Graphene is a potential energy storage material for supercapacitor electrodes because of its unique electronic and physical properties. In this study, graphene was functionalized chemically. The functionalized graphene (G) is an ideal substrate for anchoring MnO2 nanoflower (NF) through controlled electrodeposition to improve the performance of supercapacitors. The controlled weight ratio of functionalized graphene and MnO2 NF is 1:8. The G/MnO2 NF electrodes exhibit excellent electrochemical performance with a high specific capacitance of 320.59 F g−1 at a current density of 0.5 A g−1 and excellent cycling stability with 95.5% capacitance retention over 3000 cycles. Symmetric supercapacitors with G/MnO2 NF hybrid materials were also assembled as electrodes. The cells exert promising characteristics with a specific capacitance of 55.37 F g−1 at a scan rate of 5 mV s−1, maximum energy density of 5.67 Wh kg−1, and power density of 5.11 kW kg−1. The facile and low-cost preparation technique of functionalized graphene and high-performance G/MnO2 NF nanocomposites may provide a new paradigm for fabricating supercapacitors with superior performance.

While supercapacitors can deliver high electrical power, their low energy density limits their application. Here, we designed and fabricated a facile asymmetric supercapacitor (ASC) with excellent electrochemical performance, where MnO 2 nanoflowers (NFs) and La 2 O 3 nanospheres (NSs) were successfully electrodeposited onto carbon paper as work electrodes in an aqueous 0.5 M Na 2 SO 4 electrolyte. Such nanostructures endow the electrodes with short electrons, ion diffusion paths, and abundant charge adsorption sites. The assembled MnO 2 NF//La 2 O 3 NS asymmetric cell presents a gravimetric energy density of 80.56 Wh kg −1 , a volumetric energy density of 0.74 mWh cm −3 at 35.71 mA cm −3 , and excellent cycle performance. Moreover, a packaged device displays a superior energy density of 0.49 mWh cm −3 with a power density of 94.29 mW cm −3 . The satisfactory improvement in performance mainly stems from the homogeneous nanostructured architecture and an extended workable potential region of 0− 2.0 V. The resulting supercapacitors could have great potential for designing high energy and power density devices as effective power sources.

Crystalline iron oxides/hydroxides are generally preferred as supercapacitor electrode materials instead of the low-crystalline structure, despite the fact that an amorphous phase could have a comprehensive electrochemical performance owing to its structural disorder. Herein, we present a facile and scalable method for preparing amorphous FeOOH nanoflowers@multi-walled carbon nanotubes (FeOOH NFs@ MWCNTs) composites. The resulting hybrid nanoflowers hold a distinctive heterostructure composed of a self-assembled amorphous FeOOH nanofilm on the MWCNTs surface. The low-crystalline 1FeOOH NFs@1MWCNTs composites at pH 8 exhibit a high comprehensive capacitive performance, which may be attributed to the advantageous structural features. In a −0.85 to 0 V vs Ag/AgCl potential window, the prepared hybrid electrode delivers a high specific capacitance of 345 F g −1 at a current density of 1 A g −1 , good cycling stability (76.4% capacity retention over 5000 consecutive cycles), and outstanding rate performance (167 F g −1 at 11.4 A g −1 ). This work may trigger the possibilities of these nanomaterials for further application in supercapacitor electrodes, specifically low-crystalline oxide/ hydroxide-based electrode materials.

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In this work, we study the optical properties of a class of magnetically charged rotating black hole spacetimes. The black holes in question are assumed to be immersed in the quintessence field, and subsequently, the resulting black hole shadows are expected to be modified by the presence of the dark energy. We investigate the photon region and the black hole shadow, and in particular, their dependence on the relevant physical conditions such as the state parameter of the quintessence, the angular momentum, and the magnitude of the magnetic charge. It is shown that the photon regions sensitively depend on the horizon structure and possess intricate features. Moreover, from the viewpoint of a static observer, we explore a few observables, especially those associated with the distortion of the observed black hole shadows.