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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]

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]

Flow field design and optimization are critical for the proton exchange membrane (PEM) fuel cells to meet the requirement of ultra-high power density commercial applications. However, the multi-physics transport mechanism inside such large-scale PEM fuel cells has not been fully understood. In this study, we have developed a three-dimensional (3D) PEM fuel cell model. It is first validated against the experimental data obtained from a small-size cell. Thereafter, based on this model, the performance characteristics of a large fuel cell (cell area: 245.76 cm2) assembled with a partially narrow flow field are elucidated, while the full bipolar plate (BP) and cell morphology are also considered. It is found that the partially narrow flow field can not only significantly increase the net power density of PEM fuel cells, but also effectively improve the uniform distribution of species with the staggered partially narrow (SPN) zone arrangement between adjacent channels. While this flow field can improve the cell performance, the blindly increasing of the narrow zone numbers may play a negative impact on the net power density due to the dramatic increase in pressure drop. Finally, the partially narrow channel can indeed provide improved drainage capacity. • Liquid water cooling is considered in the large-scale 3D model of PEM fuel cell. • Comprehensive comparison between the partially narrow and parallel flow fields. • The partially narrow channel has the advantage of enhancing oxygen convection. • The drainage mechanism of the partially narrow channel is clearly presented. [ABSTRACT FROM AUTHOR]

• The full-morphology simulation of the large-scale automobile PEM fuel cell is proposed. • All components, the realistic morphology of distribution area and the coolant flow is fully considered. • The advantages and disadvantages and its influence on physical and chemical processes of double-cell structure are deeply analyzed. • Novel double-cell structure can significantly improve power density (almost 20%) under actual operating conditions. The structural design of PEM fuel cell is crucial to improving its power density, and the cell structure largely depends on the bipolar plate (BP). This study compares the conventional single-cell structure and double-cell structure through three-dimensional (3D) large-scale (cell area: 312 cm2) full-morphology simulation. As for the double-cell structure, the channels are arranged in a dislocation manner and there is one cooling flow field per two cells. For the structure of the BP, we also fully considered the realistic morphology of distribution area and the coolant flow. It is found that the heat dissipation effect of double-cell structure is worse but the performance is very close compared to single-cell structure. Moreover, its volumetric power density is significantly improved (∼ 20%) due to the reduction in height. It is also found that increasing the velocity of coolant in the double-cell structure increases the performance first and then decreases. [ABSTRACT FROM AUTHOR]

Summary: A three‐dimensional (3D) multi‐phase numerical model of proton exchange membrane fuel cell (PEMFC) is built. The catalyst layer (CL) spherical agglomerate model is used to replace traditional homogenous model, which can predict the concentration loss in PEMFC more accurately. Utilizing this multi‐phase model, the PEMFC with 3D fine mesh flow field is investigated at length, and the liquid water distribution in 3D flow field is qualitatively compared with the experimental image in previous literature. It is found that the 3D fine mesh flow field can improve the reactant gas supply from flow field to porous electrodes significantly and facilitate liquid water removal in PEMFC simultaneously. Therefore, it reduces the concentration loss of PEMFC effectively without increasing the pumping power loss thanks to the greatly increased mass transfer area between gas diffusion layer (GDL) and flow field and vertical flow design of hydrogen and air, which also make the reaction rate distribution in CL more uniform. However, the decreased contact area between GDL and bipolar plate in 3D flow field may decrease PEMFC performance at the current densities where ohmic loss is dominated, but its effect is insignificant. A comprehensive three‐dimensional (3D) multi‐phase computational fluid dynamics numerical model is developed, in which the spherical agglomerate model of catalyst layer is introduced to better reflect the concentration loss in proton exchange membrane fuel cell (PEMFC). Utilizing this model, the PEMFC with 3D fine mesh flow field is simulated in detail, and the liquid water distribution in 3D fine mesh flow field is qualitatively compared with the experimental image in previous literature. [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]

• An improved agglomerate sub-model of catalyst layer is developed. • Oxygen local transport resistance is clarified with three individual parts. • Effects of Pt loading and Pt particle dispersion are considered. • The CL agglomerate sub-model is incorporated into 3D PEM fuel cell model. • Fine channel geometry helps improve gas distribution and cell performance. An improved agglomerate sub-model of catalyst layer (CL) involving actual agglomerate size and oxygen local transport characteristics is developed and incorporated into a three-dimensional (3D) multi-phase model of proton exchange membrane (PEM) fuel cell. This makes it capable to consider the effect of platinum (Pt) loading on oxygen transport and fuel cell performance more accurately. Oxygen local transport resistance near the catalyst surface is divided into three parts caused by liquid water blockage, ionomer coverage and Pt/carbon agglomeration, respectively. The resistances caused by ionomer coverage and Pt/carbon agglomeration are two major sources of oxygen local transport resistance. They have opposite variation trends as Pt loading changes. However, the ionomer resistance increases dramatically when Pt loading is lower than 0.1 mg cm−2 because of the much harder transport process through a relatively heavier ionomer coating. The simulation results agree with the experimental data reasonably under different cathode Pt loadings (from 0.3 to 0.025 mg cm−2), for both polarization curves and local transport resistance. In addition, a transport dominance parameter is defined to judge whether the concentration loss predominates the electrochemical reaction. A value greater than 10% can be seen as a symbol of local oxygen starvation. Using this model, fine channel geometry with extremely small channel and rib widths is investigated, and the highest net output power in this study is corresponding to 0.2 and 0.6 mm for channel (rib) width and height. [ABSTRACT FROM AUTHOR]

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]

[Display omitted] • Method of coupling FEM model with "3D + 1D" model for large-scale PEMFC is proposed. • Non-uniform contact resistance distribution is investigated utilizing this method. • Performance reduces slightly when considering non-uniform contact resistance. • Current density gets more uneven when considering non-uniform contact resistance. • Deformed GDL under assembly affects both concentration loss and ohmic loss. The assembly of proton exchange membrane (PEM) fuel cell has a significant influence on contact pressure of BP and GDL, which affects key parameters of GDL including contact resistance, porosity, and permeability. In this study, a large-scale finite element method (FEM) PEM fuel cell model is developed considering realistic assembly, which is assembled by 14 bolts. The contact pressure at the interface of GDL and BP is converted into non-uniform contact resistance incorporated into a self-developed "3D + 1D" full PEM fuel cell multi-phase model with the active area of 108 cm2. The "3D + 1D" model simplifies part of components along through-plane direction into 1D model to improve calculation efficiency and stability. The results show that the performance reduces slightly when considering non-uniform contact resistance compared with that considering uniform contact resistance. The uniformity of current density and temperature distributions reduces evidently when considering non-uniform contact resistance affecting the performance and durability, which demonstrates the necessity of treatment of non-uniform contact resistance. Furthermore, the effects of porosity and permeability of deformed GDL under different preloading torques on performance are investigated. It is found that the contact resistance reduces first and then flats as the preloading torques increase, which results in the same trend of electronic ohmic loss, while the concentration loss nearly linearly increases. The simulation shows that the PEM fuel cell shows the best performance when the preloading torque is 3 Nm. This study provides some meaningful guidance for PEM fuel cell stack assembly. [ABSTRACT FROM AUTHOR]

• A self-adaptive water transition mechanism in catalyst layer is proposed. • Data from commercial-level laboratory is comprehensively validated. • On-board various operating conditions are considered. • Influence of simulation scale is investigated. It is of great significance to gain deeper and clearer understanding of the transport mechanism inside proton exchange membrane (PEM) fuel cell under on-board conditions to propel its commercialization process. This study investigates detailed water transition mechanism in PEM fuel cell catalyst layer from the perspective of macroscale performance model. Full layout of single cell structure and variable operating conditions are considered. Six combinations of water transition mechanism are analyzed and a self-adaptive mechanism related with local vapor saturation state is proposed, which is determined and validated by comparing the simulation results with experimental data from commercial-level laboratory. The influence of simulation scale is also investigated by comparing calculation results of typical single-channel domain with practical single-cell domain. Results show that appropriate water transition mechanism equips the model with decent adaptability to multi-condition prediction. Single-channel simulation domain tends to gain misjudgment on water removal capability and could be used for preliminary evaluation. Full-scale single-cell simulation domain should be the first choice for structure designing work, especially under practical working condition. The proposed method serves as a potential solution to multi-condition simulation with good adaptability and fidelity, which is one of the urgent requirements for PEM fuel cell R&D. [ABSTRACT FROM AUTHOR]

• Feasibility of MF in AAEMFC is investigated by numerical study for the first time. • The model is validated with experimental data from both the literature and this study. • The MF improves the performance significantly, especially at high current density. • Water transport and distribution are analyzed to explain the performance improvement. • MF prevents the AAEMFC from flooding in anode and drying out in cathode. Metal foam (MF) material is a promising alternative in fuel cell for its extremely porous structure, high electrical conductivity, controllable permeability and strong mechanical strength. However, there are seldom applications of MF flow field in alkaline anion exchange membrane (AAEM) fuel cell so far. Therefore, a three-dimensional (3D) multi-phase numerical model is implemented to investigate the feasibility of MF flow field in AAEM fuel cell and validated with experimental data from both the literature and this study. The performance of AAEM fuel cell with MF flow field is compared with that with traditional serpentine flow field. The simulation results show that MF flow field is able to improve the performance of AAEM fuel cell significantly, especially at higher current density where the concentration loss is dominant. According to analysis of transports and distributions of reactants and water (including liquid water, membrane water, and water vapor), the MF flow field is proven to be beneficial to membrane hydration, anode water removal, cathode water utilization, and reactant distribution. [ABSTRACT FROM AUTHOR]