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In this study, a 3D model of a proton exchange membrane fuel cell (PEMFC) with crossed channels and an ultra-thin membrane is developed to investigate the feasibility of self-humidification; experiments utilizing a PEMFC stack with identical configurations are conducted to validate the simulation results and further investigate the effects of various operating conditions (OCs) on self-humidification. The results indicate that the crossed flow channel leads to enhanced uniformity of water distribution, resulting in improved cell performance under low/no humidification conditions. External humidifiers for the anode can be removed since the performance difference is negligible (≤3%) between RHa = 0% and 100%. Self-humidification can be achieved in the stack at 90 °C or below with an appropriate back pressure among 100–200 kPa. As the current density increases, there is a gradual convergence and crossing of the voltage at low RH with that at high RH, and the crossover points are observed at 60–80 °C with suitable pressure when successful self-humidification is achieved. Below the current density of the point, the stack's performance is inferior at lower RH due to membrane unsaturation, and conversely, the performance is inferior at higher RH due to flooding; this current density decreases with higher pressure and lower temperature. [ABSTRACT FROM AUTHOR]

Durability and remaining useful life (RUL) prediction techniques are ones of the key issues for proton exchange membrane fuel cell (FC) commercialization. Herein, the performance degradation of an FC is analyzed based on the whole lifetime experimental data (up to 6500 h). The voltage model with different patterns is developed based on the voltage data, which can be easily measured. The mechanism model is developed based on the evolution of degradation indices reflecting the degradation state. However, the former is sensitive to the local and periodic changes in the voltage curve, leading to a large prediction error, and the latter requires aging data from complex and high-cost characterization, limiting the practical applications. Therefore, a hybrid prediction model combining the voltage and mechanism model is proposed where the respective weight of each model is dynamically determined based on their local prediction errors. The results reveal that the maximum errors in RUL prediction are 9.72%, 3.90% and 2.01% for the voltage, mechanism and hybrid model, respectively, and the RUL prediction results of the hybrid model are close to actual RUL when those of the voltage model are far from the accuracy zone, indicating that the hybrid model provides credible RUL predictions with the highest accuracy. [ABSTRACT FROM AUTHOR]

The gas diffusion layer (GDL) is an important component of proton exchange membrane fuel cells (PEMFCs), and its porosity distribution has considerable effects on the transport properties and durability of PEMFCs. A 3-D two-phase flow computation fluid dynamics model was developed in this study, to numerically investigate the effects of three different porosity distributions in a cathode GDL: gradient-increasing (Case 1), gradient-decreasing (Case 3), and uniform constant (Case 2), on the gas–liquid transport and performance of PEMFCs; the novelty lies in the porosity gradient being along the channel direction, and the physical properties of the GDL related to porosity were modified accordingly. The results showed that at a high current density (2400 mA·cm−2), the GDL of Case 1 had a gas velocity of up to 0.5 cm·s−1 along the channel direction. The liquid water in the membrane electrode assembly could be easily removed because of the larger gas velocity and capillary pressure, resulting in a higher oxygen concentration in the GDL and the catalyst layer. Therefore, the cell performance increased. The voltage in Case 1 increased by 8% and 71% compared to Cases 2 and 3, respectively. In addition, this could ameliorate the distribution uniformity of the dissolved water and the current density in the membrane along the channel direction, which was beneficial for the durability of the PEMFC. The distribution of the GDL porosity at lower current densities had a less significant effect on the cell performance. The findings of this study may provide significant guidance for the design and optimization of the GDL in PEMFCs. [ABSTRACT FROM AUTHOR]

Generally, the unit cell in a proton exchange membrane fuel cell (PEMFC) stack is divided into different zones according to the characteristics of the bipolar plate. There is a zone that has been neglected, which we define as the "neck zone" for the first time in this work. Uneven stress and deformation are prone to appearing in the neck zone due to its unique structure. A three-dimensional finite element model was applied to study the influence of the membrane electrode assembly (MEA) frame materials on the mechanical characteristics of the neck zone. In addition, the sealing and the water–gas transport performances of the neck zone were evaluated via the stress fluctuation and deformation. It was found that even with the commercial polyethylene naphthalate (PEN) frame, a leak point would be generated at the region with the lowest stress, reducing the performance and even causing safety hazards. The invasion rate was proposed to assess the water–gas transport ability. When an inappropriate frame material was adopted, the invasion rate went up to 32.4%, severely hindering the water and the air transport. It was concluded that MEA frames with a higher elastic modulus and thickness are preferred for the neck zone to obtain a high property of sealing and water–gas transport. [ABSTRACT FROM AUTHOR]

Metasurfaces based on metal-dielectric-metal structures have been an effective means to comprehensively suppress infrared radiation. In this paper, we propose the idea of discretization to divide the circular resonator into countless rectangular elements and establish a complex equivalent LC circuit model, which provides a rapid design method for broadband absorption metasurfaces. The metasurface composed of two circle-shaped metal-dielectric-metal resonators were preliminarily designed based on impedance matching, and the geometric parameters and materials were optimally decided through numerical simulation. To validate the simulated result, we experimentally prepared a sample of the designed metasurface, the measured spectrum has revealed the radiative cooling ability (60% absorption over a range of 5–8 μm) and achieved infrared stealth (nearly 90% reflectance in the two atmospheric windows). Furthermore, the method provides potential applications to other requirements of thermal radiation regulation and theoretical support for establishing the model of metasurfaces with other configurations. [ABSTRACT FROM AUTHOR]

The proton exchange membrane fuel cell (PEMFC) has bright prospects in energy applications, but its durability and cost still affect its commercialization. In this work, a group of membrane electrode assemblies (MEAs) were tested to study the quick evaluating method for predicting their lifetimes. MEA1 was tested under the real constant load till the end of its lifetime and MEA2 was tested with a quick evaluating method. The data were treated with the particle filter algorithm to eliminate the influence of all kinds of errors, including the system error and random error. Based on this, the lifetime prediction model was developed. For a degradation rate of 10% of the initial working voltage, the lifetime of MEA1 was 6140 h; that of MEA2 was 3575 h if predicted with the test data directly, and 6776 h if the data was treated with the particle filter algorithm. The relative errors for both cases were about 41.8% and 10.3%, respectively, when compared with the lifetime of MEA1; indicating that the prediction accuracy was greatly improved. Furthermore, it was found that the voltage degradation rate was nonlinear when the whole lifetime of the MEA was considered, and the degradation rate increased significantly near the end period. In the quick evaluating method employed in most studies, the lifetime prediction model uses a linear degradation rate, which tends to cause errors; therefore, further research is needed. [ABSTRACT FROM AUTHOR]

A two-dimensional geometric model is developed for a polymer electrolyte based on the liquid water penetration mechanism in the membrane electrode assemblies under the action of capillary pressure. The effects of the diameter, number, and distribution of cracks in the micro-pore layers (MPLs) of the modeled MEA on the performance of the PEMFC are simulated to investigate the influence of mass transfer across the membrane. The results indicate that liquid water in the catalyst layer (CL) of the MEA can be discharged to gas channels through the cracks in MEA under the action of capillary pressure, thereby alleviating the flooding in the CL and enhancing the diffusion of oxygen to the CL. When the proportion of the total area of cracks in the active area of the MEA was 8%–12%, crack diameter was 20–30 µm, and cracks were distributed uniformly. MEAs with and without cracks were prepared, fuel cells were assembled, and their performance was measured. The effects of cracks on mass transfer were then verified. This study helps prepare MEAs with controllable cracks. [ABSTRACT FROM AUTHOR]

SUMMARY Hydrogen permeation across the membrane is unavoidable in proton exchange membrane fuel cells, especially for super-thin membranes, which lowers the open-circuit voltage and could even be a safety concern. In this paper, hydrogen permeation across two membranes (25-um-thick Nafion® 211 and 18-um-thick reinforced composite membrane) are evaluated at various temperatures, relative humidity (RH), and gas pressure differences between the anode and cathode. The results indicate that the hydrogen permeation rate in both membranes increases almost exponentially with temperature and linearly with pressure differences. Compared with RH, the effects of temperature and pressure differences are more crucial to hydrogen permeability. However, the effect of RH on the hydrogen permeation is quite complicated. The permeability exhibits a minimum value at intermediate RH (approximately 40% RH) for both applied membranes. The permeability of Nafion® 211 appears more sensitive to RH than that of reinforced composite membrane at elevated temperature. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]