Quantification of ion confinement and desolvation in nanoporous carbon supercapacitors with modelling and in situ X-ray scattering

Abstract

A detailed understanding of confinement and desolvation of ions in electrically charged carbon nanopores is the key to enable advanced electrochemical energy storage and water treatment technologies. Here, we present the synergistic combination of experimental data from in situ small-angle X-ray scattering with Monte Carlo simulations of length-scale-dependent ion arrangement. In our approach, the simulations are based on the actual carbon nanopore structure and the global ion concentrations in the electrodes, both obtained from experiments. A combination of measured and simulated scattering data provides compelling evidence of partial desolvation of Cs+ and Cl ions in water even in mixed micro–mesoporous carbons with average pore size well above 1 nm. A tight attachment of the aqueous solvation shell effectively prevents complete desolvation in carbons with subnanometre average pore size. The tendency of counter-ions to change their local environment towards high confinement with increasing voltage determines conclusively the performance of supercapacitor electrodes.

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Figure 1: Combined X-ray scattering and modelling approach.
Figure 2: The degree of confinement and desolvation.
Figure 3: Quantifying the local rearrangement of ions as a function of charge.
Figure 4: Impact of local environment on the capacitive performance of carbon electrodes.

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Acknowledgements

O.P., C.P. and C.K. acknowledge financial support from the Austrian Klima- und Energiefonds via the FFG programme ‘Energieforschung’ (Project: Hybrid Supercap). We are grateful to G. Fritz-Popovski and R. Meisels (both MU Leoben) for helpful discussions on GRFs and on electrostatics, and to all colleagues at the Institute of Physics (MU Leoben) who provided CPU power. The access to the EVA HPC Cluster (K. Flicker, ZID, MU Leoben, and T. Antretter, Institute of Mechanics, MU Leoben) for providing extensive computational time is also gratefully acknowledged. All authors acknowledge the synchrotron radiation source ELETTRA (Trieste, Italy) for providing beam time. The authors thank D. Weingarth and S. Fleischmann (both INM) for discussions. V.P., A.S. and N.J. thank E. Arzt (INM) for his continuing support.

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Contributions

C.P., C.K., M.B. and H.A. carried out the in situ scattering experiments. N.J. and A.S. supported the electrochemical measurements. C.P., C.K. and M.A.H. developed the simulation toolkit. V.P. and O.P. conceptualized the work. All authors contributed to data analysis and C.P., V.P. and O.P. wrote the paper.

Corresponding authors

Correspondence to V. Presser or O. Paris.

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The authors declare no competing financial interests.

Supplementary information

Supplementary Information

Supplementary Figures 1–5, Supplementary Discussion, Supplementary References. (PDF 1203 kb)

41560_2017_BFnenergy2016215_MOESM79_ESM.wmv

3D plot of the ion-populated structure of activated carbon (AC1). (WMV 22153 kb)

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3D plot of the ion-populated structure of activated carbon (AC1). (WMV 22153 kb)

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Prehal, C., Koczwara, C., Jäckel, N. et al. Quantification of ion confinement and desolvation in nanoporous carbon supercapacitors with modelling and in situ X-ray scattering. Nat Energy 2, 16215 (2017). https://doi.org/10.1038/nenergy.2016.215

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