Effect of catalyst layer microstructures on performance and stability for high temperature polymer electrolyte membrane fuel cells

The microstructures of catalyst layers (CLs) provide the paths for phosphoric acid (PA) invasion and decide the amount and distribution of PA in CLs, which is essential to improve the performance and stability of high temperature polymer electrolyte membrane fuel cells (HT-PEMFCs). In this work, the CLs with different microstructures are constructed and the effects of Pt loading on the performance and degradation of HT-PEMFCs are studied. The results show the CLs with flat surface slow down the process of PA invasion and well-developed pore structures promote the redistribution of PA, which results in low mass transfer resistance. Therefore, the peak power density of HT-PEMFC based on CLs prepared by ultrasonic-spraying is 1.4 times than that by screenprinting, while the performance degradation is only 11% after accelerated stress test of 30,000 cycles with the Pt loading of 0.5 mg cm-2. Distribution of relaxation times analysis is used to assist the electrochemical impedance spectroscopy to further distinguish the different physicochemical process within cells. The result reveals that mass transfer is affected greatly by the effects of microstructures and Pt loadings, and gets deterioration gradually with the invasion of PA into CLs, which not only makes Pt particle growth but decreases kinetics of oxygen reduction reaction.