Objective

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Thermal management is crucial for ensuring the performance， safety， and longevity of proton exchange membrane fuel cells （PEMFCs）. While excessively high temperatures can degrade the membrane electrode assembly and cause irreversible damage， excessively low temperatures impede reaction kinetics and may even lead to flooding. Consequently， it is essential to implement appropriate thermal management strategies to maintain the operating temperature of PEMFCs within an optimal range and ensure a uniform temperature distribution inside the stack. However， air cooling tends to produce uneven temperature distributions along the flow path due to the low specific heat capacity of air. Liquid cooling requires pumps to drive the coolant through the cooling channels， which incurs additional parasitic power losses and thereby reduces overall system efficiency. To mitigate the parasitic power consumption associated with conventional air and liquid cooling， this study proposes a novel passive cooling scheme that integrates vapor chambers （VCs） into a PEMFC stack for thermal management.

Methods

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Both theoretical analysis and experimental approaches were employed to evaluate the heat transfer performance of a standalone VC and a fuel cell stack integrated with VCs. First， the heat generation and transfer mechanisms within the fuel cell and heat transfer characteristics of the VC were analyzed. Based on the capillary force limit， the relationship between the structural dimensions of the VC and its maximum heat transfer capacity was determined. Subsequently， an ultra-thin VC with a heat transfer capacity exceeding 40 W and thickness of only 1.32 mm was designed and manufactured according to the heat dissipation requirements of a 200 W open-cathode PEMFC stack. In the thermal performance test of the single VC， a silicone heating pad was bonded to the VC's evaporator side using thermal grease. The heating power was varied from 0 to 48 W using a resistive load to simulate PEMFC heat generation. Additionally， a custom-made aluminum alloy cold plate was attached to the VC's condenser side to dissipate heat， with the cooling water flow rate maintained at 0.1 L/min. Twenty-four thermocouples were evenly spaced at 20-mm intervals on the opposite face of the VC. Temperatures were recorded via a data logger and subsequently transmitted to a computer for storage and analysis. After verifying the heat dissipation capability， five VCs were integrated into a 200 W PEMFC stack to conduct a rapid start-up load test， where the current was ramped from 0 to 40 A within 45 s. A thermocouple was installed in the cathodic central flow channel of the cathode of each cell to monitor temperature variations. The hydrogen supply pressure at the anode was 0.05 MPa， and the oxygen flow rate at the cathode was 0.03 m³/s. The ambient temperature and relative humidity were 26.3 ℃ and 63%， respectively.

Results and Discussions

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In the single VC test， when the heating power was varied， the VC rapidly reached a new equilibrium state within each 6-min test cycle， demonstrating excellent thermal response. From 0 to 48 W， the maximum temperature difference across the VC consistently remained below 3 ℃. At 48 W （a heat flux of 22.7 W/cm² across the VC cross-section）， the maximum temperature difference was only 2.6 ℃， and the thermal resistance was 0.054 ℃/W， exhibiting a downward trend with increasing heat load. These results indicate that the manufactured VC possesses excellent temperature-equalizing capability. Following the start-up test， the average output voltage of the VC stack was 5.27 V， compared with 4.33 V for the conventional stack， representing a 21.7% improvement. The temperatures of 10 cells in the VC stack ranged from 47.0 to 52.5 ℃， yielding a maximum inter-cell temperature difference of 5.5 ℃. In contrast， the cells in the conventional stack exhibited a range of 53.2 to 63.3 ℃， with a maximum inter-cell temperature difference of 10.1 ℃. The integrated VC effectively prevented performance degradation arising from non-uniform stack operating temperatures.

Conclusions

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To improve the thermal management of PEMFC

stacks， this study integrates a passive heat transfer unit， namely， a VC， into an open-cathode fuel cell stack. The fabricated VC operates at a heat flux of only 0.052 W/cm

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on the evaporator side and exhibits a thermal resistance of only 0.054 ℃/W under a heat load of 48 W， demonstrating excellent thermal response and heat transfer performance. The integration of the VC into the stack enables rapid dissipation of heat generated by electrochemical reactions while maintaining a uniform temperature distribution throughout the stack. This approach effectively mitigates performance degradation arising from inadequate thermal management， thereby providing a valuable reference for optimizing the thermal management design of automotive fuel cell stacks.