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Issue 3, 2018
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Combining battery-like and pseudocapacitive charge storage in 3D MnOx@carbon electrode architectures for zinc-ion cells

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Abstract

We demonstrate that electrodes comprising nanoscale, birnessite-type manganese oxide affixed to carbon nanofoam paper (MnOx@CNF) exhibit two distinct charge-storage mechanisms—battery-like Zn2+ insertion/de-insertion and pseudocapacitance—when electrochemically cycled in aqueous electrolytes that include both Na+ and Zn2+ salts. When the mixed-electrolyte composition is 0.75 M Na2SO4 + 0.25 M ZnSO4 (i.e., “6[Na+] : 1[Zn2+]”), the MnOx@CNF electrode delivers high specific capacity at low rates, approaching theoretical capacity for Zn2+ insertion/de-insertion at MnOx. At high rates (>10C) the Na+-supported pseudocapacitance mechanism maintains charge-storage capacity well above that observed with electrolytes that contain only ZnSO4. Impedance analysis was performed to discriminate between these distinct charge-storage mechanisms by visualizing the frequency- and potential-dependent capacitance as 3D Bode plots. In the 6[Na+] : 1[Zn2+] electrolyte, the potential-independent pseudocapacitance is augmented by reversible Zn2+-based redox processes between 1.4 and 1.8 V vs. Zn/Zn2+. Galvanostatic testing with two-electrode zinc-ion cells that pair MnOx@CNF with a zinc foil negative electrode proves the practical performance advantages of combining pseudocapacitance and Zn2+-insertion mechanisms: higher energy efficiency and greater specific power in the 6[Na+] : 1[Zn2+] electrolyte compared to 1 M ZnSO4.

Graphical abstract: Combining battery-like and pseudocapacitive charge storage in 3D MnOx@carbon electrode architectures for zinc-ion cells

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Publication details

The article was received on 06 Nov 2017, accepted on 15 Dec 2017 and first published on 19 Dec 2017


Article type: Paper
DOI: 10.1039/C7SE00540G
Citation: Sustainable Energy Fuels, 2018,2, 626-636
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    Combining battery-like and pseudocapacitive charge storage in 3D MnOx@carbon electrode architectures for zinc-ion cells

    J. S. Ko, M. B. Sassin, J. F. Parker, D. R. Rolison and Jeffrey W. Long, Sustainable Energy Fuels, 2018, 2, 626
    DOI: 10.1039/C7SE00540G

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