Accelerated Life-time Tests including Different Load Cycling Protocols for High Temperature Polymer Electrolyte Membrane Fuel Cells

다국어 초록 (Multilingual Abstract)

The purpose of this work is to identify new accelerated life-time (ALT) test protocols for polymer electrolyte membrane fuel cell (PEMFC), which function at conditions of high temperature and low humidity (under 120<SUP>o</SUP>C 40%RH). A design of accelerated life protocols was studied to observe degradation phenomena under different load step cycling conditions, compared with the constant voltage test at 0.6V. The effects of changes in frequency and potential range are explored, and different degradation rates are revealed. The test protocol of constant voltage test, load step cycling and with different potential range show total performance decay rates of 5.3mA.cm<SUP>-2</SUP>.h<SUP>-1</SUP>, 8.4mA.cm<SUP>-2</SUP>.h<SUP>-1</SUP> and 10.2mA.cm<SUP>-2</SUP>.h<SUP>-1</SUP>, respectively, while the highest total decay rate of load step cycling with frequency change is 17.0mA.cm<SUP>-2</SUP>.h<SUP>-1</SUP> including a rapid decrease of current density after 450 cycles under 120<SUP>o</SUP>C 40%RH. In respect to the operation of 500 cycles (35h), material degradation failure mechanisms are investigated according to the electro- and physico-chemical characteristics of the MEA. The performances assessed by the life-time evaluation methods are strongly related to the increase in the membrane resistance and the release of the sulfate and fluoride ions, dominated more at a higher cycling frequency. Furthermore, in the contrast to the starting MEA, Pt aggregations of the catalysts and a decline in the electrochemical surface area (ECSA) are clearly observed at the end of the testing especially with a wider sweeping range, corresponded to the decrease in the electrochemical properties.