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Effects of interlayer confinement and hydration on capacitive charge storage in birnessite


Nanostructured birnessite exhibits high specific capacitance and nearly ideal capacitive behaviour in aqueous electrolytes, rendering it an important electrode material for low-cost, high-power energy storage devices. The mechanism of electrochemical capacitance in birnessite has been described as both Faradaic (involving redox) and non-Faradaic (involving only electrostatic interactions). To clarify the capacitive mechanism, we characterized birnessite’s response to applied potential using ex situ X-ray diffraction, electrochemical quartz crystal microbalance, in situ Raman spectroscopy and operando atomic force microscope dilatometry to provide a holistic understanding of its structural, gravimetric and mechanical responses. These observations are supported by atomic-scale simulations using density functional theory for the cation-intercalated structure of birnessite, ReaxFF reactive force field-based molecular dynamics and ReaxFF-based grand canonical Monte Carlo simulations on the dynamics at the birnessite–water–electrolyte interface. We show that capacitive charge storage in birnessite is governed by interlayer cation intercalation. We conclude that the intercalation appears capacitive due to the presence of nanoconfined interlayer structural water, which mediates the interaction between the intercalated cation and the birnessite host and leads to minimal structural changes.

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Fig. 1: Conceptual comparison of cation adsorption at a planar electrochemical interface and into a nanoconfined interlayer of an electrode material.
Fig. 2: Structure and morphology of electrodeposited birnessite thin films.
Fig. 3: Electrochemical and structural behaviour of birnessite in 0.5 M K2SO4.
Fig. 4: Cation-dominated capacitive charge storage in birnessite.
Fig. 5: Changes in the local and electronic structures of birnessite during K+ and H2O (de)intercalation.
Fig. 6: Effect of charge stratification on the K+–OMn distance.

Data availability

Experimental data (electrochemistry, Raman, XRD, EQCM and AFM) and simulation data (ReaxFF and DFT) are available in this repository: Boyd, S., Ganeshan, K., Tsai, W.-Y., Tao Wu, Saeed, S., Jiang, D., Balke, N., van Duin, A. & Augustyn, V. Effects of interlayer confinement and hydration on capacitive charge storage in birnessite. (Materials Cloud Archive 2021.X, 2021);

Code availability

The DFT simulations were performed using VASP, which is available under license from VASP ( The ReaxFF simulations were performed using the ReaxFF module within the ADF code. ADF is available under license from SCM Amsterdam ( Force fields and input files associated with this work can be obtained by a request through the Penn State Materials Computation Center website:


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This work was supported as part of the Fluid Interface Reactions, Structures and Transport, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Basic Energy Sciences at Oak Ridge National Laboratory under contract no. DE-AC0500OR22725 with UT Battelle, LLC (V.A., N.B., D.-E.J. and A.C.T.v.D.). S.B. acknowledges a graduate fellowship through the National Science Foundation Graduate Research Fellowship Program under grant no. 571800. This work was performed in part at the Analytical Instrumentation Facility (AIF) at North Carolina State University, which is supported by the State of North Carolina and the National Science Foundation (award no. ECCS-1542015). The AIF is a member of the North Carolina Research Triangle Nanotechnology Network (RTNN), a site in the National Nanotechnology Coordinated Infrastructure (NNCI). Operando AFM was conducted at the Center for Nanophase Materials Sciences, which is a US Department of Energy Office of Science User Facility.

Author information




S.B. and V.A. developed the experimental study. S.B. performed materials synthesis, aqueous electrochemistry, Raman, XRD and EQCM. S.S. performed non-aqueous electrochemistry. S.B., W.-Y.T. and N.B. performed AFM. K.G. performed ReaxFF simulations. T.W. performed DFT simulations. N.B., D.-E.J., A.C.T.v.D. and V.A. supervised the project. All authors contributed to the discussion of the results and writing the paper.

Corresponding author

Correspondence to Veronica Augustyn.

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The authors declare no competing interests.

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Peer review information Nature Materials thanks Thierry Brousse, Patrice Simon and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–17, Tables 1 and 2, and Methods.

Supplementary Video 1

ReaxFF GCMC simulation intercalating K+ cations and H2O molecules in dry MnO2. The local inhomogeneity of species intercalation causes wrinkling of the MnO2 layers.

Supplementary Video 2

ReaxFF GCMC simulation intercalating K+ cations into MnO2·0.25(H2O).

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Boyd, S., Ganeshan, K., Tsai, WY. et al. Effects of interlayer confinement and hydration on capacitive charge storage in birnessite. Nat. Mater. 20, 1689–1694 (2021).

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