title: Mesoporous manganese oxide nanowires for high-capacity, high-rate, hybrid electrical energy storage.
abstract: Arrays of mesoporous manganese dioxide, mp-MnO(2), nanowires were electrodeposited on glass and silicon surfaces using the lithographically patterned nanowire electrodeposition (LPNE) method. The electrodeposition procedure involved the application, in a Mn(ClO(4))(2)-containing aqueous electrolyte, of a sequence of 0.60 V (vs MSE) voltage pulses delineated by 25 s rest intervals. This "multipulse" deposition program produced mp-MnO(2) nanowires with a total porosity of 43-56%. Transmission electron microscopy revealed the presence within these nanowires of a network of 3-5 nm diameter fibrils that were X-ray and electron amorphous, consistent with the measured porosity values. mp-MnO(2) nanowires were rectangular in cross-section with adjustable height, ranging from 21 to 63 nm, and adjustable width ranging from 200 to 600 nm. Arrays of 20 nm × 400 nm mp-MnO(2) nanowires were characterized by a specific capacitance, C(sp), of 923 ± 24 F/g at 5 mV/s and 484 ± 15 F/g at 100 mV/s. These C(sp) values reflected true hybrid electrical energy storage with significant contributions from double-layer capacitance and noninsertion pseudocapacitance (38% for 20 nm × 400 nm nanowires at 5 mV/s) coupled with a Faradaic insertion capacity (62%). These two contributions to the total C(sp) were deconvoluted as a function of the potential scan rate.
authors.affiliation: Department of Chemistry, University of California, Irvine, California 92697, United States.
authors.forename: Wenbo
authors.initials: W
authors.lastname: Yan
authors.forename: Talin
authors.initials: T
authors.lastname: Ayvazian
authors.forename: Jungyun
authors.initials: J
authors.lastname: Kim
authors.forename: Yu
authors.initials: Y
authors.lastname: Liu
authors.forename: Keith C
authors.initials: KC
authors.lastname: Donavan
authors.forename: Wendong
authors.initials: W
authors.lastname: Xing
authors.forename: Yongan
authors.initials: Y
authors.lastname: Yang
authors.forename: John C
authors.initials: JC
authors.lastname: Hemminger
authors.forename: Reginald M
authors.initials: RM
authors.lastname: Penner