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Author: Amenitsch, H. × Type: Article ×

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Now showing 1 - 3 of 3
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    Salt concentration and charging velocity determine ion charge storage mechanism in nanoporous supercapacitors
    (London : Nature Publishing Group, 2018) Prehal, C.; Koczwara, C.; Amenitsch, H.; Presser, V.; Paris, O.
    A fundamental understanding of ion charge storage in nanoporous electrodes is essential to improve the performance of supercapacitors or devices for capacitive desalination. Here, we employ in situ X-ray transmission measurements on activated carbon supercapacitors to study ion concentration changes during electrochemical operation. Whereas counter-ion adsorption was found to dominate at small electrolyte salt concentrations and slow cycling speed, ion replacement prevails for high molar concentrations and/or fast cycling. Chronoamperometry measurements reveal two distinct time regimes of ion concentration changes. In the first regime the supercapacitor is charged, and counter- and co-ion concentration changes align with ion replacement and partially co-ion expulsion. In the second regime, the electrode charge remains constant, but the total ion concentration increases. We conclude that the initial fast charge neutralization in nanoporous supercapacitor electrodes leads to a non-equilibrium ion configuration. The subsequent, charge-neutral equilibration slowly increases the total ion concentration towards counter-ion adsorption.
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    Author Correction: Salt concentration and charging velocity determine ion charge storage mechanism in nanoporous supercapacitors
    ([London] : Nature Publishing Group UK, 2019) Prehal, C.; Koczwara, C.; Amenitsch, H.; Presser, V.; Paris, O.
    Correction to: Nature Communications; https://doi.org/10.1038/s41467-018-06612-4; published online 08 October 2018 The original version of this Article contained an error in the Acknowledgements, which was incorrectly omitted from the end of the following: ‘The research leading to these results has received funding from the European Community’s Horizon 2020 Framework Programme under grant agreement nº 730872.’ This has been corrected in both the PDF and HTML versions of the Article.
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    Tracking the structural arrangement of ions in carbon supercapacitor nanopores using in situ small-angle X-ray scattering
    (Cambridge : Royal Society of Chemistry, 2015) Prehal, C.; Weingarth, Daniel; Perre, Emilie; Lechner, R.T.; Amenitsch, H.; Paris, O.; Presser, Volker
    The charge storage mechanism and ion arrangement inside electrically charged carbon nanopores is a very active research field with tremendous importance for advanced electrochemical technologies, such as supercapacitors or capacitive deionization. Going far beyond the state of art, we present for the first time a comprehensive study of tracking ion electrosorption in aqueous electrolytes during charging and discharging of porous carbon electrodes using in situ X-ray scattering. We provide novel and quantitative insights into the local concentration of anions and cations and demonstrate that the global number of ions within the pores does not vary during charging and discharging. In addition, we have unique access to the spatial arrangement of ions inside carbon nanopores by using a simple, yet powerful two-phase model. Applying this model to our data, we show that double-layer formation is accomplished by a unique combination of preferred counter-ion adsorption directly at the pore wall which drains ions from their local surrounding inside carbon nanopores. Effectively, this leads to a situation which globally appears as ion swapping.