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Activated carbon (AC) is a low-cost porous material with high conductivity and a specific surface area. Recently, commercially available AC has been replaced by waste-derived activated carbons (WDACs) as they are renewable, cost-effective, and eco-friendly. The synthesis of metal–organic frameworks (MOFs) embedded in the WDAC matrix as a composite electrode is carried out for energy storage applications. Briefly, the zinc-based zeolitic imidazole framework (ZIF-8) is combined with waste paper-derived activated carbon (PAC-800) and used to fabricate a solid-state symmetrical supercapacitor that delivered an energy density of 37.1 Wh kg–1at a power density of 880.1 W kg–1. Compared to pristine materials (ZIF-8 and PAC-800 alone), the electrochemical performance of the PAC-800/ZIF-8 composite electrode is greatly enhanced due to the mesoporous nature of ZIF-8.

The electric double layer capacitor (EDLC) mechanism offered by carbon frameworks alone cannot suffice the unprecedented demand for energy. Hence, including a pseudocapacitive material (conducting polymer) in the carbon framework can impart additional pseudocapacitance to the material, thereby improving its electrochemical performance. Herein, human hair as a biowaste resource with inherent heteroatoms has been subjected to chemical activation at 800 °C to yield human hair-derived activated carbon (HHAC). Subsequently, an in situ chemical oxidation technique has been employed to generate the composite of HHAC and polypyrrole (HHAC/PPy). The HHAC/PPy composite when tested in 1 M H2SO4outperforms pristine HHAC and PPy, with a higher specific capacitance of 358 F/g compared to 274 and 53 F/g obtained for individual materials, respectively (at 0.5 A/g). Moreover, the HHAC/PPy composite also solved the problem of low cyclic stability in the conducting polymers by maintaining 84.2% of the initial capacitance after 5000 charge–discharge cycles. In addition, a HHAC/PPy//HHAC asymmetrical supercapacitor device was assembled in an aqueous electrolyte (1 M H2SO4), which delivered an ultrahigh energy density of 53.3 W h/kg with a respectable power density of 408.5 W h/kg that can help in avoiding costly and toxic organic electrolytes. Our study achieved an electroactive carbon material with the synergy of both EDLC and pseudocapacitance materials, which has great potential for supercapacitor applications.

The performance and operation of an energy storage device are significantly influenced by the electrolyte and electrode materials. Therefore, it is crucial to develop an electrode material with a rational design and achieve compatibility with the electrolyte. In this study, we prepare Ni-MOF derived nickel phosphides/carbon (NP@C) nanostructure as an electrode for supercapacitor application. The as synthesized material provides more redox-active sites, better spatial utilization, improved conductivity, and a high-polarized surface that will speed up ion migration at electrode/electrolyte. Also, the usage of redox additive electrolyte (0.2 M K3[Fe (CN)6] in 1 M Na2SO4) further complements the redox active sites and hence the improved charge transport. Therefore, NP@C electrode achieved a remarkable 2136.3 F/g of capacitance at 3 A/g with 90.6 % of capacitance retention after 5000 charge-discharge cycles. In addition, the surface-diffusion studies confirms that NP@C shows high diffusion contribution of 82.6 % in redox electrolyte than that of 25.1 % in 1 M Na2SO4. Furthermore, NP@C//NP@C symmetric supercapacitor device in redox additive electrolyte also delivered remarkable performance rendering high energy density of 52.5 Wh/kg at a power density of 750 W/kg. In addition, NP@C//NP@C also shows the long-term stability with attenuating only 7.2 % of initial capacitance value after 10000 charge-discharge cycles. In addition to this, the device performs extremely well when tested for self-discharge studies. Hence, this study demonstrates the perfect harmony of NP@C electrodes and redox additive electrolyte to fabricate a high-performance supercapacitor.

Transition metal dichalcogenides (TMDs) are generating immense research interest in the field of supercapacitors owing to their 2D morphology and other existing material properties. Nonetheless, more research efforts are needed to address their low conductivity and relatively poor cycle stability. In the present work, an asymmetrical supercapacitor (ASC) is assembled using a WS2/carbon composite as a positive electrode and nanoporous carbon (NPC) (derived from zeolitic imidazolate framework (ZIF-8)) as a negative electrode. In the presence of 1 M H2SO4aqueous electrolyte, the above ASC has yielded excellent electrochemical performance due to the efficient combination of the feature of redox active WS2nanorods and highly conductive NPC. In individual studies, the WS2/Z8-800 (positive) and Z8-800 (negative) electrodes have delivered specific capacitances of 248.7 and 437.6 F/g, respectively. The full ASC has been charged-balanced to fabricate a 1.4 V device, which has delivered an energy density of 25 Wh/kg upon discharging at a power rate of 801 W/kg. The study should also open up future opportunities to explore other sulfide based TMDs in conjugation with nanoporous carbon for the development of advanced supercapacitors.

The present investigation reported metal-free hierarchical porous and robust Nitrogen (N), Sulphur (S) co-doped carbon (NS-CoP@C) electrode for supercapacitor application. The NS-CoP@C was synthesized by single-step carbonization and activation of thiourea co-doped aniline-pyrrole co-polymer (CoP). The thiourea acted as a doping as well as activating agent. The data of three different electrode materials PANI-PPy co-polymer (CoP), PANI-PPy co-polymer derived Carbon (CoP@C) and N, S co-doped carbon derived from PANI-PPy co-polymer (NS-CoP@C) are compared in the present report. The electrode materials were initially characterized by various spectroscopic techniques. It is observed that among the three electrode material, NS-CoP@C possess higher specific surface area (SSA), high pore volume and hierarchal porous structure with a better mesopore-to-micropore volume ratio. In a three-electrode system, NS-CoP@C possesses a high specific capacitance of 344.2 F/g @ 0.5A/g. Moreover, NS-CoP@C electrode was used to fabricate an all solid-state (PVA-1 M H2SO4polymer gel electrolyte) and aqueous (1 M H2SO4electrolyte) symmetrical supercapacitor devices in the two-electrode system. This NS-CoP@C electrode was used as both positive and negative electrode material in both types of devices. Among them, the solid-state device operates at a wide potential window of 2 V, as a consequence delivering an implausible energy and power density of 45.25 Wh/kg and 1025.64 W/kg while maintaining a capacity retention of 90.1 % even after 8500 charge-discharge cycles. Hence, the excellent performance of conducting PANI-PPy co-polymer-derived N, S co-doped carbon paved new ground for developing an alternative electrode for futuristic energy storage devices.

The conversion of plastic waste into high-value metal-organic framework (MOF) materials has currently grabbed the attention as an important research area for mitigating environmental and economic issues. Due to their large surface area and high porosity, MOFs have a significant advantage as supercapacitor electrode material. In this study, MOFs (Cu-MOF, Zr-MOF, and Ti-MOF) were produced from plastic wastes (PET bottles) using hydrothermal approach. These MOFs were tested electrochemically in 1 M H2SO4electrolyte using three-electrode setup. Among them, Cu-MOF (104.8 F/g at 0.5 A/g) showed higher capacitance and increased diffusion contribution (78.4 %) than its counterparts Zr-MOF (70.5 F/g at 0.5 A/g; 70.4 %) and Ti-MOF (55.5 F/g at 0.5 A/g; 67.5 %). Further, solid-state symmetrical supercapacitor devices have been assembled using all the plastic wastes derived MOFs viz. Cu-MOF//Cu-MOF, Zr-MOF//Zr-MOF, and Ti-MOF//Ti-MOF. Among them, Cu-MOF//Cu-MOF symmetric supercapacitor device performed better than the others by rendering energy density of 18.2 Wh/kg at 825 W/kg power density along with a cyclic stability of 87 % after 10,000 charge-discharge cycles. These studies open new avenues to utilize waste PET bottles to synthesize high functional MOFs for next generation supercapacitors.

The present study reported the performance of free-standing carbon nanofibers decorated with copper-metal-organic frameworks (Cu-MOFs). A green electrospinning technique was utilized to obtain nanofiber sheets that were carbonized and activated to produce activated carbon nanofiber sheets (ACNFs). These ACNFs consist of inherent oxygen functionalities of the lignin that can aid the growth of MOF structure on it in a single step, which motivated us to do this work. Cu-MOF particles were in-situ grown over the surface of ACNFs using a hydrothermal-assisted technique. The developed materials were characterized using FESEM, Raman Spectroscopy and BET analysis in order to identify morphological, porosity, and surface area transformations. Along with these, Cyclic Voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS), and Galvanostatic Charge-Discharge (GCD) studies were performed to compare the electrochemical performance of the Cu-MOF, ACNF, and Cu-MOF@ACNF as electrode materials for supercapacitors. Among three electrodes, the Cu-MOF@ACNF sheet reveals a higher specific capacitance of 303.2 F/g compared to ACNF (203.3 F/g) and Cu-MOF (68.2 F/g) at the same current density of 1 A/g. Based on the higher performance of Cu-MOF@ACNF two types of symmetrical devices, i.e., aqueous (using electrolyte-impregnated filter paper) and solid-state devices (using a polymeric gel electrolyte), were fabricated. The all-solid-state supercapacitor device was found to feature high flexibility, stand-alone characteristics, and excellent performance as an electrode with a working potential window of 0–2.0 V. The device demonstrates a high energy density of 78.71 Wh/kg and a power density of 1050.0 W/kg, along with high coulombic efficiency (99.8 %) after 10,000 cycles. The achieved performance is superior to many published reports, revealing that the developed composite materials hold prospect for applications in green and high-performance flexible energy storage devices.

Pineapple peel has been chosen as a biowaste precursor to synthesize activated carbon viaKOH activation at 800 °C (PP-800). Further, the in situchemical oxidation method was used to synthesize a composite of PP-800 with polyaniline (PANI). The successful formation of the composite (PP-800/PANI) was confirmed viaX-ray diffraction (XRD), and Raman and Fourier-transform infrared (FTIR) spectra. PP-800/PANI when tested in 1 M H2SO4in a three-electrode configuration showed a higher specific capacitance (377 F/g) than that of PP-800 (328 F/g) and PANI (92.4 F/g) at 2 A/g. This is due to the significant enhancement in the diffusion contribution for PP-800/PANI (86.25%) than that of PP-800 (61.7%) and PANI (49.9%) counterparts at 20 mV/s, which leads to the maximum utilization of the electrochemical surface area. Further, an asymmetrical supercapacitor device, PP-800/PANI//PP-800, was fabricated, which delivered a high energy density of 51.2 Wh/kg at a decent power density of 380 W/kg with 90% cyclic stability after 10,000 charge–discharge cycles.

Organic molecules-based supercapacitors have piqued interest as an efficient energy storage component. In this study, an organic composite based asymmetric supercapacitor has been developed using optimized amount of perylene diimide (PDI) in combination with activated carbon. The composite sample with 1 wt% PDI showed remarkable electrochemical performance, with a specific capacitance/(specific capacity) of 617 F/g/(171.3 mAh/g) at 0.5 A/g, higher than that of the individual components. Further, the assembled asymmetric device PPAC/PDI-1//PPAC delivered a high energy density of 62.3 Wh/kg at a power density of 455 W/kg, while retaining 91.4 % of its initial specific capacitance after 10,000 charge-discharge cycles. This study provides an avenue for the utilization of organic molecules for super-capacitor application owing to its polarity and conjugation with carbon.

•Activated 2-D carbon nanofabric was electrospun using lignin as a green precursor.•The low-environment impact solvent (Q3C Class) was explored for electrospinning.•High electrochemical enactment as compared to powder and crushed activated carbon.•Flexible supercapacitor device shows stable performance in different bending modes.•High energy (65.52 Wh/kg), power (1036.27 W/kg) density with high cyclic stability.

Date seeds are the by-product of date fruits, which are abundant all over the world mainly in Middle East. Herein, we report a facile transformation of waste date seeds into highly porous activated carbon (D-800) via simple one-pot hydrothermal carbonization followed by KOH activation route. The resultant date seeds derived activated carbon was then co-doped with nitrogen and sulphur (NSD-800) via effective binary heteroatom doping method. The NSD-800 material has interconnected pores like framework, which facilitate significant ion storage and fast ion transport. Heteroatom doping produces a faradaic contribution in addition to the EDLC (electric double layer capacitor) characteristics of the carbon which facilitates the faster diffusion process. Hence, NSD-800 demonstrate promising electrochemical performance achieving a high specific capacitance of 298.5 F/g at 0.5 A/g using 1 M H2SO4electrolyte. Furthermore, symmetrical and asymmetrical supercapacitor (SC) devices were fabricated using these electrode materials for comparison purpose. It is found that D-800//NSD-800 asymmetric SC device shows superior electrochemical performance delivering high energy density of ~30 Wh/kg at a power density of 394 W/kg along with extraordinary cyclic stability of 92.7 % after 10,000 charge-discharge cycles. This intriguing performance notably bestows NSD-800 with promising prospects as electrode material for supercapacitor application.