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Self-Assembly of Parallelly Aligned NiO Hierarchical Nanostructures with Ultrathin Nanosheet Subunits for Electrochemical Supercapacitor Applications Jie Min, Jun Liu, Ming Lei, Wenjun Wang, Yakun Lu, Linyu Yang, Qian Yang, Gang Liu, and Nan Su ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.5b09997 • Publication Date (Web): 17 Dec 2015 Downloaded from http://pubs.acs.org on December 17, 2015
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Self-Assembly of Parallelly Aligned NiO Hierarchical Nanostructures with Ultrathin Nanosheet Subunits for Electrochemical Supercapacitor Applications ＊
Jie Min,a Jun Liu,a, Ming Lei,b Wenjun Wang,c Yakun Lu,a Linyu Yang,a Qian Yang,a Gang Liu,d, ＊
a
and Nan Sua
School of Materials Science and Engineering, Central South University, Changsha 410083, Hunan, China.
b
State Key Laboratory of Information Photonics and Optical Communications, Beijing University of Posts and Telecommunications, Beijing 100876, China.
c
Beijing National Laboratory for Condensed Matter physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
d
Department of Hepatobiliary Pancreas Surgery, Xiangya Hospital, Changsha, Hunan 410008, China.
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KEYWORDS: P123-assisted self-assembly, parallelly aligned NiO hierarchical nanostructures, ultrathin nanosheet subunits, layers controllable, multilevel mesopores, supercapacitor, high-rate performance
ABSTRACT: Parallelly aligned NiO hierarchical nanostructures were fabricated using a templated self-assembly method followed by calcinations, where rationally employed Pluronic triblock copolymers (P123) are acting as molecular templates for geometrical manipulation of nanocrystals and short-chain alcohols are acting as co-solvents and co-surfactants. Such aligned nanostructure is constructed orderly with several ultrathin two-dimensional (2D) nanosheet subunits with an exceptionally small thickness of only 3 nm in a high degree of orientation and separation. Moreover, the number of assembled nanosheets in a unit can be tuned by changing the concentration of the involving P123. This is the first time to synthesize highly hierarchicallyordered and bilaterally symmetrical nanostructures, distributed in diameter of around 200-300 nm, via self-assembly in the liquid phase without solid substrates. The as-synthesized NiO delivered high capacitances of 418 F/g at the current density of 2 A/g with well cycling stability (still maintained 85% after 2000 cycles) and 333 F/g at 10 A/g in rates performance after 60 cycles. These fine electrochemical performances are supposed to be attributed to the hierarchical structures with high specific surface area (SSA, ~164.87 m2/g) and ordered multilevel
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mesopores, which facilitate the electrolyte accessibility and provide more active sites for redox reaction.
1. Introduction Supercapacitors, also known as electrochemical capacitors, are widely investigated due to their long lifespan, high reliability and high power density.1-4 Compared with electrical double-layer capacitors that store charges via reversible ion absorption on the surface, pseudocapacitors exhibit higher electrochemical capacitance, owing to their fast and reversible Faradic redox reactions.5-7 Transition metal oxides are reported to be a class of promising active materials for lithium-ion batteries and pseudocapacitors due to their multiple oxidation states.8-12 Among them, NiO has been suggested as a viable candidate to replace the excellent but costly RuO2, basing on its high theoretical specific capacitance (2573 F/g within 0.5 V), easy availability and fast Faradaic reactions.13 Unfortunately, the real performance of NiO-based electrodes is still far below its theoretical value. Further researches indicated that the performance of supercapacitors is controlled by reaction kinetics, depending on their mechanism of storing charges on the nearsurface.14 Thus, controlling the architecture of the nanomaterials has been of great interest.15 Regarding the advanced nanotechnology, two-dimensional (2D) “graphene-like” nanosheets, especially those with a thickness of
