MF-4SC Membranes Research Articles

Performance of Hydrogen Fuel Cell MEAs Based on Perfluorinated Nanocomposite Membranes Modified by Polyaniline

This work summarizes the results obtained from the modification of perfluorinated sulfocationic MF-4SC membranes by in situ polymerization of aniline. The transport properties of polyaniline/MF-4SC composite membranes after different times of polymerization have been analyzed. It is observed that after 3 h of aniline polymerization, composite membranes exhibit higher protonic conductivity compared to the pristine sample. The performance of fuel cells containing membrane electrode assemblies (MEAs) from MF-4SC and polyaniline/MF-4SC has also been studied. The kinetic parameters governing the voltage dependence on current density have been estimated and the results have been fitted to a previously established one-dimensional isothermal model by Springer et al. [ J. Electrochem. Soc. 138 , 2334 (1991)] . Good agreement between experimental data and model has been found for low density currents. Some insights about the membrane proton conductivity mechanism are given.

Influence of incorporated nanoparticles on the ionic conductivity of MF-4SC membrane

Hypothesis of semielasticity of walls of membrane pores was proposed as an explanation of increase in the ionic conductivity in composite ion-exchange membranes containing incorporated nanoparticles of inorganic species and polyaniline.

Diffusion of solutions in the course of the matrix synthesis of composite membranes MF-4SC—polyaniline and their transport properties

The dependence of the kinetics of diffusion transfer of solutions through MF-4SC and MC-40 ion-exchange membranes during the matrix synthesis of polyaniline on the composition of feed solutions and the nature of the initiating agents and the polymer matrix is studied. The effect of the conditions of the modification of the parent membrane on the resultant physicochemical characteristics is studied. The conditions of synthesis for the preparation of MF-4SC—polyaniline (emeraldine) composites with an optimized combination of conducting and diffusion characteristics are found. The contribution of electron conductivity to the overall proton-electron conductivity of the composite films is estimated.

Sorption and conducting properties of perfluorinated MF-4SC membranes in aqueous solutions containing phenylammonium ions

A comparative study of the sorption effect is performed for nitrogen-containing ammonium, phenylammonium (PhA+), and tetrabutylammonium (TBA+) cations on conducting and hydrophilic properties of protonic form of perfluorinated sulfocationite MF-4SC membrane. Conductometric method was used to study thermodynamic equilibria in the systems of perfluorinated MF-4SC membrane—aniline in the acid solutions of variable composition (PhA+/HCl and PhA+/H2SO4). Concentration constants of ion-exchange equilibrium are calculated for a MF-4SC membrane on the basis of these data. These constants in the solutions of aniline with HCl and H2SO4 are 10.3 and 27.0, accordingly. The choice of sulfuric acid as background electrolyte for matrix polyaniline synthesis is substantiated.

Perfluorinated nanocomposite membranes modified by polyaniline: Electrotransport phenomena and morphology

This work summarizes results on the modification of perfluorinated sulfocationic membranes MF-4SC by in situ chemical polymerization of aniline. The investigation of transport properties of polyaniline/MF-4SC composite membranes after bulk modification – conductivity, diffusion and electroosmotic permeability, proton permselectivity – as well as porosimetry and polarization behavior is carried out as functions of aniline polymerization parameters and acid concentration. The fibrous-cluster model of a composite membrane is proposed for the estimation of transport and structural parameters, taking into account different mechanism of charge transfer in structural fragments of the composite. The atomic force microscopy images and curves of water distribution on the effective pore radii in the composite membranes testify to a morphological transition from the nano- to the microsize of polyaniline inclusions with increasing the aniline polymerization time. This effect is confirmed by the analysis of two-phase model transport and structural parameters. High values of the “true” proton transport numbers of composites are obtained and discussed. The dynamic hydration numbers of protons and chloride co-ions are estimated using the “true” transport numbers of protons and the electroosmotic coefficients of composites. The current–voltage curves of composite membranes in the “free standing” state after bulk and surface modification by polyaniline are investigated. The effect of stabilization of limiting current density is observed for MF-4SC membrane after bulk modification. The effect of current–voltage curves asymmetry is observed for different orientation of the polyaniline layer towards the current direction for an anisotropic composite membrane after surface modification.

Template synthesis and electrotransport behavior of polymer composites based on perfluorinated membranes incorporating polyaniline

A method of chemical template synthesis is described for producing composites based on a perfluorinated matrix with polyaniline chains implanted. It has been shown that the choice of experimental and conditioning techniques is relevant for the composites’ investigation. The conductivity, diffusion permeability, selectivity, and electroosmotic permeability of the composites have been investigated in comparison with the same properties of the initial MF-4SC membrane. A model describing the transport behavior of the composites in the doped state as a fibrous-cluster system is proposed. A set of transport and structural parameters of the composites in a H2SO4 solution has been calculated and an analysis of the results observed has been carried out. The set of electrotransport properties is explained by the morphological features of the composites, taking into account the redox heterogeneity of polyaniline. The contribution of electron conductivity to the mixed conductivity of composites with a certain saturation degree by polyaniline has been estimated.

Effect of conditioning techniques of perfluorinated sulphocationic membranes on their hydrophylic and electrotransport properties

The effect of perfluorinated sulphocation-exchange membrane conditioning on their hydrophilic and electrotransport properties was studied. Exchange capacity and water content of MF-4SC membranes having been exposed to conditioning were determined by different chemical techniques. The estimated values were compared to the same characteristics after thermal pre-treatment by sequent boiling in hydrogen peroxide, water, acid and water. Dependences of electrical conductivity, diffusion and electro-osmotic permeability upon sodium chloride concentration were determined for MF-4SC, Nafion-115 and -117 provided that the conditioning techniques varied. Consistent increase of the electrotransport membrane characteristics due to the water content increase and water energy state alteration after the membranes were thermally treated was established. It was shown that MF-4SC, Nafion-115 and -117 conditioning by this method leads to formation of ion-conducting polymeric membranes identical in the structure and transport properties.