Ice Formation and Distribution in the Catalyst Layer During Freeze-Start Process - CRYO- SEM Investigation

• Published in: ECS transactions Vol. 11; no. 1; pp. 595 - 605
• Main Authors: Li, Jing, Lee, Stephen, Roberts, Joy
• Format: Journal Article
• Language: English
• Published: 28.09.2007
• ISSN: 1938-5862; 1938-6737
• DOI: 10.1149/1.2780973

Ice distribution in the catalyst layer (CL) and gas distribution layer (GDL) of PEM fuel cells under isothermal constant voltage (ICV) operation at subzero temperature was determined using CRYO-FESEM. The analysis method was designed to ensure that the entire experiment was carried out under subzero ({degree sign}C) conditions so that the water is always kept in a frozen state without thawing. Under a moderately wet shutdown, the porosity of the cathode CL decreased from an initial, dry porosity of 65% to 15.9% for the purge only sample and to 8.2% for a sample at a full ICV state. At the full ICV state, the gas was not able to reach the active sites and the reaction ceased. Two distinct regions with different porosities in the CL were observed at the half ICV state, which indicates that ice in the CL melted at the beginning of the ICV operation.