Search Results (36)

The rational design of electrode architectures is essential for advancing high-performance supercapacitors. In this study, Nd₂O₃ electrodes with controlled structural features were developed via a polyacrylic acid (PAA)-assisted hydrothermal approach. By systematically tuning PAA concentration, the growth mechanism of Nd₂O₃ was effectively regulated, leading to a distinct morphological transition from compact agglomerates to well-defined hierarchical structures. The optimized Nd₂O₃-P2 electrode exhibits a porous and interconnected architecture, providing enhanced electrolyte accessibility and shortened ion diffusion pathways. This structural optimization significantly improves electrochemical performance, delivering a high areal capacitance of 26.889 F/cm² at 10 mA/cm², along with excellent rate capability and reduced internal resistance. Kinetic analysis reveals that charge storage is predominantly governed by diffusion-controlled Faradaic processes, with the optimized structure facilitating rapid ion transport and efficient redox activity. Additionally, the electrode demonstrates excellent cycling durability, retaining 87.08% capacitance over 12,000 cycles. An asymmetric supercapacitor assembled using Nd₂O₃-P2 and activated carbon achieves stable operation up to 1.5 V, delivering good capacitance retention (81.2%) after 7000 cycles. This work highlights the effectiveness of PAA-induced structural tuning and provides a practical strategy for developing advanced rare earth oxide-based electrodes for energy storage applications. Full article

The increasing accumulation of poly(ethylene terephthalate) (PET) waste poses a significant environmental challenge and highlights the need for sustainable, value-added recycling strategies. In this study, porous carbon derived from PET was synthesized via carbonization and chemical activation and subsequently combined with manganese dioxide (MnO₂) to fabricate hybrid electrodes for aqueous supercapacitors. The PET-derived carbon exhibits a highly microporous structure with a large specific surface area and functions as a conductive and mechanically stable matrix that improves MnO₂ dispersion, charge transport, and electrochemical utilization. Systematic electrochemical investigations reveal strongly electrolyte-dependent charge-storage behavior. In an alkaline electrolyte, the capacitance is dominated by MnO₂ pseudocapacitive redox reactions, whereas in a neutral electrolyte, the response is primarily governed by electric double-layer charge storage. In a ferricyanide-containing redox-active electrolyte, additional electrolyte-mediated faradaic processes significantly enhance the apparent electrochemical performance. Under these conditions, the hybrid electrodes deliver a high apparent specific capacitance of 240–250 F g⁻¹ at moderate current densities. The electrodes further demonstrate stable cycling behavior and high apparent Coulombic efficiency, reflecting time-dependent utilization of both MnO₂ pseudocapacitance and redox-active electrolyte species during charge–discharge. Crucially, this work demonstrates that PET-derived carbon/MnO₂ hybrid electrodes exhibit complex, electrolyte-controlled charge-storage mechanisms and underscores the critical role of electrolyte selection in accurately interpreting electrochemical metrics and optimizing the performance of sustainable supercapacitors based on recycled polymer-derived carbons. Full article

A hybrid material based on the copolymerization of EDOT (3,4-ethylenedioxythiophene) and Py (pyrrole), 1:1 monomer ratio, onto multi-walled carbon nanotubes (MWCNTs) was synthesized through a multistep functionalization approach. The resulting P(EDOT-co-Py)@MWCNT hybrid, poly(3,4-ethylenedioxythiophene-co-pyrrol)@MWCNT hybrid, was characterized by Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA). These characterizations confirmed the successive functionalization steps, the effective anchoring of the monomers, and the subsequent formation of the copolymer. Transmission electron microscopy (TEM) images revealed a homogeneous polymer coating along the nanotube surface while preserving the structural integrity of the MWCNTs throughout the functionalization and polymerization processes. The P(EDOT-co-Py)@MWCNT hybrid was evaluated as an active electrode material for aluminum-ion storage in an aqueous aluminum sulfate electrolyte. The system exhibited two distinct charge-storage mechanisms: at high current densities, proton surface adsorption dominated, whereas at lower rates, a faradaic contribution associated with polymer chain redox activity and the reversible extraction/insertion of Al³⁺ became prevalent. The hybrid electrode delivered high specific capacities, reaching 200.6, 106.3, and 44.3 mAh g⁻¹ at 0.10, 0.25, and 0.50 A g⁻¹, respectively. These values are comparable to—or even exceed—those reported for similar cathodic materials designed for Al³⁺ storage, highlighting P(EDOT-co-Py)@MWCNT hybrid as a highly promising cathode candidate for aqueous aluminum-ion energy-storage systems. Full article

Precise morphology engineering is essential for enhancing the charge-storage capabilities of cobalt molybdate (CoMoO₄). In this study, cobalt molybdate (CoMoO₄, abbreviated as CoMo), cobalt molybdate–cetyltrimethylammonium bromide (CoMo-CTAB), and cobalt molybdate–cetyltrimethylammonium bromide/polyethylene glycol (CoMo-CTAB/PEG) electrodes were synthesized through a cationic–nonionic surfactant-assisted hydrothermal route. he introduction of CTAB promoted the formation of well-defined nanoflake structures, whereas the synergistic CTAB/PEG system produced a highly porous and interconnected nanosheet architecture, enabling enhanced electrolyte diffusion and redox accessibility. As a result, the CoMo-CTAB/PEG electrode delivered a high areal capacitance of 10.321 F cm⁻² at 10 mA cm⁻², markedly outperforming CoMo-CTAB and pristine CoMo electrodes. It also exhibited good rate capability, maintaining 63.64% of its capacitance at 50 mA cm⁻². Long-term cycling tests revealed excellent durability, with over 83% capacitance retention after 12,000 cycles and high coulombic efficiency, indicating highly reversible Faradaic behavior. Moreover, an asymmetric pouch-type supercapacitor device (APSD) assembled using the optimized electrode demonstrated robust cycling stability. These findings underscore surfactant-directed morphology modulation as an effective and scalable strategy for developing high-performance CoMoO₄-based supercapacitor electrodes. Full article

In this study, Ni/Mn-doped cobalt–reduced graphene oxide (Co-RGO) composites were successfully synthesized as advanced electrode materials for supercapacitors. The structural and morphological properties of the composites were characterized using FTIR, XRD, SEM, TEM, and UV–Vis spectroscopy. Their electrochemical performance was evaluated through electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and galvanostatic charge–discharge (GCD). Among the prepared samples, Co-RGO doped with Ni/Mn at a 40:10 ratio exhibited the most outstanding capacitive behavior, achieving a specific capacitance of 7414 F g⁻¹ at a current density of 10 A g⁻¹, along with a high energy density of 565 Wh kg⁻¹ and a power density of 4998 W kg⁻¹. The high capacitance arises from faradaic pseudocapacitive reactions rather than electric double-layer capacitance, eliminating the need for a large surface area. These results confirm that Ni doping significantly enhances pseudocapacitance and conductivity in the Co-RGO matrix, making Ni/Mn (40:10)–Co-RGO a potential material for advanced energy storage systems. Full article

In this study, thin molybdenum nitride (MoN_x) layers were directly synthesized on molybdenum foil via thermal treatment under an NH₃ atmosphere, and their phase evolution, structural characteristics, and electrochemical performance were investigated. The thickness and morphology of the MoN_x layers were controlled by varying ammonolysis time and temperature, while subsequent annealing in N₂ converted the nitride layer into MoO₂. Meanwhile, oxidation in air yielded crystalline MoO₃ layers. X-ray diffraction and X-ray photoelectron spectroscopy confirmed progressive oxidation of molybdenum, with Mo 3d binding energies increasing in the sequence of Mo < MoN_x < MoO₂ < MoO₃, consistent with their nominal oxidation states. Electrochemical characterization revealed that both MoN_x/Mo and MoO₂/Mo electrodes exhibit notable pseudocapacitive behavior in 0.5 M H₂SO₄ electrolyte, with areal specific capacitances reaching up to 520 mF cm⁻² at 10 mV s⁻¹. Increasing layer thickness led to enhanced capacitance, likely due to an increase in the electrochemically accessible surface area and the extension of ion diffusion pathways. MoO₂-coated samples showed stronger faradaic contribution and superior rate capability compared to MoN_x counterparts, along with a gradual shift from predominantly electric double-layer capacitance toward hybrid pseudocapacitive charge storage mechanisms. Full article

The global transition toward renewable energy sources has intensified in response to escalating environmental challenges. Nevertheless, the inherent intermittency and instability of renewable energy necessitate the development of reliable energy storage technologies. Supercapacitors are particularly notable for their high specific capacitance, rapid charge and discharge capability, and exceptional cycling stability. Concurrently, the increasing demand for efficient and sustainable energy storage systems has stimulated interest in multifunctional electrode materials that integrate electrocatalytic activity with electrochemical energy storage. Two-dimensional transition metal dichalcogenides (TMDs), owing to their distinctive layered structures, large surface areas, phase state, energy band structure, and intrinsic electrocatalytic properties, have emerged as promising candidates to achieve dual functionality in electrocatalysis and electrochemical energy storage for asymmetric supercapacitors (ASCs). Specifically, their unique electronic properties and catalytic characteristics promote reversible Faradaic reactions and accelerate charge transfer kinetics, thus markedly enhancing charge storage efficiency and energy density. This review highlights recent advances in TMD-based multifunctional electrodes. It elucidates mechanistic correlations between intrinsic electronic properties and electrocatalytic reactions that influence charge storage processes, guiding the rational design of high-performance ASC systems. Full article

The advancement of efficient energy conversion and storage technologies is fundamentally linked to the development of electrochemical systems, including fuel cells, batteries, and electrolyzers, whose performance depends on key electrocatalytic reactions: hydrogen evolution (HER), oxygen evolution (OER), oxygen reduction (ORR), carbon dioxide reduction (CO₂RR), and nitrogen reduction (NRR). Beyond catalyst design, the electrolyte microenvironment significantly influences these reactions by modulating charge transfer, intermediate stabilization, and mass transport, making electrolyte engineering a powerful tool for enhancing performance. This review provides a comprehensive analysis of how fundamental electrolyte properties, including pH, ionic strength, ion identity, and solvent structure, affect the mechanisms and kinetics of these five reactions. We examine in detail how the electrolyte composition and individual ion contributions impact reaction pathways, catalytic activity, and product selectivity. For HER and OER, we discuss the interplay between acidic and alkaline environments, the effects of specific ions, interfacial electric fields, and catalyst stability. In ORR, we highlight pH-dependent activity, selectivity, and the roles of cations and anions in steering 2e⁻ versus 4e⁻ pathways. The CO₂RR and NRR sections explore how the electrolyte composition, local pH, buffering capacity, and proton sources influence activity and the product distribution. We also address challenges in electrolyte optimization, such as managing competing reactions and maximizing Faradaic efficiency. By comparing the electrolyte’s effects across these reactions, this review identifies general trends and design guidelines for enhancing electrocatalytic performance and outlines key open questions and future research directions relevant to practical energy technologies. Full article

Supercapacitors are promising energy storage devices that combine high power density, fast charge/discharge rates, and excellent cycling stability. However, their relatively low energy density compared to batteries remains a major challenge. To address this limitation, redox additive electrolytes have emerged as a key strategy to introduce reversible Faradaic reactions, significantly enhancing the energy storage capacity of supercapacitors. This mini-review systematically summarizes recent advancements in the use of redox-active species across aqueous, non-aqueous, and solid-state/gel electrolytes. We highlight the role of both inorganic and organic redox additives, detailing their mechanisms, advantages, and limitations in improving energy density and stability. Furthermore, we discuss the challenges associated with redox species, such as solubility, long-term stability, and parasitic side reactions, which hinder their practical applications. Future research directions are proposed to optimize redox-active materials and electrolyte systems, aiming to develop next-generation supercapacitors with superior energy density, extended cycling life, and enhanced applicability. Full article

Hybrid supercapacitors (HSCs) have garnered growing interest for their ability to combine the high energy storage capability of batteries with the rapid charge–discharge characteristics of supercapacitors. This review examines the evolution of HSCs, emphasizing the synergistic mechanisms that integrate both Faradaic and non-Faradaic charge storage processes. Transition metal oxides (TMOs) are highlighted as promising battery-type electrodes owing to their notable energy storage potential and compatibility with various synthesis routes, including hydro/solvothermal methods, electrospinning, electrodeposition, and sol–gel processes. Particular attention is directed toward Ti-, Co-, and V-based TMOs, with a focus on tailoring their properties through morphology control, composite formation, and doping to enhance electrochemical performance. Overall, the discussion underscores the potential of HSCs to meet the growing demand for next-generation energy storage systems by bridging the gap between high energy and high power requirements. Full article

The concept of pseudocapacitance is explored as a rapid and universal method for the state of health (SOH) determination of batteries and supercapacitors. In contrast to this, the state of the art considers the degradation of a series of full charge/discharge cycles. Lithium-ion batteries, sodium-ion batteries and supercapacitors of different cell chemistries are studied by impedance spectroscopy during lifetime testing. Faradaic and capacitive charge storage are distinguished by the relationship between the stored electric charge and capacitance. Batteries with a flat voltage–charge curve are best suited for impedance spectroscopy. There is a slight loss in the linear correlation between the pseudocapacitance and Ah capacity in regions of overcharge and deep discharge. The correct calculation of quantities related to complex impedance and differential capacitance is outlined, which may also be useful as an introductory text and tutorial for newcomers to the field. Novel diagram types are proposed for the purpose of the instant performance and failure diagnosis of batteries and supercapacitors. Full article

Lithium perchlorate-doped polypyrrole growing on titanium substrate (LiClO₄-PPy/Ti) has been fabricated to act as electroactive electrode material for feasible electrochemical energy storage. A theoretical and experimental investigation is adopted to disclose the conductivity, electroactivity properties and interfacial interaction-dependent capacitance of LiClO₄-PPy/Ti electrode. The experimental measurement results disclose that LiClO₄-PPy/Ti reveals lower ohmic resistance (0.2226 Ω cm⁻²) and charge transfer resistance (2116 Ω cm⁻²) to exhibit higher electrochemical conductivity, a more reactive surface, and feasible ion diffusion to present higher double-layer capacitance (0.1930 mF cm⁻²) rather than LiClO₄/Ti (0.3660 Ω cm⁻², 65,250 Ω cm⁻², 0.0334 mF cm⁻²). LiClO₄-PPy/Ti reveals higher Faradaic capacitance caused by the reversible doping and dedoping process of perchlorate ion on PPy than the electrical double-layer capacitance of LiClO₄/Ti caused by the reversible adsorption and desorption process of the LiClO₄ electrolyte on Ti. Theoretical simulation calculation results prove that a more intensive electrostatic interaction of pyrrole N···Ti (2.450 Å) in LiClO₄-PPy/Ti rather than perchlorate O···Ti (3.537 Å) in LiClO₄/Ti. LiClO₄-PPy/Ti exhibits higher density of states (57.321 electrons/eV) at Fermi energy and lower HOMO-LUMO molecule orbital energy gap (0.032 eV) than LiClO₄/Ti (9.652 electrons/eV, 0.340 eV) to present the enhanced electronic conductivity. LiClO₄-PPy/Ti also exhibits a more declined interface energy (−1.461 × 10⁴) than LiClO₄/Ti (−5.202 × 10³ eV) to present the intensified interfacial interaction. LiClO₄-PPy/Ti accordingly exhibits much higher specific capacitances of 0.123~0.0122 mF cm⁻² at current densities of 0.01~0.10 mA cm⁻² rather than LiClO₄/Ti (0.010~0.0095 mF cm⁻², presenting superior electroactivity and electrochemical capacitance properties. LiClO₄-PPy/Ti could well act as the electroactive supercapacitor electrode for feasible energy storage. Full article

Among electrochemical energy storage (EES) technologies, rechargeable batteries (RBs) and supercapacitors (SCs) are the two most desired candidates for powering a range of electrical and electronic devices. The RB operates on Faradaic processes, whereas the underlying mechanisms of SCs vary, as non-Faradaic in electrical double-layer capacitors (EDLCs), Faradaic at the surface of the electrodes in pseudo-capacitors (PCs), and a combination of both non-Faradaic and Faradaic in hybrid supercapacitors (HSCs). EDLCs offer high power density but low energy density. HSCs take advantage of the Faradaic process without compromising their capacitive nature. Unlike batteries, supercapacitors provide high power density and numerous charge–discharge cycles; however, their energy density lags that of batteries. Supercapatteries, a generic term that refers to hybrid EES devices that combine the merits of EDLCs and RBs, have emerged, bridging the gap between SCs and RBs. There are numerous articles and reviews on EES, and many of those articles have emphasized various aspects of HSCs and supercapatteries. However, there are no recent reviews that dealt with supercapatteries in general. Here, we review recently published critically selected articles on supercapatteries. The review discusses different EES devices and how supercapatteries are different from others. Also discussed are properties, design strategies, and future perspectives on supercapatteries. Full article

LiFePO₄ is a common electrode cathode material that still needs some improvements regarding its electronic conductivity and the synthesis process in order to be easily scalable. In this work, a simple, multiple-pass deposition technique was utilized in which the spray-gun was moved across the substrate creating a “wet film”, in which—after thermal annealing at very mild temperatures (i.e., 65 °C)—a LiFePO₄ cathode was formed on graphite. The growth of the LiFePO₄ layer was confirmed via X-ray diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy. The layer was thick, consisting of agglomerated non-uniform flake-like particles with an average diameter of 1.5 to 3 μm. The cathode was tested in different LiOH concentrations of 0.5 M, 1 M, and 2 M, indicating an quasi-rectangular and nearly symmetric shape ascribed to non-faradaic charging processes, with the highest ion transfer for 2 M LiOH (i.e., 6.2 × 10⁻⁹ cm²/cm). Nevertheless, the 1 M aqueous LiOH electrolyte presented both satisfactory ion storage and stability. In particular, the diffusion coefficient was estimated to be 5.46 × 10⁻⁹ cm²/s, with 12 mAh/g and a 99% capacity retention rate after 100 cycles. Full article

Developing advanced carbon materials by utilizing biomass waste has attracted much attention. However, porous carbon electrodes based on the electronic-double-layer-capacitor (EDLC) charge storage mechanism generally presents unsatisfactory capacitance and energy density. Herein, an N-doped carbon material (RSM-0.33-550) was prepared by directly pyrolyzing reed straw and melamine. The micro- and meso-porous structure and the rich active nitrogen functional group offered more ion transfer and faradaic capacitance. X-ray diffraction (XRD), Raman, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET) measurements were used to characterize the biomass-derived carbon materials. The prepared RSM-0.33-550 possessed an N content of 6.02% and a specific surface area of 547.1 m² g⁻¹. Compared with the RSM-0-550 without melamine addition, the RSM-0.33-550 possessed a higher content of active nitrogen (pyridinic-N) in the carbon network, thus presenting an increased number of active sites for charge storage. As the anode for supercapacitors (SCs) in 6 M KOH, RSM-0.33-550 exhibited a capacitance of 202.8 F g⁻¹ at a current density of 1 A g⁻¹. At a higher current density of 20 A g⁻¹, it still retained a capacitance of 158 F g⁻¹. Notably, it delivered excellent stability with capacity retention of 96.3% at 20 A g⁻¹ after 5000 cycles. This work not only offers a new electrode material for SCs, but also gives a new insight into rationally utilizing biomass waste for energy storage. Full article