Modification of Nafion® Thermoplastic Precursor to Enable Reprocessing of Fuel Cell Manufacturing Scraps

To reach national clean hydrogen goals by 2050, hydrogen energy technologies must be massively scaled while costs are reduced. Both fuel cells and electrolyzers rely on proton exchange membranes (PEMs), which are based on polyfluorinated sulfonic acid (PFSA) ionomers. PFSA-PEMs, like Nafion® (Chemours) and Aquivion® (Solvay), are expensive and hazardous to produce, and they are also not recyclable owing to their non-processable nature. In fact, the materials are manufactured via a thermally processable precursor that is irreversibly converted to the PFSA-PEM. Unused manufacturing scraps and end-of-life (EOL) membranes therefore contribute to a significant amount of hazardous fluorinated waste. Developing novel methods to reuse PFSA-PEM manufacturing scraps would reduce emissions and hazards associated with conventional EOL methods, while enabling reuse in new electrolyzers/fuel cells would reduce emissions and hazards associated with their manufacturing. Recycling PFSA-PEMs has been found to significantly reduce the cost of hydrogen energy. We will explore two approaches toward circular PFSA-PEMs. Both approaches focus on modifying the material at the precursor stage using modern click chemistry. The first approach is to create a covalent adaptable network (CAN) by introducing dynamic crosslinks that exchange during heating. CAN materials, the core technology of RockyTech, Ltd., are well-known for endowing thermal processability to conventionally non-processable materials. After conversion of the precursor, the CAN structure will allow thermal reprocessability (self-healing) to the PFSA-PEM for further lifecycles. Our second approach is to increase solvent reprocessability by making hydrophilic modifications to the precursor. These modifications will increase the PFSA-PEM’s dispersability in wateralcohol mixtures under mild conditions, in contrast to the current harsh temperature and pressure requirements, which have not been accepted by industry as a feasible recycling method. In Phase I, we will modify PFSA-PEM precursors with the (1) CAN approach and (2) hydrophilic modification approach, for thermal and solvent-based reprocessing, respectively. The modified precursors will be converted to the PFSA-PEM ionomers and subsequently evaluated for recyclability and performance in electrochemical test cells. Effects of the modifications on polymer physical properties will be closely analyzed after each unit operation. In Phase II, we will look past manufacturing scrap recycling toward EOL membrane recycling. Realizing circular PFSA-PEMs will not only reduce hazardous fluorinated waste issues, but also reduce the costs, hazards, and emissions of new manufacturing. Our chemical modification approaches are simple and will not impair membrane performance. Thus, our technology can be feasibly integrated into current PFSA-PEM manufacturing processes, promoting commercial adoption by producers such as Chemours and Solvay. We will establish relationships with these companies during Phase I and II research.