L. Wang, S.G. Advani, A.K. Prasd
University of Delaware,
Keywords: self-healing, PEMFC, Nafion
Summary:Defects in the form of pinholes and cracks can occur in the membrane due to a combination of chemical and mechanical degradation mechanisms during operation of the polymer electrolyte membrane fuel cell. Such defects are impossible to detect and repair in an operating fuel cell, and the only solution is to replace the entire membrane electrode assembly which is prohibitively expensive. The possibility of employing self-healing polymeric materials that can heal such defects in-situ is an exciting prospect for extending the working life and safety of such systems. We have developed a self-healing composite membrane containing urea-formaldehyde microcapsules prefilled with Nafion solution. The microcapsules are designed to rupture if they experience elevated localized stress in the vicinity of the defects and release the prefilled Nafion solution to repair the defects by filling the pinhole or the crack with the Nafion in-situ thus healing the membrane. The fuel cell performance of a 6wt% microcapsules/Nafion membrane compared well with that of a pure recast Nafion membrane. An accelerated stress test of 200 hours of OCV hold with RH cycling confirmed that the self-healing concept could greatly extend the lifespan of fuel cell membranes. The idea has been filed as a patent application with the US Patent Office (US2015042847).