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- ItemMonitoring the thermally induced transition from sp3-hybridized into sp2-hybridized carbons(Amsterdam [u.a.] : Elsevier Science, 2021) Schüpfer, Dominique B.; Badaczewski, Felix; Peilstöcker, Jan; Guerra-Castro, Juan Manuel; Shim, Hwirim; Firoozabadi, Saleh; Beyer, Andreas; Volz, Kerstin; Presser, Volker; Heiliger, Christian; Smarsly, Bernd; Klar, Peter J.The preparation of carbons for technical applications is typically based on a treatment of a precursor, which is transformed into the carbon phase with the desired structural properties. During such treatment the material passes through several different structural stages, for example, starting from precursor molecules via an amorphous phase into crystalline-like phases. While the structure of non-graphitic and graphitic carbon has been well studied, the transformation stages from molecular to amorphous and non-graphitic carbon are still not fully understood. Disordered carbon often contains a mixture of sp3-, sp2-and sp1-hybridized bonds, whose analysis is difficult to interpret. We systematically address this issue by studying the transformation of purely sp3-hybridized carbons, that is, nanodiamond and adamantane, into sp2-hybridized non-graphitic and graphitic carbon. The precursor materials are thermally treated at different temperatures and the transformation stages are monitored. We employ Raman spectroscopy, WAXS and TEM to characterize the structural changes. We correlate the intensities and positions of the Raman bands with the lateral crystallite size La estimated by WAXS analysis. The behavior of the D and G Raman bands characteristic for sp2-type material formed by transforming the sp3-hybridized precursors into non-graphitic and graphitic carbon agrees well with that observed using sp2-structured precursors.
- ItemEffect of pore geometry on ultra-densified hydrogen in microporous carbons(Amsterdam [u.a.] : Elsevier Science, 2021) Tian, Mi; Lennox, Matthew J.; O’Malley, Alexander J.; Porter, Alexander J.; Krüner, Benjamin; Rudić, Svemir; Mays, Timothy J.; Düren, Tina; Presser, Volker; Terry, Lui R.; Rols, Stephane; Fang, Yanan; Dong, Zhili; Rochat, Sebastien; Ting, Valeska P.Our investigations into molecular hydrogen (H2) confined in microporous carbons with different pore geometries at 77 K have provided detailed information on effects of pore shape on densification of confined H2 at pressures up to 15 MPa. We selected three materials: a disordered, phenolic resin-based activated carbon, a graphitic carbon with slit-shaped pores (titanium carbide-derived carbon), and single-walled carbon nanotubes, all with comparable pore sizes of <1 nm. We show via a combination of in situ inelastic neutron scattering studies, high-pressure H2 adsorption measurements, and molecular modelling that both slit-shaped and cylindrical pores with a diameter of ∼0.7 nm lead to significant H2 densification compared to bulk hydrogen under the same conditions, with only subtle differences in hydrogen packing (and hence density) due to geometric constraints. While pore geometry may play some part in influencing the diffusion kinetics and packing arrangement of hydrogen molecules in pores, pore size remains the critical factor determining hydrogen storage capacities. This confirmation of the effects of pore geometry and pore size on the confinement of molecules is essential in understanding and guiding the development and scale-up of porous adsorbents that are tailored for maximising H2 storage capacities, in particular for sustainable energy applications.
- ItemResolving mobility anisotropy in quasi-free-standing epitaxial graphene by terahertz optical Hall effect(Amsterdam [u.a.] : Elsevier Science, 2021) Armakavicius, Nerijus; Kühne, Philipp; Eriksson, Jens; Bouhafs, Chamseddine; Stanishev, Vallery; Ivanov, Ivan G.; Yakimova, Rositsa; Zakharov, Alexei A.; Al-Temimy, Ameer; Coletti, Camilla; Schubert, Mathias; Darakchieva, VanyaIn this work, we demonstrate the application of terahertz-optical Hall effect (THz-OHE) to determine directionally dependent free charge carrier properties of ambient-doped monolayer and quasi-free-standing-bilayer epitaxial graphene on 4H–SiC(0001). Directionally independent free hole mobility parameters are found for the monolayer graphene. In contrast, anisotropic hole mobility parameters with a lower mobility in direction perpendicular to the SiC surface steps and higher along the steps in quasi-free-standing-bilayer graphene are determined for the first time. A combination of THz-OHE, nanoscale microscopy and optical spectroscopy techniques are used to investigate the origin of the anisotropy. Different defect densities and different number of graphene layers on the step edges and terraces are ruled out as possible causes. Scattering mechanisms related to doping variations at the step edges and terraces as a result of different interaction with the substrate and environment are discussed and also excluded. It is suggested that the step edges introduce intrinsic scattering in quasi-free-standing-bilayer graphene, that is manifested as a result of the higher ratio between mean free path and average terrace width parameters. The suggested scenario allows to reconcile existing differences in the literature regarding the anisotropic electrical transport in epitaxial graphene. © 2020 Elsevier Ltd
- ItemA review of electrical and thermal conductivities of epoxy resin systems reinforced with carbon nanotubes and graphene-based nanoparticles(Amsterdam [u.a.] : Elsevier Science, 2022) Mousavi, Seyed Rasoul; Estaji, Sara; Kiaei, Hediyeh; Mansourian-Tabaei, Mohammad; Nouranian, Sasan; Jafari, Seyed Hassan; Ruckdäschel, Holger; Arjmand, Mohammad; Khonakdar, Hossein AliEpoxy (EP) resins exhibit desirable mechanical and thermal properties, low shrinkage during cuing, and high chemical resistance. Therefore, they are useful for various applications, such as coatings, adhesives, paints, etc. On the other hand, carbon nanotubes (CNT), graphene (Gr), and their derivatives have become reinforcements of choice for EP-based nanocomposites because of their extraordinary mechanical, thermal, and electrical properties. Herein, we provide an overview of the last decade's advances in research on improving the thermal and electrical conductivities of EP resin systems modified with CNT, Gr, their derivatives, and hybrids. We further report on the surface modification of these reinforcements as a means to improve the nanofiller dispersion in the EP resins, thereby enhancing the thermal and electrical conductivities of the resulting nanocomposites.
- ItemA new strategy to improve viscoelasticity, crystallization and mechanical properties of polylactide(Amsterdam [u.a.] : Elsevier Science, 2021) Huang, Ying; Müller, Michael Thomas; Boldt, Regine; Zschech, Carsten; Gohs, Uwe; Wießner, SvenBiodegradable polylactide/masticated natural rubber (PLA/mNR) blends were prepared by electron induced reactive processing (EIReP) without using any chemical additives. The PLA/mNR blends showed droplet-matrix morphology with decreased mNR particle size after EIReP treatment. The absolute value of complex viscosity and storage modulus increased significantly for the EIReP modified blends, suggesting the improved melt strength and elasticity. The crystallization investigation showed that the cold crystallization peak of PLA phase gradually disappeared after EIReP modification. Instead, the crystallization peak arose during melt cooling process. Consequently, the crystallinity of PLA phase increased from 6.2% to 39.0% as the mNR content increased from 0 to 20 wt%. It was found that the softening temperature of PLA examined by dynamic mechanical analysis increased effectively with the characters of higher modulus compared to the non-modified blends. The EIReP modified blends exhibited excellent mechanical properties with 7-fold increase of impact toughness compared with neat PLA, implying a superior interfacial adhesion and chain interactions between the two polymer phases. Furthermore, the thermogravimetric analysis demonstrated that the thermal stability was slightly enhanced for the EIReP modified blends.
- ItemExamining the early stages of thermal oxidative degradation in epoxy-amine resins(Amsterdam [u.a.] : Elsevier Science, 2020) Morsch, Suzanne; Liu, Yanwen; Lyon, S.B.; Gibbon, S.R.; Gabriele, Benjamin; Malanin, Mikhail; Eichhorn, Klaus-JochenEpoxy-amine resins continue to find widespread use as the binders in protective and decorative organic coatings, as the matrix in composite materials, and as adhesives. In service, exposure to the environment ultimately results in oxidative deterioration of these materials, limiting the performance lifetime. Defining this auto-oxidation process is therefore a key challenge in developing more durable high-performance materials. In this study, we investigate oxidative degradation of a model resin based on diglycidyl ether of bisphenol-A (DGEBA) and an aliphatic amine hardener, triethylenetetraamine (TETA). Using infrared spectroscopy, we find that prior to the expected detection of formate groups (corresponding to the well-known radical oxidation mechanism of DGEBA), a band at 1658 cm−1 forms, associated with amine cross-linker oxidation. Infrared microspectroscopy, in-situ heated ATR-infrared, Raman spectroscopy and AFM-IR techniques are thus employed to investigate the early stages of resin oxidation and demonstrate strong parallels between the initial stages of cured resin degradation and the auto-oxidation of TETA cross-linker molecules.
- ItemExperimental multi-scale approach to determine the local mechanical properties of foam base material in polyisocyanurate metal panels(Amsterdam [u.a.] : Elsevier Science, 2021) Gahlen, P.; Fröbel, S.; Karbach, A.; Gabriel, D.; Stommel, M.Polyisocyanurate (PIR) foams were examined regarding their local chemical composition using ATR-IR spectroscopy. As a special parameter the PIR: Amide III intensity ratio is to be mentioned, which represents the quantity of the formed PIR groups. Based on the local PIR: Amide III intensity ratio, the mechanical properties (Young's modulus) of the foam base material were analyzed at defined positions by AFM and Nanoindentation. It turned out that the AFM method is only suitable for qualitative analysis, because the values differ strongly from macroscopic measurements. For the measurements using nanoindentation, a new embedding method was developed, which achieves significantly more realistic and reproducible results compared to the embedding method used in the literature and shows a very good agreement with the macroscopic values. In general, it has been shown that a higher PIR: Amide III intensity ratio tends to lead to a higher Young's modulus. Nevertheless, there are other, currently unknown characteristic values which also influence the Young's modulus.
- ItemInvestigating the morphology of bulk heterojunctions by laser photoemission electron microscopy(Amsterdam [u.a.] : Elsevier Science, 2022) Niefind, Falk; Shivhare, Rishi; Mannsfeld, Stefan C.B.; Abel, Bernd; Hambsch, MikeThe nanoscale morphology of bulk heterojunctions is highly important for the charge dissociation and transport in organic solar cells and ultimately defines the performance of the cell. The visualization of this nano-morphology in terms of domain size and polymer orientation in a fast and straightforward way is therefore of great interest to evaluate the suitability of a film for efficient solar cells. Here, we demonstrate that the morphology of different blends of poly(3-hexylthiophene-2,5-diyl) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) can be imaged and analyzed by employing photoemission electron microscopy.
- ItemTubular hollow fibre electrodes for CO2 reduction made from copper aluminum alloy with drastically increased intrinsic porosity(Amsterdam [u.a.] : Elsevier Science, 2020) Bell, Daniel; Rall, Deniz; Großeheide, Maren; Marx, Lennart; Hülsdünker, Laura; Wessling, MatthiasElectrochemical reduction of CO2 to higher-order hydrocarbon products offers a significant contribution to the challenge of a circular economy. In the pursuit of better copper metal catalyst, it was early on realized that increasing productivity of copper catalysts systems is reliant on high surface area per volume. Tubular gas diffusion electrodes offer such properties. In this work, we present a methodology to fabricate tubular hollow fibre copper electrodes with drastically increased intrinsic porosity. Our described method utilizes a standard dealloying process of copper aluminium particles to induce an intra-particle nanoporosity. The specific surface area increases from 0.126 m2 g−1 before dealloying to 6.194 m2 g−1 after dealloying. In comparison to conventional planar copper electrodes and literature data from conventional copper hollow fibres, the intra-particle porosity leads to a drastically increase in electrochemical activity. Electrochemical measurements reveal increased current densities at low over-potentials in comparison to conventional copper electrodes under identical experimental conditions emphasizing the significant impact of the porosity on the electrode performance. The presented method can be easily transferred to other alloy particles, highlighting its versatility for electrode fabrication. © 2019 The Author(s)
- ItemEmerging, hydrogen-driven electrochemical water purification(Amsterdam [u.a.] : Elsevier Science, 2022) Suss, M.E.; Zhang, Y.; Atlas, I.; Gendel, Y.; Ruck, E.B.; Presser, V.Energy-efficient technologies for the remediation of water and generation of drinking water is a key towards sustainable technologies. Electrochemical desalination technologies are promising alternatives towards established methods, such as reverse osmosis or nanofiltration. In the last few years, hydrogen-driven electrochemical water purification has emerged. This review article explores the concept of desalination fuel cells and capacitive-Faradaic fuel cells for ion separation.