Performance test and degradation analysis of direct methanol fuel cell membrane electrode assembly during freeze/thaw cycles

▶ The performance test of DMFC MEAs during freeze/thaw cycling was investigated. ▶ Degradation mechanisms of the post-mortem MEAs were discovered. ▶ Microstructural damage was the major disadvantage to drop the cell performance. ▶ A strategy was designed to prevent the membrane from broken. ▶ The methanol solution inside the DMFC stack was forbidden to be frozen. Performance and degradation of direct methanol fuel cell (DMFC) membrane electrode assembly (MEA) are analyzed after repeated freeze/thaw cycles. Three different MEAs stored at −20°C for 8h with the anode side full of methanol solution are selected to test the effects of low temperatures on performance. After the cell heated to 60°C within 30min, they are inspected to determine the degradation mechanism. The resistance R obtained by the polarization curve is essential for identifying the main component affecting cell performance. The electrochemical impedance spectroscopy (EIS) technique is used to characterize the DMFC after freeze/thaw cycles. Thus, deterioration is assessed by measuring the high-frequency resistance (HFR) and the charge-transfer resistance (CTR). The electrochemical surface area (ECA) is employed to investigate not only the actual chemical degradation but also membrane status since sudden loss of ECA on the cathode side can result from a broken membrane. Moreover, a strategy is designed to simulate actual conditions that may prevent the membrane from being broken. A DMFC stack without any heating or heat-insulation devices shall avoid to be stored at subzero temperatures since the membrane will be useless due to frozen of methanol solution.