Composite Nafion Membranes with CaTiO3-? Additive for Fuel Cell applications

Manufacturing ion-conducting membranes with high ionic conductivity and durability is a crucial challenge in the development and large-scale distribution of electrochemical energy conversion devices. Perfluorosulfonic acid polymers are the state-of-the-art solid electrolytes used in low temperature proton exchange membrane (PEM) fuel cells and electrolyzers [1]. Desirable PEMs must be highly proton conductive under hot and dry conditions, thermally and dimensionally stable, impervious to fuels, as well as to electrons. In the present work, composite membranes based on a Nafion polymer matrix, incorporating a nonstoichiometric calcium titanium oxide (CaTiO3-?) additive, were synthesized and characterized [2,3]. Fundamental characterizations, by means of thermal and dynamic mechanical analyses, as well as of broadband dielectric spectroscopy, were carried out. Composite electrolytes, containing 5 and 10 wt.% of the CaTiO3-? additive, with respect to the dry Nafion content (respectively, M5 and M10), were compared to a plain, additive-free Nafion membrane. The membrane with the lower amount of additive displayed the highest water affinity and the highest conductivity, indicating that a too-high dose of additive can be detrimental for these particular properties. The mechanical behavior of the composite membranes is similar to that of plain Nafion, slightly improved by the filler addition. These findings indicate that perovskite oxides can be useful as a waterretention and reinforcing additive in proton-exchange membranes for fuel cell applications. Indeed, the composite membranes developed in this study were evaluated in a DMFC single cell at 30 °C, 60 °C, 90 °C and 110 °C. Interestingly, when the operation temperature is raised to 110°C, the cell adopting M5 composite membrane shows the best electrochemical performance, as a result of the enhanced M5 thermal stability. [1] Siracusano, S.; Oldani, C.; Navarra, M.A; Tonella, S.; Mazzapioda, L.; Briguglio, N.; Aricò, A.S. Chemically stabilised extruded and recast short side chain Aquivion® proton exchange membranes for high current density operation in water electrolysis. J. Membr. Sci. 578 (2019) 136-148. [2] Mazzapioda, L.; Navarra, M.A.; Trequattrini, F.; Paolone, A.; Elamin, K.; Martinelli, A.; Palumbo, O. Composite Nafion membranes with CaTiO3-? additive for possible applications in electrochemical devices. Membranes 9 (2019) 143-154. [3] Mazzapioda, L.; Lo Vecchio, C.; Paolone, A.; Aricò, A.S.; Baglio, V.; Navarra, M.A. Enhancing oxygen reduction reaction catalytic activity using a sub-stoichiometric CaTiO3-? additive. ChemElectroChem 6 (2019) 5941-5945.