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Author: Gollas, Bernhard × End date: 2024 × Start date: 2020 × Has files: Yes ×

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    Persistent and reversible solid iodine electrodeposition in nanoporous carbons
    (Berlin : Springer Nature, 2020) Prehal, Christian; Fitzek, Harald; Kothleitner, Gerad; Presser, Volker; Gollas, Bernhard; Freunberger, Stefan A.; Abbas, Qamar
    Aqueous iodine based electrochemical energy storage is considered a potential candidate to improve sustainability and performance of current battery and supercapacitor technology. It harnesses the redox activity of iodide, iodine, and polyiodide species in the confined geometry of nanoporous carbon electrodes. However, current descriptions of the electrochemical reaction mechanism to interconvert these species are elusive. Here we show that electrochemical oxidation of iodide in nanoporous carbons forms persistent solid iodine deposits. Confinement slows down dissolution into triiodide and pentaiodide, responsible for otherwise significant self-discharge via shuttling. The main tools for these insights are in situ Raman spectroscopy and in situ small and wide-angle X-ray scattering (in situ SAXS/WAXS). In situ Raman confirms the reversible formation of triiodide and pentaiodide. In situ SAXS/WAXS indicates remarkable amounts of solid iodine deposited in the carbon nanopores. Combined with stochastic modeling, in situ SAXS allows quantifying the solid iodine volume fraction and visualizing the iodine structure on 3D lattice models at the sub-nanometer scale. Based on the derived mechanism, we demonstrate strategies for improved iodine pore filling capacity and prevention of self-discharge, applicable to hybrid supercapacitors and batteries.
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    Author Correction: Persistent and reversible solid iodine electrodeposition in nanoporous carbons
    ([London] : Nature Publishing Group UK, 2020) Prehal, Christian; Fitzek, Harald; Kothleitner, Gerald; Presser, Volker; Gollas, Bernhard; Freunberger, Stefan A.; Abbas, Qamar
    Correction to: Nature Communications https://doi.org/10.1038/s41467-020-18610-6, published online 24 September 2020.
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    Reduced Faradaic Contributions and Fast Charging of Nanoporous Carbon Electrodes in a Concentrated Sodium Nitrate Aqueous Electrolyte for Supercapacitors
    (Weinheim [u.a.] : Wiley-VCH, 2019) Abbas, Qamar; Gollas, Bernhard; Presser, Volker
    The Faradaic processes related to electrochemical water reduction at the nanoporous carbon electrode under negative polarization are reduced when the concentration of aqueous sodium nitrate (NaNO3) is increased or the temperature is decreased. This effect enhances the relative contribution of ion electrosorption to the total charge storage process. Hydrogen chemisorption is reduced in aqueous 8.0 m NaNO3 due to the low degree of hydration of the Na+ cation; consequently, less free water is available for redox contributions, driving the system to exhibit electrical double-layer capacitive characteristics. Hydrogen adsorption/desorption is facilitated in 1.0 m NaNO3 due to the high molar ratio. The excess of water shifts the local pH in carbon nanopores to neutral values, giving rise to a high overpotential for dihydrogen evolution in the latter. The dilution effect on local pH shift in 1.0 m NaNO3 can be reduced by decreasing the temperature. A symmetric activated carbon cell assembled with 8.0 m NaNO3 exhibits a high capacitance and coulombic efficiency, a larger contribution of ion electrosorption to the overall charge storage process, and a stable capacitance performance at 1.6 V. © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim