Effect of ice formation on catalyst layer resistance and reaction distribution at PEFC cold startup

Abstract

This study investigated freezing behaviors in the catalyst layer (CL) during the cold start-up of PEFC at a constant temperature, −20 °C. The previous research by the authors showed that ice is formed in the CL at low current density, whereas ice is distributed biased toward GDL side at high current density. The research also presented a possibility that this phenomenon is caused by increase in electrical resistance of the CL due to ice formation. To validate this possibility, the electric resistance measurement of the CL using a DC resistance meter was attempted. As a measurement method, a specially-designed cell with a split current collector was developed to measure the in-plane electric resistance directly without the effect of nearby CL. Ice formation in the CL was observed by a cryo-SEM and similar cold start characteristics were confirmed using the cell. However, the measured value of the DC resistance was very unstable and it was impossible to evaluate the resistance change before and after the cold start-up accurately. To investigate the causes of the instability, electric resistance measurements using various components including a CL coated Teflon sheet were conducted. The results showed that the polymer membrane influences the instability of the resistance measurement.