Growth of Manganese Oxide Nanoflowers on Vertically-Aligned Carbon Nanotube Arrays for High-Rate Electrochemical Capacitive Energy Storage

Abstract

Manganese oxide nanoflower/carbon nanotube array (CNTA) composite electrodes with hierarchical porous structure, large surface area, and superior conductivity was controllable prepared by combining electrodeposition technique and a vertically aligned CNTA framework. This binder-free manganese oxide/CNTA electrode presents excellent rate capability (50.8% capacity retention at 77 A/g), high capacitance (199 F/g and 305 F/cm 3 ), and long cycle life (3% capacity loss after 20 000 charge/discharge cycles), with strong promise for high-rate electrochemical capacitive energy storage applications.In development of energy storage devices, nanostructured electrode materials have attracted great interest, as they show not only higher capacities but also better rates than traditional materials. 1-6 Nanostructured electrode materials are key components in the advancement of future energy technologies; thus, strategies for preparing high-performance nanomaterials are required. 5 However, direct synthesis of complex nanostructures still remains a challenge in areas of materials science. 7,8 Nowadays, much research on electrochemical capacitors (ECs) is aimed at increasing power and energy densities as well as lowering fabrication costs while using environmentally friendly materials. Specifically, it was found that RuO 2 exhibits prominent capacitive properties as ECs electrode materials; 9 however, its high cost excludes it from wide application. Relatively low cost materials such as MnO x and NiO x can also be used as electrode materials, but their poor rate capability need to be enhanced. 10,11 Manganese oxides (MO) have been thoroughly investigated because of their importance in industrial applications, such as catalysis and energy storage. [12][13][14][15][16] Over the years various nanostructured manganese oxides, including dendritic clusters, nanocrystals with different shapes, nanowires, nanotubes, nanobelts, and nanoflowers, have been synthesized. [17][18][19][20][21][22][23][24] In order to greatly increase electrochemical performance of manganese oxides, a hierarchical porous structure 25 with high electronic conductivity 26 must be considered. Nevertheless, up to now, no method has been reported to fabricate hierarchical porous and binder-free manganese oxide composite electrodes with superior electronic conductive paths. In this paper, we realized this goal by a combination of a carbon nanotube array (CNTA) framework and an electrodeposition technique to fabricate a composite structure, that is, well-dispersed manganese oxide nanoflowers on a vertically aligned CNTA. CNTA is excellent for electrodepositing transition metal oxides because of its regular pore structure, high surface area, homogeneous property (binderfree), and excellent conductivity. [27][28][29][30] The experimental results show that the manganese oxide/CNTA composite electrode exhibits superior rate performance (50.8% capacitance retention at 77 A/g) in an EC, thus, making it very promising for high-rate electrochemical capacitive energy ...

Extracting the Full Potential of Single‐Walled Carbon Nanotubes as Durable Supercapacitor Electrodes Operable at 4 V with High Power and Energy Density

“…Thus far, CNT electrodes have not only achieved notable energy and power performance (7 Wh kg − 1 , 20 kW kg − 1 ), [ 8 ] they have also enabled new functionalities such as fl exible [ 9 ] and transparent [ 10 ] supercapacitors. Moreover, nanostructured CNT composites [ 11 ] have shown exceptionally high capacitance (100 F g − 1 ) at high discharge rate (77 A g − 1 ). Although each of these studies has shown advantageous individual properties of CNTs for supercapacitors, a comprehensive demonstration of their full potential as electrodes meeting all relevant criteria for practical devices has yet to be presented.…”

Enormous shrinkage of carbon nanotubes by supersonic stress and low-acceleration electron beam irradiation

“…4,5 For single-walled carbon nanotubes (SWCNTs), a substantial nanotube surface area per unit volume can be automatically determined if both the diameter and the packing density of the nanotubes are specified. Therefore, the artificial decoration of the SWCNT surface with a functional group 6,7 drastically increases the surface area, up to 1300 m 2 /g, and the performance (energy density of 94 Wh/kg and power density of 210 kW/kg) almost reaches their ideal values. 8 Despite such superior characteristics of a CNT-based supercapacitor, further improvement of its storage density is required for practical applications such as electrical vehicles.…”

Nanocarbon-based electrochemical systems for sensing, electrocatalysis, and energy storage

“…One way to improve the energy density of CNT-based supercapacitors is through incorporation of pseudo-6 capacitive materials (e.g., redox polymers [17,157,158] and metal oxides [159][160][161] in most cases). [162] For example, Mao 7 et al [17] showed that a polyvinylferrocene (PVF)/CNT hybrid had a much higher specific capacitance and energy 8 density than did each of the individual components alone.…”

“…The PVF/CNT hybrid can be prepared by an efficient, 9 low-cost, solution-based process, and the nanostructures and electrochemical performance of the hybrid can be 10 easily varied by adjusting the composition of the precursor solution before deposition. Zhang et al [159] grew man-11 ganese oxide (MO) "nanoflowers" on CNT arrays (CNTAs) (Figure 3e, 3f). The resulting composite exhibited…”

“…[151] . Fig 3e-3h: reprinted with permission from ref [159] . Fig 3i-3l: reprinted with permission from ref [5] .…”