title: Miniature asymmetric ultracapacitor of patterned carbon nanotubes and hydrous ruthenium dioxide.
abstract: A symmetric ultracapacitor CNT_CNT and an asymmetric ultracapacitor CNT_hRuO(2) of mini size have been prepared with patterned carbon nanotubes (CNT) and hydrous ruthenium dioxide. Galvanostatic charge/discharge results indicate that CNT_hRuO(2) is the superior one in both power and energy densities. In a potential window 2.0 V, the CNT_hRuO(2) cell displays an energy density of 24.0 W h kg(-1) at a power density of 22.9 kW kg(-1). Its power density can be raised to 41.1 kW kg(-1) at the expense of the energy density, which drops to 6.8 W h kg(-1). On the other hand, CNT_CNT performs at a lower level, delivering 5.2 W h kg(-1) at 5.5 kW kg(-1). The favorable charge/discharge performance of CNT_hRuO(2) is attributed to hydrous RuO(2), whose pseudocapacitance drives the other electrode of the vertical CNT array to work harder and makes more use of its double-layer capacitance. The analysis of individual electrode capacitance indicates that the high capacitance of hRuO(2) also causes a disproportion in voltage partition, which restricts the low limit of cycling current in an extended potential window. On energy cycling, CNT_hRuO(2) demonstrates sufficient stability in 10,000 cycles, after an initial 13% drop in capacitance.
authors.affiliation: Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan.
authors.forename: Chun-Hung
authors.initials: CH
authors.lastname: Chen
authors.forename: Dah-Shyang
authors.initials: DS
authors.lastname: Tsai
authors.forename: Wen-Hung
authors.initials: WH
authors.lastname: Chung
authors.forename: Yi-Deng
authors.initials: YD
authors.lastname: Chiou
authors.forename: Kuei-Yi
authors.initials: KY
authors.lastname: Lee
authors.forename: Ying-Sheng
authors.initials: YS
authors.lastname: Huang