Effect of Time on a Hierarchical Corn Skeleton-Like Composite of CoO@ZnO as Capacitive Electrode Material for High Specific Performance Supercapacitors

Recovery of heavy metal complexes from wastewaters: A critical review of mechanisms and technologies

Heavy metal complexes (HMCs) pose significant ecological challenges while also holding attractive economic value. This review comprehensively summarizes advanced techniques for recovering HMCs from wastewater, including reductive recovery, oxidative decomplexation-recovery, and non-redox separation. Physical and chemical separation approaches utilize specific properties of metal complexes for efficient segregation. Specifically, we explore oxidative decomposition techniques, emphasizing the underlying mechanisms and practical application for selective and non-selective decomplexation techniques. The crucial role of cathodic potential on the efficiency and selectivity of electrochemical reduction processes is also examined. In addition, a comprehensive cost assessment, including energy consumption, associated with these recovering processes is investigated, and opinions on the inadequacy of current studies are provided. Overall, this review uniquely integrates findings on selective physical separation, oxidation, and reduction processes as well as the cost assessments for these techniques, providing a novel and comprehensive perspective on heavy metal recovery. It aims to bridge existing gaps in literature and advance the development of effective recovery methodologies for HMCs.

Preparation of high-performance adsorption carbon materials via hydrothermal carbonization of agricultural solid waste-grapevines

This study uses grapevine agricultural waste to prepare grapevine-derived biobased activated carbon (AGV) through chemical activation with NaOH after hydrothermal carbonization. A comprehensive analysis of the adsorption performance and mechanisms of AGV for methylene blue (MB) was conducted. The results demonstrated that AGV possesses a highly developed reticular pore structure, with a specific surface area of 3230.57 m2 g-1 and is rich in oxygen functional groups (OFGs). At pH 7.0, AGV achieved a removal rate of 90 % within 30 min, with a maximum adsorption capacity of 661.7 mg g-1, surpassing that of most previously reported activated carbons. Adsorption followed the Langmuir isotherm and pseudo-second-order kinetics, with thermodynamics confirming endothermic and spontaneous MB adsorption. The adsorption mechanism primarily involves chemical adsorption, including electrostatic interactions, pore filling, hydrogen bonding, acid-base interactions, and π-π stacking. The AGV maintained 86.7 % adsorption efficiency after 5 cycles, demonstrating excellent recyclability. This study provides a novel approach for preparing high-performance adsorption materials from waste biomass.

Enhanced supercapacitor performance using EG@COF: a layered porous composite

In this work, to address the issue of poor conductivity in COFs, a layered porous composite (EG@COF) was successfully synthesized. A redox-active COF (DAAQ-TFP COF) was grown on the surface of expanded graphite (EG) through a solvent-free in situ synthesis. SEM analysis displayed that the obtained composite (EG@COF) possessed a layered porous structure. Further investigations revealed that EG not only improved electrical conductivity but also regulated the pore size of the COFs. This structure was highly conducive to enhancing the specific capacitance of the electrode material. An electrochemical study demonstrated that the specific capacitance of EG@COF-3 reached 351 C g-1 at 1 A g-1, with 94.4% capacitance retention after 10 000 cycles. The excellent capacitance retention was attributed to the stable backbone of the COF. Meanwhile, an asymmetric supercapacitor (ACS) comprising activated carbon (AC) and EG@COF exhibited an energy density of 16.4 W h kg-1 at a power density of 806.0 W kg-1.

Recent advances in the synthesis and application of graphene aerogel and silica aerogel for environment and energy storage: A review

Aerogel materials have gained considerable attention in recent years due to their promising applications in environmental and energy storage fields, owing to their exceptional properties, including high porosity, ultra-low thermal conductivity, low density, and high specific surface area. This review begins by examining novel synthesis techniques, including sol-gel processing, chemical crosslinking, and templating, that enhance both the microstructural and functional properties of aerogels. Next, we explore the applications of graphene and silica aerogels in environmental and energy conservation technologies. Graphene aerogels, in particular, demonstrate significant potential in water purification by effectively removing antibiotics, offering a new approach to water treatment. The combination of silica aerogels with phase change materials, along with their use in supercapacitors, demonstrates their potential for energy conservation. Additionally, we discuss the synergistic effects of silica and graphene aerogels, which further broaden their applications. Finally, the paper concludes by summarizing the potential of graphene and silica aerogels as functional materials for environmental applications and outlining the challenges and future directions for their development and industrial use.

Advancements in iron-based photocatalytic degradation for antibiotics and dyes

The accelerated growth of the economy and advancements in medical technology have led to the discharge of a diverse range of organic pollutants into water sources. Recent investigations into water treatment have demonstrated the potential for integrating photocatalysis with techniques such as photocatalytic persulfate activation and the Photo-Fenton process for more efficient wastewater management. Iron-based photocatalysts responsive to visible light offer several advantages, including non-toxicity, safety, affordability, and excellent chemical and optical properties. Currently, there is a notable increase in research activity focused on the iron-based photocatalytic degradation of antibiotics and dyes. Given their abundance, cost-effectiveness, and eco-friendliness, iron-based photocatalysis shows considerable promise for various applications, including water treatment, air purification, and energy conversion. The use of iron-based photocatalysts has been demonstrated to facilitate the production of more reactive oxygen radicals, achievable through the Photo-Fenton process, direct photocatalysis, and the photocatalytic activation of persulfates. This approach has been demonstrated to enhance the degradation efficiency of antibiotics and dyes. Ongoing research encompasses the preparation and refinement of iron-based materials, exploration of photocatalytic mechanisms, and expansion of practical applications. Future directions include material innovation, elucidation of mechanisms, scaling up applications, and multifunctionalization, with the objective of enhancing photocatalytic efficiency, transitioning the technology from laboratory settings to practical scales, and providing effective solutions to environmental challenges and energy constraints.

Nickel vanadate nitrogen-doped carbon nanocomposites for high-performance supercapacitor electrode

A nickel-vanadium-based bimetallic precursor was produced using the polymerization process by urea-formaldehyde copolymers. The precursor was then calcined at 800 °C in an argon ambiance to form a Ni3V2O8-NC magnetic nanocomposite. Powerful techniques were used to study the physical characteristics and chemical composition of the fabricated Ni3V2O8-NC electrode. PXRD, Raman, and FTIR analyses proved that the crystal structure of Ni3V2O8-NC included N-doped graphitic carbon. FESEM and TEM analyses imaging showed the distribution of the Ni3V2O8 nanoparticles on the layered graphitic carbon structure. TEM images showed the prepared sample has a particle size of around 10-15 nm with an enhanced active site area of 146 m2/g, as demonstrated by BET analysis. Ni3V2O8-NC nanocomposite exhibits magnetic behaviors and a magnetization saturation value of 35.99 emu/g. The electrochemical (EC) studies of the synthesized Ni3V2O8-NC electrode proceeded in an EC workstation of three-electrode. In a 5 M potassium hydroxide as an electrolyte, the cyclic voltmeter exhibited an enhanced capacitance (CS) of 915 F/g at 50 mV/s. Galvanic charge-discharge (GCD) study also exhibited a superior capacitive improvement of 1045 F/g at a current density (It) of 10 A/g. Moreover, the fabricated Ni3V2O8-NC nanocomposite displays a good power density (Pt) of 356.67 W/kg, improved ion accessibility, and substantial charge storage. At the high energy density (Et) of 67.34 W h/kg, the obtained Pt was 285.17 W/kg. The enhanced GCD rate, cycle stability, and Et of the Ni3V2O8-NC magnetic nanocomposite nominate the sample as an excellent supercapacitor electrode. This study paves the way for developing effective, efficient, affordable, and ecologically friendly electrode materials.

N, S, O Self-Doped Carbon Derived from Grapefruit Peel for High-Performance Supercapacitors

The development of high-capacity carbon for supercapacitors is highly desirable but challenging. In this work, we design a N, S, O self-doped carbon electrode (NSOC-800) with high capacitance and good stability via the carbonization of grapefruit peel via a one-step KOH activation method without extra dopants. The existence of heteroatoms enables the NSOC-800 to have a high specific capacitance of 280 F/g and a great cycling performance, with 90.1% capacitance retention after 5000 cycles. Moreover, the symmetric supercapacitor with NSOC-800 electrodes delivers a maximum energy density of 5 Wh/kg with a power density of 473 W/kg. Such a promising method to achieve carbon materials with self-doping heteroatwoms is of great significance for developing highly efficient electrodes for energy storage devices.

Phase-Independent Reactive Power Compensation Based on Four-Wire Power Converter in the Presence of Angular Asymmetry between Voltage Vectors

The paper presents the reactive power compensation method that allows for reducing the active power flow even in the presence of angular asymmetry between voltage vectors of the utility grid. Reactive power compensation ensures the reduction of power transmission losses and therefore brings significant economic benefits to electricity consumers. The concept of the alternating current/direct current (AC/DC) converter for prosumer applications operating as a local reactive power compensator has been proposed. The system is driven by a multi-resonant algorithm, allowing for independent control of the reactive power in each phase. The proposed method was validated experimentally by using a prototype of the converter, programmable AC source, and grid impedance model. The method made it possible to cover the reactive power demand without unnecessary active power generation and thus to improve the efficiency of the analyzed prototype. This solution can be implemented particularly in radial grids and non-urban areas.

Automatic Generation Control of Multi-Source Interconnected Power System Using FOI-TD Controller

Automatic Generation Control (AGC) delivers a high quality electrical energy to energy consumers using efficient and intelligent control systems ensuring nominal operating frequency and organized tie-line power deviation. Subsequently, for the AGC analysis of a two-area interconnected hydro-gas-thermal-wind generating unit, a novel Fractional Order Integral-Tilt Derivative (FOI-TD) controller is proposed that is fine-tuned by a powerful meta-heuristic optimization technique referred as Improved-Fitness Dependent Optimizer (I-FDO) algorithm. For more realistic analysis, various constraints, such as Boiler Dynamics (BD), Time Delay (TD), Generation Rate Constraint (GRC), and Governor Dead Zone (GDZ) having non-linear features are incorporated in the specified system model. Moreover, a comparative analysis of I-FDO algorithm is performed with state-of-the-art approaches, such as FDO, teaching learning based optimization, and particle swarm optimization algorithms. Further, the proposed I-FDO tuned controller is compared with Fractional Order Tilt Integral Derivative (FOTID), PID, and Integral-Tilt Derivative (I-TD) controllers. The performance analysis demonstrates that proposed FOI-TD controller provides better performance and show strong robustness by changing system parameters and load condition in the range of  ± 50%, compared to other controllers.

Enhancing electrochemical performance of electrode material via combining defect and heterojunction engineering for supercapacitors

The poor conductivity and deficient active sites of transition metal oxides lead to low energy density of supercapacitors, which limits their wide application. In this work, double transition metal oxide heterojunctions with oxygen vacancy (V_o-ZnO/CoO) nanowires are prepared by effective hydrothermal and thermal treatments. The formation of the heterojunction results in the redistribution of interface charge between ZnO and CoO, generating an internal electric field to accelerate the electron transport. Meanwhile, oxygen vacancies can enhance the redox reaction activity to further improve the electrochemical kinetics of the electrode material. Therefore, the prepared V_o-ZnO/CoO can provide a superior specific capacity of 845 C g^-1 (1 A g^-1). An asymmetric supercapacitor with the V_o-ZnO/CoO as positive electrode shows a higher energy density of 51.6 Wh kg^-1 when the power density reaches 799.9 W kg^-1. This work proposes a synergistic combination of defect and heterojunction engineering to improve the electrochemical properties of materials, providing an important guidance for material design in energy-storage field.

Synthesis of a NiMoO4/3D-rGO Nanocomposite via Starch Medium Precipitation Method for Supercapacitor Performance

This paper presents research on the synergistic effects of nickel molybdate and reduced graphene oxide as a nanocomposite for further development of energy storage systems. An enhancement in the electrochemical performance of supercapacitor electrodes occurs by synthesizing highly porous structures and achieving more surface area. In this work, a chemical precipitation technique was used to synthesize the NiMoO4/3D-rGO nanocomposite in a starch media. Starch was used to develop the porosities of the nanostructure. A temperature of 350 °C was applied to transform graphene oxide sheets to reduced graphene oxide and remove the starch to obtain the NiMoO4/3D-rGO nanocomposite with porous structure. The X-ray diffraction pattern of the NiMoO4 nano particles indicated a monoclinic structure. Also, the scanning electron microscope observation showed that the NiMoO4 NPs were dispersed across the rGO sheets. The electrochemical results of the NiMoO4/3D-rGO electrode revealed that the incorporation of rGO sheets with NiMoO4 NPs increased the capacity of the nanocomposite. Therefore, a significant increase in the specific capacity of the electrode was observed with the NiMoO4/3D-rGO nanocomposite (450 Cg−1 or 900 Fg−1) when compared with bare NiMoO4 nanoparticles (350 Cg−1 or 700 Fg−1) at the current density of 1 A g−1. Our findings show that the incorporation of rGO and NiMoO4 NP redox reactions with a porous structure can benefit the future development of supercapacitors.

Electrochemical Assessment of As-Deposited Co(OH)2 by Electrochemical Synthesis: The Effect of Synthesis Temperature on Performance

In this paper, the influence of an electrolytic temperature bath was used in the electrodeposition process on the size, color, and shape of the as-deposited Co(OH)2, and the electrochemical performance was investigated. Three different temperatures of 25, 60, and 95 °C were evaluated for the electrodeposition of Co(OH)2 on stainless steel plates (SSP). The electrochemical performance of the as-deposited electrodes (SSP) was measured in a symmetric electrochemical cell (EC) arrangement. XRD, SEM, and N2 physisorption analyses were carried out to evaluate the structure and morphological composition, along with the textural properties. Results showed that the hexagonal platelet micro-clusters of Co(OH)2 are formed in a mixed composition of both α-Co(OH)2 and β-Co(OH)2 phases, with the α-Co(OH)2 phase being the major phase formed in the electrodeposition process at temperatures below 95 °C, as suggested by the XRD analysis. Electrochemical cell performances were evaluated by galvanostatic cycling, results showed maximum areal capacity values of 1.97, 2.69, and 4.34 mA h cm–2 at a charge/discharge current of 6.25mA cm–2, for the as-deposited materials at 25, 60 and 95 °C, respectively. The specific power of the EC reached up to 19 kW kg–1 for the EC obtained material at 60 °C, with a specific energy of 2.8 W h kg–1. The maximum specific energy was reached at a current density of 6.25 mA cm−2, with a value of 10.79 W h kg–1 for the EC at 60 °C. These results offer some insight into how the morphology and composition of thin films can be tuned by the electrochemical synthesis temperature, yielding different electrochemical performances and areal capacity behaviors.

Facilely Synthesized NiCo2O4/NiCo2O4 Nanofile Arrays Supported on Nickel Foam by a Hydrothermal Method and Their Excellent Performance for High-Rate Supercapacitance

NiCo2O4 nanoleaf arrays (NCO NLAs) and NiCo2O4/NiCO2O4 nanofile arrays (NCO/NCO NFAs) material was fabricated on flexible nickel foam (NF) using a facile hydrothermal approach. The electrochemical performance, including the specific capacitance, charge/discharge cycles, and lifecycle of the material after the hydrothermal treatment, was assessed. The morphological and structural behaviors of the NF@NCO NLAs and NF@NCO/NCO NFAs electrodes were analyzed using a range of analysis techniques. The as-obtained nanocomposite of the NF@NCO/NCO NFAs material delivered outstanding electrochemical performance, including an ultrahigh specific capacitance (Cs) of 2312 F g−1 at a current density of 2 mA cm−2, along with excellent cycling stability (98.7% capacitance retention after 5000 cycles at 5 mA cm−2). These values were higher than those of NF@NCO NLAs (Cs of 1950 F g−1 and 96.3% retention). The enhanced specific capacitance was attributed to the large electrochemical surface area, which allows for higher electrical conductivity and rapid transport between the electrons and ions as well as a much lower charge-transfer resistance and superior rate capability. These results clearly show that a combination of two types of binary metal oxides could be favorable for improving electrochemical performance and is expected to play a major role in the future development of nanofile-like composites (NF@NCO/NCO NFAs) for supercapacitor applications.

Fabrication of Hierarchical NiMoO4/NiMoO4 Nanoflowers on Highly Conductive Flexible Nickel Foam Substrate as a Capacitive Electrode Material for Supercapacitors with Enhanced Electrochemical Performance

Hierarchical NiMoO4/NiMoO4 nanoflowers were fabricated on highly conductive flexible nickel foam (NF) substrates using a facile hydrothermal method to achieve rapid charge-discharge ability, high energy density, long cycling lifespan, and higher flexibility for high-performance supercapacitor electrode materials. The synthesized composite electrode material, NF/NiMoO4/NiMoO4 with a nanoball-like NF/NiMoO4 structure on a NiMoO4 surface over a NF substrate, formed a three-dimensional interconnected porous network for high-performance electrodes. The novel NF/NiMoO4/NiMoO4 nanoflowers not only enhanced the large surface area and increased the electrochemical activity, but also provided an enhanced rapid ion diffusion path and reduced the charge transfer resistance of the entire electrode effectively. The NF/NiMoO4/NiMoO4 composite exhibited significantly improved supercapacitor performance in terms of a sustained cycling life, high specific capacitance, rapid charge-discharge capability, high energy density, and good rate capability. Electrochemical analysis of the NF/NiMoO4/NiMoO4 nanoflowers fabricated on the NF substrate revealed ultra-high electrochemical performance with a high specific capacitance of 2121 F g−1 at 12 mA g−1 in a 3 M KOH electrolyte and 98.7% capacitance retention after 3000 cycles at 14 mA g−1. This performance was superior to the NF/NiMoO4 nanoball electrode (1672 F g−1 at 12 mA g−1 and capacitance retention 93.4% cycles). Most importantly, the SC (NF/NiMoO4/NiMoO4) device displayed a maximum energy density of 47.13 W h kg−1, which was significantly higher than that of NF/NiMoO4 (37.1 W h kg−1). Overall, the NF/NiMoO4/NiMoO4 composite is a suitable material for supercapacitor applications.

Enhanced electrochemical performance of nanoplate nickel cobaltite (NiCo2O4) supercapacitor applications

Well-ordered, unique interconnected nanostructured binary metal oxides with lightweight, free-standing, and highly flexible nickel foam substrate electrodes have attracted tremendous research attention for high performance supercapacitor applications owing to the combination of the improved electrical conductivity and highly efficient electron and ion transport channels. In this study, a unique interconnected nanoplate-like nickel cobaltite (NiCo2O4) nanostructure was synthesized on highly conductive nickel foam and its use as a binder-free material in energy storage applications was assessed. The nanoplate-like NiCo2O4 nanostructure electrode was prepared by a simple chemical bath deposition method under optimized conditions. The NiCo2O4 electrode delivered an outstanding specific capacitance of 2791 F g-1 at a current density of 5 A g-1 in a KOH electrolyte in a three-electrode system as well as outstanding cycling stability with 99.1% retention after 3000 cycles at a current density of 7 A g-1. The as-synthesized NiCo2O4 electrode had a maximum energy density of 63.8 W h kg-1 and exhibited an outstanding high power density of approximately 654 W h kg-1. This paper reports a simple and cost-effective process for the synthesis of flexible high performance devices that may inspire new ideas for energy storage applications.

Facile synthesis of NF/ZnOx and NF/CoOx nanostructures for high performance supercapacitor electrode materials

NF/ZnOx nanocone and NF/CoOx nanoparticle electrode materials were fabricated on a nickel foam surface using a simple chemical bath deposition approach and assessed as an electrode material for high-performance supercapacitors.