Filters

20143

More filters

20193
Reset filters

Settings

search.filters.applied.f.access: openAccess × Author: Presser, Volker × End date: 2014 × Start date: 2014 × Publisher: Cambridge : Royal Society of Chemistry × WGL Institute: INM ×

Search Results

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    One-step synthesis of nanocrystalline transition metal oxides on thin sheets of disordered graphitic carbon by oxidation of MXenes
    (Cambridge : Royal Society of Chemistry, 2014) Naguib, Michael; Mashtalir, Olhar; Lukatskaya, Maria R.; Dyatkin, Boris; Zhang, Chuanfang; Presser, Volker; Gogotsi, Yuri; Barsoum, Michael W.
    Herein we show that heating 2D Ti3C2 in air results in TiO2 nanocrystals enmeshed in thin sheets of disordered graphitic carbon structures that can handle extremely high cycling rates when tested as anodes in lithium ion batteries. Oxidation of 2D Ti3C2 in either CO2 or pressurized water also resulted in TiO2–C hybrid structures. Similarly, other hybrids can be produced, as we show here for Nb2O5/C from 2D Nb2C.
  • Thumbnail Image
    Item
    An electrochemical in situ study of freezing and thawing of ionic liquids in carbon nanopores
    (Cambridge : Royal Society of Chemistry, 2014) Weingarth, Daniel; Drumm, Robert; Foelske-Schmitz, Annette; Kotz, Rüdiger; Presser, Volker
    Room temperature ionic liquids (RTILs) are an emerging class of electrolytes enabling high cell voltages and, in return, high energy density of advanced supercapacitors. Yet, the low temperature behavior, including freezing and thawing, is little understood when ions are confined in the narrow space of nanopores. This study shows that RTILs may show a tremendously different thermal behavior when comparing bulk with nanoconfined properties as a result of the increased surface energy of carbon pore walls. In particular, a continuous increase in viscosity is accompanied by slowed-down charge-discharge kinetics as seen with in situ electrochemical characterization. Freezing reversibly collapses the energy storage ability and thawing fully restores the initial energy density of the material. For the first time, a different thermal behavior in positively and negatively polarized electrodes is demonstrated. This leads to different freezing and melting points in the two electrodes. Compared to bulk, RTILs in the confinement of electrically charged nanopores show a high affinity for supercooling; that is, the electrode may freeze during heating.
  • Thumbnail Image
    Item
    Carbon flow electrodes for continuous operation of capacitive deionization and capacitive mixing energy generation
    (Cambridge : Royal Society of Chemistry, 2014) Porada, S.; Weingarth, Daniel; Hamelers, H.V.M.; Bryjak, M.; Presser, Volker; Biesheuvel, P.M.
    Capacitive technologies, such as capacitive deionization and energy harvesting based on mixing energy (“capmix” and “CO2 energy”), are characterized by intermittent operation: phases of ion electrosorption from the water are followed by system regeneration. From a system application point of view, continuous operation has many advantages, to optimize performance, to simplify system operation, and ultimately to lower costs. In our study, we investigate as a step towards second generation capacitive technologies the potential of continuous operation of capacitive deionization and energy harvesting devices, enabled by carbon flow electrodes using a suspension based on conventional activated carbon powders. We show how the water residence time and mass loading of carbon in the suspension influence system performance. The efficiency and kinetics of the continuous salt removal process can be improved by optimizing device operation, without using less common or highly elaborate novel materials. We demonstrate, for the first time, continuous energy generation via capacitive mixing technology using differences in water salinity, and differences in gas phase CO2 concentration. Using a novel design of cylindrical ion exchange membranes serving as flow channels, we continuously extract energy from available concentration differences that otherwise would remain unused. These results may contribute to establishing a sustainable energy strategy when implementing energy extraction for sources such as CO2-emissions from power plants based on fossil fuels.