Nanoarchitectonics of fibrous clays as fillers of improved proton-conducting membranes for fuel-cell applications

Abstract

This work reports on the development of various nanostructured materials based on the assembly of SiO₂, TiO₂ and ZnO nanoparticles to sepiolite fibers (Sep) and their incorporation as a filler of Nafion to improve their performance as proton exchange membrane for fuel cells applications. Various nanoarchitectures, SiO₂-Sep, TiO₂-SiO₂-Sep and ZnO@SiO₂-Sep, were prepared following a colloidal route based on the controlled hydrolysis of alkoxide precursos (tetramethoxysilane and titanium tetraisopropoxide) in the presence of hexadecyltrimethylammonium-sepiolite. The SiO₂ and TiO₂ nanoparticles were consolidated after a thermal treatment that also removes the surfactant and assures their assembly to the clay. In the case of the ZnO@SiO₂-Sep nanostructured material, previously formed ZnO nanoparticles were assembled to the intermediated produced after the hydrolysis-polycondensation of tetramethoxysilane on the organoclay, followed by a thermal treatment that consolidates the nanoarchitecture. The resulting nanoarchitectures were characterized by XRD, FTIR, SEM, TEM and N₂ adsorption-desorption isotherms, confirming the formation of the nanoparticles and their assembly through silanol groups at the external surface of the clay. Nafion-based composite membranes were prepared using as nanofiller the produced SiO₂-Sep, TiO₂-SiO₂-Sep and ZnO@SiO₂-Sep nanoarchitectures. Thermal properties, water uptake and proton conductivity of the resulting composite membranes were evaluated in comparison to those of a neat Nafion membrane to ascertain their potential usefulness for applications in PEMFC.