Gas Diffusion Research Articles

Effect of Non-ionic Surfactant on Fe-N-C Catalyst Layers under HT-PEMFC Conditions

The effect of different non-ionic surfactant contents on Fe-N-C gas diffusion electrode (GDE) coating and performance is investigated. GDEs are tested under high temperature polymer electrolyte membrane fuel cell (HT-PEMFC) conditions at 160 °C and concentrated phosphoric acid electrolyteFe-N-C-based GDEs are fabricated through ultrasonic spray coating with Tergitol contents of 0, 1, 20 and 50 wt% in the catalyst layer (CL). Thereby, the PTFE to catalyst ratio is kept constant at 1.0 in the CL. The H2O contact angle decreases with increasing Tergitol™ content in the CL, revealing an increased wettability. H3PO4 contact angles of Tergitol containing GDEs show a same wettability at room temperature as at 160 °C. GDE half-cell setup investigations show, that Tergitol leads to flooding of the electrode by the electrolyte and coverage of the active sites by the surfactant and thus a performance decay.

Effect of Non-ionic Surfactant on Fe-N-C Catalyst Layers under HT-PEMFC Conditions

The effect of different non-ionic surfactant contents on Fe-N-C gas diffusion electrode (GDE) coating and performance is investigated. GDEs are tested under high temperature polymer electrolyte membrane fuel cell (HT-PEMFC) conditions at 160 °C and concentrated phosphoric acid electrolyteFe-N-C-based GDEs are fabricated through ultrasonic spray coating with Tergitol contents of 0, 1, 20 and 50 wt% in the catalyst layer (CL). Thereby, the PTFE to catalyst ratio is kept constant at 1.0 in the CL. The H2O contact angle decreases with increasing Tergitol™ content in the CL, revealing an increased wettability. H3PO4 contact angles of Tergitol containing GDEs show a same wettability at room temperature as at 160 °C. GDE half-cell setup investigations show, that Tergitol leads to flooding of the electrode by the electrolyte and coverage of the active sites by the surfactant and thus a performance decay.

Advances in Fuel Cell Performance Using Simulation Analysis in Toshiba Energy Systems & Solutions Corporation

The influence of channel and rib width of bi-polar plates on gas diffusion performance was investigated by simulation and experimental measurement. Simulation results showed that a ch./rib ratio of about 2 is a compromise between diffusivity and resistance, and that higher performance can be expected. The advanced cell with bi-polar plates with this flow channel geometry was fabricated and its performance was evaluated. IV characteristics of advanced cell exceeded simulation results, indicating that the effect of improved GDL/MPL tortuosity on diffusion performance was greater than expected.

From Catalyst Ink to PEM Fuel Cell Stack: First Full-Size Screen Printed Catalyst Layers Tested within a Generic Stack

This study presents a comprehensive investigation and research platform to introduce a production process chain from catalyst ink to a generic stack level. Screen printed catalyst layers are upscaled to meet industrial active areas of 283 cm² and decal transferred onto the polymer electrolyte membrane with a roll calender, which process parameters were optimized. Afterwards, the subgaskets and gas diffusion layers were applied, and a short stack has been assembled. For the first time, screen printed catalyst layers have been tested within a short stack of automotive size, showing the same performance as its commercial references. This sets the starting point for a successful manufacturing process and stack testing platform, which is valuable especially for CCM material and component manufacturers as well as the research community.

Spontaneous formation of reactive redox radical species at the interface of gas diffusion electrode

The aqueous interface-rich system has been proposed to act as a trigger and a reservoir for reactive radicals, playing a crucial role in chemical reactions. Although much is known about the redox reactivity of water microdroplets at “droplets-in-gas” interfaces, it remains poorly understood for “bubbles-in-water” interfaces that are created by feeding gas through the porous membrane of the gas diffusion electrode. Here we reveal the spontaneous generation of highly reactive redox radical species detected by using electron paramagnetic resonance under such conditions without applying any bias and loading any catalysts. In combination with ultraviolet-visible spectroscopy, the redox feature has been further verified through several probe molecules. Unexpectedly, introducing crown ether allows to isolate and stabilize both water radical cations and hydrated electrons thus substantially increasing redox reactivity. Our finding suggests a reactive microenvironment at the interface of the gas diffusion electrode owing to the coexistence of oxidative and reductive species.

Spatially Resolved Analysis of the Influence of Three-Dimensional Flow Field Structures on Loss Processes in PEMFCs

This study introduces a novel measurement device and technique to spatially resolve the influence of 3D flow field structures consisting of extended metal meshes on the performance distribution in PEMFCs. The newly designed segmented cell enables not only the measurement of the current distribution but also local electrochemical impedance spectra, subsequently analyzed by the distribution of relaxation times. The 3D flow field structures provide, despite of an increased HFR, an advantage at high current densities. The spatially resolved DRT analysis enabled the identification of polarization processes revealing that the gas diffusion process is greatly reduced compared to a conventional channel-rib design. In particular, the 3D coarse mesh shows promising advantages for application under high current densities. The findings from this study provide valuable insights into the local power and resistance distribution, enabling optimization of the flow field design and improvement of the performance of fuel cells with large active areas.

Understanding the Impact of Gas Diffusion Layer Degradation on Water Inventory in Low Temperature PEM Fuel Cells for Heavy Duty Vehicles Application: Operando X-Ray and Neutron Imaging Study

Samples from two materials representing the condition at begin and end of life, were selected from testing of commercial, state-of-the-art PEM fuel cell stacks. Using small-area single cell setups specifically developed for visualization purposes, operando synchrotron and neutron imaging experiments to visualize water dynamics and distribution within these cells were performed. In this study, the effects of aging on water inventory in the gas diffusion layers throughout the lifespan of the cells are investigated. The findings provide insights into how aging influences water management, which is crucial for optimizing the performance and longevity of PEM fuel cells for heavy-duty applications.

Advances in Fuel Cell Performance Using Simulation Analysis in Toshiba Energy Systems & Solutions Corporation

The influence of channel and rib width of bi-polar plates on gas diffusion performance was investigated by simulation and experimental measurement. Simulation results showed that a ch./rib ratio of about 2 is a compromise between diffusivity and resistance, and that higher performance can be expected. The advanced cell with bi-polar plates with this flow channel geometry was fabricated and its performance was evaluated. IV characteristics of advanced cell exceeded simulation results, indicating that the effect of improved GDL/MPL tortuosity on diffusion performance was greater than expected.

From Catalyst Ink to PEM Fuel Cell Stack: First Full-Size Screen Printed Catalyst Layers Tested within a Generic Stack

This study presents a comprehensive investigation and research platform to introduce a production process chain from catalyst ink to a generic stack level. Screen printed catalyst layers are upscaled to meet industrial active areas of 283 cm² and decal transferred onto the polymer electrolyte membrane with a roll calender, which process parameters were optimized. Afterwards, the subgaskets and gas diffusion layers were applied, and a short stack has been assembled. For the first time, screen printed catalyst layers have been tested within a short stack of automotive size, showing the same performance as its commercial references. This sets the starting point for a successful manufacturing process and stack testing platform, which is valuable especially for CCM material and component manufacturers as well as the research community.

Understanding the Impact of Gas Diffusion Layer Degradation on Water Inventory in Low Temperature PEM Fuel Cells for Heavy Duty Vehicles Application: Operando X-Ray and Neutron Imaging Study

Samples from two materials representing the condition at begin and end of life, were selected from testing of commercial, state-of-the-art PEM fuel cell stacks. Using small-area single cell setups specifically developed for visualization purposes, operando synchrotron and neutron imaging experiments to visualize water dynamics and distribution within these cells were performed. In this study, the effects of aging on water inventory in the gas diffusion layers throughout the lifespan of the cells are investigated. The findings provide insights into how aging influences water management, which is crucial for optimizing the performance and longevity of PEM fuel cells for heavy-duty applications.

The Effects of Contact By the Catalyst Layer and the Gas Diffusion Layer Interface on the Performance of a PEFC with Marimo-like Carbon

When assembling a proton exchange membrane fuel cell (PEMFC), a clamping pressure is applied to all the components. The catalyst layer (CL) and gas diffusion layer (GDL) are compressed to the gasket thickness by the clamping during assembly. This compression increases the conductivity of the protons and electrons while reduces the size of the pores, which are the removal channels for the generated water and the diffusion channels for the fuel and air gases. We evaluated the effect of the CL compression prepared with the Marimo-like carbon (MC) regarding the I-V performance. The MC is a higher order structure of carbon fibers. The maximum power density was the highest (237 mW cm-2) at the 22% compression ratio. The excessive compression was suggested to have a higher effect on blocking the diffusion channels of the fuel and air gases than on improving the conductivity.

Self-Supporting Microporous Layer for Polymer Electrolyte Fuel Cells Using Thin Carbon Mesh Gas Diffusion Layer

The gas diffusion layers (GDLs) used in polymer electrolyte fuel cells (PEFCs) are relatively thick compared with the electrocatalyst layer and electrolyte membrane. Reducing GDL thickness is expected to reduce gas transport resistance. Such thin GDLs with high electrical conductivity enable higher power density per volume of cell stacks. Here, thin MPL/GDLs are fabricated by printing a highly conductive microporous layer (MPL) on carbon meshes or carbon nanotube sheets as a substrate to create tailored self-supporting MPLs. The electrical conductivity was improved by optimizing the carbon black material used in the MPL, and carbon nanotubes were added to tailor a pore structure within the MPL. The thickness of the resulting MPL/GDLs is approaching 50 µm, which is not only thinner than the current MPL/GDL, but also results in lower gas transport resistance. The thinner MPL/GDLs are a promising solution to increase the power density of PEFC cell stacks.

Physiopathology of High-Altitude Pulmonary Edema.

The air-blood barrier is well designed to accomplish the matching of gas diffusion with blood flow. This function is achieved by maintaining its thickness at ∼0.5 µm, a feature implying to keep extravascular lung water to the minimum. Exposure to hypobaric hypoxia, especially when associated with exercise, is a condition potentially leading to the development of the so-called high-altitude pulmonary edema (HAPE). This article presents a view of the physiopathology of HAPE by merging available data in humans exposed to high altitude with data from animal experimental approaches. A model is also presented to characterize HAPE nonsusceptible versus susceptible individuals based on the efficiency of alveolar-capillary oxygen uptake and estimated morphology of the air-blood barrier.

Water Permeability and Oxygen Transport Resistance of Hydrophilic and Hydrophobic Composite Microporous Layer Coated Gas Diffusion Layer

Enhancing water management to mitigate the performance impact of humidity fluctuations is crucial in PEFC applications. A novel microporous layer (MPL) incorporated with both hydrophilic and hydrophobic properties, applied to the gas diffusion layer (GDL), has been developed and demonstrated to enhance robustness under varying humidity levels. This study utilized water permeability test results to analyze the composite MPL, distinguishing between hydrophobic and hydrophilic absolute permeability ratios. By elucidating these ratios, insights into their roles in liquid water distribution and oxygen transport resistance were gained, distinguishing the composite MPL from conventional hydrophobic and hydrophilic MPLs. Ultimately, the performance of the composite MPL under high and low humidity conditions highlighted its robustness across diverse humidity environments.

Water Permeability and Oxygen Transport Resistance of Hydrophilic and Hydrophobic Composite Microporous Layer Coated Gas Diffusion Layer

Enhancing water management to mitigate the performance impact of humidity fluctuations is crucial in PEFC applications. A novel microporous layer (MPL) incorporated with both hydrophilic and hydrophobic properties, applied to the gas diffusion layer (GDL), has been developed and demonstrated to enhance robustness under varying humidity levels. This study utilized water permeability test results to analyze the composite MPL, distinguishing between hydrophobic and hydrophilic absolute permeability ratios. By elucidating these ratios, insights into their roles in liquid water distribution and oxygen transport resistance were gained, distinguishing the composite MPL from conventional hydrophobic and hydrophilic MPLs. Ultimately, the performance of the composite MPL under high and low humidity conditions highlighted its robustness across diverse humidity environments.

Improved Understanding of PEMFC Stack Durability Testing through Comprehensive In-Situ and Ex-Situ Characterization Techniques

Durability testing of Proton Exchange Membrane Fuel Cells for mobile applications remains a critical challenge. While most academic studies focus on single-cell testing, there are only few publications on stack testing of technical relevant sizes. This study utilizes comprehensive characterization techniques to enhance understanding of PEMFC stack durability, aiming to meet the currently targeted durability targets. A 5,500-hour long-term test, based on the Auto Stack Industry (ASI) test protocol, was performed on a 7-cell short stack of 240 cm² active area. In-situ techniques, such as spatially resolved current density measurement, cyclic voltammetry, and electrochemical impedance spectroscopy, provided real-time degradation insights, while ex-situ methods, including FIB-SEM analysis, infrared thermography or contact angle measurements provided information on material degradation mechanisms. Membrane degradation was found to be negligible. Slight thinning of the cathode indicates carbon corrosion of the catalyst support. Catalyst aging was observed in the form of Pt band formation and Co leaching. Gas diffusion layers showed hydrophobicity loss, and increased resistance in bipolar plates contributed to reduced performance. Our findings demonstrate that PEMFC stacks operated under automotive drive cycle protocols can meet the actual targeted durability objectives. Moreover, it illustrates the degradation phenomena that occur under realistic operating conditions and modes, and how they evolve over the duration of thousands of hours of operation.

Spatially Resolved Analysis of the Influence of Three-Dimensional Flow Field Structures on Loss Processes in PEMFCs

This study introduces a novel measurement device and technique to spatially resolve the influence of 3D flow field structures consisting of extended metal meshes on the performance distribution in PEMFCs. The newly designed segmented cell enables not only the measurement of the current distribution but also local electrochemical impedance spectra, subsequently analyzed by the distribution of relaxation times. The 3D flow field structures provide, despite of an increased HFR, an advantage at high current densities. The spatially resolved DRT analysis enabled the identification of polarization processes revealing that the gas diffusion process is greatly reduced compared to a conventional channel-rib design. In particular, the 3D coarse mesh shows promising advantages for application under high current densities. The findings from this study provide valuable insights into the local power and resistance distribution, enabling optimization of the flow field design and improvement of the performance of fuel cells with large active areas.

Numerical Investigation on Two-Phase Flow Pressure Drop in Cathode Channels of Proton Exchange Membrane Fuel Cells

As liquid water is produced by electrochemical reactions in a proton exchange membrane (PEM) fuel cell, liquid–gas two-phase flow forms within the porous structure of the electrodes and gas channels (GCs), resulting in complex gas pressure drop within GCs. This study investigates the two-phase flow pressure drop in a GC connected with a fibrous gas diffusion layer (GDL) using volume of fluid simulations. Fibrous GDLs are stochastically reconstructed to give a rather realistic liquid water breakthrough, and the effect of GDL straight and curved carbon fibers is studied. The results show that droplet breakthrough position and breakthrough size are dependent on the carbon fiber shape, resulting in further distinct pressure drop in GCs. It is also found that the two-phase flow pressure drop has no close correlation with the water content within the GC but a strong relationship with the liquid flow types. Specifically, the cross-section liquid area variation along the gas flow direction is found to be proportional to the pressure drop variation. This study aims to provide the information required for an accurate two-phase flow pressure drop prediction model.

Improved Understanding of PEMFC Stack Durability Testing through Comprehensive In-Situ and Ex-Situ Characterization Techniques

Durability testing of Proton Exchange Membrane Fuel Cells for mobile applications remains a critical challenge. While most academic studies focus on single-cell testing, there are only few publications on stack testing of technical relevant sizes. This study utilizes comprehensive characterization techniques to enhance understanding of PEMFC stack durability, aiming to meet the currently targeted durability targets. A 5,500-hour long-term test, based on the Auto Stack Industry (ASI) test protocol, was performed on a 7-cell short stack of 240 cm² active area. In-situ techniques, such as spatially resolved current density measurement, cyclic voltammetry, and electrochemical impedance spectroscopy, provided real-time degradation insights, while ex-situ methods, including FIB-SEM analysis, infrared thermography or contact angle measurements provided information on material degradation mechanisms. Membrane degradation was found to be negligible. Slight thinning of the cathode indicates carbon corrosion of the catalyst support. Catalyst aging was observed in the form of Pt band formation and Co leaching. Gas diffusion layers showed hydrophobicity loss, and increased resistance in bipolar plates contributed to reduced performance. Our findings demonstrate that PEMFC stacks operated under automotive drive cycle protocols can meet the actual targeted durability objectives. Moreover, it illustrates the degradation phenomena that occur under realistic operating conditions and modes, and how they evolve over the duration of thousands of hours of operation.

Simulation of Gas Diffusion–Adsorption Coupling in Adsorbents for Optimizing Pore Structures

Simulation of Gas Diffusion–Adsorption Coupling in Adsorbents for Optimizing Pore Structures