▪ Abstract The main obstacles to greater commercialization of polymer electrolyte fuel cells are mostly related to the low-proton conductivity at low-relative humidity of the known ionomeric membranes, to their high methanol permeability and poor mechanical properties above ∼130°C. A possible solution for these problems has been found in the development of composite membranes, where particles of suitable fillers are dispersed in the ionomer matrix. The preparation methods for obtaining composite membranes are described, and recent work dealing with composite ionomeric membranes containing silica, heteropolyacids, layered metal phosphates, and phosphonates is reviewed. Finally, new strategies for the preparation of nano-composite membranes and for the filling of porous polymeric membranes with highly conductive zirconium phosphonates are described. The expected influence of size and orientation of these particles on membrane properties, such as conductivity and permeability to methanol, is also discussed.

Composite Membranes for Medium-Temperature PEM Fuel Cells

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 (–SO3H, –PO3H2, –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).

Design and properties of functional hybrid organic–inorganic membranes for fuel cells

Layered and pillared metal(IV) phosphates and phosphonates

Solid acid membranes for high temperature (¿140° C) proton exchange membrane fuel cells

Fast proton conduction in inorganic ion-exchange compounds

On the mechanism of diffusion and ionic transport in crystalline insoluble acid salts of tetravalent metals—I Electrical conductance of zirconium bis (monohydrogen ortho-phosphate) monohydrate with a layered structure

G. Levi

Papers

On the mechanism of diffusion and ionic transport in crystalline insoluble acid salts of tetravalent metals—I Electrical conductance of zirconium bis (monohydrogen ortho-phosphate) monohydrate with a layered structure

Inorganic ion exchange membranes consisting of microcrystals of zirconium phosphate supported by Kynar