A versatile ionic liquid-assisted approach to synthesize hierarchical structures of β-Ni(OH)2 nanosheets for high performance pseudocapacitor

This work describes a versatile hydrothermal approach to synthesize different types of hierarchical structures composed of single crystalline beta-Ni(OH)(2) nanosheets. We use the ionic liquid (IL) 1-butyl-3-methylimidazolium chloride (BmimCl) as a structure directing agent, which allows the formation of films consisting of beta-Ni(OH)(2) nanosheets on the nickel foam substrate. It is found that the IL not only controls the formation of the sheet-like structure, but also promotes the growth of the nanosheets on the substrate, building an intimate contact between the active hydroxide film and the conducting metal foam. This IL agent is so effective that such a hierarchical film can also be obtained with different thickness and organization if different nickel salt precursor is used. When these film samples were applied as the electrode materials for pseudocapacitor, they exhibited promising capacitive properties with a high capacitance of about 700 F g(-1) even at a high charge-discharge current rate of 5 A g(-1) for prolonged cycling. (C) 2015 Elsevier Ltd. All rights reserved.