Herein, we report the electrochemical energy storage performance of δ-MnO2 (K-birnessite MnO2) as supercapacitor electrode material in Na2SO4 aqueous electrolyte. The electrode exhibited considerable electrochemical performances due to the fast intercalation/deintercalation reactions of Na+ on the pseudocapacitive MnO2 surface. However, a long-term cyclic stability test of the electrode at a low specific current (1 A g−1) demonstrated a decline in its initial capacitance value to the tune of ~ 21%. To quantify the above discrepancy, the electrochemical intercalation of Na+ ions on the electrode surface was quantitatively studied employing electrochemical impedance spectroscopy, EDAX analysis and X-ray photoelectron spectroscopy. Further, the surface of the electrode was analyzed by performing complete charge and charge/discharge measurements at a low specific current of 0.1 A g−1. These results disclosed that, besides the surface intercalation/deintercalation reactions, some Na+ ions have permanently substituted into the bulk (layer) of δ-MnO2 by replacing the host K ions from the layered nanostructure. Thus, this finding suggests that Na+ ions replaced in the site of K in δ-MnO2 considerably affect the electrochemical properties of the supercapacitor electrode.
|Journal||Journal of Alloys and Compounds|
|State||Published - 5 Feb 2022|
Bibliographical noteFunding Information:
The author H. Jung acknowledges the Basic Science Research Program through the National Research Foundation of Korea (NRF) of Korea, South Korea funded by the Ministry of Education (No.: NRF-2016R1D1A1B01009640 ).
The author B.C. Kim acknowledges the National Research Foundation of Korea (NRF) grant funded by the South Korea government (MSIT) (No. 2020112382 ).
© 2021 Elsevier B.V.
- Impedance spectroscopy
- Ion intercalation
- Layered nanostructure
- Manganese oxide