Low Temperature Proton Exchange Membrane Fuel Cell Research Articles

Experimental and numerical investigations on synergistic coupling of metal hydride hydrogen storage systems with low-temperature proton exchange membrane fuel-cell

Hydrogen has emerged as a promising alternative for various energy needs, and metal hydride hydrogen systems offer significant potential due to their near-ambient working conditions and safe storage. This study presents experimental and numerical investigations on a lab-scale metal hydride fuel cell system to showcase its viability in addressing future energy demands. The experimental setup includes a 41-tube Metal Hydride (MH) reactor with an outer cooling jacket, containing 3.75 kg of La0.7Ce0.1Ca0.3Ni5. The output of the reactor is coupled to a 1 kW fuel cell, with controlled hydrogen discharge at temperatures ranging from 30 to 50 °C through numerical modelling. The study found that maintaining the reactor at 40 °C was sufficient to sustain the required bed pressure for a 1 kW fuel cell. Numerical simulations revealed that a 1 kW fuel cell operating at a current density of 0.8 A/cm2 and 50 °C rejected approximately 1.3 kW of waste heat. Moreover, 3.75 kg MH reactor could discharge hydrogen at a constant rate of 13 l/min for 36.3 min with just 125–225 W of heat input, highlighting the thermal coupling potential between these systems. The energy efficiency of the coupled MH-PEMFC system increased by 1.8 times to reach 49 % at 50 °C. Additionally, the waste heat generated proved sufficient to provide the required endothermic heat to multiple MH reactors, with a single reactor utilizing only 16.3 % of the total waste heat. This integrated system demonstrates promising efficiency and sustainability for future energy applications.

Impact of flow configuration and temperature on water flooding and membrane water content of low-temperature proton exchange membrane fuel cell

Low-temperature proton exchange membrane fuel cells (LT-PEMFCs) have emerged as promising candidates in transportation due to zero-emission, high power density and efficiency. Issues such as liquid water flooding and membrane drying significantly reduce their performance and durability during higher current density operations. Although many simplified 1-D and 2-D models have been proposed, they do not aid in understanding water dynamics and membrane water content for different flow configurations and operating temperatures. This work focuses on the development of a 3-D, multiphase, non-isothermal, physics-based model of the LT-PEMFC to address the above-mentioned issues. The model is validated with experiments performed on a 32 cm2 LT-PEMFC at 40 °C with a hybrid flow configuration. The results suggest that the hybrid configuration provides a power density enhancement of 12 % compared to the parallel configuration at 70 °C. Due to this performance improvement, ΔT of the hybrid configuration has reached 7 °C, which is slightly higher than the parallel configuration's ΔT of 5.7 °C. With an increase in operating temperature from 40 °C to 70 °C, the hybrid configuration experiences a 50% enhancement in the power density. For both temperatures, the hybrid configuration shows a consistent increment in the saturation from inlet to outlet, which creates a favorable pathway for water removal from the cell. The findings from this work suggest that the hybrid configuration is superior to the parallel configuration in terms of power density output, water removal capacity and membrane water content. This work provides valuable insight into overcoming key issues of liquid water flooding and membrane durability.

Optimizing adhesive rheology for stencil printing of fuel cell sealings using supervised machine learning

In a single low-temperature proton exchange membrane fuel cell (LT-PEMFC) stack, the sealings are responsible for preventing leakages, providing electrical insulation and compensating assembly tolerances. This study investigates stencil printing to produce fuel cell sealings and aims to identify reliable conditions to print layer thicknesses of at least 500 μm, typically used for this application and substantially exceeding the current state-of-the-art. First, rheological and print experiments were conducted with 25 distinct adhesives, including ultraviolet (UV) curable acrylics and epoxies, to determine their printability. An adhesive was considered printable when it detached from the stencil without forming bubbles, a print defect that significantly diminishes the process stability. This had to be accomplished at two different squeegee speeds (40 and 160 mm/s), confirming the robustness of the adhesive for the print process. In addition, the impact of the aperture orientation, aperture aspect ratio (AR) and separation speed of the substrate from the stencil were evaluated. Here, it was detected that a multivariable criterion was necessary to reliably predict printability. Thus, classification models based on binary logistic regression, a simple supervised machine learning technique, were proposed using the thixotropy index TI (indicator for viscosity recovery ability), steady-state viscosity at 100 s−1, adhesive surface tension and aperture AR as predictors. The derived models achieved a prediction accuracy ≥88.2%, demonstrating adequate generalisation. Moreover, it was identified that increasing TI is the most effective approach to achieve printability. Finally, the driving physical mechanisms influencing the obtained print results were assessed, and it was shown that a TI value of about 50 Pa s/s is required to reach the minimum layer thickness.

Transient Characteristics of the Low-Temperature PEMFC: A Comparative Analysis Using a Physics-Based Model

Low-temperature proton exchange membrane fuel cells (LT-PEMFCs) have experienced a considerable technological leap in the last few decades for transportation and stationary applications. Specifically, the precious metal loading in the catalyst layers (CLs) is notably decreased while enhancing the overall cell performance.1 However, the durability and cost remain major factors that affect the widespread commercialization of the LT-PEMFC. Though this can be achieved with further material development, some existing issues may be resolved by implementing effective design and control strategies. A good understanding of fuel cell water dynamics is required to improve durability and performance. Although some dynamic characteristics can be observed from the experiments, a physics-based model of the LT-PEMFC is necessary to study in-depth transient responses under various conditions like current profiles, operating temperatures, pressure, and humidification levels. Lately, the transient analysis of the fuel cell has gained more attention to elucidate the complex transport phenomena.2 Several transient models of the LT-PEMFC are reported to capture the two-phase behavior inside the cell. Usually, these models are 1D, 2D, or single channel 3D with assumptions like isothermal operation, vapor-equilibrated membrane, simplified reaction kinetics, and more.3–5 Hence, they do not provide spatio-temporal insights into the cell performance containing water dynamics with various flow configurations.The current study focuses on a transient physics-based model of the LT-PEMFC for dynamic analysis across its thickness and flow channels. The membrane used in LT-PEMFC requires humidification to enhance the ionic conductivity and function properly.6 This study considers Schroeder’s paradox for the membrane, which exhibits a different water uptake behavior in the presence of saturated water vapor and liquid water.7 The water uptake property is strongly dependent on the temperature. Therefore, we have developed a single polynomial expression for the membrane water uptake, including temperature and water activity dependency. Using the governing equations & empirical correlations from the numerical and experimental studies, we develop a comprehensive 3D, multiphase, non-isothermal, transient physics-based model of the LT-PEMFC that can closely approximate the liquid water transport under various operating conditions. It is a Multiphysics model that couples electrochemical reactions, porous media flow, transport of reactant species, liquid water transport, heat generation, charge transfer, and ionomer water transport. COMSOL Multiphysics is used to solve the model. It provides a spatio-temporal water distribution inside the membrane, CL, microporous layer, gas diffusion layer, and flow channels. Experiments are performed on 32 cm2 LT-PEMFC with the hybrid flow configuration at 75 °C and 80% RH to validate the physics-based model in the steady state condition. The validation study suggests that the present multiphase model estimates the LT-PEMFC performance with an acceptable RMS current density error of 15 mA/cm2. The simulations are operated in the Galvano-dynamic mode, and the corresponding LT-PEMFC response for the hybrid configuration is shown in Figure 1(a) at various operating pressures. Also, the preliminary results of the liquid water saturation under the channel and rib are incorporated in Figure 1(b). It shows that the water accumulation under the rib is more than the channel due to lower local temperature and weaker convection under the rib, promoting water vapor condensation. Further, the comparison between hybrid and parallel configurations is performed and illustrated in this presentation. Another objective is to study how quickly the liquid water saturation and membrane water content react upon changing the load cycle, RH, operating temperature, and flow configuration. This work is an important step toward understanding the impact of various flow configurations and operating conditions on the water dynamics and membrane water content inside the LT-PEMFC. The developed physics-based model would be extended further by considering the membrane deformation due to the shrinking-swelling under the humidification and thermal cycling, which is critical for the performance and degradation.

Porous Electrode Optimization for PEMFCs Using 3D Printing Technology

Proton Exchange Membrane Fuel Cells (PEMFCs) represent a class of fuel cells that transform the chemical energy of fuels, ideally hydrogen and oxygen, into electrical power. Utilized in diverse applications, PEMFCs power vehicles and supply backup energy to buildings. The core of a PEMFC is the membrane electrode assembly (MEA), composed of a polymer electrolyte membrane, an anode, and a cathode. Oxygen, protons, and electrons merge at the cathode, forming water. One challenge PEMFCs face is water-induced cathode flooding at low temperatures, a consequence of the electrochemical reaction's water accumulation. This reduces the oxygen supply, potentially leading to decreased cell performance or even failure. This issue can have substantial undesired consequences, as PEMFCs depend on oxygen availability at the cathode to generate electricity.Gas Diffusion Layers (GDLs) serve as critical PEMFC components, providing porous structures that facilitate reactant access to the catalyst layer and enabling electron flow through the external circuit. GDLs also offer structural support and promote reactant distribution across the membrane surface. Water accumulation in the cathode may cause pore clogging within the GDL, restricting reactant flow, and reducing cell performance. Additionally, water build-up increases pressure drop across the GDL, hindering reactant access to the catalyst layer and diminishing fuel cell efficiency.Three-dimensional (3D) printing has emerged as a potential technique for fabricating GDLs in PEMFCs. 3D printing enables the creation of GDLs with ordered pore size structures, offering a more uniform surface than traditional GDLs with randomly oriented fibres. This uniformity enhances reactant distribution across the membrane surface and mitigates water accumulation risks. In addition, to prevent cathode flooding, 3D printed GDLs are immersed in PTFE solution to increase hydrophobicity.This talk delves into the creation and evaluation of 3D printed carbonized GDLs for PEMFC implementation. A desktop 3D printer constructed a polymer framework, which was subsequently carbonized in a high-temperature tube furnace. Isothermal thermogravimetric analysis (TGA) tests were performed to identify weight change across a temperature range of 30-900 °C under an N2 atmosphere, optimizing the carbonization step to reduce structural distortion and increase electrical conductivity.The 3D printed GDLs displayed pore size diameters spanning 80 to 120 μm and fibre radii of 20-30 μm. The 3D printing technique produced GDLs characterized by a consistent, planar structure without blocked pores that are normally caused by excess resin residue. Electrical conductivity assessments were conducted on the carbonized specimens, and tensile and compression tests measured their mechanical properties.GDLs possessing minimal pore sizes and thicknesses were integrated into membrane electrode assemblies (MEAs) and examined in low-temperature PEMFCs. Diverse spraying methodologies were investigated, involving either the catalyst being sprayed onto the 3D printed GDL or the membrane receiving a catalyst coating. Commercial MEAs, comprising Nafion membranes and platinum electrodes, acted as benchmarks for MEAs featuring 3D printed GDLs. Furthermore, the current challenges facing 3D printed GDLs, including material selection, production consistency, compatibility with other PEMFC components, costs, and scaling up are highlighted in the talk.These findings underscore the promise of 3D printed carbonized GDLs in boosting PEMFC performance, showing their potential as a cost-effective and proficient substitute for conventional carbon paper based GDLs. Figure 1

Pressure and Impedance Based in Situ Diagnostic Methods for Water Management in Proton Exchange Membrane Fuel Cells Applications

Recent advancements in proton exchange membrane fuel cells (PEMFCs) have led to significant developments in low-carbon transport technology, enabling the generation of clean, efficient electricity with minimal noise and toxic emissions for heavy-duty applications. However, effective water management remains a critical challenge in PEMFCs due to the intricate phase changes and liquid-gas transport processes within key components, which significantly impact cell performance and longevity in industrial applications. Given the rapid dynamics of water activities and material responses within cells, in situ diagnostic techniques for water management in PEMFCs are essential for optimizing cell performance and extending the lifespan of fuel cell stack and system.Water, electrochemically produced on the cathode side, can cause potential flooding in key components including the catalyst layer (CL) and gas diffusion layers (GDLs), impeding air/oxygen supply to the cathode side. To characterize the performance loss induced by water flooding, Electrochemical Impedance Spectroscopy (EIS) is commonly employed as a fuel cell diagnostic tool. EIS records the contributions of different polarization processes to the global impedance with individual time constants during operation. However, the interpretation of complex EIS spectra can be very challenging, as polarization processes may overlap in frequency and be difficult to identify. To address this issue, Distribution of Relaxation Times (DRT) analysis is implemented as a powerful tool that allows for a clear separation and quantification of the polarization processes showing as peaks in a frequency domain [1]. Thus, we utilize EIS-based DRT analysis as an in-situ diagnostic tool to detect cathode flooding during cell operation. To validate this approach, we have conducted tests on a 300 cm2 low temperature PEMFC, varying one operation parameter at a time and evaluating its effects on cathode flooding by studying the frequency and height evolution of DRT peaks.Nevertheless, water flooding is not confined to the cathode side, as water can also permeate through the proton exchange membrane (PEM) and reach the anode side, resulting in potential fuel starvation on the cathode's counterpart and subsequent degradation of carbon-based materials. To address the sensitivity limitation of the EIS-based DRT method in detecting anode flooding, we employ an in-house developed pressure drop indicator (PDI) tool, as a non-invasive and real-time approach for diagnosing water flooding in the anode. The PDI tool assesses the pressure drop across anode channels, which is a function of the liquid water contents in bipolar plates considering the pressure reduction mainly caused by the frictional drag [2]. The effectiveness of the PDI tool is validated through cell testing at different water flooding levels by varying relative humidity and pressure conditions. This technique offers timely and sensitive detection of anode water flooding in PEMFCs, which is crucial for alarming irreversible material degradation in the electrode and facilitating appropriate follow-up actions.To conclude, we have developed and employed in situ PDI and EIS-based DRT methods within our water management framework for diagnosing water flooding in both the anode and cathode of PEMFCs in industrial applications. The combination of these techniques offers real-time and accurate assessments on water management conditions, which is crucial for optimizing overall performance and longevity of PEMFC stacks and systems.[1] Heinzmann, M., Weber, A., Ivers-Tiffée, E. (2018). Advanced impedance study of polymer electrolyte membrane single cells by means of distribution of relaxation times. Journal of Power Sources, 402, 24-33.[2] Barbir, F., Gorgun, H., & Wang, X. (2005). Relationship between pressure drop and cell resistance as a diagnostic tool for PEM fuel cells. Journal of Power Sources, 141(1), 96-101. Figure 1

In-Situ Spectroscopic Investigation of 3-D Gas Diffusion Electrodes for Fuel Cell Reactions in Half-Cell Setups

Significant work has already been done in understanding proton exchange membrane fuel cells (PEMFC) over the past decades. In-situ visualization of the fuel-cell reactions has developed considerably and has also helped in understanding the challenges which still exist in various steps of electrochemical processing. Gas diffusion electrode half-cells have been widely promoted for fundamental catalysis research and when coupled with techniques like X-ray absorption spectroscopy (XAS) can be used for in-situ/operando studies of the reaction mechanisms in fuel cell reactions. This is particularly important to address the challenges in low temperature PEMFCs (eg. degradation of catalyst during durability tests) as well as high temperature PEMFCs (eg. poisoning of the Pt catalyst and low oxygen solubility in phosphoric acid).In this presentation, an effort will be made to illuminate the catalytic characteristics during oxygen reduction reaction using in-situ XAS. The co-adsorption of H3PO3 and CO on platinum catalysts will be investigated using the Δµ XANES technique by following the signatures of different species adsorbed on the catalyst surface, and the Efix technique which follows the variation of signal intensity at a fixed energy near to the white line to follow the changes in Pt oxidation. During CO removal through cyclic voltammetry in the presence of 800 µM H3PO3 (as shown in the figure provided) it is possible to see a clear change in signal intensity around the potential of 250 mVAg/AgCl, which was associated with the oxidation of H3PO3 to H3PO4, since CO oxidation takes place at higher potentials (above 600 mVAg/AgCl). It is also interesting to note that when oxidizing H3PO3 to H3PO4, the platinum surface significantly reduced. With these experiments, it can be concluded that the Efix technique has a great potential to better understand what happens to Pt during the oxidation of H3PO3, as well as to identify more clearly the oxidation potential of this species, which is not easy to do based on the electrochemical data alone. Considering that this species is one of the main species responsible for the poisoning of the Pt catalyst during the operation of fuel cells, it is extremely important to understand the life cycle of this compound so that the operating conditions can be adapted to maximize the performance of the catalyst and develop new catalysts more resistant to poisoning by phosphorous species for HT-PEMFCs.Acknowledgements:Prof. Matthias Arenz from University of Bern, Martin Prokopand Tomàs Bystrom from University of Chemistry and Technology Prague, Michael Haumann, Freie Universität Berlin are gratefully thanked for their collaboration. German Research Foundation DFG Project ID RO 2454/19-1, the Bavarian Gender Equality Grant 2019-2021 (for Women in Academia), Petra III DESY (Hamburg, Germany), a member of the Helmholtz Association HGF, P65 beamline (I-20211432) and KMC-3 beamline BESSY (Berlin,Germany). Figure 1

Analysis and evaluation of fuel cell technologies for sustainable ship power: Energy efficiency and environmental impact

Amid growing emphasis on achieving carbon neutrality, this study conducts a thorough assessment of different fuel cell technologies for their suitability as primary ship power sources. The primary goal is to evaluate the energy efficiency and carbon footprint impacts associated with adopting fuel cells for ship propulsion. The analysis employs simulation modeling and comparative evaluation to establish key indices: energy efficiency design index (EEDI), energy efficiency operational index (EEOI), and carbon footprint design index (CFDI). These indices consider factors like system weight, maintenance cycle, and fuel economy, ensuring a comprehensive comparison under consistent ship design parameters. Results reveal that liquefied natural gas fuel cells, direct methanol fuel cells, and low-temperature proton exchange membrane fuel cells (LT-PEMFC) outperform other fuel cell systems in terms of energy efficiency and carbon emissions reduction. Their respective EEDI values stand at 11.62, 12.72, and 10.05 g CO2/ton·km, accompanied by corresponding EEOI values of 0.10, 0.13, and 0.11 g CO2/ton·km. Additionally, CFDI values are calculated as 39.10 %, 19.45 %, and 11.64 %, respectively. Notably, the comprehensive assessment underscores LT-PEMFC as the most viable option for ship propulsion, offering improved energy utilization, reduced carbon impact, and decreased operational expenses. These findings contribute valuable insights into the appropriateness of diverse fuel cell technologies for ship power applications, considering both their energy efficiency and environmental implications.

Critical performance comparisons between the high temperature and the low temperature proton exchange membrane fuel cells

Currently, there are only some general concepts about the performance difference between an LT-PEMFC (low temperature proton exchange membrane fuel cell) and an HT-PEMFC (high temperature proton exchange membrane fuel cell), i.e., no literature has been found to conduct direct comparisons between them. In this research, for the first time, according to the same level (low level, medium level or high level) under the same operating condition type (operating temperature or cathode air utilization rate), the tested I-V performance, EIS (electrochemical impedance spectroscopy), LSV (linear sweep voltammetry), and calculated ECSA (electrochemical surface area) are compared between LT-PEMFC and HT-PEMFC. Some mechanisms are further disclosed, for instance, the higher Pt loading in the catalyst layer of an HT-PEMFC and its elevated operating temperature do not result in improved performance, compared to that of the LT-PEMFC. This is attributed to the lower apparent exchange current density in the case of HT-PEMFC.

Boosting the power density of the H3PO4/polybenzimidazole high-temperature proton exchange membrane fuel cell to >1.2 W cm−2 via the deposition of acid-based polymer layers on the catalyst layers

The high-temperature proton exchange membrane fuel cells (HT-PEMFCs) based on H3PO4/polybenzimidazole (PBI) membrane have drawn much attention in recent years. However, the power density of the H3PO4/PBI based membrane electrode assembly (MEA) is still much lower than that of the common perfluorosulfonate membranes based low-temperature proton exchange membrane fuel cells (LT-PEMFCs). Regulation and control of redistribution of H3PO4 in the MEA is a most important issue for the power density improvement of H3PO4/PBI based MEA. Herein, a MEA with new structure is proposed, in which a layer of PBI without H3PO4 doping (referred to as the acid-based polymer layers or APL) is deposited on the catalyst layers. With the application of APL, the peak power density of the H3PO4/PBI based MEA is 902 mW cm−2 in H2/air, and 1.289 W cm−2 in H2/O2 at 180 °C, which is the highest performance for H3PO4/PBI based HT-PEMFC reported in the literature. The results shows that the APL could effectively promote the reasonable redistribution of H3PO4 along the cross section in the MEA, construct more three phase boundaries (TPBs), enhance the electrochemical active surface area (ECSA), thus boosting the performance of H3PO4/PBI based HT-PEMFC.

Understanding heat and charge transfer in a low temperature PEM Single Cell: a simulation tool development

This work is a study of coupled charges and heat transfers phenomena on a low temperature PEMFC single cell. A one-dimensional steady state model was developed to compute current and temperature distributions in a PEMFC single cell whatever the operating conditions. The work comprises of three parts: Firstly, a literature survey was conducted to describe the principle of a PEMFC and the fundamental operations. A state of the art of the previous modeling works on the PEMFC was also presented in this part. Secondly, the developed model using the basic relations to describe heat and charges transfer phenomena occurring in the single PEM cell was presented. Finally, a simple simulation tool called FCvb was performed and optimized using Visual Basic Excel and referring to the previous relations in the developed model. To finalize this study, a conclusion and perspectives were presented in the last part of this work.

Design and analysis of a hybrid space heating system based on HT-PEM fuel cell and an air source heat pump with a novel heat recovery strategy

This work analyzes the performance of a system integrating high temperature proton exchange membrane fuel cell (HT-PEMFC) and air source heat pump (ASHP) technologies for residential space heating. The main goal is to improve energy conversion efficiency for a residential building in the Canadian climate, in which methane is normally used to feed traditional systems (e.g., boilers and/or furnaces), due to its considerable local availability. On the other hand, ASHP technology is characterized by high efficiency, but normally fails to perform well in cold climates, due to the reduction of the coefficient of performance (COP) and ice formation on the evaporator. Due to the higher attention paid to low temperature PEMFC system (LT-PEMFCS) till now, it is here investigated if significant improvements can be obtained with a higher temperature PEMFCS, by thus fully exploiting the higher quantity and better quality of recoverable waste heat compared to LT-PEMFCSs, particularly aiming at mitigating the afore-mentioned low-temperature related issues. A mathematical model for the system components is proposed to perform parametric analyses aimed at assessing the variation of efficiency as a function of both environmental and load conditions. The results show that the ASHP COP increases by more than 77% when the HT-PEMFCS works at its nominal (5.3 kW) power and/or inlet air has a high relative humidity (RH), i.e., close to 100%. The proposed HT-PEMFC system configuration was able to reach a total COP higher than 1.5, leading to a reduction of the needed primary energy needed and a consequent reduction of the operating costs by up to 60% compared to boilers.

Analysis and comparison of innovative PEMFC systems coupled with an ASHP for space heating in cold climates

In this study, two integrated systems are proposed and analysed: an air source heat pump (ASHP) coupled with either high-temperature proton exchange membrane fuel cells (HT-PEMFCs) or low-temperature proton exchange membrane fuel cells (LT-PEMFCs), where the exhaust gases from the PEMFCs are used to increase the external air temperature to the evaporator of the ASHP. The objective is to understand how the proposed systems behave in a cold climate region and determine which of the systems is better to couple with an ASHP for domestic space heating purposes in a cold climate. The novelty of the work lies in the idea of recovering heat from the exhaust gases from the fuel reformer and PEMFCs and mixing them with external air, before sending it to the ASHP as the inlet air. Grey-box models are employed to model the PEMFCs, whereas the hypothesis of the chemical equilibrium of reacting species is considered in the reformer model. Steady state analyses are considered to understand the performances of the proposed systems compared to two different types of furnaces: high-efficiency and mid-efficiency ones. The results indicate that the HT-PEMFCs are the best for the case studied here, with performances up to 100% greater than the mid-efficiency furnace and up to 63% more than the high-efficiency one. A scenario analysis on a simple pay back is also carried out, and the return on the investment costs in the 2024 scenario is about 24 years if compared to the high efficiency furnace and 14 if compared to the mid-efficiency one, whereas the corresponding numbers are 19 and 11 years, respectively, for the 2030 scenario.

Effects of gas-diffusion layer properties on the performance of the cathode for high-temperature polymer electrolyte membrane fuel cell

The role of the gas-diffusion layer (GDL) in high-temperature polymer electrolyte fuel cell (HT-PEMFC) differs from that in low-temperature PEMFC GDL due to operating conditions and environment. Determining the GDL's structural parameters that affect its transport properties, and how these properties impact HT-PEMFC performance was urgently required. Four commercial GDLs were employed in HT-PEMFC cathode's GDE and was examined using X-μCT, mercury intrusion porosimetry, and an optical microscope to analyze structural parameters and characteristics. Fractal theory was applied to comprehend the gas transmission property of GDL, and the validity of the theory was confirmed through ex-situ through-plane gas permeability measurement. The analysis indicated that the porosity of GDL influenced by the crack region of the MPL has more impact on the GDL's gas transmission than its thickness. After that, we established a correlation between HT-PEMFC cathode performance and GDL porosity and theoretical gas transmission properties using R2 coefficient of determination.

CFD simulation of water droplet adhesion on the GDL of a low temperature PEM FC in air cross-flow conditions

Water management is a critical challenge in low temperature (LT) Proton Exchange Membrane Fuel Cells (PEM FC); condensed liquid appears mainly at the cathode side, where water from the reduction reaction is generated. Differences in concentration may result in the transfer of water to the anode side across the membrane electrode assembly (MEA). Excessive liquid can negatively affect fuel cell performance, causing low efficiency and instability. This occurs due to water movement through porous layers and channels that are the essential pathways for the reactant gas to reach the MEA. However, water is necessary in the PEM FC for enhancing ion conductivity of the membrane. The present study can contribute to the optimization of LT PEM FCs by analysing the water behaviour under flow conditions. The widely used Volume Of Fluid (VOF) method is adopted for simulating multiphase flow. CFD simulation of droplet adhesion on the gas diffusion layer (GDL) is performed to describe the interaction between water and gas flow. Deformation and oscillations of droplets with diameters in the 0.3-1.0 mm range are investigated by considering airflow rates up to 15.0 m/s. CFD analysis is validated by optical data from digital imaging with high spatial (up to 5.8 μm/pixel) and temporal (up to 1.0 ms) resolution.

Insights into Degradation of the Membrane-Electrode Assembly Performance in Low-Temperature PEMFC: the Catalyst, the Ionomer, or the Interface?

Here, we report a study on the structural characteristics of membrane electrode assembly (MEA) samples obtained from a low-temperature (LT) polymer electrolyte membrane (PEM) fuel cell (FC) stack subjected to long-term durability testing for ∼18,500 h of nominal operation along with ∼900 on/off cycles accumulated over the operation time, with the total power production being 3.39 kW h/cm2 of MEA and the overall degradation being 87% based on performance loss. The chemical and physical states of the degraded MEAs were investigated through structural characterizations aiming to probe their different components, namely the cathode and anode electrocatalysts, the Nafion ionomer in the catalyst layers (CLs), the gas diffusion layers (GDLs), and the PEM. Surprisingly, X-ray diffraction and electron microscopy studies suggested no significant degradation of the electrocatalysts. Similarly, the cathode and anode GDLs exhibited no significant change in porosity and structure as indicated by BET analysis and helium ion microscopy. Nevertheless, X-ray fluorescence spectroscopy, elemental analysis through a CHNS analyzer, and comprehensive investigations by X-ray photoelectron spectroscopy suggested significant degradation of the Nafion, especially in terms of sulfur content, that is, the abundance of the -SO3- groups responsible for H+ conduction. Hence, the degradation of the Nafion, in both of the CLs and in the PEM, was found to be the principal mechanism for performance degradation, while the Pt/C catalyst degradation in terms of particle size enlargement or mass loss was minimal. The study suggests that under real-life operating conditions, ionomer degradation plays a more significant role than electrocatalyst degradation in LT-PEMFCs, in contrast to many scientific studies under artificial stress conditions. Mitigation of the ionomer degradation must be emphasized as a strategy to improve the PEMFC's durability.

Effects of Impurities and Operating Mode on The Dynamics of Direct Butane Proton-Exchange Membrane Fuel Cells

Maximizing the energy density of a portable power system is an important design factor since those systems have stringent maximum mass constraints. While Lithium-ion batteries are currently the standard choice for power systems in the scale of 10-100 watts, direct hydrocarbon Proton-exchange membrane fuel cells (PEMFC) have the potential to be more energy-dense than batteries at those scales even with efficiencies as low as %10. PEMFC are simple and operate at low temperatures which make them a suitable choice for portable power generation. Because of their low operating temperature, they are usually fueled by hydrogen. However, hydrogen is hard to store and handle, which makes it an unsuitable fuel for portable power applications. Alternatively, Hydrocarbon fuels, such as butane, are easier to store and safer to handle. Additionally, hydrocarbon fuels are ~50 times more energy dense than state of the art Lithium-ion batteries. For those reasons, it is desirable to develop a direct butane PEMFC for portable power applications. Limited work has been done in the past to demonstrate the viability of direct butane fuel cells, mainly because of the low reactivity of hydrocarbon in low temperature PEMFC. EH Kong et. al. demonstrated a working direct butane PEMFC by adding trace amounts of unsaturated hydrocarbons to the butane and operating the cell in “load-interrupt” mode. The authors proposed that butane might be converting active catalyst sites to inactive sites, causing the fuel cell to ‘extinguish’. Thus, the addition of unsaturated hydrocarbons and the load-interrupt operating mode can circumcise this saturation process. In this work, we demonstrate the repeatability of the direct butane PEMFC results produced by EH Kong et. al. on a custom-built fuel cell testing apparatus and explore methods to explain the current dynamics of the cell.For the experimental setup, we used a 25cm2 membrane electrode assembly (MEA). It consisted of treated Nafion N-177 layer directly painted with a catalyst layer on the anode and cathode sides. The catalyst layer is obtained from an ink that is prepared by mixing platinumblack, water, and 5% Nafionsolution. The Nafion N-177 layer is prepared using the manufacturer standard pretreatment procedure. Once assembled, the MEA layer is then pressed at 120 °C and 500 lbs. for 25 min. We then load the MEA layer into the fuel cell hardware, which includes the fuel cell, humidifiers, and heaters, and test the cell electrical performance at temperatures below (100C).Using the fuel cell testing apparatus, we confirm that for high purity butane (>%99.99) the PEMFC does not start and no open circuit voltage is detected. However, the PEMFC is started when unsaturated hydrocarbons are added to the butane fuel stream as shown in previous work. Specifically, the addition of ethylene at concentrations of 2000 ppm allows the PEMFC to operate continuously at low temperatures (<100C). Previously observed current dynamics were also reproduced. The current density of the fuel cell peaks in the beginning of the cell operation and decreases over time until it reaches steady state. It was observed that operating the cell in a load-interrupt mode, where the current is set to zero for 5 seconds every 25 second of operation, increases the average power density of the cell, when compared to the galvanostatic operating mode. Further we investigate the effect of different additives to butane. Specifically, we explore the effect of adding different concentration of hydrogen to the butane stream to analyze whether the interaction between the two fuels is independent or synergetic. Furthermore, we produce Electrochemical Impedance spectrums of the direct butane PEMFC to gain insights about cell resistances including mass transport limitations.For future work, we are interested in in-situ measurement techniques that allow us to observe the intermediates on the catalyst surface. Such data might allow us to verify and inform the empirical dynamical model proposed in previous work to explain the direct butane PEMFC current dynamics.

PBI-Membrane for High-Temperature PEMFC

High-temperature proton exchange membrane fuel cells (PEMFCs) are particularly attractive because of the potential benefits of faster electrode kinetics, high tolerance to fuel impurities, no humidification requirements, and simplified system design.1 The present work focuses on ongoing work based on membrane electrode assemblies (MEAs) for high temperature proton exchange membrane fuel cells. HT-PEMFCs were operated at 160-170 °C using humidified synthetic reformate. We have illustrated that an increase in the pressure of the in-going gases to 2 barG increases - as expected - the performance, E.g. the power density was improved from 0.32 W/cm2 at 0 barG to 0.48 W/cm2 at 2 barG at 170 °C. More data will be shown at the meeting.Fig 1: a) IV curves b) dependence of power density on back pressure, operating conditions: backpressure (0.4–2 barG), temperature: 170 °C, and λRef/ λAir (1.3 /2.5)Continuous operation and more than 290 start stop cycles have been performed in order to study the degradation effects of both continuous operation and of repeated start stops. Start stop cycles led to a degradation of 0.01 mV/cycle.The durability of HT-PEMFC can now be considered similar to low temperature PEMFC. We have proved more than 15,000 hours in single cells at 0.3 A/cm2. The degradation rate is around 4 μV/h for approx. 13,000 hours. Graphs of single cell performance during operation have shown very stable behavior for over 10,000 with an overall degradation of 9 μV/h at a current density of 0.4 A/cm2.Reference1) O. Jensen, D. Aili, H. A. Hjuler, Q. Li, High Temperature Polymer Electrolyte Membrane Fuel Cells - Approaches, Status and Perspective, ISBN 978-3-319-17081-7; DOI 10.1007/978-3-319-17082-4, Springer International Publishing, New York, 2015. Figure 1

Control‐oriented estimation of the exchange current density in PEM fuel cells via stochastic filtering

Increasing efficiency and durability of fuel cells can be achieved through advanced model-based optimal control of its operating conditions, and the efficient online estimation of fuel cell parameters and internal states is fundamental for the implementation of such advanced controllers. The exchange current density is a driving parameter of performance for the catalyst layer of proton exchange membrane fuel cells (PEMFC). This study presents a control-oriented, stochastic filtering approach for online, continuous estimation of the exchange current density in low-temperature PEMFCs. The fuel cell is framed as a Markov model where the exchange current density is posed as the stochastic hidden state. The physics-based static equation of the exchange current density is converted into a state transition equation. This transition equation and the equation for cell voltage are used in the stochastic state estimator to approximate the posterior probability distribution of the exchange current density. In order to highlight the usefulness of the approach, the estimated value of the exchange current density is used to approximate the trend of the electrochemical active surface area (ECSA) in the catalyst layer and train a nonlinear auto-regressive model. This data-driven model is used to forecast the evolution in the ECSA associated with long-term degradation. The estimation algorithm is successfully implemented and tested in two different experimental datasets.

High Power Density Fuel Cell Systems for Portable Electric Generators

It is of utmost importance to develop light weight fuel cell stacks and find the ways to integrate these to light weight and low temperature fuel cell systems. In order to meet the future energy demands non-polluting, compact, transportation and portable applications are required. Current energy systems have lower power density (kW/kg) resulting in optimized power only at higher overall weight. Systems with higher power density demands higher initial setup costs. Low temperature PEMFC, on other hand offers various advantages but fails to provide the required output without exceeding the weight of the fuel cell stack and thereby fuel cell systems. A fuel cell system consists of a fuel cell stack, compressed gas in cylinder, pressure relief valves, regulators, water pump, sensors and cvm. A fuel cell stack is the main component consisting of one of the devices with maximum weight and cost contribution. In such case, developing a system with stack having higher power density reduces overall weight and increases power density (kW/kg). PowerUP Energy Technologies has developed light weight fuel cell stack to achieve higher power density. Experiments considering flow field designs, recirculation strategy, different anode configuration has been a subject of study. Dead-end anode, closed cathode configuration of fuel cell stack further improves fuel utilization. Recirculation line of hydrogen if further added can improve in overall fuel utilization. Counter flow arrangement for reactant distribution further removes the necessity of humidifying the gases. This result in removal of humidifiers and thereby reducing the weight of the fuel cell system in total. Portable fuel cell systems have flexibility for ease in transportation and stationery solutions. Furthermore, lighter fuel cell stacks add advantage for higher output power at lower overall weights. This stack developed is further optimized with improved flow field designs and design of manifold. These fuel cell stacks are used in PowerUP’s portable fuel cell electric generators that are more efficient and sustainable than the currently used fossil fuel based solutions.