Understanding the MXene Pseudocapacitance

doi:10.1021/acs.jpclett.8b00200

Title: Understanding the MXene Pseudocapacitance

Abstract

MXenes have attracted great attention as next-generation capacitive energy-storage materials, but the mechanisms underlying their pseudocapacitive behavior are not well understood. Here we provide a theoretical description of the surface redox process of Ti3C2Tx (T = O, OH), a prototypical MXene, in 1 M H2SO4 electrolyte, based on joint density functional theory with an implicit solvation model and the analysis of Gibbs free energy under a constant-electrode potential. From the dependence of the O/OH ratio (or the surface H coverage) and the surface charge on the applied potential, we obtain a clear picture of the capacitive energy-storage mechanism of Ti3C2Tx that shows good agreement with previous experimental findings in terms of the integral capacitance and Ti valence change. We find a voltage-dependent redox/double-layer co-charging behavior: the capacitive mechanism is dominated by the redox process, but the electric double-layer charge works against the redox process. This new insight may be useful in improving the capacitance of MXenes.

Authors:

Zhan, Cheng ^[1];

^[2]; Lukatskaya, Maria ^[3];

^[4];

^[3];

^[1]

Department of Chemistry, University of California, Riverside, California 92521, United States
Department of Physics and Engineering Physics, Tulane University, New Orleans, Louisiana 70118, United States
Department of Materials Science and Engineering and A. J. Drexel Nanomaterials Institute, Drexel University, Philadelphia, Pennsylvania 19104, United States
Computational Sciences and Engineering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States; Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States

Publication Date:: 2018-02-20

Research Org.:: Lawrence Berkeley National Laboratory-National Energy Research Scientific Computing Center; Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

Sponsoring Org.:: USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)

OSTI Identifier:: 1493989

Alternate Identifier(s):: OSTI ID: 1484259

Grant/Contract Number:: AC02-05CH11231; AC05-00OR22725

Resource Type:: Accepted Manuscript

Journal Name:: Journal of Physical Chemistry Letters

Additional Journal Information:: Journal Volume: 9; Journal Issue: 6; Journal ID: ISSN 1948-7185

Publisher:: American Chemical Society

Country of Publication:: United States

Language:: English

Subject:: 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats


                    Zhan, Cheng, Naguib, Michael, Lukatskaya, Maria, Kent, Paul R.  C., Gogotsi, Yury, and Jiang, De-en. Understanding the MXene Pseudocapacitance.  United States: N. p., 2018. 
        Web.  doi:10.1021/acs.jpclett.8b00200.

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                    Zhan, Cheng, Naguib, Michael, Lukatskaya, Maria, Kent, Paul R.  C., Gogotsi, Yury, & Jiang, De-en. Understanding the MXene Pseudocapacitance.  United States.  doi:10.1021/acs.jpclett.8b00200.

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                    Zhan, Cheng, Naguib, Michael, Lukatskaya, Maria, Kent, Paul R.  C., Gogotsi, Yury, and Jiang, De-en. Tue .  
        "Understanding the MXene Pseudocapacitance".  United States.  doi:10.1021/acs.jpclett.8b00200.  https://www.osti.gov/servlets/purl/1493989.

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@article{osti_1493989,

  title        = {Understanding the MXene Pseudocapacitance},

  author       = {Zhan, Cheng and Naguib, Michael and Lukatskaya, Maria and Kent, Paul R.  C. and Gogotsi, Yury and Jiang, De-en},

  abstractNote = {MXenes have attracted great attention as next-generation capacitive energy-storage materials, but the mechanisms underlying their pseudocapacitive behavior are not well understood. Here we provide a theoretical description of the surface redox process of Ti3C2Tx (T = O, OH), a prototypical MXene, in 1 M H2SO4 electrolyte, based on joint density functional theory with an implicit solvation model and the analysis of Gibbs free energy under a constant-electrode potential. From the dependence of the O/OH ratio (or the surface H coverage) and the surface charge on the applied potential, we obtain a clear picture of the capacitive energy-storage mechanism of Ti3C2Tx that shows good agreement with previous experimental findings in terms of the integral capacitance and Ti valence change. We find a voltage-dependent redox/double-layer co-charging behavior: the capacitive mechanism is dominated by the redox process, but the electric double-layer charge works against the redox process. This new insight may be useful in improving the capacitance of MXenes.},

  doi          = {10.1021/acs.jpclett.8b00200},

  journal      = {Journal of Physical Chemistry Letters},

  number       = 6,

  volume       = 9,

  place        = {United States},

  year         = {2018},

  month        = {2}

}

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DOI: 10.1021/acs.jpclett.8b00200

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Figures / Tables:

Figure 1: Partially protonated Ti₃C₂O₂ as a prototypical MXene electrode in an acidic electrolyte: side view (left) and top view (right). The 2D material has an ideal surface area (counting two sides) of ∼479 m²/g.

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