James H. Dickerson

Gas Diffusion Mechanisms and Models

The one-dimensional diffusion of gas molecules in porous media involves molecular interactions between gas molecules as well as collisions between gas molecules and the porous media (Joshi et al. in J. Phys. D Appl. Phys. 40:7593–7600, 2007 [1], Cannarozzo et al. in J. Appl. Electrochem. 38:1011–1018, 2008 [2], Veldsink et al. in Chem. Eng. J. Biochem. Eng. J. 57:115–125, 1995 [3]).

Size- and dimensionality-dependent optical, magnetic and magneto-optical properties of binary europium-based nanocrystals: EuX (X = O, S, Se, Te)

Europium chalcogenides (EuX, X = O, S, Se, Te), a class of prototypical Heisenberg magnetic semiconductors, exhibit intriguing properties in optics, magnetism, and magneto-optics at the nanoscale, and have broad application potential in optical/magnetic sensors, spintronics, optical isolators, etc. EuX nanocrystals (NCs) exhibit enhanced properties, such as high saturation magnetization, a strong magneto-optic effect (Faraday rotation), and high magneto resistance, which are all unanimously dependent on the NCs size, shape, and surface information. In this report, we give an overview of the fundamental properties of bulk EuX, and illustrate the quantum confinement effects on the optical, magnetic and magneto-optical properties of EuX nanostructures. We then focus on doping and self-assembly-two efficient methods that enhance magnetic properties by manipulating magnetic coupling in EuX nanostructures. In particular, we look towards future research on Eu(2+) NCs, which along with the overview provides an up-to-date platform for evaluating the fundamental properties and application potential of Eu-based semiconductors.

Polyamic acid: nanoprecipitation and electrophoretic deposition on porous supports

Polyamic acid (PAA, a precursor of polyimide) was synthesized from 4,4′-oxydiphthalic anhydride and 4,4′-oxydianiline. PAA, dissolved in dimethylsulfoxide (DMSO), was precipitated into colloidal particles after its injection into acetone. The resulting particle size distribution was found to depend on aging time of PAA solutions, their concentration, and the manner in which the solutions were mixed with acetone. PAA particles of any size down to 10xa0nm appeared to be achievable by decreasing the acetone/DMSO ratio. Particles in DMSO/acetone suspensions were found to have a significant negative zeta potential. Therefore, there was no need to add organic bases to form PAA anions, in contrast to all previously published studies on the PAA electrodeposition. EPD was performed onto porous stainless-steel or alumina disks, which are suitable supports (reinforcements) for membranes. The slow evaporation of DMSO residue yielded dried polymer layers, comprised of 50–100xa0nm PAA globules. The outer surface of layers was usually covered with a very thin, continuous PAA skin. Such supported PAA layers—after a simple imidization step via a heat treatment—could be applied as thermally resistant membranes for gas separation.

Ultrathin Y2O3:Eu3+nanodiscs: spectroscopic investigations and evidence for reduced concentration quenching

Here, we report the synthesis and spectral properties of ultrathin nanodiscs (NDs) of Y2O3:Eu3+. It was found that the NDs of Y2O3:Eu3+ with a thickness of about 1 nm can be fabricated in a reproducible, facile and self-assembling process, which does not depend on the Eu3+ concentration. The thickness and morphology of these NDs were determined with small angle x-ray scattering and transmission electron microscopy. We found that the crystal field in these nanoparticles deviates from both the cubic and monoclinic characteristics, albeit the shape of the 5D0xa0→xa07F J (Jxa0=xa00, 1, 2) transitions shows some similarity with the transitions in the monoclinic material. The Raman spectra of the non-annealed NDs manifest various vibration modes of the oleic acid molecules, which are used to stabilise the NDs. The annealed NDs show two very weak Raman lines, which may be assigned to vibrational modes of Y2O3 NDs. The concentration quenching of the Eu3+ luminescence of the NDs before annealing is largely suppressed and might be explained in terms of a reduction of the phonon density of states.

Introduction to Gas Transport in Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) produce electricity by oxidizing fuel gases. The biggest characteristic of SOFCs is their high energy conversion efficiency, up to 60–80 % in theory, since the conversion efficiency is not limited by the Carnot cycle due to the absence of combustion in SOFC devices. Other advantages of SOFCs include fuel flexibility, low emission, long-term stability, and relatively low cost. The major challenge associated with SOFCs is their high operating temperatures, typically above 500 °C. For SOFCs to find a large range of applications for electricity generation in the twenty-first century, numerous efforts are needed to lower the operating temperatures and to enhance the practical conversion efficiency at moderate operating temperatures. The key is to improve mass transfer involved in SOFCs. Since SOFCs operate with gaseous fuels and oxidants, gas transport in the porous electrodes largely influences their performance. In this chapter, a brief introduction to SOFCs will be first given. The main issues to be solved, gas transport phenomenon, as well as the scientific problems in this field will then be depicted in later chapters.

Solid Oxide Fuel Cells with Improved Gas Transport

Solid oxide fuel cell (SOFC) is a type of fuel cell which is able to utilize various fuels, including hydrogen, natural gas, and even traditional fossil fuel, to generate electricity with a conversion efficiency larger than 60 %.

Diffusivity Measurement Techniques

One of the major activities in the field of mass transport of solid oxide fuel cells (SOFCs) is the development of facile diffusivity measurement techniques. In this chapter, techniques for diffusivity measurement of porous electrodes are overviewed, with an emphasis on the authors’ contributions in this area. The correlations of the diffusivity with concentration polarizations in SOFCs also are illustrated thoroughly in this chapter.

Optimal packing size of non-ligated CdSe nanoclusters for microstructure synthesis

Structural and electrostatic properties of nanoclusters of CdSe of diameter 1–2u2009nm are studied with first principle calculations to determine the optimal size for synthesizing microstructures. Based on robustness of the core structure, i.e., the retention of tetrahedral geometry, hexagonal ring structure, and overall w u¨rtzite structure to surface relaxations, we conclude that nanoclusters of ∼2u2009nm diameter are the best candidates to form a dense microstructure with minimal interstitial space. Se-terminated surfaces retain a zigzag structure as Se atoms are pulled out and Cd atoms are pulled in due to relaxation, therefore, are best suited for inter-nanocluster formations.