Heterogeneous catalyst-layer model-based analysis of loss mechanisms in polymer electrolyte membrane fuel cells

Comprehending the loss mechanisms in each process (i.e., activation, oxygen and vapor diffusion, and proton and electron conduction) in polymer electrolyte membrane fuel cells is necessary to enhance their power density. However, a numerical analysis of overvoltage and resistance for each process considering heterogeneous-structure effects has not been conducted. This study extends a pre-validated heterogeneous catalyst-layer model to evaluate the overvoltage and resistance by process. During a single-cell test, impedance is measured under various operating conditions, followed by distribution of relaxation times (DRT) analysis. In the simulations, the overvoltage and resistance are separated by process to identify dominant factors. Activation and proton-conduction resistances have similar dependencies on cell voltage and relative humidity, while oxygen-diffusion resistance exhibits different dependencies. Most of the parameter dependencies are corroborated by the experimental results of the DRT analysis, thereby confirming the model's validity. This versatile model can adapt to different electrode structures and operating conditions.