In Situ NMR and Electrochemical Quartz Crystal Microbalance Reveal the Structure of the Electric Double-Layer in Supercapacitor Electrodes
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Griffin, J., Forse, A., Tsai, W., Taberna, P., Simon, P., & Grey, C. (2015). In Situ NMR and Electrochemical Quartz Crystal Microbalance Reveal the Structure of the Electric Double-Layer in Supercapacitor Electrodes. Nature Materials, 14 812-819. https://doi.org/10.1038/nmat4318
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.
A.C.F., J.M.G. and C.P.G. acknowledge the Sims Scholarship (A.C.F.), EPSRC (through the Supergen consortium for J.M.G.) and the EU ERC (through an Advanced Fellowship to C.P.G.) for financial support. P.S. and W.-Y.T. acknowledge support from the European Research Council (ERC, Advanced Grant, ERC-2011-AdG, Project 291543–IONACES). P.S. also acknowledges financial support from the Chair ‘Embedded Multi-Functional Nanomaterials’ from the Airbus Group Foundation. A.C.F. and J.M.G. thank the NanoDTC Cambridge for travel funding.
UNIVERSITY OF OXFORD (FB EPSRC) (EP/L019469/1)
EPSRC (via Imperial College London) (EP/K002252/1)
External DOI: https://doi.org/10.1038/nmat4318
This record's URL: https://www.repository.cam.ac.uk/handle/1810/248674