Optimization strategy for air-cooled proton exchange membrane fuel cells: Tailoring porosity and configuration of microporous layer to enhance transmembrane water transport

To address the performance degradation of air-cooled proton exchange membrane fuel cells (PEMFCs) caused by proton exchange membrane (PEM) dehydration under harsh operating conditions of low humidity and high air flow rates, and to fill the research gap where the microporous layer (MPL) in such systems lacks systematic optimization and is neglected in most existing models, this study focuses on the regulation of MPL porosity and configuration, systematically revealing its mechanism of action on water and oxygen transport as well as the performance of air-cooled PEMFCs. A three-dimensional non-isothermal two-phase numerical model was established to investigate the influence laws of MPL porosity (0.3–0.6) and three typical configurations, namely without MPL, anode MPL (AMPL), cathode MPL (CMPL). The results show that the low-porosity MPL (0.3) increases the PEM water content by 25.22% by enhancing water retention capacity and suppressing Joule heating, thereby significantly reducing ohmic loss. Furthermore, the low-porosity MPL effectively improves the in-plane uniformity of current density distribution by regulating the mass transfer and water retention capacities in the regions beneath the ribs and channels, respectively. There exists a significant difference in the water transport regulation mechanisms between the AMPL and CMPL configurations: the AMPL slightly increases the resistance to cathode-to-anode transmembrane water transport, leading to a decrease in membrane hydration; in contrast, the CMPL promotes cathode-to-anode transmembrane water transport by increasing the cathode-side water discharge resistance, which elevates the PEM hydration by 8.38% and achieves a voltage gain of 10.72%. The innovatively proposed Double-CMPL configuration (double cathode MPLs and anode MPL-free) further enhances the transmembrane water flux, resulting in a 10.43% further increase in PEM water content, an additional 6.10% voltage improvement compared with the CMPL configuration at 1.2 A/cm 2 , and a 30.0% reduction in the standard deviation of current density distribution. Based on the above findings, a core design guideline for the optimization of the membrane electrode assembly (MEA) of air-cooled PEMFCs is formulated: on the premise of avoiding severe oxygen mass transfer limitation, maintain a high PEM hydration state through the combined design of “targeted increase in cathode-side water discharge resistance and targeted reduction in anode-side water transport resistance”. This study provides theoretical support and an engineering pathway for the MEA structural design of high-performance, low-humidity-tolerant air-cooled PEMFCs.