Ionomer content effect on charge and gas transport in the cathode catalyst layer of proton-exchange membrane fuel cells

摘要

Proton-exchange membrane fuel cell (PEMFC) performance is strongly related to the complex transport of gas and charge carriers in the cathode catalyst layer. Thus, we investigated the transport properties of catalyst layers at different ionomer/carbon ratios, ranging from 0.1 to 1, focusing on oxygen, proton and electron transport. Oxygen transport was studied using the limiting current technique, separately analyzing the contributions of molecular, Knudsen, and ionomer transport resistances by changing the temperature and gas pressure. The proton and electron resistance of the catalyst layers were determined by impedance spectroscopy and current voltage measurements, respectively. The results showed that the performance of fuel cells can be enhanced by selecting a suitable ionomer/carbon ratio and that increasing the ionomer content decreases the proton resistance and increases the electron resistance of catalyst layers. Accordingly, low oxygen transport and proton resistance at an ionomer/carbon ratio of 0.6 (26.5%wt.) led to the highest fuel cell power density (595 mW cm(-2)). These results fully support well-established in numerous works optimal ionomer content, revealing the underlying mechanisms of high fuel cell performance. Furthermore, the porosimetry results and electron microscopy measurements confirmed that transport properties strongly affect fuel cell performance.