Study on the effect of inorganic radical scavenger in composite membrane for high chemical stability of polymer electrolyte membrane fuel cells

Abstract

Recently, the most challenging issue of fuel cells is durability. For the wide commercialization of transportation and stationary power generation systems, more than tens of thousands of hours of reliable operation is necessary. Achieving these levels of durability would require the durable membranes and catalysts for the advanced fuel cells. The membranes for PEMFCs are known to experience severe chemical degradation by radicals during a long-term operation. The most widely used membrane, Nafion, has high proton conductivity and good chemical stability, but, critical drawbacks like high cost and limited operating temperature. To solve the problems, hydrocarbon (HC) based polymers have been focused as promising alternative membranes. The alternative HC membranes, however, have shown much lower chemical stability against radicals than Nafion. In this study, radical scavenger, MnO2 was introduced in electrolyte membranes to improve the chemical stability of HC membranes. The radical scavenger is known to have multivalent nature of ions, which can change its ionic states to scavenge radicals. When Fenton’s test was conducted, the chemical stability of composite membranes was notably enhanced due to the radical scavengers. The proton conductivity, however, decreased with the MnO2 content, because the embedded inorganic nanowire seemed to be a barrier of proton conducting channels. The dimensional stability and tensile strength were additionally enhanced, which is by a mechanically supporting filler of MnO2. In respect of the performance, although the unit cell with the composite membrane (sPEEK-1.0) showed lower cell performance than the cell with the pristine sPEEK, the OCV and the performance of it after the accelerated durability test (OCV holding) maintained higher than that of sPEEK. The evidence suggests that the composite membrane with radical scavengers demonstrated the enhanced chemical stability and durability.