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Issue 7, 2013
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Unraveling the potential and pore-size dependent capacitance of slit-shaped graphitic carbon pores in aqueous electrolytes

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Abstract

Understanding and leveraging physicochemical processes at the pore scale are believed to be essential to future performance improvements of supercapacitors and capacitive desalination (CD) cells. Here, we report on a combination of electrochemical experiments and fully atomistic simulations to study the effect of pore size and surface charge density on the capacitance of graphitic nanoporous carbon electrodes. Specifically, we used cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) to study the effect of potential and pore size on the capacitance of nanoporous carbon foams. Molecular dynamics simulations were performed to study the pore-size dependent accumulation of aqueous electrolytes in slit-shaped graphitic carbon pores of different widths (0.65 to 1.6 nm). Experimentally, we observe a pronounced increase of the capacitance of sub-nm pores as the applied potential window gets wider, from a few F g−1 for narrow potential ranges (−0.3 to 0.3 V vs. Ag/AgCl) to ∼40 F g−1 for wider potential windows (−0.9 V to 0.9 V vs. Ag/AgCl). By contrast, the capacitance of wider pores does not depend significantly on the applied potential window. Molecular dynamics simulations confirm that the penetration of ions into pores becomes more difficult with decreasing pore width and increasing strength of the hydration shell. Consistent with our experimental results, we observe a pore- and ion-size dependent threshold-like charging behavior when the pore width becomes comparable to the size of the hydrated ion (0.65 nm pores for Na+ and 0.79 nm pores for Cl ions). The observed pore-size and potential dependent accumulation of ions in slit-shaped carbon pores can be explained by the hydration structure of the ions entering the charged pores. The results are discussed in view of their effect on energy-storage and desalination efficiency.

Graphical abstract: Unraveling the potential and pore-size dependent capacitance of slit-shaped graphitic carbon pores in aqueous electrolytes

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Publication details

The article was received on 24 Sep 2012, accepted on 18 Dec 2012 and first published on 18 Dec 2012


Article type: Paper
DOI: 10.1039/C2CP43361C
Citation: Phys. Chem. Chem. Phys., 2013,15, 2309-2320
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    Unraveling the potential and pore-size dependent capacitance of slit-shaped graphitic carbon pores in aqueous electrolytes

    R. K. Kalluri, M. M. Biener, M. E. Suss, M. D. Merrill, M. Stadermann, J. G. Santiago, T. F. Baumann, J. Biener and A. Striolo, Phys. Chem. Chem. Phys., 2013, 15, 2309
    DOI: 10.1039/C2CP43361C

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