Membrane Fuel Cell (PEMFC) . This electrode substrate is a multi-functional material with several properties. All these requirements are best met by carbon fibres based materials, woven carbon or paper. In this work, the attention is focused on a new family of GDL which are produced by an Italian company, SAATIgroup. In particular a new class of carbon cloth with different surface treatments have been considered: a sample without surface treatment, a samples with a plasma treatments and a sample coated with PTFE. All these GDLs were coated with a microporous layer (MPL) to optimize the water management and the ultimate electrochemical performance of a PEM. The morphological and electrical characterization of all the samples was carried out by means of different techniques. Moreover, as the aim of this work was to study the effects of gas and water transportation on cell performance by applying MPLs, fuel cell tests have been conducted to relate their characteristics to the polarization curves.