Advanced Supercapacitors Research Articles

A facile ion-conversion-exchange strategy for designing nitrogen-doped CoMoO4@Co3O4 double-shell nanoboxs: A competitive candidate for supercapacitor and oxygen evolution reaction

Co3O4 has been paid much attention in the field of supercapacitors and oxygen evolution reaction attributed to its high theoretically specific capacitance, earth abundant, cost-effective, and environment friendly. However, the commercial application of Co3O4 was greatly limited by the poor electrical conductivity and inferior active sites. Herein, the N-CoMoO4@Co3O4 double-shell nanoboxs were successfully prepared through in situ ion-conversion-exchange treatment coupled with the following calcination process. The hollow/porous transition metal oxide-based nanomaterials delivered large surface areas and rich active sites, and boosted electron transfer. Hybridizing with other components increased electrochemical reactive active sites, optimized the superiority of different components. The nitrogen doping resulted in high density of surface reaction sites. As a result, the obtained N-CoMoO4@Co3O4 double-shell nanoboxs performed superior specific capacitance (520 F/g), favorable charge/discharge rate and remarkable cycling stability. Moreover, the advanced asymmetrical supercapacitors prepared by N-CoMoO4@Co3O4 double-shell nanoboxs supplied remarkable energy density. Furthermore, when employed as oxygen evolution reaction electrocatalysts, N-CoMoO4@Co3O4 double-shell nanoboxs yielded favorable desirable overpotential (380 mA/cm2) and low Tafel slope of 87.8 mV/dec. Overall, this work provided theoretical guidance for the design of efficient dual-function electrocatalysts.

Highly Stable Two-Dimensional Cluster-Based Ni/Co-Organic Layers for High-Performance Supercapacitors.

Basic requirements for advanced and practical supercapacitors need electrode materials with strong stability, high surface area, well-defined porosity, and enhanced capability of ion insertion and electron transfer. It is worth mentioning that the two-dimensional cluster-based Ni/Co-organic layer (Ni0.7Co0.3-CMOL) inherits high stability from the Kagóme lattice and shows excellent pseudocapacitance behavior. As an optimized atomic composition, this crystalline CMOL exhibits excellent performance and stability both in 1.0 M KOH and All-Solid-State Flexible Asymmetric Supercapacitor (ASCs). The specific capacitance values are 1211 and 394 F g-1 and the energy density is 54.67 Wh kg-1 at 1 A g-1. Good cycling stability is characterized by its capacitance retention, maintained at 92.4% after 5000 cycles in a three-electrode system and 90% after 2000 cycles at 20 A g-1 for assembled All-Solid-State Flexible ASCs. An in situ XRD technique was used in the three-electrode system, which showed that there was no signal of crystalline substance that affected the cyclic stability of the material while charging and discharging. These superior results prove that Ni0.7Co0.3-CMOL is a promising candidate for supercapacitor applications.

Heat-Resistant, Robust, and Hydrophilic Separators Based on Regenerated Cellulose for Advanced Supercapacitors.

Separators in supercapacitors (SCs) typically suffer from defects of low mechanical property, limited ion transport, and electrolyte wettability, and poor thermal stability, impeding the development of SCs. Herein, high-performance regenerated cellulose (RC) based separators are designed that are fabricated by effective hydrolytic etching of inorganic CaCO3 nanoparticles from a filled RC membrane. The as-prepared RC separator displays excellent comprehensive performances such as higher tensile strength (75.83MPa) and thermal stability (200°C), which is superior to commercial polypropylene-based separator (Celgard 2500) and sufficient to maintain their structural integrity even at temperatures in excess of 200°C. Benefiting from its hydrophilicity, high porosity, and outstanding electrolyte uptake rate (208.5%), the RC separator exhibits rapid transport and permeability of ions, which is 2.5× higher than that of the commercial nonwoven polypropylene separator (NKK -MPF30AC-100) validated by electrochemical tests in the 1.0m Na2 SO4 electrolyte. Results show that porous RC separator with unique advantages of superior electrolyte wettability, mechanical robustness, and high thermal stability, is a promising separator for SCs with high-performance and safety.

Impact of hybridization on specific capacitance in hybrid NiO/V2O5@graphene composites as advanced supercapacitor electrode materials

Currently, hybrid composites are considered promising materials in energy applications. Among various approaches for synthesizing hybrid composites, the solution combustion approach has attracted significant research interest worldwide due to its high versatility, efficiency, simplicity, scalability, reproducibility, and cost-effectiveness. Further, solution combustion synthetic techniques have recently been regarded as one of the more facile methods for developing effective supercapacitor electrodes. This paper provides the synthesis of vanadium pentoxide (V2O5), nickel oxide-vanadium pentoxide (NiO/ V2O5), and nickel oxide-vanadium pentoxide-Graphene (NiO/ V2O5@Graphene) nano-composites using solution combustion method. The importance of the hybridization of transition metal oxide with other-transition metal oxide and carbon derivatives is studied systematically. The obtained materials are characterized by X-ray diffraction, UV-Visible spectroscopy, Fourier transform infrared spectroscopy, Field emission scanning electron microscopy, Energy-dispersive X-ray analysis, Cyclic voltammetric analysis, Galvanostatic charge-discharge, and Electrochemical impedance. The average crystalline sizes are calculated as 27 nm, 24 nm, and 14 nm for V2O5, NiO/ V2O5, and NiO/ V2O5@Graphene nano-composites. The UV-Visible, Fourier transform infrared, and Energy-dispersive X-ray spectroscopy analysis confirms the formation of synthesized materials. Field emission scanning electron microscopy provides the distribution of NiO/ V2O5 nano-composite over the graphene sheet. The electrochemical performance of V2O5 is improved drastically with the simultaneous hybridization of two metal oxides. Further, the addition of graphene makes a small enhancement in the specific capacitance of the nano-composites. The order of specific capacitance is V2O5 (328 F/g) ˂ NiO/V2O5 (918 F/g) ˂ NiO/V2O5@Graphene (939 F/g). The solution resistance and charge transfer resistance of the modified electrodes are in the order of V2O5 (1.59 Ω) ˃ NiO/V2O5 (0.85 Ω) ˃ NiO/V2O5@Graphene (0.73 Ω) and V2O5 (5.66 Ω) ˃ NiO/V2O5 (1.35 Ω) ˃ NiO/V2O5@Graphene (0.17 Ω) respectively, which supports the enhancement in specific capacitance upon hybridization. The obtained materials are cost-effective, low-toxic, and efficient, hence would be appropriate for industrial use.

Biomass derived carbonaceous materials with tailored superstructures designed for advanced supercapacitor electrodes

Supercapacitors (SC), as one of the most competitive energy storage devices, are receiving great attention in R&D community. Carbonaceous materials for supercapacitor electrodes with high performance possess many attractive advantages, such as large specific surface area (SSA), hierarchical porous superstructures and excellent conductivity. Herein, biomass based materials are often utilized as versatile precursors for activated carbon production due to their inherent merits, including low cost, abundance, renewability, high carbon content, environmental friendliness, genetically unique nature structure. As known, the capacitance performance of biomass based carbon-assembled supercapacitors is mainly directly proportional to the exceptional skeleton robustness, high SSA and electroactive site content within carbonaceous framework. In this review, special attentions will be paid to the latest research progress of carbonaceous materials derived from biomass with tailored hierarchical superstructures to highlight their impact on the electrochemical performance of assembled supercapacitor. The objective of this paper is to present a critical review on the most recent publication related to biomass oriented carbonaceous electrodes for outstanding supercapacitor electrodes. Furthermore, the perspective for the progress and development of biomass based carbonaceous electrodes for high performance supercapacitors will also be provided, to underscore the current critical issues and future opportunities. • Carbon derived from biomass with tailored structure for supercapacitors was reviewed. • Methods for activating carbon with improved capacitance were reviewed and discussed. • Biomass based carbon and their key parameters/ characterizations were summarized. • The reasons why biomass derived carbon are suitable for electrodes were demonstrated. • Preparation methods and applications of biomass derived carbon were summarized and prospected.

Superior capacitive performance of spherical MnV2O6·2H2O-graphene nanosheet hybrid as electrode material for asymmetric supercapacitor

The evolution of advanced supercapacitors depends highly on the design and synthesis of electrodes with rational morphology and structure. In this paper, a facile methanol-assisted solvothermal method is reported for the synthesis of spherical hydrated manganese vanadate (MnV2O6·2H2O)-reduced graphene oxide (rGO) nanosheets hybrid. In particular, the utilization of methanol can not only change the isotropy growth of MnV2O6 but also suppresses the phase-transformation process (from orthorhombic to monoclinic) by preventing the deintercalation of crystal water. Remarkably, the MnV2O6·2H2O exhibits a superior specific capacity of 1678.5 F g−1 which is nearly four times more than that of MnV2O6 (410.2 F g−1) at 2 A g−1. After integrating with graphene, MnV2O6·2H2O spheres are uniformly encapsulated by graphene sheets with a size reduction from 1 μm to 200 nm. And a “GO-assisted Ostwald ripen-splitting” mechanism is proposed to explain the formation of MnV2O6·2H2O-rGO. Consequently, the MnV2O6·2H2O-rGO hybrid exhibits significantly improved conductivity, enhanced specific capacity (1976.3 F g−1 at 2 A g−1) and good rate capability (1422.5 F g−1 at 10 A g−1 and 1155.5 F g−1 at 20 A g−1) as well as excellent cycling stability (94.2% capacitance retention after 10,000 cycles). Moreover, the assembled asymmetric supercapacitor using MnV2O6·2H2O-rGO (the positive electrode) and activated carbon (the negative electrode) shows a superior energy density of 51.5 Wh⋅kg−1 at the power density of 849.2 W kg−1.

Nickel carbonate Hydroxide-based Core-Triple-Shelled nanofibers with ultrahigh specific capacity for flexible hybrid supercapacitors

Designing novel efficient electrode materials with controlled hierarchical structure and composition for advanced supercapacitors remains a great challenge. Herein, a core-triple-shelled hierarchical GCNF/PANI/NCO nanostructure has been designed and fabricated by sequential growth of the conductive polyaniline (PANI) layers and nickel carbonate hydroxide (Ni2(CO3)(OH)2) nanosheets on the graphene-coated electrospun carbon nanofibers (GCNF) via a facile wet-chemical strategy. Taking full advantage of the free-standing architecture of graphene-coated electrospun carbon nanofibers, high conductivity and flexibility of the PANI layers, and abundant active sites of Ni2(CO3)(OH)2 nanosheets, the optimal GCNF/PANI/NCO (2 h) electrode exhibits a high specific capacitance of 1565F g−1 at 1 A/g and enhanced rate capability, which are higher than those of the GCNF, GCNF/PANI, and GCNF/NCO (2 h) electrodes at the same situation, and also exceeds most of the reported nickel carbonate hydroxide-based electrodes in literature. The superior performance should be mainly ascribed to the collaborative contribution of each component. Moreover, a self-assembled GCNF/PANI/NCO//AC hybrid supercapacitor delivers a high energy density of 35.4 Wh kg−1@750 W kg−1 and a long cycle lifespan. This strategy enables the controllable synthesis of core-triple-shelled hierarchical materials applicable to advanced electrochemical applications.

Flexible Carbon Dots‐Intercalated MXene Film Electrode with Outstanding Volumetric Performance for Supercapacitors

Abstract2D MXenes have emerged as promising supercapacitor electrode materials due to their metallic conductivity, pseudo‐capacitive mechanism, and high density. However, layer‐restacking is a bottleneck that restrains their ionic kinetics and active site exposure. Herein, a carbon dots‐intercalated strategy is proposed to fabricate flexible MXene film electrodes with both large ion‐accessible active surfaces and high density through gelation of calcium alginate (CA) within the MXene nanosheets followed by carbonization. The formation of CA hydrogel within the MXene nanosheets accompanied by evaporative drying endow the MXene/CA film with high density. In the carbonization process, the CA‐derived carbon dots can intercalate into the MXene nanosheets, increasing the interlayer spacing and promoting the electrolytic diffusion inside the MXene film. Consequently, the carbon dots‐intercalated MXene films exhibit high volumetric capacitance (1244.6 F cm−3 at 1 A g−1), superior rate capability (662.5 F cm−3 at 1000 A g−1), and excellent cycling stability (93.5% capacitance retention after 30 000 cycles) in 3 m H2SO4. Additionally, an all‐solid‐state symmetric supercapacitor based on the carbon dots‐intercalated MXene film achieves a high volumetric energy density of 27.2 Wh L−1. This study provides a simple yet efficient strategy to construct high‐volumetric performance MXene film electrodes for advanced supercapacitors.

Superbases-templated carbons doped with electrochemically active oxygen as advanced supercapacitor electrodes

Templating techniques have been widely adopted for the synthesis of porous carbons, such as oxygen-doped porous carbon nanosheets (O-PCNs), but the effect of the surface characteristics of templates on the surface functionality and performance of a derived carbon has not been well studied. Herein, a series of laboratory-made superbases of K/Mg(OH)2 with different K/Mg ratios were employed as template to fabricate nanocarbon materials. The aim is to find out how the strength of template basicity could influence the surface functionalities and the supercapacitor performances of the derived O-PCNs. The resulting materials are rich in conjugated hydroxyl and carbonyl groups that are electrochemically active owing to the protection of the conjugated hydroxyl group by KOH and the dehydrogenation step catalyzed by magnesium oxide. Systematic investigations revealed that with the increase of basic strength, the content of the derived electrochemically active oxygen species in the forms of conjugated carbonyl (CO) and hydroxyl (COH) first increases from 8.4 atom% to 11.4 atom% then decreases to 9.25 atom%. Moreover, the microporosity of the O-PCNs stepwise increases with the rise of KOH loading, ascribable to the effect of KOH etching on the carbon skeleton. The O-PCN-20 templated by 20 % K/Mg(OH)2 is rich in porosity, large in surface area (930 m2/g) and high in active oxygen content (11.4 atom%). With high active surface area and extra Faradaic capacitance, O-PCN-20 exhibited superior supercapacitor performances including large specific capacitance of 375 F/g@1.0 A/g, high rate capability of 81.1 % (from 1.0 A/g to 20 A/g), energy density of 25.7 Wh/kg@900 W/kg and excellent cycling stability with near 100 % capacitance retentions after 10 000 cycles and more than 86.2 % capacitance retention over 20 000 cycles at large current density of 10 A/g, indicating O-PCN-20 has potential to be used as electrode material for energy storage devices.

Recent Advanced Supercapacitor: A Review of Storage Mechanisms, Electrode Materials, Modification, and Perspectives.

In recent years, the development of energy storage devices has received much attention due to the increasing demand for renewable energy. Supercapacitors (SCs) have attracted considerable attention among various energy storage devices due to their high specific capacity, high power density, long cycle life, economic efficiency, environmental friendliness, high safety, and fast charge/discharge rates. SCs are devices that can store large amounts of electrical energy and release it quickly, making them ideal for use in a wide range of applications. They are often used in conjunction with batteries to provide a power boost when needed and can also be used as a standalone power source. They can be used in various potential applications, such as portable equipment, smart electronic systems, electric vehicles, and grid energy storage systems. There are a variety of materials that have been studied for use as SC electrodes, each with its advantages and limitations. The electrode material must have a high surface area to volume ratio to enable high energy storage densities. Additionally, the electrode material must be highly conductive to enable efficient charge transfer. Over the past several years, several novel materials have been developed which can be used to improve the capacitance of the SCs. This article reviews three types of SCs: electrochemical double-layer capacitors (EDLCs), pseudocapacitors, and hybrid supercapacitors, their respective development, energy storage mechanisms, and the latest research progress in material preparation and modification. In addition, it proposes potentially feasible solutions to the problems encountered during the development of supercapacitors and looks forward to the future development direction of SCs.

RGO nanosheet wrapped β-phase NiCu2S nanorods for advanced supercapacitor applications.

A new integration strategy of transition metal sulfide with carbon-based materials is used to boost its catalytic property and electrochemical performances in supercapacitor application. Herein, crystalline reduced graphene oxide (rGO) wrapped ternary metal sulfide nanorod composites with different rGO ratios are synthesized using hydrothermal technique and are compared for their physical, chemical, and electrochemical performances. It is found that their properties are tuned by the weight ratios of rGO. The electrochemical investigations reveal that β-NiCu2S/rGO nanocomposite electrode with 0.15 wt.% of rGO is found to possess maximum specific capacitance of 1583 F g-1 at current density of 15mAg-1 in aqueous electrolyte medium. The same electrode shows excellent cycling stability with capacitance retention of 89% after 5000 charging/discharging cycles. The reproducibility test performed on NiCu2S/rGO nanocomposite electrode with 0.15 wt.% of rGO indicates that it has high reproducible capacitive response and rate capability. Thus, the present work demonstrates that the β-NiCu2S/rGO nanocomposite can serve as a potential electrode material for developing supercapacitor energy storage system.

Fabrication of novel coral reef-like nanostructured ZnFeNiCo2S4 on Ni foam as an electrode material for battery-type supercapacitors

Battery-type electrode materials have recently been explored as a novel class of high-capacity cathode materials in the development of hybrid supercapacitors. In the study, a novel nano coral-reef ZnFeNiCo2S4 quaternary sulfide was synthesized in two easy hydrothermal stages on a Ni Foam (NF) substrate for advanced battery-type supercapacitors. In three or two electrode systems, the ZnFeNiCo2S4/NF was applied as a potential electrode for battery-type supercapacitors. According to the result, the ZnFeNiCo2S4/NF electrode was successfully synthesized as a binder-free electrode on the Ni foam. The electrochemical investigation of the ZnFeNiCo2S4/NF showed a high specific capacity of 1778 C g−1 at a current density of 3 A g−1 with excellent cycling stability of 86.1% capacity retention and 100% coulombic efficiency at 6 M KOH as the electrolyte. The battery-type symmetric supercapacitor measured a specific capacitance of 162.3 C g−1 at a current density of 2 A g−1 with a specific energy of 33.8 Wh kg−1 at a specific power of 2519.25 W kg−1. On the contrary, asymmetric supercapacitors exhibit excellent cycling stability, approximately 94.7% capacity retention after 6000 cycles, and a 100% coulombic efficiency. Due to their excellent electrochemical characteristics, the high-performance ZnFeNiCo2S4 nano coral reef-like structure is a promising electrode material for high-performance supercapacitors.

Bioinspired design of graphene-based N/O self-doped nanoporous carbon from carp scales for advanced Zn-ion hybrid supercapacitors

Integrating the superiorities of high power density of supercapacitors and high energy density of batteries, safe and low cost aqueous Zn-ion hybrid supercapacitors (ZIHSCs) are regarded as a promising alternative for next generation energy storage devices. As potential cathode materials for ZIHSCs, porous carbon/graphene have been widely investigated recently, whereas the adjustment of their composition and structure to achieve favorable features of sustainability, long lifespan and high activity remains a challenge. Herein, a graphene-based N/O co-doped porous carbon is successfully constructed via an efficient approach of the carbonization and sequent KOH activation using renewable carp scales as carbon source. The unique lamellar structure with the exterior layer of hydroxyapatite and the beneath well-arranged collagen fibrils (rich in N and O) functions as catalytic base for the growth of graphene structure over the exterior layer and affords the self-doping with N and O heteroatoms, respectively. Expectedly, the resultant carbon possesses a hybrid structure of graphene base and nanoporous amorphous carbon, together with a proper N/O co-doping, resulting in fast electrochemical kinetics and abundant Zn2+ storage active sites for high power and energy outputs. Consequently, as-assembled aqueous ZIHSC displays a high specific capacity of 138.8 mAh g − 1 at 0.1 A g − 1, admirable rate capability of 61.7% retention rate at a 200-fold higher current, and attractive energy density of 111.1 Wh kg−1 at 100 W kg−1. More excitingly, as-constructed quasi-solid ZIHSC exhibits a satisfactory specific capacity of 117.8 mAh g − 1, a high energy density of 88.9 Wh kg−1 and a high power density of 10 kW kg−1, together with excellent cycling stability (capacity retention of 87.2% after 10,000 charge-discharge cycles at 5 A g − 1) and outstanding mechanical flexibility. Therefore, the designed conversion of carp scales to advanced carbons by taking advantages of its inherent composition and structure opens up hereditary view to construct high performance ZIHSCs from biomass sources.

Self-assembly of biomass derivatives into multiple heteroatom-doped 3D-interconnected porous carbon for advanced supercapacitors

The rational design of the pore structure of carbon materials is of great significance for solving the low specific capacitance and poor rate performance of supercapacitors. Herein, we propose a multiple heteroatom-doped three-dimensional (3D) interconnected carbon material obtained from the self-assembly of biomass derivatives including chitosan and sodium lignosulfonate with the assistance of boric acid. The amino group of chitosan protonated by boric acid can form electrostatic adsorption and hydrogen bonding with the sulfonic acid group of sodium lignosulfonate to form a carbon network structure. Boric acid also acts as a template, and in combination with KOH activation, further promotes the formation of the hierarchical porous structure, resulting in the as-prepared carbon possessing a high specific surface area of 2700.65 m2 g−1. As the electrode material in 6 M KOH electrolyte, it manifests a decent specific capacitance of 332 F g−1 at 1 A g−1 in the three-electrode system, while the symmetric electrode achieves a high energy density of 17.7 W h kg−1 at 166.4 W kg−1. Moreover, the contribution rate of the fast and slow kinetic process, as well as the fast diffusion of electrolyte ions are deeply revealed through the ultrafast charge/discharge and the ion diffusion kinetics analysis, respectively. The symmetric electrode in PVA/KOH gel electrolyte maintains 97% capacitance retention and 100% Coulombic efficiency over 10000 cycles, indicating excellent cycling stability.

Efficient dual conductive network based on layered double hydroxide nanospheres and nanosheets anchored in N-carbon nanofibers for asymmetric supercapacitors

A green electrode material with dual conductive networks via electrospinning with carbonization and co-precipitation method is constructed. Nitrogen-based carbon nanofiber network (CCP-N) is used as the inner-conductive, electrochemical-active substrate and flexible skeleton. The Co Ni layered double hydroxide (Co Ni LDH) nanosheets and flower-like nanospheres, which randomly and closely covering the surface of CCP-N, respectively, just as the fungus grow on trunks in nature, is regarded as outer-conductive and active substance collector in order to provide abundant active centers, sufficient reaction interface to advance fast electrolyte ions diffusion and electrons transport. Furthermore, the growth process of Co Ni LDH on CCP-N is observed by controlling growth time and the Co/Ni ratio of the precursor solution. It is found that the optimal Co/Ni ratio was 2:1, while that optimal growth time is 12 h. The specific capacitance of Co Ni LDH@CCP-N electrode reaches 1319.4 F g-1 at 1 A g-1. The assembled asymmetric supercapacitor device (CCP-N @ Co Ni LDH//CCP-N) possesses a high energy density of 48.1 W h kg-1 at power density of 576.8 W kg-1, excellent cycling stability of 82.2% retention after 10,000 cycles. The results clearly indicate the Co Ni LDH@CCP-N materials have enormously potential in energy storage. This work puts forward a novel strategy for the design and fabrication of green and advanced supercapacitors materials with high power density and energy density.

Biomass-derived graphene-like carbon nanoflakes for advanced supercapacitor and hydrogen evolution reaction

It is valuable that graphene-like carbon materials are prepared from the biomass resources due to their unique two-dimensional structure, heteroatom enriched, and high specific surface area. Herein, we use egg white and graphene oxides as precursor and employ post-hydrothermal carbonization approach, freeze-drying technique, carbonization, and activation methods by KOH to prepare the graphite carbon nanoflakes with Fe7C3 @graphite carbon nanoflakes hybrid materials. Morphology tests imply that the formation of graphite carbon nanoflakes are mainly depended by activation step, it implies that carbon flakes are exfoliated via introducing K+ into carbon layers and further destroying the van der Waals force (VDWF). As a result, this hybrid materials exhibit an attractive capacitance (528 mF·cm−2 @1 mA·cm−2) and durability (91 @10 mA·cm−2, 4000 cycles). For hydrogen evolution reaction (HER), the as-collected samples also deliver a low overpotential and remarkable stability. We believe that the as-obtained hybrid materials have a greatly application value in energy storage devices.

Mechanochemical synthesis of ZIF(Zn, Co)/NixCoyAlz-LDH composite by solid state ion exchange as advanced materials for pseudocapacitor electrode

Metal-organic frameworks (MOFs), and layered double hydroxides (LDHs) as worthy hot-spot materials have gained substantial attention for electrochemical energy storage and conversion applications as a result of their structural diversities, excellent physical properties, and promising electrochemical performance. In this work, we synthesized composite materials comprised of ZIF-8 and NiCoAl-LDHs via a mechanochemical method and in-situ solid state ion exchange. The findings have shown that the synergetic effects between ZIF-8 and LDHs in composite materials and tuning of the percentages of Ni and Co in LDHs have a positive contribution to enhancing electrochemical performance in supercapacitors. In this regard, among pure LDHs and ZIF-8\\NixCoyAl0.33 LDHs, ZIF-8\\Ni(17%)Co(50%)Al(33%)-LDH indicated higher specific capacitance of 256 F g−1 and higher rate of performance. In ZIF-8/Ni(17%)Co(50%)Al(33%)-LDH, LDH nanosheets’ structure improves the conductivity of ZIF-8, and optimized bimetal Ni-Co provides more active sites. In addition, the asymmetric supercapacitor (ASC) assembled by ZIF-8/Ni(17%)Co(50%)Al(33%)-LDH as the cathode and activated carbon (AC) as the anode achieved a good performance in terms of specific capacity, energy density, and cyclic stability. For instance, the ASC delivered a maximum energy density of 184 Wh kg−1 at 1291 W kg−1 and outstanding capacitance retention of 91% after 5000 cycles. This study demonstrates that the interaction between different element ratios in LDHs and the composition of LDHs with ZIFs (porous and redox-active MOFs) has significant effects on using ZIFs/LDHs electrode materials in advanced supercapacitor applications.

Wet chemical synthesis of Gd+3 doped vanadium Oxide/MXene based mesoporous hierarchical architectures as advanced supercapacitor material

In this paper, Gd 3+ doped V 2 O 5 /Ti 3 C 2 T x MXene (GVO/MX) hierarchical architectures have been synthesized by wet chemical approach. As prepared GVO/MX composite, along undoped VO and unsupported GVO were well characterized by XRD, FESEM, EDX, FT-IR and BET techniques. Electrochemical performance of VO, GVO and GVO/MX was evaluated by CV, GCD and EIS measurements. Among the three electrodes, GVO/MX composite exhibited highest electrochemical activity with the optimum specific capacitance of 1024 Fg -1 at 10 mVs −1 . The specific capacitance of GVO/MX was ∼1.7 and ∼3 times higher than unsupported GVO (585 Fg -1 ) and VO (326 Fg -1 ), respectively. The cyclic life of GVO/MX with capacitance retention 96.12% was observed at 60 mVs −1 . EIS measurements showed reduction in electrochemical impedance for GVO/MX as compared to GVO and VO. The corresponding impedance values of Rct and Resr for GVO/MX were calculated as 18 Ω and 1.8 Ω, respectively. The superior capacitive ability of GVO/MX can be ascribed to its unique morphology, short diffusion path and high surface area of fabricated composite. Considering it, the present work provides a feasible strategy to fabricate highly effective electrode materials for next generation energy storage devices.

Highly graphitized lignin-derived porous carbon with hierarchical N/O co-doping “core-shell” superstructure supported by metal-organic frameworks for advanced supercapacitor performance

Porous carbon nanoparticles have been widely utilized as electrode materials for electric double-layer capacitors (EDLCs) owing to their rich microporous and mesoporous structures. Herein, we successfully prepared lignin@ZIF-8 based carbon with hierarchical porous “core-shell” graphitized superstructure (KGC-EHL@ZIF-8) fabricated by carbonized ZIF-8 NPs as “core” and lignin derived graphitized porous carbon layer as “shell” via a two-stage carbonization-graphitization process for advanced supercapacitor performance. The prepared KGC-EHL@ZIF-8 NPs possess a high graphitization degree, high porosity with micro/meso porous hierarchical structure and high content of N/O co-dopants induced by the synergistic effects of ZIF-8 NPs coupling potassium hydroxide (KOH) activation treatment, thus guaranteeing excellent electrochemical performance. As a result, the graphitization degree of lignin-derived porous carbon “shell” structure increased with KOH ratio, and the maximum specific surface area of 2307.3 m2·g−1 was successfully obtained at a mass ratio (KOH/C-EHL@ZIF-8 NPs) of 1:1. The maximum specific capacitance within three-electrode system was 462.6 F·g−1 at 0.5 A·g−1 with a porous carbon “shell” thickness of around 75.25 nm. Moreover, the areal energy density of assembled supercapacitor can reach to 1.95 mWh·cm−2 at a power density of 27.44 mW·cm−2. This study put forward a novel strategy to efficiently harness lignin combined with a metal–organic framework for the construction of porous electrodes with hierarchical nanostructure for high-performance supercapacitors.

High-performance hybrid supercapacitor enabled by advantageous heterojunction boosted starfish-like ZnCo-S electrode

Transition metal sulfides are regarded as attractive battery-type electrode materials for hybrid supercapacitors (HSCs) owing to their pronouncedly elevated theoretical capacity and good electrical conductivity. The rational design and manufacturing of multiphase materials are efficient strategies for improving electrode materials' electrochemical performance. Therefore, starfish-like ZnCo-S sulfide composite electrode materials were constructed as advanced hybrid supercapacitor electrode materials by co-precipitation and hydrothermal methods. The ZnCo-S features a higher specific surface area, multi-level pore structure, and heterogeneous interfacial effect, which can contribute abundant active sites and shorter charge transport paths for electrochemical reactions, resulting in distinguished electrochemical performance. The specific capacity of ZnCo-S sulfide composite electrode material is as high as 1171.6 C g−1 at 2 A g−1. The assembled solid-state hybrid supercapacitor has outstanding energy density (64 Wh kg−1) and power density (16 kW kg−1) with a capacity retention rate of 92.7% after 10,000 cycles.