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

Polymer electrolyte fuel cells (PEFCs) are attracting attention as energy device of low environmental impact because of their high generation efficiency and their emitting only water. The gas supplied to the PEFC is humidified, and water is produced at the cathode catalytic layer by the electrochemical reaction between oxygen and protons. The gas diffusion layer (GDL) and micro porous layer (MPL) in PEFC plays an important role in the transport of oxygen and water. When liquid water accumulates in the GDL, the supply of oxygen to the cathode is inhibited, resulting in poor generation performance. In order to maintain the performance of PEFCs, it is important to manage the water in the cell.Attempts have been made to visualize the liquid water in GDLs and MPLs for better GDL and MPL design; X-ray micro computed tomography (micro-CT) is one powerful tool for this. Visualization of liquid water in GDLs and MPLs using micro-CT has so far revealed the behavior of the produced water[1,2]. However, in previous studies, it has been difficult to visualize liquid water in the catalyst layer, which is the reaction field where the water is produced. This is because the spatial resolution of micro-CT is larger than a µm, which is insufficient for analyzing liquid water in the catalytic layer. X-ray CT measurements with a resolution of at least 150 nm are needed to measure the distribution of liquid water in the cross section of the catalyst layer. In this study, a measurement system to reveal the distribution of liquid water in the catalyst layer was developed using a 150 nm-spatial-resolution X-ray CT with a synchrotron radiation x-ray microscope called X-ray nano-CT.A GDL specimen prepared cut to a disk shape with 1 mm diameter. The GDL specimen mounted on a copper stage with high thermal conductivity connected Peltier element module. The micro-CT and nano-CT measurements were carried out in BL20XU beamline at SPring-8, Japan. An X-ray beam energy was 30 keV with a double crystal monochromator. The nano-CT measurements were performed using Zernike phase contrast with voxel size of 38.4 nm. We measured the micro-CT and nano-CT of the dry condition of the GDL specimen. Then, the GDL specimen injected liquid water was scanned. Injection of liquid water into the GDL specimen is not easy because of water-repellent of GDLs. Helium gas saturated water vapor at 40 °C was sprayed to the GDL at 30 ml/min, then the GDL cooled to 10 °C using a Peltier element module and the vapor was condensed inside of the GDL. The measurement setup is shown in Figure 1. This water injection in GDL method was based on the method reported by Kato et al [2].Figure 2 shows the optical system of the nano-CT used in this study. The optical system of this nano-CT provides a condenser zone plate for sample illumination, a Fresnel zone plate for enlarged image, and phase ring for Zernike phase contrast. These optics allow CT with a high spatial resolution of 150 nm to be measured even for materials with low X-ray absorption.A three-dimensional structure of GDL was revealed by CT measurements in each scale order. The distribution of liquid water in GDL were visualized with nanoscale spatial resolution (Figure 3). We have successfully visualized the three-dimension distribution of liquid water in the GDL with nm order scale using nano-CT. The newly established nano-CT with a spatial resolution of 150 nm order is extremely useful for elucidating liquid-water behavior in PEFCs containing catalyst layers, which was not clear before. Acknowledgements This work is based on results obtained from a NEDO FC-Platform project commissioned by the New Energy and Industrial Technology Development Organization (NEDO). This study was partially supported by the Synchrotron radiation experiments performed at BL20XU of SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) (Proposal numbers 2021A2009, 2021B1015).

Polymer electrolyte fuel cell (PEFC) is promising as a next generation power source for vehicles due to the high efficiency. To make the PEFC commercially competitive, the reduction of the cost is necessary. For the reduction of the cost of PEFC, it is required to increase the maximum current density. Under the high current density operation, the water produced in a catalyst layer (CL) accumulates in a gas diffusion layer (GDL) and the supply of oxygen is suppressed. Therefore, the water transport in the GDL is important to increase the maximum current density of PEFC. To improve the water transport in the GDL, the wettability distribution is important factor. Utaka el al. showed that better cell performance is obtained by forming the hydrophilic region in the hydrophobic GDL because the water transport in the GDL is controlled by the hydrophilic region (1). Similarly, Forner-Cuenca et al. showed that the cell performance is improved by the GDL with the hydrophilic region (2). There are some reports which showed the water transport is improved by the control of the wettability of the GDL. However, these reports are focused on the planer distribution in the GDL and the effect of the wettability distribution in the thickness direction is not clear. For the optimization of GDL structure, it is necessary to clarify the effect of the wettability distribution in the thickness direction. Therefore, in this study, the effect of the wettability distribution in the thickness direction was investigated. To evaluate the water transport in the GDL with the wettability distribution in the thickness direction, a lattice Boltzmann method (LBM) was used (3). Figure 1 shows the simulation domain and boundaries. The size of GDL is 80μm × 80μm × 80μm and the porosity of GDL is 70%. The bottom of the simulation domain is assumed the micro-porous layer (MPL) and it is treated as a solid wall. MPL crack as inlet boundary is set in the MPL. The top of the simulation domain is outlet boundary. The four sides of the simulation domain are solid walls. The contact angle of GDL, MPL and side walls is set 130º. The density of the two-phase in the simulation is set identical to water, ρ = 978kg/m3. The interfacial tension between the two-phase is σ = 6.40×10-2N/m, and liquid and gas viscosities are μL = 4.04×10-4Pa∙s and μG = 2.30×10-5Pa∙s respectively. Figure 2 shows simulation results of water transport in GDL. Figure 2 (a) shows the result for the GDL without the wettability distribution. The contact angle of the GDL is uniform (130 º). Figure 2 (b) shows the result for the GDL with the wettability distribution in the thickness direction. The contact angle from the GDL surface to the depth of 16 μm is 50º and the other regions of the GDL is 130º. In these figures, the water is shown in red. With the water transport in the GDL without the wettability distribution (Fig. 2 (a)), the water was inflowed to the large pore in the center of the GDL (0.32ms). The water was spread in the large pore (0.96ms). After the much water was accumulated in the GDL, the water was reached at the GDL surface (1.9ms). With the water transport in the GDL with the wettability distribution in the thickness direction (Fig. 2 (b)), the water was inflowed to the large pore in the center of the GDL and the water accumulated in the GDL as well as the GDL without the wettability distribution (0.32ms, 0.96ms). When the water was reached at the hydrophilic region in the top of GDL, the water in the GDL was pulled up to the GDL surface and the amount of the water in the center of the GDL was reduced (1.2ms). Compared with the GDL without wettability distribution, the time when the water reached the GDL surface was earlier in the GDL with wettability distribution. Therefore, the water transport in the thickness direction is improved by the wettability distribution in the thickness direction. In the final full paper, the large-scale simulation including the rib and channel will be carried out and the effect of the wettability in the thickness direction will be discussed. Reference (1) Y. Utaka, R. Koresawa, J. Power Sources, 363, 227-233 (2017). (2) A. Forner-Cuenca, J. Biesdorf, V. Manzi-Orezzoli, L. Gubler, T. J. Schmidt, P. Boillat, J. Electrochem. Soc., 163 (13), F1389 (2016). (3) S. Sakaida, Y. Tabe, and T. Chikahisa, J. Power Sources, 361, 133-143 (2017). Figure 1

Proper water management in cathode porous electrode of polymer electrolyte fuel cells (PEFCs) is essential for achieving better performance. Especially at high current densities, excessive water produced by oxygen reduction reaction (ORR) on cathode side is rapidly condensed in catalyst layer (CL) and gas diffusion layer (GDL). When the open pores in cathode CL and the interface between CL and GDL are filled with liquid water, oxygen cannot be supplied to the reaction sites. This phenomenon, called “water flooding”, is a critical barrier for high efficiency and high power density operation. To alleviate this issue, it is necessary to understand and control liquid water transport inside cathode porous electrode. It is well known that microporous layer (MPL) plays a critical role in suppressing liquid water flooding in PEFCs [1,2]. MPL is a much thinner and finer porous layer, which is typically composed of carbon black (CB) particles and PTFE, and inserted between cathode CL and GDL. Nam et al. [2] experimentally and numerically investigated the vapor condensation and liquid water breakthrough in porous layers, and showed that inserting MPL between CL and GDL reduces the size and saturation level of interfacial water droplets on CL surface. However, there is a risk that MPL addition on cathode side increases oxygen transport resistance through porous layers. In general, MPL is formed by coating the slurry of CB powder and PTFE onto GDL substrate and then heat-treated. Its pore structure is complicatedly affected by various fabrication parameters such as CB loading, PTFE/CB ratio, coating and dry processes. To control interfacial water transport between cathode CL and GDL and minimize water flooding, it is essential to optimize the fabrication parameters of MPL determining its microstructure. In this study, we focused on CB loading as one of the major fabrication parameters of MPL, and analyzed the pore structure of MPLs with different CB loadings using SEM-EDX and mercury porosimetry. Furthermore, the operation test and the optical visualization of liquid droplet behavior in the cathode electrode were conducted using a transparent cell, and the influence of CB loading of MPL on its microstructure, the interfacial water transport and the performance characteristics of PEFC was discussed. In the experiment, the MPLs were coated on the hydrophobized carbon paper (Toray, TGP-H-060) by using the doctor-blade technique. The SEM-EDX observation revealed that the average thickness of two MPLs with 1.0 and 4.0 mg/cm2 CB are 33.7 and 123.6 um, respectively. When the CB loading is increased from 1.0 to 4.0 mg/cm2, the thickness of MPL is enlarged approximately 3.7 times. Subsequently, the operation test of a PEFC was carried out at 70 oC under high-humidity conditions, and the effect of CB loading of MPL on the I-V characteristics was investigated. The MPL addition on the cathode side drastically improves the limiting current density, because it suppresses the formation of liquid water film at the CL/GDL interface and reduces the concentration overpotential. In addition, the cell voltage in the high current density range increases with an increase in CB loading of MPL. Since the thick MPL raises the temperature near the cathode reaction sites, the rate of condensation of product water at the CL decreases in the case of 4.0 mg/cm2CB. Therefore, the thick MPL with high CB loading beneficially reduces water flooding at the cathode CL/MPL interface and improves the cell performance.

The influence of gas diffusion layer (GDL) design parameters on the performance of a polymer electrolyte fuel cell (PEFC) was evaluated using a test apparatus in which the clamp pressure on the cell could be accurately controlled. The PEFC performance varies significantly depending on the humidity of the supplied gas. Under moderate humidity, the PEFC performance is enhanced when using an untreated GDL with high air permeability. Under high humidity, improved performance is achieved using a GDL with PTFE hydrophobic treatment. A microporous layer (MPL) coated GDL significantly reduces flooding on the electrode, resulting in a decrease in the concentration overpotential. This enhances the PEFC performance at high current densities. A substrate with high air permeability for the MPL coated GDL enhances the ability of the MPL to prevent flooding. Under low humidity, the MPL is also effective to prevent drying-up of the membrane electrode assembly (MEA), resulting in enhanced performance. A substrate with low air permeability for the MPL coated GDL is effective for the prevention of drying-up.

In order to widen the market application of the polymer electrolyte fuel cell (PEFC), the output power of the PEFC system must be increased. One of the barriers is the cell voltage loss under high current density conditions. This is mainly caused by the deteriorated reactant mass transport, which is blocked by the water flooding at the catalyst layer (CL), microporous layer (MPL), and gas diffusion layer (GDL). Modifying the MPL coated on the GDL is an accessible way to provide better water management for PEFCs to elongate the operating range of the cell, so a novel MPL-coated GDL should be developed to realize the goal. Previously, we evaluated double MPL-coated GDLs, which coated a thin hydrophilic layer on the hydrophobic MPL-coated GDL in the through-plane direction. The extra hydrophilic layer was influential in promoting the introduction of water into the small pores of the hydrophobic MPL, enhancing the ability to reduce flooding, and the oxygen transport resistance under high humidity conditions can be declined.The present study evaluates a novel composite MPL that the hydrophobic and hydrophilic pores are randomly allocated in the same layer. Excess water is expelled from the hydrophilic pores while maintaining gas transport by the hydrophobic pores. To determine the appropriate hydrophobic and hydrophilic compositions, we first evaluated the most commonly used hydrophobic polytetrafluoroethylene (PTFE) binder, and the contact angle of PTFE-MPL was 136°. Polyvinyl alcohol (PVA) was chosen as the hydrophilic binder, and the contact angle of PVA-MPL was 105°. The slurry containing PTFE, PVA, carbon black, and distilled water was mixed using a mixer and then spread on the carbon paper substrate by a bar coating machine. The temperature was heated at 350°C to sinter the MPL on the substrate. However, the sintering temperature of PVA should be lower than 150°C, so the PVA in the composite MPL was burned and led to a similar contact angle as the PTFE-MPL. Meanwhile, the performance enhancement could not be obtained compared with a PTFE-MPL-coated GDL. Oppositely, when decreasing the sintering temperature to 150C°, the PTFE-PVA composite MPL demonstrated strong hydrophilicity with a small contact angle value, and the performance was exacerbated than the PTFE-MPL. Therefore, to coordinate the lower sintering temperature of PVA, polyvinylidene difluoride (PVDF) was selected as the hydrophobic binder. The contact angle of PVDF-MPL was 143°. After the PVA was preserved, the unexpectedly strong hydrophilicity was exhibited in PVDF-PVA composite MPL, aggravating the liquid water accumulation in the MPL and without performance improvement. Finally, the Nafion ionomer with relatively weak hydrophobicity was used for the composite MPL. As a hydrophilicity complement, titanium dioxide (TiO2) particles were added to the slurry to control hydrophilicity. The contact angle of Nafion/TiO2-MPL was 113°. Similarly, the Nafion/TiO2-PVDF composite MPL indicated a contact angle of 114°, and the water permeability test proved that separate hydrophobic and hydrophilic pores were generated.The oxygen transport resistances were measured based on the limiting current density values of polarization curves to evaluate the ability of the MPL-coated GDL to reduce flooding under high humidity conditions. The active area of the MEA was 1.0 cm2, and the cell temperature was kept at 35°C. Pure hydrogen and diluted oxygen (2 vol% O2 and 98 vol% N2) gases were supplied at the anode and cathode, respectively, and the flow rates were set at 1000 cm3 min-1. The relative humidity of gases supplied to the anode and cathode was 200%RH, and the gas backpressure was set at zero. The oxygen transport resistance of the Nafion/TiO2-PVDF composite MPL-coated GDL was lower than that obtained with a commercial SGL-22BB GDL. Thus, an appropriate composite MPL-coated GDL effectively enhanced PEFC performance under high humidity conditions.

Ex-situ visualization of the wet domain in the microporous layer in a polymer electrolyte fuel cell by X-ray computed tomography under water vapor supply

The diffusion media (DM) of polymer electrolyte fuel cells (PEFCs) typically consists of a macro-substrate (or gas diffusion layer, GDL) coated with a micro-porous layer (MPL). The GDL portion is manufactured from carbon fibers/binder and is often treated with polytetrafluoroethylene (PTFE) to increase the hydrophobicity. Similarly, the MPL is manufactured from a slurry containing carbon nanoparticles and PTFE. While the distribution of PTFE undoubtedly influences water transport within the DM, the actual 3-D distribution of PTFE is extremely difficult to capture using a single, standalone device. Therefore, the objective of this work is to examine the impact of PTFE distribution on water transport by generating various PTFE distributions within the measured 3-D structures of DM materials.A commercial DM sample was previously analyzed using X-ray computed tomography (XCT) and focused ion beam-scanning electron microscopy (FIB-SEM) to capture the 3-D structures of the GDL and MPL regions, respectively [1]. In this study, three different PTFE distribution cases are generated on the internal surface of the measured GDL structure: i) random PTFE surface pixels; ii) random PTFE surface clusters; and iii) wetting of PTFE into GDL crevices to mimic the PTFE treatment process used during manufacturing. Similarly, cases (i) and (ii) are generated in the measured MPL structure. In each case, PTFE is assigned to existing solid pixels so that the structure of the measured sample is preserved.The well-established pore morphology or full morphology (FM) model [1,2], used for determining capillary pressure-saturation behavior in uniformly wetting pore structures, was recently extended to account for locally different wetting surfaces in a structure [3,4]. The extended-FM approach is applied here in 3-D to capture the impact of the PTFE distributions on water transport in the DM, by assuming one contact angle for the carbon fiber/binder surface and a different contact angle for the hydrophobic PTFE surface. Two uniform surface conditions (i.e., traditional FM approach) are also considered for comparison: one in which an average contact angle for carbon fiber/binder and PTFE is assumed, and another in which PTFE is neglected (i.e., untreated GDL sample). The capillary pressure-saturation results are compared with experimental and modeling studies available in literature.

In-plane and through-plane electrical conductivities and contact resistances of a Mercedes-Benz catalyst-coated membrane, gas diffusion and micro-porous layers and a Ballard graphite bipolar plate: Impact of humidity, compressive load and polytetrafluoroethylene

1. Introduction Various carbon materials are currently used in PEFCs.1,2 In particular, relatively expensive porous carbon materials such as carbon fiber cloth and carbon paper with a thickness of around 0.2 mm are commonly used as the gas diffusion layers (GDLs), which ensure gas flow, electron transport, and water management in fuel cells.3,4 However, electrical conductivity of these carbon materials could be lower than that of metallic materials. Another technical issue is the reduction of GDL thickness to achieve higher power density per cell stack volume, which could however lead to a decrease in mechanical strength of GDLs.5 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 using metallic GDLs for PEFCs, by varying materials, thickness, porosity, and preparation conditions. 2. Experimental Ti fiber sheets and stainless steel mesh sheets were used as GDL substrates, and Sn coating was made on the sheets. Then, current-voltage characteristics of the cells using these GDLs were evaluated. Five types of porous metallic sheets were used as GDLs: (i) Ti fiber sheet with a porosity of 70% and thickness of 100 μm, (ii) Ti fiber sheet with Sn plating layer (Sn/Ti sheet), (iii) Ti fiber sheet with Pt nanoparticles and Sn plating layer (Sn/Pt/Ti sheet), (iv) SUS316 mesh with a porosity of 60% and thickness of 32 μm, and (v) SUS316 mesh with porous Sn layer. For all the evaluations, the electrocatalyst layers were prepared by dispersing Pt/C (Pt 46.5%, TEC10E50E, Tanaka Kikinzoku Kogyo Corp., Japan), 99.5% ethanol, pure water, and 5% Nafion solution using an ultrasonic homogenizer. The dispersions were printed on the electrolyte membrane (Nafion 212) using a spray printer (C-3 J, Nordson). The electrode area was 1.0 cm2 (1.0 cm × 1.0 cm), and the Pt loading on both electrodes was 0.3 mg-Pt cm-2. The metallic GDL was used for the cathode, and a carbon paper (EC-TPI-060T) was used as the standard GDL for the anode. In the electrochemical characterization of this study, electrochemical impedance spectroscopy (EIS, 1255WB, Solatron) was applied to measure the current-voltage characteristics and to separate overvoltages. 3. Results and discussion I-V characteristics of the cells with the MEAs (i) to (v) are shown in Figure 1. Decrease in cell performance was mainly caused by an increase in ohmic losses. Comparing the MEA (i) and the MEA (iv), Ti fiber sheet showed higher electrical conductivity than stainless steel mesh sheet. Comparing the MEA (i) and the MEA (ii), it was confirmed that the Sn plating on the Ti fiber contributed to a reduction of ohmic loss and concentration overvoltage. Furthermore, the current-voltage curve of the MEA (iii) indicates higher conductivity than that of the MEA (ii), suggesting that the Pt coating promoted the Sn plating or acted as catalysts on the electrocatalyst layer side during the operation of the cell. When the SUS316 mesh sheet was used for the MEA (iv), the concentration overvoltage tended to fluctuate in each measurement. For the MEA (v), a decrease in cell performance was observed. These could be caused by, e.g., degradation of stainless steel due to strong acidity, and contact resistance between the Sn porous layer and the mesh sheet. Further study is in progress to improve I-V characteristics of MEAs by optimizing materials and structure of metallic GDLs. Acknowledgement Financial support from New Energy and Industrial Technology Development Organization (NEDO) is gratefully acknowledged (Contract No. 20001214-0). References Takahashi, T. Ikeda, K. Murata, O. Hotaka, S. Hasegawa, Y. Tachikawa, M. Nishihara, J. Matsuda, T. Kitahara, S. M. Lyth, A. Hayashi, and K. Sasaki, J. Electrochem. Soc., 169, 044523 (2022).Larminie, and A. Dicks, Fuel Cell Systems Explained, John Wiley & Sons, (2006).Kitahara, T. Konomi, H. Nakajima, and J. Shiraishi, kikaib, 76(761), 101 (2010).A. Reiser, L. Bregoli, T. W. Patterson, J. S. Yi, D. Yang, M. L. Perry, and T. D. Jarvi, Electrochem. Solid-State Lett., 8, A273 (2005).N. Hussain, E. V. Steen, S. Tanaka, and P. Levecque, J. Power Sources, 337, 18 (2017).

Effects of porosity distribution variation on the liquid water flux through gas diffusion layers of PEM fuel cells

Resolving macro- and micro-porous layer interaction in polymer electrolyte fuel cells using focused ion beam and X-ray computed tomography

Self-startup of polymer electrolyte fuel cell (PEFC) without external heating is advantageous for the system. It is generally recognized that the produced ice accumulating in the cathode catalyst layer (CL) reduce the electrochemically active area (ECA) for oxygen reduction reaction (ORR) and the open pore volume for oxygen diffusion. Visualization results obtained from a transparent PEFC shows the importance of the catalyst layer design and gas purge to freeze-starts.1,2 A cyclic voltammetry (CV) technique was developed to investigate the effect of ice formation in the cathode CL on electrochemically active Pt area during and post subzero startup of a PEFC.3Mechanical stress built in the cell during cold start may limit its lifetime. To our knowledge, no work has been done about mechanical stress during cold start in PEFC.A cyclic voltammetry (CV) technique is developed to further investigate the effect of membrane thickness and startup current density on cumulative product water, rate of ice formation in electrode and rate of water absorption by ionomer and membrane in PEFC during cold start. Figure 1a shows typical CVs of the cathode prior to and post cold start. Obviously, the electrochemically active Pt surface area of the cathode CL post cold start is lower than that prior to. It is found that thick membrane offers much more capacity for water to be absorbed by the membrane at −10oC and −20oC. The product water almost does not increase with membrane thickness for starting from −30oC because water absorption by the membrane is negligible. The rate of ice formation in cathode catalyst layer increases with current density but decreases with the startup temperature. The rate of water absorption by the membrane increases with the startup temperature, current density and membrane thickness. A mathematical model is developed to investigate mechanical stress during cold start in PEFC. Ice produced in the catalyst layer forces the catalyst layer to expand. Figure 1b shows the effect of cold-start temperature on stress during cold start. Cold starting from low temperature brings high compress mechanical stress. Cold starting from low temperature also bring high strain in CL, but low strain in the membrane. The membrane is compressed during cold start from -30oC. That is because the amount of water absorbed by membrane is negligible but CL expands a lot. This work demonstrates the effect of thickness of gas diffusion layer (GDL), micro-porous layer (MPL) and CL on the mechanical stress built in the membrane. Membrane constraint is considered in the model.4The simulation result shows that mechanical stressed during purge, cool down and cost start operation do not vary serious due to elastic and porous MPL and GDL. The model is to help elucidate the fundamental physics of ice formation in the PEFC during cold start.Figure 1. (a) Cyclic voltammograms of the cathode prior to and post cold start at startup temperature of −10oC and −30oC. (CCM-25 mm. m Pt=0.4 mg/cm2. Startup conditions: i start=0.05 A/cm2, x H2=14.35, x air=12.06, RHH2=RHair=0%, p H2=p air=1 atm. CV conditions: T CV=T start, n=50 mV/s, F N2=F H2=40 mL/min, RHN2=RHH2=0%.) and (b) Effect of cold-start temperature on stress during cold start (lInitial= 6.0).

X-ray Tomographic Analysis of Porosity Distributions in Gas Diffusion Layers of Proton Exchange Membrane Fuel Cells

Computation of oxygen diffusion properties of the gas diffusion medium -microporous layer assembly from the combination of X-ray microtomography and focused ion beam three dimensional digital images

The polymer electrolyte membrane (PEM) fuel cell is a promising alternative power source for electric vehicles, forklifts, and stationary backup power due to its high power density, low operating temperature, and clean emissions. The gas diffusion layer (GDL) facilitates the transport of heat, reactant gases, water vapor, and liquid water in the PEM fuel cell. The GDL is a highly porous material composed of dense arrays of carbon fibers, resins, and polytetrafluoroethylene (PTFE). Additionally, it is typically coated with a micro porous layer (MPL), which results in the reduction of contact resistance at the catalyst layer interface and the overall improvement in water management. Effective water management must be achieved within the GDL over the entire operating lifetime in order to improve the commercial success of PEM fuel cells. Investigations into the effects of ageing on water management within the GDLs can be useful tools to guide this success. Water is required to maintain polymer electrolyte membrane hydration and ionic conductivity; however, excess water tends to accumulate in the catalyst layer, GDL, and flow channels. This accumulation limits mass transport and leads to performance losses. Therefore, effective water management in the GDLs is essential for improving cell performance, durability, and stability. Most GDL research has been focused on the impact of GDL materials and microstructure design on overall performance, rather than durability. Decreased GDL hydrophobicity has been found after only a few hundred hours of operation (1, 2). Therefore, a clear understanding of the influence of GDL degradation on the liquid water behavior is essential. As a tool to visualize this behaviour, synchrotron X-ray radiography is a powerful technique for visualizing liquid water transport behavior within an operating PEM fuel cell. High intensity X-rays generated at the BMIT-BM beamline of the Canadian Light Source were used for identifying liquid water inside the GDLs and capturing the multiphase flow behavior in an operating PEM fuel cell. Figure 1 is an example synchrotron X-ray radiograph of the fuel cell in operando, illustrating the spatial distribution of liquid water. The observed pixel brightness was correlated to the presence of liquid water, and the saturation profile across the GDL thickness was obtained. In this study, as-received fresh GDLs were immersed in a 35wt % solution of H2O2 at 90o C for 12 hours in order to perform an accelerated artificial ageing process. As-received fresh and artificially aged GDLs were then used to assemble specialized fuel cells for synchrotron imaging. Both the electrochemical performance and liquid water transport behavior were observed for a range of current densities. Additionally, the effect of changes in relative humidity on performance was compared to investigate the effect of artificial ageing. Notable differences in cell performance and liquid water transport behavior were observed at steady state operating conditions. The cell with aged GDLs showed lower cell voltage and higher quantities of liquid water than those of as-received fresh GDLs. The impacts of aging on the liquid water distributions within the GDL and on cell performance will be presented in this work. The objective of current work is to highlight the potential degrading effect on liquid water management in long term fuel cell operation.