Microporous layers based on poly(vinylidene fluoride) and sulfonated poly(vinylidene fluoride)

Abstract

In this study, electrically conductive microporous layers (MPLs) were prepared through the phase inversion technique by coagulation in a water bath of a mixture of either poly(vinylidene fluoride) or sulfonated poly(vinylidene fluoride) and graphite and carbon black as electrically-conductive fillers (ECFs). The novel gas diffusion layers (GDL) were obtained by casting the MPLs on a wet proof carbon cloth. Poly(vinylidene fluoride) (PVDF), due to its excellent chemical stability, thermal resistance and hydrophobic character was proposed in place of the more expensive and less processable PTFE. Moreover, sulfonated poly(vinylidene fluoride) (PVDFS, 1.9% sulfonation degree) it was investigated as binding agent in order to obtain MPLs with improved characteristics especially in view of the possibility of preparation of gas diffusion electrodes (GDEs) by the deposition of electro-active catalysts. MPLs morphology, water contact angle, electrical resistance, and through-plane air permeability were carefully examined. The PVDF and PVDFS MPLs were assembled with a catalysts coated Nafion membrane and the performance of the resulting membrane electrode assemblies were compared in a fuel cell fed with air and hydrogen. While electrical resistance of MPLs was slightly influenced by the different preparation conditions, the air permeability considerably increased by switching the solvent from N-methyl-2-pyrrolidone (NMP) to dimethyl sulfoxide (DMSO) and by increasing the air exposure time of the composite film after casting as confirmed by the morphological analysis through scanning electron microscopy. As an indication of the MPLs performance, at the operating current density of 0.60 A cm−2, the single cell voltage of the proton exchange membrane fuel cell (PEMFC) was enhanced from about 0.43 to 0.5 V for PVDF based MPLs to about 0.60 V of PVDFS based MPL. The use of the phase inversion technique open several possibilities to tailor the MPL structure to specific fuel cell applications and moreover offers a more straightforward and scalable preparation method.