Robust three‐dimensionally printed polypropylene/highly sulfonated polysulfone composites for potential applications in fuel cells

Abstract

Summary Advanced ion‐conducting composites were prepared by ionomer synthesis, fused deposition modeling (FDM) 3D‐printing, surface modification, and pore‐filling. The cost‐effective, mechanically robust, and inert microporous substrates of polypropylene were made by FDM printing. Three infill contents of 30, 50, and 70 vol% of polypropylene were designed. A synthesized highly sulfonated hydroquinone‐based polysulfone, with 80% degree of sulfonation (DS), was used as the pore material. Nucleophilic aromatic substitution on difluorodiphenyl sulfone was used to synthesize the highly sulfonated ionomer. Pore‐filling of the designed printed substrate was done via 10 w/v% of the ionomer solution. Oxygen plasma treatment was applied to enhance the compatibility of the substrate and the pore material's interfaces. Modification of porous substrate was confirmed by alteration of surface polar characteristics and roughness from contact angle measurements and atomic force microscopy, respectively. Confinement of highly sulfonated ionomer by the robust structure resulted in the preparation of electrolyte with controlled water uptake, no in‐plane swelling, high conductivity (up to 0.417 S/cm at 60°C under 100% relative humidity), and current density of about 836 mA.cm−2 at 60°C under 100% relative humidity. Regarding the presence of commodity polypropylene in the structure, the performance was good, compared to commercial Nafion membrane, with a cell current density of about 1120 mA.cm−2.