Issue 22, 2015

Defective by design: vanadium-substituted iron oxide nanoarchitectures as cation-insertion hosts for electrochemical charge storage

Abstract

Vanadium-substituted iron oxide aerogels (2 : 1 Fe : V ratio; VFe2Ox) are synthesized using an epoxide-initiated sol–gel method to form high surface-area, mesoporous materials in which the degree of crystallinity and concentration of defects are tuned via thermal treatments under controlled atmospheres. Thermal processing of the X-ray amorphous, as-synthesized VFe2Ox aerogels at 300 °C under O2-rich conditions removes residual organic byproducts while maintaining a highly defective γ-Fe2O3-like local structure with minimal long-range order and vanadium in the +5 state. When as-synthesized VFe2Ox aerogels are heated under low partial pressure of O2 (e.g., flowing argon), a fraction of vanadium sites are reduced to the +4 state, driving crystallization to a Fe3O4-like cubic phase. Subsequent thermal oxidation of this nanocrystalline VFe2Ox aerogel re-oxidizes vanadium +4 to +5, creating additional cation vacancies and re-introducing disordered oxide domains. We correlate the electrochemical charge-storage properties of this series of VFe2Ox aerogels with their degree of order and chemical state, as verified by X-ray diffraction, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy. We find that the disordered O2-heated VFe2Ox aerogel yields the highest Li+- and Na+-insertion capacities among this series, approaching 130 mA h g−1 and 70 mA h g−1, respectively. Direct heat-treatment of the VFe2Ox aerogel in flowing argon to yield the partially reduced, nanocrystalline form results in significantly lower Li+-insertion capacity (77 mA h g−1), which improves to 105 mA h g−1 by thermal oxidation to create additional vacancies and structural disorder.

Graphical abstract: Defective by design: vanadium-substituted iron oxide nanoarchitectures as cation-insertion hosts for electrochemical charge storage

Supplementary files

Article information

Article type
Paper
Submitted
26 Feb 2015
Accepted
03 May 2015
First published
14 May 2015

J. Mater. Chem. A, 2015,3, 12059-12068

Author version available

Defective by design: vanadium-substituted iron oxide nanoarchitectures as cation-insertion hosts for electrochemical charge storage

C. N. Chervin, J. S. Ko, B. W. Miller, L. Dudek, A. N. Mansour, M. D. Donakowski, T. Brintlinger, P. Gogotsi, S. Chattopadhyay, T. Shibata, J. F. Parker, B. P. Hahn, D. R. Rolison and J. W. Long, J. Mater. Chem. A, 2015, 3, 12059 DOI: 10.1039/C5TA01507C

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