Influence of external clamping pressure on nanoscopic mechanical deformation and catalyst utilization of quaternion PtC catalyst layers for PEMFCs

Abstract

The external clamping pressure (CP) has a significant influence on the morphology, transport characteristics, and performance of catalyst layers (CLs) of the proton exchange membrane fuel cells (PEMFCs). Therefore, comprehensive understanding the nanoscale mechanical deformation and its impact on the utilization of precious platinum catalysts are extremely important for designing effective CLs. In this study, the effect of external CP on the morphology, interconnectivity and electrochemical catalyst utilization of CLs is explored. The quaternion carbon-supported platinum (PtC) CL agglomerate nanostructures are reconstructed for the predetermined fuel cell catalyst compositions containing platinum (Pts) supported on carbon black, ionomers, and pores. The compression model is developed using an effective medium theory based on a unit cell and implemented on the reconstructed CL domain with a 98% confidence level. The results of CL compression model are validated based on the experimental data from previous studies. The effect of compression on the thickness, porosity, local pore size distribution, electron-conducting PtC, and proton-conducting electrolyte are investigated in detail because these parameters are critical for the transport properties and performance of the CLs. Moreover, the numerical experiments are repeated for a range of CL compositions by varying the ionomer-to-carbon weight ratio (I/C) from 0.5 to 1.2 for different CPs (0, 1, and 2 MPa). The numerical results show that the interconnectivities of PtC, ionomer, and pore phases are strongly dependent on the applied CPs. Finally, the electrochemical performance of the CLs is compared for the maximum electrochemical catalyst utilization factor (ECUF) to enhance overall fuel cell performance. Insights gathered from this modeling study can be used for further investigation of mass transfer in compressed PtC CLs for better understanding fuel cell performance.