Search Results (2,913)

The development of low-cost, environmentally friendly, and electrochemically stable electrode materials remains a significant challenge for supercapacitors. In the present study, composite materials based on a montmorillonite K10 clay support were synthesized and characterized. Coconut shell-derived activated carbon, manganese dioxide (MnO₂), and/or activated carbon (YP-80F) modified with silver nanoparticles were utilized as functional additives to the clay matrix. The aim of this work is to enhance the specific capacitance and electrochemical stability of the materials through a synergistic effect between these individual components. The novelty of this study lies in the integration of montmorillonite K10-based nanocomposites with an ion-exchange hydrogel membrane and in the investigation of the synergistic effects of different functional additives on the electrochemical performance of supercapacitors. The electrodes were fabricated using a casting method, while a commercial membrane, pre-soaked in a sodium sulfate solution, was employed as both separator and electrolyte. The membrane functions as an ion-exchange hydrogel, contributing to high ionic conductivity and reduced interfacial resistance. The electrochemical results indicate that the presence of additives significantly improves electron transport within the system, while the K10 clay support acts as a stable structural framework. The obtained results demonstrate the potential of clay-based nanocomposites integrated into gel-polymer systems for the development of efficient, low-cost, and environmentally friendly next-generation supercapacitors. Full article

As global power systems transition toward increasing penetration of renewable energy sources (RESs), such as solar and wind, maintaining frequency stability in converter-dominated low-inertia grids has become a critical challenge. This review examines the role of inertia in power system dynamics, emphasising the consequences of reduced mechanical inertia, the resulting increase in the rate of change of frequency (RoCoF), and the associated stability risks in grids with high inverter-based penetration. Inertial, primary, and secondary frequency response mechanisms are discussed alongside potential cascading failures, protection system triggering, and pathways toward fully renewable grids are assessed. Virtual inertia techniques, including synchronverters, swing-equation-based methods, virtual synchronous generators (VSGs), droop control, Virtual Oscillator Control (VOC), and matching control, are evaluated in terms of benefits, limitations, implementation complexity, and Technology Readiness Levels (TRLs). A key contribution is a multi-criteria evaluation framework that classifies these methods by control adaptability, scalability, and communication requirements, providing system operators with a structured basis for strategy selection. A comparative assessment of Phase-Locked Loop (PLL) synchronisation methods, including SRF-PLL, DDSRF-PLL, FLL-PLL, and Kalman filter-based approaches, is presented under weak-grid, unbalanced, and harmonic-distorted conditions. The integration of virtual inertia with energy storage technologies, such as batteries, supercapacitors, and flywheels, is also discussed, along with its role as an ancillary service within evolving electricity markets and grid codes. Collectively, this study provides a unified reference to advance intelligent, scalable, and deployment-ready frequency control in low-inertia renewable power systems, offering both theoretical insights and practical guidance for future high-RES grid architectures. Full article

Hybrid Energy Storage Systems (HESSs) have emerged as an inevitable solution in modern power systems and transport electrification. An HESS combines two or more complementary storage technologies—such as Batteries (BTs) with Supercapacitors (SCs), or BTs with thermal or mechanical energy storage, etc., to leverage their virtues. The robustness of HESS configurations is of utmost importance for exploring failure analysis and resilience approaches in BT-SC-based HESSs, which are crucial for long-term reliability, safety, and contributions towards future decarbonization goals. Hence, based on this motivation, this work focuses on the study of conventional and advanced HESS configurations, together with a method of configuration selection. Subsequently, the review aims to obtain a systematic identification, characterization, and understanding of the reasons behind HESS failures. This paper thus defines what HESS failures are and their possible mitigations, discussing many state-of-the-art research studies that may help researchers in finding correct and updated literature content concerning this research area. Finally, future trends and developments in BT-SC-based HESSs are discussed. Full article

Electroless nickel–phosphorus (Ni–P) coatings were deposited on steel substrates for 20, 40, and 60 min to examine the effect of deposition time on their pseudocapacitive behavior in an alkaline electrolyte. The coatings were characterized by scanning electron microscopy (SEM/EDS), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy (EIS). Although coating mass, thickness, and roughness increased monotonically with deposition time, the electrochemical response showed a pronounced maximum at 40 min. The 40 min coating exhibited the highest areal capacitance in both CV and GCD measurements, reaching 33.1 ± 1.8 mF cm^–2 at 10 mV s^–1 and 426.5 ± 9.8 mF cm^–2 at 5 mA cm^–2, whereas the 60 min coating showed substantially lower capacitance. SEM and AFM confirmed progressive nodular coarsening and increasing surface roughness with time, but these geometric parameters alone did not explain the non-monotonic capacitance trend. In contrast, XPS revealed that the 40 min coating possessed the highest surface Ni content, while prolonged deposition led to a more P-enriched outermost surface. EIS further showed that the 40 min coating had the most favorable local high-frequency interfacial response, whereas the 60 min coating exhibited the highest local polarization. The results demonstrate that the electrochemical performance of electroless Ni–P coatings is more closely associated with the composition and accessibility of the activated near-surface region than with coating thickness or roughness alone, and that 40 min represents an interfacial optimum under the applied deposition conditions. Full article

Recently, aqueous asymmetric supercapacitors (ASCs) have attracted considerable attention as safe and high-power energy storage devices. However, achieving high energy density while maintaining long-term cycling stability remains a significant challenge. Herein, an aqueous ASC employing a Mo_1.33CT_x/CNT negative electrode and a hydrated V₂O₅·nH₂O/CNT positive electrode in a 5 M LiCl electrolyte is reported. The Mo_1.33CT_x i-MXene was synthesized via hydrothermal selective etching of an i-MAX precursor, whereas hydrated V₂O₅·nH₂O nanoflakes were prepared with peroxide-assisted hydrothermal treatment. The ordered-vacancy Mo_1.33CT_x i-MXene provides a stable negative potential window, redox-active sites, and favorable conditions for reversible Li⁺ intercalation/deintercalation, thereby contributing to pseudocapacitive charge storage. The assembled ASC delivered a stable operating voltage of 1.7 V, a specific capacitance of 61 F·g⁻¹ at 1 A·g⁻¹, an energy density of 25.2 Wh·kg⁻¹ at 883 W·kg⁻¹ and 86% capacitance retention after 10,000 cycles. Electrochemical impedance spectroscopy revealed relatively low internal resistance and efficient ion transport within the layered electrode architectures. These results highlight the strong potential of ordered-vacancy MXene/vanadium oxide systems for advanced aqueous energy storage applications. Full article

Namibia’s rural communities continue to experience limited and unreliable electricity access despite the potential of the country’s exceptional solar, wind, and biomass renewable energy resources. Conventional grid extension remains financially and technically impractical for dispersed off-grid settlements, underscoring the need for cost-effective, renewable-based alternatives. This paper presents a resource-driven design and multi-objective optimization framework for Hybrid Renewable Energy Systems (HRESs) tailored to Namibia’s off-grid communities. The proposed model integrates solar PV, wind turbines, biomass generators, and hydrogen-based fuel cells with a hybridized energy storage consisting of batteries, supercapacitors, and hydrogen tanks. Using the Non-dominated sorting Genetic Algorithm-II (NSGA-II), the system simultaneously minimizes Total Life Cycle Cost (TLCC), Levelized Cost of Electricity (LCOE), Loss of Power Supply Probability (LPSP), carbon dioxide (CO₂) emissions, and Wasted Renewable Energy (WRE). The framework is applied to three rural villages, Oluundje, Ombudiya, and Onguati, using high-resolution, site-specific renewable resource datasets and community-level load forecasts. The results demonstrate that resource-aligned configurations substantially improve system reliability (up to 99.28%), reduce LCOE (0.0023–0.0811 USD/kWh), and optimize dispatch behaviour across seasonal variations. Storage hybridization further enhances stability by balancing transient and long-duration deficits. Compared to existing diesel mini-grids, the optimized HRESs achieve markedly superior techno-economic and environmental performance. The proposed framework offers a scalable, adaptable, and policy-ready tool for accelerating sustainable rural electrification in Namibia. Full article

A fuel cell (FC)/supercapacitor (SC) hybrid powertrain is proposed for rubber tire gantry (RTG) cranes, aiming to address their characteristics of high peak/low average power demand and huge potential energy recovery. Unlike conventional design methods that neglect the coupling effects of energy management strategies (EMSs), this paper adopts a joint optimization (JO) for the powertrain parameters’ design. Parameters are preliminarily sized based on routine container handling tasks, then refined via a dynamic programming (DP)-based EMS for secondary optimization to minimize the total crane operation costs that cover hydrogen consumption as well as FC degradation. Iterations of the optimization process continue until targets are met. The results indicate that the JO framework achieves dual energy-economic goals, exhibiting a 57.33% enhancement in fuel economy compared to diesel-powered cranes through port validation while concurrently decreasing the SC’s capacity redundancy by 12.7%. These findings aid FC/SC RTG crane configuration design in ports. Additionally, the theoretical optimal operation cost obtained by the DP-based EMS can be used as a benchmark for evaluating other EMSs. Full article

The increasing penetration of inverter-based resources has significantly reduced system inertia, motivating the emergence of Fast Frequency Response (FFR) as a dedicated ancillary service. Existing methods for enabling wind power systems to deliver FFR universally treat the wind farm as a single equivalent turbine under uniform wind conditions, an assumption that is invalid in real large-scale wind farms where heterogeneous turbine types, rated capacities, inertia constants, and spatially non-uniform wind speed distributions render uniform allocation strategies suboptimal or operationally unsafe. This paper proposes a centralized wind farm-level FFR control framework that coordinates heterogeneous wind turbine generators (WTGs) and supercapacitor energy storage systems (SCESSs) through a prioritized two-tier dispatch hierarchy, in which SCESSs are assigned the highest dispatch priority and WTGs are engaged only when aggregate storage capacity is insufficient. A constrained optimization problem is formulated to allocate the individual FFR contribution of each WTG by minimizing the total kinetic energy extracted from the wind farm, while enforcing torque, electrical power, and rotor speed constraints for every unit with respect to turbine type, inertia constant, and prevailing wind condition. A coordinated rotor speed recovery strategy further eliminates secondary frequency disturbances during the post-FFR transition. The proposed framework is validated on a 138 MW heterogeneous wind farm simulation model comprising both Doubly-Fed Induction Generator and Permanent Magnet Synchronous Generator units interconnected to a modified IEEE 14-bus test system. The proposed method achieves a 38.85% improvement in frequency nadir relative to a baseline with no FFR provision, outperforming all investigated state-of-the-art approaches, while reducing total kinetic energy extraction from the wind turbine generators and eliminating secondary frequency disturbances during the post-FFR recovery phase. Full article

Transition-metal sulfides are promising electrode materials for high-performance supercapacitors but are often limited by poor conductivity, particle agglomeration, and insufficient active sites. Herein, Co-doped NiS₂ with tunable sulfur vacancies was directly grown on flexible carbon cloth via a facile one-step solvothermal method by systematically controlling sulfur source ratio, Ni:Co ratio, temperature, and reaction time. Structural analyses reveal that the optimized conditions of S:(Ni + Co) = 3:1, Ni:Co = 2:1, 160 °C, and 15 h promote the formation of phase-pure Co-doped NiS₂ hierarchical microspheres with enhanced crystallinity and abundant active sites from the synergistic interaction between Ni and Co. Consequently, the optimized electrode delivers an impressive capacitance of 1296 F g⁻¹ at a current density of 1 A g⁻¹, along with excellent rate performance, retaining more than 88% of its capacitance after 1500 charge/discharge cycles at current densities ranging from 2 to 20 A g⁻¹. This work highlights the critical role of synthesis parameter engineering in regulating defect chemistry, structure, and electrochemical performance in advanced energy storage applications. Full article

The conversion of bio-waste into functional energy materials provides a robust platform for addressing both environmental and energy challenges. In this paper, discarded absorbent pads are transformed into carbon-rich frameworks, which is followed by the fabrication of composites through the incorporation of Cu₄SnS₄ (CSS) for dual electrochemical applications. Integrating CSS into the waste-derived carbon matrix induces strong synergistic effects, improving electrical conductivity, increasing active-site availability, and accelerating charge-transfer kinetics. Comprehensive physicochemical analyses confirmed the successful formation of a well-integrated heterostructure composite with favorable structural and surface characteristics. Electrochemical evaluations further demonstrated that CSS-modified carbon exhibits superior bifunctional performance. In a two-electrode configuration, the composite delivers an energy density of 12.08 Wh kg⁻¹ at a power density of 250 W kg⁻¹ along with excellent cycling stability in supercapacitor applications. As an electrocatalyst, it achieves a low overpotential of 268 mV at −10 mA cm⁻² and a small Tafel slope of 75 mV dec⁻¹, reflecting efficient reaction kinetics. The strong durability observed in both systems underscores the structural integrity and long-term operational stability of the material. Overall, this paper advances a sustainable waste-to-resource strategy for fabricating multifunctional carbon-based composites, offering a promising platform for integrated energy-storage and hydrogen-generation technologies. Full article

Thermal regulation of electrode materials offers an effective strategy for optimizing electrochemical kinetics in phosphate-based energy-storage systems. In this work, cobalt phosphate (Co₃(PO₄)₂) (CoP) electrodes were directly synthesized on nickel foam through a hydrothermal route and subsequently annealed at different temperatures (300, 400, and 500 °C) to investigate the influence of thermal treatment on structural evolution and supercapacitive behavior. X-ray diffraction confirmed the formation of crystalline CoP, while FESEM analysis revealed a strong dependence of morphology on annealing temperature, with CoP-400 exhibiting a well-developed interconnected plate-like architecture favorable for ion transport. XPS and elemental mapping verified the successful incorporation and uniform distribution of Co, P, and O species. Electrochemical investigations demonstrated that annealing temperature critically governs charge-storage behavior, ion diffusion, and mass transport properties. Among all electrodes, CoP-400 exhibited the best electrochemical performance, delivering a high areal capacitance of 28.62 F/cm² at 20 mA/cm², together with the highest ionic diffusion coefficient, lowest equivalent series resistance (0.39 Ω), and dominant diffusion-controlled charge-storage contribution (89%). Furthermore, CoP-400 retained 84.44% capacitance after 12,000 cycles. An asymmetric supercapacitor assembled using CoP-400//AC achieved an areal capacitance of 302 mF/cm², an energy density (ED) of 0.094 mWh/cm², and excellent cycling stability. These findings highlight annealing-engineered CoP as a promising electrode material for high-performance asymmetric supercapacitors. Full article

With the rapid advancement of portable wearable electronics, flexible supercapacitors have ushered in new development opportunities. In recent years, MXene and its composites have demonstrated potential as advanced supercapacitor electrode materials due to their outstanding theoretical capacitance, specific surface area, conductivity, hydrophilicity, and mechanical flexibility. This review traces the development of MXene and summarizes common synthesis strategies, with a focus on the effects of different preparation methods on its structure and properties. Departing from previously reported work, this review draws from the practical requirements of flexible supercapacitors to conduct an in-depth analysis of the key factors influencing the charge storage, rate capability, cycling life, and mechanical flexibility of the devices. It summarizes common design strategies for MXene composites currently used to enhance device performance. Additionally, this study analyzes key challenges facing MXene-based electrode materials, including issues such as self-stacking of layers, insufficient oxidation stability, limited energy density, and structural degradation under complex deformation conditions. Mitigation strategies are summarized, including optimizing synthesis methods and constructing composite systems integrating carbon materials, conducting polymers, and transition metal compounds. Finally, future research directions for MXene in flexible energy storage are explored, emphasizing the need to achieve a balance between performance and manufacturability through synergistic regulation at structural design, interfacial engineering, and device levels. This review aims to provide theoretical guidance for the development of practical MXene-based wearable energy storage devices. Full article

Binder-free NiMn₂O₄@NiCo₂O₄ nanocomposites with NiMn₂O₄ nanoparticle (NP) surface coverage on NiCo₂O₄ nanosheets (NSs) are fabricated on nickel foam (NF) via a two-step microwave-assisted hydrothermal (MAH) method combined with annealing treatment, which can be used as a high-performance electrode material for supercapacitors. Specifically, a tulle-like NiCo₂O₄ nanosheet framework is first in situ grown on NF, followed by the growth of NiMn₂O₄ NPs on the surface of NiCo₂O₄ NSs via a secondary MAH process. To investigate the effect of the second-step holding time (HT) of MAH on material performance, a series of experiments were carried out with an HT of 15, 30, 45, and 60 min, and the microstructures and electrochemical properties of the products were analyzed. Structural characterization results confirm the successful synthesis of well-defined NiMn₂O₄-NPs@NiCo₂O₄-NSs composites. Electrochemical tests demonstrate that the product at an HT of 30 min has the best electrochemical performance with a higher specific capacitance of 441.56 F·cm⁻² at 1 A·cm⁻² and cycling stability (75% capacitance retention after 5000 cycles at 15 A·cm⁻²). The superior electrochemical properties are mainly attributed to the unique porous tulle-like NS structure with the largest specific surface area of the 30 min product. This distinctive structure affords abundant electrochemical active sites, effectively prevents structural collapse during long-term cycling, and shortens the transmission and diffusion pathways of electrons and electrolyte ions. The optimized NiMn₂O₄@NiCo₂O₄ electrode material presents extensive application prospects for high-performance supercapacitors. Full article

Two semiflexible piezoelectric composite plate structures were developed, incorporating 1 × 9 and 2 × 9 arrays of PZT elements mounted on brass discs and mechanically secured by pop rivets within a thin plastic foil spacer positioned between two copper-clad PCB layers. This configuration provides reliable electrical contact, adequate mechanical compliance, and efficient conversion of mechanical vibration energy into electrical energy. In addition, a multifunctional thermoelectric device was realized, consisting of four cubic modules arranged around a rectangular tube and enabling both handheld operation and coupling to hot or cold surfaces. Each cube is equipped with optimized finned heat sinks and integrates four thermoelectric elements on each face. Experimental results show that each cube generates approximately 6 mW, when handheld and with icy water injected into the central tube, demonstrating its suitability as a compact and versatile thermal energy harvester. Under low-light conditions, a solar panel is supplemented by this hybrid piezoelectric–thermoelectric energy harvesting system that combines the output of a piezoelectric composite plate with the dual outputs of a thermoelectric device using an electronically isolated summing block to ensure source decoupling. Energy storage and management are implemented using a capacitor buffer for the piezoelectric device, two voltage boosters for the thermoelectric outputs, and an automatic ultra-low-power pulse width modulation buck regulator for charging supercapacitors at 5 V. Full article

The explosive demand for flexible wearable and portable devices imposes stringent requirements on the mechanical, energy storage, and sensing properties of functional materials. Although two-dimensional (2D) transition metal carbides and nitrides (MXene) possess high conductivity and pseudocapacitance, their severe self-restacking and intrinsic brittleness restrict their practical applications. Herein, a facile vacuum filtration and hot-pressing densification strategy is proposed to fabricate nacre-inspired MXene-based films. By incorporating one-dimensional (1D) high-aspect-ratio TEMPO-oxidized cellulose nanofibrils (TOCNFs), the self-restacking of MXene is effectively suppressed. The optimal M20F5 composite film exhibits a coordinated electromechanical balance, maintaining an electrical conductivity of 1.07 × 10⁶ S m⁻¹ while enduring 2124 folding cycles. For energy storage, the assembled symmetric supercapacitor delivers a specific capacitance of 828.92 F g⁻¹ at 0.5 mA cm⁻² and maintains an energy density of 13.75 Wh kg⁻¹ at a power density of 9500 W kg⁻¹. Furthermore, acting as a piezoresistive sensor, the film achieves reliable detection, spanning from bimodal gait recognition to subtle physiological pulses. This work establishes a viable material design strategy for next-generation supercapacitors and intelligent wearable systems. Full article