Cathode Gas Diffusion Layer Research Articles

Multi-parameter optimization of stepwise distribution of parameters of gas diffusion layer and catalyst layer for PEMFC peak power density

Gas diffusion layer and catalyst layer are important parts in a proton exchange membrane fuel cell, and the structure parameters can affect cell performance. Because the electrochemical reaction inside the cell is not uniform, it is particularity important to explore the uneven distribution of each structure parameter. Thus, a fuel cell model including agglomerate and optimization algorithm is built to study the optimal step-wise parameter distribution. These parameters include cathode gas diffusion layer porosity, platinum loading, ionomer content and carbon loading inside cathode catalyst layer. The four parameters are calculated comprehensively to obtain the optimal three segments distribution along three directions of the coordinate axis. The results show that the parameters obtained are various at different voltages and directions. The results along Z-Axis has the best positive effect on cell performance. In the results no matter which direction is, the maximum peak power density all occurs when the optimization voltage is 0.4 V. The cell can operate in wide voltage range by selecting the parameters obtained at 0.4 V along Z-Axis, and the current density can be improved at least 1.859 %. Bidirectional mass transfer at the interface between two domains can be enhanced for the model with optimal parameters.

Acceleration of through-plane water removal in polymer electrolyte fuel cell by channel hydrophilization and electrode perforation

To alleviate water flooding in cathode electrodes of polymer electrolyte fuel cells (PEFCs), it is essential to design the optimum channel/electrode structure for rapid water removal. This study presented a novel hybrid structure with the channel hydrophilization and electrode perforation for accelerating the through-plane water discharge and demonstrated the effect of its structure on the water transports in the cathode channel and gas diffusion layer (GDL) of a working PEFC with optical and X-ray imaging. The results revealed that the hydrophilization of the channel walls encourages the through-plane water suction form the GDL to the channel. Furthermore, the electrode perforation promotes the in-plane water discharge from the fine porous media to the large penetration grooves and holes. The synergistic effect of these two water transports in the hybrid structure effectively alleviates the flooding in the porous layers and enhances the oxygen diffusibility, resulting in significant improvement of the cell performance. • Water flooding in porous electrodes of polymer electrolyte fuel cells (PEFCs). • Design of the optimum channel/electrode structure for rapid water removal. • Novel hybrid structure with channel hydrophilization and electrode perforation. • Investigation of the water transport in a PEFC using optical and X-ray imaging.

Pore-Scale Modeling of Mass Transport in Partially Saturated Cathode Gas Diffusion Layers of Proton Exchange Membrane Fuel Cell

Proton exchange membrane fuel cells (PEMFCs) have the advantages of high specific power, good stability, and zero emissions, making them clean and efficient energy conversion devices. Water management is one of the technical challenges limiting the development of PEMFC, with liquid water blocking the pores and increasing the resistance to mass transport. In this paper, a two-dimensional (2D) multiphase lattice Boltzmann (LB) model is developed to obtain the liquid water morphology within the gas diffusion layer (GDL). A 2D multicomponent flow Lattice Boltzmann model considering electrochemical reactions is established to investigate the effects of water saturation, activation overpotential, and pressure difference between the inlet and outlet gas channels on mass transport. At high water saturation, the liquid water forms water films within the GDL preventing reactive gas transport and water vapor are blocked near the catalyst layer making it difficult to remove. The PEMFC can achieve higher current densities at high activation overpotentials, but oxygen starvation will be exacerbated. Increasing the pressure difference between the inlet and outlet gas passages effectively increases the oxygen concentration and reduces the water vapor concentration in the GDL. The present study improves the understanding of the effect of GDL microstructure on mass transport and performance of PEMFC from the mesoscopic scale.

A Path to Significant Reduction of the Interfacial Contact Resistance of Sintered Titanium Porous Transport Layers in Advanced Proton Exchange Membrane Water Electrolyzers

Proton exchange membrane water electrolyzers (PEMWEs) are a leading industry solution to large scale production of green hydrogen, and as a form of energy storage [5]. The PEMWEs have the advantages of having greater energy efficiency, higher product purity, and are environmentally friendly. Within the construction of a PEMWE stack, there are many catalysts coated membranes (CCMs) sandwiched between anode porous transport layers (PTLs) and cathode Gas Diffusion Layers. The PTL is constructed of sintered titanium powder or fibers. The Ti-PTL is on the anode side of a PEMWE cell where the water diffuses towards the CCM. The anode half-cell reaction or oxygen evolution reaction (OER) occurs on this side of the cell. This is important as the PTL is in contact with the bipolar plate (BPP) and the anode catalyst layer [9].A key aspect plaguing the PEMWEs is the highly oxidative and corrosive environment that is typically observed on the anode side. This significantly affects the interfacial contact resistance (ICR) of the components as the corrosion can cause the ohmic resistance of the PTL to increase. In order to combat the corrosion in the PTLs, in this work we use two thin film deposition methods, Physical Vapor Deposition (PVD) and Vacuum Sputtering, to deposit protective metal layers on top of the state-of-the-art Ti PTLs [2]. The explored metal coatings of interest are Platinum (Pt) and Gold (Au) [9]. For the purposes of these experiments, Au and Pt coatings with various thicknesses are deposited on Ti-PTLs by using either PVD or vacuum spattering method. As deposited thin films are characterized by scanning electron microscopy (SEM), digital optical microscopy, and inductively coupled plasma (ICP) analysis. Also, the in-plane conductivity and the ICR of all samples of interest are measured before and after the electrochemical tests by using the 4-probe method and in-house build setup for ICR measurements. The optimal deposition parameters for fabrication of thin, continuous and smooth Pt and Au protective coatings that result in minimum ICR and improved in-plane conductivity of the PTLs of interest are identified, and the results will be reported at the ECS 241 meeting.

(Invited, Digital Presentation) Accelerated Stress Test Development for PEM Water Electrolyzers

The use of clean hydrogen around the world is expected to significantly increase in the coming decades as various countries move towards their carbon neutral goals. The United States has committed significant funds ($9.5 Billion over the next 5 years) to the demonstration of a clean hydrogen infrastructure with electrolysis ($1 Billion in research over the next 5 years) being one of the key enabling technologies. Polymer electrolyte membrane water electrolyzers (PEMWE) for hydrogen production are expected to play a critical role in this transition to a hydrogen economy. The DOE has formed a consortium (H2NEW : Hydrogen from the next generation of electrolyzers of Water) to overcome technical barriers to affordable, reliable and efficient electrolyzer development. The consortium is working on various aspects of PEMWEs to improve their durability, decrease their cost, improve manufacturability and demonstrate economic feasibility. As part of this effort, the consortium is developing accelerated stress tests (ASTs) for PEMWEs. The DOE in collaboration with National Laboratories and the U.S. Drive Fuel Cell Technical team has developed a set of validated and widely accepted ASTs for fuel cells. While these fuel cell ASTs have spurred significant materials development over the past decade, there is no accepted set of ASTs for PEMWEs.This talk will summarize our recent learnings from the development of PEMFC ASTs and how these apply to PEMWEs. While several materials including the cathode catalyst, membrane, and cathode gas diffusion layer are similar between these two systems, there are significant differences in the operating conditions and materials used at the anode of the electrolyzer. The key to successful AST development is to ensure that the stressors accelerating the degradation mechanisms are relevant to the operating conditions encountered in the intended application. An AST working group (ASTWG) that includes various U.S. electrolyzer manufacturers has been established within the consortium to incorporate feedback from commercial electrolyzer systems. Literature reports have demonstrated that both potential cycling1 and transition through Ir/IrOx redox potential2 (during open circuit operation or shutdown of electrolyzer) can be detrimental to the anode catalyst. Membrane degradation occurs under electrolyzer conditions and is accelerated with increasing temperature and low current density operation.3 The effect of electrolyzer operating conditions on both membrane and anode catalyst durability will be discussed in this talk. The various stressors leading to increased degradation of both anode catalysts and membranes will be discussed and potential PEMWE ASTs will be proposed. Acknowledgement This research is supported by the U.S. Department of Energy (DOE) Hydrogen and Fuel Cell Technologies Office, through the H2NEW consortium.References M. Alia, S. Stariha, and R. L. Borup, J. Electrochem. Soc., 166, F1164–F1172 (2019). Weiß, A. Siebel, M. Bernt, T. H. Shen, V. Tileli and H. A. Gasteiger, Journal of The Electrochemical Society, 2019, 166, F487-F497 Marocco, K. Sundseth, T. Aarhaug, A. Lanzini, M. Santarelli, A. O. Barnett and M. Thomassen, Journal of Power Sources, 2021, 483, 229179.

Manufacture and Performance of 3D Printed Carbonised Gas Diffusion Layers

Proton exchange membrane fuel cells (PEMFC) electrochemically combine hydrogen and oxygen to produce electrical energy, heat and water. Therefore, PEMFC offer an alternative to vehicle electrification and reduction of greenhouse gas emissions. However, material limitations under high current density conditions limit the efficiency due to water flooding subsequent mass transport overpotential.The cathode gas diffusion layer of PEMFC is conventionally a carbon paper material, due to its high electrical conductivity, permeability and mechanical strength. Whereas the porosity and thickness can be controlled, the exact microstructural features are unknown, resulting from the web of randomly orientated fibres. If the microstructural features of the porous layer can be designed, improvements in water flooding and mass transport could be established.This research talk focuses on the series of studies from concept, simulation and manufacturing of designed microstructures using 3D printing and carbonisation. We investigate the potential improvements to electrical/thermal conductivity, permeability and reduction in the saturation using computational fluid dynamics. Furthermore, the impact of the porous microstructure in a lab scale set up is replicated to understand the effects of under-rib convection and oxygen consumption at the catalyst layer.With a readily available 3D printing method, prototype materials; resembling those evaluated in the simulation studies are manufactured and carbonised into glassy carbon microstructures. The morphology of carbon was limited by the maximum temperature of the furnace. The resulting structures have in-plane dimensions of 2 cm x 2 cm and through-plane between 400 – 800 µm. They were tested for electrical conductivity with a value of approximately 130 S m-1.Through a controlled carbonisation process, structural damage was minimised and the structures were introduced into a membrane electrode assembly (MEA) via spraying and hot pressing. The resulting MEA was tested in a lab cell to understand further considerations that limit the correct implementation of the 3D printed layers. In-homogenous MPL and CL formation along with membrane cracking are hypothesised to be causes of overpotentials.Figure 1 – Design process of simulation to manufacture, with simulations of (a) electrical potential, (b) water flooding and (c) oxygen distribution in a designed carbon microstructure. (d) and (e) optical microscope images of printed precursor material and final carbonised structures. Figure 1

Optimization of gas diffusion layer thickness for proton exchange membrane fuel cells under steady-state and load-varying conditions

This work proposes a design principle of the optimal thickness for cathode gas diffusion layers (GDLs) of proton exchange membrane fuel cells (PEMFCs) based on a balance of cell performances under both steady-state and load-varying conditions. Using a three-dimensional and two-phase model, the effects of cathode GDL thickness (50, 100, 200, and 400 μm) on steady-state performances and transient response characteristics are studied. The results show that under steady-state conditions, an extremely thin cathode GDL would lead to non-uniform oxygen and liquid water distributions, whereas an especially thick cathode GDL would increase oxygen transport resistance. Thus, there is an optimal cathode GDL thickness, yielding the best steady-state performance. A current overshoot phenomenon, arising from high local oxygen concentrations at cathode catalyst layers (CLs), is observed when the load voltage decreases abruptly. Thinner cathode GDLs would weaken the overshoot and shorten the recovery time of current density. Conversely, low local oxygen concentrations at cathode CLs caused by high liquid water saturation levels lead to a current undershoot phenomenon when the load voltage increases abruptly. Thinner cathode GDLs would strengthen the undershoot but shorten the recovery time of current density. The optimal choice of cathode GDL thickness should weigh up the steady-state and the transient performance. Based on this principle, the optimal cathode GDL thickness is selected as 100 µm.

Oxygen Electrochemical Production from Air by High Performance Anion Exchange Membrane Electrode Assemble Devices

CoNi and FeCoNi hydroxide with narrow voltage distance between oxygen reduction reaction and oxygen evolution reaction was synthetized by electro-deposition in low solvent concentration. 5cm2 Membrane electrode assemble (MEA) electrolyzers composed with anion exchange membrane, homogenerated catalyst on both cathode and anode gas diffusion layer (GDL) was fabricated for oxygen electrochemical production from air. The current and yield of binary CoNi device reached up to 466.7mA and 4.4mmol/h (94.7% conversion rate) at 1.2V. The ternary FeCoNi device showed only 0.5% degradation from 394.0mA during 12h. The applicability of oxygen production from air by high performance electrochemical devices was demonstrated.

Effect of liquid water in flow channel on proton exchange membrane fuel cell: Focusing on flow pattern

The liquid water in channel is a critical factor affecting the oxygen transport and fuel cell performance. However, the research considering the real gas–liquid interface is insufficient and the effect of flow pattern on mass transfer is still not clear. In this research, the volume of fluid model is added into the fuel cell model to track the two-phase flow in cathode channel (CCH) and a two-dimensional multi-phase fuel cell model is established and validated. The result shows that the liquid water in CCH could change the gas flow path by forming the variable cross-section gas channel. Then it changes the oxygen concentration and distribution, and finally affects the fuel cells performance. The flow pattern is founded to be the critical factor affecting the performance. The initial film flow leads to the long-time large-area water coverage on the cathode gas diffusion layer surface, and the serious local oxygen starvation and current density degradation. When the water content is 10.0%, the average and minimum current density decreases by 4.23% and 7.49% respectively. Besides, the initial slug flow has server deformation and fragmentation, which leads to the output performance fluctuation. Besides, the initial droplet flow has small effect on the performance, and even strengthen the performance by enhancing the local oxygen transportation. Based on this research, regulating the flow pattern is the key means to improve the influence of two-phase flow on fuel cell performance.

Power evolution of fuel cell stack driven by anode gas diffusion layer degradation

Recent research has revealed that gas diffusion layer degradation has a crucial effect on fuel cell stack power density evolution. There have been several investigations focused on the influence of cathode gas diffusion layer degradation on stack performance. However, the degradation behavior and contribution of the anode gas diffusion layer on stack output power remain to be studied. Here, the 1000 h durability test of a stack was conducted under the New European Driving Cycle condition, and the effect of anode gas diffusion layer failure on the stack output power was evaluated. Carbon corrosion is the main attenuation characteristic of the anode gas diffusion layer, which significantly reduces its mechanical strength, and decreased the support capacity of the anode gas diffusion layer. Moreover, carbon corrosion also leads to exposure of new hydrophilic surfaces, reducing the hydrophobicity of the gas diffusion layer. In addition, the loss of hydrophobic agents is also one of the main characteristics of anode gas diffusion layer attenuation, which is the main reason for hydrophobicity loss. The decreased hydrophobicity will significantly improve the water retention capacity, and reduce the back diffusion of cathode water. As a result, mass transfer resistance will increase at a high current density. In conclusion, we verified the crucial impact of anode gas diffusion layer on cell output power density, and provide a new idea for the stack power attenuation investigation.

Three-dimensional numerical study of a cathode gas diffusion layer with a through/in plane synergetic gradient porosity distribution for PEM fuel cells

This study proposes a through-plane (TP) and in-plane (IP) synergetic (SYN) gradient porosity distribution (GPD) in the cathode gas diffusion layer (CGDL) to enhance the mass transfer and water removal of a polymer electrolyte membrane (PEM) fuel cell. The novel SYN-GPD CGDL is comparatively evaluated with TP-GPD, IP-GPD and uniform porosity distribution (UPD) CGDL by implementing a three-dimensional multiphase fuel cell model. The results show that a higher porosity within CGDL near the cathode flow channel (CFC) for TP-GPD CGDL, however, a higher or lower porosity near the cathode outlet for IP-GPD CGDL improves the mass transfer and water removal within fuel cell, which benefitting the uniform distributions of oxygen and current density, and the cell performance. Additionally, as compared with the TP-GPD, IP-GPD and UPD CGDL, the SYN-GPD CGDL has a greater advantage in the enhancement of mass transfer and water removal, consequently resulting in much more homogeneous internal physical quantity profiles and a higher overall cell performance. Ultimately, the optimal SYN-GPD CGDL improves the maximum power density by 6.73%, while reducing the coefficient variations (CVs) of the oxygen mass fraction and current density by approximately 10.24% and 40.69%, respectively, compared with those of the UPD CGDL.

Method for Analyzing 2D X-Ray Transmission Images for Operando Liquid Water Distribution in a Polymer Electrolyte Fuel Cell

There is a potential to increase the zero-emission polymer electrolyte fuel cell (PEFC) efficiency through high power density operation. However, water management issues become significant under these conditions, necessitating improved water management strategies [1]. As a precursor, understanding of liquid water distribution is instrumental to developing optimal water management strategies.Various techniques including neutron imaging, electron microscopy, and X-ray imaging have been used to study liquid water transport in fuel cells. Of these, the X-ray computed tomography (XCT) method has provided unprecedented insights gained through in-operando visualization, yielding 3-dimensional (3D) information [2, 3]. The 3D grayscale data set is obtained by first acquiring multiple projections of the sample at different angles which are then reconstructed to yield a 3D representation. The 3D representation may then be processed to segment features such as liquid water and other features of interest [3, 4]. However, the acquisition of such 3D datasets typically takes several hours on a lab-scale XCT instrument [5]. This may sometimes result in a dataset that is difficult to interpret if the imaged sample evolves significantly during the acquisition time. Furthermore, phenomena of interest, such as liquid water distribution may sometimes be challenging to capture with 3D datasets. In this work, we therefore explore the use of transmission radiograph imaging to further understand the distribution of liquid water in an operating fuel cell.The method developed involves the analysis of in-operando transmission images within the framework of the X-ray attenuation laws to provide qualitative, as well as quantitative saturation and liquid water distribution information. Sequential images of a miniaturized operating fuel cell were acquired at 0- and 90-degree angles to the fuel cell plane within a laboratory XCT equipment, while cell operational conditions were controlled by an external fuel cell test station. This approach trades off 3D information for short time scans afforded by 2D acquisition procedure, enabling the identification of liquid water droplet breakthrough dynamics at the cathode gas diffusion layer, as shown in Figure 1. The observed liquid water breakthrough yields new findings on the nature of liquid water distribution in the flow channels, often elusive to 3D approaches. Methods and analysis developed may therefore be used to augment information derived from 3D visualization methods. Acknowledgments Funding for this research was provided by the Natural Sciences and Engineering Research Council of Canada, Ballard Power Systems, Canada Foundation for Innovation, British Columbia Knowledge Development Fund, Canada Research Chairs. References Jiao K and Li X 2011 Progress in energy and combustion Science 37 221–291.Nagai Y, Eller J, Hatanaka T, Yamaguchi S, Kato S, Kato A, Marone F, Xu H and B¨uchi F N 2019 Journal of Power Sources 435 226809.Eller J, Roth J, Marone F, Stampanoni M and B¨uchi F N 2016 Journal of The Electrochemical Society 164 F115.White R T, Eberhardt S H, Singh Y, Haddow T, Dutta M, Orfino F P and Kjeang E 2019 Scientific reports 9 1–12.Withers P J, Bouman C, Carmignato S, Cnudde V, Grimaldi D, Hagen C K, Maire E, Manley M, Du Plessis A and Stock S R 2021 Nature Reviews Methods Primers 1 1–21. Figure 1

3D Visualization of Liquid Water Penetration from MPL to Substrate Layer in PEFC Using in-Situ X-Ray Tomographic Microscopy

Polymer electrolyte fuel cells (PEFCs) play an important role in solving environmental problems and energy problems. It is required to perform them at higher current density to achieve the cost reduction. Under the circumstance, however, the cathode gas diffusion layers (GDLs) are saturated with liquid water, which is generated from the electrochemical reaction and condenses. In other words, water is one of the factors that prevents the oxygen diffusion, and clarifying the water management in GDLs is essential to perform at higher current density. At present, synchrotron-based X-ray tomographic microscopy (XTM) is the common way to observe water distribution. While its high intensity makes it possible to get high contrast data by imaging in short exposure time, it decomposes the polymer electrolyte. It is the crucial point to keep cell performance during imaging. In addition, the experiment time using synchrotron radiation facility is limited. To inspect other ways than synchrotron-based XTM, here we aim to achieve 3D visualization of liquid water penetration in GDLs using laboratory-based in-situ XTM. Besides, we aim to evaluate the relationship between water distribution and GDL structure. To get 3D data of liquid water penetration in GDLs using Rigaku nano3DX, which is the laboratory-based X-ray imaging, the fuel cell with an active area 1.0 × 1.0 mm2 was applied. The cell equipped with Toray TGP-H-060 coated with micro porous layer (MPL) was used. 3D data that spatial resolution was 2.16 um was taken. By applying phase retrieval process and image processing, MPL, fiber, water and air were classified. As a result, we have succeeded in the 3D visualization of liquid water penetration from MPL to substrate layer under room temperature. Then, the volume of water captured by XTM was compared with that detected by X-ray radiography to verify that XTM could capture water precisely. This is because some water which is moving during imaging cannot be captured after reconstruction. The total scan time was about 3 hours, which is longer than that of synchrotron-based XTM. It took about 14 second to get an image by X-ray radiography. As a result, though the amount of water near the separator captured by XTM was fewer than that detected by X-ray radiography, the amount of water near MPL and substrate layer was almost the same. The results showed that the liquid water distribution obtained by laboratory-based XTM is reliable. Figure shows 3D images of cathode GDL and water at current density of 0.75, 1.0, 1.25, 1.5 A/cm2. We have identified that water passed through the cracks of MPL and remained in substrate layer where was close to the boundary between MPL and substrate layer. In addition, the effective pore diameter of substrate layer which water remained in was analyzed, and it was identified that water tended to remain in the bigger pore diameter. This is because substrate layer we used is hydrophobic. The result indicates that the existence of cracks on MPL has a strong influence on liquid water distribution and oxygen transport to the catalyst layer. Figure 1

PEFCs Using Metallic Ti and Sn Gas Diffusion Layers

Introduction Many types of carbon materials are used in PEFCs. Especially, gas diffusion layer (GDL), with a thickness of ca. 0.2 mm are made of relatively expensive carbon fibers. In general, metallic materials can be more electronically conductive than carbon black based materials, and thinner GDLs could be prepared using metals. Here in this study, we evaluate and compare several types of metallic materials to apply as GDLs. Using such alternative metallic GDLs, current-voltage (I-V) characteristics were measured and overvoltages were separated. The purpose of this study is to examine possibilities of metallic GDLs for PEFCs, by varying materials, thickness, porosity, and preparation conditions. Experimental We measured I-V characteristics of PEFCs using metallic GDLs. Four types of porous metallic sheets were used as GDLs, shown in Figures 1 to 3: (i) Ti fiber-based sheet (porosity: 70%; thickness: 200μm; Nikko Techno Ltd.), (ii) Ti fiber-based sheet with porous Sn layer, (iii) Ti punching metal sheet (sheet thickness: 12μm; hole diameter: 300μm; Fukuda Metal Foil & Powder Co., Ltd.), and (iv) Sn punching metal sheet (sheet thickness: 100μm; hole diameter: 300μm, Fukuda Metal Foil & Powder Co., Ltd.). Except for cathode-side GDLs, standard materials were used such as Pt/C electrocatalyst (Tanaka Kikinzoku Kogyo, TEC10E50E). Electrochemical impedance spectroscopy (EIS, Solartron 1255WB) was used to separate overvoltages in the electrochemical characterization. Results and discussion I-V characteristics of the cells with the cathode GDLs (i) to (iv) are shown in Figure 4. Decrease in cell performance was mainly caused by an increase in ohmic losses. Comparing these GDLs, Sn-based materials are generally more conductive than Ti-based materials to decrease ohmic losses, but concentration overvoltage can also be high when the GDLs (ii) and (iv) were used. Both contact and internal resistance were reduced when using the porous Ti punching metal sheet instead of the Ti fiber sheet. Further study is in progress to increase I-V characteristics of MEAs by optimizing materials selection and structure. Acknowledgement Financial support from New Energy and Industrial Technology Development Organization (NEDO) is gratefully acknowledged (Contract No. 20001214-0). References Larminie，A. Dicks，Fuel Cell Systems Explained, 2nd Edition, John Wiley & Sons, West Sussex, England, 2003.T．Kitahara，T．Konomi，H．Nakajima, and J．Shiraishi， Japan Soc. Mech. Engineers, B76 (761) 101 (2010), in Japanese.S．Matsumoto，M．Nagamine，Z．Noda，J．Matsuda，S．M．Lyth，A．Hayashi，and K．Sasaki，J ． Electrochem ．，165 (14)，1165 (2018).C．A．Reiser，L．Bregoli，T．W．Patterson，J．S．Yi，J．D．yang，M．L．Perry，and T．D．Jarvi，Electrochem . Solid-State Lett.，8 (6)，A273 (2005). Figure 1

Modeling Anion Exchange Membrane Fuel Cell Performance and Its Stability: Validation, High-Temperature Operation and More

The increasingly high level of activity in Anion Exchange Membrane Fuel Cell (AEMFC) research and development over the past several years has included a strong component of computational modeling studies. While most of these have concentrated on various aspects of cell performance, our group's efforts are focused on the analysis of both performance and its stability [1,2]; in contrast with performance, the current state of the art of AEMFCs with respect to performance stability falls significantly short of what is required.In this contribution, we will describe our modeling approach which involves both 1-D and 3-D time dependent analyses of AEMFC operation. We account for mass transport, electrochemical phenomena, and ionomer degradation kinetics across the cell, involving a five-layer membrane electrode assembly. This includes a cathode gas diffusion layer (GDL), a cathode catalytic layer (CL), a membrane, an anode CL, and an anode GDL; in the case of 3D modeling gas flow channels are also included. Details of the models, associated simplifying assumptions and our numerical approach will be provided. This will be followed by the description of a number of sample studies.First, we will discuss validation via the comparison of cell performance and its stability against experimental data for different design and operating parameters. Next, we will present the application of our modeling approach in an effort to explore the effect of high-temperature operation on AEMFC performance and its stability. Our modeling results demonstrate the beneficial impact of using high operating temperature on AEMFC performance; this is attributed to better electrochemical kinetics, and reduced mass transfer limitations. Nontrivial benefits with respect to performance stability will also be demonstrated. Additional studies to be discussed include the analysis of Anion Exchange Ionomer (AEI) hydroxide conductivity and its impact on AEMFC performance and stability, as well as the analysis of performance using different gas flow channel geometries.

(Invited) Synchrotron X-Ray and Pulsed Neutron Imaging of Water Transport Distribution in Fuel Cells

In order to realize a sustainable energy society, it is necessary to optimize energy and effectively utilize it by combining an electric grid and a hydrogen grid instead of the conventional fossil fuel-dependent type. Hydrogen has a high affinity with renewable energy and can be produced from various primary energies, so it is positioned as a promising energy in the future. We position fuel cell vehicles (FCVs) powered by hydrogen as the ultimate eco-friendly car, and are making vigorous efforts to develop high performance/reliability and low cost FCVs.Polymer electrolyte fuel cells (PEFCs) convert the chemical energy stored in hydrogen into electricity, with water as the only by-product. The inherent advantages of a PEFC include high electric energy efficiency and power density, low operating temperature and fast start-up, along with reduced environmental impact. PEFCs are regarded as a clean and efficient powertrain technology for automotive applications, serving as replacements for conventional internal combustion engines.PEFCs consist of an electrolyte membrane sandwiched between an anode and a cathode, and both the anode and cathode have laminated structures composed of a catalyst layer (CL) and gas channels in contact with a gas diffusion layer (GDL). When hydrogen and oxygen flow through the gas channels, an electrochemical reaction occurs in the CL, producing a by-product of water in addition to electrical power. The water generated by power generation then passes through the cathode GDL to the gas channel, and is finally discharged to the outside of the vehicle.The performance of fuel cells is greatly affected both by materials such as catalysts and electrolytes, and by how efficiently water generated by power generation is discharged, that is the essential role in water management function. To achieve a high-power density, it is really important to design sophisticated water management from water generation on the catalyst of FC to drainage outside the vehicle. Regarding the water management in PEFCs, it is necessary to manage it on a very wide scale from nanometer to millimeter. Based on the viewpoint that FC multiscale analysis linking materials, devices and vehicles is essential to achieve high performance by water management, we are currently constructing our original multiscale analysis combining quantum beam analysis using X-ray and neutron which enables liquid water visualization, as shown in Figure.In this presentation, I will exhibit two topics. First, I report improving water management in GDL through microporous layer (MPL) modifications [1]. Advanced 4D operando X-ray imaging (3D structure plus time) was employed to analyse the water content in GDLs, and demonstrated that the superior performance of cells with large MPL pores is due to the efficient formation of water pathways. The second is pulsed neutron imaging for differentiation of ice and liquid water distribution [2]. Energy-resolved neutron imaging is a methodology capable of distinguishing between liquid water and ice, and is effective for investigating ice formation in PEFCs operating in a subfreezing environment. We have enabled the observation of liquid water/ice distributions in a large field of view (300 mm × 300 mm) by manufacturing a sub-zero environment chamber that can be cooled down to -30 oC, as a step towards in situ visualition of full-size fuel cells.We hope that these studies will lead to the development of next generation FCVs. Figure 1

Investigating temperature-driven water transport in cathode gas diffusion media of PEMFC with a non-isothermal, two-phase model

Temperature distribution affects water transport in the porous medium layer of proton exchange membrane fuel cell (PEMFC) by phase-change-induced (PCI) flow. Thus, it is meaningful to reveal the role of PCI flow in removing water. In the present work, a 1-D, non-isothermal, two-phase model is employed to investigate the water transport in cathode gas diffusion layer (GDL) and micro porous layer (MPL). A dimensionless parameter Ts is also proposed to characterize the relation between PCI flow and capillary-driven (CD) flow. It is found that elevating the operating temperature (from 323.15 K to 363.15 K) can facilitate the PCI flow. The high anode and low cathode relative humidity (RHa90%/RHc50%) case contributes to the optimal output performance, corresponding to the largest Ts number and thermal strain. The thermal strain is insignificant compared with the swelling strain and the hygrothermal strain is influenced by the combination of output performance, water distribution and operating conditions. Furthermore, reducing water saturation (sc) at the GDL/gas channel (GC) interface (from 0.12 to 0.0) is conducive to enhancing the proportion of PCI flow in GDL and MPL. By adjusting the operating temperature, inlet RH and removing water at the GDL/GC interface in time enable enhancement of PCI flow and better performance. This work aims to provide a valuable reference for understanding the water transport process and optimizing water management.

Collaborative Design for Uneven Physical Structures of Multi-Layers in PEMFC

A collaborative design for the uneven distributions of a flow channel, gas diffusion layer porosity and catalyst layer porosity are newly proposed to improve the utilization ratio of the membrane electrode assembly of the proton exchange membrane fuel cell. The effects of the uneven design of the rib width and of the uneven porosity parameters of the cathode and anode gas diffusion layer and catalyst layer on the fuel cell performance were studied in detail. Numerical simulations were designed and implemented for validation. The results show that the fuel cell performance could be improved through the collaborative design of uneven distributions for different layers. The rib width gradually decreasing and the porosity of the cathode gas diffusion layer and the cathode catalyst layer gradually increasing along the fluid flow direction would contribute to a better design compared to the regular even design. The new uneven design can make the fuel penetrate into the catalyst layer in time to participate in the reaction, improve the utilization rate of the membrane electrode assembly, and greatly improve the performance of the fuel cell.

Effects of cathode gas diffusion layer type and membrane electrode assembly preparation on the performance of immobilized glucose oxidase‐based enzyme fuel cell

AbstractDifferent cathode configurations with carbon paper (CP) and carbon cloth (CC) gas diffusion layer (GDL) are combined with Nafion® 115 for GOx enzyme fuel cells. Catalyst‐coated Nafion membrane (without a GDL) has resulted with highest impedance and lowest polarization response. Hot pressing of cathode gas diffusion electrode (GDE) onto the Nafion or physical placement onto the alternative chitosan membrane has reduced interface resistance 10 times compared with no‐GDL case. The best performance for the Nafion membrane is 2.1 mA cm−2 current density with hot‐pressed CC‐GDE. Smallest high‐frequency electrolyte (0.55 ohm) and charge transfer resistances (0.15 ohm) were measured with physically placed CC‐GDE on the alternative chitosan membrane resulting in maximum short current density of 3 mA cm−2 with a 4‐cm2 single enzyme fuel cell.

Droplet dynamic characteristics on PEM fuel cell cathode gas diffusion layer with gradient pore size distribution

Understanding of droplet dynamic characteristics on gas diffusion layer (GDL) of polymer electrolyte membrane (PEM) fuel cell is of great importance for cell performance improvement. This study comprehensively investigated droplet dynamic characteristics on fuel cell cathode GDL with gradient pore size distribution (GPSD). The influence of different pore sizes, GPSD and wettabilities of GDL on droplet dynamic characteristics is numerically evaluated by using the volume of fluid (VOF) method through the analysis of the interaction among the forces over droplet. Results indicate that droplet has a relatively short detachment time and a smaller detachment radius on superhydrophobic and superhydrophilic GDLs compared with on a moderately hydrophobic GDL regardless of pore size. Moreover, large pores can facilitate droplet detachment, but increase droplet detachment radius and pressure drop. Compared with uniform (U)PSD, for transverse (T)-GPSDs with a small pore distance at a relatively low airflow velocity or a large pore distance at a high airflow velocity, or for the longitudinal (L)-GPSD with a large pore in the upstream and a small pore in the downstream at a large pore distance, the droplet detachment time decreases by 34.3% and 25.2% with a reduction of pressure drop, respectively.