Charge Storage Capacity Research Articles

The relationship between the high-frequency performance of supercapacitors and the type of doped nitrogen in the carbon electrode

Nitrogen doping has been widely used to improve the performance of carbon electrodes in supercapacitors, particularly in terms of their high-frequency response. However, the charge storage and electrolyte ion response mechanisms of different nitrogen dopants at high frequencies are still unclear. In this study, melamine foam carbons with different configurations of surface-doped N were formed by gradient carbonization, and the effects of the configurations on the high-frequency response behavior of the supercapacitors were analyzed. Using a combination of experiments and first-principle calculations, we found that pyrrolic N, characterized by a higher adsorption energy, increases the charge storage capacity of the electrode at high frequencies. On the other hand, graphitic N, with a lower adsorption energy, increases the speed of ion response. We propose the use of adsorption energy as a practical descriptor for electrode/electrolyte design in high-frequency applications, offering a more universal approach for improving the performance of N-doped carbon materials in supercapacitors

Capacity augmentation strategy in α-Fe2O3 nanoparticles through multifaceted structural and electrochemical analyses

Hematite (α-Fe₂O₃) has garnered significant research interest for supercapacitor applications, but capacity fading and limited cyclic life remain serious challenges. In this context, the present research provides a comprehensive study of the factors that significantly impact charge kinetics within the electrode and at the solid/electrolyte interface. By integrating structural and electrochemical analyses, this study offers an effective strategy to enhance the capacity of α-Fe₂O₃ nanoparticles through rigorous scientific analysis and identification of various qualitative and quantitative factors that influence charge storage capacity. A simple one-step co-precipitation method was adopted to synthesize porous α-Fe₂O₃ nanoparticles. The quantitative analysis of charge kinetics demonstrated the domination of diffusion-controlled charge storage as the main contributor to the total charge storage. The α-Fe₂O₃ nanoparticles-based electrode delivered a high energy density of 24.6 Wh kg⁻1 at an impressive power density of 478.7 W kg⁻1. Additionally, it displayed a capacity retention of 79 % over 10,000 cycle operations. The choice of electrode material and the superior porous nanoarchitecture have proven to be advantageous for high-performance supercapacitor applications, offering fast electron/ion transport.

A study on the evolution of hydrothermally synthesized MoS2 on thermal annealing and development of novel MoS2-MoO3 hybrid nanostructure for supercapacitor applications

The electrochemical capacitor also known as supercapacitor is a high-performance energy storage device with exceptional properties. We report the evolution of structural, morphological, optical, and thermal properties of MoS2 on thermal annealing along with its supercapacitor study. The pristine MoS2 is synthesized via the hydrothermal method at 200°C and the material is annealed in the presence of air at 250°C, 300°C, and 350°C. The 300°C annealed sample has shown a hybrid MoO3-xMoS2-y phase characterized by morphology of mixed flower-like and nano brick-like structures, marking the first time report of this novel formation. The evolution of the novel MoO3-xMoS2-y phase can be attributed to the intervention of lattice and interstitial oxygen species during synthesis. Electrochemical analysis is employed to study the supercapacitor nature of the materials. The electrochemical study revealed that the hybrid structure has a higher charge storage capacity than MoS2 or MoO3. The calculated specific capacitance from the galvanostatic charge-discharge curve of MoO3-xMoS2-y in 0.1M NaOH is observed to be 1.71mF/cm2, five times greater than other samples. Furthermore, the capacitor behavior of MoO3-xMoS2-y is studied in different electrolytes such as KOH, NaOH, and Na2SO4 at a concentration of 3M. The intercalation-assisted faradaic process is observed to be the major charge storage mechanism of the hybrid structure. Developing novel nanostructures with distinct properties is crucial for advancing supercapacitors to achieve optimal performance.

Fractal supported electrochemical analysis of MoO3 decorated AlOOH binary composite for supercapacitor application

The AlOOH/MoO3 binary composite electrodes are synthesized by layer-by-layer method to enhance the supercapacitive property of AlOOH by taking advantage of multiple oxidation states of molybdenum. The X-ray diffraction characterization reveals the polycrystalline nature of nanocomposite. The elements and their chemical states are analysed using X-ray photoelectron spectroscopy. The binary composite exhibits interconnected network-like morphology resembling a fractal nature. The three-electrode measurement in 1 M KOH electrolyte shows the highest specific capacity (Cs) of 1638.15 C g-1@ 5 mV s-1 for binary composite, which is greater than the capacity of individual components. Also, we get Cs of 1124.41 C g-1 for 10 cycle MoO3 while its theoretical capacity is 1005 C g-1. The excellent electrochemical performance is a consequence of multiple redox active sites present in the nanocomposite, lower resistance, porous interconnected network-like structure, and shorter relaxation time. The synergy of AlOOH with MoO3 enhances its charge storage capacity. The obtained electrochemical results are also theoretically supported by fractal analysis. Among all the electrodes, the 10 cycle AlOOH/MoO3 nanocomposite displays high value of fractal dimension, which is advantageous for supercapacitor application. Furthermore, we have fabricated a symmetric supercapacitor device to understand the practicality of current work. The fabricated device displays Cs of 68.41 F g-1 within 1.6 V potential window with ∼71 % capacity retention and 100 % coulombic efficiency after 7000 charge-discharge cycles. The highest energy density of 24.32 Wh kg-1 is achieved for the power density of 3907 W kg-1.

Transparent MXene Microelectrode Arrays for Multimodal Mapping of Neural Dynamics.

Transparent microelectrode arrays have proven useful in neural sensing, offering a clear interface for monitoring brain activity without compromising high spatial and temporal resolution. The current landscape of transparent electrode technology faces challenges in developing durable, highly transparent electrodes while maintaining low interface impedance and prioritizing scalable processing and fabrication methods. To address these limitations, we introduce artifact-resistant transparent MXene microelectrode arrays optimized for high spatiotemporal resolution recording of neural activity. With 60% transmittance at 550 nm, these arrays enable simultaneous imaging and electrophysiology for multimodal neural mapping. Electrochemical characterization shows low impedance of 563 ± 99 kΩ at 1 kHz and a charge storage capacity of 58 mC cm⁻² without chemical doping. In vivo experiments in rodent models demonstrate the transparent arrays' functionality and performance. In a rodent model of chemically-induced epileptiform activity, we tracked ictal wavefronts via calcium imaging while simultaneously recording seizure onset. In the rat barrel cortex, we recorded multi-unit activity across cortical depths, showing the feasibility of recording high-frequency electrophysiological activity. The transparency and optical absorption properties of Ti₃C₂Tx MXene microelectrodes enable high-quality recordings and simultaneous light-based stimulation and imaging without contamination from light-induced artifacts.

Enhancing quantum capacitance in BNyne/Graphene heterostructures through transition-metal dopants for high-performance supercapacitors

Using Density functional theory (DFT), we investigated the charge storage capacity, quantum capacitance (CQ), geometry and electronic structures of BNyne/graphene heterostructures (BNyneGHs), as well as the impact of transition-metal dopants on their CQ. Our results showed that doping was more effective than vacancy defects in improving the CQ of BNyneGHs. Ti-doped BNyneGHs exhibited the highest CQ value of 360.08 μF/cm2, making them ideal positive electrode materials for supercapacitors (SCs). The presence of doping agents was found to enhance the density of states (DOS) around the Fermi level, resulting in improved CQ. Our calculations identified potential cathode or anode materials for high-energy-density SCs, providing theoretical support for the design of high-capacitance SCs.

Enhancement of charge storage capacity in two-leg pseudo-spin ladder CaCu2O3 compound through Li-doping

Nanostructured 2-leg pseudo spin-ladder compound CaCu2O3 has been synthesized by chemical co-precipitation method and a significant improvement in its charge storage capacity has been realized through Li-doping. The fabricated electrode based on Li-doped CaCu2O3 exhibited higher specific capacitance of 321.26 F/g at 1.5 A g-1 when compared to that of 205.45 F/g for undoped CaCu2O3 system. Moreover, the electrode revealed an excellent cyclic stability (5000 cycles) with capacitance retention of 91.96 % of its initial value. An asymmetric supercapacitor fabricated using nano-flakes shaped Li-CaCu2O3 and activated carbon showed a notable energy density of 36.72 Wh/kg and power density of 1406 W/kg which maintains the energy density of 7.81 Wh/kg even at higher power density of 7031.25 W/kg. Among various Li-doped samples, 2.5 wt.% Li-CaCu2O3 exhibited the best storage capacity. This improvement has been attributed to the intrinsic off-stoichiometric (Ca0.86Cu2.14O2.93) and spin ladder structure of CaCu2O3 which allows Li to intercalate and improve the storage performance. Moreover, higher reactive surface area due to nano-flake morphology and porous structure of Li-CaCu2O3 may enhance the permeability of electrolytic ions, thereby improving the performance of the fabricated supercapacitor compared to undoped CaCu2O3 with rod-like morphology. These findings underscore the potential of Li-CaCu2O3 as a promising candidate material for fabricating supercapacitor devices.

Influences of solvents and monomer concentrations on the electrochemical performance and structural properties of electrodeposited PEDOT films: a comparative study in water and acetonitrile.

Poly(3,4-ethylenedioxythiophene) (PEDOT) has emerged as a promising coating for neural electrodes especially through convenient electrodeposition methods. To investigate the influences of solvents and EDOT monomer concentrations on the electrochemical performance and structural characteristics of PEDOT, both aqueous and acetonitrile solutions were employed with varying monomer concentrations during deposition. The prepared PEDOT films were examined for the surface morphology, electrochemical performance, and chemical structures. The results showed that an increase in EDOT concentration in either solvent led to PEDOT films with improved charge storage capacity and reduced impedance magnitude. At equivalent monomer concentrations, PEDOT films generated in acetonitrile exhibited a rougher surface texture and better electrochemical performance. Notably, the growth rate of charge storage capacity of PEDOT prepared in acetonitrile relative to the deposited charge density was 2.5 times that of PEDOT prepared in water. These findings could help to the optimization of PEDOT coating preparation to enhance electrode performance.

Enhancing the charge storage capacity of ultrathin metal–organic framework nanosheets with CO2-derived carbon nanotubes

Metal-organic frameworks (MOFs) hold promise as efficient electrode materials for supercapacitors, but their practical application is hindered by the intrinsic low electrical conductivity. Here, we employ CO2-derived carbon nanotubes based on molten salt electrolysis (MSE-CNTs) as the framework to guide the growth of nickel-based MOF (Ni-MOF). The resulting MSE-CNTs/Ni-MOF composite exhibits an impressive specific capacitance of 1714.2 F g−1 at 1 A g−1, 1.45 and 1.26 times greater than bare Ni-MOF (1185.7 F g−1) and CVD-CNTs/Ni-MOF (1364.3 F g−1, the composite of Ni-MOF and commercial CNTs produced by chemical-vapor-deposition), respectively. Moreover, the assembled hybrid supercapacitor (MSE-CNTs/Ni-MOF//active carbon) achieves a remarkable specific capacitance of 136.5 F g−1 at 1 A g−1 and an energy density of 54.8 Wh kg−1 at 850 W kg−1, standing among the best of the state-of-the-art. The superior capacitive performance of MSE-CNTs/Ni-MOF than CVD-CNTs/Ni-MOF can be attributed to the better electrical conductivity of MSE-CNTs, the thinner nanosheet architecture of MSE-CNTs/Ni-MOF, and the effective electrically conductive network within the composite. This work marks a paradigm shift from greenhouse gas CO2 to excellent energy storage materials, paving the way for addressing both the energy and climate issues simultaneously.

Se-doped cobalt-nickel sulfide hollow nanospheres with heterostructure and engineered defects as high-performance electrode for supercapacitors

Porous structures with heterogeneous interfaces and defects are an important way to enhance electrochemically active sites and facilitate electron transfer, while also improving the permeability of the electrolyte and the rate of ion transport. In this study, Se-doped cobalt-nickel sulfide (Se-CoNi2S4) hollow nanospheres with heterostructure and defects were prepared from CoNi metal-organic framework (MOF) as substrate by sequential sulfidation and selenization treatments. Notably, the hollow structure not only offers additional ion transport channels to promote rapid transfer of ions in the electrolyte but also provides an increased number of electrochemically active sites. The morphology and electrochemical performance of Se-CoNi2S4 nanospheres with different levels of Se doping were compared. From the results, Se doping not only enhances the conductivity of CoNi2S4 but also increases its charge storage capacity. As an electrode material, the synthesized Se-CoNi2S4 composite that was synthesized demonstrated a notable specific capacitance of 1260 F g−1 at 1 A g−1. Additionally, when Se-CoNi2S4 was utilized as the anode and activated carbon served as the cathode in an asymmetric supercapacitor, it achieved an energy density of 44.6 Wh kg−1 at a power density of 827 W kg−1. After undergoing 10,000 cycles, this device demonstrated exceptional cycling stability, retaining 80.2 % of its initial capacitance. Therefore, the synthesized electrode material Se-CoNi2S4 has significant potential for energy storage applications.

Hydrothermally synthesized copper telluride nanoparticles: First approach to flexible solid-state symmetric supercapacitor

Supercapacitors, with their high-power density, rapid charge–discharge rates, and long cycle life, have emerged as promising energy storage devices for numerous applications. Among the various materials explored for supercapacitor electrodes, copper-based chalcogenides have gathered significant attention due to their intriguing electrochemical properties and simple synthesis routes. While there have been thorough investigations in other fields, only a limited number of studies have focused on the specific application of copper telluride nanoparticles as supercapacitors. In this study, we present a novel approach utilizing hydrothermally synthesized copper telluride (Cu2-xTe) nanoparticles as binder-free electrodes on flexible stainless steel (SS) substrates. The Cu2-xTe nanoparticles, with their small particle (38 nm) and highly crystalline structure, enhance charge storage and promotes a pseudocapacitive behavior, resulting in a high specific capacitance [381 F/g (163 mF/cm2) at 2 mV/s] in a 2 M KCl electrolyte solution. Moreover, we studied and explained the distinct contributions of surface-controlled and diffusion-limited processes to the overall charge storage capacity of the electrode. Our pioneering effort includes the fabrication and analysis of flexible, symmetric solid-state supercapacitor devices utilizing Cu2-xTe electrodes with PVA-LiClO4 gel electrolyte. These devices demonstrate an energy density of 11 Wh/kg, a power density of 800 W/kg, and an impressive 85 % retention of cyclic stability after 5000 cycles.

Efficacy of Capacitive Deionization Flow Cell Fabricated with Carbon Nanomaterial Modified Electrodes

The supply of freshwater is becoming a serious global challenge. Capacitive deionization (CDI) has been recognized as apromising and smart desalination technique to solve it. Carbonaceous materials, due to their non-toxic characteristics, areused for filtration, adsorption, and water deionization. In this study, a newly designed, homemade low CDI system wasfabricated, and carbon as electrode material was prepared from waste leather through a one-step activated pyrolysis process. Carbonaceous materials prepared at different temperatures were characterized by Fourier-transform infrared (FTIR), scanning electron microscopy (SEM), and X-ray diffraction (XRD) techniques. The charge storage capacity of the carbon materials casted on a glassy carbon electrode was evaluated using cyclic voltammetric and galvanostatic chargingdischarging techniques. The fabricated CDI system could be successfully used for the study of the removal capacity of NaCl from an aqueous solution. The removal capacity of carbon prepared at 600 °C from leather is 11.58 mgg1, which is about three times higher than commercial activated carbon at flow rate and applied potential of 23 mL min–1 and 1.0 V, respectively. Dhaka Univ. J. Sci. 72(2): 52-60, 2024 (July)

CO2- tolerant CuFe2O4 as Bifunctional Electrocatalyst for Transition from Rechargeable Li-O2 to Li-CO2 Batteries

CO2-tolerant rechargeable Lithium-Air batteries are seen as a high-performing alternative to Li-ion batteries. They utilize O2 from the air, reducing it at the cathode to form lithium peroxide (Li2O2) during discharge which is then oxidized to form lithium-metal and freeing O2 during charging. Most of the present studies involve pure O2 as the cathode material instead of aerial O2, which has a stiff-challenge due to atmospheric CO2 which produces Li2CO3 during discharge, posing a resistive load on the battery if not re-oxidized on charging. Ideally, presence of CO2 should enhance the charge-storage capacity if it is cycled reversibly. Thus, present research aims at taking advantage of both O2 and CO2 by employing metallic Cu on CuFe2O4 catalyst, synthesized from a one-step auto-combustion route. The Cu metal present in the catalyst leads to a low surface-area, yet the catalyst demonstrates excellent oxygen reduction reaction and moderate oxygen evolution reaction activity. excellent CO2 reduction reaction activity, oxidizing both the Li2O2 and the Li2CO3 during charge in both 10% CO2 and 100% CO2 atmospheres. The fabricated Li-CO2 battery operates for practical application, suggesting the suitability of the catalyst for the transition from practical Li-O2 battery to Li-Air battery.

Scanning Electrochemical Microscopy Meets Optical Microscopy: Probing the Local Paths of Charge Transfer Operando in Booster-Microparticles for Flow Batteries.

Understanding the oxidation/reduction dynamics of secondary microparticles formed from agglomerated nanoscale primary particles is crucial for advancing electrochemical energy storage technologies. In this study, the behavior of individual copper hexacyanoferrate (CuHCF) microparticles is explored at both global and local scales combining scanning electrochemical microscopy (SECM), for electrochemical interrogation of a single, but global-scale microparticle, and optical microscopy monitoring to obtain a higher resolution dynamic image of the local electrochemistry within the same particle. Chronoamperometric experiments unveil a multistep oxidation/reduction process with varying dynamics. On the one hand, the global SECM analysis enables quantifying the charge transfer as well as its dynamics at the single microparticle level during the oxidation/reduction cycles by a redox mediator in solution. These conditions allow mimicking the charge storage processes in these particles when they are used as solid boosters in redox flow batteries. On the other hand, optical imaging with sub-particle resolution allows the mapping of local conversion rates and state-of-charge within individual CuHCF particles. These maps reveal that regions of different material loadings exhibit varying charge storage capacities and conversion rates. The findings highlight the significance of porous nanostructures and provide valuable insights for designing more efficient energy storage materials.

Structural, optical and dielectric properties of (AZT) aluminum doped zinc titanate nano-composites

Aluminum-doped Zinc Titanate (AZT) AlxZn1-xTiO3 ( for x= 0.20,0.40,0.60,0.80) nanoparticles are synthesized through low temperature hydrothermal method and their physical properties such as structure, surface, energy gap and dielectric characteristics were investigated using X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), Transmission Electron Microscopy (TEM), UV-visible spectroscopy and impedance analysis. XRD analysis indicated structural transformation of tetragonal phase for samples of x = 0.20 to 0.60 and some secondary phases for x=0.80. It was found that lattice constants of the sample decrease with increasing aluminium content. The morphology of nano-composites, as evidenced by FESEM and TEM imaging, displayed the formation of nano-spheres and nano-rods. The impedance and dielectric modulus analysis for the current samples revealed their dielectric behaviour, microstructure and conduction procedure. However negative dielectric property was seen in nano-composite with x=0.60. All samples with x ranging between 0.2 to 0.8 displayed high ac-electrical conductivity at 1 MHz frequency. These samples are well suitable for charge storage capacitors and as perfect absorbers.

Engineering Mn Vacancies to Enhance Ion Kinetics in Layered Manganese Silicate for High-Energy and Durable Intercalation Pseudocapacitance.

Transition metal silicates (TMSs) are potential electrodes for aqueous metal-ion intercalation pseudocapacitors owing to their superior theoretical capacity and high structural stability. However, the narrow interlayer spacing and intrinsic inert basal plane of TMSs lead to sluggish ions and charge transfer, causing an undesirable energy storage performance. Herein, rich Mn vacancies are introduced in layered manganous silicates (M2-xS@FA) to expedite K+ diffusion, while enhancing charge storage capacity and prolonging lifespan. In situ characterizations validate the K+ intercalation pseudocapacitance mechanism with evident crystal structure and valence state variations in M2-xS@FA. Both theoretical calculations and electrochemical experimental evaluations elucidate the imperative role of Mn vacancies in enhancing K+ diffusion kinetics and electron transfer through increased interlayer spacing and activated basal plane. Mn vacancies further boost the charge storage capacity by providing additional K+ storage sites, while simultaneously reinforcing local atomic bonding within M2-xS@FA, thereby augmenting structural stability. The assembled aqueous asymmetric solid-state cell, featuring a M2-xS@FA cathode, demonstrates exceptional power and energy densities (144.08 W h kg-1 at 375.80 W kg-1) and ultralong lifespan (100% capacity retention after 10,000 cycles). This work heralds a paradigm whereby modulating cation vacancies in layered TMSs significantly enhances K+ storage and stability for high-energy intercalation pseudocapacitance.

Multifunctional polymeric coating on stainless steel current collectors in aqueous energy storage devices

Herein, low cost stainless steel foils are employed as current collectors in aqueous Na-ion supercapacitors, while the foils are coated with following conducting polymers, namely, polyimide (PI), Schiff base polymer (SBP), polyanthraquinone sulfide (PAQS) and polyaniline (PANI). The foremost purpose of these polymeric coatings is the prevention of corrosion, and the resultant improvements in device performances. Notwithstanding, these polymeric coatings provide few additional benefits in device characteristics, and these are following: (i) enhancement of electrolyte stability window, (ii) contributing charge storage capacitance, (iii) conversion of 2D pristine substrate to 3D porous current collector. The four coating polymers are electrochemically characterized, and PI is selected for fabricating Na-ion supercapacitor cells. The PI-coating reduces the stainless steel’s corrosion rate ∼ 68 times, expands the electrolyte stability window ∼ 1.2 times, and delivers ∼ 2 times higher capacitance with respect to pristine current collector, whereas no appreciable interfacial resistances are observed. The supercapacitor cell with PI-functionality demonstrates ∼ 6.6 times improved capacitance than that of pristine cell at 25 mA/g current density, while > 95 and ∼ 90 % Faradaic efficiencies are noted for former and latter, respectively. The distinct enhancement of cell performances clearly demonstrates the effectiveness of multifunctional polymeric coating on corrosion-prone metallic current collectors.

One-Step Synthesis of Heterostructured Mo@MoO2 Nanosheets for High-Performance Supercapacitors with Long Cycling Life and High Rate Capability.

Supercapacitors have gained increased attention in recent years due to their significant role in energy storage devices; their impact largely depends on the electrode material. The diversity of energy storage mechanisms means that various electrode materials can provide unique benefits for specific applications, highlighting the growing trend towards nanocomposite electrodes. Typically, these nanocomposite electrodes combine pseudocapacitive materials with carbon-based materials to form heterogeneous structural composites, often requiring complex multi-step preparation processes. This study introduces a straightforward approach to fabricate a non-carbon-based Mo@MoO2 nanosheet composite electrode using a one-step thermal evaporating vapor deposition (TEVD) method. This novel electrode features Mo at the core and MoO2 as the shell and demonstrates exceptional electrochemical performance. Specifically, at a current density of 1 A g-1, it achieves a storage capacity of 205.1 F g-1, maintaining virtually unchanged capacity after 10,000 charge-discharge cycles at 2 A g-1. The outstanding long-cycle stability is ascribed to the vertical two-dimensional geometry, the superior conductivity, and pseudocapacitance of the Mo@MoO2 core-shell nanosheets. These attributes significantly improve the electrode's charge storage capacity, charge transfer speed, and structural integrity during the cycling process. The development of the one-step grown Mo@MoO2 nanosheets offers a promising way for the advancement of high-performance, non-carbon-based supercapacitor nanocomposite electrodes.

Enhanced electron transfer kinetics via constructing co-catalytic system of cerium oxide and carbon dots enabling efficient electrosynthesis of hydrogen peroxide in neutral media

The sluggish kinetics coupled with the competition of four-electron pathway in neutral media diminishes the production efficiency of hydrogen peroxide (H2O2) via the two-electron oxygen reduction reaction (2e− ORR). To address this dilemma, this contribution proposes one electron modulation strategy to expedite the charge transfer capability by integrating carbon dots with CeO2 (CDs/CeO2) for the efficient neutral electrosynthesis of H2O2. It was found that the integration could effectively bolster both the activity and selectivity of 2e− ORR on CDs and CeO2. Remarkably, the highest 2e− selectivity could reach up to 92 % for the optimized CDs/CeO2, substantially surpassing that (77 %) of pristine CeO2, together with about 1.5 times enhancement of activity. Meanwhile, it also delivered a superior long durability at 20 mA cm−2 for 24 h and a high Faraday efficiency of 97 %. Further in-situ transient potential scanning (TPS) technique revealed that the pseudo-capacitance and charge storage capacity of CeO2 were significantly tuned by CDs during dynamic ORR process, being conducive to the reaction kinetics and the 2e− selectivity. The findings in this work not only extends the co-catalytic system based on CDs and rare earth materials for 2e− ORR, but also offers novel insights into correlation between their electron distribution dynamics and 2e− ORR performance.

Nickel sulfide nanoparticles decorated on carbon spheres derived from Verbena officinalis for high-performance asymmetric all-solid-state flexible supercapacitors

The crafting and development of electrode materials possessing extensive energy storage capacities, alongside their adherence to environmental and economic principles, along with their outstanding capacitive behaviors, stand as pivotal elements in propelling the technological progress of supercapacitors. In this study, we utilized discarded Verbena officinalis (VOCs) as a carbon substrate and successfully synthesized porous hollow carbon spheres through an in-situ hydrothermal method, subsequently depositing NiS nanoparticles to form a shell-like structured material. The optimized VOCs/NiS-3 composite material exhibited an exceptional specific capacitance of 202.8 mAh g−1 at a current density of 1.0 A g−1; it maintained 71 % of its capacitance even at a high current density of 10 A g−1 (144.2 mAh g−1). After enduring 10,000 charge-discharge iterations, the preservation of charge storage capacity was 81.7 %, highlighting the material's outstanding performance in terms of rapid charge-discharge rates and enduring stability. Furthermore, within a PVA/KOH gel electrolyte, we fabricated an asymmetric all-solid-state supercapacitor device that delivered an energy density of 32.58 Wh k g−1 at a power density of 800 W k g−1. The device sustained a capacitance loss rate of 9.9 % and a coulombic efficiency of 96.8 % after 5000 cycles. Even after 3000 repeated bending at 120°, the capacitance retention reached 88.3 %, indicating the device's exceptional specific capacitance, flexibility and longevity. This research offers a renewable and waste-resource recycling design strategy for synthesizing outstanding-performance, flexible, all-solid-state supercapacitor electrode materials with NiS deposited on discarded biomass carbon, unveiling considerable potential for enhancing energy storage efficiency.