Porous Gas Diffusion Layer Research Articles

Enhanced water management in PEMFC cathode using streamlined baffles

This research investigates the impact of baffle configurations on water management within Polymer Electrolyte Membrane Fuel Cells (PEMFCs) using novel flow fields in configurations featuring staggered and parallel streamlined baffles. Utilizing the Volume of Fluid method, the two-phase flow is modeled within computational domains that encompass the flow field above the porous Catalyst and Gas Diffusion Layers. A key feature is the use of Dynamic Contact Angle model, accounting for surface tension and wall adhesion over time, which provides detailed insights into liquid water movement and pressure changes. Streamlined baffles significantly enhance water removal and reactant transport by creating circulations and increasing flow velocities. The parallel-baffle configuration demonstrated the highest water removal capability, reducing water content in flow channels by 20.08 % compared to straight channels and offering a more uniform distribution of reactants. Both baffled configurations improve performance by promoting reactant infiltration and water expulsion, but they also increase pressure drops. The parallel configuration experiences the highest pressure drop, about 4.5 times greater than the conventional straight channel, illustrating a trade-off between better water management and energy efficiency. This study provides important insights into how baffled flow field designs in PEMFCs influence flooding behavior and potentially overall performance.

The Impact of Catalyst Layer Fabrication Procedure on Layer Morphology, Transport Properties and Performance in Low-Temperature PEM Fuel Cell

Hydrogen mobility represents a progressive, low carbon imprint option for the replacement of internal combustion engines. A core of this technology is low-temperature fuel cell with proton-exchange membrane (LTPEMFC), using hydrogen and atmospheric oxygen as fuel and oxidant, respectively. The membrane-electrode assembly (MEA) which makes up a cell consists of polymer electrolyte membrane, cathodic and anodic catalyst layers and carbon-based porous gas-diffusion layers. LTPEMFC require Pt catalyst on both the anode and the cathode in non-negligible total amount, increasing investing costs for stack unit. In order to maximise fuel cell performance, the formation of three-phase boundary has to be achieved during deposition of catalyst layers, interconnecting Pt nanoparticles on carbon support and ionomer with membrane in complex, porous structure. The quality of catalyst layer determines to high degree final MEA performance.Catalyst layers can be deposited either on gas-diffusion layers or onto the membrane, with latter being considered a more advantageous and feasible approach. Deposition itself can be realised by various methods, including airbrush spraying, decal printing, doctor blade deposition from paste and, most often used nowadays, ultrasonically-assisted spray coating. Each of these methods brings its own advantages and disadvantages, though the common problem of these methods is low suitability for serial production. On the other hand, the quality of so-prepared catalyst layers is sufficient. Methods for large-capacity coating of catalyst layers, especially roll-to-roll technology have exactly opposite pros and cons, high output but unsatisfactory layer quality. An interesting alternative to state-of-the-art catalyst layer fabrication procedures is inkjet printing.Inkjet printing is a well-established technology, though the application in LTPEMFC field brings various issues, mainly connected to quality of layers and prevention of nozzle-clogging during the deposition. Solving of these issues, however, will result in technology suitable for catalyst layer printing, combining high production throughput, very good reproducibility, minimal losses of the ink, suitability to additive manufacturing and possibility of printing specific geometries with gradient layer thickness. Accordingly, the goal of this study is the comparison of catalyst layers, deposited onto the membrane by ultrasonically-assisted spray coating and inkjet printing, in terms of morphology, electric conductivity, permeability and performance in LTPEMFC, using commercially-available materials for layer fabrication.Catalyst layers of the same composition and Pt loading were deposited by either ultrasonically-assisted spray coating or inkjet printing onto FTO conductive glass for the determination of electric conductivity, onto gas-diffusion layer for permeability determination in Loschmidt cell and FIB-SEM morphology studies and onto the membrane for the fabrication of MEA and evaluation of its performance in LTPEMFC. Characterisation of layers deposited on materials above underlined feasibility of inkjet printing for catalyst layer fabrication. In comparison with sprayed layers, layers prepared by inkjet printing tend to be thinner, more homogenous and compact. This results in superior electric conductivity but lower permeability at the same time. Single cell tests proved that performance of inkjet-printed layers is at least on par with sprayed ones, surpassing them with optimised ink composition and Pt loading. Overall, inkjet printing technology is a highly attractive technology for industrial catalyst layer production with great possibilities for contributing to decrease LTPEMFC unit’s investment costs.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 958174. This project is co-financed from the state budget by the Technology agency of the Czech Republic under the M-ERA.Net Programme, project No. TH80020006. This work was supported by the project "The Energy Conversion and Storage", funded as project No. CZ.02.01.01/00/22_008/0004617 by Programme Johannes Amos Commenius, call Excellent Research. This project is co-financed with tax funds on the basis of the budget passed by the Saxon state parliament.

Manufacturing protocol and post processing of ultra-thin gas diffusion layer using advanced scanning techniques

The typical commercial size of a Gas Diffusion Layer (GDL) for Proton Exchange Membrane Fuel Cell (PEMFC) application is around 180 μm up to 290 μm. GDL facilitates the diffusion of reactants to the catalyst layers and liquid removal from the membrane to the flow field. In this regard, GDL should be a porous region with conductive materials as thin as possible to reduce the size and the costs. Lowering the thickness of the GDL also results in better performance of the stack since it increases the speed of reactants to reach the catalysts. However, the main obstacle is the formation of ultra-thin porous GDL, which can be also named as standalone microporous layer (MPL). The novelty of this study is the manufacturing process and production of ultra-thin porous GDL with carbon and Polytetrafluoroethylene (PTFE) as the main materials. The produced GDL has the thickness of 28.9 μm, which has been measured using microscope imaging. This novel GDL can be used as the conductive diffusive region inside the PEM fuel cells, Alkaline fuel cells, and the cathode of PEM and Alkaline electrolyzers. Additionally, the novel invention can be considered as a 2D membrane for carbon capture purposes after being functionalized.

Impact of gas diffusion layer architecture on the performances of Cu-based electrodes for CO2 electroreduction to ethylene in flow reactors

Electrocatalytic CO2 reduction reaction (CO2RR) is a promising strategy to convert CO2 into fuels and building blocks for chemicals, exploiting renewable energy sources. Flow cells using gas diffusion electrodes (GDEs) instead of simple H-cells are required to achieve higher production rates. In a GDE, CO2 diffuses through a porous gas diffusion layer (GDL) and reaches the active sites located in the catalyst layer; the GDL is a crucial component that can affect the performance of the GDE. In this work, we aimed to establish the parameters of the GDL that influence the selectivity toward the different CO2 reduction products in an alkaline flow reactor. We employed commercial Cu nanoparticles as electrocatalyst and selected a range of market-available GDLs: the structure, composition, and type of cracks of the GDL greatly influence the Faradaic Efficiency (FE) of CO, H2, and ethylene (C2H4). With the emphasis on C2H4, it was found that using a crack-free GDE is essential to get higher FEC2H4. At the same time, larger and more abundant cracks are detrimental to C2H4 production and promote hydrogen evolution: for instance, the FEC2H4 varies in the wide range of 13–32%, from the highly cracked to the crack-free GDL. The presence of both sulfur and oxygen in the microporous layer (MPL) of the GDL helps shift the CO2RR selectivity toward CO. The (in)stability of the GDEs at high current density has been correlated with a change in the wetting properties of the GDE and a loss in hydrophobicity.

Influence of the material properties and the process parameters on the ablation behavior for the laser structuring of the diffusion media for fuel cells

Hydrogen-powered polymer electrolyte membrane fuel cells (PEMFCs) show promising potential to power a wide range of mobile and stationary applications and to reduce greenhouse gas emissions significantly. In PEMFCs, the oxygen transport and the water transport are essential for a long lifetime and high-performance characteristics. The diffusion media (DM), located between the bipolar plate and the catalyst-coated membrane, is a crucial component of the fuel cell that significantly affects the cell-internal processes. Usually, the DM is a two-layer material system consisting of a microporous layer based on carbon black particles coated onto a porous gas diffusion layer (e.g., carbon paper). The properties of the microporous layer regarding the water transport at high current densities and, consequently, the fuel cell’s performance and lifetime can be improved by laser structuring. Within this work, different microporous layers with varying binder content and porosities were structured by locally ablating the material using ultrashort-pulsed laser radiation in the infrared wavelength range. The effect of varying process parameters was additionally investigated. Furthermore, the ablation efficiencies were calculated for increasing pulse repetition rates to qualify a process window for an industrial structuring process. The size of the micro-drillings and the heat-affected zone surrounding the hole were evaluated through topographic and microstructure analyses using a laser scanning microscope and a scanning electron microscope with energy-dispersive x-ray spectroscopy. The results showed a rather small influence of the porosity and composition of the microporous layer on the ablation behavior. In contrast, the laser structuring parameters influenced the micro-drilling geometry significantly.

Self-Supporting Microporous Layer for Polymer Electrolyte Fuel Cells

Introduction Improving power density is desired in research and development of polymer electrolyte fuel cells (PEFC) [1-5]. A reduction of gas diffusion resistance by down-thinning the gas diffusion layer (GDL) less than 50 μm is desirable [2]. Whilst both the electrocatalyst layers and electrolyte membrane are around 10 μm, the GDL is still relatively thick at about 150 μm [1]. The previous study investigated the possibility and technical issues in using high-strength and thin, porous metallic GDLs [3]. Based on such previous studies, this study aims to develop a self-supporting thin MPL/GDL with improved power density by creating conductive paths and reducing contact resistance with microporous layer (MPL) deposited on various GDLs. Experimental In this study, MPL was screen-printed on various mesh GDLs as substrates. Cells were fabricated by using these materials, and current-voltage characteristics and microstructural observations were performed. Stainless steel (SUS316 977mesh, 28 μm thick), titanium (200mesh, 152 μm thick), and carbon fiber (45 μm thick) were used as mesh GDL materials. The MPLs were composed of carbon black, carbon nanotubes, polytetrafluoroethylene (PTFE), and solvent (a mixture of polyethylene glycol 600 and pure water), which were mixed, screen printed, and heat treated at 300°C for 30 min to fabricate the MPL/GDL. Conventional materials such as Pt/C (TEC10E50E, Tanaka Kikinzoku, Japan) were used for preparing membrane-electrode-assemblies (MEAs). In the electrochemical characterization of this study, current-voltage characteristics were evaluated using an electrochemical impedance analyzer (SAS SP-240, Bio-Logic Science Instruments, France), and various overvoltages were separated. Results and discussion Figure 1 shows the current-voltage characteristics of cells using various MPL/GDLs. The thickness of MPL/GDLs fabricated was ranging from 62 to 180 μm. For comparison, the characteristics of a cell using a standard material, commercially available MPL/GDL (22BB, SGL Carbon, Germany), are also shown. The results indicate that the use of any kind of these MPLs improves cell performance. The electrochemical performance with metallic GDLs was considerably improved by applying MPLs. In particular, GDLs with metallic meshes made of SUS316 show a significant improvement in current-voltage characteristics by depositing MPLs. The activation overvoltage and ohmic overvoltage were comparable to those of 22BB, the commercial GDL/MPL. This is because the contact resistance between the GDL and the catalyst layer is reduced by the carbon component in the MPL, and the electrical conductivity is improved. The concentration overvoltage was also suppressed by depositing the MPL. The cell performance with MPL3/SUS316 977mesh was comparable to that of 22BB. In the future, we aim to further reduce the concentration overvoltage by optimizing e.g., the content of hydrophilic components in MPLs. Acknowledgment This paper is based on results obtained from a project, JPNP20003, commissioned by the New Energy and Industrial Technology Development Organization (NEDO). References Takahashi, T. Ikeda, K. Murata, O. Hotaka, S. Hasegawa, Y. Tachikawa, M. Nishihara, J. Matsuda, T. Kitahara,M. Lyth, A. Hayashi, and K. Sasaki, J. Electrochem. Soc., 169, 044523, (2022).New Energy and Industrial Technology Development Organization (NEDO), Roadmap of Fuel Cells for Heavy-Duty Vehicles, 48, (2022), (in Japanese), https://www.nedo.go.jp/content/100944011.pdf Yamamoto, M. Yasutake, Z. Noda, S. M. Lyth, J. Matsuda, M. Nishihara, A. Hayashi, and K. Sasaki, ECS Trans., 109 (9),265 (2022).Larminie and A. Dicks, Fuel Cell Systems Explained, 2nd ed., John Wiley & Sons, England, 2003.Kitahara, T. Konomi, H. Nakajima, and J. Shiraishi, Kikai B, 76 (761), 101, (2010). Figure 1

Influence and Optimization of Gas Diffusion Layer Porosity Distribution along the Flow Direction on the Performance of Proton Exchange Membrane Fuel Cells

Influence and Optimization of Gas Diffusion Layer Porosity Distribution along the Flow Direction on the Performance of Proton Exchange Membrane Fuel Cells

Generative design of large-scale fluid flow structures via steady-state diffusion-based dehomogenization

A computationally efficient dehomogenization technique was developed based on a bioinspired diffusion-based pattern generation algorithm to convert an orientation field into explicit large-scale fluid flow channel structures. Due to the transient nature of diffusion and reaction, most diffusion-based pattern generation models were solved in both time and space. In this work, we remove the temporal dependency and directly solve a steady-state equation. The steady-state Swift-Hohenberg model was selected due to its simplistic form as a single variable equation and intuitive parameter setting for pattern geometry control. Through comparison studies, we demonstrated that the steady-state model can produce statistically equivalent solutions to the transient model with potential computational speedup. This work marks an early foray into the use of steady-state pattern generation models for rapid dehomogenization in multiphysics engineering design applications. To highlight the benefits of this approach, the steady-state model was used to dehomogenize optimized orientation fields for the design of microreactor flow structures involving hundreds of microchannels in combination with a porous gas diffusion layer. A homogenization-based multi-objective optimization routine was used to produce a multi-objective Pareto set that explored the trade-offs between flow resistance and reactant distribution variability. In total, the diffusion-based dehomogenization method enabled the generation of 200 unique and distinctly different microreactor flow channel designs. The proposed dehomogenization approach permits comprehensive exploration of numerous bioinspired solutions capturing the full complexity of the optimization and Swift-Hohenberg design space.

Porous Carbon Fiber Flow Fields for Heavy-Duty Polymer Electrolyte Fuel Cell (PEFC) Applications

The US Department of Energy (DOE) interim (2030) targets for polymer electrolyte fuel cells (PEFCs) in heavy duty vehicle applications accentuate reduced system cost (US $80/kW), increased peak efficiency (68%), and longer system lifetime (25,000 hrs) [1]. The bipolar plate in a PEFC has to serve several functions such as uniform reactant distribution with minimum pressure loss, efficient product water removal, and maintain high electronic and thermal conductivity. Multiple studies [e.g., 2-4] describe novel materials and engineered designs potentially meet these performance and durability requirements; however, cost is the limiting factor in most cases. For example, the cost of a state-of-the art stainless steel (SS 316L) plate, already approaching minimum feasible plate thickness, is estimated to be (US $3.5/kWnet), which is 17% higher than current DOE target [1]. Thus, low-cost substrate alternatives are required to reduce the cost and facilitate commercialization in heavy-duty applications. One such alternative is a novel PEFC architecture [5] utilizing a laminated structure consisting of flat thin metal foils that separate flow fields with channels formed into the porous gas diffusion layer (GDL). This architecture enables the use of much thinner metal plates compared to stamped ones, reducing the overall system mass and cost. The current study explores the performance of a wide aspect ratio (200 mm x 30 mm) PEFC test fixture with porous carbon fiber flow field compared to conventional solid flow field over a wide range of operating conditions. The wide aspect ratio and channel/rib dimensions for both the porous and the conventional solid flow field are chosen to provide a reasonable pressure loss relevant to heavy-duty PEFC stack application. This new architecture is expected to enable comparable system performance while reducing plate weight and cost.

Investigation of flow characteristics on porous gas diffusion layer microstructure that generated with binder and polytetrafluoroethylene distribution

The drainage properties of a gas diffusion layer (GDL) are essential factors in the performance of proton exchange membrane fuel cells. The GDL consisting of a three-dimensional (3D) carbon paper microstructure was developed and meshed with pore-scale reconstruction models in this paper. Localized binder and polytetrafluoroethylene (PTFE) structures were added to the carbon paper microstructure through 3D morphological imaging processing. The monitoring data of 1000 planes were multi-peaky fitted as a function of gas permeability and height to amend the macroscopic porous medium model. We analyzed drainage properties under different contact angles (θ) for the carbon paper with binder and PTFE. We described the mutual intrusion of moisture and air in GDL under different pressure differences. The results show that the pore-scale reconstruction model has the advantages of describing the flow in GDL accurately and with details, detecting low-flow resistance channels that spontaneously formed in GDL, and describing the variation of permeability as a function of location. In a hydrophobic environment, the liquid film connected to a GDL is challenging to split spontaneously. At the same time, the splitting motion of discrete droplets is more prominent than that of the liquid film. The pressure that enables complete water intrusion into the GDL is between 1 and 10 MPa.

Modification and durability of carbon paper gas diffusion layer in proton exchange membrane fuel cell

To solve the durability problem caused by carbon corrosion in the porous carbon paper gas diffusion layer (GDL) of proton exchange membrane fuel cell (PEMFC), a Cr7C3 ceramic coating on porous carbon paper by molten salt method was prepared. The obtained Cr7C3 coating is dense and shows good adherent with the carbon paper. Based on the corrosion resistance testes, it is concluded that the Cr7C3 coated carbon paper can keep high chemical stability in the long-time acid immersion accelerated corrosion tests and simulated cathodic proton exchange membrane fuel cells environment. The carbon paper with Cr7C3 coating shows a small current density with a value of about 1.1 × 10−5 A cm−2 in the potentiostatic polarization test under 1 M H2SO4 + 2 ppm HF at 70 °C and1.4 VSCE for 72 h. Meanwhile, the resistivity of carbon paper with Cr7C3 coating prepared is 30% lower than that of pure carbon paper, and the conductivity is 1.5 times that of pure carbon paper.

Pore-Scale Saturation and Liquid Water Pathways in PEFCs: Insights from Correlative 2D and 3D X-Ray Imaging

Improving the efficiency of polymer electrolyte fuel cells (PEFCs) through high power density operation necessitates liquid water management in the cathode gas diffusion layer (GDL), where liquid water saturation inhibits oxygen diffusivity. To this end, there have been numerous efforts aimed at understanding liquid water transport behaviour to guide GDL design improvements. X-ray imaging of representative in-operando miniaturized PEFC samples has been instrumental to much of recent progress [1–4] in understanding liquid water distribution patterns. Radiographic two-dimensional (2D) images have enabled visualization of liquid water dynamics [3] while three-dimensional (3D) computed tomography images have provided pore-scale information of liquid water saturation states in the GDL [2] and of its transport mechanism [4]. However, how liquid water pathways are formed and the likelihood for preferential pathways remain unclear.In this work, we investigate factors that influence liquid water distribution and pathway definition using correlative rapid 2D and long duration 3D operando X-ray datasets which enable a visualization of liquid water breakthrough dynamics and the corresponding pore-scale interactions in the GDL. The correlated images together with GDL pore structure visualization are used to identify three characteristic pore-scale saturation behaviour with sample regions highlighted in Fig. 1. These regions include locations with restricted liquid water breakthrough, locations with apparent large breakthrough porous pathways where breakthrough liquid water is observable at least in the 2D images, and similarly porous regions where no liquid water breakthrough is observed. It is found that the behaviour shown in the identified regions are strongly linked to local pore-scale structural characteristics and capillary pressure distribution in the GDL. Investigating the 3D virtual GDL from around the microporous layer through to the channel interface, it is shown that liquid water pathways get increasingly defined with a decrease in spatial uniformity towards the flow channels. Pore-scale analysis and observed flow mechanisms show that the defined pathways are locally accessible paths of least capillary resistance dictated by pore radius and associated hydrophobicity. These findings highlight the important role that pore scale topology plays in addition to pore size distribution for future GDL design aimed at improving water management. Keywords— operando, fuel cell, water, pore structure, X-ray imaging 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, Western Economic Diversification Canada, and Canada Research Chairs.

An innovative application of multiple impinging jet flow field in fuel cells

AbstractThe flow field in a fuel cell is expected to distribute the reactants as uniformly as possible over the active plate, support the reasonable pressure drop across the channel and maximize the mass transfer through the catalyst layers. To simultaneously accomplish these requirements, an innovative multiple impingement jet flow field (MIJFF) is proposed in this study. A three‐dimensional thermo‐fluid simulation is used to evaluate the proposed idea and compare its performance against the commonly used parallel field flow (PFF). The domain of calculations includes a channel with multiple impingement jets linked to a porous gas diffusion layer under low Reynolds flow conditions. The results reveal that the suggested MIJFF design significantly increases the transport of the reactant gases through the catalyst layer. The penetration depth into the catalyst layer in the MIJFF arrangement is higher than that of the PFF setup and the use of the catalyst layer is optimized, which in turn can lead to a reduction of the activation drop. Compared to a PFF design under similar operating conditions, the mean Nusselt number is shown to increase by a factor of about 3.5 in the MIJFF setup. Furthermore, the temperature is more uniformly distributed in the MIJFF pattern which results in more effective distribution of the reactant gases over the active surface. The current study shows that under equal pressure drop conditions, the MIJFF exhibits a much higher performance than a PFF channel design. That is while the corresponding flow rate for the MIJFF is much lower than that of PFF.

Improvement of catalyst utilisation in PEM fuel cells through inhomogeneous distribution of Pt under channels and ribs

The non-uniform distribution of platinum across the channel and rib area within the cathode catalyst layers of proton exchange membrane fuel cells was experimentally and numerically studied. A two-dimensional, two-phase flow, isothermal model was developed to investigate the influence of various parameters on the current density with respect to electrode surface area and platinum loading. Approximately 70% cell performance was retained when no platinum was placed under the rib. Owing to the slow oxygen supply to the rib area, increasing the platinum loading significantly reduced the effective oxygen concentration under the rib, leading to low platinum utilisation in this region. The large channel/rib width ratio and highly porous gas diffusion layer improved the cell performance when the conductivity was sufficiently high. The optimal platinum loading under the rib matched the oxygen consumption rate under the rib and the rate of oxygen supply to the rib area from the channel.

Two-phase Flow Dynamics at the Interface Between GDL and Gas Distributor Channel Using a Pore-Network Model

For improved operating conditions of a polymer electrolyte membrane (PEM) fuel cell, a sophisticated water management is crucial. Therefore, it is necessary to understand the transport mechanisms of water throughout the cell constituents especially on the cathode side, where the excess water has to be removed. Pore-scale modeling of diffusion layers and gas distributor has been established as a favorable technique to investigate the ongoing processes. Investigating the interface between the cathode layers, a particular challenge is the combination and interaction of the multi-phase flow in the porous material of the gas diffusion layer (GDL) with the free flow in the gas distributor channels. The formation, growth and detachment of water droplets on the hydrophobic, porous surface of the GDL have a major influence on the mass, momentum and energy exchange between the layers. A dynamic pore-network model is used to describe the flow through the porous GDL on the pore-scale. To capture the droplet occurrence and its influence on the flow, this dynamic two-phase pore-network model is extended to capture droplet formation and growth at the surface of the GDL as well as droplet detachment due to the gas flow in the gas distributor channels. In this article, the developed model is applied to single- and multi-tube systems to investigate the general drop behavior. These rather simple test-cases are compared to experimental and numerical data available in the literature. Finally, the model is applied to a GDL unit cell to analyze the interaction between two-phase flow through the GDL and drop formation at the interface between GDL and gas distributor channel.

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.

Experimental Characterization of Anisotropic Mechanical and Thermal Properties of Gas Diffusion Layers

Gas diffusion layer (GDL) is a vital component in proton exchange membrane fuel cells (PEMFC) due its main functions to conduct electrons and heat between the adjacent fuel cell components, provide preferential pathways for product water removal and to provide uniform reactant gas flow distribution to the electrode surface. Because of the anisotropic GDL microstructure, the transport properties vary in the through-plane and in-plane direction. Furthermore, during fuel cell stack assembly pressures exerted on the flowfield land compress the GDL under land cause changes of the GDL microstructure. While moderate compression increases GDL thermal conductivity due to increased fiber-fiber contacts, excessive compression may impede diffusive and liquid water transport due to loss of GDL pore volume. Detailed knowledge of how thermal conductivity is affected by the anisotropic nature of gas diffusion layers under compression is imperative in order to provide a better understanding on how thermal gradients influence two-phase transport during PEMFC operation. Previous research efforts have focused on steady-state methods for measuring effective through-plane GDL thermal conductivity [1][2][3][4] and effective in-plane GDL thermal conductivity [5][6] but to the best of our knowledge no studies have been conducted to measure effective in-plane GDL thermal conductivity for a variety of different GDL types under compression.This study attempts to fill that gap by using specially designed in-house tools to characterize the influence of GDL anisotropy on effective thermal conductivity as a function compression for different GDL types. Furthermore, a comprehensive ex-situ mechanical study is conducted to characterize the compliance matrix for different GDL types. Early results indicate a highly non-linear compressive behaviour in the GDL through-plane direction with large variations for the different GDL types. Moreover, the flexural modulus is found to be highly anisotropic where stiffness in the GDL machine direction (MD) is consistently larger compared to stiffness in GDL cross machine direction (CMD). This work will provide a foundation for a numerical study to couple an anisotropic GDL structural model with a non-isothermal two-phase model to investigate the effects of inhomogenous compression on two-phase transport. Keywords: GDL, PEMFC, ex-situ, anisotropy, modulus, microstructure, mechanical, compression, characterization, MD, CMD, through-plane, in-plane, thermal conductivity[1] G. Karimi, X. Li, P. Teertstra, Electrochim. Acta (2010).[2] R. Bock, A.D. Shum, X. Xiao, H. Karoliussen, F. Seland, I. V. Zenyuk, O.S. Burheim, J. Electrochem. Soc. 165 (2018) F514–F525.[3] G. Unsworth, N. Zamel, X. Li, Int. J. Hydrogen Energy (2012).[4] E. Sadeghi, N. Djilali, M. Bahrami, J. Power Sources (2011).[5] E. Sadeghi, N. Djilali, M. Bahrami, J. Power Sources (2011).[6] N. Alhazmi, D.B. Ingham, M.S. Ismail, K.J. Hughes, L. Ma, M. Pourkashanian, Int. J. Hydrogen Energy (2013).

Modeling of Two Phase Flow in a Hydrophobic Porous Medium Interacting with a Hydrophilic Structure

Fluid flow through layered materials with different wetting behavior is observed in a wide range of applications in biological, environmental and technical systems. Therefore, it is necessary to understand the occuring transport mechanisms of the fluids at the interface between the layered constituents. Of special interest is the water transport in polymer electrolyte membrane fuel cells. Here, it is necessary to understand the transport mechanisms of water throughout the cell constituents especially on the cathode side, where the excess water has to be removed. This is crucial to choose optimal operating conditions and improve the overall cell performance. Pore-scale modeling of gas diffusion layers (GDLs) and gas distributor has been established as a favorable technique to investigate the ongoing processes. Investigating the interface between the hydrophobic porous GDL and the hydrophilic gas distributor, a particular challenge is the combination and interaction of the different material structures and wetting properties at the interface and its influence on the flow. In this paper, a modeling approach is presented which captures the influence of a hydrophilic domain on the flow in a hydrophobic porous domain at the interface between the two domains. A pore-network model is used as the basis of the developed concept which is extended to allow the modeling of mixed-wet interactions at the interface. The functionality of the model is demonstrated using basic example configurations with one and several interface pores and it is applied to a realistic GDL representation in contact with a channel-land structured gas distributor.

Overall and local effects of operating parameters on water management and performance of open-cathode PEM fuel cells

Water management in open-cathode PEM fuel cells is challenging due to direct supply of ambient air. In this contribution, the water transport mechanisms and local water distributions in open-cathode PEM fuel cells are studied using local current measurement and various electrochemical methods. The results show local membrane dehydration occurs and the water distribution is much uneven when current density is lower than 200 mA cm−2. As operating current increases, the water content of membrane increases rapidly until the membrane is fully hydrated and the local water distribution also becomes more uniform. Whereas, liquid water begins to accumulate in gas diffusion layer and catalyst layer when the current density is over 700 mA cm−2. Furthermore, the effects of operating conditions are investigated. On the one hand, when the current density is lower than 500 mA cm−2, improving temperature and air velocity can reduce cell performance as too much water is removed out of fuel cell, leading to membrane dehydration. On the other hand, when the current density is above 600 mA cm−2, increasing cell temperature and air velocity can improve cell performance by removing excessive water in pores of gas diffusion layer and catalyst layer. The experimental fuel cell achieves the best performance with the temperature of 45℃ and air velocity of 2.2 m/s.

Narrow Pressure Stability Window of Gas Diffusion Electrodes Limits the Scale-Up of CO2 Electrolyzers.

Electrochemical CO2 reduction is a promising process to store intermittent renewable energy in the form of chemical bonds and to meet the demand for hydrocarbon chemicals without relying on fossil fuels. Researchers in the field have used gas diffusion electrodes (GDEs) to supply CO2 to the catalyst layer from the gas phase. This approach allows us to bypass mass transfer limitations imposed by the limited solubility and diffusion of CO2 in the liquid phase at a laboratory scale. However, at a larger scale, pressure differences across the porous gas diffusion layer can occur. This can lead to flooding and electrolyte breakthrough, which can decrease performance. The aim of this study is to understand the effects of the GDE structure on flooding behavior and CO2 reduction performance. We approach the problem by preparing GDEs from commercial substrates with a range of structural parameters (carbon fiber structure, thickness, and cracks). We then determined the liquid breakthrough pressure and measured the Faradaic efficiency for CO at an industrially relevant current density. We found that there is a trade-off between flooding resistance and mass transfer capabilities that limits the maximum GDE height of a flow-by electrolyzer. This trade-off depends strongly on the thickness and the structure of the carbon fiber substrate. We propose a design strategy for a hierarchically structured GDE, which might offer a pathway to an industrial scale by avoiding the trade-off between flooding resistance and CO2 reduction performance.