Journal
NATURE MATERIALS
Volume 14, Issue 8, Pages 812-+Publisher
NATURE PUBLISHING GROUP
DOI: 10.1038/NMAT4318
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Funding
- Sims Scholarship
- EPSRC (through Supergen consortium)
- EU ERC
- European Research Council (ERC, Advanced Grant ERC-AdG) [291543-IONACES]
- Chair 'Embedded Multi-Functional Nanomaterials' from Airbus Group Foundation
- NanoDTC Cambridge
- EPSRC [EP/K002252/1, EP/L019469/1] Funding Source: UKRI
- Engineering and Physical Sciences Research Council [EP/L019469/1, EP/K002252/1] Funding Source: researchfish
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Supercapacitors store charge through the electrosorption of ions on microporous electrodes. Despite major efforts to understand this phenomenon, a molecular-level picture of the electrical double layer in working devices is still lacking as few techniques can selectively observe the ionic species at the electrode/electrolyte interface. Here, we use in situ NMR to directly quantify the populations of anionic and cationic species within a working microporous carbon supercapacitor electrode. Our results show that charge storage mechanisms are different for positively and negatively polarized electrodes for the electrolyte tetraethylphosphonium tetrafluoroborate in acetonitrile; for positive polarization charging proceeds by exchange of the cations for anions, whereas for negative polarization, cation adsorption dominates. In situ electrochemical quartz crystal microbalance measurements support the NMR results and indicate that adsorbed ions are only partially solvated. These results provide new molecular-level insight, with the methodology offering exciting possibilities for the study of pore/ion size, desolvation and other effects on charge storage in supercapacitors.
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