Characteristics Of Gas Diffusion Layer Research Articles

Durability analysis of polymer electrolyte membrane fuel Cell's gas diffusion layer based on distribution relaxation time analysis: Influence of the presence or absence of a micro-porous layer

The U.S. Department of Energy accelerated stress test carbon protocol emphasizes improving the durability of both the catalyst layer and the micro-porous layer (MPL) carbon support. This underscores the need for research focused solely on the degradation of the Gas Diffusion Layer (GDL). Traditionally, electrochemical impedance spectroscopy impedance data used to analyze resistance due to GDL durability has been interpreted through equivalent circuit models. However, this method simplifies simultaneous response and multiple models for the same data, which reduces the objectivity of the analysis. Therefore, this study analyzed the durability characteristics of GDLs with and without MPLs using distribution of relaxation times, a method less prone to subjectivity. In short, the results showed that substrates without MPL are more susceptible to performance degradation and loss, and highlighted the emergence of Warburg resistance due to limited diffusion under harsh environmental conditions.

Comparative study on carbon corrosion characteristics of gas diffusion layer in PEMFCs under two accelerated stress tests

As a key component of proton exchange membrane fuel cell, the durability of gas diffusion layer (GDL) is directly related to the overall life of fuel cell. Carbon corrosion is a critical factor influencing the durability of GDL, damaging its pore structure and reducing its hydrophobicity, thus affecting the internal water management of fuel cells. At present, although there are many accelerated stress testing (AST) methods for studying carbon corrosion, there is a lack of indicators between these methods to comprehensively compare and analyze the corrosion of GDL. Herein, two ASTs, i.e., steady-state durability testing at a constant-potential of 1.4 V (vs. RHE) and dynamic testing of a voltage triangular-wave of 1–1.5 V (vs. RHE), are used to assess the durability of cathode GDL. The results reveal that the variation rates of pore volume and hydrophobicity of GDL after 6000 cycles of triangular-wave AST are faster than those after 24 hours of constant-potential AST. By comparing the variation rates of oxygen mass transfer resistance and mass transfer impedance (Rmt) of GDL, it is found that the corrosion rate of triangular-wave AST is 6.75 times higher than that of constant-potential AST under the same corrosion degree.

Variation in performance and characteristics of long-term operated gas diffusion layer in a fuel cell electric vehicle

Proton-exchange membrane fuel cells (PEMFCs) operate at low temperatures and are used in household appliances and vehicles because of their high power density and fast start-up/shut-down capabilities. Previous research has focused on improving the performance of PEMFCs by enhancing their structures and constituent materials of their components. However, as PEMFCs are being commercialized, their durability remains a critical challenge that needs to be addressed. Although numerous studies have evaluated the durability of membrane electrode assemblies (MEA), limited research has been conducted on the durability of gas diffusion layers (GDL). The GDL, with its nanometer-to micrometer-sized pores and thickness of hundreds of microns, is prone to mechanical degradation during long-term operation. Moreover, the GDL is susceptible to carbon corrosion because it primarily consists of carbon materials, similar to the catalyst layer. Therefore, to ensure the performance and longevity of PEMFCs, it is of utmost importance to investigate the durability of the GDL. This study quantitatively investigates the variations in the performance and mechanical and chemical characteristics of GDLs during an extended period of operation in a fuel cell electric vehicle (FCEV), and two types of GDLs are analyzed.

An Experimental Study on the Correlation between Characteristics of Gas Diffusion Layer and Performance Depending on Relative Humidity Variation in Proton Exchange Membrane Fuel Cell

As it is well known, Gas diffusion Layer(GDL) is a fundamental element to provide more efficient water transport in Proton Exchange Membrane Fuel Cell(PEMFC). Numerous previous studies showed how important and critical GDL is in PEMFC. There have been many efforts to improve the performance of GDL, such as studies on properties, structural improvement, and hydrophobic coating on substrate and micro porous layer. Through these efforts, PEMFC has been developed and also the relationship between GDL and each component was investigated well.Relative Humidity(RH) is an important factor that affects proton conductivity and mass transport and is also an factor to be considered for water management. Although it should be relatively clear, it is necessary to compare and verify between the numerical study and experimental study since they does not always matches.In this study, the results were compared with the physical properties of each GDL based on experimental data applying GDL with different characteristics. We studied to reveal the correlation between data such as thickness, porosity, and pore distribution of GDL and I-V Polarization curve conducted by changing RH conditions to investigate performance.

Degradation mechanism analysis of substrate and microporous layer of gas diffusion layer in proton exchange membrane fuel cell

Robust electrochemical corrosion of gas diffusion layers (GDL) in proton exchange membrane fuel cell (PEMFC) could cause significant decline of cell performance. However, the detailed mechanism still remains elusive. Herein, the structural characteristics of GDL after electrochemical accelerated stress test (AST) and sequent impacts on the mass-transfer performance of membrane electrode assemblies were explored. With the electrochemical corrosion duration increasing, polytetrafluoroethylene (PTFE) peeling and carbon fibers exposure were observed on substrate layer surface, while corrosion pores were detected on microporous layer (MPL). Both substrate layer and MPL experienced significant increase in surface roughness, which was reflected in the surface and bulk resistance. Surface contact angle and water permeability threshold tests showed that surface and internal hydrophobicity of GDL degraded comprehensively. More significant carbon corrosion in MPL and PTFE loss in substrate layer were revealed by X-ray photoelectron spectroscopy and thermogravimetric analysis. Collectively, worse power density and severe ohmic and mass-transfer polarization after AST were confirmed and the oxygen mass-transfer performance was analyzed in single-cell tests. This work clearly explains the distinctive degradation mechanisms of the substrate layer and MPL and provides guidance for the design and application of GDL.

Pore Engineering in Gas Diffusion Layer of Phthalocyanine Cobalt Cathode to Promote Electrochemical CO2-to-CO Reduction

While substantial electrocatalysts have been proposed and efficiently catalyze CO2 to multiple products, mass transport is becoming a major constraint to further improve the performance of CO2 electrochemical reduction reaction (CO2ERR). Gas diffusion electrode (GDE) technique has been identified as an effective way to overcome the confined mass transfer of CO2. While many research efforts have focused on the catalyst layer (CL), considerably fewer efforts have focused on the gas diffusion layer (GDL), the support and substrate of GDE. Herein, we studied the effect of the GDL on the performance of phthalocyanine cobalt (CoPc)-based GDE to catalyze CO2 to CO with a special emphasis on the hydrophilicity, porosity, and wettability. We demonstrate a facile and reproducible method of PTFE impregnation to tune the hydrophobicity and pore characteristics of GDL, to enhance CO2ERR. Using a proper designed GDL as the substrate, the CoPc-based GDE achieves a high current density of 321.7 mA cm−2 and Faradaic efficiency for CO of 98.4% at a cathode potential of −1.2 V (vs RHE), representing the highest performance of CoPc-based GDEs reported in the literature.

Flow Characteristics of Fibrous Gas Diffusion Layers Using Machine Learning Methods

The material characteristics of gas diffusion layers are relevant for the efficient operation of polymer electrolyte fuel cells. The current state-of-the-art calculates these using transport simulations based on their micro-structures, either reconstructed or generated by means of stochastic geometry models. Such transport simulations often require high computational resources. To support material characterization using artificial-intelligence-based methods, in this study, a convolutional neural network was developed. It was trained with results from previous transport simulations and validated using five-fold cross-validation. The neural network enables the permeability of paper-type gas diffusion layers to be predicted. A stochastic arrangement of the fibers, four types of binder distributions, and compression of up to 50% are also considered. The binder type and compression level were features inherent to the material but were not the subject of the training. In this regard, they can be seen as features hidden from the training process. Nevertheless, these characteristics were reproduced with the proposed machine learning model. With a trained machine learning model, the prediction of permeability can be performed on a standard computer.

Degradation Effect of Gas Diffusion Layer on Water Transport in Polymer Electrolyte Membrane Fuel Cell

Hydrogen is converted to electric power by proton exchange membrane fuel cells (PEMFCs), which have received significant attention for transportation applications because of their high energy efficiency. In order to ensure the long-term stability, understanding about their long-term durability is essential because the operating performance deteriorates over time. Gas diffusion layers (GDLs) manage the transport of water generated from the CL during chemical reactions, and the degradation of the GDL significantly deteriorate the fuel cell performance. Compared to the fresh GDL, the water transport characteristics of GDL aged by inserting hydrogen peroxide solutions are investigated. The dynamic movement of the water meniscus inside the GDL is visualized using synchrotron X-ray imaging. Unlike the pristine GDL having snap-off patterns, water continuously transports through the degraded GDL representing the piston-like movement, and pressure fluctuations are not observed. This difference shows the change of the dominant local transport mechanisms due to GDL degradation. The temporal pressure variations are simultaneously measured, and the pressure and time at breakthrough (BT) are compared. The aged GDL exhibits a larger BT pressure and requires a longer time to achieve the first BT. Longer BT time in the degraded GDL can reflect a higher water saturation level. GDL degradation leads to the loss of polytetrafluoroethylene (PTFE) which is commonly treated to ensure efficient mass transport by restraining water clogging in the GDL pores due to the increase of hydrophobicity. Despite the reduction in hydrophobicity, The PTFE loss can increase BT pressure by reducing the pore size and the actual path length of the water flow. The increase in the BT time and BT pressure, as well as continuous transport, can disrupt fuel supply to chemical reaction sites, thereby deteriorating the PEMFC performance. This study provides a comprehensive understanding of the effect of GDL degradation on mass transport in PEMFCs. Figure 1

Intelligent optimization of clamping design of PEM fuel cell stack for high consistency and uniformity of contact pressure

ABSTRACT In the proton exchange membrane fuel cell (PEMFC), the uneven distribution of contact pressure on the gas diffusion layer (GDL) will lead to the increase in local contact voltage, thus increasing the ohmic loss of the stack, and will affect the porosity to change the reaction gas concentration. Therefore, it is essential to optimize the consistency and uniformity of contact pressure. In this paper, the bolt-encapsulated different scale stack models are established. The influence of the cell number on the distribution characteristics of the contact pressure on the outermost and innermost GDLs in different stacks is discussed. According to the GDL contact pressure distribution characteristics in the 6-stack, it is found that it can be used as the data extraction model for optimizing the clamping condition of the 80-stack. Subsequently, the optimal Latin hypercube design is used to randomly generate 280 data sets with different clamping conditions, and a data-driven surrogate model based on the Support Vector Regression is used to predict the contact pressure distribution characteristics of GDLs in the 6-stack according to changes in clamping condition. Then, the surrogate model is taken as the fitness evaluation function in Gray Wolf Optimizer, and the clamping condition of the 80-stack is optimized, which improves the uniformity and consistency of the contact pressure distribution on the GDL by 66.67%. This paper proposes a strategy to optimize the clamping condition of large-scale stacks based on the calculation and prediction of the contact pressure distribution on the GDLs in small-scale stacks.

Microscale Investigation of the Transport Characteristics in Surface-Treated Gas Diffusion Layers with Gradient Porosities for Fuel Cell Applications

In the present study, microscale transport phenomena in gas diffusion layers (GDLs) with gradient porosities are investigated statistically. A series of GDLs are randomly generated with linear and nonlinear gradient porosities at a 95% confidence level to reflect the heterogeneous microstructures. Straight-cylindrical carbon fibers with a uniform diameter are randomly arranged layer-by-layer and then treated with various polytetrafluoroethylene (PTFE) loadings. Furthermore, the reactant transport phenomena throughout the GDLs are simulated using lattice Boltzmann method (LBM). Then, the corresponding mass transport characteristics (i.e., permeability, tortuosity, and effective diffusion coefficient) are predicted in a series of GDL samples. The predicted data reveal an inverse relationship between permeability and PTFE loading. Moreover, the results show that GDLs with gradient porosities are more favourable to the reactant gas diffusion, leading to larger permeability than those of GDLs with uniform porosities. Besides, electrical and thermal conductivities of GDLs are computed in both in-plane and through-plane directions, and show good agreement with published experimental data. These statistical results show that the microscopic transport characteristics of PTFE-treated GDLs with gradient porosities are strongly affected by porosity distribution and PTFE loading. The proposed model can be utilized to optimize GDL structures and investigate the effect of PTFE on microscale transport characteristics of GDLs.

Performance improvement for air-cooled open-cathode proton exchange membrane fuel cell with different design parameters of the gas diffusion layer

Air-cooled open-cathode LTPEMFC (AO-LTPEMFC) has been developed as a new power source for the portable power supply. The effect of the gas diffusion layer (GDL) on AO-LTPEMFC operation in challenging ambient air conditions was investigated in the present study. The effect of the content of polytetrafluoroethylene (PTFE) on the substrate layer and microporous layer (MPL), the thickness of GDL and the pulse width modulation (PWM) of the fan on cell performance as well as the cathode outlet surface temperature distribution were investigated. The polarization curves, electrochemical impedance spectroscopy (EIS) and dynamic voltage test were used to correlate the structural characteristics of GDL with heat dissipation, oxygen transport and water management in AO-LTPEMFC. The results showed that GDL with appropriate PTFE content in the substrate layer and MPL could significantly optimize cell performance. In addition, the thickness of GDL also had a certain impact on the mass and heat transfer of the fuel cell, while the water management in GDL was affected by PWM of the fan, simultaneously. Combined with the practice process, the optimum values of the substrate layer PTFE content, MPL layer PTFE content and thickness of GDL were identified to be 10%, 40%, and 200 μm, respectively.

Characterization of Effective In-Plane Electrical Resistivity of a Gas Diffusion Layer in Polymer Electrolyte Membrane Fuel Cells through Freeze–Thaw Thermal Cycles

The electrical property of gas diffusion layers (GDLs) plays a significant role in influencing the overall performance of polymer electrolyte membrane fuel cells (PEMFCs). The electrical degradation performance of GDLs has not been reported sufficiently. Understanding the electrical degradation characteristics of GDLs is vital to better fuel cell performance, higher efficiency, and longer service time. This paper investigated the effective in-plane electrical resistivity of a commercial GDL by considering environmental and assembly conditions similar to those in use for the operation of PEMFCs. The effective in-plane electrical resistivity of the GDL, subjected to a series of freeze–thaw thermal cycles, was characterized to study its progressive electrical degradation with thermal cycles. Experimental results indicated that, under low compressive loads, the effective in-plane electrical resistivity of the commercial GDL showed weak anisotropy, and was greatly influenced by the transformation of carbon fiber connection in the porous layer. In particular, the thermal aging treatment on the GDL through the first 100 freeze–thaw cycles contributed a lot to its in-plane electrical degradation performance.

An experimental investigation of three-dimensional mechanical characteristics of gas diffusion layers in proton electrolyte membrane fuel cells

In this study, three-dimensional (3D) orthotropic mechanical properties of a commercial gas diffusion layer (GDL) are experimentally investigated. Although GDL is an important 3D structural membrane in proton electrolyte membrane fuel cells (PEMFCs), most papers have merely considered its in-plane linear isotropic characteristics due to the lack of 3D anisotropic mechanical performance investigation. In real operating PEMFCs, GDL is nonlinear orthotropic composite and its mechanical characteristics affect the overall performance of PEMFCs, seriously and directly. In this research, as considering GDL’s valid configuration in PEMFCs, mechanical tests such as compression test, tension test, and shear test are conducted to study its 3D mechanical behavior. Test results present that the GDL behaves in an orthotropic and nonlinear manner. In addition, microstructures of the GDL are observed through scanning electron microscope (SEM) images, to explain its different kinds of mechanical failure performance.

Study on the characteristics of GDL with different PTFE content and its effect on the performance of PEMFC

The content of Polytetrafluoroethylene (PTFE) is the key factor to determine the hydrophobicity and heat transfer characteristics of the gas diffusion layer (GDL), which directly affects the performance of the proton exchange membrane fuel cell (PEMFC). The PTFE content of GDL materials changes due to the complex and variable working conditions and the accumulation of working hours in fuel cells. In order to study the effect of PTFE content and external load on the thermal conductivity of GDL materials, a new method based on Fiber Bragg Grating (FBG) sensing technology was proposed to measure the thermal conductivity of GDL materials. The thermal conductivity of GDL materials with different PTFE content was measured by FBG temperature sensor, and the effect of different PTFE content on the performance of fuel cell was studied. The experimental results show that the hydrophobicity of GDL material increases with the increase of PTFE content, and different PTFE content of GDL materials have different effects on the performance of PEMFC. The difference of thermal conductivity of GDL material with different PTFE content can be measured by using FBG sensing measurement technology, which reflects the change of GDL material properties due to the difference of PTFE content in the GDL material. The results of this study provide guidance for the method of detecting the change of internal material characteristics of PEMFC.

Effect of the pore size variation in the substrate of the gas diffusion layer on water management and fuel cell performance

The gas diffusion layer (GDL) is a key component of a proton exchange membrane (PEM) fuel cell due to its role as a pathway for fuel, air, and water. GDL determines the mass balance and water management in the PEM fuel cell. Thus, an investigation of the optimal structural characteristics of the GDL with improved water management is important to ensure high performance of the PEM fuel cell. In this study, a PEM fuel cell model that considers the structural characteristics of GDL is developed, and the various the GDL structural characteristics are analyzed and validated. Specifically, the effects of pore size variation in the substrate of the GDL on water management and cell performance are investigated. Two GDL samples with different pore sizes are evaluated according to the porosity, pore size, thickness, and internal contact angle to understand the basic structural characteristics of the GDL. The GDL structural parameters with the basic characteristics are incorporated into the developed model. The cell performance is predicted to be relative to the two-phase mass transport inside the GDL. The characteristics of the micro-porous layer (MPL) and MPL penetration part are found to be affected by the variation in the macro-pore size of the substrate. The water management capability of the GDL varies with these differences with respect to water retention and removal characteristics. Under the condition of relative humidity (RH) 100%, the averaged saturation value of the MPL and MPL penetration part of the GDL with small macro-pore in the substrate is 18.8% higher than that of the GDL with large macro-pore in the substrate. The cell performance is also affected by the operating conditions of relative humidity and current load. The voltage of the GDL with small macro-pore in the substrate at the current density of 1.6A/cm2 is 10.3% lower than that of the GDL with large macro-pore in the substrate under RH 100%.

Different Methods for Determining Porosity of Gas Diffusion Layer using X-ray Microtomography

Gas diffusion layer (GDL) is a crucial component in polymer electrode membrane fuel cells. Being highly porous, this layer facilitates transport of species from the flow field to the reaction sites and vice versa. One of the main characteristics of GDLs is porosity, which has been measured using a number of different methods including 3D X-ray microtomography (μ XCT). Despite the extensive use of this technique in investigating the properties of GDLs, there are variations in the results since the surface of the three dimensional volume used to obtain the bulk porosity of GDLs is difficult to quantify. In this paper, a robust surface identification method, referred to as “Rolling Ball”, is introduced to identify systematically the surface and hence porosity of GDLs from μ XCT datasets. In this method, the diameter of the GDL carbon fiber is used as the characteristic length in combination with a Distance Transform (DT) to robustly identify the surface topology. This method is then used to estimate porosity of four different samples of a highly porous GDL, SGL 25BA. The results between different samples show great consistency. A comparison with other methods is also performed, and variations in the bulk and in-plane porosity are observed. The main advantage of the proposed Rolling Ball method compared to prior methods used in the literature is that it uses the carbon fiber diameter to identify the surface results in a systematic fashion. This methodology can be easily applied to other highly porous media.

Theoretical study of the influence of material parameters on the performance of a polymer electrolyte fuel cell

The paper presents a systematic investigation of the influence of alterations in the values of the polymer electrolyte membrane, catalyst layers and gas diffusion layer characteristics on the performance of a PEMFC. The individual influences of 25 material properties were tested using CFD simulation on a single channel fuel cell.The calculations of PEMFC performance were conducted by increasing and decreasing the values of each tested parameter, and comparing the results to a reference case. The dependencies of the current density on the following quantities were analysed in detail: 1) the cell potential, 2) the power density, 3) the membrane over-potential, 4) the mean water concentration in the PEM, 5) the relative humidity at the interface CCL/GDL, and 6) the total water flux through the PEM.The results showed that the variations in the conductivities and thicknesses of the PEM and GDL, as well as variations in GDL porosity, led to significant changes in fuel cell performance. The characteristics of the anode catalyst layer had little influence on fuel cell behaviour. Increasing the thickness and exchange current density of the cathode catalyst layer increased the current densities, while the reduction of the transfer coefficient decreased fuel cell performance.

Carbon nanotubes grown in situ on carbon paper as a microporous layer for proton exchange membrane fuel cells

The performance of proton exchange membrane fuel cell (PEMFC) is greatly influenced by the characteristics of gas diffusion layer (GDL). Herein, in situ grown carbon nanotubes (CNTs) on carbon paper as a gas diffusion layer (GDL) were fabricated by a plasma-enhanced chemical vapor deposition (PECVD) process. Fuel cells using CNT-based GDLs with nickel (II) nitrate loading of 1.6 mg cm−2 show better performance compared with the GDLs which employ Vulcan XC-72 as the MPL. The pore size distribution and the gas permeability results revealed that the increasing density of CNT layer had two main effects on the pore structure of GDL: firstly, the increasing density of CNT layer decreased the macro pore volume and the open through pore volume of CNT-based GDL; secondly, the increasing density of CNT layer decreased the micro pore diameter of CNT-based GDL. The data obtained from the vapor permeability and the fuel cell performance tests indicated that the water flooding can be reduced by applying CNT-based GDLs. The electrochemical impedance spectroscopy (EIS) confirmed that the CNT-based GDL can effectively promote the mass transfer in the FCs which was attributed to its suitable hydrophobicity and proper structure.

Experimental investigation of liquid water droplet removal in a simulated polymer electrolyte membrane fuel cell gas channel with gas diffusion layer characteristics

Since the accumulation of liquid water droplets in gas flow channels significantly affects the performance of polymer electrolyte membrane (PEM) fuel cells, a comprehensive understanding of liquid water removal from the cell is of great importance to achieve optimal water management. This study is mainly concerned with the ex situ measurement of water droplet growth and its removal in a non-reacting simulated cathode channel for PEM fuel cells. To this end, the dynamic behavior of a liquid water droplet at the gas flow channel/gas diffusion layer (GDL) interface was investigated experimentally using a specially designed transparent cell device with different GDLs. The effects of the GDL parameters (GDL thickness and micro-porous layer (MPL) inclusion) on water droplet removal are mainly investigated by analyzing the contact angle hysteresis with inlet air flow rate (Reynolds number). The critical Reynolds number is employed to evaluate the droplet removal from the GDL surface. It is observed that the water droplet on a thinner GDL tends to be removed under a higher critical Reynolds number. In addition, it is shown that the GDL with an MPL requires a higher critical Reynolds number for the water droplet removal under the same droplet height. The results suggest that the structure of the GDL sample has considerable influence on the water droplet removal. It is thought that the data obtained from this study can provide useful insight into the design of a GDL with enhanced water removal capability for PEM fuel cells.

Gas Diffusion Layer Materials and their Effect on Polymer Electrolyte Fuel Cell Performance – Ex Situ and In Situ Characterization

AbstractThe gas diffusion layer (GDL) has a vital role in the operation of a polymer electrolyte fuel cell (PEFC). Therefore, studying GDL characteristics and their effect on the cell performance is fundamental for the development of more efficient PEFCs.The work presented covers a selection of commercially available GDL types used in fuel cell development. It highlights some key GDL properties and their influence on PEFC performance. The results show that GDL materials have a direct effect on the ohmic and mass transport losses in the membrane electrode assembly (MEA). They also show that studying the effect of GDL properties on the performance is rather complex, due to the many interrelated properties.The study shows that GDL thickness has a significant effect on the mass transport properties of MEA, but has minimal effect on the ohmic losses. The bulk density of the substrate has a significant effect on the water transport properties and the maximum current density achieved. It is also found that woven and non‐woven GDLs achieve comparable performance at optimized operating conditions. Moreover, the felt fiber structure has higher ohmic resistance but achieves better performance than that of straight fiber carbon paper due to its enhanced water transport ability.