The process of embedding polypyrrole (PPy) on the surface of a Nafion Ò membrane was studied. Three methods of PPy synthesis directly on the membrane surface were compared. The diffusion method based on the separation of monomer and oxidant (peroxidisulphate) solutions by the membrane to be modified is proposed as the most promising one. The monomer diffuses through the membrane to the oxidant side, where it is polymerized. In this case sulphate is incorporated into the film as a counter-ion. PPy film prepared in this way adheres well to the Nafion Ò surface and shows promising electrochemical activity. The permeability of the composite for monomer in comparison to self-standing Nafion Ò film is reduced significantly. This may be important for the potential application of this composite, especially in a direct methanol fuel cell, as an alternative membrane-electrode assembly (MEA), particularly with regard to the currently used MEA's permeability for fuel.

Diffusion coefficients of H ϩ and Na ϩ ions in sulfonated poly͑2,6-dimethyl-1,4-phenylene oxide͒ ͑PPO͒ intermolecularly crosslinked with poly͑2-butylaniline͒ ͑PBA͒ or poly-͓2,2Ј-(m-phenylene)-5,5Ј-bibenzimidazole͔ ͑PBI͒ were evaluated by conductivity and H ϩ /Na ϩ ion exchange measurements. Ion exchange capacity and transport properties of the PPO membranes with a degree of sulfonation higher than 30% are comparable to those of Nafion. The observed deterioration of ion exchange capacity and ion transport with increasing content of the cross-linking agent is related to the partial occupation of the fixed sulfo groups by the tertiary nitrogen groups present in PBA and PBI.

Heterogeneous ion-exchange membranes were prepared by mixing small particles of sulfonated poly(1,4-phenylene sulfide) or sulfonated styrene-divinylbenzene copolymer with a matrix polymer. Four kinds of polymers were tested as a matrix: highly flexible linear polyethylene, medium-flexible fluoroelastomer, rigid polystyrene (all highly hydrophobic) and hydrophilic cellulose prepared by hydrolysis of cellulose acetate butyrate. Membrane morphologies were studied by scanning electron microscopy, IR spectroscopy and density measurements. Subsequently, the membranes were characterised with respect to their swelling in water, electrochemical characteristics and transport properties. Ion-exchange capacity and proton conductivity together with the permeability to hydrogen and methanol were investigated. The important impact of the ion-exchange particles as well as of the polymer matrix used was observed. The increasing rigidity of the polymer matrix resulted in a decrease in membrane permeability, but at the same time in deterioration of its ion-exchange capacity and subsequently of the proton conductivity, too. This was explained in terms of the limited elasticity of the polymer matrix, in each sample under study, which does not allow the ion-exchange particles to swell to an identical degree.Keywords Ion-exchange membrane Á Heterogeneous membrane Á Ion-exchange capacity Á Proton conductivity Á Permeability List of symbolsA Membrane active area (m 2 ) c Molar concentration (mol m -3 ) C Ion-exchange capacity (mol kg -1 ) D Diffusion coefficient (m 2 s -1 ) DS Degree of swelling e 0 Electron charge (C) F Faraday's constant (C mol -1 ) j Current density (A m -2 ) k Boltzmann constant (J K -1 ) M Partial molar volume of water (m 3 mol -1 ) n Molar amount (mol) N Number of water molecules absorbed per one ion-exchange group N MeOH Number of methanol molecules transported by a proton p Pressure (Pa) P Permeability (m 2 s -1 ) R Universal gas constant (J mol -1 K -1 ) T Temperature (K) V Volume (m 3 ) w Weight (kg) z Charge numberGreek symbols d Thickness (m) q Density (kg m -3 )

The present study focuses on the problem of using conducting polymers (CPs) in proton exchange membrane fuel cell technology. It covers the electrocatalytic properties of the CP/Pt composite, permeability of the CP film for H 2 , fixation of the compact CP film on the top of the Nafion Ò membrane and first results of its utilization in a fuel cell. The present results did not confirm a previously reported increase in CP/Pt composite electrocatalytic activity when compared to the commercially available carbon supported catalysts. The main reason seems to be the very low permeability of the compact CP film for the fuel. This may be an advantage with respect to the minimization of fuel cross-over, which is a serious problem in the direct methanol fuel cell. On the other hand, it represents a serious danger in water management of the fuel cell. This fact has been recognized and alternative solutions are presented.

The process of polypyrrole ͑PPy͒ embedding on the surface of a Nafion membrane was studied. The diffusion method was used for synthesis of the composite. An attempt was made to incorporate Nafion chains instead of sulfate into the PPy film as a counterion. The prepared composites were characterized with respect to their permeability to a monomer and methanol. Compared with a self-standing Nafion membrane, the permeability of the composite is reduced by several orders of magnitude. The incorporation of Nafion into the PPy film resulted in enhanced composite permeability to methanol. It can, therefore, be used to a limited extent to tune its properties. This may be of great importance in a potential application of this composite in polymer electrode membrane fuel cells as an alternative membrane electrode assembly.