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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.

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.