Molecular understanding of charge storage and charging dynamics in supercapacitors with MOF electrodes and ionic liquid electrolytes

Abstract

We performed constant-potential molecular dynamics simulations to analyse the double-layer structure and capacitive performance of supercapacitors composed of conductive metal–organic framework (MOF) electrodes and ionic liquids. The molecular modelling clarifies how ions transport and reside inside polarized porous MOFs, and then predicts the corresponding potential-dependent capacitance in characteristic shapes. The transmission line model was adopted to characterize the charging dynamics, which further allowed evaluation of the capacitive performance of this class of supercapacitors at the macroscale from the simulation-obtained data at the nanoscale. These ‘computational microscopy’ results were supported by macroscopic electrochemical measurements. Such a combined nanoscale-to-macroscale investigation demonstrates the potential of MOF supercapacitors for achieving unprecedentedly high volumetric energy and power densities. It gives molecular insights into preferred structures of MOFs for accomplishing consistent performance with optimal energy–power balance, providing a blueprint for future characterization and design of these new supercapacitor systems.

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Fig. 1: Schematics of molecular simulations of MOF-based supercapacitors.
Fig. 2: In-pore charge/ion density and orientation distributions.
Fig. 3: Capacitance and energy density.
Fig. 4: Charging process at nanoscale.
Fig. 5: Electrochemical measurement of Ni3(HITP)2 electrodes in a symmetrical supercapacitor cell.
Fig. 6: Capacitive performance predicted for practical cell-size supercapacitors.

Data availability

The theoretical and experimental data presented in this work are available from the corresponding authors on reasonable request.

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Acknowledgements

G.F., S.B., Ming Chen, L.N., Mingyu Chen, T.W., J.W., R.W. and J.F. acknowledge the funding support from the National Natural Science Foundation of China (51876072, 51836003) and Shenzhen Basic Research Project (JCYJ20170307171511292). S.B. and R.W. thank the China Scholarship Council for financial support. A.A.K. acknowledges the Leverhulme Trust for funding (RPG-2016-223), HUST for the support of this project through the HUST Honorary Professorship, and Imperial College for the support of this form of collaboration between the involved HUST and Imperial groups, and thanks the Imperial College–MIT seed fund for supporting the collaboration between the two universities. M.D., H.B. and T.C. thank the Army Research Office (W911NF-17-1-0174) for support. The computation was completed using the Tianhe II supercomputer in the National Supercomputing Center in Guangzhou. Part of the characterization was performed at the Analytical & Testing Center of HUST.

Author information

G.F. and A.A.K. set the strategy of this project in consultation with M.D.; G.F. devised simulation approaches; G.F. and M.D. designed the experiment. S.B. performed the major part of the MD simulations with participation of Ming Chen, R.W. and J.F.; Ming Chen did all density functional theory calculations; H.B., L.N., Mingyu Chen, T.W., J.W. and T.C. carried out the experiment, in which L.N. developed MOF synthesis procedures; G.F., S.B., Ming Chen, L.N., Mingyu Chen and A.A.K. analysed the data and wrote the manuscript; G.F., S.B., A.A.K., Ming Chen, H.B. and M.D. contributed to the discussion of results, editing and revising the paper.

Correspondence to Alexei A. Kornyshev or Guang Feng.

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Supplementary Figs. 1–29, discussion and Tables 1–6.

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Bi, S., Banda, H., Chen, M. et al. Molecular understanding of charge storage and charging dynamics in supercapacitors with MOF electrodes and ionic liquid electrolytes. Nat. Mater. (2020). https://doi.org/10.1038/s41563-019-0598-7

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