This critical review presents a discussion on the major advances in the field of organic-inorganic hybrid membranes for fuel cells application. The hybrid organic-inorganic approach, when the organic part is not conductive, reproduces to some extent the behavior of Nafion where discrete hydrophilic and hydrophilic domains are homogeneously distributed. A large variety of proton conducting or non conducting polymers can be combined with various functionalized, inorganic mesostructured particles or an inorganic network in order to achieve high proton conductivity, and good mechanical and chemical properties. The tuning of the interface between these two components and the control over chemical and processing conditions are the key parameters in fabricating these hybrid organic-inorganic membranes with a high degree of reproducibility. This dynamic coupling between chemistry and processing requires the extensive use and development of complementary ex situ measurements with in situ characterization techniques, following in real time the molecular precursor solutions to the formation of the final hybrid organic-inorganic membranes. These membranes combine the intrinsic physical and chemical properties of both the inorganic and organic components. The development of the sol-gel chemistry allows a fine tuning of the inorganic network, which exhibits acid-based functionalized pores (-SO(3)H, -PO(3)H(2), -COOH), tunable pore size and connectivity, high surface area and accessibility. As such, these hybrid membranes containing inorganic materials are a promising family for controlling conductivity, mechanical and chemical properties (349 references).

Organic-inorganic hybrid membranes of Nafion and mesoporous silica containing sulfonic acid groups were synthesized using the sol-gel process with the goal of increasing the proton conductivity and water retention at higher temperatures and lowering relative humidities as well as improving the dimensional stability. These hybrid membranes were prepared via in situ co-condensation of tetraethoxysilane and chlorosulfonylphenethylsilane via self-assembly route using organic surfactants as templates for the tuning of the architecture of the silica or hybrid organosilica components. In this paper, we describe the elaboration and characterization of new hybrid membranes all the way from the precursor solution to the evaluation of the fuel cell performances. These hybrid materials were extensively characterized with the determination of their physicochemical and electrochemical properties. The membrane containing functionalized silica showed a higher ionic exchange capacity and greater water management than standard Nafion. The hybrid membranes showed improved proton conductivity at 95 °C and over the whole range of relative humidity in comparison to recast Nafion and Nafion 112 membranes.