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NMR Spectroscopy Reveals the Charging Mechanisms of Supercapacitors

Seminar Group: 

Speaker: 

Alexander C. Forse

Address: 

Department of Chemistry
University of Cambridge, UK

Date: 

Monday, April 27, 2015 - 4:00pm

Location: 

MRL Room 2053

Host: 

Prof. Ram Seshadri

Supercapacitors are high power energy storage devices that store charge by the electrostatic adsorption of ions at the electrode-­‐electrolyte interface.[1] NMR methods have recently been developed to study the structure  and dynamics of this interface in porous carbon electrode materials.[2,3] Density functional theory calculations  and experimental NMR spectra have shown that the chemical shifts observed for adsorbed ions are sensitive to the local structure  of  the  carbon  surfaces,  affording  a  new  method  to  characterise  carbon  structures.[4]  In  situ  NMR experiments performed on working supercapacitors have then allowed us to study the mechanisms of  charge storage. Measurements at different charge states have revealed that a number of different charging  mechanisms can operate.[5,6] Ion adsorption, desorption and exchange can all contribute, with the exact mechanism depending on the electrode polarisation and the choice of electrolyte. Further experiments,[7] as well as lattice simulations,[8] on ionic liquids have shown that the lineshape of the resonance arising from adsorbed  ions is related to their mobility. This has allowed us to rationalise the different power performances of  supercapacitors  with  different electrolytes.

References:

1.    Simon, P.; Gogotsi, Y. Nat. Mater. 2008, 7, 845. 

2.    Forse, A. C.; Griffin, J. M.; Wang, H.; Trease, N. M.; Presser, V.; Gogotsi, Y.; Simon, P.; Grey, C. P. Phys. Chem. Chem. Phys.

2013, 15, 7722. 

3.    Borchardt, L.; Oschatz, M.; Paasch, S.; Kaskel, S.; Brunner, E. Phys. Chem. Chem. Phys. 2013, 15, 15177. 

4.    Forse, A. C.; Griffin, J. M.; Presser, V.; Gogotsi, Y.; Grey, C. P. J. Phys. Chem. C 2014, 118, 7508. 

5.    Wang, H.; Forse, A. C.; Griffin, J. M.; Trease, N. M.; Trognko, L.; Taberna, P.-­‐L.; Simon, P.; Grey, C. P. J. Am. Chem. Soc. 2013,

135, 18968.

6.    Griffin, J. M.; Forse, A. C.; Wang, H.; Trease, N. M.; Simon, P.; Grey, C. P. Faraday Disc. 2014, 176, 49. 

7.    Forse, A. C.; Griffin, J. M.; Merlet, C.; Bayley, P. M.; Wang, H.; Simon, P.; Grey, C. P. unpublished-­‐work 2015