Recycling of Perfluorosulfonic Acid-Based Membranes and Their Re-Application in Pem Fuel Cells

Abstract

Polymer electrolyte membrane fuel cells (PEMFC) are lagging in commercialization due to the high cost of noble metal catalysts (e.g., Pt) and perfluorosulfonic acid-based (PFSA) membranes. Recycling and reusing these components at the end of life (EoL) could increase the viability and decrease the environmental impact of PEMFCs. In this work, we demonstrate an environmentally friendly method for recycling PFSA membranes based on a hydrothermal treatment using only water as a reactant, which is essential for upscaling to an industrial application. In addition, we focused on the recycling process itself and the membrane's recovery as a water-based dispersion. But also investigated the structural, chemical, and mechanical properties and the electrochemical performance of the membranes after being re-cast from the water-based dispersion (denoted as recycled membranes). We investigated two different ionomers, a short-side chain (SSC) ionomer with an equivalent weight of 800 (3M-800EW) and a long-side chain (LSC) ionomer with an equivalent weight of 1000 (3M-1000EW), both obtained from 3M. Both membrane types could be dispersed and recycled by hydrothermal treatment. Thermal and mechanical analysis of the recycled membranes showed no significant property changes. In addition, no changes in the chemical structure of the ionomers were observed by IR, Raman, and NMR spectroscopy. The recycling step increased both the water uptake and retention behavior. We attribute this to the enlargement of the water channels observed in the SAXS analysis. Full cell tests under standard (80 °C) and harsher (120 °C & 130 °C) cell conditions showed a similar or enhanced peak power density (PPD) for the recycled membranes.

Keywords: PFSA recycling, PEM fuel cells, Water retention, SAXS study, in-situ Raman, Solid-state NMR spectroscopy