X-ray photoelectron spectroscopy and in situ X-ray absorption spectroscopy studies on reversible insertion/desertion of dicyanamide anions into/from manganese oxide in ionic liquid

Jeng-Kuei Chang*, Ming Tsung Lee, Wen Ta Tsai, Ming Jay Deng, I. Wen Sun

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

74 Scopus citations

Abstract

Pseudocapacitive characteristics of manganese (Mn) oxide were recognized in aprotic ionic liquid (IL), namely, butylmethylpyrrolidinium - dicyanamide (BMP - DCA), within a potential window of 3 V. The electrochemical energy storage mechanism was examined using X-ray photoelectron spectroscopy and in situ X-ray absorption spectroscopy. It was confirmed that the DCA- anions, instead of the bigger BMP+ cations, were the working species that compensate the Mn valent state variation upon charging and discharging in the IL electrolyte. During oxidation of the Mn oxide electrode, to keep the charges balanced, the quasi-linear DCA- anions were inserted into the tunnels between the MnO6 octahedral units, expanding the structural framework. Importantly, a highly reversible process was observed during the subsequent reduction step. XPS depth profiling analyses showed that the electrochemical reaction thickness was approximately 50 nm.

Original languageEnglish
Pages (from-to)2688-2695
Number of pages8
JournalChemistry of Materials
Volume21
Issue number13
DOIs
StatePublished - 14 Jul 2009

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