*Article* **Composite Nafion Membranes with CaTiO 3** − δ **Additive for Possible Applications in Electrochemical Devices**

#### **Lucia Mazzapioda 1, Maria Assunta Navarra 1, Francesco Trequattrini 2, Annalisa Paolone 3, Khalid Elamin 4, Anna Martinelli 4 and Oriele Palumbo 3,\***


Received: 30 September 2019; Accepted: 28 October 2019; Published: 31 October 2019

**Abstract:** A composite membrane based on a Nafion polymer matrix incorporating a non-stoichiometric calcium titanium oxide (CaTiO3−<sup>δ</sup>) additive was synthesized and characterized by means of thermal analysis, dynamic mechanical analysis, and broadband dielectric spectroscopy at di fferent filler contents; namely two concentrations of 5 and 10 wt.% of the CaTiO3−<sup>δ</sup> additive, with respect to the dry Nafion content, were considered. The membrane with the lower amount of additive displayed the highest water a ffinity and the highest conductivity, indicating that a too-high dose of additive can be detrimental for these particular properties. The mechanical properties of the composite membranes are similar to those of the plain Nafion membrane and are even slightly improved by the filler addition. These findings indicate that perovskite oxides can be useful as a water-retention and reinforcing additive in low-humidity proton-exchange membranes.

**Keywords:** Nafion; CaTiO3-δ; inorganic filler; composite electrolyte
