Development of the electrically modified Nafion membranes for energy conversion systems

Abstract

In this study, Nafion had been electrically modified to control the ion channel and enhance its efficiency. In first part of the study, the research was focused on the proof of concept to modify the nano-structure of Nafion membrane. Two kinds of electrically treated Nafion membranes which are in-plane and through-plane modified membrane showed nearly doubled proton conductivity compared to the pristine membrane The increased proton conductivity was caused by the modified structure which can be observed by TEM. In TEM images, we observed that the size of ion channels aggregations decreased and the number of ion aggregation increased, simultaneously. The change makes the surface area of ion channel and they enhance the proton conductivity. The increased crystallinity of electrically modified membrane which had been observed with XRD also contributed to high proton conductivity. The electrical modification technique was applied to pore-filling membranes which would be used to single cell of PEMFC. The pore-filling Nafion/PTFE membrane cast without electric field showed lower proton conductivity compared to casting membranes. Otherwise, the proton conductivity of pore-filling membrane cast with electric field showed similar conductivity with the casting membrane. The developed membrane even maintained their conductivity at above 120 ℃, while the proton conductivity of casting Nafion membrane was dropped to zero. This was also applied to single cell test of the membranes. The single cell using developed membrane had advantages in high temperature, in which the single cell using PTFE and electric field showed higher performance than the single cell using pristine membrane. The developed Nafion membrane was also applied to VRFB system. To reduce the crossover of vanadium species, silica particle was added to Nafion solution and it was cast as membranes. VRFB using Nafion/silica membrane cast with electric field showed higher performance compared to pristine membrane and also outstanding durability.