Supercapacitors are electrochemical energy-storage devices that exploit the electrostatic interaction between high-surface-area nanoporous electrodes and electrolyte ions. Insight into the molecular mechanisms at work inside supercapacitor carbon electrodes is obtained with (13)C and (11)B ex situ magic-angle spinning nuclear magnetic resonance (MAS-NMR). In activated carbons soaked with an electrolyte solution, two distinct adsorption sites are detected by NMR, both undergoing chemical exchange with the free electrolyte molecules. On charging, anions are substituted by cations in the negative carbon electrode and cations by anions in the positive electrode, and their proportions in each electrode are quantified by NMR. Moreover, acetonitrile molecules are expelled from the adsorption sites at the negative electrode alone. Two nanoporous carbon materials were tested, with different nanotexture orders (using Raman and (13)C MAS-NMR spectroscopies), and the more disordered carbon shows a better capacitance and a better tolerance to high voltages.
International audienceCharacterisation of uranium oxides in different conditions is a challenge both in nuclear and environment sciences. We focus here on U4O9, which is a superstructure of UO2. Homogeneous U4O9 powder was fabricated and characterised by Raman spectroscopy. The Raman spectrum of a pure-phase U4O9 is, for the first time, completely described and interpreted. U4O9 Raman spectrum derives from the well characterised one of UO2. Besides reminiscent modes of UO2, a band at 630 cm-1, which has a specific response to polarised light, was interpreted as characteristic of clusters of interstitial oxygen atoms. These experimental data will help to rationalise the interpretation of UO2 damaged samples
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