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To meet the demands for high power density, enhancing the water discharge capacity of proton exchange membrane fuel cells (PEMFCs) is imperative. The microporous layer (MPL), placed between a catalyst layer and gas diffusion layer, plays a crucial role in water management for PEMFCs. In this study, we fabricated electrospun MPLs of different pore sizes and characterized their morphology and pore structures. The mercury intrusion test showed that the mean pore sizes of electrospun MPLs are about 1.2–2.3 μm, much larger than commercial MPL's (about 70 nm). The electrospun MPLs were assembled in single PEMFCs to test their performance and Electrochemical Impedance Spectroscopy (EIS). The results demonstrate that the electrospun MPLs with a pore size exceeding 1.9 μm significantly enhance water discharge and oxygen transport at the cathode relative humidity (RH) of 50 % and 100 %. Moreover, the EIS testing and fitting outcomes indicate that when the PEMFC performance is dominated by mass transport under high current density and 100 % cathode RH, the electrospun MPLs with a pore size exceeding 1.9 μm exhibit a better water discharge capacity and lower mass transport resistance. • Electrospun MPLs have larger pore sizes (>1 μm) than commercial ones (∼100 nm). • Electrospun MPLs of a pore size exceeding 1.9 μm enhance water discharge. • Fuel cell performance was improved at cathode relative humidity >50 %. [ABSTRACT FROM AUTHOR]

Next‐generation ultrahigh power density proton exchange membrane fuel cells rely not only on high‐performance membrane electrode assembly (MEA) but also on an optimal cell structure. To this end, this work comprehensively investigates the cell performance under various structures, and it is revealed that there is unexploited performance improvement in structure design because its positive effect enhancing gas supply is often inhibited by worse proton/electron conduction. Utilizing fine channel/rib or the porous flow field is feasible to eliminate the gas diffusion layer (GDL) and hence increase the power density significantly due to the decrease of cell thickness and gas/electron transfer resistances. The cell structure combining fine channel/rib, GDL elimination and double‐cell structure is believed to increase the power density from 4.4 to 6.52 kW L−1 with the existing MEA, showing nearly equal importance with the new MEA development in achieving the target of 9.0 kW L−1. [ABSTRACT FROM AUTHOR]

The internal water and thermal state and performance of an air-cooled proton exchange membrane (PEM) fuel cell stack are strongly determined by the fan arrangement and operational characteristics. This study presents an innovative method to investigate the influence of fan on stack performance through integration of fan's full morphology, including the fan blade, grill between the fan and stack, etc. into a three-dimensional (3D) multiphase stack model. The multiple reference frame (MRF) model is implemented to simulate the air flow field caused by the rotation of fan and the multiple transfers coupled with electrochemical reactions is considered in the 3D stack model in detail. Through this integrated model, the influence of the air supply mode, fan number and duty ratio on stack performance and the distribution characteristics are investigated in detail. It is found that the air flowing into each cell in the fan-cooled stack is highly non-uniform, which increases the variations of oxygen concentration, temperature, and voltage in the stack. In comparison with the blowing mode, the suction mode helps to promote the uniformity of air supply with a lower air flow velocity. [ABSTRACT FROM AUTHOR]

This study presents a comprehensive system-level analysis model for evaluating performance characteristics of a hundred-kilowatt proton exchange membrane fuel cell (PEMFC) test system. Unlike conventional power-focused systems, the test system has a more complex architecture and numerous balance of plants (BOPs). The developed model integrates detailed input-output traits of each system component. The energy efficiency ratio (EER) and energy conversion efficiency (η) are introduced as metrics for assessing net power consumption and conversion capability of the test system. By simulating various operational scenarios (considering temperature, load current, cathode pressure, humidity, and PEMFC power), the model predicts the behaviors of BOPs and energy flow relations. The changing rules of the EER and η are also investigated. An increase in temperature, current, and cathode pressure leads to an improvement in EER. Increasing operating temperature, cathode pressure, and humidity can enhance η. Key findings suggest optimal conditions for system self-sufficiency include an operating temperature below 90 °C, load current over 1200 mA cm−2, and air humidity under 90%. Furthermore, the PEMFC power is advisable to configure between 50% and 100% of the test system's maximum power. These insights are pivotal for improving the design and functionality of PEMFC testing equipment, further contributing significant advancements to fuel cell technology. • A system-level analysis model for a hundred-kilowatt PEMFC test system is developed. • The system model contributes to predict operating and energy flow parameters. • Two system indicators are proposed to assess the test system operating performance. • The necessary conditions for the test system to achieve self-sufficiency is determined. [ABSTRACT FROM AUTHOR]

Segmented proton exchange membrane (PEM) fuel cells are widely implemented in measuring their internal spatially distributed variables (e.g. current density and temperature). However, the difference between the segmented and ordinary fuel cells in spatial distribution characteristics has not been fully understood. In this work, we studied the spatial distribution characteristics in segmented fuel cells (cell area: 366.6 cm2) utilizing a three-dimensional (3D) large-scale fuel cell model that considers the full morphologies of metallic bipolar plates (BPs) and dot-matrix hydrogen, air and coolant flow distribution zones, including the current density, temperature, water content, etc., and compared with those in ordinary fuel cells. It is found that placing a segmented print circuit board (PCB) next to the bipolar plate (BP) component has little influence on fuel cell performance and internal distribution characteristics, whereas the measured current density distribution in the PCB still has inconsistency with that in the ordinary fuel cell, indicating that the influence of segmentation on electron conduction cannot be neglected. In the fuel cell with segmented BP and PCB, the fuel cell performance decreases significantly mainly due to increased electrical and ionic ohmic loss. In addition, the BP's segmentation significantly influences on the water and thermal state inside the whole fuel cell, leading to inconsistency in the measured temperature, relative humidity (RH) and current density distributions with ordinary fuel cells. [ABSTRACT FROM AUTHOR]

Self-humidification is becoming a popular strategy for water management in proton exchange membrane fuel cells (PEMFCs), owing to the advantages of decreased volume, cost, and parasitic power of the hydrogen fuel cell engine. Membrane dehydration is one of the key issues that seriously affect the performance and lifespan of PEMFCs under low humidity conditions. In this work, an electrospinning approach was employed to fabricate gas diffusion layers (e-GDLs) composed of nanosized carbon fibers with a nanoscale pore structure. Further, a vapor deposition of Dow Corning Sylgard 184 was utilized to apply a hydrophobic coating to enhance the hydrophobicity of the e-GDL. The fabricated e-GDL can help alleviate the dehydration of the catalyst-coated membrane by increasing the breakthrough pressure. The breakthrough pressure of the e-GDL is five folds higher than that of the current commercial GDL, owing to the combined effects of the nanostructure and enhanced hydrophobicity. This superior characteristic is expected to effectively alleviate membrane dehydration under low humidity conditions. In addition, the e-GDL has excellent elastic deformability, which can effectively alleviate the irreversible damage caused by the pre-tightening force in the stack assembly process, thus enhancing the durability and lifetime of PEMFCs. [ABSTRACT FROM AUTHOR]

• Full-scale 3D simulation for air-cooled PEM fuel cell stack was presented; • The stack polarization curve and temperature distribution were validated; • Oxygen content becomes lower at a higher temperature site in the stack; • Thermal behavior has a decisive effect on the distributions of temperature, gas, etc.; • Increasing the air flow rate benefits the uniform distribution of oxygen, water, etc. This study presents one of the first full-scale stack three-dimensional (3D) simulations for proton exchange membrane (PEM) fuel cell to investigate temperature distribution, cell/stack performance, and impact of air cooling. The stack consists of 30 cells with the active area of 50 mm × 200 mm for each fuel cell. The manifold and all the basic components are included in the computational domain, while the flow field structure is treated as porous media in order to reduce the computational burden. The model predictions are validated against the experimentally measured voltage and detailed temperature distribution under different currents. It is found that significant differences in temperature are present between the fuel cells at the two sides and that in the middle, and the oxygen content becomes lower at a higher temperature site due to the local increased water vapor concentration. As a consequence, thermal behavior has a decisive effect on the distributions of temperature, reactant concentration, membrane hydration, current density, etc., inside this air-cooled stack. It is also found that increasing the cooling air flow rate not only decreases the stack temperature, but also reduces the temperature variation, which further benefit the uniform distributions of oxygen, water vapor, etc. in the stack. [ABSTRACT FROM AUTHOR]

Mitigating flow maldistribution plays a crucial role in next-generation industry-used parallel-based flow field design for polymer exchange membrane fuel cells (PEMFCs), especially for larger-size cells and higher current density. In this study, a model reduction framework is proposed to alleviate flow maldistribution among parallel gas flow channels and associated computational burden. The gas flow features and electrochemical kinetics of four mitigation strategies including expanded manifold, partially porous media, dot matrix, and partially narrow structures are investigated in detail. The results indicate that the fuel cell model and a fluid flow model without the reactions show similar maldistribution features among parallel channels. The observed flow maldistribution can be effectively reduced by mitigating designs. Expanding the manifold space significantly alleviates the vortex impeding the gas entry to individual channel inlet, and the inlet exhibits better flow uniformity and pressure drop in the direction perpendicular to the channel than in the parallel to. The fully-inserted and manifold-inserted porous media methods present symmetrical quadratic-shaped flow patterns among channels, while that of the partially-inserted porous media inside channels is unsymmetrical. Additionally, the concentration loss with a partially narrowed design decreases by 44.7%, 12.9%, and 24.2% compared with the expanded manifold, partial porous media, and dot matrix designs at 1.8 A cm−2 owing to better flow uniformity and mass transport. These model framework and mitigation strategies are valuable for designing future high-performance industrial PEMFCs. • A model reduction framework is proposed to mitigate flow maldistribution quickly. • The flow and electrochemical features of four mitigation strategies are elucidated in detail. • Expanding the manifold alleviates the vortex impeding gas entry to subchannel inlet. • The partially narrowed design is superior owing to better flow uniformity and mass transport. [ABSTRACT FROM AUTHOR]

Proton exchange membrane fuel cells (PEMFCs) with ultrahigh power density are highly required in recent years. In this work, breakthrough is achieved in electrical conductivity and anticorrosion capacity for the graphite-resin composite bipolar plates (BPs) under the limitation of greatly reduced thickness by high molding and high impregnation pressures (HH-BP). Interconnected laminar structure of expanded graphite (EG) is well preserved during the resin impregnation process. The power density (>1 W/cm2@ 2.75 A/cm2, 75 % RH) and limiting current density (∼3.25 A/cm2@ 0.3 V, 75 % RH) are much higher for fuel cells assembled with HH-BP compared to those under other different combinations of molding and impregnation pressures. The enhancement in power density is attributed to the decreased ohmic resistance induced by the ultrahigh electrical conductivity as confirmed in electrochemical impedance spectroscopy (EIS). Ultrathin composite BPs with high electrical conductivity provide an effective approach for enhancing the power density of PEMFCs. [Display omitted] • Graphite-resin composite bipolar plate (BP) was prepared by molding and impregnation process. • Ultrathin BP was obtained using high molding pressure and high impregnation pressure (HH-BP). • The electrical conductivities and anti-corrosion capacity were greatly enhanced for the HH-BP. • The power density and limiting current density were enhanced for fuel cell assembled with HH-BP. • Enhanced fuel cell electrochemical performance is due to high electrical conductivity of HH-BP. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) porous flow fields have been utilized to achieve ultrahigh power density for proton exchange membrane fuel cells (PEMFCs). However, issues such as the severe corrosion and high interface contact resistance of 3D porous flow field limit the effective enhancement in power density. In this work, porous flow fields with various pore structures, i.e., Ni foam and Ti felt are employed and further decorated with carbon coating using the chemical vapor deposition (CVD) method to improve the anti-corrosion capacity. Meanwhile, the through-plane electrical conductivity and hydrophobicity are collectively improved for Ni foam and Ti felt by the carbon coating. Single fuel cell (FC) tests show that both the peak power density (PPD) and limiting current density (LCD) are improved for PEMFCs assembled with C@Ni foam and C@Ti felt flow fields in the cathode. The corresponding electrochemical impedance spectroscopy (EIS) confirms that the improved PPD (C@Ti felt) is attributed to the collective improvements in electrical conductivity and anti-corrosion capacity, and the improved LCD (C@Ni foam) is attributed to enhanced water removal capacity. The triple improvements in the intrinsic property of porous flow field materials obtained in this work are expected to offer novel approaches for developing PEMFCs with ultrahigh power density. [Display omitted] • Carbon coating is introduced in porous flow field by chemical vapor deposition (CVD). • Through-plane contact resistance is reduced for C@Ni and C@Ti porous flow field. • Anticorrosion capacity was enhanced for C@Ni and C@Ti porous flow field materials. • Water removal capacity is improved for C@Ni and C@Ti porous flow field materials. • Electrochemical performance is enhanced for fuel cell with C@Ni and C@Ti. [ABSTRACT FROM AUTHOR]