Mixed valence Zn-Co-layered double hydroxides and their exfoliated nanosheets with electrode functionality

Myong A. Woo, Min Sun Song, Tae Woo Kim, In Young Kim, Ji Yun Ju, Young Soo Lee, Seung Joo Kim, Jin Ho Choy, Seong Ju Hwang

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110 Scopus citations


New phases of Zn-Co-layered double hydroxides (Zn-Co-LDHs) were synthesized for the first time via a co-precipitation reaction using hydrogen peroxide as an oxidant. According to powder X-ray diffraction and field emission-scanning electron microscopy, both nitrate- and sulfate-forms of the Zn-Co-LDHs crystallized with the brucite-type layer structure having interlayer nitrate and sulfate anions, respectively, and commonly showed plate-like morphology with a crystal size of several hundred nanometers. dc magnetic susceptibility measurements revealed that the Zn-Co-LDHs displayed ferromagnetic/ antiferromagnetic transitions below 15 K and the magnetic moment calculated from the paramagnetic region (30-300 K) indicated the co-existence of weak field Co2+ and strong field Co3+ ions. The mixed oxidation state of Co2+/Co3+ was confirmed by the results of iodometry and X-ray absorption near-edge structure spectroscopy. The heat-treatment for the Zn-Co-LDHs at elevated temperatures produced mixed metal oxide nanocomposites composed of spinel ZnCo2O4 and wurzite ZnO phases. The colloidal suspension of exfoliated Zn-Co-LDH nanosheets could be synthesized by dispersion of the pristine LDH materials in formamide, which was confirmed by the Tyndall phenomenon, high resolution-transmission electron microscopy/selected area electron diffraction, and UV-vis spectroscopy. The Zn-Co-LDH film fabricated with the restacked nanosheets exhibited pseudocapacitive behavior with a large specific capacitance and a good capacitance retention. The present findings underscore that the newly synthesized mixed valence Zn-Co-LDH phases showed promising functionality as a supercapacitor electrode material and also showed interesting magnetic coupling behavior.

Original languageEnglish
Pages (from-to)4286-4292
Number of pages7
JournalJournal of Materials Chemistry
Issue number12
StatePublished - 28 Mar 2011


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