High performance flexible solid-state asymmetric supercapacitors from MnO₂/ZnO core–shell nanorods//specially reduced graphene oxide

Abstract

With a view to developing flexible solid-state asymmetric supercapacitors, we have specially designed and nanoscopically engineered two types of electrodes: a MnO 2 /ZnO core-shell nanorod array and a HIreduced graphene oxide assembly, both deposited in situ on a carbon cloth. These materials were thoroughly characterized by structural and spectroscopic techniques. The flexible solid-state asymmetric supercapacitors with cathodes and anodes made of these materials have demonstrated superior performance characteristics. They can be cycled in a wide potential window of 0-1.8 V for 5000 cycles with only 1.5% capacitance loss. The demonstrated volumetric energy density of 0.234 mW h cm À3 and volumetric power density of 0.133 W cm À3 are much higher than those of similar devices reported previously in the literature.

Scalable self-growth of Ni@NiO core-shell electrode with ultrahigh capacitance and super-long cyclic stability for supercapacitors

“…Significantly, although our asfabricated ANF//RGO-ASC device only has a small voltage window of 1.5 V, the maximum volumetric energy density reached 1.06 mWh cm À3 . This value is substantially higher than that of recently reported symmetric SCs (SSCs) and most of ASCs with larger operation potential windows, such as graphene-SSC (0.07 mWh cm À3 ), 1 MnO 2 /CNP-SSC (0.12 mWh cm À3 ), 25 TiN-SSC (0.05 mWh cm À3 ), 29 ZnO@MnO 2 //RGO-ASC (0.24 mWh cm À3 , 1.8 V) 24 and TiO 2 @MnO 2 //TiO 2 @C-ASC (0.30 mWh cm À3 , 1.8 V), 28 are comparable with that of VO x //VN-ASC (0.61 mWh cm À3 , 1.8 V) 9 and MnO 2 /RGO//RGO-ASC (0.72 mWh cm À3 , 1.8 V). 16 Moreover, the ANF//RGO-ASC device also exhibited a superior power density of 0.42 W cm À3 , which is considerably higher than that of SSCs and ASCs.…”

“…As shown in Figure 5d, the ANF//RGO-ASC device achieved the highest volumetric capacitance of 3.42 F cm À3 at 6 mA cm À2 , which is substantially higher than the values reported recently for other ASCs, such as an NiO//RGO-ASC device (1.37 F cm À3 at 1 mA cm À2 ), 39 an MnO 2 /RGO//RGO-ASC device (1.60 F cm À3 at 4 mA cm À2 ), 16 a VO x //VN-ASC device (1.35 F cm À3 at 0.5 mA cm À2 ), 9 a TiO 2 @MnO 2 //TiO 2 @C-ASC device (0.67 F cm À3 at 0.5 mA cm À2 ) 28 and a ZnO@MnO 2 //RGO-ASC device (0.52 F cm À3 at 0.5 mA cm À2 ). 24 In addition, when the current density increased from 6 to 20 mA cm À2 , the ANF//RGO-ASC device retained 58% of its capacitance, demonstrating its good rate capability, and more than 95% of the coulombic efficiency was retained at any current density.…”

“…16 Moreover, the ANF//RGO-ASC device also exhibited a superior power density of 0.42 W cm À3 , which is considerably higher than that of SSCs and ASCs. 1, [23][24][25][26][27][28][29] After charging at a current density of 20 mA cm À2 for 10 s, a tandem device with three ANF//RGO-ASC devices in series could power a light-emitting diode array display (4-5 V) for B1 min (inset in Figure 5). Moreover, because of the unique porous structure and strong mechanical properties, the volumetric performance of the ANF//RGO-ASC device can be further improved by compression of the device.…”

Graphene based metal and metal oxide nanocomposites: synthesis, properties and their applications

“…They make use of different potential windows of the two electrodes in order to increase the maximum operation voltage in the cell system, which may resul in an enhanced specific capacitance and improved energy density. 323 In a recent study, an asymmetric supercapacitor with high energy density has been developed using HRG/MnO 2 nanocomposites as positive electrode and activated carbon nanofibers (ACN) as negative electrode in a neutral aqueous Na 2 SO 4 electrolyte. 324 The composite material exhibits maximum energy density of 51.1…”

α-Fe2O3-Based Core-Shell-Nanorod–Structured Positiveand Negative Electrodes for a High-Performance α-Fe2O3/C//α-Fe2O3/MnOxAsymmetric Supercapacitor

“…8 The energy density of supercapacitors can be enhanced by increasing their capacitance as well as their operating-potential window, which can be achieved more easily with asymmetric supercapacitors (ASCs) than with the symmetric supercapacitors (SSCs) since, with suitable combination of positive and negative electrode materials, the operational potential window as high as 2 V has been achieved even with aqueous electrolytes. 6,[9][10][11][12][13][14] In recent years, efforts have been expended to explore several ASCs with different electrode materials based on redox-active transition-metal oxides, like RuO 2 , 15 SnO 2 , 23 etc., which are not commercially viable owing to their high cost and environmental incompatibility. Accordingly, there is need to explore certain alternative combinations of positive and negative electrode materials to design a high-performance, cost-effective and environmentally benign ASC.…”