Mesoporous Manganese Oxide Nanowires for High-Capacity, High-Rate, Hybrid Electrical Energy Storage

• Published in: ACS nano Vol. 5; no. 10; pp. 8275 - 8287
• Main Authors: Yan, Wenbo, Ayvazian, Talin, Kim, Jungyun, Liu, Yu, Donavan, Keith C, Xing, Wendong, Yang, Yongan, Hemminger, John C, Penner, Reginald M
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 25.10.2011
• Subjects: Adjustable; Arrays; Capacitance; Electrodeposition; Energy storage; Insertion; Nanostructure; Nanowires; Porosity; pseudocapacitance; photolithography; lithium ion; cathode; battery; electrodeposition
• ISSN: 1936-0851; 1936-086X; 1936-086X
• DOI: 10.1021/nn2029583

Arrays of mesoporous manganese dioxide, mp-MnO2, 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(ClO4)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-MnO2 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-MnO2 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-MnO2 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.