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An experimental in situ study was performed to investigate the effects of the catalyst layer (CL) and cathode microporous layer (MPLc ) perforation on the water management and performance of polymer electrolyte membrane fuel cells (PEMFCs). Polymeric pore formers were utilized to produce perforated CL and MPL structures. High-resolution neutron tomography was employed to visualize the liquid water content and distribution within different components of the cell under channel and land regions. The results revealed that at humid conditions, the perforated layers enhanced the liquid water transport under the channel regions. Moreover, at high current densities, the performance was improved for the cells with perforated layers compared to a baseline cell with non-perforated layers, owing to reduced mass transport losses.

The influence of porosity modification of both the cathode microporous layer (MPL) and catalyst layer (CL) of a low temperature polymer electrolyte membrane fuel cell (PEMFC) is studied with a neutron radiography technique to determine the water distribution and transport inside the cell. Three types of cathode MPLs with varying porosity distributions are made by introducing Chemisnow® monodisperse spherical polymer particles with 1.5 μm and 30 μm diameters inside the MPL slurry. CLs with three different porosities are manufactured by incorporation of 0 to 10 wt.% polystyrene particles with 0.5 μm diameters. Water thicknesses are measured inside the cell components at relative humidity of 120% with an increasing current density up to 1 A/cm². The results indicate that introducing micro pores into the structure of the MPL and CL may lead to the extraction of the excess water through these pores, leaving smaller pores accessible for the reaction gases and better cell performance.

Neutron tomography is used to visualize the effect of hydrophobicity variations within the micro porous layer (MPL) and membrane electrode assembly (MEA) of a low-temperature polymer electrolyte fuel cell (PEMFC) on the detailed distribution of water in an operating cell. MEAs and MPLs manufactured in-house with different degrees of wettability are implemented in miniature fuel cells featuring an active area of 8 cm², which are specifically designed for neutron imaging experiments. The tomographies are obtained with a pixel size of 13 µm while maintaining the same operating conditions for all cells for comparability. The quantitative analysis of the water content in two of these cells next to the lands and the channels of the flow field is shown in Figure 1. It can be clearly observed that the implementation of a hydrophobic MEA significantly changes the overall water distribution within the cell. In contrast to the reference MEA, where more water is found in the catalyst layers compared to the membrane, the hydrophobic MEA has a higher water content inside its membrane. Implementing a GDL with a more hydrophobic MPL on the cathode side shows a higher water content inside the GDL substrate under the lands compared to the channels. This information can significantly help the optimization of material designs and can also provide valuable data for modeling and simulations of water distributions inside PEMFCs. We will show a detailed analysis of hydrophobicity changes on the water distribution inside the cell components, characterization results of various MPLs and MEAs regarding wettability and porosity analysis as well as performance results at different operating conditions Figure 1

In a flow battery setup, carbon felt materials are compressed to obtain higher performance from the battery. In this work, a commercially available carbon felt material, commonly used as electrodes in Vanadium Redox Flow Battery setups was evaluated for the transport properties (diffusivity, permeability, pressure drop required for maintaining flow, among others) while under seven set levels of compression, using an image analysis coupled with pore network modeling approach. X-ray computed tomography has been used to obtain the microstructure of a commercially available electrode under compressed conditions. An open-source pore network modeling tool, OpenPNM has been used to investigate the transport properties of the porous felt material at each of the set compression levels. The results from the modeling are compared against experimentally obtained electrolyte transport patterns visualized using synchrotron X-ray radiography. The electrical resistance of the carbon felt electrode was measured experimentally using a four-probe method. The compression resulted in a 58% reduction in permeability, and a 25% reduction in single-phase diffusion. This combination of ex-situ characterization of the electrical and fluid transport through the electrodes provides valuable data for modeling flow battery systems, and validating hypothesis from in situ testing.

This work describes the effects of catalyst layers (CLs) consisting of hydrophobic PTFE on the performance and water management of PEM fuel cells. Catalyst inks with various PTFE contents were coated on Nafion membranes and characterized using contact angle measurements, SEX-EDX, and mercury porosimetry. Fuel cell tests and electrochemical impedance spectroscopy (EIS) were conducted under varying operating conditions for the prepared materials. At dry conditions, CLs with 5 wt.% PTFE were advantageous for cell performance due to improved membrane hydration, whereas under humid conditions and high air flow rates CLs with 10 wt.% PTFE improved the performance in high current density region. Higher PTFE contents (≥20 wt.%) increased the mass transport resistance due to reduced porosity of the CLs structure. Operando neutron radiography was utilized to study the effects of hydrophobicity gradients within CLs and cathode microporous layer (MPLC) on liquid water distribution. More hydrophobic CLs increased the water content in adjacent layers and improved performance, especially at dry conditions. MPLC with higher PTFE contents increased the overall liquid water within the CLs and GDLs and escalated the water transfer to the anode side. Furthermore, the role of back-diffusion transport mechanism on water distribution was identified for the investigated cells.

In this study, the effect of the catalyst layer (CL) and the cathode microporous layer (MPL-C) porosity on the performance and water content of the polymer electrolyte membrane (PEMFC) is investigated. Monodispersed polystyrene (PS) particles are used as pore formers to fabricate CL and MPL with different degrees of porosities. Specially developed miniature Single single cells for neutron imaging experiments with an active area of 8 cm² are implemented with the in-house made catalyst coated membranes and cathode MPLs. The cathode MPLs were coated on a 29 BA substrate, and commercial 29 BC SGL were used on the anode side as the gas diffusion layers (GDLs). Neutron tomography is used to investigate the water content and distribution inside the operating fuel cells. The quantitative analysis of the water thickness under the channels of the cells at RH=120% and I=1 A.cm-2 is shown in figure 1.a. It is observed that the water content has decreased for cell 3 ( CL: 10 wt.% PS, MPL: 10 Vol.% PS) compared to cell 2 ( CL: 5wt.% PS, MPL:10 Vol.% PS) and cell 1 (Reference CL and MPL (without PS)). Polarisation curves for these three cells are provided in Figure 1.b. At current densities higher than I=1 A.cm-2 performance has increased for cell 2 and 3 where the components had higher porosity degree compared to the cell 1 which has a reference CL and reference cathode MPL. The results show that addition of macropores could facilitate the transport of gases and the removal of water at the mass transport regions. This method is currently under investigation by the authors. Further results will be provided in the presentation. Figure 1

The influence of porosity modifications of either microporous layer (MPL) or the catalyst layer of a low temperature Polymer Electrolyte Membrane Fuel Cell (PEMFC) on the performance of the cell has been investigated in many studies. However, we have been focusing in our study on the interactive impact of this morphological modification of both cathode MPL and catalyst layer in the water distribution and transport inside the cell and consequently also on the performance of the cell. In this study, three types of cathode MPLs with different porosity distributions and three type of membrane electrode assemblies (MEA) with different porosity of the catalyst layer are manufactured. Five one-cell fuel cells are investigated using combinations of those in-house made layers. To modify the porosity of the cathode MPL polymer particle in two sizes of 30 µm and 1.5 µm from company Chemisnow® are introduced into the carbon slurry, which are then evaporated out of the MPL during the sintering process. For the catalyst layers, 0.5 µm Polystyrene particles are mixed in the electrode slurry with variable weight fractions and then washed out of the dried MEA. A more detailed description of the production procedure of these layers will be demonstrated in the presentation. Performance of fuel cells using these five combination of cathode MPL and electrode are measured using a Fuel Cell with 25 cm² active area and 3 serpentine channel flow fields. Neutron Radiography is used to investigate the water distribution dynamics and water content of the fuel cell. For this purpose, a specially designed single cell with 8 cm² active area and 3 serpentine channel flow fields is used. The measurements are obtained at two different humidity values on both cathode and anode inlet gases of RH=70% and RH=120% and different current densities. With an exposure time of 10 s, images with 12.4 µm pixel size are achieved. The quantitative analysis of the water thickness in the cathode GDL and cathode electrode of 5 cells at RH=120% for an increasing current density is shown at an exemplary radiogram for water distribution inside the cell with our reference cathode MPL and electrode (without porosity modification). Also the Current (ICell) and Voltage (VCell) evolution of the same cell is shown in figure 1. All cells have reached a water content plateau even before reaching the highest current density of 1A/cm². The cell with a porous catalyst layer and a double layer cathode MPL shows the highest water content on the cathode side of the cell, whereas the cell with a highly porous catalyst layer and a porous MPL shows the lowest water content of all cells, comparable to the water thickness observed for the cell without modified layers. Further results of both water content and performance dependent on porosity changes will be provided in the presentation. Figure 1

The water inventory of PEMFC components strongly influences the performance under two-phase operating conditions. Within this work, the influence of hydrophobicity variation within electrode and microporous layer (MPL) on cell performance will be presented. Different weight percentages of PTFE is used in the catalyst and MPL inks as an additive in order to increase the hydrophobicity. The fabrication method for the membrane electrode assembly (MEA) is based on spraying the catalyst ink onto the membrane and coating MPL ink onto the GDL substrate using a doctor blade method. Fuel cell tests are carried out with a 25 cm² active area single cell at different relative humidities (RH) and oxygen flow rates to investigate the effect of PTFE on the ability of MEA and MPL on water management. Electrochemical impedance spectroscopy is performed as a diagnostic tool to investigate the reaction kinetics and mass transport. In order to assess the wettability of MEAs contact angle measurements were carried out. The materials are characterized by mercury porosimetry and scanning electron microscopy. Figure 1 shows the performance curve for cell 1 (conventional MEA +Conventional MPL), cell 2( MEA with 5 wt.% PTFE +Conventional MPL) and cell 3 (Conventional MEA+ MPL with 40 wt.% PTFE ) at different relative humidities. At dry conditions (RH=70%) cell 2 has a higher limiting current density compared to the other cells, which could be the indication that the hydrophobic electrode keeps the membrane material in the catalyst layer better hydrated. At over humidified conditions (RH=120%) the limiting current density value has decreased for cell 1 and 2 compared to the standard conditions (RH=100%) as a result of mass transport limitations. On contrary, Cell 3 shows an improved performance in high current density region at humid conditions, illustrating the ability of hydrophobic MPL to prevent the accumulation of liquid water at the interphase of MPL and catalyst layer at cathode side. In the presentation of the ongoing work, additional results, including HFR data will be reported. Figure 1

Neutron radiography imaging is employed to investigate the effect of hydrophobicity gradients between the membrane electrode assembly (MEA) and microporous layer (MPL) of a low-temperature polymer electrolyte membrane fuel cell (PEMFC) on the water distribution and transport in operating cells. Single cells specially developed for neutron imaging experiments with an active area of 8 cm² are equipped with in-house made MEAs and MPLs featuring different degrees of wettability. Imaging is performed with a pixel size of 13 µm and the cells are operated at two different current densities of 1 and 0.75 A cm-2 and a relative humidity of RH=70% and RH=120% at a temperature of 55°C. A first quantitative analysis of the water thickness in electrodes and gas diffusion layers (GDLs) of 3 cells at RH=120% and i=1 A cm-2 as well as an exemplary radiogram for the water distribution inside one of the cells is shown in figure 1. It is observed that the implementation of both a more hydrophobic MEA and MPL results in an increase of overall water content inside the cell. Nevertheless, the effect of a more hydrophobic MPL on the increase of the water content of the cell, under the operating conditions investigated here, is apparently more significant compared to the effect of a more hydrophobic MEA. As expected, the amount of water found on the cathode side is higher than on the anode side for all components of the cell. The sudden accumulation of water on anode side which is appearing in periodic peaks with equal time intervals is associated to an increased rate of back diffusion mechanisms. The cell with a more hydrophobic MEA has decreased the magnitude of these fluctuation peaks by 30%, whereas this reduction ratio is 60% for the cell with more hydrophobic MPL, resulting to a more balanced water profile across the membrane. In this presentation, we will show further morphological and wetting property characterization results of various MEAs and MPLs and analyze the effect of hydrophobicity on the dynamical changes of water distribution and transport at different operating conditions. Figure 1