Heterostructural Graphene Quantum Dot/MnO₂ Nanosheets toward High‐Potential Window Electrodes for High‐Performance Supercapacitors

Abstract

a great deal of research effort has been devoted on high energy density supercapacitors. According to the equation of energy density E = 1/2 CV 2 , the energy density (E) of supercapacitors can be enhanced by increasing either voltage window (V) or specific capacitance (C). [5] For high specific capacitance, one of the research efforts should concentrate on using transition metal oxides (TMO) (e.g., MnO 2 , RuO 2 ) as electrode materials. [6,7] They can provide great specific capacitance due to the pseudocapacitive characteristic. [8,9] Among TMO materials, MnO 2 is one of the most potential materials for supercapacitors due to its high theoretical specific capacitance, environmental friendliness, and the high practical voltage window (about 1 V). [2] However, it has suffered from intrinsically low conductivity and specific surface area, which severely restrict its further development in practical application of supercapacitors. In this regard, integrating nanostructured MnO 2 and conductive carbon materials to fabricate novel hybrid nanostructures is a plausible solution to overcome this obstacle. [4] Further, some research efforts have been accordingly performed to synthesize hybrid nanostructures electroactive materials for constructing supercapacitors with considerable performance. Some researchers accordingly synthesized highperformance nanostructured MnO 2 -carbon materials electrodes, whose specific capacitance is close to theoretical value. However, the undesirable contact resistances that produced by the weak and noncoherent TMO/conductor interfaces lead to sluggish kinetics for charge transport, which requires further improvement. [10,11] In order to further improve the energy density, some researchers have concentrated on enlarging the voltage window of supercapacitors. The applications of aqueous electrolytes have been limited by their theoretical voltage window (≈1.23 V) and the practical voltage window is mostly lower than about 1 V for supercapacitors. [12] To extend the voltage window, various techniques have been applied, such as dual shuttle-ion electrolytes, [13,14] pH adjustment of electrolytes, [15] and concentrated electrolytes. [16][17][18] All of these methods have complex processing technologies and sacrifice capacitance, so being difficult for practical applications. Recently, Zhu and co-workers

The Research Development of Quantum Dots in Electrochemical Energy Storage

“…Thanks to their high electrical conductivity, large surface area, tunable photoluminescence, great dispersion in diverse solvents, and superb mechanical, optical, and electric properties, GQDs have been considered as suitable materials for energy storage devices, bioimaging devices, and fuel cells. Graphene even won the Nobel Prize in 2010 . GQDs are made of single or few‐layer graphene with ultrasmall sizes of merely a few nanometers .…”

“…And, whenever QDs are used in an electrochemical device, the electrochemical signature of the QD based electrode must be shown. These excellent properties guarantee remarkable applications of QDs in a variety of fields, such as biomolecular analysis, sensors, organic photovoltaic devices, fluorescence, photochemical reagents, solar cells, light‐emitting diodes, and catalysis . Taking all of the above into consideration, it is hardly surprising that QDs have recently gained widespread applications in the areas of batteries and ECs ( Scheme ).…”

Cadmium Sulfide Quantum Dots–Organometallic Halide Perovskite Bilayer Electrode Structures for Supercapacitor Applications

“…The EIS measurements were performed by applying AC voltage with 10 mV amplitude in the frequency range at the open circuit potential. The areal capacitance (C A ) was calculated from CV curves by integrating discharge current I (see Equation :…”

“…The specific energy density (E s ) of a super capacitor is related to it specific capacitance (C s ) and the window voltage (V) according to the equation . Therefore, increasing either V or C s , or both will enhance the energy …”

All Hierarchical Core–Shell Heterostructures as Novel Binder‐Free Electrode Materials for Ultrahigh‐Energy‐Density Wearable Asymmetric Supercapacitors

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] Supercapacitors (SCs), especially fiber-shaped supercapacitors (FSCs) with their tiny volume, remarkable flexibility, and excellent stitchability as well as fast charge-discharge capability, a high power density, and a long cycle life, are promising energy storage and supply devices. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] Supercapacitors (SCs), especially fiber-shaped supercapacitors (FSCs) with their tiny volume, remarkable flexibility, and excellent stitchability as well as fast charge-discharge capability, a high power density, and a long cycle life, are promising energy storage and supply devices.…”