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Cite This: ACS Appl. Mater. Interfaces 2018, 10, 23721−23730
Ultrathin Metal−Organic Framework Nanosheet-Derived Ultrathin Co3O4 Nanomeshes with Robust Oxygen-Evolving Performance and Asymmetric Supercapacitors Guijuan Wei,†,§ Zhen Zhou,§ Xixia Zhao,§ Weiqing Zhang,‡ and Changhua An*,†,‡,§ †
Tianjin Key Laboratory of Organic Solar Cells and Photochemical Conversion, School of Chemistry and Chemical Engineering and Tianjin Key Laboratory of Advanced Functional Porous Materials, Institute for New Energy Materials & Low-Carbon Technologies, Tianjin University of Technology, Tianjin 300384, P. R. China § College of Science and College of Chemical Engineering, China University of Petroleum, Qingdao 266580, P. R. China Downloaded via TUFTS UNIV on July 19, 2018 at 19:57:01 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.
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S Supporting Information *
ABSTRACT: Ultrathin metal−organic framework (MOF) nanosheets possessing inherent advantages of both two-dimensional (2D) features and MOFs are attracting intensive research interest. The direct manufacture of MOF nanosheets is still a challenge up to now. Here, we have developed a novel bottom-up approach to synthesize zeolitic imidazolate framework-67 (ZIF-67) nanosheets, which can be in situ converted into Co3O4 ultrathin nanomeshes after thermal treatment. Interestingly, the obtained Co3O4 nanomeshes are rich in oxygen defects, providing fruitful active sites for the faradaic reaction. The modified electrode exhibits a large specific capacitance (1216.4 F g−1 at 1 A g−1), as well as a high rate capability (925.5 F g−1 at 20 A g−1). Moreover, an asymmetric supercapacitor made of Co3O4//activated carbon shows an energy density of 46.5 Wh kg−1 at 790.7 W kg−1. Furthermore, the 2D Co3O4 ultrathin nanomeshes show an outstanding performance for the oxygen evolution reaction with an overpotential of 230 mV at the onset potential and a small Tafel slope of 74.0 mV dec−1. The present method presents a facile avenue to the preparation of other 2D ultrathin metal oxide nanostructures with various applications in energy catalysis and conversion. KEYWORDS: two-dimensional MOF, cobalt oxide, oxygen evolution, supercapacitor
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INTRODUCTION Metal−organic frameworks (MOFs) have been used for gas adsorption and separation, new energy production, and catalysis, due to their tunable structure with high surface areas, and well-developed pores.1−3 In the past few years, the control over the shaped MOFs with different dimensions has been a hot topic to optimize their performances. Twodimensional (2D) ultrathin MOF nanosheets have been receiving increasing attention in the field of new energy production.4,5 Their inherent advantages include: (i) nanoscale sheets allow rapid mass transport and superior electron transfer; (ii) enhanced well-defined interfaces between the electrolyte and electrode ensure the fast charge transfer along the 2D basal planes, consequently enhancing the catalytic performance; (iii) highly open structures make extremely high percentages of exposed surface atoms, which possess coordinately unsaturated metal sites to achieve high catalytic activity. To date, top-down (delamination of bulk MOFs) and bottom-up methods (direct growth of 2D MOF nanosheets from solution) can be used to prepare 2D MOF nanosheets. The former one is facile and efficient to weaken the interlayer force in MOFs by sonication or shaking operation.6−8 © 2018 American Chemical Society
However, it is not viable to synthesize high quality MOF nanosheets on a large scale (the yield
