Combined
molecular dynamics (MD) simulation and experiment are
adopted to gain the mechanism of water content on the electrochemical
surface area (ECSA) of the catalyst layer in a proton exchange membrane
fuel cell. The morphology of water domains in the catalyst layer has
a strong impact on the ECSA via MD simulation. The morphology of the
water domains is isolated water clusters at low water content, resulting
in the poor ECSA due to the lack of proton transport paths. The transport
paths of protons tend to be quickly established with increasing water
content during the transition process of the morphology of water domains
from isolated water clusters to the water channel network, thereby
leading to the rapid increase of the ECSA. However, the slight increase
of the ECSA at high water content mainly results from the improved
contact area between water domains and Pt particle instead of the
formation of new transport paths. In addition, the stronger binding
of water molecules and the Pt particle at low temperature results
in a higher ECSA.
<div class="section abstract"><div class="htmlview paragraph">Compared with conventional flow field, metal foam has been increasingly used for gas distributor in the PEM (proton exchange membrane) fuel cell due to its high porosity and conductivity, which significantly enhances the species transport under high current density condition. In this study, the cell performances with metal foam and graphite parallel flow field are compared under normal and subzero temperature conditions. Besides, electrochemical impedance spectroscopy (EIS) is recorded to characterize the Ohmic, polarization and polarization resistance. Under normal condition, the cell with metal foam exhibits three times better performance than the one with parallel flow field. Meanwhile, the effects of inlet gas humidity and flow rates on cell performance are also studied, indicating that the cathode flooding easily occurs due to its difficult water removal. However, the high flow rate can greatly ease the cathode water flooding. Under subzero temperature condition, metal foam cell shows higher startup voltage and better ice storage capability. In addition, the effects of start-up temperature and current density on cold start performance of PEM fuel cell are studied and the high frequency resistance (HFR) is also utilized to characterize the water content and ice formation/melting in cell. The experimental results show that low initial water content, high startup temperature, and low startup current density are beneficial to PEM fuel cell cold start performance. Overall, the results shown in this study will facilitate a further understanding of the PEM fuel cell with metal foam flow field.</div></div>
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