Adam G. Simmonds

New Infrared Transmitting Material via Inverse Vulcanization of Elemental Sulfur to Prepare High Refractive Index Polymers

Polymers for IR imaging: The preparation of high refractive index polymers (n = 1.75 to 1.86) via the inverse vulcanization of elemental sulfur is reported. High quality imaging in the near (1.5 μm) and mid-IR (3-5 μm) regions using high refractive index polymeric lenses from these sulfur materials was demonstrated.

Inverse vulcanization of elemental sulfur with 1,4-diphenylbutadiyne for cathode materials in Li–S batteries

High sulfur content copolymers were prepared via inverse vulcanization of sulfur with 1,4-diphenylbutadiyne (DiPhDY) for use as the active cathode material in lithium–sulfur batteries. These sulfur-rich polymers exhibited excellent capacity retention (800 mA h g−1 at 300 cycles) and extended battery lifetimes of over 850 cycles at C/5 rate.

Directing the Deposition of Ferromagnetic Cobalt onto Pt-tipped CdSe@CdS Nanorods: Synthetic and Mechanistic Insights

A methodology providing access to dumbbell-tipped, metal-semiconductor and metal oxide-semiconductor heterostructured nanorods has been developed. The synthesis and characterization of CdSe@CdS nanorods incorporating ferromagnetic cobalt nanoinclusions at both nanorod termini (i.e., dumbbell morphology) are presented. The key step in the synthesis of these heterostructured nanorods was the decoration of CdSe@CdS nanorods with platinum nanoparticle tips, which promoted the deposition of metallic CoNPs onto Pt-tipped CdSe@CdS nanorods. Cobalt nanoparticle tips were then selectively oxidized to afford CdSe@CdS nanorods with cobalt oxide domains at both termini. In the case of longer cobalt-tipped nanorods, heterostructured nanorods were observed to self-organize into complex dipolar assemblies, which formed as a consequence of magnetic associations of terminal CoNP tips. Colloidal polymerization of these cobalt-tipped nanorods afforded fused nanorod assemblies from the oxidation of cobalt nanoparticle tips at the ends of nanorods via the nanoscale Kirkendall effect. Wurtzite CdS nanorods survived both the deposition of metallic CoNP tips and conversion into cobalt oxide phases, as confirmed by both XRD and HRTEM analysis. A series of CdSe@CdS nanorods of four different lengths ranging from 40 to 174 nm and comparable diameters (6-7 nm) were prepared and modified with both cobalt and cobalt oxide tips. The total synthesis of these heterostructured nanorods required five steps from commercially available reagents. Key synthetic considerations are discussed, with particular emphasis on reporting isolated yields of all intermediates and products from scale up of intermediate precursors.

Molecular Ordering in Monolayers of an Alkyl-Substituted Perylene-Bisimide Dye by Attenuated Total Reflectance Ultraviolet–Visible Spectroscopy

Surface-relative orientational parameters were determined for monolayer films of N, N′-ditridecylperylenetetracarboxylic dianhydridediimide (C13-PTCDI) in terms of the relative electronic transition dipole strengths, providing a three-dimensional view of the absorption dipole distribution. In order to obtain a macroscopically ordered film, C13-PTCDI was deposited by (1) horizontal Langmuir–Blodgett (LB) transfer onto methyl- and phenyl-silanized glass, and (2) vapor deposition onto oriented films of poly(tetrafluoroethylene) (PTFE) on glass. Films of LB-deposited C13-PTCDI were found to be completely isotropic prior to annealing. After annealing, these films remained isotropic in the plane of the substrate while the out-of-plane anisotropy was significantly enhanced. In contrast, films of C13-PTCDI vapor deposited onto oriented poly(tetrafluoroethylene) (PTFE)-modified substrates yielded films with a high degree of both in- and out-of-plane anisotropy. Atomic force microscopy (AFM) images of both the LB- and vapor-deposited films show substantial differences in film morphology and long-range order. These results demonstrate that molecular orientation in C13-PTCDI films can be controlled by varying substrate surface chemistry and post-deposition processing.

Analytical multimode scanning and transmission electron imaging and tomography of multiscale structural architectures of sulfur copolymer-based composite cathodes for next-generation high-energy density Li-S batteries

Poly[sulfur-random-(1,3-diisopropenylbenzene)] copolymers synthesized via inverse vulcanization represent an emerging class of electrochemically active polymers recently used in cathodes for Li-S batteries, capable of realizing enhanced capacity retention (1,005 mAh/g at 100 cycles) and lifetimes of over 500 cycles. The composite cathodes are organized in complex hierarchical three-dimensional (3D) architectures, which contain several components and are challenging to understand and characterize using any single technique. Here, multimode analytical scanning and transmission electron microscopies and energy-dispersive X-ray/electron energy-loss spectroscopies coupled with multivariate statistical analysis and tomography were applied to explore origins of the cathode-enhanced capacity retention. The surface topography, morphology, bonding, and compositions of the cathodes created by combining sulfur copolymers with varying 1,3-diisopropenylbenzene content and conductive carbons have been investigated at multiple scales in relation to the electrochemical performance and physico-mechanical stability. We demonstrate that replacing the elemental sulfur with organosulfur copolymers improves the compositional homogeneity and compatibility between carbons and sulfur-containing domains down to sub-5 nm length scales resulting in (a) intimate wetting of nanocarbons by the copolymers at interfaces; (b) the creation of 3D percolation networks of conductive pathways involving graphitic-like outer shells of aggregated carbons;

Multiscale Structural Architectures of Novel Sulfur Copolymer Composite Cathodes for High-Energy Density Li-S Batteries Studied by Analytical Multimode STEM Imaging and Tomography

Li-S rechargeable batteries are considered to be a promising light-weight, low-cost, and environmentally friendly candidate for next generation energy storage owing to high theoretical specific capacity of 1,672 mAh/g and high specific energy of 2,567 Wh/kg, which is 5 times that of current Li-ion technology. However, practical use of Li-S batteries remains limited because they suffer from gradual capacity fading caused by insulating properties of sulfur and polysulfide shuttle. Recently, poly(sulfur-random-(1,3diisopropenylbenzene) (poly(S-r-DIB)) copolymers have been introduced for their use as active materials in cathodes for Li-S batteries, and were found to be capable of realizing enhanced capacity retention (1005 mAh/g at 100 cycles) and a five-fold increase in lifetime (over 500 cycles) as compared to conventional sulfur-carbon cathodes [1, 2]. These materials are typically organized in a rough hierarchical 3D architecture which contains multiple components and is quite challenging to understand and characterize.

M0S2-S8 Composite Cathodes for Long Cycle Life High Performance Li-S Batteries Studied by FESEM and High-Resolution AEM

The development of next generation electrical energy storage driven by ever increasing demand is pushing electrochemical power sources beyond the barriers of current Li-ion batteries towards multicomponent composite electrode materials exploring new chemistries with higher energy densities, longer cycle life, and improved safety while being sustainable, “green”, low cost, and reliable. With theoretical specific energy (2600 Wh kg) and specific capacity (1672 mAhg), which are the highest among all solid elemental redox couples, Li-S battery is regarded as a prospective technology for near-future commercialization in emerging applications (high-altitude pseudosatellites, long-range electric vehicles (>550 km), portable electronics, and stationary grid energy storage) [1]. Remaining obstacles for the practical realization of Li-S battery technology are, however, pronounced capacity fading, poor Coulombic efficiency, and limited cycle life, which all are to various extend related to parasitic diffusion of soluble lithium polysulfides (Li2Sx, x = 3÷8) during cycling from a sulfur-carbon cathode to a Li metal anode (a “polysulfide shuttle” effect). In order to decrease the effective diffusion length of the polysulfides and enhance cell performance via binding Li2Sx to the cathode surface, nanostructured layered transition metal dichalcogenides MX2 (M = Mo, Ti, X = S, Se), have been employed. MoS2-elemental sulfur (-S8) composites recently introduced as a new active material for cathodes in Li-S cells exhibited extended cycle life up to 1000 cycles, high capacity retention and exceptional rate capability with the delivery of reversible capacity up to 500 mAhg at 5 C rate [2]. In this work, we explore mechanistic roots for these remarkable improvements using cold-electron gun field-emission SEM (C-FESEM) and high-resolution analytical scanning/transmission electron microscopy (AS/TEM) to characterize the surface topography, morphology, interfaces, and elemental distributions in MoS2-S8 composite-based cathodes. The cathodes were fabricated by ballmilling of a mixture of MoS2-S8 composite (1:1 by mass), conductive carbon, and poly(ethylene) binder in a 75:20:5 mass ratio. Low voltage C-FESEM observations show that 10-50 m diameter and 20-500 nm-thick crystalline MoS2 platelets and sulfur microparticles are regularly distributed throughout the cathode matrix comprising carbons and PE binder practically with no cracks usually formed in S8-carbon cathodes due to mechanical stresses induced during drying of deposited cathode films (Fig. 1a). Characterization of sulfur distributions in MoS2:S8 composites by EDXS is challenging and requires appropriate standards and fitting references because of severe overlapping of MoL-series and SK-series with only a 17 eV separation between the major characteristic SK (2.307 keV) and MoL (2.293 keV) lines (Fig. 1b), On the other hand, with EELS (Figs. 1c and 1d), owing to its higher energy resolution, one can distinguish molybdenum (the Mo M4,5-edge (227 eV), the Mo L2,3-edge (2520 eV) and sulfur (the S L2,3-edge (165 eV) and the S K-edge (2472 eV)). Morphological, crystallographic, and compositional C-FESEM and AS/TEM analyses of the cathodes reveal 3D agglomerates formed by flakes of mechanically disrupted layered MoS2 platelets and exfoliated nanosheets with large-area interfaces primarily on basal planes surrounded by aggregated 30-60 nm carbon particles and extended microand mesoporosity, which serve as electron and ion transport pathways, respectively. HRTEM observations (Fig. 2) indicate that 2D nature and large 0.62 nm (002) interlayer separation in 2H-MoS2 crystallites provide perfect locations to accommodate and anchor lithium polysulfides suppressing the shuttle effect. These findings demonstrate significant implications from the incorporation of MoS2-S8 composites into the cathodes on the performance of Li-S batteries. 1972 doi:10.1017/S1431927617010522 Microsc. Microanal. 23 (Suppl 1), 2017

Waveguide-Based Chemical and Spectroelectrochemical Sensor Platforms

Here we review the progress in the development of waveguide-based spectroelectrochemical platforms, with special emphasis on the most recent technologies: the electroactive fiber-optic chip (EA-FOC) and chip-like spectroelectrochemical platforms using organic light emitting diode (OLED) light sources coupled with organic photovoltaic photodetectors (OPV-PD). Both technologies simplify spectroelectrochemical data collection through eliminating the need for free-space optics and benefit from the increased sensitivity of waveguide based devices producing new chemical sensor platforms.

A planar integrated photometer/refractometer using an organic light emitting diode light source and an organic photovoltaic detector

A simple refractometer/photometer is described which uses a vacuum-deposited multilayer organic light emitting diode (OLED) light source and a vacuum-deposited planar heterojunction organic photovoltaic (OPV) detector, separated from each other on a thin glass attenuated total reflectance (ATR) element by 1-2 cm. A portion of the light output from the OLED light source is internally reflected in the ATR element, and the evanescent field from this internally reflected light interacts with solutions of variable refractive index in the region between the OLED and OPV. We document here the simple construction principles for devices of this type, and the characterization of the operation of this first-generation device in terms of i) photocurrent in the OPV detector versus light output from the OLED and ii) the response of the device to solutions of differing refractive index. In these first-generation devices we estimate a sensitivity to changes in refractive index of +/- of 10-3 units.