Brett A. Holmberg

Nafion-bifunctional silica composite proton conductive membranes

Sol–gel derived sulfonated phenethylsilica with hydrophilic –Si-OH and proton conductive –SO3H functional groups was used as a bifunctional additive to improve the proton conductivity and water uptake characteristics of Nafion. Nafion-bifunctional silica (NBS) composite membranes were prepared by casting Nafion–ethanol solutions mixed with sulfonated phenethylsilica sol. The ion exchange capability of NBS composite membranes increases linearly with the amount of bifunctional silica incorporated, and is about 1.9 × 10−3 mol SO3H g−1 for NBS with 7.5 wt% silica. Liquid water uptake measurements showed that NBS composite membranes have higher water uptake (g H2O g−1 composite membrane) than bare recast Nafion while the degree of hydration (i.e., nH2O–SO3H) remains fairly constant. The NBS composite membranes showed improved proton conductivity when compared with bare recast Nafion and Nafion 117 membranes at 80 °C and over a range of relative humidity.

Homogeneous polymer–zeolite nanocomposite membranes by incorporating dispersible template-removed zeolite nanocrystals

Homogeneous polymer–zeolite membranes were fabricated by incorporation of dispersible template-removed zeolite A nanocrystals into polysulfone. SEM, XRD, N2 adsorption–desorption measurements were used to characterize the zeolite A nanocrystals. The uniformity of the polysulfone–zeolite A nanocomposite membranes was examined by SEM. Air separation measurements of the nanocomposite membranes showed enhanced performance in O2/N2 selectivity and O2 permeability. The polysulfone–zeolite nanocomposite membrane with 25 wt% zeolite A loading exhibited an O2/N2 selectivity of 7.7 and O2 permeability of 1.8 Barrers whereas the pure polysulfone membrane had an O2/N2 selectivity of 5.9 and O2 permeability of 1.3 Barrers.

Nanostructured zeolite 4A molecular sieving air separation membranes

A novel membrane forming strategy is reported to probe the intrinsic O2/N2 selectivity of zeolite 4A membrane and to fabricate highly selective nanocomposite membranes by using a nanocrystal-derived hierarchical porous zeolite 4A membrane whose non-zeolitic mesoporsity is filled with a nonpermeable polymer material (polyfurfuryl alcohol).

An Apparatus for Direct Proton Conductivity Measurement of Powdered Materials

An apparatus with multiple sample cells for direct two-electrode electrochemical measurement of powdered materials (e.g., nanoparticles) has been designed and fabricated. Polyetherimide (PEI, ULTEM 1000) is chosen as the cell material because it is optically transparent, electrically insulating, and mechanically and chemically stable up to 170°C. The sample cells are slim with high length-to-electrode-area ratio so that efficient, reliable, and nondestructive measurements of proton conductivity can be obtained on 20-30 mg powder samples using impedance spectroscopy at less than 2×10 5 Hz while still being able to eliminate the effects of contact resistance. Several electrode materials have been evaluated and data show 80%Pt-20%Ir electrodes adequately acid-resistant to avoid metal ion poisoning of the ion conductor.