We demonstrate a facile efficient way to fabricate activated carbon nanosheets (ACNSs) consisting of hierarchical porous carbon materials. Simply heating banana leaves with K2CO3 produce ACNSs having a unique combination of macro‐, meso‐ and micropores with a high specific surface area of ∼1459 m2 g−1. The effects of different electrolytes on the electrochemical supercapacitor performance and stability of the ACNSs are tested using a two‐electrode system. The specific capacitance (Csp) values are 55, 114, and 190 F g−1 in aqueous 0.5 M sodium sulfate, organic 1 M tetraethylammonium tetrafluoroborate in acetonitrile, and pure ionic liquid 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([BMIM][PF6]) electrolytes, respectively. The ACNSs also shows the largest potential window of 3.0 V, the highest specific energy (59 Wh kg−1) and specific power (750 W kg−1) in [BMIM][PF6]. A mini‐prototype device is prepared to demonstrate the practicality of the ACNSs.

Ternary transition metal sulfides have emerged as promising electrode materials for next-generation supercapacitors because of their potential ability to simultaneously ensure high conductivity and stability during electrochemical reactions. In the...

Supercapacitor is considered a promising energy storage device due to its high‐power density and high specific capacitance. Electrode materials and electrolytes are major components of supercapacitors. The most used electrolytes are not biocompatible, which limits their practical applications. Bio‐electrolytes often cause low performances of supercapacitors. However, the inadequate performances of bio‐electrolytes for supercapacitor applications could be improved using redox molecules. Here, we are reporting the development of a novel redox bio‐electrolyte based on pivalic acid (PA) and ascorbic acid (AA). The salts of PA and AA served as the bio‐electrolyte and redox molecules, respectively. It is worth to note that PA which can be generated from bio‐sources and industrial wastes, is soluble in alkaline solutions. AA is found in most living organisms, including plants. The developed supercapacitor with the bio‐based redox electrolyte provides a specific capacitance of 308 Fg−1 at a current density of 1 Ag−1 and achieved an energy density of 15 Whkg−1 at a power density of 300 Wkg−1. The supercapacitor demonstrates a good coulombic efficiency of ∼97% with capacitance retention of ∼72% after 10000 charge‐discharge cycles. This study is expected to widen the applications of bio‐based redox electrolytes for practical electrochemical energy storage applications and enables access to greener and more sustainable energy storage technology.

This work reports the rational design of MnOx nanorods on 3D crushed reduced graphene oxide (MnOx/C-rGO) by chemical reduction of Ni-incorporated graphene oxide (GO) followed by chemical etching to remove Ni. The resulting MnOx/C-rGO composite synergistically integrates the electronic properties and geometry structure of MnOx and 3D C-rGO. As a result, MnOx/C-rGO shows a significantly higher specific capacitance (Csp) of 863 F g−1 than MnOx/2D graphene sheets (MnOx/S-rGO) (373 F g−1) and MnOx (200 F g−1) at a current density of 0.2 A g−1. Furthermore, when assembled into symmetric supercapacitors, the MnOx/C-rGO-based device delivers a higher Csp (288 F g−1) than MnOx/S-rGO-based device (75 F g−1) at a current density of 0.3 A g−1. The superior capacitive performance of the MnOx/C-rGO-based symmetric device is attributed to the enlarged accessible surface, reduced lamellar stacking of graphene, and improved ionic transport provided by the 3D architecture of MnOx/C-rGO. In addition, the MnOx/C-rGO-based device exhibits an energy density of 23 Wh kg−1 at a power density of 113 Wkg−1, and long-term cycling stability, demonstrating its promising potential for practical application. Graphical Abstract

This study reports a simple one-step hydrothermal method for the preparation of a Ni(OH) 2 and MnO 2 intercalated rGO nanostructure as a potential supercapacitor electrode material. Having highly amorphous rGO layers with turbostratic and integrated wrinkled flower-like morphology, the as-prepared electrode material showed a high specific capacitance of 420 F g –1 and an energy density of 14.58 Wh kg –1 with 0.5 M Na 2 SO 4 as the electrolyte in a symmetric two-electrode. With the successful intercalation of the γ-MnO 2 and α-Ni(OH) 2 in between the surface of the as-prepared rGO layers, the interlayer distance of the rGO nanosheets expanded to 0.87 nm. The synergistic effect of γ-MnO 2 , α-Ni(OH) 2 , and rGO exhibited the satisfying high cyclic stability with a capacitance retention of 82% even after 10 000 cycles. Thus, the as-prepared Ni(OH) 2 and MnO 2 intercalated rGO ternary hybrid is expected to contribute to the fabrication of a real-time high-performing supercapacitor device.

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We are reporting the preparation of a self-doped mesoporous activated carbon by the treatment of waste collected from car engine exhaust. The waste was pyrolyzed at 850°C in N 2 atmosphere using KOH activating agent. Highly porous activated carbon was obtained with the presence of N, O, S, and P as self-dopant. A high specific surface area of 410 m 2 g −1 with the pore volume of 0.5947 cm 3 g −1 was achieved. Electrode prepared with the activated carbon showed a high specific capacitance (280 Fg −1 ) using a 1-butyl-3-methylimidazolium chloride electrolyte. It retained 95% of initial capacitance after 10,000 cycles, demonstrated high cyclic stability and sustainability.