There is a need to understand the structure properties of gas-diffusion layers (GDLs) in order to optimize their performance in various electrochemical devices. This information is important for mathematical modelers, experimentalists, and designers. In this article, a comprehensive study of a large set of commercially available GDLs' porosity, tortuosity, and pore-size distribution under varying compression is presented in a single study using X-ray computed tomography (CT), which allows for a noninvasive measurement. Porosities and PSDsare directly obtained from reconstructed stacks of images, whereas tortuosity is computed with a finite-element simulation. Bimodal PSDsdue to the presence of binder are observed for most of the GDLs, approaching unimodal distributions at high compressions. Sample to sample variability is conducted to show that morphological properties hold across various locations. Tortuosity values are the lowest for MRC and Freudenberg, highest for TGP, and somewhere in-between for SGL papers. The exponents for the MRC and Freudenberg tortuosity have very small dependence on compression because the shapes of the pores are spherical indicating minimal heterogeneity. From the representative elementary volume studies it is shown that volumes of 1x1 mm in-plane and full thickness in through-plane directions accurately represent GDL properties.

This work describes the performance improvement of a polymer electrolyte fuel cell with a novel class of microporous layers (MPLs) that incorporates hydrophilic additives: one with 30 μm aluminosilicate fibers and another with multiwalled carbon nanotubes with a domain size of 5 μm.Higher current densities at low potentials were observed for cells with the additive-containing MPLs compared to a baseline cell with a conventional MPL, which correlate with improvements in water management. This is also observed for helium and oxygen experiments and by the lower amount of liquid water in the cell, as determined by neutron radiography. Furthermore, carbon-nanotube-containing MPLs demonstrates improved durability compared to the baseline MPL. Microstructural analyses including nanotomography demonstrate that the filler material in both the additive-containing MPLs provide preferential transport pathways for liquid water, which correlate with ex situ measurements. The main advantage provided by these MPLs is improved liquid-water removal from the cathode catalyst layer, resulting in enhanced oxygen delivery to the electrocatalyst sites.

Microcavity micropillars are structures composed of two high-reflectivity distributed Bragg reflectors (DBRs) placed either side of an active dipole emitter. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] This structure is then vertically etched to form a pillar. The three-dimensional confinement of the optical field within a micropillar has profound effects on fundamental light-emission processes. The most important of these results from reduced-mode volume (termed the Purcell Effect [17] ), which can cause a significant enhancement in the spontaneous emission rate by up to five times. [1,2,16] Furthermore, micropillars can sustain a series of discrete laterally confined modes, [3,4,9,13,15] which show no dispersion. [15] This permits photons that are emitted (via a particular mode) to be collected with high efficiency. When a single quantum emitter is placed within a micropillar, an efficient source of anti-bunched single photons can be created. [10,11,16] Such light sources are anticipated to find applications in quantum-cryptography [18] and quantum-computation systems. [19,20] Micropillars are also an exciting tool for studying fundamental processes such as light-matter coupling. In particular, recent reports have demonstrated strong optical coupling between a single quantum dot (QD) within a micropillar and a discrete optical mode.[12] The resultant polariton states are anticipated to be of significant importance in the development of quantum-computation systems. [19] Until now, the only material systems used as the active dipole emitters in micropillars are inorganic semiconductors, such as InAs [9][10][11] and InGaAs [12] quantum dots or CdTe quantum wells. [13] There is, however, buoyant interest in the physics and applications of organic materials in photonics. Apart from simple one-dimensional planar organic cavities, [21][22][23][24][25][26][27] optical confinement has also been studied in a large range of different structures containing active organic chromophores.These include dye-doped polymer spheres, [28] organic microdiscs and polymer microspheroids, [29] polymer microrings, [30] dye-doped photonic crystals, [31][32][33][34] organic slab waveguides, [35] polymeric distributed-feedback lasers, [36] micromolded polymer films, [37] and polymer-filled circular gratings.[38] Despite significant activity in organic photonics, the creation of micropatterned organic structures is at a less advanced stage compared to progress made using inorganic semiconductors. This in part results from an increased sensitivity of organic thin films to the techniques commonly used to create high-resolution structures. There are, in fact, very pressing reasons to explore organic materials in new types of photonic structure, as such materials can often display optical properties not readily emulated using inorganic semiconductors. For example, the large oscillator strengths of organic (Frenkel) excitons can result in enhanced light-matter interactions, evidenced by "giant" Rabi splittings at room temperature. [22...

We report the fabrication of high-finesse strongly coupled microcavities composed of a polystyrene film doped with the dye tetraphenyl–porphyrin zinc positioned between two high reflectivity dielectric mirrors. The bottom mirror was deposited by plasma enhanced chemical vapor deposition, and was composed of 11 λ/4 thick (silicon oxide/silicon nitride) pairs. The organic layer was deposited on to this by spin coating. Finally, the top mirror was deposited by thermal evaporation and consisted of 12 λ/4 thick (tellurium oxide/lithium fluoride) pairs. Such cavities are characterized by Q factors of between 440 and 620. Strong coupling was evidenced via white light reflectivity measurements. Due to the high cavity Q factor, a Rabi splitting of 135 meV at resonance was very clearly resolved.

Synchrotron x-ray imaging techniques, like x-ray computed tomography (CT) and radiography have proven instrumental in expanding the communities knowledge of complex transport and reaction kinetics in electrochemical devices such as fuel cells and electrolyzers. This work presents the development of novel x-ray CT imaging techniques for operando visualization of water within low temperature fuel cells at spatial resolutions spanning the micro and nano scales. The design of operando sample holders, for both micro x-ray CT and nano CT experiments is described in depth, and prototypes of these sample holders were evaluated across a set of requirements, the most important of which are x-ray transmissibility, electrical conductivity and mechanical stability. Water segmentation from micro x-ray CT data was enabled by an image subtraction method, where the image without water is subtracted from the one with water. Through iterative experimentations, the operando nano CT cell was developed to optimize mechanical compression, electric conductivity and gas flow. While three-dimensional fuel cell reconstructions were shown possible, there remain challenges to overcome at typical lower energies (8 keV) due to beam damage, whereas it is not as significant for higher energies (>17.5 keV).