Confined PFSA-Zeolite Proton Conducting Membrane: The Effects of Confinement and Zeolite-Type

Perfluorosulphonic acid (PFSA) membranes are a well-known proton exchange membrane and the 'gold standard' commercial Nafion membrane is renowned for its excellent proton conductivity and long term stability under fully hydrated conditions. However, their efficiency is highly dependent on the hydration level of the membrane, making water management an important issue. Traditionally, these membranes use external humidifying equipments to ensure optimum operation, which often translates to an increase in costs and lower efficiency. Thus, the PFSA membranes are highly sensitive to temperature, making operations at temperatures higher than 80^oC difficult, although a higher temperature would increase the efficiency of the electrocatalysts and improve its poison tolerance. A proton conducting membrane that can operate effectively without humidifying aid and at higher temperature operations is very attractive.

Recently our lab reported a novel self-humidifying membrane that is obtained by confining Nafion PFSA within zeolite-coated pores of a stainless steel foil that displays superior performances compared to the commercial Nafion 117 membrane. A multi-layered zeolite was deposited on the stainless steel; a nonporous silicalite-1 zeolite layer served as an insulating and anti-corrosion coating, a thin layer of nanozeolites (including LTA, BEA, FAU, and MFI) for water retention and a surface layer of HZSM-5 zeolite as a protective layer. This work investigates the effect of confinement on the physicochemical and thermomechanical properties of PFSA. We also explore the effect of water retention properties of various zeolites on the performance of the PEMFC.