Mitigation of PEMFC Degradation upon Freeze-Thaw Cycling using a Methanol-Water Solution as Antifreeze

Abstract

One of the challenges for PEMFCs for fuel cell electric vehicle is to ensure cold start capability and high durability under freeze-thaw (F/T) cycling. Today, polymer electrolyte fuel cells in automotive applications undergo gas purging conditioning to remove residual water from the cells before a cold shut-down to avoid damage due to freezing water. In this study, an alternative conditioning procedure is examined with an alcohol-water solution used as antifreeze. Since MEA components are not affected by the required methanol concentrations which have to be 40vol% to prevent water freezing at -30°C, methanol solutions have generally a great potential to be used as antifreeze in PEMFC. In order to demonstrate the suitability of methanol as antifreeze, F/T cycling tests have been performed using methanol as antifreeze and with conventional dry gas purging of the cell. The results clearly show that performance degradation upon freeze-thaw cycling, which is observed when applying dry gas purging before the tests, is mitigated when flooding the cell with the methanol solution. Specifically, using the antifreeze, performance losses are observed at high current densities only and the peak performance of the cell does not decrease. Moreover, cold stat-up procedures are examined to allow a start-up of the cell after flooding with the antifreeze. Even though the antifreeze exhibits superior properties regarding mitigation of degradation, the start-up of the cell is challenging due to methanol residues in the MEA components.