Beyond Nafion withFluorine-Free sPSU–sNIMMembranes: Nanostructured Proton Pathways for Harsh Fuel Cell Environments

Challenges and opportunities in modelling of proton exchange membrane fuel cells (PEMFC)

High-temperature proton exchange membrane fuel cells (HT-PEMFCs) based on phosphoric acid doped polybenzimidazole (H3PO4/PBI) membrane operate at elevated temperatures between 150 ºC and 180 ºC. The HT-PEMFC stacks have much simpler water and thermal management than lower-temperature PEM fuel cells and can operate on reformat gas. These advantages make this type of fuel cells an interesting candidate for auxiliary and stationary power units. At this moment, however, no commercial HT-PEMFCs have been developed to meet the reliability and cost requirements.One of the main reasons that limit the wide application of HT-PEMFCs is the sluggish oxygen reduction reaction (ORR) rate in concentrated phosphoric acid. Despite good physical and chemical properties, phosphoric acid is a rather poor fuel cell electrolyte. The slow ORR kinetics in concentrated phosphoric acid is still not completely understood, and it is believed to be related to strong adsorption of phosphoric acid species on the surface of the platinum catalyst.Fluorinated acids as alternative electrolytes might hold the key to overcoming this obstacle. They seem to adsorb less strongly on platinum compared with phosphoric acid, which may increase the ORR rate and lead to high-performance fuel cells. In addition, these novel acids are ideal model systems to study the influence of adsorbates on ORR.Appleby and Baker [1] were among the first who proposed trifluoromethane sulfonic acid (CF3SO3H) as an alternative electrolyte for phosphoric acid fuel cells. Later, Yeager and his co-workers adopted the idea and conducted a more extensive research on fluorinated acids such as monofluorophosphoric acid [FPO(OH)2] and trifluoromethane sulfonic acid. The quest for novel electrolyte compounds that have the physical and chemical properties to meet the HT-PEMFC requirements remains challenging. An ideal candidate material should be both electrochemically and thermally stable, and it should have a very low vapour pressure over the operating temperature range of HT-PEMFCs. Recently, a number of perfluoroalkyl- phosphonic and phosphinic acids with different chain length have been successfully synthesized. These compounds might have the desired properties to serve as electrolytes for HT-PEMFCs. Besides their higher O2solubility they show significant advantages over phosphoric acid, such as a high protonic conductivity under unhydrous conditions [2]. Furthermore, these strong acids tend not to have specific adsorption on the platinum surface.Here, we report cyclic voltammetry (CV) and rotating disc electrode (RDE) experiments with small amounts of phosphoric acid and novel perfluorinated electrolyte candidates added into the perchloric acid electrolyte. Noticeable differences in the voltammograms (Fig. 1) and significant impact on the RDE kinetic current (Fig. 2) were observed. For a more thorough analysis of the adsorption mechanism, electrochemical impedance spectroscopy (EIS) measurements were carried out. Evaluation of the charge transfer resistance for the ORR on platinum was found to be in good agreement with the RDE measurements.Additionally, preliminary experiments were performed to assess the effectiveness of such alternative electrolytes for practical fuel cell applications. Perfluorinated acids were added into the catalyst layer of a HT-PEMFC. First results on the influence on membrane electrode assembly (MEA) performance will be presented.

High temperature proton exchange membrane fuel cells (HT-PEMFCs) have attained much attention for recent decades, as providing several merits over low temperature PEMFCs (LT-PEMFCs) such as simplified fuel cell system and wider applicable fuel options from high CO tolerance.To date, most studies on HT-PEMFC have been focused on phosphoric acid-doped polybenzimidazole (PA-PBI) based system. Worth to note, the durability of this PA-PBI based system is still controversial, showing limited durability under dynamic condition, i.e. high current density, repetitive start up/shut down, thermal cycle, etc., which is due to PA loss from the membrane-electrode-assembly (MEA). To address this issue and further enhance the efficiency and durability of HT-PEMFC systems, a new concept of ion-pair HT-PEMFC was recently introduced. This concept has led to high HT-PEMFC performance with ~ 800 mW cm-2 peak power density under air condition and longer durability over 2,500 h, especially showing a superior durability to conventional HT-PEMFCs based on polybenzimidazole (PBI) membranes.1 Here, we investigate how PA works and moves in HT-PEMFC MEAs, both for PA-PBI based and ion-pair based systems. PA distribution and PA loss in MEAs, which determine the performance and durability of the system, are explored by titration before and after five different accelerated stability test conditions and a clear difference is indicated between PA-PBI system and ion-pair based system.2 Based on these analyses, we suggest our perspectives on MEA design for PA-based HT-PEMFCs. Lim, K. H.; Lee, A. S.; Atanasov, V.; Kerres, J.; Park, E. J.; Adhikari, S.; Maurya, S.; Manriquez, L. D.; Jung, J.; Fujimoto, C.; Matanovic, I.; Jankovic, J.; Hu, Z.; Jia, H.; Kim, Y. S. Protonated phosphonic acid electrodes for high power heavy-duty vehicle fuel cells, Nature Energy, 7, 248 (2022).Lim, K. H.; Matanovic, I.; Maurya, S.; Kim, Y.; Castro, E. S.; Jang, J-H.; Park, H.; Kim, Y. S. High temperature polymer electrolyte membrane fuel cells with high phosphoric acid retention, ACS Energy Letters, 8, 529 (2023).

Polymer electrolyte membrane fuel cells (PEFCs) as one of fuel cell systems, offer a board range of benefits, including: (1) high efficiency, (2) clean process (no CO2 emission), (3) compact design1, and (4) quiet operation. As one of solutions to current technical problems, PEFC operation at high temperature (low humidity) has been considered as a promising system to reduce cost of PEFCs. High temperature PEFCs have some additional merits such as fast reaction kinetic, low activation energy for power generation and high CO catalyst poisoning tolerance2. These advantages make high temperature PEFCs very attractive. However, there are also some technical barriers to develop this attractive system. Especially, harsh environment such as high temperature and low humid condition are very severe for polymer electrolyte membranes (PEMs) as components of PEFCs. Sulfonated poly(ether sulfone)s (SPESs) have been commonly developed as hydrocarbon-type PEMs3,4for high temperature PEFCs, because of the high durability at high temperature condition. Several kinds of SPESs with different structures were investigated previously. However, most of them used only aromatic chain as backbone, which lead the membranes to be tough. In this research, we have investigated a series of copolymerized sulfated poly (ether sulfone) (SPES) with aliphatic chain for high temperature PEFCs. Sulfuric acid was attached to the hydroxyl group connected to the aliphatic main chain. The attached sulfuric acid would be able to move easily and work as a proton conductor because aliphatic unit is more flexible than aromatic unit. We evaluated the basic property of the aliphatic SPES as high temperature PEMs although chemical stability of the aliphatic unit is not higher than that of the aromatic unit. SPES shown in Figure 1 was prepared by sulfation of the hydroxyl group of aliphatic PES. Purification and protonation of the obtained SPES were carried out thoroughly by dialysis from SPES HCl aq. The structure of SPES was confirmed by 1H NMR. SPES films were prepared by cast method. SPES DMSO solution was cast on a petri dish and dried at 60 ˚C in vacuo overnight. The membrane showed hydrophobicity. This property indicated that it showed strong durability against water, which is necessary in fuel cell system. Thermal stability of PEMs is significantly required for high temperature PEFC operation. The obtained SPES was investigated by TGA/DSC experiment as shown in Figure 2. From the result of TGA, SPES had three stages of weight loss. The weight loss was assigned to the removing of water from 66 ˚C to 100 ˚C, thermal decomposition of sulfuric acid2from 176 ˚C to 343 ˚C and the thermal decomposition of the main chain from 343 ˚C to 600 ˚C. And DSC result indicated that no glass transition temperature was observed from SPES at operation temperature region for high temperature PEFC (<120 ˚C). In addition, the proton conductivity of SPES film was observed. The obtained proton conductivity was 0.3 mS/cm at 120 ˚C, 100%RH, which may be caused the high hydrophobic and long distance between sulfonic acid group. We introduce more sulfuric acid group in SPES, and the effect of the sulfuric acid amount and introduction position of sulfonic acid on the proton conductivity is discussed and an optimum condition for preparing MEA for high temperature PEFC is investigated. Reference T. Husaboe, J. A. Rittenhouse, M. D. Polanka, P. J. Litke, J. Hoke, AIAA Paper. DOI, 10, (2013).S. Bose, T. Kuila, T.X. Nguyen, N. H. Kim, K. T. Lau, J. H. Lee, Prog. Polym. Sci., 36, 813 (2011).Y. S. Ye, J. Rick, B. J. Hwang, Polymers, 4, 913 (2012).M. Ulbricht, Polymer, 47, 2217 (2006). Figure 1

This paper addresses the feasibility of Proton Exchange Membrane Fuel Cells (PEMFC) to reduce the climate impact of civil aviation from a performance calculation perspective. PEMFC systems are considered one of the most promising and suitable approaches to mitigate climate effects as they do not cause local CO2 or NOx emissions when fueled with green hydrogen. However, the thermal management of fuel cells and electric components represents a major challenge: Despite the large amounts of waste heat generated, very limited optimal operating temperature ranges must be respected. At the same time, these components and the required heat exchanger impose a significant mass penalty that must be considered in the overall aircraft mass and thrust requirements. A PEMFC model and a heat exchanger model based on the Effectiveness-Number of Transfer Units (ϵ-NTU) method are implemented in the Modular Aircraft Engine Performance Tool for Sustainable Aviation (MAPLE) to evaluate their performance and mass. Various propulsion configurations are then developed and derived from the literature, including all-electric and gas turbine hybrid-electric fuel cell engines with low- and high-temperature PEMFC. In a preliminary analysis, an A320 with turbofan or electric fan engines and an ATR72 with turboprop or electric propeller engines are investigated along representative flight missions in terms of propulsion power requirements and waste heat generation. Optimization of the fuel cell size, thermal management system, and hybridization strategy is then applied to attainable configurations in order to minimize additional mass, fuel consumption, and thus emissions and climate impact compared to conventional gas turbine engines. Overall, the use of PEMFCs with green hydrogen is indeed promising to alleviate the climate impact of civil aviation by reducing CO2 and NOx emissions for hybrid-electric concepts, while eliminating them for all-electric architectures. However, among the all-electric configurations, only an ATR72 derivative powered by high-temperature PEMFCs is feasible from a performance perspective, whereas an all-electric A320-sized aircraft is not viable due to prohibitive cooling requirements and mass penalties. The hybridization of both aircraft categories with both PEMFC types is possible and leads to combined CO2 and NOx reductions of 7–40% depending on the aircraft, mission, fuel cell type, and permissible gas turbine surge margins.

Effect of Flow Pattern on Single and Multi-stage High Temperature Proton Exchange Membrane Fuel Cell Stack Performance

Recently, the polymer electrolyte membrane fuel cells (PEMFCs) have attracted the great attention as energy conversion devices for powertrain for the fuel cell electric vehicle and a residential combined heat and power system due to the zero-emission of harmful gas and high energy efficiency. To overcome of the drawbacks of perfluorosulfonic acid (PFSA) membrane and Pt poisoning by CO, the high-temperature PEMFC (HT-PEMFC) has been developing over decades, which has significant advantages as compared to low-temperature PEMFC (LT-PEMFC). For example, it has a much better fuel tolerance, enhanced the reaction kinetics and a simple water management [1,2]. However, the practical power density of membrane electrode assembly (MEA) for HT-PEMFC is much lower than that of LT-PEMFC because of the huge activation loss by acid poisoning [3–5]. Thus, a large amount of Pt is required in the electrode to ensure the sufficient power and long-term durability, which is a critical issue for HT-PEMFC. Therefore, one of the most critical issue for the HT-PEMFC is the decreasing the Pt amount in the electrode without sacrificing the MEA performance [5]. In addition, the fabrication of electrode using the advanced supported catalyst is the very important topic for revealing the improved catalytic activity into performance of MEA [2,5]. In this study, various formulation parameters for making the catalyst slurry using ball-milling were investigated to obtain the smooth electrode for MEA. The parameters are the presence of a viscosity agent, the solid content, and the amount of binder for the MEA of HT-PEMFC. When the viscosity agent is added in the 2.5 wt.% in the catalyst slurry, the slurry is very suitable for making a coated electrode on the gas diffusion layer (GDL). On the contrary, while when the amount of viscosity agent is increased over than 5 wt.%, the electrode is not completely dried. The optimum solid content of catalyst in the slurry was determined in the range of 12 wt.% because if the amount of catalyst exceeded the 14wt.%, the electrode is peeled off severely after drying. The open circuit voltage and performance of MEA under HT-PEMFC condition is depended significantly on the amount of polyvinylidene fluoride (PVDF) in the catalyst slurry. The voltage at a very small current density at 0.008A/cm2 of MEAs with different amount of PVDF was decreased from 0.775 to 0.735 V by increasing the 10wt.% to 30 wt.% of PVDF, which provide the increase of the activation overpotential by poisoning of phosphoric acid on the Pt catalyst. However, the performance of MEA at 0.6A/cm2 was maximized as 0.44 V at the 30wt.% of PVDF in the catalyst slurry, which suggests that the Ohmic overpotential decreased with increasing the PVDF amount. In summary, for maximizing the MEA performance under HT-PEMFC at 150℃, the various conditions for the manufulation of electrode was invesitgated. The amount of PVDF has a significant effect on the performance of MEA. [1] J. Zhang, Y. Xiang, S. Lu, and S. P. Jiang, Adv. Sustainable Syst. 2, 1700184 (2018). [2] D. J. You, D. H. Kim, J. R. De Liled, C. Li, S. G Lee, J. M. Kim, and C. Pak, Appl. Catal. A: General 562, 250–257 (2018). [3] R. E. Rosli, A. B. Sulong, W. R. W. Daud, M. A. Zulkifley, T. Husaini, M. I. Rosli, E. H. Majlan, and M. A. Haque, Int. J. Hydrogen Energy 42, 9293–9314 (2017). [4] A. Chandan, M. Hattenberger, A. El-kharouf, S. Du, A. Dhir, V. Self, B. G. Pollet, A. Ingram, and W. Bujalski, J. Power Sources 231, 264–278 (2013). [5] S.-W. Choi, J. O. Park, C. Pak, K.H. Choi, J.-C. Lee, and H. Chang, Polymers 5, 77–111 (2013).

Proton exchange membrane fuel cells (PEMFC) are inherently prone to degradation, therefore, despite relatively high efficiency, cost minimization and related durability of the PEMFC systems represent one of the key challenges. To overcome this challenge, it is important that all subsystems are effectively monitored and managed, which should be realized in a cost-effective manner. This opens an emerging area of model-based monitoring, diagnostics and management, which is the focus of this paper.Performance and degradation phenomena in fuel cells are inherently interlinked with internal states of PEMFCs. Therefore, knowledge of internal states opens unprecedented monitoring and management functionalities, which are associated with State-of-Operation-Conditions (SoOC). In addition, knowledge on parameters associated with the rate and efficiency of reactions as well as of transport mechanisms provides crucial insight into the fuel cell performance, while variation of these parameters with time is associated with State-of-Health (SoH). Since application of multiple physical intra-cell sensors does not comply with the cost-effective constraint, internal states of the FC and model parameters should be observer and identified just from measured lumped voltage and current.This challenge is tackled by proposing an advanced model-based methodology for deciphering internal states of the FC and parameters associated with the rate and efficiency of reactions as well as of transport mechanisms using measured lumped voltage and current values as inputs to the model. Proposed model-based methodology is based on a computationally efficient multi-scale simulation framework for PEMFCs, which cover low-temperature (LT) and high-temperature (HT) PEMFCs including relevant submodels. This framework, hence, includes the state-of-the-art submodels for virtual replication of key aspects of PEMFC performance encompassing spatially resolved dynamics of liquid water, membrane water uptake, and impact of the gas crossover effects on mixed potentials [1,2]. One of the key merits of the proposed multi-scale simulation framework is its computational efficiency, as the full model runs significantly faster than real-time, thereby opening new perspectives in observer functionalities.The paper also elaborates an innovative State-of-X (SoX) diagnostic methodology for FCs, which comprises on-line real-time capable SoOC observer and cloud-based SoH observer. On-line real-time capable SoOC observer of internal states of the FC is based on the multi-scale simulation framework for PEMFCs coupled with an advanced observer algorithm based on the Unscented Kalman Filter (UKF). Cloud-based SoH observer is based on the same multi-scale simulation framework for PEMFCs coupled with parameter identification techniques and methods for assessing uniqueness of parameter identification. This innovative SoX diagnostics methodology also complies with the realistic use cases, as on-line SoOC observer makes possible advanced virtual sensing of intra-fuel cell states in real-time, which is crucial for advanced diagnostics and control as well as management of FCs, while cloud-based SoH observer identifies parameters associated with the rate and efficiency of reactions as well as of transport mechanisms on demand, as for example during regular checks or when SoH changes to the extent, which requires parameter updates. As on-line SoOC observer and cloud-based SoH observer share the same modelling basis, updates in SoH diagnostics enable seamless transfer of updated parameters and associated states from the cloud to the on-line SoOC observer.Presented results confirm capability of the on-line SoOC observer to decipher internal-states of the LT and HT PEMFCs with high fidelity just from measured lumped voltage and current, characterizing the proposed observer as a real-time capable virtual sensor of fields of internal-sates of the FC. Furthermore, the cloud-based SoH observer is shown to be able to identify the loss of intrinsic exchange current density, increase of ohmic resistivity of the membrane and reduction of combined diffusivity at the anode and at the cathode with high fidelity also just from measured lumped voltage and current. These results clearly demonstrate prediction capability of the proposed SoX methodology based on the multi-scale simulation framework.Presented methodology and results, therefore, indicate that proposed model-based methodology for real-time deciphering of intra-fuel cell states and cloud-based updates of model parameters pushes boundaries of advanced SoOC and SoH diagnostics and opens new perspectives in monitoring, diagnostics, and controlling of FCs.

Given environmental friendliness, high‐temperature proton exchange membrane fuel cells (HT‐PEMFCs) can be the alternative power source for clean power generation. However, neither developments nor strategies of diffusion media are actively conducted yet to achieve high‐performance HT‐PEMFCs. Herein, a nanoporous carbon nanotube (CNT) sheet, a new anode diffusion layer between the gas diffusion layer|bipolar plate interface that improves fuel cell performance and durability by CNT purification for facilitating fuel accessibility with uniform interfacial contact for reducing acid loss, is reported. Configuration of the optimal CNT‐inserted fuel cell is examined and proposed under the operating temperature of 140–200 °C. The underlying mechanism of this new diffusion layer with multiphysics simulation elucidates that the nanoporous nature induces gas‐wall collision, enabling uniform dispersion within adjacent diffusion media. These fuel cells outperform performance over two times higher and have a voltage decay rate nearly two times lower than conventional HT‐PEMFC.

The development of reliable power sources is important for the continuous operation of various electric equipment in unmanned aircraft and the field environment. Currently electric power delivery to such systems is mainly by battery packs. An alternative is to use fuel cells (FCs). FCs are electrochemical devices that are used to convert chemical energy of fuels such as hydrogen and methanol to electricity. Methanol is an attractive fuel because it is liquid at ambient temperature, has a much higher energy density than hydrogen and low reforming temperature (220–300 °C). Thus, integration of methanol steam reformers (MSRs) with FCs makes it possible to continuously produce electricity. The key challenge in such power system is the development of fuel cells which can be effectively operated at compatible temperature range of MSR, i.e., 220–300 °C in order to increase synergetic heat integration and system reliability. Herein, the latest development of high temperature polymer electrolyte membrane fuel cells (HT‐PEMFCs) is critically reviewed. The prospect of the integrated HT‐PEMFCs‐MSR as a reliable and compact power source is discussed. The results indicate that phosphoric acid doped polybenzimidazole (PA/PBI) membranes with in situ formed phosphosilicate nanocluster proton carriers show the technical feasibility of the development of HT‐PEMFCs at temperatures of 200–300 °C.

The Corrosion Characteristics of Graphite Coatings on Nickel Foam and Their Applications in High-Temperature Proton Exchange Membrane Fuel Cells

A non-pgm Metal Organic Framework (MOF) catalyst was evaluated for durability in the high-temperature environment associated with HT-PEMFCs under various conditions. Due to the higher PGM loading typically required for these systems, it is an ideal candidate for research regarding non-PGM catalysts. However, a common issue regarding non-PGM materials is their lack of durability in the low temperature humidified environment of a PEMFC, and until these issues are resolved, it will continue to provide a hindrance towards mass commercialization. Prior work had demonstrated the high performance of this particular catalyst[1], initially in RDE and low temperature fuel cells, and now in HT-PEMFCs. Membrane Electrode Assemblies (MEAs) were tested at 200˚C using a commercial polybenzimidazole (PBI) membrane, and were evaluated under several durability criteria, including constant voltage testing at various potentials (for demonstration of prolonged use), temperature cycling (to mimic startup/shutdown) and corrosion testing to evaluate losses in these primarily carbon-based materials. Early indications demonstrate a highly stable catalyst, as after nearly 40 hours of non-continuous chronoamperometric testing, the fuel cell demonstrated negligible performance losses at 650mV in air at 2.5bar total pressure. Acknowledgment: The authors gratefully acknowledge the financial support from the Department of Energy-Energy Efficiency and Renewable Energy, Fuel Cell Technology Office under an Incubator grant (DE-EE0006965). Use of the Stanford Synchrotron Radiation Light source, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515. Use of Beamline 2-2 at SSRL was partially supported by the National Synchrotron Light Source II, Brookhaven National Laboratory, under U.S. Department of Energy Contract No. DE-SC0012704. Use of the beamline 9-BM in Advanced Photon Source, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Argonne National Laboratory, was supported by the U.S. DOE under Contract No. DE-AC02-06CH11357. MRCAT operations are supported by the Department of Energy and the MRCAT member institutions. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.

In this study, triazole based ionic liquid doped sulfonated polysulfone (SPSU) composite membranes were evaluated for high temperature proton exchange membrane fuel cell (PEMFC) systems. SPSU obtained by sulfonation of aromatic polysulfone (PSU) polymer matrix was used in the preparation of composite electrolytes. Sulfonated polymer matrices were doped with three different triazole-based ionic liquids (TIL-1, TIL-2 and TIL-3) synthesized within the scope of the study and composite membrane series were formed. Structural, thermal and mechanical characterizations were performed by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA), respectively. Proton conductivities were measured over a wide temperature range (380-450 K) and the effectiveness of composite membranes in high temperature PEMFC systems was evaluated. As a result of TGA analysis, all triazole based ionic liquid doped membrane series exhibited high thermal resistance. It was observed that the proton conductivity of the composite structures was greatly improved with high temperature proton conductivity measurements (8.05 mS/cm for SPSU; 58.1 mS/cm for SPSU/TIL-3(1.0)) and the obtained membranes could be an alternative in high temperature PEMFCs.

High temperature proton exchange membrane fuel cell (HT-PEMFC) has been one of the most promising candidates for the power source of vehicles. Correspondingly, as a factor significantly influencing the performance of the HT-PEMFC, the structure of the flow channel has been extensively discussed. In this study, the multi-channel flow patterns of fuel cell was proposed, and the effect of the channel number on the fuel cell performance was investigated by numerical simulations. The results showed that the HT-PEMFC with multi flow channels performed a power density of 0.392 W cm-2, better than that of single-channel fuel cell. Furthermore, after a comprehensive consideration of performance and production cost, the bipolar plates with three flow channels is recommended. It is noted that the as-designed flow pattern contributes to the improvement of the HT-PEMFC power density.

Introduction:Hydrogen technologies, especially the Proton Exchange Membrane Fuel Cell (PEMFC), are promising alternative power sources, due to their low to non-carbon emission, high power density, high efficiency, and fast start-up. Despite their high potential and expected major impact on the economy of the future, there are still challenges to overcome, before PEMFCs can be globally commercialized. Soon, PEMFCs operated above 100°C are expected to be used for automobiles, due to their use of smaller and lighter radiators, higher reaction rates and lower susceptibility to catalyst poisoning. To achieve this goal however, high-temperature PEMFCs need a higher performance, stability, and durability, while reducing the cost at the same time. The performance, durability and stability of a fuel cell are related to the distribution of physical and chemical parameters, like e.g., oxygen partial pressure (p(O2)). During the operation of the fuel cell, the distribution of those parameters is inhomogeneous.[1] Therefore, we used an in-house developed 3-dimensional non-destructive real-time/space visualization system to achieve an understanding of the p(O2) inside the fuel cell during operation at higher temperatures.Experimental:The PEMFC used for this experiment has an active area of 4 cm2 and uses 10 straight gas flow channels. Prior to the assembling, 5 pinholes with a diameter of 90 µm were manufactured into the GDL on the cathode side both underneath the rib and the gas flow channel (Fig. 1). Those pinholes are also manufactured into the current collector and insulator of the PEMFC on cathode side. The holes are used to insert optical fibers from outside the cell to approximately 20 µm (adjustable with an accuracy of 1 µm) above the catalyst layer of the CCM. Prior to the use, the fibers with a core diameter of 10 µm are etched in HF solution to reduce their clad diameter from 125 to 50 µm. Furthermore, the apex of the fiber is cleaved perpendicular to the axis of the fiber. Before insertion an oxygen sensitive dye (PtTFPP, (Fig. 2)) is applied to the apex of the fibers. PtTFPP has absorption peaks at 407, 530 and 540 nm and an emission peak at 650 nm. The emission peak is quenched by oxygen partial pressure, and the emission intensity decreases monotonically with increasing oxygen partial pressure. For the excitation, a laser with a wavelength of 532 nm is used and the emitted light is captured by a CCD camera.[2] Visualizations were carried out at 80, 90, 100, 110 and 120 oC at a constant water vapor pressure of 37.97 kPa, which equals 80, 53.6, 36.8, 25,9 and 18.5% RH respectively, at increasing current densities. Prior to the visualization, calibrations, and performance tests in form of IV and CV were carried out for each temperature. The gas flow rate during the experiments was set to 100 mL/min Air/H2 (parallel flow) at cathode and anode respectively. Results and Discussion:The IV performance tests showed decreasing cell performance with increasing temperatures, which was expected because of the increasing resistance due to drying out of the membrane. Furthermore, a decrease of the ECSA was observed with increasing temperatures, which could also be due to the drying out of the membrane as well as the binding material around the catalyst nanoparticles which reduces gas diffusion and the effective catalyst surface area. In this first try, the monitoring was done with 3 fibers under one rib located near the inlet, the middle of the cell and near the outlet of the cell. With increasing current density, the oxygen partial pressure was decreasing at every temperature. Interestingly, the oxygen partial pressure distribution changed with increasing temperature. The reason for the changing oxygen partial pressure distribution could be due to accumulation of heat (Fig. 3) and increasing water vapor pressure at higher temperatures. Further experiments with 5 fibers including measurements in the gas flow channel as well as measurements with back pressure to increase the cell performance will be done shortly to confirm this finding.[1] Y. Kakizawa, C. L. Schreiber, S. Takamuku, M. Uchida, A. Iiyama, J. Inukai, Visualization of the oxygen partial pressure in a proton exchange membrane fuel cell during cell operation with low oxygen concentrations, J. Power Sources, 483, 229193 (2021).[2] Y. Kakizawa, T. Kobayashi, M. Uchida, T. Ohno, T. Suga, M. Teranishi, M. Yoneda, T. Saiki, H. Nishide, M. Watanabe, A. Iiyama, J. Inukai, Oscillation mechanism in polymer electrolyte membrane fuel cell studied by operando monitoring of oxygen partial pressure using optical probes, J. Surf. Finish. Soc. Jpn, 72, 230 (2021). Figure 1