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Summary: The flow field of the proton exchange membrane fuel cell (PEMFC) controls mass and water transfer; it significantly impacts the fuel cell's performance. It is critical to innovate the flow field design for optimizing the performance. This paper proposes a new‐designed flow field (NDFF) patterned with the built‐in blockage and trap‐shape rib association. The novel design was analyzed numerically and experimentally. A three‐dimensional isothermal numerical model was first established based on COMSOL software. This model demonstrated that the NDFF transformed the traditional diffusion mass transfer into the optimized diffusion and convection mass transfer combination. Compared with the conventional straight flow field, the effective mass transfer coefficient was considerably improved. Moreover, the new‐designed structures enforced cyclical variation of local velocity and pressure, forming forced‐convection, which was beneficial for water management. At 0.45A·cm−2, the steady‐state voltage and the initial dynamic response voltage were increased by 0.08 V and 0.16 V; power density was increased by 20.1%. The experimental results were collected to validate the enhanced performance of PEMFC with the NDFF. Energy efficiency ratio (EER) was proposed as an evaluation criterion; EER results suggested NDFF can improve the net output power. Highlights: A new flow field patterned with built‐in blockage and trap shape rib associationEnergy efficiency ratio, effective mass transfer coefficient used for evaluationSteady‐state and dynamic performances are greatly improved at an increased Energy efficiency ratio [ABSTRACT FROM AUTHOR]

Summary: Thermal and water management are crucial factors affecting the performance of proton‐exchange membrane fuel cells (PEMFCs). In this study, a semiconductor cooler was installed at the cathode outlet of a dead‐ended fuel cell stack, to condense the water vapor in the stack, and subsequently realize efficient thermal and water management. The temperature distribution characteristics were experimentally studied using a self‐built dead‐ended PEMFC stack test platform. The effects of operating temperature, current density, and condensation temperature were analysed in detail. The results showed that the output performance of the dead‐ended fuel cell stack could be efficiently improved by cathode moisture condensation. The temperature difference in the stack with cathode moisture condensation was much smaller than that without it. The output voltage of the stack could be increased by up to 6.02% with cathode moisture condensation, at an operating temperature of 70°C; and the maximum temperature difference could be reduced by 92.8% upon applying the semiconductor cooler with a condensation temperature of 5°C. Furthermore, the current density significantly affected the temperature distribution. Upon increasing the current density from 0.3 to 0.7 A/cm2, the temperature difference increased from 1.37°C to approximately 3°C, due to the large amount of water generated by electrochemical reaction at high current density. [ABSTRACT FROM AUTHOR]

Summary: Carbon corrosion in the catalyst is an important factor limiting the lifetime of proton exchange membrane fuel cells (PEMFCs). The water distribution inside the PEMFC directly determines the carbon support's corrosion rate in the catalyst. This study first investigates the water mole fraction distribution in the catalyst under different operating conditions, such as relative humidity (RH), temperature, pressure. It then divides the catalyst into different flooded areas according to the relationship between the water vapor partial pressure and saturated vapor pressure. Finally, it investigates the carbon corrosion characteristic of each region. The carbon corrosion of the catalyst is mainly divided into the corrosion in the non‐flooded area and the corrosion in the flooded area. The results show that the decay rate of carbon support is around 4% after 5000 hours of operation in the non‐flooding area. However, the degradation of the carbon support in the flooded area after 100 hours is as high as around 97.76%. Therefore, how to avoid flooding is the important issue that needs to be considered in the PEMFC. Moreover, increasing the pressure and RH promote the carbon corrosion in both cases, while increasing the temperature increases the carbon corrosion reaction rate, but it is beneficial to alleviate water flooding. Highlights: Water distribution and carbon corrosion under different working conditions.Divide the catalyst into varying levels of flooded areas.The carbon corrosion degree in the flooded area is as high as 97.76% after 100 hours.Increasing temperature increases the corrosion rate, but alleviates water flooding. [ABSTRACT FROM AUTHOR]

Summary: Load changing performance is significant for the application of proton exchange membrane fuel cells (PEMFCs). This paper compares experimental results of the hydrogen‐air and hydrogen‐oxygen PEMFC and analyzes their dynamic performance under various operating conditions. We use electrochemical impedance spectroscopy to investigate the intrinsic mechanism during load changing. Due to the higher oxygen concentration, the hydrogen‐oxygen PEMFC responds faster (within 1 second) and operates more steadily than the hydrogen‐air PEMFC (2‐20 seconds). The experimental results show that the total polarization resistance of the hydrogen‐air PEMFC and the Ohmic resistance of the hydrogen‐oxygen PEMFC decrease dramatically with the appropriately increased operating temperature. Whereas at over‐elevated operating temperature, the resistance value increases due to the dehydration of the membrane electrode assembly. Load changing performance can be improved by increasing operating pressure and relative humidity. Increased stoichiometry is beneficial for the hydrogen‐air PEMFC, while the opposite trend is observed for the hydrogen‐oxygen PEMFC. Novelty statement: Comparison of experimental results of hydrogen‐air and hydrogen‐oxygen proton exchange membrane fuel cell (PEMFC), dynamic performance at start‐up, and load changing performance are studied.Two PEMFCs' performances are quite different at various operating conditions. Overall, H2/O2 PEMFCs response faster (1 second) and operate more steadily than H2‐air (2‐20 seconds).Ohmic, polarization, and mass transfer resistance values are measured and analyzed. [ABSTRACT FROM AUTHOR]

Thermal management has been considered as one of the most important issues for the operation of proton exchange membrane fuel cells (PEMFCs). Phase change affects the performance and even the heat balance of the stack during operation. A 46 single cell PEM stack with anode and cathode humidification is developed to investigate, both theoretically and experimentally, the effect of phase change on the heat generation and removal characteristics of the stack. The results show that the heat removed by the coolant water is greater than that generated by the electrochemistry reaction, and heat released due to the phase change of water vapor cannot be neglected. Heat generated in the stack can be removed completely by the coolant water, which need to be forced cooling for recycling use when the current density reaches 1000 mA·cm−2. The arithmetic product of the specific heat capacity and mass of the stack can be used as a novel criterion to evaluate the validity of the heat balance in the system. The exothermic reaction is very fast in the stack, which consequently requires bipolar plates with high heat conductivity coefficient to improve the temperature uniformity at the elevated operational current density. Copyright © 2014 John Wiley & Sons, Ltd. [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]