title: The critical role of point defects in improving the specific capacitance of δ-MnO2nanosheets.
abstract: 3D porous nanostructures built from 2D δ-MnO2nanosheets are an environmentally friendly and industrially scalable class of supercapacitor electrode material. While both the electrochemistry and defects of this material have been studied, the role of defects in improving the energy storage density of these materials has not been addressed. In this work, δ-MnO2nanosheet assemblies with 150 m2g-1specific surface area are prepared by exfoliation of crystalline KxMnO2and subsequent reassembly. Equilibration at different pH introduces intentional Mn vacancies into the nanosheets, increasing pseudocapacitance to over 300 F g-1, reducing charge transfer resistance as low as 3 Ω, and providing a 50% improvement in cycling stability. X-ray absorption spectroscopy and high-energy X-ray scattering demonstrate a correlation between the defect content and the improved electrochemical performance. The results show that Mn vacancies provide ion intercalation sites which concurrently improve specific capacitance, charge transfer resistance and cycling stability.
authors.affiliation: Kazuo Inamori School of Engineering, Alfred University, Alfred, New York 14802, USA.
authors.forename: Peng
authors.initials: P
authors.lastname: Gao
authors.affiliation: Kazuo Inamori School of Engineering, Alfred University, Alfred, New York 14802, USA.
authors.forename: Peter
authors.initials: P
authors.lastname: Metz
authors.affiliation: Kazuo Inamori School of Engineering, Alfred University, Alfred, New York 14802, USA.
authors.forename: Trevyn
authors.initials: T
authors.lastname: Hey
authors.affiliation: Kazuo Inamori School of Engineering, Alfred University, Alfred, New York 14802, USA.
authors.forename: Yuxuan
authors.initials: Y
authors.lastname: Gong
authors.affiliation: Kazuo Inamori School of Engineering, Alfred University, Alfred, New York 14802, USA.
authors.forename: Dawei
authors.initials: D
authors.lastname: Liu
authors.affiliation: Kazuo Inamori School of Engineering, Alfred University, Alfred, New York 14802, USA.
authors.forename: Doreen D
authors.initials: DD
authors.lastname: Edwards
authors.affiliation: Hitachi High-Technologies Canada, Inc., 89 Galaxy Blvd, Suite 14, Toronto, Ontario, Canada M9W 6A4.
authors.forename: Jane Y
authors.initials: JY
authors.lastname: Howe
authors.affiliation: Cornell High Energy Synchrotron Source, Cornell University, Ithaca, New York 14853, USA.
authors.forename: Rong
authors.initials: R
authors.lastname: Huang
authors.affiliation: Kazuo Inamori School of Engineering, Alfred University, Alfred, New York 14802, USA.
authors.forename: Scott T
authors.initials: ST
authors.lastname: Misture