Severin Vierrath

Influence of carbon substrate on the electrochemical performance of carbon/manganese oxide hybrids in aqueous and organic electrolytes

Manganese oxide presents very promising electrochemical properties as an electrode material in supercapacitors, but there remain important open questions to guide further development of the complex manganese oxide/carbon/electrolyte system. Our work addresses specifically the influence of carbon ordering and the difference between outer and inner porosity of carbon particles for the application in aqueous 1 M Na2SO4 and 1 M LiClO4 in acetonitrile. Birnessite-type manganese oxide was hydrothermally hybridized on two kinds of carbon onions with only outer surface area and different electrical conductivity, and conventional activated carbon with a high inner porosity. Carbon onions with a high degree of carbon ordering, high conductivity, and high outer surface area were identified as the most promising material, yielding 179 F g−1. Pore blocking in activated carbon yields unfavorable electrochemical performances. The highest specific energy of 16.4 W h kg−1 was measured for a symmetric full-cell arrangement of manganese oxide coated high temperature carbon onions in the organic electrolyte. High stability during 10 000 cycles was achieved for asymmetric full-cells, which proved as a facile way to enhance the electrochemical performance stability.

Three-dimensional morphology of the interface between micro porous layer and catalyst layer in a polymer electrolyte membrane fuel cell

Interfaces between the different layers in proton exchange membrane fuel cells are expected to influence transport properties and therefore cell performance. So far the interface between micro porous layer (MPL) and catalyst layer (CL) has been difficult to investigate due to its nanometer scale morphology. We apply focused ion beam scanning electron microscopy tomography with pore contrasting via atomic layer deposition to reconstruct a representative volume of 5.1 μm × 1.5 μm × 4.5 μm containing CL, MPL and their interface. We find that platinum in the CL results in brighter SEM image intensities, compared to the MPL. This allows (i) estimating the extension of the interfacial region (530 nm), (ii) evaluating Pt-content homogeneity in the CL and (iii) calculating the individual roughnesses for the CL (102 nm) and for the MPL (129 nm). We further calculate porosity, pore sizes, and oxygen diffusivities. Thus, we find that the values of the parameters of the interfacial region are between those of the CL and the MPL, meaning that on the investigated scale, the interface is a homogeneous transitional region. A representativeness analysis shows that our reconstructed volume is sufficiently large concerning all calculated parameters.

Three-Dimensional Analysis of the Porosity in MgB 2 Wires Using FIB Nanotomography

Porosity is one of several current limiting mechanisms in MgB2 wires. We have compared the microstructural homogeneity and the porosity distribution in different ex situ and in situ MgB2 powder-in-tube wires. The submicrometer structure was determined using focused ion beam nanotomography. The ex situ wires exhibit an isotropic microstructure, which has been quantified in terms of an identical tortuosity in transverse and longitudinal filament direction. The very homogenous microstructure in the new ex situ wire generation is probably one reason for its strongly improved critical current density. The in situ wire has an anisotropic microstructure with a lower tortuosity in the axial direction. The microstructural inhomogeneity of the in situ filaments makes microstructural characterization and the comparison between materials and superconducting properties particularly challenging.

Children with social anxiety disorder show blunted pupillary reactivity and altered eye contact processing in response to emotional faces: Insights from pupillometry and eye movements

Cognitive models and adult research associate social anxiety disorder (SAD) with hypervigilant-avoidant processing of social information, such as eye contact. However, processing biases in childhood SAD remain mostly unexplored. We examined 10- to 13-year-old childrens eye contact processing and pupil dilation in response to happy, neutral, and angry faces in three groups: SAD (n = 31), mixed anxiety disorders (MAD; n = 30), and healthy controls (HC; n = 32). Compared to HC, SAD children showed faster first fixations on the eye region of neutral faces and shorter first fixation durations on the eye region of all faces. No differences between the two clinical groups emerged in eye movement results. SAD girls showed reduced pupil dilation in response to happy and angry faces compared to MAD and to happy faces compared to HC. SAD boys showed reduced pupil dilation in response to neutral faces compared to HC. Dimensionally, reduced pupil dilation was linked to social anxiety severity while eye movements were correlated with mixed anxiety and depressive severity. Results suggest that hypervigilant-avoidant eye contact processing and a blunted pupillary reactivity characterize children with SAD. Both transdiagnostic and disorder-specific processing biases are relevant for the understanding of childhood SAD.