Gas Diffusion Media Research Articles

Fabrication Method for Laboratory-Scale High-Performance Membrane Electrode Assemblies for Fuel Cells

Custom catalyst-coated membranes (CCMs) and membrane electrode assemblies (MEAs) are necessary for the evaluation of advanced electrocatalysts, gas diffusion media (GDM), ionomers, polymer electrolyte membranes (PEMs), and electrode structures designed for use in next-generation fuel cells, electrolyzers, or flow batteries. This Feature provides a reliable and reproducible fabrication protocol for laboratory scale (10 cm2) fuel cells based on ultrasonic spray deposition of a standard Pt/carbon electrocatalyst directly onto a perfluorosulfonic acid PEM.

Gas Diffusion Media for Open-Cathode Fuel Cells in Atmospheric Flight

Operating a proton exchange membrane fuel cell (PEMFC) in a planar, open cathode configuration can enable significant reductions in overall device weight and system complexity compared to a conventional fuel cell stack. This decrease in device weight makes an array of open-cathode, planar fuel cells a compelling candidate power source for unmanned aerial vehicles. The flow of ambient air over vehicle-mounted cells can improve oxygen, waste heat, and water transport between the catalyst layer and bulk air. We previously studied the effect of environmental conditions on cell polarization and found that ambient temperature, relative humidity, altitude and air speed all influence cell temperature, which affects water balance and oxygen transport to the catalyst layer. In this work, we relate gas diffusion media (GDM) properties to cell polarization behavior in a broad range of anticipated flight conditions. We study the effect of gas diffusion layer thickness and porosity on cell polarization and discuss its influence on cell temperature, oxygen transport and water management. Similarly, we investigate the polytetrafluoroethylene (PTFE) content in the GDM and the influence of hydrophobicity on cell water management and performance in a broad range of anticipated flight conditions. We use cyclic voltammetry and AC impedance spectroscopy to characterize performance losses associated with GDM properties to guide GDM selection.

Structural Effects of Non-Uniform Deformation of Porous-Streaming Paths on Transport Phenomena and Electrochemical Reactions in Polymer Electrolyte Fuel Cells

Unified fuel cell reaction modeling was proposed to predict the effects of local deformation of porous-streaming paths (i.e. gas diffusion media (GDM)) on transport phenomena of polymer electrolyte fuel cells (PEFCs) by structural and electrochemical approaches. First, structural analysis is conducted to figure out non-uniform behavior of GDM with bipolar plate channels under the stack clamping pressure. The deformation results enables the exact determination of flow properties of porous media (i.e. permeability and porosity). After recalculation process of flow paths, computational fuel cell analysis in the deformed regions is performed to visualize flow patterns and estimate the electrochemical performance of PEFCs. The results show that water transport in deformed GDM restricts the smooth transport of reactant gas leading to significant mass transport losses. Therefore, combined structural-fluidic analyses with electrochemical reaction provide insight into high-current density PEFC system.

Laboratory-Scale Method for Fabricating High Performance Catalyst-Coated Membranes and Membrane Electrode Assemblies

Laboratory-made membrane electrode assemblies (MEAs) for proton exchange membrane fuel cells typically perform poorly compared to commercial ones. A key issue is the difficulty with making a high performance catalyst coated membranes (CCMs) at the laboratory scale by unautomated processes that often leads to irreproducible results due to lack of control of important parameters in the catalyst layer (CL). We have developed a method to fabricate reproducible CCMs with high activity using direct ultrasonic spray deposition of electrocatalysts onto a heated commercial perfluorosulfonic membrane. The CCMs are optimized by varying the number of catalyst layers sprayed, the height of spay nozzle from the membrane, and the pressure used for hot pressing on CLs after spraying. Nitrogen adsorption and scanning electron microscopy (SEM) are used to investigate the effects of ionomer/carbon ratio (I/C) on the surface area, pore structure and morphology of the CLs. How the CCMs are assembled into MEAs is another key issue in the fuel cell performance, particularly the compression, which governs the porosity of the CL and gas diffusion media and resistance. The resulting MEAs are analyzed by I-V polarization, cyclic voltammetry and electrochemical impedance spectroscopy. A comparative study is also made with CCMs prepared with low equivalent weight Nafion ionomer in the CLs. Operating the cell at 80°C and 50 % RH, a cell voltage of 0.6 V a current density of 971 ± 41mA cm-2 is achieved in Air/H2 at a stoichiometric ratio of 2/2 at ambient pressure and increased to 1432 ± 131 mA cm-2 at a back pressure of 150 KPa. These tools can be used to guide the laboratory development and understanding of new catalyst layer structures and catalyst compositions.

X-ray Tomographic Investigation of Water Distribution in Polymer Electrolyte Membrane Fuel Cells with Different Gas Diffusion Media

In this study, water transport in polymer electrolyte membrane fuel cells (PEMFCs) is investigated by synchrotron X-ray tomography. The measurement technique is used to reveal the relationship between the structure of the gas diffusion media (GDM) and the water distribution. It is shown how the water distribution and transport is visualized and quantitatively analyzed. We present investigations on three different GDM: A GDM with a modified microporous layer (MPL), a thick GDM with limited back diffusion and a reference material.

Computational Modelling of Cationic Contamination in PEFCs: a Multiphase Mixture Approach

Cationic contamination of polymer electrolyte fuel cells (PEFCs) is dependent on a liquid water transport mechanism as the cations transport with the liquid water to reach the polymer membrane. A steady state, one dimensional, multiphase model is developed to examine the role of a hydrophobic microporous layer in the transport of liquid water across a two layer gas diffusion media (GDM). At low current density operation (0.2A/cm2), an evaporation front occurs within GDM as water enters the hydrophobic zone, preventing cations from reaching the cathode catalyst layer.

PTFE mapping in gas diffusion media for PEMFCs using fluorescence microscopy

Differentiating between the various polytetrafluoroethylene based structures inside polymer electrolyte membrane fuel cells with a degree of certainty is necessary to optimize manufacturing processes and to investigate possible degradation mechanisms. We have developed a novel method using fluorescence microscopy for distinguishing the origin and location of PTFE and/or Nafion® in Membrane Electrode assemblies and the gas diffusion media from different sources and stages of processing. Fluorescent material was successfully diffused into the PTFE based structures in the GDM by addition to the ‘ink’ precursor for both the microporous layer and the catalyst layer; this made it possible to map separately both layers in a way that has not been reported before. It was found that hot pressing of membrane coated structures resulted in physical dispersion of those layers away from the membrane into the GDM itself. This fluorescence technique should be of interest to membrane electrode assembly manufacturers and fuel cell developers and could be used to track the degradation of different PTFE structures independently in the future.

A completely spray-coated membrane electrode assembly

We present a proton exchange membrane fuel cell (PEMFC) manufacturing route, in which a thin layer of polymer electrolyte solution is spray-coated on top of gas diffusion electrodes (GDEs) to work as a proton exchange membrane. Without the need for a pre-made membrane foil, this allows inexpensive, fast, large-scale fabrication of membrane-electrode assemblies (MEAs), with a spray-coater comprising the sole manufacturing device. In this work, a catalyst layer and a membrane layer are consecutively sprayed onto a fibrous gas diffusion layer with applied microporous layer as substrate. A fuel cell is then assembled by stacking anode and cathode half-cells with the membrane layers facing each other. The resultant fuel cell with a low catalyst loading of 0.1mgPt/cm2 on each anode and cathode side is tested with pure H2 and O2 supply at 80°C cell temperature and 92% relative humidity at atmospheric pressure. The obtained peak power density is 1.29W/cm2 at a current density of 3.25A/cm2. By comparison, a lower peak power density of 0.93W/cm2 at 2.2A/cm2 is found for a Nafion NR211 catalyst coated membrane (CCM) reference, although equally thick membrane layers (approx. 25μm), and identical catalyst layers and gas diffusion media were used. The superior performance of the fuel cell with spray-coated membrane can be explained by a decreased low frequency (mass transport) resistance, especially at high current densities, as determined by electrochemical impedance spectroscopy.

Effects of Cell Construction Parameters on the Performance of Lithium-Air (Li-O2) Batteries

Lithium ion batteries (LIB) are widely used in small portable devices and still represent one of the best options available for large-scale power sources such as electric vehicles (EVs) and renewable energy storage systems (ESS). The low theoretical specific energy (~400 Wh Kg-1) of current LIB is insufficient for emerging technologies, thus many researchers have investigated novel battery systems with high specific energy to replace current LIB. Among various candidates, lithium-air (Li-O2) batteries have received much attention due to the very high theoretical specific energy (~3500 Wh kg-1, Li2O2), abundant oxygen source and simple reaction chemistry (2Li+ O2 + 2e- à Li2O2, Eo = 2.96V vs. Li/Li+). Although the advantages of Li-O2 batteries are attractive, the practical adoption of Li-O2 batteries has been restricted by a large irreversible capacity, poor cycle retention characteristics, and low energy efficiency due to the large hysteresis of charge/discharge and side reactions between battery components. Here, we report our recent findings in exploration of new electrolytes and oxygen cathodes in order to develop Li-Air batteries with sustainable, high-energy density. We investigated the performance of Li-O2 batteries using various porous carbon materials, electrolytes based on both organic and ionic liquids, and additives such as redox mediators. Various carbon substrates (such as Super-P, CNT, graphene and Ketjen black, Figure 1) were used to construct a porous cathode structure. It appears that their electrochemical properties (relevant to Li-Air batteries) are different due to their dissimilar morphology and surface area. We also conducted experiments with various electrolytes including some additives (LiNO3, LiI, etc.) as shown in Figure 2. Ionic liquids are promising electrolytes owing to relatively high electrochemical and chemical stabilities, along with safety benefits and environmental friendliness. Recently, the use of redox mediators has been identified as a promising route for reducing the overpotentials of the charge process. Based on these studies, we also investigated the effects (nature and concentration) of solvents (ionic liquids, ethers, and their mixtures) and redox mediators in electrolytes on the charging potential and reversibility of oxygen cathodes. Furthermore, we have used different porous carbon fiber papers as both a current collector and gas diffusion media. It appears that the physical oxygen diffusion property is closely linked to the capacity and cycling performance of Li-Air batteries due to the different sizes and connectivity of pores in different gas diffusion media. Electrochemical characterization techniques were combined with microanalysis (SEM, XRD) to optimize the electrode structures and performance. It is hoped that this study will provide some useful insights to the design criteria for high-performance Li-Air batteries. Figure 1

Experimental determination of optimal clamping torque for AB-PEM Fuel cell

<span lang="EN-GB">Polymer electrolyte Membrane (PEM) fuel cell is an electrochemical device producing electricity by the reaction of hydrogen and oxygen without combustion. PEM fuel cell stack is provided with an appropriate clamping torque to prevent leakage of reactant gases and to minimize the contact resistance between gas diffusion media (GDL) and bipolar plates. GDL porous structure and gas permeability is directly affected by the compaction pressure which, consequently, drastically change the fuel cell performance. Various efforts were made to determine the optimal compaction pressure and pressure distributions through simulations and experimentation. Lower compaction pressure results in increase of contact resistance and also chances of leakage. On the other hand, higher compaction pressure decreases the contact resistance but also narrows down the diffusion path for mass transfer from gas channels to the catalyst layers, consequently, lowering cell performance. The optimal cell performance is related to the gasket thickness and compression pressure on GDL. Every stack has a unique assembly pressure due to differences in fuel cell components material and stack design. Therefore, there is still need to determine the optimal torque value for getting the optimal cell performance. This study has been carried out in continuation of deve­lopment of Air breathing PEM fuel cell for small Unmanned Aerial Vehicle (UAV) application. Compaction pressure at minimum contact resistance was determined and clamping torque value was calcu­la­ted accordingly. Single cell performance tests were performed at five different clamping torque values i.e 0.5, 1.0, 1.5, 2.0 and 2.5 N m, for achieving optimal cell per­formance. Clamping pressure distribution tests were also performed at these torque values to verify uniform pressure distribution at optimal torque value. Experimental and theoretical results were compared for making inferences about optimal cell perfor­man­ce. A clamp­ing torque value of 1.5 N m was determined experimentally to be the best for getting optimal performance as well as uniform pressure distribution for this specific fuel cell.</span>

Multidisciplinary approaches to metallic bipolar plate design with bypass flow fields through deformable gas diffusion media of polymer electrolyte fuel cells

In this study, multidisciplinary approaches to optimizing serpentine gas flow channels stamped on sheet metal with various design parameters (i.e., channel-to-rib width ratio, draft angle, inner fillet radius, and channel depth) are implemented to identify the fluid–structure interaction characteristics of locally deformed gas diffusion media (GDM) and the rate of entropy generation for bypass flow through the porous GDM. First, static structural analysis is conducted to demonstrate the GDM deformation by stack compression and its mechanical effects on fluidic properties of GDM experimentally and numerically. The GDM-channel model results agree with the experimental results within a maximum error of less than 10%. Emphasis is placed on understanding how the reactant gas flow through GDM effectively transports the oxygen gas to catalyst layers. Next, parametric studies are conducted to identify the dominant design effects on the fluidic performance over the entire computational domain. Subsequently, a design optimization method is applied to obtain the most favorable flow channel designs with trapezoidal cross-sections. In the optimized serpentine channel design, the maximized oxygen transport ratio is predicted to be 0.718 at the interface between the GDM and catalyst layers under the constraint of total pressure drop.

X-ray tomographic investigation of water distribution in polymer electrolyte membrane fuel cells with different gas diffusion media

Water transport in polymer electrolyte membrane fuel cells (PEMFCs) is investigated by synchrotron X-ray imaging as a non-destructive testing method. Two different measurement techniques, namely in-situ radiography and quasi-in-situ tomography were combined to reveal the relationship between the structure of the microporous layer (MPL) and the water flow at different operation temperatures. It is shown how water distribution and transport are quantified and visualized. With this method, investigations of different cell materials at different operating parameters such as cell current, gas humidity, gas flow, etc. are conducted.

Investigation of water transport dynamics in polymer electrolyte membrane fuel cells based on high porous micro porous layers

In this study, synchrotron X-ray imaging is used to investigate the water transport inside newly developed GDM (gas diffusion medium) in polymer electrolyte membrane fuel cells. Two different measurement techniques, namely in-situ radiography and quasi-in-situ tomography were combined to reveal the relationship between the structure of the MPL (microporous layer), the operation temperature and the water flow. The newly developed MPL is equipped with randomly arranged holes. It was found that these holes strongly influence the overall water transport in the whole adjacent GDM. The holes act as nuclei for water transport paths through the GDM. In the future, such tailored GDMs could be used to optimize the efficiency and operating conditions of polymer electrolyte membrane fuel cells.

Impact of Compressive Stress on MEA Pore Structure and Its Consequence on PEMFC Performance

One of the most important factors in the assembly of polymer electrolyte membrane fuel cells (PEMFCs) is to set the appropriate normal compressive stress to the cell to balance the conflicting demands of mitigating gas leaks and decreasing contact resistance without damaging the porous components so that optimal performance is obtained. Herein we systematically evaluate the influence of compressive stress (0 to 1.4 MPa) on membrane electrode assemblies (MEAs) composed of spray-coated catalyst layers (CLs) and gas diffusion media (GDM) containing both a gas diffusion layer (GDL) and a microporous layer (MPL) by changing the gasket thickness. The CL structure is unaltered at the levels of compressive stress evaluated in this study, as confirmed by postmortem scanning electron microscopy and electrochemical evaluation. However, the pore structure of the MPL of the GDM is significantly altered at compressive stresses ≥0.96 MPa, resulting in a loss of up to 95% of the cumulative pore volume in the MPL. This collapse of the MPL structure results in up to a 19% decrease in current density in the mass transport region of the polarization curve. Oxygen gain voltage analysis confirms that the mass transport limitation occurs in the GDM. We conclude that compressive stress must be optimized around the MPL and that cross-sectional SEM is an effective tool for observing changes in the overall porosity in MEA components.

Effect of N and C on surface formation of jagged - nodular and nitride-carbide structure on hard chrome steel during thermochemical treatment

The morphology of surface structure was changed from jagged to nodular structure. Martensite structure is formed from hard chrome plating after the oxidised diffusion of nitriding process. The investigation was conducted using SEM, EDAX, AFM and spectroscopy. This phenomenon belongs to an unusual structure. The morphology of crack density that disappears depends on the diffusion media of nitriding process. Such phenomena also happened under hard chrome plating forming carbide and bainite structure. With the changed structure of layers plating, friction and wear characteristic of hard chrome plating became better. Hard chrome coated tool steel substrate of AISI 4140 type was nitridised (550oC, 4 hours of boost phase and 2 hours of diffusion phase) without gas diffusion media. The analysis of AFM shows the roughness value of the surface was increase after the treatment of nitriding. The nodular structure would provide width of oil storage as greater self lubricant. The structure formed can be illustrated like an area of farm. The structure could also omit the jagged area. The mechanism of nitrogen atom deposition that is interesting and relatively new was observed in this research as well.

Effect of N and C on surface formation of jagged - nodular and nitride-carbide structure on hard chrome steel during thermochemical treatment

The morphology of surface structure was changed from jagged to nodular structure. Martensite structure is formed from hard chrome plating after the oxidised diffusion of nitriding process. The investigation was conducted using SEM, EDAX, AFM and spectroscopy. This phenomenon belongs to an unusual structure. The morphology of crack density that disappears depends on the diffusion media of nitriding process. Such phenomena also happened under hard chrome plating forming carbide and bainite structure. With the changed structure of layers plating, friction and wear characteristic of hard chrome plating became better. Hard chrome coated tool steel substrate of AISI 4140 type was nitridised (550ºC, 4 hours of boost phase and 2 hours of diffusion phase) without gas diffusion media. The analysis of AFM shows the roughness value of the surface was increase after the treatment of nitriding. The nodular structure would provide width of oil storage as greater self lubricant. The structure formed can be illustrated like an area of farm. The structure could also omit the jagged area. The mechanism of nitrogen atom deposition that is interesting and relatively new was observed in this research as well.

High Surface Area Carbon Electrodes for Bromine Reactions in H2-Br2 Fuel Cells

In a hydrogen-bromine (H2-Br2) fuel cell, the Br2 reactions don't require precious metal catalysts, hence porous carbon gas diffusion media (GDM) are widely used as electrodes. However, the specific surface areas of the commercial carbon gas diffusion electrodes (GDEs) are quite low and need to be enhanced. In order to improve the active surface area of carbon GDEs, a study was conducted to grow multi-walled carbon nanotubes (MWCNTs) directly on the carbon electrode fiber surface. Both constant and pulse current electrodeposition techniques were used to deposit Co nanoparticles to catalyze the MWCNT growth. The MWCNTs were grown in the presence of a mixture of acetylene, argon, and hydrogen gases using the chemical vapor deposition process. Based on the results obtained from SEM, TEM, and EDX analysis, MWCNT growth following the tip model was confirmed. The results from the multi-step chronoamperometry study have shown that the synthesized carbon GDEs with MWCNTs have 7 to 50 times higher active surface area than that of a plain GDE. The performance of a single layer of the best MWCNT GDE measured in a H2-Br2 fuel cell was found to be equal or slightly higher compared to that obtained using a three-layer plain carbon electrode.

Development and Characterization of Non-Conventional Micro-Porous Layers for PEM Fuel Cells

Gas diffusion medium (GDM) is a crucial component in proton exchange membrane fuel cells (PEMFCs). Being composed of a gas diffusion layer (GDL) with a micro-porous layer (MPL) coated onto it, it ensures a proper water management due to the highly hydrophobic materials employed in cell assembly. In current commercial applications, the desired water repellent behaviour is usually obtained by using polytetrafluoroethylene (PTFE). In this work, Fluorolink® P56 (Solvay Specialty Polymers, Milan, Italy), a commercially available, anionic, segmented high molecular weight polyfluorourethane with perfluoropolyether groups was extensively evaluated as an alternative to PTFE for micro-porous layer hydrophobization. A change in polymer used is desirable in order to simplify the production process, both in terms of ink formulation and thermal treatment, as well as to get a higher hydrophobicity and, consequently, more efficient water management. Innovative prepared samples were compared to a PTFE-based GDM, in order to assess differences both from morphological and from an electrochemical point of view.

Accelerated Stress Tests on Fuel Cell Cathode Catalysts: A Material Balance Approach Combining Modeling and Experiment

Proton Exchange Fuel Cells (PEFCs) represent an environmentally benign power sources for automotive transportation. The current major hurdles for the mass commercialization of automotive PEFC technology are cost and durability of the cathode catalyst layer. Catalyst degradation occurs due to voltage transients experienced by the cathode catalyst during normal drive cycles and start-up/shut-downs (SUDS). Urban drive cycles involve rapid stop-go transients (idle-to-peak power) that take the cathode catalyst potential from >0.9 V (idle) to around 0.6 V (peak power). Frequent potential changes with high peak potentials (> 1.2 V) drastically accelerate the loss of active catalyst particles and the decay of the of electrochemically active surface area (ECSA). The main degradation mechanisms affecting the carbon-supported Pt-based catalyst are dissolution/redeposition, coagulation and detachment. Accelerated stress tests (ASTs), performed to decouple and quantify contributions of different catalyst degradation mechanisms are typically performed ex situ to eliminate degradation effects caused by the other materials within the cell, such as the proton conducting membrane and the gas diffusion media. The AST results presented herein evaluated Pt/C degradation under operationally relevant conditions temperature (22°C and 70°C), upper potential limit (UPL, 0.9 V and 1.2 V) and potential wave form (triangle vs. square waves). A comprehensive material balance analysis was performed to track changes in the state of Pt during the AST. This analysis included the determination of ECSA, particle size distribution and amount of dissolved Pt in the electrolyte solution. These results were analyzed with a dynamic model that couples the three catalyst degradation mechanisms to quantify their relative contributions. The model relates the kinetic rates of the degradation processes to the evolution of the particle size distribution. The loss of ECSA during 25,000 AST cycles at 70°C by periodically performing cyclic voltammetry (0.02 V « 0.6 V at 10 mV sec-1) and integrating the hydrogen desorption charge (210 µC cm2). Generally, ECSA loss was found to be accelerated by the SW profile and by the high UPL of 1.2V. The Pt particle size distribution was measured by Transmission Electron Microscopy (TEM). The beginning of life (BOL) particle median size was 2 nm. Figure 1 shows the change in the particle size distribution after 25,000 AST cycles at 70°C. The tests with higher UPL had the most significant increase in mean particle size and width of the distribution. The combined modeling and material balance preliminary results demonstrate a significant role of the effective surface tension of the catalyst dominating the kinetics of the dissolution/Redeposition mechanism at 1.2 V, suggesting that Pt dissolution is strongly coupled to Pt oxide formation and reduction. The analysis fit the enhanced degradation due to the square wave acceleration of dissolution/Redeposition compared to the triangular wave. Figure 1. Histograms from TEM particle size analysis for 25k AST cycles at 70°C. Upper potential limit of (A) 0.9V and (B) 1.2V. Lines are simulated particle size distributions from dynamic model analysis. Figure 1

In-Situ Measurement of Oxygen Particial Pressure on the Surface of a Cathode GDL with Automotive Compatible Operating Conditions

Improvement of the area specific power density of a proton exchange membrane fuel cell (PEMFC) can reduce the total active area of the membrane electrode assembly (MEA). Reducing the total active area of the MEA is a significant opportunity to reduce the cost of a fuel cell because it can reduce the amount of the expensive materials in the MEA, including platinum based electrocatalysts, polymer electrolyte membranes, and gas diffusion media. Mass transport overpotential at high current densities is the major barrier to achieving high area specific power density. Oxygen partial pressure in the cathode is highly linked to the mass transport performance. Therefore, direct measurement of the oxygen partial pressure at the cathode is required for mass transport studies. A novel method has been developed to directly measure the oxygen partial pressure in the cathode flow field during fuel cell operation. This method uses fluorophore materials with fluorescent luminescence that is sensitive to oxygen quenching as described by the Stern-Volmer equation. The measurement range of oxygen partial pressure is dependent on the sensitivity of oxygen quenching of the fluorophore materials. Oxygen quenching rate should be modified to meet a desired range of oxygen partial pressure measurement. In the previous study, the fluorophore material with a platinum porphyrin based fluorophore, which is highly sensitive to oxygen quenching, dispersed in the polymer binder of poly-heptafluoro-n-butly, methacrylate-co-hexafluroisoporopyl, and methacrylate, a.k.a. FIB polymer, was developed. This material showed a sufficient level of intensity of fluorescent luminescence for 7 kPa to 53 kPa oxygen partial pressure. The detected oxygen partial pressure was calibrated within the acceptable temperature sensitivity, between 40°C to 90°C. This range covers the typical operating condition of an automotive PEMFC. The ink of this fluorophore material was sprayed on the surface of the cathode flow field. An in-situ measurement of the oxygen partial pressure at the cathode flow field was demonstrated to investigate the effectiveness of water management in the cathode flow field. However, this fluorophore ink material was too thick to use on the surface of the cathode GDL, because the ink materials clogged the pores of the GDL and lowered the fuel cell performance. In this study, this fluorophore ink material, platinum porphyrin based fluorophore in FIB polymer, was modified. A newly developed thinner fluorophore ink material was sprayed on the surface of the cathode GDL and it was confirmed that the fuel cell performance was not affected by the sprayed ink materials. Concurrently, it was confirmed that the oxygen quenching rate of this fluorophore materials were retained. The Stern-Volmer calibration indicates a small deviation of calibration curves between the fluorophore materials sprayed on the flat glass surface and the porous GDL surface. Numbers of bright spots were observed on the Stern-Volmer calibrated image of the GDL surface. These bright spots were considered to be corresponding to the shadow of the excitation light on the rough GDL surface. When two excitation light sources were used from different angles, the deviation was significantly mitigated. The fluorophore ink modification in this study enabled accurate in-situ oxygen partial pressure measurements on the surface of the cathode GDL to cover the typical operating conditions of an automotive PEMFC. Combined with the previously developed method of oxygen partial pressure on the flow field wall, further analysis was enabled. A significant oxygen partial pressure difference is observed between on the top ceiling of the flow field channel and on the surface of GDL. It was considered that the oxygen concentration in the cathode flow field exhibits a clear gradient from the top wall of the channel towards the GDL surface. This suggests that oxygen was drawn to the GDL surface in a laminar flow scenario in the fuel cell cathode. Detailed analysis will be discussed at the ECS meeting.