An inexpensive bio-mass-derived hard carbon from tamarind pods was used as an anode, and nitrogen and nitrogen (N)/sulfur (S) co-doped graphene were used as a cathode for novel hybrid Na-ion supercapacitors. The structural and surface morphological analyses are investigated using a range of techniques. The 3D network of the heteroatom-doped graphene skeleton edges for N and NS-doping conformations were assigned as N-RGOs (N1s-5.09 at.%) and NS-RGOs (N1s-7.66 at.% and S1s-2.22 at.%) based on energy dispersive X-ray spectroscopy elemental mapping. The negative electrode (T-HC) hard carbon was pre-treated by pre-sodiation with a half-cell process by galvanostatic charge–discharge in a sodium-ion battery at 0.01–2.5 V vs. Na/Na⁺. The T-HC//NS-RGO, T-HC//N-RGO, and T-HC//RGO were used to construct the Na-ion supercapacitor device. In the CV experiments, the electrochemical galvanostatic charge–discharge was studied at 1.0–4.2 V. The specific capacitance was 352.18 F/g for the T.HC/NS-RGO device and 180.93 F/g for the T.HC/N-RGO device; both were symmetric devices. T.HC/NS-RGO device performance revealed excellent cycling stability, with T-HC//NS-RGO showing 89.26% capacitance retention over 5000 cycles. A carbon–carbon symmetric device, such as a Na-ion hybrid capacitor, can exhibit the characteristics of both batteries and supercapacitors for future electric vehicles.

This study successfully demonstrates the synthesis of foxtail millet carbon-activated (FMCA) materials using a two-step carbonization process from foxtail millet husk (FMH). The pre-carbonized biomass-derived millet husk was chemically activated with KOH at 500 °C and subsequently carbonized in an inert argon atmosphere at 800 °C in a tubular furnace. XRD analysis revealed a diffraction peak at 2θ = 23.67°, corresponding to the (002) plane, indicating the presence of graphitic structures. The Raman analysis of FMCA materials showed an intensity ratio (I_G/I_D) of 1.13, signifying enhanced graphitic ordering and structural stability. The as-prepared FMC and FMCA electrode materials demonstrate efficient charge storage electrochemical symmetric devices. Electrochemical analysis revealed the charge–discharge curves and a specific capacitance of Csp (FMC//FMC) 55.47 F/g and (FMCA//FMCA) 82.94 F/g at 0.5 A/g. Additionally, the FMCA//FMCA symmetric device exhibits superior performance with a higher capacity retention of 94.89% over 5000 cycles. The results confirm the suitability of FMCA for energy storage applications, particularly in electrochemical double-layer capacitors (EDLCs), making it a promising material for next-generation supercapacitors.

In this study, sugarcane bagasse (SCB), an abundant agricultural byproduct, was transformed into activated carbon via a controlled thermochemical pyrolysis route for high-performance energy storage applications. Herein, we utilized the activated carbon derived from pure sugarcane bagasse (SCB-AC) and further activated using KOH (SCB-KOH-AC) as an electrode material in aqueous symmetric supercapacitor configurations. The synthesized activated carbon was subjected to analysis using a range of characteristics including FT-Raman spectroscopy, which was employed to confirm the functional groups present in the carbon materials. The XPS analysis provided insights into the elemental composition and ionic states. The SEM analysis revealed that both activated carbon and KOH/activated carbon materials exhibited a layered or stacked, albeit slightly random, orientation. Electrochemical studies demonstrated that the synthesized carbon electrodes exhibited impressive specific capacitance values of (SCB) activated carbon (132.20 F/g) and KOH-activated, pure SCB AC (SCB-A) 253.41 F/g at 0.5 A/g. Furthermore, the SCB KOH-activated carbon (AC) electrode revealed a higher specific capacitance value and A//SCB-A symmetric devices delivered energy density reaching 17.91 Wh/kg and power density up to 2990 W/kg. The KOH-activated carbon electrode demonstrated remarkable cycling stability retaining 93.89%, even after 10,000 cycles. These results suggest that the sugarcane bagasse-derived activated carbon is a sustainable and low-cost candidate for next-generation supercapacitor electrodes. The results demonstrate enhanced capacitance, stability, and pore structure tailored for energy storage applications. The KOH-activated carbon SCB carbon symmetric device with symmetric electrodes exhibited a suitable bio-mass carbon for future energy storage applications.

A single production of nitrogen-doped graphene nanosheets was developed in this present work from a spent Zn-C primary battery. The electrochemically exfoliated nitrogen-doped graphene nanosheets (EC-N-GNS) was applied in supercapacitor symmetric devices. As-prepared EC-N-GNS was utilized for a symmetric supercapacitor with natural seawater multivalent ion electrolyte. The recycling of graphite into nitrogen-doped graphene was characterized by X-ray diffraction and RAMAN spectroscopy. The few-layered morphological structures of EC-N-GNS were analyzed by field emission scanning electron microscope and field emission transmission electron microscope. The electrochemical analysis of the cyclic voltammetry curves observed an electrochemical double-layer capacitor (EDLC) behavior with a potential window of −0.8 V to +0.5 V. The electrochemical galvanostatic charge—discharge study was obtained to be maximum specific capacitance (Csp)—67.69 F/g and 43.07 F/g at a current density of 1 A/g. We promising the facile single-step electrochemically exfoliated EC-N-GNS was obtained from a waste zinc-carbon primary battery to recycle the graphite electrodes. The superior electrochemical performance comparatively bulk graphite and EC-N-GNS for potential energy storage supercapacitor applications.

The creation of effective supercapacitor materials is still a priority in the quest to improve energy storage technology. Herein, we present a novel nanocomposite composed of carbon nanoparticles (CNPs) and colloidal SnO₂ quantum dots (c-SQDs) or colloidal SnO₂ ultrasmall nanoparticles, synthesized through a facile sonochemical-assisted hydrothermal approach. The XRD and XPS analyses confirmed the successful synthesis and composition of the CNP/c-SQD nanocomposite. Morphology studies revealed a well-dispersed morphology with intimate interfacial interactions between the CNPs and c-SQDs. Specifically, the nanocomposite exhibited a high specific capacitance of 569 F/g at a current density of 1 A/g, surpassing conventional carbon-based supercapacitors. Furthermore, the nanocomposite displayed excellent stability with 99% capacity retention after 5000 cycles, indicative of its superior cyclability. These results underscore the potential of the CNP/c-SQD nanocomposite as a promising electrode material for high-performance supercapacitor applications, offering enhanced charge storage capacity, stability, and cyclability. This study contributes to the advancement of energy storage technologies, paving the way for the development of efficient and sustainable electrochemical energy storage devices.