Origin of capacitance decay for a flower-like δ-MnO2 aqueous supercapacitor electrode: The quantitative surface and electrochemical analysis

C. Justin Raj, Ramu Manikandan, Periyasamy Sivakumar, David O. Opar, A. Dennyson Savariraj, Won Je Cho, Hyun Jung, Byung Chul Kim

Research output: Contribution to journalArticlepeer-review

32 Scopus citations

Abstract

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.

Original languageEnglish
Article number162199
JournalJournal of Alloys and Compounds
Volume892
DOIs
StatePublished - 5 Feb 2022

Keywords

  • Impedance spectroscopy
  • Ion intercalation
  • Layered nanostructure
  • Manganese oxide
  • Supercapacitor

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