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AbstractSupercapacitors have become a viable and environmentally friendly option for energy storage. Over the years, transition metal oxides have been used in supercapacitor applications because of their superior electronic conductivity and robust redox reactions. In this paper, we study the morphological, structural, and supercapacitance characteristics of NiCo2O4 nanorods at diverse synthesis temperatures and times. Utilizing XRD and FE-SEM, the crystalline structure and morphology were investigated. The Raman spectroscopy was used to determine the defects in nanostructures. The electrochemical techniques were used to examine the supercapacitance performance. Within a 0.8 V potential frame, the NiCo-160/24 had a significant specific capacitance of 118.46 Fg−1 at 0.14 Ag−1 in 1 M KOH showing an increment of ∼50% in specific capacitance as compared to NiCo-125/12. The promising supercapacitive performance of NiCo-160/24 paves its way to be utilized as electrode material in supercapacitor industry. [ABSTRACT FROM AUTHOR]

The intercalation-type graphite anode with a diffusion-controlled storage mechanism has fundamental limitations for low-temperature performance. Pseudo-capacitance has fast reaction kinetics and is not controlled by diffusion. Therefore, pseudo-capacitance may improve the low-temperature performance of lithium-ion batteries. In this work, hard carbon spheres (HCSs) are prepared by carbonizing polymer, and KOH-activated hard carbon spheres (K-HCSs) are also prepared to optimize their structure. Compared with the HCSs anode, the K-HCSs anode exhibits a higher initial specific capacity of 118 mAh g−1 at − 20 ℃. Moreover, the K-HCSs anode demonstrates a high capacity of 75 mAh g−1 after 300 cycles with a current density of 0.5 A g−1 at − 20 ℃. CV results display that the K-HCSs anode has higher pseudo-capacitance (79.76%) than the HCSs anode (78.13%) at − 20 ℃. The enhanced pseudo-capacitance can be ascribed to the abundant defects of K-HCSs. [ABSTRACT FROM AUTHOR]

Electrochemical impedance spectroscopy (EIS), characterized by its non‐destructive and in situ nature, plays a crucial role in comprehending the thermodynamic and kinetic processes occurring within Li‐ion batteries. However, there is a lack of consistent and coherent physical interpretations for the EIS of porous electrodes. Therefore, it is imperative to conduct thorough investigations into the underlying physical mechanisms of EIS. Herein, by employing reference electrode in batteries, we revisit the associated physical interpretation of EIS at different frequencies. Combining different battery configurations, temperature‐dependent experiments, and elaborated distribution of relaxation time analysis, we find that the ion transport in porous electrode channels and pseudo‐capacitance behavior dominate the high‐frequency and mid‐frequency impedance arcs, respectively. This work offers a perspective for the physical interpretation of EIS and also sheds light on the understanding of EIS characteristics in other advanced energy storage systems. [ABSTRACT FROM AUTHOR]

Polyanionic structures, (MO4)n−, can be beneficial to the transport of lithium ions by virtue of the open three-dimensional frame structure. However, an unstable interface suppresses the life of the (MO4)n−-based anode. In this study, MnWO4@C nanorods with dense nanocavities have been synthesized through a hydrothermal route, followed by a chemical deposition method. As a result, the MnWO4@C anode exhibits better cycle and rate performance than MnWO4 as a Li-ion battery; the capacity is maintained at 718 mAh g−1 at 1000 mA g−1 after 400 cycles because the transport of lithium ions and the contribution of pseudo-capacitance are increased. Generally, benefiting from the carbon shell and electrolyte additive (e.g., FEC), the cycle performance of the MnWO4@C electrode is also effectively improved for lithium storage. [ABSTRACT FROM AUTHOR]

By using Centella asiatica leaf extract, reduced graphene oxide (rGO) decorated PbS/CdO nanocomposite (rPC) was synthesized by reducing graphene oxide. To investigate the photocatalytic, electrochemical, and antibacterial properties of the synthesized rPC NC, different analytical techniques were employed and compared with those of the PbS/CdO NC synthesized by chemical precipitation. The XRD analysis of both samples revealed cubic structured peaks of PbS and CdO. Pb, S, Cd, O, and C can be detected from rPC's EDS spectrum. PC and rPC exhibited band gap energies of 2.28 and 2.21 eV, respectively. Both samples show FTIR peaks related to lead sulfide and Cd–O stretching vibrations. Interstitial sulfur and singly occupied oxygen vacancy peaks are evinced in the PL spectra. The PL intensity for rPC is reduced, which is indicative of low recombination rates for photogenerated e−/h+ pairs. Photodegradation efficiencies against methyl violet were 81.2 and 93.4% for PC and rPC catalysts. Electrochemical and antibacterial properties of PC improved with rGO inclusion. [ABSTRACT FROM AUTHOR]

Highlights Incorporation of Schottky Junction increases the pseudocapacitive mechanism at higher current rate. The pseudocapacitance behavior of the positive and negative electrodes is balanced to construct a solid-state supercapattery device. An energy density of 236.14 Wh kg−1 is achieved for solid-state supercapattery device.

Organic supercapacitors are considered attractive alternatives to traditional inorganic‐based charge storage devices due to their synthetic versatility, low cost, and environment‐friendliness features. Photopolymerized anthraquinone‐polydiacetylene is employed as a core component in high‐performance asymmetric supercapacitors (ASCs). Specifically, interspersed polydiacetylene‐anthraquinone/polyaniline (PANI) electrodes are prepared via drop‐casting and used as cathodes in devices employing polypyrrole/reduced graphene oxide anodes using aqueous or ionic liquid electrolytes. The excellent electrochemical properties of the polydiacetylene‐anthraquinone/PANI electrodes, specifically high capacitance (specific capacitance ≈720 F g−1 at 1 A g−1), long discharge time, and cycling stability, are ascribed to the superior redox profile of the anthraquinone and ambipolar charge transport associated with the polydiacetylene framework. The asymmetric supercapacitor prepared using the polydiacetylene‐anthraquinone/PANI electrodes displays a high energy density of 36 Wh kg−1 at a power density of 995 W kg−1, underscoring possible utilization of the anthraquinone‐polydiacetylene derivative in practical energy storage devices. [ABSTRACT FROM AUTHOR]

Highlights: Incorporation of Schottky Junction increases the pseudocapacitive mechanism at higher current rate. The pseudocapacitance behavior of the positive and negative electrodes is balanced to construct a solid-state supercapattery device. An energy density of 236.14 Wh kg−1 is achieved for solid-state supercapattery device. Pseudo-capacitive negative electrodes remain a major bottleneck in the development of supercapacitor devices with high energy density because the electric double-layer capacitance of the negative electrodes does not match the pseudocapacitance of the corresponding positive electrodes. In the present study, a strategically improved Ni-Co-Mo sulfide is demonstrated to be a promising candidate for high energy density supercapattery devices due to its sustained pseudocapacitive charge storage mechanism. The pseudocapacitive behavior is enhanced when operating under a high current through the addition of a classical Schottky junction next to the electrode–electrolyte interface using atomic layer deposition. The Schottky junction accelerates and decelerates the diffusion of OH‒/K+ ions during the charging and discharging processes, respectively, to improve the pseudocapacitive behavior. The resulting pseudocapacitive negative electrodes exhibits a specific capacity of 2,114 C g−1 at 2 A g−1 matches almost that of the positive electrode's 2,795 C g−1 at 3 A g−1. As a result, with the equivalent contribution from the positive and negative electrodes, an energy density of 236.1 Wh kg−1 is achieved at a power density of 921.9 W kg−1 with a total active mass of 15 mg cm−2. This strategy demonstrates the possibility of producing supercapacitors that adapt well to the supercapattery zone of a Ragone plot and that are equal to batteries in terms of energy density, thus, offering a route for further advances in electrochemical energy storage and conversion processes. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel CoO/Co/C 2D nanosheet was prepared by using cellulose nanofibers. • The unique structure of CoO/Co/C 2DNS provides additional lithium storage sites. • High reversible capacity of 500 mAh g−1 can obtained even at 10 A g−1. • Superior long-range cycling performance up to 800 cycles at 2 A g−1 can be achieved. Nano-sized two-dimensional carbonaceous materials have been widely used as the matrix for alloying-type and conversion-type anode materials for Li-ion batteries (LIBs) to improve structural stability and rate performance. However, relevant synthesis usually requires rigorous conditions and chronic reaction processes. Herein, we have designed a simple solvothermal reaction and heat treatment to prepare a novel CoO/Co/C two-dimensional nanosheet (CoO/Co/C 2DNS) by adopting cellulose nanofibers (CNFs) as the precursor. The unique characteristics of CNFs facilitate the uniform distribution of active materials on the surface and the construction of two-dimensional nanostructure via self-assembly. It is worth noting that CoO/Co/C 2DNS exhibits a striking synergistic effect since the porous 2D carbon framework offers additional pseudo-capacitance and enhances the electronic conductivity, while the ultrafine active materials encapsulated inside shorten the Li-ions diffusion pathways and relieve the volume change. Benefit from the unique structure, the composite anode delivered outstanding rate performance (∼500 mAh g−1 at 10 A g−1) and superior long-range cycling performance up to 800 cycles even at 2 A g−1. This work provides a new strategy for the synthesis of nano-sized 2D composite, offering a promising route to construct high performance conversion-type anodes for next-generation LIBs. [ABSTRACT FROM AUTHOR]

In this study, an effective sonochemical reactor was used to synthesize Mn0.5Cu0.5LaxFe2−xO4 nanoferrites with different compositions of x = 0.03, 0.06, 0.09, and 0.12. Mn0.5Cu0.5LaxFe2−xO4 nanoferrites were subjected to X-ray diffraction (XRD), ultraviolet-diffuse reflectance spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, vibrating sample magnetometer, and electrochemical impedance spectroscopy to investigate their optical, magnetic, electrical, and structural properties. An image of the formation of a cubic crystalline structure was obtained by XRD patterns. An increase in the amount of La3+ ions in Mn0.5Cu0.5LaxFe2−xO4 nanoferrites could explain the decrease in crystallite size. The impedance analysis revealed the presence of pseudocapacitance and resistive behavior in Mn0.5Cu0.5LaxFe2−xO4 nanoferrites. Further, the addition of La3+ ions led to a little decrease in the conductivity of Mn0.5Cu0.5LaxFe2−xO4 nanoferrites. The hysteresis loops enhanced the soft ferromagnetic behavior of Mn0.5Cu0.5LaxFe2−xO4 nanoferrites. A decrease in saturation magnetization and an increase in coercivity were observed with an increase in the La content of Mn0.5Cu0.5LaxFe2−xO4 nanoferrites. [ABSTRACT FROM AUTHOR]

The electrochemical-grade natural graphite flake prices are increasing day by day. Reusing and recycling graphite materials from the spent lithium-ion battery (LIB) is a prospective way to overcome the issue. This report presents the synthesis of reduced graphene oxide (RGO) from spent LIB by the improved Hummers method followed by calcination at 600 °C (RGO-600). S, N-RGO-600 was prepared by doping sulfur and nitrogen with RGO-600 through hydrothermal synthesis. Assynthesized S, N-RGO-600s have sheet-like morphology having uniform heteroatom doping. S- and N-doped RGO-600 delivers 375 F g−1 at 5 A g−1 compared to RGO-600 of 233 F g−1 and retains > 98% capacitance over 20,000 cycles. The lead–carbon hybrid ultracapacitors fabricated using in-situ activated PbO2 as cathode and S, N-RGO-600 composite electrode as anode deliver a specific capacitance of 564 F g−1 at 5 A g−1 and retain 90% capacitance after 15,000 cycles. The high capacitance and stable cycle life of RGO and S, N-RGO are due to easy access of electrolyte ions through mesoporous and layered graphitic carbons with redox-active functional moieties of sulfur and nitrogen. This work illustrates an easy and scalable synthesis root for RGO and S, N-RGO. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Chinese fir sawdust-derived porous carbon (NPC) was successfully synthesized. • Low-temperature NaOH/urea and melamine phosphate are conducive to NPC performance. • The NPC has a hierarchical pore structure and reasonable N, P heteroatom groups. • The symmetric supercapacitor exhibits a high energy density of 15.9 Wh/kg. The development of heteroatom-doped porous carbon derived from biomass waste with high-performance electrodes for supercapacitors has been drawn extensive research. Herein, N, P co-doped porous carbon (NPC) was successfully synthesized using Chinese fir sawdust as a carbon source, NaOH as an activator, urea as a nitrogen source, and melamine phosphate as the phosphorus and nitrogen source by pretreatment with low-temperature NaOH/urea system. The low-temperature pretreatment and melamine phosphate greatly promoted the porous structure and uniform distributions of heteroatom about the NPC. The optimized NPC exhibits high specific surface area (1849 m2/g), hierarchical porous structure with high mesoporosity (87.3 %), appropriate heteroatom content (3.32 at% N, 0.36 at% P), and excellent wettability. This unique facilitates improved electrolyte diffusion efficiency and ion transfer rate. In the three-electrode system, the specific capacitance of the NPC electrode is as high as 260 F/g at 0.5 A/g and remains at 235 F/g at 10 A/g, and the charge transfer resistance is very low (0.08 Ω). In addition, the assembled symmetric supercapacitors deliver an energy density of 15.9 Wh/kg at a power density of 246 W/kg, a long cycling life with 90 % capacitance retention after 5000 cycles. The environment-friendly NPC has a broad development prospect for carbon-based high-performance electrodes for supercapacitors. [ABSTRACT FROM AUTHOR]

[Display omitted] • Investigated the effects of neutral, cationic, and anionic surfactants on ZnCo 2 O 4 nanomaterial. • The ZnCo 2 O 4 nanomaterials were synthesized via a straightforward hydrothermal-annealing method. • The ionic nature of the surfactants influenced the charge-storage of ZnCo 2 O 4 nanomaterials. • ZnCo 2 O 4 − SDS exhibited high specific capacitance with 93% stability over 50,000 cycles. Surface properties of nanomaterials are directly related to their electrochemical performance, with surfactants playing an essential role in their cost-effective synthesis as structure-directing agents and templates. This research article discusses the effects of neutral, cationic, and anionic surfactants on the capacitance of bimetallic ZnCo 2 O 4 nanomaterial, synthesized via a straightforward hydrothermal-annealing method. We investigated how cationic (cetyl-trimethyl ammonium bromide), anionic (sodium dodecyl sulphate), and non-ionic (urea) surfactants influence the electrochemical characteristics of ZnCo 2 O 4 nano-powders. All three surfactant-based ZnCo 2 O 4 electrodes exhibited Faradaic behaviour during electrochemical tests. The ionic nature of the surfactants significantly impacted the charge-storage mechanism, with specific capacitance values rising in the order of Urea (550 Fg−1) < C-TAB (740 Fg−1) < SDS (980 Fg−1) at a 1 Ag−1 in half-cell studies. The ZnCo 2 O 4 -SDS displayed the highest surface redox reactivity and superior electrochemical performance, with 426 Fg−1 in full-cell studies, energy density of 230 WhKg−1 (1 Ag−1), power density of 18,213.9 WKg−1 (10 Ag−1), and 93 % capacitance retention is observed over 50,000 cycles (50 Ag−1). [ABSTRACT FROM AUTHOR]

Summary: Carbon and metal oxide nanocomposites have been extensively studied as electrode materials to develop energy and power‐dense supercapacitors in recent years. Nevertheless, nano carbons with improved porosity and functional moieties are the most eco‐friendly and cost‐effective supercapacitor materials. In this work, carbon nano‐onions (CNOs) synthesized by a single‐step flame soot collection method, subsequently calcined at 600°C in an inert environment (CNO‐600), are used as electrode material for the supercapacitors. CNO‐600 s have a layer‐by‐layer nano onion structure with a ~25 nm particle size and a Brunauer–Emmett–Teller surface area of 147 m2 g−1. CNO‐600 delivers 266 and 186 F g−1 of capacitance at 0.5 A g−1 for half cells and symmetric ultracapacitors, respectively. Ultracapacitors show capacitance retention of 91% with 20 000 GCD cycles in 1 M H2SO4 electrolyte. The stable capacitance of CNO‐600 is due to easy intercalation/de‐intercalation of electrolyte ions and electrons in the layer‐by‐layer structure of CNOs, contributing to pseudocapacitive charge storage with electric double layer capacitor behavior. The lead‐carbon hybrid ultracapacitor fabricated using CNO‐600 as anode material and PbO2 as cathode delivers a specific capacitance of 515 F g−1 at 1 A g−1 in 4.5 M H2SO4 electrolyte in the voltage range of 2.3 and 0.6 V. The substantial improvement of charge storage in CNO‐based symmetric and lead‐carbon hybrid system, demonstrate an excellent opportunity for the development of high‐performance supercapacitors. [ABSTRACT FROM AUTHOR]

Due to its properties (stable, affordable and non‐toxic), titanium dioxide (TiO2) has a promising future as electrode material for sodium‐ion batteries (SIBs). Its Na+ insertion/deinsertion mechanism, on the other hand, results in poor electronic conductivity and sluggish ionic diffusivity, leading to rapid capacity fading. Herein, a molten salt method is employed to creat abundant carbon pores framework, being capable of supporting plentiful ultra‐fine TiO2 adhering (U‐TiO2/C). With this unique porous structure of lots of exposed active sites, the U‐TiO2/C composite provides a faster ions transport and volume expansion buffer zone during cycling. As anode for SIBs, the U‐TiO2/C manifests splendid electrochemical performance. Specifically, the U‐TiO2/C electrode delivers a high capacity of 202.7 mAh g−1 after 100 cycles at 0.1 A g−1 and 91.4 mAh g−1 at 1.0 A g−1 after 160 cycles. Even with the increased current density to 10.0 A g−1, the U‐TiO2/C electrode still performs a high capacity of 69.5 mAh g−1 after 2500 cycles. Detailed kinetic analysis has been investigated to quantificationally demonstrate that the surface pseudocapacitive storage behavior plays a dominant role in the enhanced sodium storage. [ABSTRACT FROM AUTHOR]

Carbon xerogels were synthesized using a soft-template route with resorcinol as the carbon source and sodium carbonate as the catalyst. The influence of the resorcinol to catalyst ratio in the range of 500–20,000 on pore structure, graphitic domains, and electronic conductivity of as-prepared carbon xerogels, as well as their performance in an aluminium ion battery (AIB), was investigated. After carbonization steps of the polymers up to 800 °C, all carbon samples exhibited similar specific volumes of micropores (0.7–0.8 cm³ g−1), while samples obtained from mixtures with R/C ratios lower than 2000 led to carbon xerogels with significantly higher mesopore diameters up to 6 nm. The best results, in terms of specific surface (1000 m² g−1), average pore size (6 nm) and reversible capacity in AIB cell (28 mAh g−1 @ 0.1 A g−1), were obtained with a carbon xerogel sample synthetized at a resorcinol to catalyst ratio of R/C = 500 (CXG500). Though cyclic voltammograms of carbon xerogel samples did not exhibit any sharp peaks in the applied potential window, the presence of both oxidation and a quite wide reduction peak in CXG500–2000 cyclic voltammograms indicated pseudocapacitance behaviour induced by diffusion-controlled intercalation/de-intercalation of AlCl4− ions into/from the carbon xerogel matrix. This was confirmed by shifting of the (002) peak towards lower 2θ angle values in the XRD pattern of the CXG500 electrode after the charging step in AIB, whereas the contribution of pseudocapacitance, calculated from half-cell measurements, was limited to only 6% of overall capacitance. [ABSTRACT FROM AUTHOR]

As emerging energy storage systems, potassium-ion batteries (PIBs) are suitable for grid-scale energy storage application due to the abundant potassium resources and low cost. It is crucial to achieve fast-charging PIBs. However, as the most promising anode candidate, graphite still faces setbacks in achieving fast charging due to poor kinetic issue. Herein, modified graphite (MG) is synthesized to realize the fast potassium ion storage. Benefiting from the enlarged graphitic space combined with unique porous microstructure, MG exhibits outstanding electrochemical performance. The optimized MG anode delivers a specific capacity of 115 mAh g−1 at 4 A g−1 and excellent cycling stability of 1500 cycles at 1 A g−1. Moreover, the full cell assembled with MG anode and Prussian Blue (PB) cathode exhibits a capacity retention of 75% after 20000 cycles at the current density of 1 A g−1. The excellent electrochemical performance is further demonstrated to be associated with dominant pseudo-capacitance behavior, i.e. surface or near-surface reversible redox reactions, which are less affected by solid electrolyte interface (SEI) than intercalation reactions. Our work proposes a strategy to optimize graphitic anode materials by regulating the microstructure and may provide insight into the synthesis of high rate carbon-based anode materials for PIBs. A low-cost modified graphite (MG) is prepared as an anode for potassium-ion batteries (PIBs), achieving higher specific capacity and superior long-term cyclic stability than pristine natural graphite. Moreover, the different impact of solid electrolyte interface (SEI) accumulation during K storage on the two K storage mechanisms (intercalation and adsorption mechanism) is investigated. [Display omitted] • A low-cost modified graphite was prepared as an anode to achieve fast-charging K-ion battery. • The first attempt to illustrate different impact of SEI on intercalation and adsorption K storage mechanisms. • Adsorption K storage mechanism is less affected by SEI than intercalation behavior. [ABSTRACT FROM AUTHOR]

Cloud‐cover‐induced frequent and sharp dips in sunlight as well as diminished solar flux during the evenings of peak energy demand are major challenges in solar energy harvesting. Persistent and memory‐based photocatalysts that efficiently operate under low light fluxes beyond sunset, are a potential solution to address and mitigate these challenges. This review describes examples of persistent photocatalysis systems based on charge injection into multivalent charge storage materials that allow post‐illumination discharging and charge carrier generation that increase or maintain the catalysis rate. Persistent photocatalysis in defect‐laden charge storage materials with multivalent states combined with slow charge release associated with electronic persistent photoconductivity results in giant persistent photocatalysis that can last more than an hour after the illumination is shut off. Strategies are suggested to develop persistent photocatalysis by improved charge separation and present figures of merit for evaluating persistent photocatalysis efficiency and performance. Furthermore, this could enable the use of such material systems in environmental applications such as photocatalytic coatings for the remediation of air pollution that continue to function into the night and self‐cleaning applications that continue to disinfect during the night. [ABSTRACT FROM AUTHOR]

CoFe2O4 composite carbon nanofibers (CoFe2O4@CNFs) are prepared by electrospinning combined with pre‐oxidation, carbonization, and extra annealing under air conditions. The effect of different extra annealing times on the structure, morphology, and electrochemical properties of the resulting CoFe2O4@CNFs are investigated. CoFe2O4@CNFs (named as CFO/C‐800‐2) with a spinel structure are successfully prepared after 2 h of extra annealing for CFO/C‐800‐0. CFO/C‐800‐2 shows a mesoporous structure with a mesoporous area of 358 m2 g−1. CFO/C‐800‐2 shows pseudocapacitance characteristics with a specific capacity of 591.8 F g−1 at a current density of 1 A g−1. The capacitance retention rate of the asymmetric supercapacitor assembled by CFO/C‐800‐2 with activated carbon (AC) can reach 87 % in the 0–1.7 V voltage window, and the energy density is 21.4 Wh Kg−1 at a power density of 850 W Kg−1 after 7000 cycles. [ABSTRACT FROM AUTHOR]

Noticeable pseudo‐capacitance behavior out of charge storage mechanism (CSM) has attracted intensive studies because it can provide both high energy density and large output power. Although cyclic voltammetry is recognized as the feasible electrochemical technique to determine it quantitatively in the previous works, the results are inferior due to uncertainty in the definitions and application conditions. Herein, three successive treatments, including de‐polarization, de‐residual and de‐background, as well as a non‐linear fitting algorithm are employed for the first time to calibrate the different CSM contribution of three typical cathode materials, LiFePO4, LiMn2O4 and Na4Fe3(PO4)2P2O7, and achieve well‐separated physical capacitance, pseudo‐capacitance and diffusive contributions to the total capacity. This work can eliminate misunderstanding concepts and correct ambiguous results of the pseudo‐capacitance contribution and recognize the essence of CSM in electrode materials. [ABSTRACT FROM AUTHOR]

The internal morphology and structure of mesoporous carbon spheres are successfully controlled by changing the pore geometry of the initial sacrificing templates. The optimized sample shows a comprehensive potassium storage performance, which is ascribed to the balancing of pseudo-capacitance-controlled process and diffusion-controlled process. [Display omitted] • Mesoporous carbon spheres (MCSs) are synthesized by sacrificed template method. • The internal morphology and structure of the MCSs are well controlled. • The optimized sample shows excellent potassium storage performance. • The good electrochemical performance is ascribed to the delicate inner structural design. Carbon materials have been considered to be potential anodes for potassium-ion batteries (PIBs). Different strategies, including designing micro-/nano-structure and porous morphology, introducing heteroatom doping, and creating carbon-based hybrids, have been employed to improve the potassium ion transport kinetics. Nevertheless, it is still a challenge to achieve satisfactory potassium storage performance due to the uncontrolled reaction kinetics of the large-sized potassium ions. Herein, we successfully synthesized mesoporous carbon spheres (MCSs) with tunable internal morphology and structure by using sacrificed template method. The optimized MCSs with novel half inner-shell structures (HIS-MCSs) show excellent electrochemical performance when used as the anode for PIBs. Specifically, a reversible specific capacity of 241.2 mAh/g is achieved at a current density of 0.1 A/g. Even at 5.0 A/g, a reversible specific capacity of 120 mAh/g can still be reached. Long-term stability tests show that the electrode holds a capacity of 166.5 mAh/g after 1000 cycles at 1.0 A/g. The good cycling stability and rate performance of the HIS-MCSs electrode are attributed to the well-defined inner structural design, in which the contribution from ion diffusion and pseudo-capacitance process are compromised. [ABSTRACT FROM AUTHOR]

• CZC-4 is produced via a novel sol-gel synthesis method using Carbamide as structure director and fuel. • CZC-4 features a unique porous flower-like structure with a self-assembled flake-like pattern. • CZC-4 exhibits impressive electrochemical performance regarding specific capacitance, stability, and energy density. • CZC-4′s electrochemical performance holds potential for diverse broader applications in materials science, including supercapacitors, metal-ion batteries, electrocatalysts, and sensors. The design and development of ultrahigh-performance nanomaterials possessing novel characteristics are needed to achieve reliable energy storage performance. To satisfy the needs, diverse electrode materials are explored. Even though carbon-based materials hold high surface area and conductivity, their specific capacitance value fails to deliver high-performance applications. Therefore, pseudocapacitive transition metal oxide is adopted to overcome these issues. Among all Zinc Cobaltite, a binary transition metal oxide is widely explored owing to its fascinating electrochemical properties. As most of the synthesis of these kinds of materials requires the hydro/solvothermal method, herein, we have proposed the concept of a facile sol-gel method to prepare this class of materials by using Carbamide as both structure director and fuel to achieve the porous flower-like Zinc Cobaltite. The prepared material delivers the notable gravimetric specific capacitance of 513.3 F g−1. Owing to its unique morphology and porous structure, ion channelization is feasible, which will enhance the electrochemical reaction. Constructed asymmetric coin cell supercapacitor showed an extraordinary specific capacitance of 106.5 F g−1 and energy density of 56.2 Wh kg−1, demonstrating an impressive ability to retain 89.6 % of its capacitance after 4000 cycles at a current density of 6 A g−1. Due to the remarkable electrochemical behavior, this work can act as a guiding tool for designing efficient and cost-effective energy storage devices that will hold prodigious potential in commercial energy storage applications. (Using Carbamide-assisted sol-gel synthesis creates porous flower-like ZnCo 2 O 4 microspheres (CZC-4), offering a practical solution for achieving high-performance asymmetric coin cell supercapacitors.) [Display omitted] [ABSTRACT FROM AUTHOR]

Vacancy defects have important impacts on the physical-chemical properties of metal oxides. In the present work, two types of Bi 2 O 3 powders with different morphologies were synthesized for supercapacitor electrodes by calcination (denoted as c-Bi 2 O 3) and two-step hydrothermal methods (donated as h-Bi 2 O 3). Vacancy clusters of V B i ‴ V O · · V B i ‴ with different concentrations were observed in these two samples by positron annihilation lifetime spectroscopy. The results of electrochemistry revealed that the charge storage behavior of h-Bi 2 O 3 with more V B i ‴ V O · · V B i ‴ defects obeyed both semi-infinite diffusion-controlled battery-type mechanism and surface-controlled pseudo-capacitance mechanism, while that of the calcined c-Bi 2 O 3 electrode with a lower concentration of V B i ‴ V O · · V B i ‴ defects followed only the semi-infinite diffusion-controlled battery-type mechanism. The pseudo-capacitance of h-Bi 2 O 3 could be attributed to the insertion/extraction process of more K+ ions in the V B i ‴ V O · · V B i ‴ surface defects. Due to the partial pseudo-capacitance and improved conductivity caused by more V B i ‴ V O · · V B i ‴ defects, the h-Bi 2 O 3 electrode had a larger capacitance (1043 F g-1 at 1 A g-1), a higher rate performance (560 F g-1 at 60 A g-1), and better cycle stability (93% retention at 50 A g-1 after 2000 cycles). Furthermore, because of the high-concentration of V B i ‴ V O · · V B i ‴ defects, the Ni/Co-MOF//h-Bi 2 O 3 asymmetric supercapacitor delivered a relatively higher specific energy density of 47 Wh kg-1 at 1125 W kg-1. Taken together, these results indicate that surface vacancy clusters play an important role in boosting the electrochemical performance of metal oxide electrodes. [ABSTRACT FROM AUTHOR]

MXene, an example of 2D transition metal carbides, has recently been explored as an energy storage material for batteries or supercapacitors due to its high electrical conductivity and tunability of functional moieties. As with other 2D nano‐materials, however, attempts to harness MXene‐based electrodes have been limited by deterioration in mass transfer owing to self‐stacking and aggregation problems of MXenes. Here, means of creating 3D‐structured MXene films having voids of controlled size using templated co‐assembly between MXene nanosheets and monodisperse colloidal particles are presented. Using a 3D‐structured MXene‐only film incorporating microscale voids as a thin‐film electrode for Li‐ion batteries yield an initial specific capacity of 435.4 mAh g−1 at a current density of 0.01 A g−1 and highly extended cyclic stability persisting 1200 cycles, approaching the reported theoretical capacity of MXene even without employing any binder or conductive species. Electrochemical analyses reveal that the improved specific capacity is attributable to enhanced contribution of pseudo‐capacitive Li‐storage compared to diffusion‐mediated capacity, as incorporated voids tend to facilitate ionic transport into the interior region of the MXene films. Therefore, this work offers a concrete understanding to realize improved electrochemical performances of 2D nanomaterial‐based electrodes, especially in the form of free‐standing thin films. [ABSTRACT FROM AUTHOR]

Nickel ferrite (NiFe 2 O 4) nanostructures (NSs) were synthesized via a low-cost and reproducible co-precipitation method. The as-synthesized material was annealed at different temperatures to investigate electrochemical performances for oxygen reduction reaction (ORR) and energy storage capacity. The X-ray diffraction (XRD) pattern confirmed the cubic structure of NiFe 2 O 4 (NF) NSs. The decreased agglomeration and increased particle size were observed by field effect scanning electron microscopy (FE-SEM) with annealing temperature. The presence of Ni–O and Fe–O bonds at tetrahedral and octahedral sites was confirmed by Fourier transform infrared (FTIR) spectroscopy. The electrochemical analysis studied using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) demonstrated that the NF NSs annealed at 900 °C exhibited impressive electrochemical activity with a specific capacitance of ∼136 F/g, outperforming samples synthesized at lower temperatures. Moreover, the electrode material displayed excellent long-term stability over 3000 cycles for ORR activity. The remarkable electrochemical performance of NF NSs at higher annealing temperatures highlights their potential for future energy storage and conversion devices. [Display omitted] • The NiFe 2 O 4 NPs were successfully synthesized by using a simple and economical co-precipitation method. • The cubic nature of the NF NPs was confirmed by XRD and HR-TEM analysis. • The NF annealed at 900 °C showing the highest capacitance of 136 F/g. • The NF NPs having excellent long-term stability over 3000 cycles. [ABSTRACT FROM AUTHOR]

SiOx is considered as a promising anode for next-generation Li-ions batteries (LIBs) due to its high theoretical capacity; however, mechanical damage originated from volumetric variation during cycles, low intrinsic conductivity, and the complicated or toxic fabrication approaches critically hampered its practical application. Herein, a green, inexpensive, and scalable strategy was employed to fabricate NG/SiOx/NG (N-doped reduced graphene oxide) homogenous hybrids via a freeze-drying combined thermal decomposition method. The stable sandwich structure provided open channels for ion diffusion and relieved the mechanical stress originated from volumetric variation. The homogenous hybrids guaranteed the uniform and agglomeration-free distribution of SiOx into conductive substrate, which efficiently improved the electric conductivity of the electrodes, favoring the fast electrochemical kinetics and further relieving the volumetric variation during lithiation/delithiation. N doping modulated the disproportionation reaction of SiOx into Si and created more defects for ion storage, resulting in a high specific capacity. Deservedly, the prepared electrode exhibited a high specific capacity of 545 mAh g−1 at 2 A g−1, a high areal capacity of 2.06 mAh cm−2 after 450 cycles at 1.5 mA cm−2 in half-cell and tolerable lithium storage performance in full-cell. The green, scalable synthesis strategy and prominent electrochemical performance made the NG/SiOx/NG electrode one of the most promising practicable anodes for LIBs.

Transition metal oxide (TMO) is an important type of conversion reaction anode for lithium ion batteries. Carbon encapsulated zinc oxide and cobalt oxide (ZnO@C, Co 3 O 4 @C) were prepared via a MOF-derived strategy. MOF precursors were firstly coated with polypyrrole (PPy) layer and then subjected to subsequent thermal treatment. Benefiting from the synergetic effect of conductive coating layer and 3D porous structure, both anodes showed attractive electrochemical performance. The ZnO@C and Co 3 O 4 @C delivered a reversible capacity of 526 and 721 mAh∙g−1 after 500 cycles at 250 mA g−1. With attractive rate performance, the ZnO@C and Co 3 O 4 @C have an average capacity of 301 and 306 mAh∙g−1 at 2.0 A g−1. Kinetic analysis revealed that lithium ion storage in both ZnO@C and Co 3 O 4 @C were dominated by a surface controlled pseudo-capacitive process. In addition, ZnO@C and Co 3 O 4 @C could even stably cycle for 1000 times at a high current density of 2.0 A g−1. • ZnO@C and Co 3 O 4 @C were prepared via a facile MOF-derived strategy. • Both ZnO@C and Co 3 O 4 @C showed stably cycle for 1000 times at a high current density of 2.0 A g−1. • Lithium storage kinetics were investigated by in-depth analysis of CV curves collected at various scan rates. [ABSTRACT FROM AUTHOR]

In this work, ternary hybrid nanocomposites with different weight percentages of rGO/Ppy/CoFe 2 O 4 and rGO/Ppy/Fe 3 O 4 were synthesized through a hydrothermal approach. Structural properties were investigated by using Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction, and transmission electron microscopy (TEM) with selected area electron diffraction. TEM studies show embedded spinel-type metal oxide nanoparticles, branched Ppy chains and Ppy particles on rGO. The results of the structural and morphological investigations clearly reveal the formation of ternary hybrid nanocomposites. The influence of the content of spinel-type metal oxides on electrochemical properties of nanocomposites was investigated via cyclic-voltammetry, electrochemical impedance spectroscopy and galvanostatic charging/discharging measurements in 1 M LiNO 3 electrolyte. The specific capacitance is found to be 261, 141, 108 and 68.3 F g−1 at 1 A g−1 for 37wt%rGO/58Ppy/5Fe 3 O 4 (FO5), 32wt%rGO/54Ppy/14Fe 3 O 4 (FO14), 37wt%rGO/58PPy/5CoFe 2 O 4 (CFO5), and 32wt%rGO/54Ppy/14CoFe 2 O 4 (CFO14), respectively. Charge storage mechanisms were interpreted through Power's law and Trasatti plot. Among these samples, FO5 exhibits high specific capacitance with good rate capacitance performance (163 F g−1 at 10 A g−1). A hybrid supercapacitor was fabricated with FO5 composite as a positive electrode, activated carbon (AC) as a negative electrode and 1 M LiNO 3 as an electrolyte. As a result, the FO5//AC cell exhibits the specific capacitance of 31.8 F g−1 at 3.0 A g−1 with excellent rate capability and good cycling performances. The energy and powder densities are found to be in the range of 17.74–4.17 Wh kg−1 and 0.3–10.4 kW kg−1 respectively with an output voltage of 0–1.6 V. Unlabelled Image • Ternary rGO/Ppy/metal oxides nanocomposites fabricated by a hydrothermal method. • 37wt%rGO/58Ppy/5Fe 3 O 4 exhibits high specific capacitance with good rate capacity. • Hybrid supercapacitor exhibits the specific capacitance of 31.8 F g−1 at 3.0 A g−1. • Energy density of hybrid cell is found to be in the range of 4.17–17.77 Wh kg−1. • Power density is found to be in the range of 0.3–10.4 kW kg−1. [ABSTRACT FROM AUTHOR]

Abstract Understanding the role of defects is important due to its influence on electrical and optical properties of SnO 2. This study reports the role of oxygen defects in SnO 2 quantum dots decorated in carbon paper for an improved electron transfer process in electrochemical applications. A simple and cost-effective chemical route for preparation of a SnO 2 -decorated carbon paper electrode is described. The pseudo-capacitance property of SnO 2 nano-materials allowed strong improvement in capacitance value compared to pristine carbon paper. Transmission electron microscopy, Raman and photoluminescence studies reveal the presence of ultra-small SnO 2 nanoparticles with defects related to prevalent oxygen vacancies. Electron paramagnetic resonance measurement indicates presence of singly charged defect in diamagnetic SnO 2. Temperature-dependent photoluminescence, vibrational studies and electron energy loss spectroscopy provide further evidence for shallow in-plane oxygen defects in the SnO 2 quantum dots, while impedance measurement discloses their significance in the electrochemical hybrid structure. Highlights • Cost-effective synthesis of SnO 2 QDs for making hybrid capacitors. • Surface-enhanced Raman spectroscopy and TEM confirmed retention of SnO 2 QD properties. • Elucidated the significance of in-plane oxygen defects in the performance of hybrid capacitors. • Observed enhanced charge transfer in SnO 2 -QD-decorated carbon electrodes by impedance spectroscopy. [ABSTRACT FROM AUTHOR]

Thin porous binder-free layers of Co hydroxide/oxide for electrochemical capacitors were formed by dealloying an electrochemically deposited binary Zn–Co alloy, consisting of single homogeneous γ-Zn21Co5 phase. Scanning electron microscopy with energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy (XPS) was used to assess the structure, thickness, and distribution of elements in the as-deposited alloy and the dealloyed layers. The most developed porous layers were formed at a dealloying potential of − 0.965 V versus Ag/AgCl. Both the as-deposited Zn–Co and the dealloyed layers were characterized by a relatively uniform distribution of the components. As determined by XPS, the top of the dealloyed layers before cycling consisted of Co(II) hydroxide with traces of Co(0) and Co(III). The capacitive properties and stability of the formed layers of porous Co oxides were assessed using the electrochemical cyclic voltammetry (CV) and the constant current charge–discharge (C–D) methods. The areal and volumetric pseudo-capacitance values of ~ 0.38 F cm−2 and ~ 880 F cm−3, respectively, were calculated for a 4.3-µm-thick layer. The stability of the studied Co hydroxide/oxides layers was evaluated by CV and C–D cycling. After 300 cycles of C–D, the retention of pseudo-capacitance ~ 80% and the Coulombic efficiency of ~ 98% were determined. The long-term pseudo-capacitance retention was estimated at ~ 78.3% of the initial value. [ABSTRACT FROM AUTHOR]

Abstract Linear and cyclic voltammetry are common method for the characterization of electrochemical capacitor electrodes. Herewith we describe an approach to modelling voltametric data to provide more detailed information about the electrode under study. The model is based upon the response of a series arrangement of a resistor and capacitor to a linearly changing potential to simulate a double layer capacitor. Also included is a term to account for redox processes in localized domains, electrode instability at the extremes of potential, as well as electrode resistance, each of which represent behaviour commonly encountered in electrochemical capacitors. Development of the model is presented, together with its application to the aqueous manganese dioxide electrode. Highlights • A model has been developed to analyze CV data from electrochemical capacitors. • Model is based on the response of a series RC circuit to a linear potential sweep. • Other components include redox process, electrode instability and resistance. • Model validity is demonstrated on the aqueous manganese dioxide electrode. [ABSTRACT FROM AUTHOR]

Abstract Zinc ferrite as an electrode material for electrochemical energy storage has attracted much attention due to its good pseudocapacitive performance. However, Li-ion diffusion behavior in zinc ferrite has not been clearly understood, therefore, further improvements are still facing challenges. Herein, we report a controlled growth of single crystal mesoporous zinc ferrite (ZnFe 2 O 4) nanowall arrays on highly flexible carbon textile for flexible supercapacitors. Li-ion hopping behavior and energy barrier in ZnFe 2 O 4 are calculated by the density functional theory. The electrode based on the ZnFe 2 O 4 nanowall arrays exhibits high specific capacity of 162.7 mAhg−1 at 3.35 Ag−1 (1170 Fg−1 at 3.35 Ag−1) with excellent capacity retention of 96.4% after 8000 cycles. Furthermore, a flexible symmetric solid-state supercapacitor based on the ZnFe 2 O 4 nanowall arrays is fabricated, which exhibits excellent capacitive performance (620 F g−1 at 5 mVs−1) with high flexibility and super-long life by retaining 97.35% of its initial capacitance after 10000 cycles, and high energy density of 85 Wh kg−1 at power density of 1000 W kg−1. The results indicate that the ZnFe 2 O 4 nanowall arrays is a promising material for the future generation of high-performance supercapacitors. The finding of Li-ion diffusion behavior presents a better understanding of the pseudocapacitive contribution of spinel structured binary metal oxides. Graphical abstract Flexible symmetric solid-state supercapacitor based on the ZnFe 2 O 4 nanowall arrays exhibits excellent capacitive performance with super-long life by retaining 97.35% of its initial capacitance after 10000 cycles, and high energy density of 85 Wh kg−1 at a power density of 1000 W kg−1. The low hopping potential barrier for Li+ ions in ZnFe 2 O 4 contributes excellent pseudocapacitive performance. Image 1 Highlights • Mesoporous spinel phase ZnFe 2 O 4 nanowall arrays are directly grown on flexible carbon textile. • The electrodes based on ZnFe 2 O 4 nanowall arrays show super stability in aqueous and solid-state electrolytes. • The assembled symmetric supercapacitor delivers high energy and power densities. • DFT calculation is employed to determine the Li+ ion diffusion paths and energy barrier in spinel phase ZnFe 2 O 4. [ABSTRACT FROM AUTHOR]

Abstract Compared to other energy storage types, capacitive energy-storage serves increasingly significant roles in shortening reversible cycling times and enlarging high power than traditional batteries. It still suffers from the low pseudo-capacitive level and short of electrodes, along with low energy density. Considering the great theoretical capacity, here 1D chain-like Co 3 O 4 is prepared though the thermal oxidation of the self-assembled rod-like Co-precursor. Followed by in-situ polymerization of pyrrole monomer, the Co 3 O 4 were encapsulated in the transparent PPy shell. Particle size-tuning, 1D architecture-altering, conducting PPy introduction could effectively broaden the energy distribution of ions, increase the speed of ions directional transferring and improve the conductivity with protecting electrode materials. As Li-storage anodes, Co 3 O 4 /PPy delivers a stable capacity of 816.6 mAh g−1 at 1.0 A g−1 after 300 cycles. 801.3 mAh g−1 at 5.0 A g−1. The capacity of full-cell still delivers 526 mAh g−1 at 3.0 A g−1 after 50 loops. Supported by detailed kinetic analysis of CV curves, it is confirmed, (1) the nature of Co 3 O 4 approaches to capacitor-like behavior; (2) its electrochemical properties are dominated by capacitive contributions with increased current density as well as cycling. This work provides an in-depth sight on Co 3 O 4 , and further improving its pseudo-capacitive behaviors. Graphical abstract fx1 Highlights • The chain-like Co 3 O 4 was obtained through Kirkendall effect. • The pseudo-capacitive nature of Co 3 O 4 was studied. • Co 3 O 4 /PPy showed the good cycling stability (800 mAh g−1 after 800 cycles). • The capacity of full-cell reached to 532 mAh g−1 at 3.0 A g−1. • The in-depth kinetic analysis was effectively performed. [ABSTRACT FROM AUTHOR]

Li-ion batteries (LIBs) are ubiquitous in mobile devices and increasingly popular for powering large-sized transportation applications. However, current LIBs are undesirable to drive the further penetration of electric vehicles due to insufficient kinetics (long charging time, limited power) and high cost. In the quest of high-power, affordable, and environmentally friendly energy storage, here we design a new type of hybrid device composed of a low-cost Na 2 Ti 3 O 7 anode and a high-voltage LiNi 0.5 Mn 1.5 O 4 cathode. For the first time, we investigated Na 2 Ti 3 O 7 nanotubes as Li + host, which exhibit superior rate performance due to the domination of Li + capacitance (over 85%) in a safe potential window (1–3 V vs . Li/Li + ). Attributing to the synergy between the pseudo-capacitive anode and the fast Li + intercalating cathode, the newly designed device delivers an extraordinary power density of 18631 W kg −1 while maintaining an energy density of 85 W h kg −1 based on total mass of cathode and anode materials. Such a combination of energy and power densities makes it exceptional compared to known LIBs and capacitors. The device also shows excellent capacity retention of 71% after 1000 cycles, highlighting the key advantages of this type of low-cost configuration towards scalable high-power energy storage application. [ABSTRACT FROM AUTHOR]

The monodispersed Ni doped MnCo 2 O 4 mesoporous microspheres were synthesized through a simple ammonium bicarbonate-assisted solvothermal route. The spinel-type crystal structure with a lattice parameter of 8.199 Å for Mn 0.8 Ni 0.2 Co 2 O 4 composition was obtained by using X-ray diffraction analysis. The Brunauer−Emmett−Teller (BET) specific surface area of the sample was found to be 75.78 m 2 g −1 with an average pore diameter of 9.88 nm. Electron microscopy studies revealed that the stable mesoporous microspheres are constituted by well-connected aggregates of nanoparticles. The influence of Ni doping on the pseudo-capacitance of MnCo 2 O 4 electrode was investigated by means of cyclic voltammetry in 6 M KOH electrolyte. We found that the spinel-type Mn 0.8 Ni 0.2 Co 2 O 4 mesoporous microspheres exhibit specific capacitances of 1822 F g −1 at a scan rate of 5 mV/s. Furthermore, the electrochemical impedance spectroscopy analysis revealed the low resistance and good electrochemical stability of the sample. [ABSTRACT FROM AUTHOR]

Constructing heterogeneous nanocomposite has attracted much attention for energy storage devices due to the fact that heterogeneous structure can boost charge transfer owing to the built-in-charge transfer driving force. Herein, a unique architecture for hetero-NiCo 2 S 4 /Co 9 S 8 nanocompiste anchored on Graphene (NiCo 2 S 4 /Co 9 S 8 @G) has been prepared by an epitaxial mechanism. The as-synthesized NiCo 2 S 4 /Co 9 S 8 @G electrode exhibits 662 and 490 mAh g −1 capacity at the first discharge/charge cycle and can be maintained at 323 mAh g −1 after 4000 cycles (from 2nd cycle only 0.008% decay per cycle) at an ultrahigh current density of 10 A g −1 . Moreover, NiCo 2 S 4 /Co 9 S 8 @G electrode can be full charged within 11 s while still achieving a specific capacity of 133 mAh g −1  at a current density of 40 A g −1 . This fascinating high-rate capability is attributed to the pseudo-capacitance contribution which can be further verified by kinetics model. This pseudo-capacitance originating from hetero structure sheds new light on the development of high-rate performance anode materials. [ABSTRACT FROM AUTHOR]

Free-standing Ti 3 C 2 T x MXene films with flexible feature are considered to be promising electrodes for the application in flexible energy devices. Exploring the different cation effect and each transport mechanism will help us to identify the optimized cation for special applications. Herein, we investigate the relationship between cation transports and capacitance behavior under different potential windows. In addition, we uncover intercalation mechanisms for Li + , Na + , and K + -containing electrolytes. As a result, we found that capacitive intercalation mechanism of characteristic cation can be influenced by different potential windows. Importantly, after 5000 charge-discharge cycles from −1 V to 0 V, the cation-intercalation behavior is demonstrated by significant electrode expansion in LiCl, NaCl, and KCl electrolytes with the increased d-spacing of 1.344 nm, 1.313 nm, and 1.305 nm, respectively. Additionally, larger size of K + with fast ion transport is involved in fast electrochemical surface adsorptions, which explains higher capacitance of 346 F cm −3 in KCl than 218 F cm −3 in NaCl electrolyte. In contrast, small ion size of Li + is vulnerable to adsorb and permeate the spacing between layers of Ti 3 C 2 T x MXene electrode, which delivers volumetric capacitance of 320 F cm −3 . The present study provides direct experimental evidence for electrochemical mechanism of cation intercalation between Ti 3 C 2 T x MXene layer sheets. [ABSTRACT FROM AUTHOR]

3D Porous carbon derived from pine needle is prepared by hydrothermal followed KOH activation process. The high surface area (1175 m 2  g −1 ) and rich hierarchical pores provide the electrode with high capacitance. And the abundant surface oxygen functional groups offer additional pseudo-capacitance, which would increase the capacitance. It delivers the capacitance of 348 F g −1 at 1 A g −1 in a three-electrode cell. The well performance and the low cost make the derived porous carbon as a promising electrode. [ABSTRACT FROM AUTHOR]

Promoting the inherent conductivity and stability can boost the possible application of most metal-organic frameworks (MOFs) in the energy storage and conversion devices. Herein, La-doped Ni-MOF materials (La-NMF) are achieved via a simple one-pot hydrothermal process, which shows an enhanced electrochemical performance and stability compared with Ni-MOF. The La-NMF electrode with 10 wt% of La doping (La-NMF-0.1) possesses the optimum performance with the specific capacity of 159.9 mA h g−1 at 1 A g−1, much higher than that of Ni-MOF (100.4 mA h g−1). Moreover, the assembled hybrid supercapacitor containing the La-NMF-0.1 positive electrode achieves a high energy density of 38.3 W h kg−1 at a power density of 375 W kg−1, and remains 86.7% of the capacity retention after 5000 cycles at 5 A g−1. The density functional theory (DFT) calculation reveals that La doping boosts the electron density at conduction band near Fermi level, which improves the capability of charge transfer and electronic conductivity of materials. The larger surface area, rapider charge transfer and more excellent electronic conductivity endow La-NMF-0.1 with a superior electrochemical performance compared to Ni-MOF. This work provides some insights for design and facile fabrication of the advanced materials in the new energy fields. [Display omitted] • La-doped Ni-MOF (La-NMF) obtained via a simple one-pot hydrothermal method. • La doping promotes the charge transfer and electrolyte diffusion of the electrode. • La-NMF exhibits a higher specific capacity than Ni-MOF. • The La-NMF-containing device shows superior energy density to many Ni-MOF based ones. [ABSTRACT FROM AUTHOR]

Three-dimensional Ni(OH) 2 /GO hydrogel has been prepared by a two-step route: formation of rGO hydrogel and depositing of Ni(OH) 2 nanoparticles inside it. Structure and composition of the as-prepared Ni(OH) 2 /GO hydrogel were measured by means of transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron (XPS), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and Raman spectroscopy. The 3D structure of graphene and the pseudo-capacitance of nickel hydroxide are found to be remarkably effective in enhancing the specific capacitance of the composite hydrogel, up to 532 F g −1 . Then, asymmetric supercapacitor was assembled by using the Ni(OH) 2 /rGO hydrogel and rGO hydrogel as the two electrodes in KOH (6.0 M) electrolyte, and it exhibited a high performance with an energy density of 28.88 Wh kg −1 and a power density of 5829.2 W kg −1 . The specific capacitance can be retained 90% of the initial value after 10000 charge/discharge cycles. The results indicate that Ni(OH) 2 /rGO hydrogel could be a potential candidate as binder-free electrode for supercapacitors, especially asymmetric supercapacitors, which has a wide range of applications in the near future. [ABSTRACT FROM AUTHOR]

This study investigates the effects of multi-walled carbon nanotubes (MWCNTs) content on the electropolymerization potential of polypyrrole (PPy) on both surfaces of carbon nanoparticle/MWCNT (CN/M)-coated Nafion membranes and on the electrical, electrochemical and electromechanical properties of PPy- electrode based soft actuators. SEM analysis revealed that the surface morphology of actuators changes considerably by altering the MWCNT content and the most porous PPy films formed in actuator comprising of 25 wt% MWCNT. The electrochemical characteristics of the prepared actuators were compared in terms of double layer capacitance ( C dl ), pseudo capacitance ( C F ) and ionic conductivity ( σ ). The capacitive nature of the prepared actuators was followed by waveform analysis of applied voltage and output current. C dl and σ increased by increasing the MWCNT content up to 25 wt% and afterward decreased considerably, while a reverse trend was observed for C F . The electrochemical impedance spectroscopy (EIS) measurements confirmed that this sample had the highest surface roughness. These data were in good agreement with the data obtained from water uptake ( WUP ) and ion exchange capacity ( IEC ) measurements. The electro-chemo-mechanical performances of the actuators were followed by studying the maximum tip displacement and I V curves. The largest tip displacement was obtained in actuators comprising of 25 wt% MWCNT which showed to have the highest capacitive characteristic (243.52 mF. cm − 2 ). The specific electro-mechanical energy efficiency (1.18) and the maximum tip displacement (25 mm) of these metal-free actuators were 18% and 9% higher than that considered for Pt-based actuators, respectively. This strategy is therefore of considerable interest for increasing the applicability of low cost carbon-based soft actuators in medicine and robotics. [ABSTRACT FROM AUTHOR]

This paper reports a dual mesoporous carbon (NDMC) with high nitrogen doping level derived from the amino production of the sucrose synthesized under hydrothermal condition. The S and total pore volume of the reported materials reaches up to 1101 and 1.67 cm g, the small mesopores center at about 3.22-3.31 nm while the larger mesopores locate at 8.98-12.58 nm. The doping content of the nitrogen heteroatoms is found to be more than 11.6 at.%, and depend on the carbonization temperature. The maximum specific capacitance of the reported materials reaches up to 512 F g due to the additional contribution of pseudo-capacitance induced by the nitrogen heteroatoms doping. The capacitance retention rate is found to be up to 95% after 1000 times cycles. The dual mesoporous structure, high specific area, additional pseudo-capacitance, enhanced wettability and conductivity are found to response for the superior capacitance performance of the reported materials. [ABSTRACT FROM AUTHOR]

This account investigated the behavior of the electrical charge storage/release in polyaniline (Pani) electrodes of a symmetric supercapacitor with 0.5 M H 2 SO 4 electrolyte. Two Pani films with different morphologies were synthesized under various reaction pressures. The structural and morphological characterizations of Pani films were carried out by Fourier Transform infrared spectroscopy (FTIR) and Field emission scanning electron microscopy (FESEM). The electrochemical behavior of Pani films was characterized by several methods, including cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) cycling and electrochemical impedance spectroscopy (EIS). The performance of the electrodes assembled in a symmetric supercapacitor configuration was also characterized by GCD in different voltage windows. The contributions from the electric double-layer capacitance (EDLC) and the pseudo-capacitance (PSC) of Pani electrodes at different potential windows were evaluated and compared. The results suggested that the specific capacitance induced from EDLC and PSC for Pani films with porous nano-network morphology were obviously higher than those generated by the granular Pani films. This was attributed to the porous nano-network structure, which had a significant role in increasing the specific surface area. For symmetric Pani supercapacitors, the induced capacitance at the negative electrode was found dominated by PSC while accumulation/release of the electric charge at the positive electrode mainly followed an EDLC mechanism. The redox potential of Pani played a cut-off point between the potential range dominated by EDLC and PSC mechanisms. A working model was proposed to describe the electrical charge storage/release processes at different electrodes assembled in a symmetric capacitor configuration. [ABSTRACT FROM AUTHOR]

With the development and popularity of portable electronic devices, there is an urgent need for flexible energy storage devices suitable for mass production. We report freestanding paper electrodes for supercapacitors fabricated via a simple but efficient two-step method. Nitrogen-doped graphene (N-rGO) was first prepared via a hydrothermal method. This not only obtained nitrogen atom-doped nanoparticles but also formed reduced graphene oxide. Pyrrole (Py) was then deposited on the bacterial cellulose (BC) fibers as a polypyrrole (PPy) pseudo-capacitance conductive layer by in situ polymerization and filtered with nitrogen-doped graphene to prepare a self-standing flexible paper electrode with a controllable thickness. The synthesized BC/PPy/N 15 -rGO paper electrode has a remarkable mass specific capacitance of 441.9 F g−1, a long cycle life (96 % retention after 3000 cycles), and excellent rate performance. The BC/PPy/N 15 -rGO-based symmetric supercapacitor shows a high volumetric specific capacitance of 244 F cm−3 and a max energy density of 67.9 mWh cm−3 with a power density of 1.48 W cm−3, suggesting that they will be promising materials for flexible supercapacitors. [Display omitted] [ABSTRACT FROM AUTHOR]

Faced with numerous challenges raised by the requirements of the modern industries for higher power and higher energy, supercapacitors study started playing an important role in offering viable solutions for some of these requirements. This paper presents the surface redox reactions based modeling in order to study the origin of high capacity of EDLC (electrical double-layer capacitor) for better understanding the working principles of supercapacitors. Some application-dependent sizing methods are also presented since proper sizing can increase the efficiency and the life cycle of the supercapacitor based systems.