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Ni (Nickel) doped zeolitic-imidazolate framework (ZIF-67) has been prepared in presence of reduced graphene oxide (rGO) to realize a ZIF-67/rGO composite. The doping level of Ni and the ratio of rGO (wt%) in the composite have been optimized to attain desirable redox activity and electrical conductivity. A partial incorporation of redox active Ni ions to substitute Co (cobalt) ions in ZIF-67 has resulted in better electrochemical characteristics by inducing additional pseudocapacitance. A finalized composite with 33% Ni and 20% of rGO (i.e, Ni 33 /ZIF-67/rGO 20) has been used as a supercapacitor electrode material to achieve a high specific capacitance of 304 F/g at a current density of 1 A/g in the presence of 1 M H 2 SO 4 as an aqueous electrolyte. The above electrode has also been tested for an all-solid-state symmetric supercapacitor in the presence of a polymer gel electrolyte (PVA/1 M H 2 SO 4). This device delivered high values of power and energy densities, i.e., 1 kW/kg and 21.5 Wh/kg, respectively. The device also exhibited an excellent cyclic stability. About 87% of capacitance could be retained even after 4500 charge-discharge cycles. The device has shown superior results for a working potential window of 0–2 V. The practical usefulness of the device has been demonstrated by preparing a symmetrical supercapacitor, which could energize a white LED for 8 min upon a charging of only 40 s. Image 1 • High surface area and conductive composite of Ni doped ZIF-67/rGO is synthesized. • The as synthesized composite is studied for 2V symmetrical supercapacitor device. • Supercapacitor displays long cycle life of 87% after 4500 charge-discharge cycles. • High values of energy (21.5 W h/kg) and power (1 kW/kg) densities are obtained. [ABSTRACT FROM AUTHOR]

Abstract The role of redox additive electrolytes in supercapacitors is gaining an increased significance. The present research work, for the first time, investigates the supercapacitor performance of a rGO/TiO 2 nanosheet composite (prepared via facile one step hydrothermal reaction route) electrode in combination with a redox additive electrolyte, i.e., 0.2 M K 3 [Fe(CN) 6 ] in 1 M Na 2 SO 4. The synergistic effects between the porous rGO/TiO 2 nanosheet electrode and the optimized redox electrolyte have helped to achieve a significantly high specific capacitance of 1565 F/g at a current density of 3 A/g (working potential window = −0.1–0.5 V). This value of specific capacitance is much higher than achievable with the application of a plain aqueous electrolyte (e.g., 1 M Na 2 SO 4). Furthermore, rGO/TiO 2 nanosheet electrodes have been used to fabricate a symmetrical supercapacitor device which has delivered an excellent specific capacitance value of 204.5 F/g at a current density of 1.5 A/g. The device also yielded promising values of energy density (15.5 Wh/kg) and power density (1.1 kW/kg) apart from showing a long-term cyclic stability (∼87%) even after 1000 continuous charge-discharge cycles. Graphical abstract Image 1 Highlights • A composite of rGO/TiO 2 nanosheets has been explored as a supercapacitor electrode. • 0.2 M K 3 [Fe(CN) 6 ] in 1 M Na 2 SO 4 has been used as an optimized electrolyte. • Selection of above electrode and electrolyte yielded high specific capacitance. • A specific capacitance of 1565 F/g has been achieved at a current density of 3 A/g. • High values of energy (15.5 Wh/Kg) and power (1.1 kW/kg) densities were achieved. [ABSTRACT FROM AUTHOR]

Abstract In pursuit of high specific capacitance and high energy density; morphology, specific surface area and conductivity of electrode material are key factors. In this context, Ni 1-x Mg x Co 2 O 4 @C (x = 0.0, 0.5) nanostructures are synthesized via facile hydrothermal route using the cotton template. Notably; the morphology altered from flowers to rods with the incorporation of cotton templates. Additionally, Mg dopant ion helps to attain greater electrical conductivity while preventing the morphology. Besides, Influence of Mg doping on the pseudocapacitance of NiCo 2 O 4 electrode was investigated by electrochemical analysis in 6 M KOH electrolyte. This remarkable synergy display superb electrochemical performance for Ni 0.5 Mg 0.5 Co 2 O 4 @C rods, i.e a high specific capacitance of 1340 Fg-1 at a current density of 1 Ag-1 and admirable cyclic stability of ∼97% up to 2000 charge-discharge cycles (at 15 Ag-1). Further, the proposed Ni 0.5 Mg 0.5 Co 2 O 4 @C rods electrode delivered high values of energy (59.5 Wh/Kg) & power (799.2 W/Kg) densities at a current density of 1 Ag-1, which is 2 times more as compared to flowers structured material. This can be attributed to increase in the specific surface area with more porous nature of rods. This work conveys the deeper understanding of the morphology and chemical composition effect on the supercapcitive performance of Ni 0.5 Mg 0.5 Co 2 O 4 @C. Thus, Ni 0.5 Mg 0.5 Co 2 O 4 @C (NMCo@C) rods may be an excellent electrode material for high-performance supercapacitor due to its exceptional electrochemical performances. Graphical abstract Image 1 Highlights • Highly porous rods structure of specific surface area of 51.78 m2g-1 is fabricated. • The specific capacitance of 1340 Fg-1 is obtained for Ni 0.5 Mg 0.5 Co 2 O 4 @C rods. • Ni 0.5 Mg 0.5 Co 2 O 4 @C rods delivers maximum energy density of 59.5 WhKg−1. • The capacitance retention of ∼97% up to 2000 charge-discharge is maintained. [ABSTRACT FROM AUTHOR]

Metal-organic frameworks (MOFs) belong to a novel class of materials with several advantages (e.g., ultrahigh porosity, tunable pore size distribution, convenience of synthesis, and structural tailor-ability). However, the insulating nature of MOFs is often recognized as a limiting factor in the extension of their applications, especially in electronic fields. In light of such limitations, various functional or conductive materials have been mixed/intercalated with MOFs to improve their potential for such applications (e.g., rechargeable batteries, optoelectronics, and supercapacitors). Lately, many of these composite materials have been recognized as next-generation electrodes for the development of efficient supercapacitors. In this review article, we have critically reviewed the recent advancements in supercapacitor applications of MOFs and their derived composite structures. Further, we have also discussed the application of various categories of electrolytes (e.g., aqueous, organic, ionic liquids, solid-state, and redox electrolytes) and their impacts on the development of MOF-based supercapacitors. [ABSTRACT FROM AUTHOR]

The pyrolysis of metal-organic frameworks (MOFs) is an effective strategy for the synthesis of novel nanoporous structures for energy storage applications. In this work, the preparation of a zirconium oxide/carbon (ZrO 2 /C) nanocomposite via the pyrolysis of UiO-66 (a zirconium-based MOF) is reported for the first time. These MOF-derived metal oxide/carbon (ZrO 2 /C) materials have a great advantage in the case of supercapacitor applications over other MOFs or their derivatives as they do not need any external conductive agent. The ZrO 2 /C electrode exhibits an excellent electrochemical performance, delivering a specific capacitance of 241.5 F/g at 1 A/g current density. A 2 V symmetrical supercapacitor device is also prepared by employing a solid-state polymer gel electrolyte. The assembled device of ZrO 2 /C electrode has delivered a high energy density of around 29 Wh/kg (at a high power density of 1.5 kW/kg) while retaining almost 97% of the specific capacitance even after 2000 continuous charge/discharge cycles. • The development of efficient supercapacitor is a viable strategy to achieve energy storage devices. • Uniformly distributed oxides/carbon/oxide-carbon structures are prepared by the pyrolysis of MOF. • ZrO 2 /C composite is prepared via one-step pyrolysis of UiO-66 (zirconium-based MOF). • Superiority of a MOF-derived ZrO 2 /C composite is demonstrated in supercapacitor applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Pencil peels is used to derive mixed phase activated carbon of high porosity and conductivity. • Asymmetrical supercapacitor is assembled using MOF derived Co 3 O 4 /WO 3 and Pencil derived activated carbon. • Asymmetrical Supercapacitor device retains long cycle life of 92.1 % after 5000 charge-discharge cycles. • The supercapacitor device shows high energy density of 50 Wh/kg at a power density of 90 W/kg. In this work, pencil peel is used to derive the mix phase activated carbon at different temperatures viz 700, 800, and 900 °C for hybrid supercapacitor applications. The derived carbon is showing the highest specific surface area for P-800 (Pencil peel@ 800 °C) sample and exhibits the graphitic and amorphous phase whose fraction can be controlled with pyrolysis temperature. Therefore, the as-prepared P-800 electrode shows the high specific capacitance of 553 F/g at a current density of 1 A/g. On the other hand, metal-organic framework (MOF) derived Cobalt-Tungsten oxide composites (Co 3 O 4 /WO 3) has been synthesized which shows a much higher specific capacitance value (544 F/g at 2 A/g) in the negative potential window. Therefore, an asymmetrical supercapacitor device has been assembled with P-800 as positive and Co 3 O 4 /WO 3 composites as a negative electrode in aqueous 1 M H 2 SO 4 (Sulfuric acid) electrolyte that delivers higher energy and power density in comparison to their symmetrical supercapacitor counterparts. [ABSTRACT FROM AUTHOR]

• Tetracyanoquinodimethane doped HKUST-1 has been explored as a battery type material. • A high specific capacity of 208.8 mAh/g (751 C/g) at 2 A/g has been achieved. • Solid-state symmetrical device has delivered high energy and power densities of 70.5 Wh/kg and 0.83 kW/kg respectively. • The energy storage device has yielded an energy efficiency of 58.6% and cyclic stability of 96%. Metal-organic frameworks (MOFs) are emerging as potential electrode materials for next-generation energy storage devices. Cu 3 (BTC) 2 (BTC = benzene tricarboxylate), also known as HKUST-1, is one of the most widely studied MOFs. In the present work, TCNQ (tetracyanoquinodimethane) doped HKUST-1, has been demonstrated as an efficient energy storage electrode material. The infiltration of TCNQ in HKUST-1 has resulted in the synthesis of a high surface area electrode material with significant electrical conductivity. TCNQ@HKUST-1 based electrode has delivered a high specific capacity of 208.8 mAh/g (751 C/g) at a current density of 2 A/g. An all-solid-state symmetrical device has been assembled using a polymer gel electrolyte, which has delivered energy and power densities of 70.5 Wh/kg and 0.83 kW/kg, respectively. Also, the device showed a maximum energy efficiency of 58.6% along with a long cycle life of 96% over 5000 successive charging-discharging cycles. The present system has yielded superior energy storage performance than most of the earlier reported MOF based electrodes. [Display omitted] [ABSTRACT FROM AUTHOR]

The application of porous and conductive composite materials in energy storage devices has received great attention in the recent years. Porous materials, such as metal-organic frameworks (MOFs), possess features like large specific surface area, mesoporous structures, and multiple reaction sites that make them attractive for energy storage devices. Further, the integration of MOFs with suitable conducting agents is a promising strategy to introduce additional conductive pathways in them, which facilitates fast charge transfer. In the present work, we report synthesis and supercapacitor application of a ZIF-67/PEDOT heterostructure composite. The prepared ZIF-67/PEDOT composite, when analyzed for electrochemical performance in three-electrode systems, has delivered a specific capacitance of 106.8 F/g at a current density of 1 A/g. This value is significantly better than that attaintable with only pristine ZIF-67 electrode (34.75 F/g at 1 A/g). Extending the study, two ZIF-67/PEDOT electrodes have been used to assemble an all-solid-state symmetrical supercapacitor, which delivers excellent values of energy density (∼11 Wh/kg) and power density (200 W/kg). Hence, this work paves the way for the potential application of ZIF-67/PEDOT composite in the development of next-generation supercapacitors. Image 1 • Incorporation of PEDOT in ZIF-67 benefits high conductivity and large specific surface area. • ZIF-67/PEDOT has been explored as a supercapacitor electrode material. • The assembled 1.6 V device delivered high energy (11 Wh/kg) and power (200 W/kg) densities. • Supercapacitor device has a long cycle life (93% capacity retention even after 4000 charge-discharge cycles). [ABSTRACT FROM AUTHOR]

Transition metal dichalcogenides (TMDs) are gaining interest in the energy sector due to its 2D chemistry and heterogeneous characteristics however its stability for the long run and poor electrical conductivity are pushing the researchers to make their hybrid. Herein we synthesized the hybrid WS 2 nanorods and Co 3 S 4 microspheres composite material which attained a high energy density of 47.3 Wh/kg along at a high-power density of 512 W/kg. The hollow Co 3 S 4 microspheres were synthesized using highly porous ZIF-67 as a precursor. Furthermore, these hollow Co 3 S 4 microspheres are in-situ modified by combining with WS 2 nanostructures to enhance its energy density. The electrodes with the synthesized hybrid material deliver the specific capacitance of 412.7 F/g at the current density of 1 A/g, Additionally, two equal weighted Co 3 S 4 /WS 2 composite electrodes are used to fabricate an all-solid-state symmetrical supercapacitor device with PVA-1M H 2 SO 4 polymer gel electrolyte, exhibiting a wide potential window of 2 V with 92% cyclic stability (2000 charge-discharge cycles) demonstrates its potential applicability for the supercapacitor application. The excellent electrochemical performance and splendid cyclic stability are attributed to the synergy of high surface area ZIF-67 derived Co 3 S 4 microsphere for fast charge transfer with 2D networked WS 2 material responsible to provide high energy density. Image 1 • A hybrid Co 3 S 4 /WS 2 composite was prepared using a one-step solvothermal method. • The hybrid composites deliver the highest specific capacitance of 412.7 F/g at the current density of 1 A/g. • A solid-state symmetrical supercapacitor was assembled with PVA-1M H 2 SO 4 gel electrolyte as a separator. • With wide potential window of 2 V, the fabricated device attained a high energy density of 47.3 Wh/kg along at a high-power density of 512 W/kg. [ABSTRACT FROM AUTHOR]

[Display omitted] • State of the art information on core–shell MOF-based supercapacitors and batteries are explored. • CSMOF structures are discussed separately in terms of properties, synthesis and their types. • CSMOF structures for supercapacitors are compared in terms of specific capacitance, capacitance retention, energy density, and self-discharge. • CSMOF structures for batteries are compared in terms of reversible capacity, initial discharge capacity, and cyclic stability. • Besides Li-ion batteries, CSMOFs are also reviewed for Na-ion, K-ion, Li-S, Li-Se, and Li-O 2 batteries. • Critical assessment and future aspects are also explored for CSMOF based energy storage devices. Core-shell metal–organic framework (CSMOF) has attracted the attention of researchers in the material science and nanotechnology research field. The structural properties of CSMOF and their derived material include extortionate specific surface area and porosity, good structural flexibility, high stability, etc. These appealing properties make CSMOF a great alternative for various practical applications. CSMOF has shown great performance as an electrode material for energy storage applications. This review is primarily focused on the factor affecting the assemblies and synthesis of core shell structures, strategy to control the assemblies, synthesis methods, and properties of different CSMOFs for energy storage devices viz. supercapacitors (SC) and batteries. After that, different CSMOF structures are compared in terms of their performance parameters for SC including specific capacitance, capacitance retention, cyclic stability, energy density, and self-discharge.On the other hand, reversible capacity, initial discharge capacity, and cyclic stability are a few performance parameters for Li-ion batteries that are also discussed for different materials.CSMOF's applications for some other batteries like Na-ion, K-ion, Li-S, Li-Se, and Li-O 2 will likewise be discussed in other sections. Eventually, the expansion and future scope of CSMOF and its derivatives are proposed for upcoming energy storage applications. [ABSTRACT FROM AUTHOR]

In the present investigation, renewable kraft lignin-based nanofibers were synthesized by facile electrospinning technique and further converted into carbon nanofibers (CNFs) by heat treatment at different temperatures (600, 800 and 1000 °C). These different heat treated carbon nanofiber mats were characterized using SEM, Raman, FTIR, BET and electrochemical workstation. These CNFs were used as a free-standing electrode and characterized for electrochemical performance using a three-electrode system. Among different electrodes, the 800 °C heat treated CNF electrode shows higher specific capacitance (196.63 F/g @ 1 A/g) as compared to the 600 and 1000 °C heat treated CNF electrodes. Based on the electrochemical performance, 800 °C heat treated CNF electrode is selected to assemble two different types of symmetrical supercapacitor devices i.e., aqueous (using 1 M H 2 SO 4) and solid-state electrolyte using PVA-1M H 2 SO 4 polymer gel. The solid-state electrolyte device operating potential window of 0–2 V which is higher than that of an aqueous electrolyte based device. In addition to this, it delivers higher energy and power density as 62.6 Wh/kg and 1.25 kW/kg respectively with an efficiency of 99.5% after 10,000 cycles. These remarkable results of Kraft lignin-derived ribbon type CNF based solid-state symmetrical supercapacitor device opens new paths for the development of futuristic carbon-based free-standing mat as energy storage devices. • Lignin (90%) based carbon nanofibers synthesized by electrospinning and heat treatment at different temperatures. • Effect of heat treatment on microstructure, surface area and functional groups has been studied extensively. • The assembled symmetrical solid state supercapacitor device operates within a wide potential window of 0–2 V. • It shows superior long cycle life of 99.5% after 10,000 charge-discharge cycles. • The solid-state supercapacitor device shows high values of energy (62.6 Wh/kg) and power (1.25 kW/kg) density. [ABSTRACT FROM AUTHOR]