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- ItemDesign of high-performance antimony/MXene hybrid electrodes for sodium-ion batteries(London [u.a.] : RSC, 2022) Arnold, Stefanie; Gentile, Antonio; Li, Yunjie; Wang, Qingsong; Marchionna, Stefano; Ruffo, Riccardo; Presser, VolkerDue to their versatile properties and excellent electrical conductivity, MXenes have become attractive materials for alkali metal-ion batteries. However, as the capacity is limited to lower values due to the intercalation mechanism, these materials can hardly keep up in the ever-fast-growing community of battery research. Antimony has a promisingly high theoretical sodiation capacity characterized by an alloying reaction. The main drawback of this type of battery material is related to the high volume changes during cycling, often leading to electrode cracking and pulverization, resulting in poor electrochemical performance. A synergistic effect of combing antimony and MXene can be expected to obtain an optimized electrochemical system to overcome capacity fading of antimony while taking advantage of MXene charge storage ability. In this work, variation of the synthesis parameters and material design strategy have been dedicated to achieving the optimized antimony/MXene hybrid electrodes for high-performance sodium-ion batteries. The optimized performance does not align with the highest amount of antimony, the smallest nanoparticles, or the largest interlayer distance of MXene but with the most homogeneous distribution of antimony and MXene while both components remain electrochemically addressable. As a result, the electrode with 40 mass% MXene, not previously expanded, etched with 5 mass% HF and 60% antimony synthesized on the surfaces of MXene emerged as the best electrode. We obtained a high reversible capacity of 450 mA h g−1 at 0.1 A g−1 with a capacity retention of around 96% after 100 cycles with this hybrid material. Besides the successful cycling stability, this material also exhibits high rate capability with a capacity of 365 mA h g−1 at 4 A g−1. In situ XRD measurements and post mortem analysis were used to investigate the reaction mechanism.
- ItemNiobium carbide nanofibers as a versatile precursor for high power supercapacitor and high energy battery electrodes(London [u.a.] : RSC, 2016) Tolosa, Aura; Krüner, Benjamin; Fleischmann, Simon; Jäckel, Nicolas; Zeiger, Marco; Aslan, Mesut; Grobelsek, Ingrid; Presser, VolkerThis study presents electrospun niobium carbide/carbon (NbC/C) hybrid nanofibers, with an average diameter of 69 ± 30 nm, as a facile precursor to derive either highly nanoporous niobium carbide-derived carbon (NbC–CDC) fibers for supercapacitor applications or niobium pentoxide/carbon (Nb2O5/C) hybrid fibers for battery-like energy storage. In all cases, the electrodes consist of binder-free and free-standing nanofiber mats that can be used without further conductive additives. Chlorine gas treatment conformally transforms NbC nanofiber mats into NbC–CDC fibers with a specific surface area of 1508 m2 g−1. These nanofibers show a maximum specific energy of 19.5 W h kg−1 at low power and 7.6 W h kg−1 at a high specific power of 30 kW kg−1 in an organic electrolyte. CO2 treatment transforms NbC into T-Nb2O5/C hybrid nanofiber mats that provide a maximum capacity of 156 mA h g−1. The presence of graphitic carbon in the hybrid nanofibers enabled high power handling, maintaining 50% of the initial energy storage capacity at a high rate of 10 A g−1 (64 C-rate). When benchmarked for an asymmetric full-cell, a maximum specific energy of 86 W h kg−1 was obtained. The high specific power for both systems, NbC–CDC and T-Nb2O5/C, resulted from the excellent charge propagation in the continuous nanofiber network and the high graphitization of the carbon structure.
- ItemVanadium pentoxide/carbide-derived carbon core-shell hybrid particles for high performance electrochemical energy storage(London [u.a.] : RSC, 2016) Zeiger, Marco; Ariyanto, Teguh; Krüner, Benjamin; Peter, Nicolas J.; Fleischmann, Simon; Etzold, Bastian J.M.; Presser, VolkerA novel, two step synthesis is presented combining the formation of carbide-derived carbon (CDC) and redox-active vanadium pentoxide (V2O5) in a core–shell manner using solely vanadium carbide (VC) as the precursor. In a first step, the outer part of VC particles is transformed to nanoporous CDC owing to the in situ formation of chlorine gas from NiCl2 at 700 °C. In a second step, the remaining VC core is calcined in synthetic air to obtain V2O5/CDC core–shell particles. Materials characterization by means of electron microscopy, Raman spectroscopy, and X-ray diffraction clearly demonstrates the partial transformation from VC to CDC, as well as the successive oxidation to V2O5/CDC core–shell particles. Electrochemical performance was tested in organic 1 M LiClO4 in acetonitrile using half- and asymmetric full-cell configuration. High specific capacities of 420 mA h g−1 (normalized to V2O5) and 310 mA h g−1 (normalized to V2O5/CDC) were achieved. The unique nanotextured core–shell architecture enables high power retention with ultrafast charging and discharging, achieving more than 100 mA h g−1 at 5 A g−1 (rate of 12C). Asymmetric cell design with CDC on the positive polarization side leads to a high specific energy of up to 80 W h kg−1 with a superior retention of more than 80% over 10 000 cycles and an overall energy efficiency of up to 80% at low rates.
- ItemMXene as a novel intercalation-type pseudocapacitive cathode and anode for capacitive deionization(London [u.a.] : RSC, 2016) Srimuk, Pattarachai; Kaasik, Friedrich; Krüner, Benjamin; Tolosa, Aura; Fleischmann, Simon; Jäckel, Nicolas; Tekeli, Mehmet C.; Aslan, Mesut; Suss, Matthew E.; Presser, VolkerIn this proof-of-concept study, we introduce and demonstrate MXene as a novel type of intercalation electrode for desalination via capacitive deionization (CDI). Traditional CDI cells employ nanoporous carbon electrodes with significant pore volume to achieve a large desalination capacity via ion electrosorption. By contrast, MXene stores charge by ion intercalation between the sheets of its two-dimensional nanolamellar structure. By this virtue, it behaves as an ideal pseudocapacitor, that is, showing capacitive electric response while intercalating both anions and cations. We synthesized Ti3C2-MXene by the conventional process of etching ternary titanium aluminum carbide i.e., the MAX phase (Ti3AlC2) with hydrofluoric acid. The MXene material was cast directly onto the porous separator of the CDI cell without added binder, and exhibited very stable performance over 30 CDI cycles with an average salt adsorption capacity of 13 ± 2 mg g−1.
- ItemRhodamine 6G and 800 intermolecular heteroaggregates embedded in PMMA for near-infrared wavelength shifting(London [u.a.] : RSC, 2022) Castillo-Seoane, Javier; Gonzalez-Garcia, Lola; Obrero-Perez, José M.; Aparicio, Francisco J.; Borrás, Ana; González-Elipe, Agustín R.; Barranco, Ángel; Sanchez-Valencia, Juan R.The opto-electronic properties of small-molecules and functional dyes usually differ when incorporated into solid matrices with respect to their isolated form due to an aggregation phenomenon that alters their optical and fluorescent properties. These spectroscopic modifications are studied in the framework of the exciton theory of aggregates, which has been extensively applied in the literature for the study of molecular aggregates of the same type of molecules (homoaggregation). Despite the demonstrated potential of the control of the heteroaggregation process (aggregation of different types of molecules), most of the reported works are devoted to intramolecular aggregates, complex molecules formed by several chromophores attached by organic linkers. The intramolecular aggregates are specifically designed to hold a certain molecular structure that, on the basis of the exciton theory, modifies their optical and fluorescent properties with respect to the isolated chromophores that form the molecule. The present article describes in detail the incorporation of Rhodamine 6G (Rh6G) and 800 (Rh800) into polymeric matrices of poly-(methyl methacrylate), PMMA. The simultaneous incorporation of both dyes results in an enhanced fluorescent emission in the near-infrared (NIR), originating from the formation of ground-state Rh6G–Rh800 intermolecular heteroaggregates. The systematic control of the concentration of both rhodamines provides a model system for the elucidation of the heteroaggregate formation. The efficient energy transfer between Rh6G and Rh800 molecules can be used as wavelength shifters to convert effectively the light from visible to NIR, a very convenient wavelength range for many practical applications which make use of inexpensive commercial detectors and systems.
- ItemOn the viscous dissipation caused by randomly rough indenters in smooth sliding motion(Amsterdam : Elsevier, 2021) Sukhomlinov, Sergey; Müser, Martin H.The viscous dissipation between rigid, randomly rough indenters and linearly elastic counter bodies sliding past them is investigated using Green’s function molecular dynamics. The study encompasses a variety of models differing in the height spectra properties of the rigid indenter, in the viscoelasticity of the elastomer, and in their interaction. All systems reveal the expected damping linear in sliding velocity at small and a pronounced maximum at intermediate . Persson’s theory of rubber friction, which is adopted to the studied model systems, reflects all observed trends. However, close quantitative agreement is only found up to intermediate sliding velocities. Relative errors in the friction force become significant once the contact area is substantially reduced by sliding.
- ItemPercolation of rigid fractal carbon black aggregates(Melville, NY : American Institute of Physics, 2021) Coupette, Fabian; Zhang, Long; Kuttich, Björn; Chumakov, Andrei; Roth, Stephan V.; González-García, Lola; Kraus, Tobias; Schilling, TanjaWe examine network formation and percolation of carbon black by means of Monte Carlo simulations and experiments. In the simulation, we model carbon black by rigid aggregates of impenetrable spheres, which we obtain by diffusion-limited aggregation. To determine the input parameters for the simulation, we experimentally characterize the micro-structure and size distribution of carbon black aggregates. We then simulate suspensions of aggregates and determine the percolation threshold as a function of the aggregate size distribution. We observe a quasi-universal relation between the percolation threshold and a weighted average radius of gyration of the aggregate ensemble. Higher order moments of the size distribution do not have an effect on the percolation threshold. We conclude further that the concentration of large carbon black aggregates has a stronger influence on the percolation threshold than the concentration of small aggregates. In the experiment, we disperse the carbon black in a polymer matrix and measure the conductivity of the composite. We successfully test the hypotheses drawn from simulation by comparing composites prepared with the same type of carbon black before and after ball milling, i.e., on changing only the distribution of aggregate sizes in the composites.