Harbin Engineering University

Abstract: Hierarchical flowerlike nickel hydroxide decorated on graphene sheets has been prepared by a facile and cost-effective microwave-assisted method. In order to achieve high energy and power densities, a high-voltage asymmetric supercapacitor is successfully fabricated using Ni(OH)2/graphene and porous graphene as the positive and negative electrodes, respectively. Because of their unique structure, both of these materials exhibit excellent electrochemical performances. The optimized asymmetric supercapacitor could be cycled reversibly in the high-voltage region of 0–1.6 V and displays intriguing performances with a maximum specific capacitance of 218.4 F g−1 and high energy density of 77.8 Wh kg−1. Furthermore, the Ni(OH)2/graphene//porous graphene supercapacitor device exhibits an excellent long cycle life along with 94.3% specific capacitance retained after 3000 cycles. These fascinating performances can be attributed to the high capacitance and the positive synergistic effects of the two electrodes. The impressive results presented here may pave the way for promising applications in high energy density storage systems.

Abstract: Asymmetric supercapacitor with high energy density has been developed successfully using graphene/MnO2 composite as positive electrode and activated carbon nanofibers (ACN) as negative electrode in a neutral aqueous Na2SO4 electrolyte. Due to the high capacitances and excellent rate performances of graphene/MnO2 and ACN, as well as the synergistic effects of the two electrodes, such asymmetric cell exhibits superior electrochemical performances. An optimized asymmetric supercapacitor can be cycled reversibly in the voltage range of 0–1.8 V, and exhibits maximum energy density of 51.1 Wh kg−1, which is much higher than that of MnO2//DWNT cell (29.1 Wh kg−1). Additionally, graphene/MnO2//ACN asymmetric supercapacitor exhibits excellent cycling durability, with 97% specific capacitance retained even after 1000 cycles. These encouraging results show great potential in developing energy storage devices with high energy and power densities for practical applications.

Abstract: In recent years, tremendous research effort has been aimed at increasing the energy density of supercapacitors without sacrificing high power capability so that they reach the levels achieved in batteries and at lowering fabrication costs For this purpose, two important problems have to be solved: first, it is critical to develop ways to design high performance electrode materials for supercapacitors; second, it is necessary to achieve controllably assembled supercapacitor types (such as symmetric capacitors including double-layer and pseudo-capacitors, asymmetric capacitors, and Li-ion capacitors) The explosive growth of research in this field makes this review timely Recent progress in the research and development of high performance electrode materials and high-energy supercapacitors is summarized Several key issues for improving the energy densities of supercapacitors and some mutual relationships among various effecting parameters are reviewed, and challenges and perspectives in this exciting field are also discussed This provides fundamental insight into supercapacitors and offers an important guideline for future design of advanced next-generation supercapacitors for industrial and consumer applications

Abstract: We present a quick and easy method to synthesize graphene–MnO2 composites through the self-limiting deposition of nanoscale MnO2 on the surface of graphene under microwave irradiation. These nanostructured graphene–MnO2 hybrid materials are used for investigation of electrochemical behaviors. Graphene–MnO2 composite (78 wt.% MnO2) displays the specific capacitance as high as 310 F g−1 at 2 mV s−1 (even 228 F g−1 at 500 mV s−1), which is almost three times higher than that of pure graphene (104 F g−1) and birnessite-type MnO2 (103 F g−1). Interestingly, the capacitance retention ratio is highly kept over a wide range of scan rates (88% at 100 mV s−1 and 74% at 500 mV s−1). The improved high-rate electrochemical performance may be attributed to the increased electrode conductivity in the presence of graphene network, the increased effective interfacial area between MnO2 and the electrolyte, as well as the contact area between MnO2 and graphene.

Abstract: Owing to its unique electrical, thermal, and mechanical properties, graphene has attracted great attention in various application areas, such as energy-storage materials, [ 1–3 ] free-standing paper-like materials, [ 4–6 ] polymer composites, [ 7–9 ] liquid crystal devices, [ 10 ] and mechanical resonators. [ 11 , 12 ] Approaches for preparing graphene include micromechanical cleavage, [ 11 , 13 , 14 ]