Optimizing the structural design of cathode catalyst layer for PEM fuel cells for improving mass-specific power density

Abstract

The design of cathode catalyst layers (CCLs) is essential for enhanced charge transfer and mass transport of proton exchange membrane fuel cells (PEMFCs). In this work, CCLs are designed to constitute the three sub-layers with different polytetrafluoroethylene (PTFE) loadings for each sub-layer. The improper addition of PTFE in the different CCL positions can increase the gas-liquid phase’s mass transfer resistance through the triple-phase boundary. Low PTFE content leads to an inefficient hydrophobic nanoparticle distribution. However, excessive PTFE causes active site losses. The high voltage loss is a common result of unsuitable PTFE content, especially within the high current density operation condition. The membrane electrode assembly (MEA) contains 10 wt% PTFE loading in the out layer (faced to the gas diffusion layer), shows the best performance. At potentials of 700 mV and 600 mV, the output current densities approach 710 and 1120 mA/cm2, respectively. Furthermore, using Electrochemical impedance spectroscopy (EIS), the effect of PTFE sub-layers position on the charging transfer impedance and the mass transfer impedance has also been analyzed in this study. It is confirmed that the performance of MEA with an appropriate PTFE gradient design is improved significantly.