Asymmetric Hybrid Supercapacitor Research Articles

Asymmetric and zinc-ion hybrid supercapacitors based on iron oxide and carbon dots

There is an urgent need to design and develop materials for high-performance electrochemical energy storage systems. This paper presents practical synthesis and novel combination of α-Fe2O3, carbon dots (CDs), and BiOCl for high performance asymmetric supercapacitors (ASCs) and zinc-ion hybrid supercapacitors (ZHSCs). The materials prepared by wet-chemical methods were probed with different analytical techniques. X-Ray Diffraction, Fourier Transform Infrared Spectroscopy) and Raman analyzes indicate presence of alkyl and aryl rich surface functional groups of CDs which contribute to conducive interface for the interplay between electrolyte and electrodes. The α-Fe2O3@CDs enabled ~20 fold increase in the electrochemical performance; 3686 F g−1 at a current density of 1 A g −1 in 2 M KOH electrolyte. However, the maximum specific capacitance of pristine α-Fe2O3 was just 184 F g−1 at the same current density. ASCs and ZHSCs were then fabricated using α-Fe2O3@CDs as the cathode along with anodes composed of BiOCl and Zn foil, respectively. The assembled ASC device achieved the potential window of 1.8 V with a high specific capacitance of 251 F g−1 at a current density of 1 A g−1. The highest energy, and power densities were 28 Wh kg−1 and 14.8 kW kg−1, respectively. The formed ZHSC exhibited the maximum specific capacitance of 449 F g−1 at a current density of 1 A g−1 with 78 % retention after 15,000 cycles. ZHSC outperformed ASC in terms of the energy and power density by ~5 (140 Wh kg−1) and ~ 2 (30 kW kg−1) times, respectively. These results position α-Fe2O3@CDs as an extremely promising material for ASCs and ZHSCs.

Synthesis of polyaniline-graphene oxide based ternary nanocomposite for supercapacitor application

This study focuses on the synthesis of Polyaniline (PANI), graphene oxide (GO), and their nanocomposites with metal oxides (MO) and hexagonal boron nitride (h-BN) for their application in the supercapacitor. In this study, PANI/GO, PANI/GO/TiO2, PANI/GO/MoS2 and PANI/GO/h-BN ternary nanocomposites were synthesized following a chemical oxidative polymerization method. The prepared nanocomposites were characterized by FTIR, XRD, TGA, SEM and electrochemical analysis. The electrochemical properties of the nanocomposites were evaluated by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), electrochemical polarization and impedance analysis. CV profile of the nanocomposite showed that incorporation of GO, MO and h-BN in the polyaniline backbone improved capacitance, energy density and power density significantly. Among the synthesized ternary nanocomposites, PANI/GO/h-BN showed highest capacitance of 946 F/g and high capacitance retention after 100 cycles of charging and discharging. Finally, a set of hybrid asymmetric supercapacitors were constructed using the synthesized nanocomposites as positive electrode and activated carbon as negative electrode. The device was assessed following the GCD method. The supercapacitor device with PANI/GO/h-BN nanocomposite as positive electrode exhibited higher specific capacitance of 351 F/g with high power density of 4500 W/kg, and it lit up a 5 mm LED for 243 min, indicating its superiority over other electrodes.

High power aqueous hybrid asymmetric supercapacitor based on zero-dimensional ZnS nanoparticles with two-dimensional nanoflakes CuSe2 nanostructures

Energy storage materials, particularly chalcogenides, are fascinating electrode materials for supercapacitors (SCs) because of their high capacitance, remarkable electrical conductivity, and multiple oxidation states contributed by numerous metal cations. Herein, a novel nanocomposite based on zinc sulfide and copper diselenide, denoted as (ZnS–CuSe2), was prepared via a sonochemical-assisted method. The structural analysis revealed the cubic structure for pure ZnS, orthorhombic for CuSe2, and co-existing cubic and orthorhombic phases for ZnS–CuSe2 nanocomposites with high purity and crystallinity. The ZnS–CuSe2 nanocomposite offered exceptional electrochemical performance with redox peaks from the CV analysis, and coupled with plateaus in the charge/discharge profile, confirming the faradaic energy storage properties with functional reversibility. Similarly, a high conductive feature of the ZnS–CuSe2 composite was revealed by impedance study, with a minor charge transfer resistance than their bulk materials. A hybrid asymmetric supercapacitor (HASCs) composed of ZnS–CuSe2//AC was constructed, which manifested an enlarged voltage window up to 1.7 V with capacitance of 95 F g−1 and a maximum specific energy of 38 Wh kg−1. Also, high power delivery was attained at 3927 Wkg-1 when specific energy goes down to 12 Wh kg− at 5 A g−1. Interestingly, only 81.8% retention was left beneath when cycled to 8000 cycles, specifying decent stability of the ZnS–CuSe2//AC HASCs.

NiZrSe3/rGO modulated porous architecture for hybrid featured asymmetric supercapacitors

Designing transition metallic chalcogenides with rGO as a potential porous platform for growth are vital to upsurge the electrochemical energy storage capabilities of supercapacitors' electrodes. This work reports hydrothermally prepared agglomerated NiZrSe3 nanoparticles and a porous NiZrSe3/rGO, where the latter exhibits superior charge storage properties. In comparison to NiZrSe3 with specific capacitance (Cs) of 1415.7 F/g, the porous modulated material NiZrSe3/rGO delivers an exceptional Cs of 2750.8 F/g at current density of 2 A/g in the 3-electrode setup. Due to its the outstanding electrochemical performance, NiZrSe3/rGO is employed as a redox featured electrode material, and further integrated with activated carbon (ActC) as a capacitive featured electrode material to construct a hybrid asymmetric supercapacitor with widened potential window and enhanced energy density. The constructed asymmetric supercapacitor unveils a specific capacitance of 140.77 F/g at current density of 1.2 A/g and rate capability of 53.6 % at 7 A/g while functioning stably under the potential range of 0–1.65 V. Moreover, it achieves extremely high energy density of 53.22 Wh/kg at power density of 990 W/kg with its long-life span in regard to cyclic stability of 80.31 % after 10,000 charging-discharging cycles. In general, this work illustrates the significance of NiZrSe3/rGO as a highly redox active cathode material in hybrid featured asymmetric supercapacitors for future renewable energy storage systems.

Synergistic Tuning of Nickel Cobalt Selenide@Nickel Telluride Core–Shell Heteroarchitectures for Boosting Overall Urea Electrooxidation and Electrochemical Supercapattery

Herein, we demonstrate the synthesis of bifunctional nickel cobalt selenide@nickel telluride (NixCo12‐xSe@NiTe) core–shell heterostructures via an electrodeposition approach for overall urea electrolysis and supercapacitors. The 3D vertically orientated NiTe dendritic frameworks induce the homogeneous nucleation of 2D NixCo12‐xSe nanosheet arrays along similar crystal directions and bring a strong interfacial binding between the integrated active components. In particular, the optimized Ni6Co6Se@NiTe with an interface coupling effect works in concert to tune the intrinsic activity. It only needs a low overpotential of 1.33 V to yield a current density of 10 mA cm−2 for alkaline urea electrolysis. Meanwhile, the full urea catalysis driven only by Ni6Co6Se@NiTe achieves 10 mA cm−2 at a potential of 1.38 V and can approach a constant level of the current response for 40 h. Besides, the integrated Ni6Co6Se@NiTe electrode delivers an enhanced specific capacity (223 mA h g−1 at 1 A g−1) with a high cycling stability. Consequently, a hybrid asymmetric supercapacitor (HASC) device based on Ni6Co6Se@NiTe exhibits a favorable rate capability and reaches a high energy density of 67.7 Wh kg−1 and a power density of 724.8 W kg−1 with an exceptional capacity retention of 92.4% after sequential 12 000 cycles at 5 A g−1.

Synthesis of hexagonal boron nitride based PANI/h-BN and PANI-PPy/h-BN nanocomposites for efficient supercapacitors

Conducting polymers based hexagonal boron nitride (h-BN) nanocomposites i.e. polyaniline (PANI)/h-BN and polyaniline -polypyrrole (PANI-PPy)/h-BN were fabricated through chemical oxidative polymerization approach. The structural, thermal, morphological, and electrochemical properties of the prepared materials were studied extensively. FTIR and XRD patterns revealed the successful fabrication of desired nanocomposites. TGA analysis showed that the presence of h-BN increases the thermal stability of both the nanocomposites (PANI/h-BN and PANI-PPy/h-BN). All the prepared materials demonstrated irregular and aggregated morphological structures with the diameters remained almost similar (100 nm). The electrochemical performance of the materials was evaluated by cyclic voltammetry (CV), electrochemical impedance (EIS) and galvanostatic charge-discharge (GCD) in three electrodes and two electrodes systems. The prepared PANI/h-BN nanocomposites exhibited the highest capacitance (927 F/g) and capacitance retention (97.6%) after 100 cycles compared to the others. The Tafel extrapolation study shows less corrosion rate for PANI/h-BN electrode, and EIS indicate higher energy storage capacity of the PANI/h-BN electrode compared to PANI-PPy/h-BN electrode. Finally, a set of hybrid asymmetric supercapacitor was successfully constructed using the synthesized nanocomposites as positive electrode and activated carbon (AC) as negative electrode. The assembled device PANI/h-BN//AC showed the highest sp. capacitance (343 F/g), power density (921 W/kg), and it lit up a 5 mm green LED for 200 min, indicating its superiority over the other supercapacitor device.

Coral-Inspired Hierarchical Structure Promotes a Win–Win on Mass Loading and Rate Capability: A Nickel–Cobalt–Zinc–Sulfide@Nickel–Cobalt Layered Double Hydroxide Electrode for a High-Performance Hybrid Supercapacitor

A hierarchical structure, defined as structural features occurring on different levels of scale, is widely used in the rational design of composite electrodes for its superiorities in abundant electrochemical active sites and functional differentiation for various components. Herein, we in situ prepare a nickel–cobalt layered double hydroxide (NiCo-LDH) nanosheet network on ultrathin nickel–cobalt–zinc–sulfide (NiCoZnSx) microplate arrays to construct a special, coral-inspired hierarchical structure. In this structure, NiCoZnSx microplate arrays not only provide plenty of rooms for nanosheet growth but also improve the ion diffusion, charge transfer, and structural stability of the composite electrode. The NiCo-LDH nanosheet network paved through the microplate surface offers a high specific surface area and capacitance. The composite electrode delivers a high specific capacitance of 8.1 F cm–2 (1928 F g–1) at a loading mass of 4.2 mg cm–2, outstanding rate capability (63% capacitance retention, 50 mA cm–2), and cycling stability (80% capacitance retention, 10 000 cycles). Furthermore, the hybrid asymmetric supercapacitor assembled by the composite electrode and active carbon exhibits a maximal power density of 80.3 mW cm–2 at an energy density of 270 μWh cm–2 with good rate capability and cycling stability. This work reveals the significance and practical potential of rational design in the electrode’s hierarchical structure for a high-performance supercapacitor.

One-dimensional partial differential model for asymmetric hybrid supercapacitor

Asymmetric hybrid supercapacitors (AHSC) are increasing in popularity due to their high energy density. This paper introduces a partial differential model for an AHSC device. The structure contains nickel hydroxide (Ni(OH)2) film as the positive electrode, activated carbon (AC) as the negative electrode, potassium hydroxide (KOH) aqueous electrolyte, and two Helmholtz layers. Potassium ions (K+) and hydroxyl ions (OH−) move under the influence of the electric field and the concentration gradient. The electrode current of pseudocapacitance is described by Frumkin–Butler–Volmer (FBV) equation. Only OH− ions were assumed to pass through the Helmholtz layer and diffuse into the interlayer of the Ni(OH)2 electrode. An AC electrode with a high specific surface area can adsorb a large number of ions to form an electric double layer (EDL). Electrons, injected OH−, and fixed holes together affect the distribution of the electric field in the positive electrode. Nernst–Planck equation, Poisson equation and modified the Ohm’s law were adopted to describe the concentration fields and electric fields. Finally, the simulation was carried out for conditions of Cyclic Voltammetry and potentiostat discharge. The validity and accuracy of the model were verified by experimental data. The performance indices and physical field variables can be estimated accurately.

MnCo2S4 nanoflowers directly grown over nickel foam as cathode for high-performance asymmetric hybrid supercapacitors

This work reports MnCo2S4 nanoflowers directly grown over nickel foam (NF) via a facile hydrothermal process for high-performance supercapacitors. The as-grown MnCo2S4 nanoflower electrode delivers a high specific capacitance of 1980 F g−1 and 1243 F g−1 at 1 A g−1 in three-electrode and symmetric two-electrode configurations respectively. It also gives a cyclic performance of 97 % and a coulombic efficiency of 98 % at 5 A g−1 after 10,000 charge-discharge cycles. Furthermore, an asymmetric supercapacitor (ASC) device is fabricated using MnCo2S4 nanoflower cathode and rGO -based anode. The asymmetric supercapacitor exhibits superior performance with an increased gravimetric capacitance of 162 F g−1 at 1 A g−1, an excellent cycle life of 99 % along with a high coulombic efficiency of 99.5 % after 10,000 cycles. The device delivers a gravimetric energy density of 73 W h kg −1 at a gravimetric power density of 151 W kg −1. The present study demonstrates the potential of MnCo2S4 nanoflower-based electrodes for supercapacitor applications.

Facile one-pot synthesis of template-free porous sulfur-doped g-C3N4/Bi2S3 nanocomposite as efficient supercapacitor electrode materials

This work develops a facile one-step template-free approach to control the porous morphology of sulfur-doped g-C3N4/Bi2S3 (Sg-C3N4/Bi2S3) for a hybrid asymmetric supercapacitor (HASC). Herein, bismuth nitrate acted as a bismuth source and played an efficient role as a temporary template that generated pores within Sg-C3N4 sheets before transforming into Bi2S3 nanoparticles. This inventive porous construction can professionally boost the electrochemical behavior of the prepared material as electrode material for supercapacitor applications. These results point to the potential of the prepared composite (Bi2S3/Sg-C3N4-II) with a porous structure to be a promising electrode material for highly efficient supercapacitors. Promisingly, the designed device can deliver maximum Es of 6.2 Wh kg−1 at the corresponding Ps of 455 W kg−1 at the current density of 0.8 A g−1. The cycling stability performance of the assembled device retained 80 % of its initial capacity after 3000 cycles, signifying the applicable potential of Bi2S3/Sg-C3N4-II for supercapacitor applications.

Hollow cotton carbon based NiCo2S4/NiMoO4 hybrid arrays for high performance supercapacitor

The design and preparation of new electrode materials with high conductivity and high energy density has become a frontier and key issue in the research of improving the performance of supercapacitor (SCs). Through the synergistic action of biomass carbon and transition bimetallic sulfide, the defects of pseudocapacitor electrode materials such as low conductivity and low energy density can be solved. On hollow cotton carbon (CC), a novel hybrid NiCo2S4/NiMoO4 arrays developed using a simple two-step hydrothermal procedure is reported. A series of characterization methods were used to characterize the samples.Experimental results demonstrated that the CC was hollow and the NiCo2S4/NiMoO4 arrays had uniformly grown on its surface. The sample demonstrated a high specific capacitance (2323 F·g−1 at a current density of 5 mA·cm−2) and outstanding electrochemical stability (90 % retention after 10,000 cycles), according to the electrochemical characteristics. Additionally, a hybrid asymmetric supercapacitor was assembled using CC/NiCo2S4/NiMoO4 (CNCNM) as the positive electrode, CC as the negative electrode, PVA/KOH as the separator and Nickel foam as current collector. The supercapacitor displayed a high energy density (86.52 Wh·kg−1 at 1006.65 W·kg−1), high specific capacitance (341.5 F·g−1 at 5 mA.cm−2), excellent cycling performance (85 % retention after 10,000 cycles), and a low charge transfer resistance. The energy storage capability was studied and a blue LED light (1.8 V) could be lit for 30 min by two similar devices connected in parallel.

PEDOT coating boosted NiCo-LDH nanocage on CC enable high-rate and durable pseudocapacitance reaction

Layered double hydroxide (LDH) is supposed to be ideal capacitive materials owing to its excellent theoretical specific capacitance. Nevertheless, the inherent defects of LDH such as unstable structure, and agglomerations along with poor conductivity, lead to low rate-capability and poor cycle stability. In this work, poly(3,4-ethylenedioxythiophene) (PEDOT)@nickel–cobalt LDH on carbon cloth ([email protected]/CC) was proposed as a highly capacity electrode material for supercapacitors. Herein, hollow NiCo-LDH nanocage was firstly assembled by NiCo-LDH nanosheets on CC (NiCo-LDH/CC) via an in-situ transformations of ZIF-67, subsequent by coating PEDOT network ([email protected]/CC) on NiCo-LDH/CC via an electrodeposition process. The unique hollow nanocage structure can effectively restrain agglomeration of the LDH nanosheets. Besides, the introduction of PEDOT not only remarkable improves the conductivity, but also protects those hollow LDH nanocages from destruction during the cycling process. Consequently, the [email protected]/CC electrode manifests outstanding capacitance properties of 1508F/g at 1 A/g, excellent rate capability of 71.9 % capacitance retention in 1–20 A/g, and remarkable cycling life of 90.1 % capacity retention at 20 A/g after 10,000 cycles. Moreover, a hybrid asymmetric supercapacitor (ASC) device was assembled by using [email protected]/CC// activated carbon. Such ASC reveals a prominent energy density of 77.1 Wh kg−1 under the power density of 750 W kg−1. This project provides new inspirations into the rational design of high-performance electrode material in application of energy storage.

Framework structured Ce2(C2O4)3·10H2O as a pseudocapacitive electrode of a hybrid (asymmetric) supercapacitor (HSC) for large scale energy storage applications.

The electrochemical kinetics of the electrode material plays a crucial role in the development of various energy storage devices such as batteries, supercapacitors, and hybrid supercapacitors. Battery-type hybrid supercapacitors are envisaged as excellent candidates to bridge the performance gap between supercapacitors and batteries. Due to its open pore framework structure and more structural stability, porous cerium oxalate decahydrate (Ce2(C2O4)3·10H2O) is found here to be a potential energy storage material partly because of the presence of planer oxalate anions (C2O42-). Superior specific capacitance equivalent to 78 mA h g-1 (capacitance: 401 F g-1) at 1 A g-1 in the potential window of -0.3 to 0.5 V was observed in an aqueous 2 M KOH electrolyte. The predominant pseudocapacitance mechanism seems to operate because of the high charge storage capacity of the electrode as intercalative (diffusion control) and surface control charges stored by the porous anhydrous Ce2(C2O4)3·10H2O, which were close to 48% and 52%, respectively, at a 10 mV s-1 scan rate. Further, in the full cell asymmetric supercapacitor (ASC) mode in which porous Ce2(C2O4)3·10H2O is the positive electrode and activated carbon (AC) is the negative electrode, at the operating potential window of 1.5 V, the highest specific energy of 96.5 W h kg-1 and a specific power of ∼750 W kg-1 at 1 A g-1 current rate and a high power density of 1453 W kg-1, the hybrid supercapacitor still attains an energy density of 10.58 W h kg-1 at a 10 A g-1 current rate, which was obtained with a high cyclic stability. The detailed electrochemical studies confirm a high cyclic stability and a superior electrochemical charge storage property of porous Ce2(C2O4)3·10H2O making it a potential pseudocapacitive electrode for use in large energy storage applications.

Cavity structured S-NiO with improved energy density for aqueous asymmetric hybrid supercapacitors by CDA mechanism

Schematic of the deposition along with the structural-morphological and electrochemical transformation of S-NiO through the cost effective CDA mechanism designed for improved energy density of a (S-NiO//KOH//graphite) AAHSc device.

High-Performance Biodegradable Energy Storage Devices Enabled by Heterostructured MoO3 -MoS2 Composites.

Biodegradable implantable devices are of growing interest in biosensors and bioelectronics. One of the key unresolved challenges is the availability of power supply. To enable biodegradable energy-storage devices, herein, 2D heterostructured MoO3 -MoS2 nanosheet arrays are synthesized on water-soluble Mo foil, showing a high areal capacitance of 164.38 mF cm-2 (at 0.5mA cm-2 ). Employing the MoO3 -MoS2 composite as electrodes of a symmetric supercapacitor, an asymmetric Zn-ion hybrid supercapacitor, and an Mg primary battery are demonstrated. Benefiting from the advantages of MoO3 -MoS2 heterostructure, the Zn-ion hybrid supercapacitors deliver a high areal capacitance (181.86 mF cm-2 at 0.5mA cm-2 ) and energy density (30.56 µWh cm-2 ), and the Mg primary batteries provide a stable high output voltage (≈1.6V) and a long working life in air/liquid environment. All of the used materials exhibit desirable biocompatibility, and these fabricated devices are also fully biodegradable. Demonstration experiments display their potential applications as biodegradable power sources for various electronic devices.

Hierarchical template-free chestnut-like manganese cobaltite for high-performance symmetric and asymmetric supercapacitor

In this work, template-free Chestnut-like MnCo2O4 microspheres are synthesized using a straight-forward hydrothermal process succeeded by calcination. Urea as a reducing/precipitating agent can play an essential role in controlling the morphology of the material without using any additional surfactants or templates. The effect of reducing agent (Urea) on the structural and morphological evolution of MnCo2O4 has been studied. The electrochemical performance of the synthesized materials is investigated in a real device two-electrode cell configuration (symmetric and asymmetric system) rather than a three-electrode configuration. The two-electrode system gives more accurate and practical evaluation of the capacitive behavior of the material. The MnCo2O4 displayed the highest capacitance of 245.34 F g−1 at 5 mV s−1 for 0–1 V in a symmetric cell configuration. It also held an energy density of 22.24 Wh kg−1 at 1500 W kg−1. The optimized sample showed outstanding cyclic performance with only 3% of capacitance loss after 5000 cycles. Based on the structural and electrochemical findings, a charge storage mechanism has been proposed for the symmetric SC. Furthermore, a hybrid asymmetric supercapacitor with MnCo2O4 as a cathode and the previously synthesized MnO2/AC as an anode is also fabricated which exhibited an energy response of 30.12 Wh kg−1 for a power of 7000 W kg−1. For practical applications, different colored LEDs (red, yellow, green, and blue) and a panel with six red LEDs have been illuminated. The panel with six red LEDs is illuminated for 12 mins. for symmetric supercapacitor and 18 mins. for asymmetric supercapacitor. All these remarkable outcomes suggested that the synthesized material has wide potential for supercapacitors.

Design and fabrication of MOF-derived leaf-like Zn-Co-S nanosheet arrays decorated with Ni-Zn-P ultrathin nanostructure for hybrid supercapacitors

Transitional Metal phosphides and sulfides are considered a promising electrode material in energy storage sources due to their high electronic conductivity, rich valences and high electrochemical activity, and excellent stability. Here, we report porous Ni-Zn-P/Zn-Co-S hybrid nanostructures on nickel foam as a novel free-binder electrode achieved via a facile three-step immersion procedure, a sulfurization process, followed by an electrodeposition approach consisting of leaf-like Zn-Co-S nanosheet arrays covered with ultrathin Ni-Zn-P nanosheets. The unique multicomponent heterostructure of Ni-Zn-P/Zn-Co-S can possess the large accessible surface area, more active sites, promotes free diffusion of electrolytes, shortens the path of electron transfer in electrochemical reaction process, and the synergistic effect from both components, leading to better electrochemical performances. The Ni-Zn-P/Zn-Co-S electrode demonstrates outstanding electrochemical performance, including ultrahigh specific capacitance of 2803 F g−1 at 1.0 A g−1, favourable rate capability, and supreme stability with 91.3% capacitance retention after 3000 cycles.More importantly, a prototype hybrid asymmetric supercapacitor is assembled based on Ni-Zn-P/Zn-Co-S as the battery-type electrode and rGO as the capacitive-type electrode. The fabricated device has a capacitance of 94.51 F g−1 at 2.3 A g−1 and demonstrates an energy density of 30.6 Wh kg−1 at a power density of 1742 W kg−1 with a remarkably long cycle life. This work delivers a simple and innovative strategy to develop advanced binder-free electrodes as a next-generation energy storage system.

Integrating the essence of metal organic framework-derived ZnCoTe–N–C/MoS2 cathode and ZnCo-NPS-N-CNT as anode for high-energy density hybrid supercapacitors

Transition bimetallic compounds are exploited as high-capacity electrode materials for supercapacitors due to their abundant electroactive sites and electrical conductivity. However, it remains grand challenge to construct supercapacitor devices that deliver high energy density. Here, we report an attractive one-stone-two-birds strategy to develop metal organic frameworks (MOFs) derived cathodes and anodes consisting of zinc cobalt telluride integrated nitrogen doped carbon (ZnCoTe–N–C) and zinc cobalt nanoparticles encased nitrogen doped carbon nanotubes (ZnCo-NPs-N-CNTs), respectively. Particularly, ZnCoTe–N–C cathode exhibited high specific capacity of 192.77 mA h g−1, which was further improved by the presence of hierarchical molybdenum disulfides (MoS2) nanosheets. Increased electrochemical active sites provided by MoS2 nanosheets energizes both the capacity and stability of the electrode. Consequently, the ZnCoTe–N–C/MoS2 electrodes showed a higher specific capacity of 342.55 mA h g−1 as well as excellent long-term stability. Besides, the ZnCo-NPs-N-CNTs demonstrated an initial capacity of 207.22 mA h g−1 and retained a high specific capacity even after 50 A g−1. The excellent electrochemical activity of the electrodes is attributed to the incorporation of redox rich bimetallic components and nitrogen rich carbon directly grown on the current collector, which reduces the dead volume and avoids volume expansion during charge discharge process. Finally, a hybrid asymmetric supercapacitor (HASCs) assembled using ZnCoTe–N–C/MoS2 and ZnCo-NPs-N-CNTs delivered a high specific energy density and power density maintaining 93.6% of its capacitance after 20,000 cycles. This study expands a way to construct a hybrid supercapacitor with well-designed structure and superior performance for clean energy storage technologies utilizing minimum resources.

Role of Halide Substitution in Perovskite‐Based Asymmetric Hybrid Supercapacitor

Organometal halide perovskites (MHPs) are widely used in energy harvesting as well as energy storage applications due to their superior optoelectronic properties. However, structural, optical, and electronic properties of these materials are strongly dependent on the halide substitution. So far methylammonium lead tri‐bromide‐perovskite‐based supercapacitors have shown an energy density in the range of 10–15 Wh kg−1. Therefore, further optimization is needed to improve the energy storage efficiency in halide perovskite‐based supercapacitors. It has been observed that the charge storage capacity increases with the increasing ionic conductivity in the perovskite active layer. Herein, a series of porous electrodes are prepared to optimize ionic conductivity by mixing powders of different halide‐based perovskite single crystals for supercapacitor application. It has been demonstrated that maximum efficiency is achieved for a specific bromide composition to iodide ratio with an energy density of ≈22 Wh kg−1 and a power density of 600 W kg−1. The ionic conductivity is improved at least by two orders to 3.2 × 10−13 m2 s−1 in the mixed halide sample than pure halide perovskites, while charge transfer resistance is decreased to 40.5 Ω cm−2. However, overall device stability and Coulombic efficiency decrease with the increasing iodide content.

Copper sulfide nanoparticles on titanium dioxide (TiO2) nanoflakes: A new hybrid asymmetrical Faradaic supercapacitors with high energy density and superior lifespan

In this research work, we have prepared nanocomposites of copper sulfide (CuS) nanoparticles (NPs) with titanium dioxide (TiO2) nanoflakes, with varying contents of CuS, via combined chemical precipitation and sol-gel methods. The effects of CuS concentration on the structural, morphological and electrochemical properties of TiO2/CuS nanocomposites for hybrid asymmetric Faradaic supercapacitors was studied for the first time. Electrochemical studies were carried out by using CV, CD, and EIS measurements in a three/two-electrode setups for both capacitive and practical aspects. When serving as an electrode material for the supercapacitors in three-electrode measurements, all the samples demonstrated a capacitive nature with a Faradaic charge storage mechanism due to the prominent redox peaks originating from their CV and voltage plateau in the CD profile. The optimized electrode ST-3 revealed the highest energy storage performance (capacitance: 853 F g−1) with low charge transfer and solution resistance compared with other electrodes (CuS: 440 F g−1, TiO2: 326 F g−1, ST-1: 535 F g−1, ST-5: 672 F g−1) at 1 Ag−1 with the superior rate capability. The ST-3//AC//KOH ASC displayed a high capacitance of 226.5 F g−1 and 80.2 F g−1 at the discharge current was prolonged from 1 to 5 A g−1 after an optimized voltage of 1.8 V in a two-electrode setup. Interestingly, an outstanding energy density of 68.4 W h kg−1 was achieved at a high-power density of 8150 W kg−1 at a discharge current of 1 and 5 A g−1, with the descent durability of 87 % at a high discharge current of 6 A g−1 when recycled for a large number of 25,000 cycles. These outstanding features highlight an appealing, low-cost, simple, and green route to synthesize other transition metal sulfides for the next-generation electronic devices.