Research Article pubs.acs.org/journal/ascecg
Fabrication of Hierarchical Porous Metal−Organic Framework Electrode for Aqueous Asymmetric Supercapacitor Weimin Gao,† Dezhi Chen,*,† Hongying Quan,‡ Ren Zou,† Wenxiu Wang,†,‡ Xubiao Luo,† and Lin Guo*,†,§ †
Key Laboratory of Jiangxi Province for Persistent Pollutants Control and Resources Recycle, School of Environmental and Chemical Engineering, Nanchang Hangkong University, No. 696, Fenghe South Avenue, Nanchang 330063, China ‡ School of Materials Science and Engineering, Nanchang Hangkong University, No. 696, Fenghe South Avenue, Nanchang 330063, China § Key Laboratory of Bio-Inspired Smart Interfacial Science and Technology of Ministry of Education, School of Chemistry and Environment, Beihang University, No. 37 Xueyuan Road, Haidian District, Beijing 100191, China S Supporting Information *
ABSTRACT: As promising electrode materials in supercapacitors, metal−organic frameworks (MOFs) have attracted significant attention. However, the poor electrical conductivity and the almost exclusively microporous structure largely limited the possibility for MOFs to fabricate high-performance electrodes of supercapacitors. To overcome these obstacles, hierarchical porous Zr-MOFs (HP-UiO-66) has been successfully fabricated using bimetallic Zn/Zr MOFs as a precursor, subsequently wiping off Zr-MOFs. When used as electrode materials for supercapacitors, under a current density of 0.2 A g−1, the specific capacitance of the prepared HP-UiO-66 is 849 F g−1, which is 8.36 times higher than the 101.5 F g−1 of bare UiO-66. The clearly enhanced electrochemical performance of HP-UiO-66 was benefited from the advantages of the hierarchical porous structure, the higher specific surface area and pore volume, as well as the sufficient surface defects. Furthermore, an aqueous asymmetric supercapacitor based on the HP-UiO-66 and porous carbon could show an energy density of 32 W h kg−1 at a power density of 240 W kg−1. This strategy may offer a versatile idea of tailoring new type of MOFs and opens the possibility of MOFs using in the future high-energy storage device. KEYWORDS: Supercapacitor, MOF, Electrode materials, Hierarchical porous, Defect
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INTRODUCTION A supercapacitor is a type of energy-storage device between double capacitance capacitor and battery, that has drawn great attention owing to high power density.1,2 To meet the requirement for higher energy and electricity supply, it is necessary to choose an appropriate and remarkable electrode material, such as carbon materials,3−7 metal oxides/sulfides8−13 and polymers.14−16 Recently, porous electrode materials have attracted intense scientific and industry attention because of their elite performance in supercapacitors.2,4,17 Whereas, traditional tailoring porous electrode materials with singlepore structures vastly limits ions and electrons diffusion. Therefore, the construction and development of porous electrode materials with favorable pore sizes are requisite, and remain a challenge. Metal−organic frameworks (MOFs), consisted of inorganic nodes and organic linkers, have emerged as a newly developed and burgeoning kind of porous solid-state materials.18 Owing to their high specific surface area and large internal pore volumes with explicit pore sizes and pore structure, MOFs have © 2017 American Chemical Society
exhibited great potential applications in electrochemical supercapacitors.2,19−23 However, most MOFs have typically poor electrical conductivity, which far prevents the use of these materials as active electrodes in supercapacitors. Therefore, most MOFs have been limited as precursors/templates for preparing porous carbons,24−29 which usually require the use of harsh pretreatment reagents such as alkali bases and high carbonization temperatures more than 800 °C. To improve the bulk electrical conductivity of MOFs, hybrid composites with conductive additives such as ZIF-67/PANI,30 Ni-MOF/CNT,31 Ni-MOFs@rGO, 32 Ni-doped MOFs/rGO,33 Mn-MOFs/ CNT34 and HKUST-1/GO/PEDOT35 were prepared and exhibited an enhanced electrochemical performance compared with pure MOFs as supercapacitor electrodes. Apart from poor conductivity, the almost exclusively microporous (
