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The performance, cost, and durability of proton exchange membrane fuel cells (PEMFCs) can be impacted by the bipolar plate's (BPP's) configuration, especially in an air-cooled PEMFC. An air-cooled PEMFC stack with concave-convex dual flow channel metallic BPPs are designed and the heat dissipation effect of the proposed BPP structure is investigated. To investigate the heat transfer and airflow processes of various concave-convex dual flow channel structures, a three-dimensional multi-physical field model with two PEMFC units is built. The results show that the heat dissipation effect can be enhanced by lengthening both sides of the BPP, and installing fans before the heat sink ribs on both sides can further enhance the heat dissipation effect. The largest temperature drop rate is 16.5% in the original BPP and air velocity increased from 1 m/s to 1.5 m/s with the current density of 400 mA/cm2. The uniformity of the MEA temperature can reach over 0.9 with the concave-convex dual channel BPPs. The heat dissipation effect can be enhanced by lengthening both sides of BPPs, shortening the cathode flow path will cause a more uniform temperature distribution. • A novel design of adding heat sink ribs on non-main flow field of the metallic BPP. • The heat dissipation efficiency of BPP C increased by 13.28% than BPP B. • Short cathode flow channel results in temperature distribution uniformity over 0.96. • The novel BPP has 6.01% thermal management efficiency improvement than BPP C. [ABSTRACT FROM AUTHOR]

Summary: Water management is important for proton exchange membrane fuel cell (PEMFC). To maintain highly efficient and stable operation of PEMFC, water generated in PEMFC needs to be migrated in time. An inner dehumidification technique is proposed to remove the water inside the PEMFC stack. Two inner condensing units are set near the cathode outlet to cooling the moisture gas. Water vapor in the flow channel will transfer directly to the outlet to supplement the vapor loss due to condensing. As a consequence, water flooding is sufficiently mitigated inside PEMFC. The experimental results show that the output voltage of the dead‐ended fuel cell stack increases by 9.77% at 1000 mA∙cm−2 when the condensing temperatures is 5°C. When the condensing temperature decreases from 20°C to 5°C, the average stack voltage can be increased by 14.3% at 500 mA∙cm−2, and the average temperature difference decreases from 3.2°C to 1.8°C. Moreover, the performance and temperature distribution uniformity are all increased with the increasing of the operation temperature due to inner moisture dehumidification. [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]

The thermal stress, which has a significant impact on the stable and prolonged operation of Solid Oxide Fuel Cells (SOFCs), can be further aggravated by the presence of local hot spots. Improving the distribution uniformity of physical quantities is of great significance to improving the internal temperature distribution of the SOFC. In this study, to improve the uniformity of temperature distribution, the thermal and flow distribution of three kinds of flow fields are investigated including Z, U, and L flow fields. The results show that the temperature distribution is dominated by the flow rate distribution. To optimize the physical quantity distribution of the designed flow channel, a novel, and easy-to-manufacture thermal management is proposed. This method is to adopt the extended ridge for controlling the flow rate into each flow channel. Moreover, a multi-population genetic algorithm is adopted to optimize the length of each extended ridge. The optimized results show that the temperature deviation in the Z, U, and L flow fields are reduced by about 64.20 %, 26.06 %, and 23.45 % respectively. This novel thermal management method enables more uniform temperature distribution and it is expected to be used in large-scale manufacturing due to its simple but subtle design. • An advanced but simple thermal uniformity management in SOFC is proposed. • The extended ridge can effectively regulate the flow rate in each flow channel. • The maximum temperature deviation can be reduced to 11K in an L-type flow field. [ABSTRACT FROM AUTHOR]

• A novel flow field called rotary l -type flow field is proposed. • The operating temperature can be reduced by up to 30 K. • At least 14% temperature gradient reduction can be gained. Solid oxide fuel cell (SOFC) is an alternative for future energy conversion systems with great potential. Long-term operation in SOFC mainly obstructs its further development. Stratification and fission can be occurred in Positive electrolyte negative (PEN) structure by severe thermal stress. By improving the temperature uniformity, localized hot spots and thermal stresses can be eliminated significantly. This study proposed a novel rotary l -type main flow field for SOFC and the thermal and flow characteristics are investigated. The temperature distribution (TD) is estimated by the temperature uniformity index. The results show that the temperature uniformity index increased at least by 40%. The largest TG of the rotary l -type flow field is 20% lower than that of co-flow and cross-flow arrangements. The average TG is 32.72% lower than the counter-flow arrangement. This flow field design provides an effective solution for the long-term operation of SOFC. [ABSTRACT FROM AUTHOR]

Water management is a key factor affecting the performance and lifetime of proton exchange membrane fuel cells. A transparent single fuel cell with an active area of 100 cm2 was designed in this paper to characterize the water distribution. High-strength transparent borosilicate glass was used as the end plate to ensure uniform clamping forces, and a water-cooling chamber was adopted for the uniform temperature distribution. The effects of temperature, humidity, flow rate and pressure on the cell performance were investigated. It was found that in a certain range, a large cathode flow resulted in a relatively stable power output and a low level of water distribution. However, a better cell performance and higher level of water distribution can be observed with lower temperature, higher operation pressure and higher humidity. The actual voltage was determined by a compensatory calculation through the voltage changes caused by all of the influencing factors, and the compensatory voltages were quite close to each other. The results showed that under 40 °C and 60 °C, 0 Bar and 1.5 Bar, and 50 RH% and 100 RH%, the compensated voltages were 0.873 V and 0.864 V, 0.869 V and 0.855 V, and 0.843 V and 0.844 V, respectively. • Water management affects the performance and lifetime of PEMFC. • The experiment was conducted by transparent PEMFC with large active area. • Effects of temperature, pressure and humidity were investigated in detail. • Consistent actual voltage was determined by a compensatory calculation. [ABSTRACT FROM AUTHOR]

Proton exchange membrane fuel cells (PEMFCs) have garnered substantial attention as highly promising devices for energy conversion. The operational lifespan and overall output performance of such stacks are inherently governed by the performance of the weakest fuel cell, a phenomenon often referred to as the "Bucket Effect." Evidently, cells located proximate to the hydrogen inlet endplate exhibit poor performance in comparison to the remaining cells in a 95 cells open-cathode fuel cell stack. In response to this challenge, an innovative approach involving endplate heating has been proposed to mitigate the observed endplate effects. Experimental validation of this approach has been conducted, yielding pertinent results. Furthermore, the internal temperature distribution across the stack exhibits an asymmetric parabolic profile, largely attributed to the intricate interplay of the endplate effects. Comparative analysis against a counterpart stack without endplate heating indicates that an application of 80 W heating power leads to a prolongation of operational duration by 156 s, while 100 W heating extends the operational period by 333 s. 80 W heating increased stack power by 31.5 W while improving output power efficiency by 1.9%, and 100 W heating increased stack power by 45.6 W while improving output power efficiency by 2.74%. [ABSTRACT FROM AUTHOR]

The temperature gradient inside an open-cathode air-cooled fuel cell is large because it uses air as its reaction and cooling media; moreover, the temperature of single cells near the endplates is low because of the high heat capacity of the endplate compared to single cells. Therefore, the cold start of open-cathode air-cooled fuel cells is difficult. In this work, the cold-start performance of an open-cathode air-cooled fuel cell stack, including the stack voltage, single-cell voltage and temperature distribution, are tested in a climatic chamber. The results show that the endplate effect has a significant adverse influence on the cold-start performance. Due to the existence of the endplate effect, the voltages of the single cells near the endplate decrease significantly. The stack can be successfully started at −5 °C without any external heating; however, when the temperature decreases below −10 °C, it cannot be started. At this time, if a certain power of endplate heating is adopted, successful cold-start can be achieved. However, if the temperature continues to decrease, the stack cannot be successfully started only through endplate heating because both the endplates and cold air affect the cold-start performance. Combining endplate and air heating may be a feasible cold-start method. • Cold-start performance of an open-cathode air-cooled fuel cell stack was tested. • In situ measurement of temperature and cell voltage distribution were conducted. • Endplate effect has a significant adverse influence on the cold-start performance. • Air-cooled stack can be successfully started at −5 °C without any external heating. • Both endplate and air heating can effectively improve the cold-start performance. [ABSTRACT FROM AUTHOR]

The air-cooled proton exchange membrane fuel cell stack composed of the metallic bipolar plate with simple system and lightweight characteristics, is regarded as an ideal power source for unmanned aerial vehicles. A zero-dimensional model is developed to analyze the operation characteristics at heights in the range of 0–3000 m. The temperature should not exceed 60 °C to ensure safe and effective operation. The peak power decreases by 20 % and the stack has good adaptability to altitudes. The performance degradation can be largely attributed to the lower oxygen pressure at high altitudes through normalization analysis. It is more significant at higher current densities owing to increased air starvation. The increase of the air stoichiometry is conducive to heat dissipation and reduces mass transfer loss. The voltage initially increases and then decreases as the air stoichiometry increases, and the optimal air stoichiometry corresponding to the maximum voltage is determined. Appropriately increasing the air stoichiometry can improve the consistency of the temperature and voltage distributions. • Air-cooled PEMFC with metallic bipolar plate is suitable for UAVs. • The temperature should not exceed 60 °C to ensure safe and effective operation. • The peak power decreases by 20 % from 0 m to 3000 m. • Oxygen pressure at high altitude greatly affects the performance degradation. • Increased air stoichiometry improves the consistency of temperature and voltage. [ABSTRACT FROM AUTHOR]

Reliable thermal management ensures stable and efficient operation of proton exchange membrane (PEM) fuel cells. An air-cooled fuel cell stack with metal bipolar plates was developed, and 32 micro-thermocouples were arranged for in situ measurement of the temperature distribution. The resistance characteristic of the stack was tested in a wind tunnel, and then the effects of hydrogen pressure and airflow rate were analyzed. The results show that the highest and average temperatures in the stack exhibit a "parabolic" distribution as well as the maximum temperature difference of each single cell on the inlet side of the cathode. However, the temperature difference on the outlet side shows an "anti-parabolic" distribution. With a decrease in the airflow rate, the temperature uniformity in the stack deteriorates gradually. When the maximum pulse width modulation (PWM) duty cycle of the fans was 70% and the current density was 500 mA/cm2, the temperature difference between different single cells and inside a single cell can reach 19.7 °C and 8.4 °C, respectively. The temperature uniformity in the stack at high current densities could be effectively improved by increasing the airflow rate. In addition, the hydrogen pressure and airflow rate have a certain effect on the voltage consistency. • An open-cathode air-cooled fuel cell stack with metal bipolar plates was developed. • The flow resistance characteristic of the fuel cell stack was tested in a wind tunnel. • In situ measurement of temperature distribution in the fuel cell stack was conducted. • The effects of anode pressure and airflow rates were analyzed in detail. • The temperature distributions inside a single cell and the stack were obtained respectively. [ABSTRACT FROM AUTHOR]

In situ measurement of temperature distribution in a Proton Exchange Membrane Fuel Cell (PEMFC) stack is conducted by embed 36 T-type thermocouples on the MEA surface in four representative cells. Temperature increasing rate can get to 2.5°Cmin−1 at 1000mAcm−2. The largest temperature difference is observed in the middle of the stack, and the temperature difference can reach 17°C at the bottom of the stack. The non-uniformity of temperature distribution is found to be improved by increasing the operation pressure, and the largest temperature difference decreases by 2.5°C when the absolute operation pressure is increasing from 100kPa to 150kPa. [ABSTRACT FROM AUTHOR]

Abstract: Temperature mapping is measured by micro-thermocouples embedded into the cathode plate of the model cell. The effects of different operation conditions on temperature distribution are investigated in detail. The results show that the temperature of the stack turns on “Parabola” distribution, and the temperature increases along the flow field from the inlet to the outlet under various conditions. Temperature difference of the single cell in the stack increases with the increased operation current density, and decreases with the increased air flow rate. The effect of the inlet air temperature on the temperature difference can be neglected in the stack, and the temperature uniformity can be improved by increasing the mass flow rate of the coolant water. [Copyright &y& Elsevier]