Perfluorosulfonic acid ionomer – silica composite membranes prepared using hyperbranched polyethoxysiloxane for polymer electrolyte membrane fuel cells

We report on the preparation and characterization of perfluorosulfonic acid ionomer (PFSA) – silica composite membranes using hyperbranched polyethoxysiloxane (PEOS) as silica precursor. The membranes were formed via an in situ sol–gel process of PEOS in a PFSA solution and subsequent solution casting. Transmission electron microscopy and small-angle X-ray scattering data showed that at low silica content ultra-small silica particles with a size smaller than the diameter of the ionic channels were homogeneously dispersed in the PFSA matrix. Such morphology leads to enhanced proton mobility as probed by impedance spectroscopy and 1H solid-state NMR, and eventually resulted in the improvement of fuel cell performance. [Display omitted] ► PFSA/silica composite membranes: morphology versus performance. ► In situ sol–gel process using hyperbranched polyethoxysiloxane as silica precursor. ► Homogeneous distribution of ultrasmall silica particles in the polymer matrix. ► Enhanced proton mobility and improved fuel cell performance at low silica content.