Broadband Dielectric Spectroscopy and Conductivity Mechanism of Nation 117 and Nafion/Zr02 Hybrid Inorganic-Organic Membranes

摘要

In this report is described the dielectric characteriation by Broadband Dielectric Spectroscopy (BDS) of a Nafion 117 reference membrane and of a hybrid inorganic-organic membrane based on Nafion and ZrO_2 nanopowders with formula Nafion/[ZrO_2]. The measurements on the two systems were collected both in completely dry and in fully-humidified (wet) conditions. Results allowed the identification of two polarization phenomena and of several dielectric relaxation modes, which were assigned taking into account: a) the primary and secondary structure of the Nafion polymer; and b) the interactions Nafion-water and Nafion-ZrO_2 nanofiller. The dependence on temperature of conductivity (σ_(dc,i)), relaxation frequencies (fk), dielectric strength (Aek) and shape parameters (m_k and nk) for the investigated systems in both dry and wet conditions is studied in detail. It is shown that the ZrCh nanofiller: a) stabilizes both the hydrophobic and the hydrophilic domains of the Nafion/[ZrO_2] membrane; and b) promotes the coupling between the various relaxation modes of Nafion. In fully-humidified conditions, the stability range of conductivity and the conductivity of the Nafion/[ZrO_2] membrane at 125°C are respectively 5°C < T < 135°C and 9.51·10~(-2) S/cm. For the pristine Nafion 117 membrane, the corresponding values are 5°C < T < 95°C and 1.2210~(-2) S/cm. Results allowed to propose a coherent model describing the conductivity mechanism in Nafion-based systems.