Effect of the micro porous layer design on the dynamic performance of a proton exchange membrane fuel cell

The mass transport characteristics of a gas diffusion layer (GDL) predominantly affect the performance of a proton exchange membrane (PEM) fuel cell. However, studies examining the transient response related to the GDL are insufficient, although the dynamic behavior of a PEM fuel cell is an important issue. In this study, the effects of the design of a micro porous layer (MPL) on the transient response of a PEM fuel cell are investigated. The MPL slurry density and multiple functional layers are treated as the variable design parameter. The results show that the transient response is determined by the capillary pressure gradient through the GDL. The trade-off relation for the PEM fuel cell performance under low and high humidity conditions due to the hydrophobic GDL is mitigated by designing a reverse capillary pressure gradient in the MPL.     

Experimental study on carbon corrosion of the gas diffusion layer in polymer electrolyte membrane fuel cells

Generally, the GDL of a PEM fuel cell experiences three external attacks: dissolution of water, erosion of gas flow, and corrosion of electric potential. Of these degradation factors, this study focuses on the carbon corrosion of electric potential and investigates its impact through the accelerated carbon corrosion test. This study confirms that carbon corrosion occurs at the GDL, which decreases the operating fuel cell’s performance. To discover the effects of carbon corrosion, the GDL property changes are measured through various devices, including a scanning electron microscopy, a thermo gravimetric analyzer, and a tensile stress test. Carbon corrosion causes not only loss of weight and thickness but also degradation of mechanical strength in the GDL. In addition, the GDL shows serious damage in its center.     

Development of a novel hydrophobic/hydrophilic double micro porous layer for use in a cathode gas diffusion layer in PEMFC

In this study, a gas diffusion layer (GDL) was modified to improve the water management ability of a proton exchange membrane fuel cell (PEMFC). We developed a novel hydrophobic/hydrophilic double micro porous layer (MPL) that was coated on a gas diffusion backing layer (GDBL). The water management properties, vapor and water permeability, of the GDL were measured and the performance of single cells was evaluated under two different humidification conditions, R.H. 100% and 50%. The modified GDL, which contained a hydrophilic MPL in the middle of the GDL and a hydrophobic MPL on the surface, performed better than the conventional GDL, which contained only a single hydrophobic MPL, regardless of humidity, where the performance of the single cell was significantly improved under the low humidification condition. The hydrophilic MPL, which was in the middle of the modified GDL, was shown to act as an internal humidifier due to its water absorption ability as assessed by measuring the vapor and water permeability of this layer.     

Experimental study of the effect of dissolution on the gas diffusion layer in polymer electrolyte membrane fuel cells

The gas diffusion layer (GDL) is important for maintaining the performance of polymer electrolyte membrane (PEM) fuel cells, as its main function is to provide the cells with a path for fuel and water. In this study, the mechanical degradation process of the GDL was investigated using a leaching test to observe the effect of water dissolution. The amount of GDL degradation was measured using various methods, such as static contact angle measurements and scanning electron microscopy. After 2000 h of testing, the GDL showed structural damage and a loss of hydrophobicity. The carbon-paper-type GDL showed weaker characteristics than the carbon-felt-type GDL after dissolution because of the structural differences, and the fuel cell performance of the leached GDL showed a greater voltage drop than that of the fresh GDL. Contrary to what is generally believed, the hydrophobicity loss of GDL was not caused by the decomposition of polytetrafluoroethylene (PTFE).     

Study on the performance of a proton exchange membrane fuel cell related to the structure design of a gas diffusion layer substrate

Although characteristics of the gas diffusion layer (GDL) affect the performance of a proton exchange membrane fuel cell (PEMFC), mass transfer mechanisms inside the GDL and the performance of the PEMFC have not been directly correlated. To determine the design parameters of the GDL, the effects of substrate design of the GDL on performance of a PEMFC are investigated. By adding an active carbon fiber (ACF), which has a high surface area, the substrate is designed to have a different pore size structure. The results show that steady-state and transient responses are determined by capillary pressure gradient characteristics of the GDL made by pore size distribution of the substrate. The small macro-pore functions as water-retaining passage and the large macro-pore functions as water-removal passage. It is concluded that both small and large macro-pore must be present on the substrate to facilitate its function in a wide range of operating conditions.     

Analysis of transient response of a unit proton-exchange membrane fuel cell with a degraded gas diffusion layer

The transient response characteristics and durability problems of proton-exchange membrane fuel cells are important issues for the application of PEM fuel cells to automotive systems. The gas diffusion layer is the key component of the fuel cell because it directly influences the mass transport mechanism. In this study, the effects of GDL degradation on the transient response of the PEM fuel cell are systematically studied using transient response analysis under different stoichiometric ratios and humidity conditions. With GDLs aged by the accelerated stress test, the effects of hydrophobicity and structural changes due to carbon loss in the GDL on the transient response of PEM fuel cells are determined. The cell voltage is measured according to the sudden current density change. The degraded GDLs that had uneven hydrophobicity distributions cause local water flooding inside the GDL and induce lower and unstable voltage responses after load changes.     

Determination of the pore size distribution of micro porous layer in PEMFC using pore forming agents under various drying conditions

In this paper, the effect of the pore size distribution of a micro-porous layer (MPL) on the performance of polymer electrolyte membrane fuel cells (PEMFC) was investigated using self-made gas diffusion layers (GDLs) with different MPLs for which the pore size distribution was modified using pore forming agents under different drying conditions. When MPL dried at high temperature, more macro pores, approximately 1,000–20,000 nm in diameter, and less micro pores, below 100 nm, were observed relative to when MPL was dried at low temperature. Self-made GDLs were characterized by a field-emission scanning electron microscope (FE-SEM), mercury porosimetry and self-made gas permeability measurement equipment. The performance of the single cells was measured under two different humidification conditions. The results demonstrate that the optimum pore size distribution of MPL depended on the cell operating humidification condition. The MPL dried at high temperature performed better than the MPL dried at low temperature under a low humidification condition; however, MPL dried at low temperature performed better under a high humidification condition.     

Effects of microporous layer penetration ratio and substrate carbonization temperature on the performance of proton exchange membrane fuel cells

The gas diffusion layer (GDL) is composed of a microporous layer (MPL) and a substrate; this substrate is generally fabricated from carbon fiber, carbonized resin, and polytetrafluoroethylene. When the MPL penetrates deeper into the substrate, the porosity and pore size of the GDL decrease, and the tortuosity increases; this leads to a reduction in the water discharge capability of the GDL. In this study, the MPL penetration ratio over the total GDL thickness was controlled using three different substrate manufacturing methods. These manufacturing methods for preventing the MPL from penetrating deeper into the substrate were based on the carbon fiber content within the substrate, the amount of carbonized resin coating on the substrate, and the approach used for loading the MPL. Furthermore, the GDLs were manufactured at different carbonization temperatures to investigate the effects of the carbonization temperature of the substrate on the performance of the proton-exchange membrane fuel cell.