Solid-state Hybrid Supercapacitor Research Articles

Multiple phase transformation of ZIF-L to LDH and Ag nanoparticles decorated on CoNi layered double hydroxides for high-performance supercapacitor and highly efficient hydrogen evolution reaction

ZIF-L-derived binary layered double hydroxide (LDH) established active catalysts have been shown to have potential as electrode materials in the development of high-performance supercapacitors (SCs) and hydrogen evaluation reactions (HER). This study uses conductive nano-silver (Ag) particles in hierarchically integrated CoNi-LDH nanosheets (NSs), which are described. The developed Ag@CoNi-LDH NSs electrode has a very high specific capacitance of 2878 F g−1 at 0.5 A g−1 and an impressive rate capability. This is due to consistent morphology, plentiful electroactive sites, homogeneous particle size, and decreased electronic/ionic impedance. The fabrication of solid-state hybrid supercapacitors (HSCs) using Ag@CoNi-LDH NSs as the positive electrode and activated carbon (AC) as the negative electrode in PVA/KOH polymer gel electrolytes has been described. The prepared supercapacitors achieve a maximum energy density of 105 Wh kg−1 at power densities of 1183 Wh kg−1, coupled with excellent initial capacitance retentions of 97 % after 20,000 cycles. Ag@CoNi-LDH NSs demonstrate effective electrocatalytic activity towards HER with an ultra-low overpotential of 26 mV at 10 mA cm−2 and the associated Tafel value of 35 mV dec−1 using 0.5 M acidic electrolyte. It is possible to attribute the extraordinary electrochemical performance to the thoughtful mixture of two electroactive materials in the future.

MnO2/AgNPs Composite as Flexible Electrode Material for Solid-State Hybrid Supercapacitor

A MnO2/AgNP nanocomposite was synthesized using a sonochemical method and investigated as an electrode material in a solid-state hybrid supercapacitor. Aquivion’s sodium and lithium electrolyte membrane serves as an electrolyte and separator. For comparison, MnO2 was used as the active material. The developed supercapacitor containing a carbon xerogel as a negative electrode, the MnO2/AgNP composite as a positive electrode and a Na+-exchange membrane demonstrated the highest performance characteristics. These results indicate that the incorporation of silver nanoparticles into the MnO2 structure is a prospect for obtaining an active composite electrode material for solid-state supercapacitors.

Fabrication of CNT-N@Manganese Oxide Hybrid Nanomaterials through a Versatile One-Pot Eco-Friendly Route toward Engineered Textile Supercapacitors.

The expansion of the Internet of Things market and the proliferation of wearable technologies have generated a significant demand for textile-based energy storage systems. This work reports the engineered design of hybrid electrode nanomaterials of N-doped carbon nanotubes (CNT-N) functionalized with two types of manganese oxides (MOs)-birnessite (MnO2) and hausmannite (Mn3O4)-and their application in solid-state textile-based hybrid supercapacitors (SCs). A versatile citric acid-mediated eco-friendly one-pot aqueous precipitation process is proposed for the fabrication of the hybrids. Remarkably, different types of MOs were obtained by simply changing the reaction temperature from room temperature to 100 °C, without any post-thermal treatment. Asymmetric textile SCs were developed using cotton fabrics coated with CNT-N and the hybrids as textile electrodes, and poly(vinyl) alcohol/orthophosphoric acid as the solid-gel electrolyte. The asymmetric devices presented enhanced energy storage performance relative to the symmetric device based on CNT-N and excellent cycling stability (>96%) after 8000 charge/discharge cycles owing to synergistic effects between CNT-N and the MOs, which endowed nonfaradaic and pseudocapacitive features to the SCs. The asymmetric SC based on CNT-N@MnO2 featured 47% higher energy density and comparable power density to the symmetric CNT-N-based device (8.70 W h cm-2 at 309.01 μW cm-2 vs. 5.93 W h cm-2 at 346.58 μW cm-2). The engineered hybrid CNT-N@MO nanomaterials and the eco-friendly citric acid-assisted one-pot precipitation route open promising prospects not only for energy storage, but also for (photo)(electro)catalysis, wastewater treatment, and (bio)sensing.

Hierarchical and Nanocrystallite-Assembled Ultraporous NiO/MnCo2O4 for All Solid-State Hybrid Supercapacitors with Robust Energy Efficiency and Extended Operational Durability.

To address the growing demand of highly Ragone efficient electrochemical energy storage devices, we have innovated a synthetic design strategy and employed a tartrate-mediated kinetic precipitation process to fabricate an ultraporous ribbon-like hierarchical microstructure of Ni-, Mn-, and Co-based ternary oxide, i.e., NiO/MnCo2O4, and employed it as a battery-type positive electrode material to assemble an ASSHSC (all-solid-state hybrid supercapacitor) device with nitrogen-doped reduced graphene oxide (N-rGO) as the positive electrode material. NiO/MnCo2O4 exhibits distinct crystallographic phase, near-perfect elemental stoichiometry, evident bulk porosity, and rich nanocrystallite assembly in the randomly arranged microstructure of near-uniform size and shape. Thorough electrochemical studies corroborate that the battery-type NiO/MnCo2O4 exhibits remarkable electrochemical reversibility during charge transfer, high efficiency in supercapacitive charge storage, low charge transfer, series and diffusion resistance. The NiO/MnCo2O4||N-rGO ASSHSC device assembled with the PVA-KOH film as the separator electrolyte offers rich charge storage physiognomies, which accentuates excellent electromicrostructural compatibility between the electrode materials in the device. The NiO/MnCo2O4||N-rGO ASSHSC device shows low charge transfer and diffusion resistance, and it also delivers high mass and areal specific capacitance/capacity, energy and power density, Ragone efficiency (∼131 Wh kg-1 at ∼2134 W kg-1 and ∼31 Wh kg-1 at ∼5005 W kg-1), and extended operational durability (98.2% specific capacitance retention after 12,000 successive GCD cycles) under high-rate working conditions. The present optimized approach to design highly efficient multiple transition-metal-based oxides as battery-type electrode materials and fabricate rich Ragone-efficient ASSHSC devices can be widely adopted in the future development of high-performance hybrid supercapacitors, which may be largely integrated in various pioneering technologies.

Design strategy for metal–organic framework assembled on modifications of MXene layers for advanced supercapacitor electrodes

The poor electronic conductivity and instability of metal–organic framework (MOFs) nanomaterials have been considered as the main reasons that hinder their practical application. Here, the bimetallic NiCo-MOF is in-situ grown by two-dimension expanded MXene to construct promising hierarchical electrodes. Benefitting from the hydroxyl group on the surface of MXene attracts metal (Ni, Co) ions by weak coordination, leading to oxygen vacancies during NiCo-MOF formation. At the same time, the density functional theory (DFT) calculation displays that the redox active center of NiCo-MOF is guaranteed to possess excellent electron and ion transport performance. Moreover, the open morphology based on expanded MXene by the hard template method can solve the re-stacking problem of MXene and provide a larger growth area for NiCo-MOF. The electrode design engineering strategy significantly improves the capacitance performance by increasing the electrochemically active site and promoting the ion dynamics. Specifically, the integrated solid-state hybrid supercapacitor (HSC) with MXene@NiCo-MOF and activated carbon (AC) exhibits energy density of 40.23 Wh·kg−1 at a power density of 1495.07 W·kg−1 and 84.4 % capacitance retention after 10,000 cycles via adopting this strategy. The strategy also provides a new route to improve the performance of flexible MXene-based supercapacitors with polyvinyl alcohol hydrogel electrolytes.

Cathodic electrophoretic deposition (EPD) of two-dimensional colloidal Ni(OH)2 and NiO nanosheets on carbon fibers (CF) for binder-free structural solid-state hybrid supercapacitor

The exponential growth of the renewable energies field and the increase of portable electric vehicles (EVs) demand a new generation of multifunctional efficient electrochemical energy storage devices (EESDs). In this work, binder-free hybrid battery-like electrodes were prepared by cathodic electrophoretic deposition (EPD). One-step (synthesis and deposition) processing of β-Ni(OH)2 was developed avoiding a previous calcination step to form NiO. The redox reaction (RR) contribution to the electrochemical performance of the hybrid electrodes was enhanced without influencing the mechanical properties of the CF substrate. Moreover, the sintering of the coated-CF under a high-vacuum atmosphere and the controlled mass deposition (<0.1 mg·cm−2) demonstrated to enhance the synergic effect of the redox reactions, ion diffusion (NiO) and the electrochemical double layer (CF) contributions. Thus, the hybrid electrodes in a half-cell configuration achieved remarkably high capacitance values (1161 F·g−1 at 2 A·g−1), while hybrid electrodes in a symmetric structural hybrid solid-state supercapacitor (HSSS) with an ionic liquid/resin structural solid-electrolyte reached a capacitance of 9.8 mF·g−1, a power and energy density of 3.5 mW·kg−1 and 1 mWh·kg−1 respectively and good electrochemical stability with a Columbic efficiency of 75 % at 0.8 mA·g−1.

Effect of in situ annealing on pulsed laser ablated mixed metal oxide (BixMyOz; M=Mn, Mo) thin film electrodes for flexible hybrid supercapacitor devices

Recently, solid-state thin film hybrid supercapacitor devices (TFHSCs) have had greater attention due to their miniaturized device assembly, portability, and superior cycling stability. Herein, for the first time, we assembled BiMnxOy ǁ PVA-KOH ǁ Bi2MoO6 thin-film solid-state supercapacitor devices by pulsed laser deposition (PLD) technique. In the present work, Bi2MoO6 and BiMnxOy thin film electrodes are fabricated at in-situ annealed conditions and their structural, morphological, and electrochemical performances are examined distinctly. We assembled a thin-film based BiMnxOy ǁ PVA-KOH ǁ BiMnxOy symmetric supercapacitor device (SSD) and that device delivers a functioning voltage of 1.4 V. Also, the device exhibits an extremely specific areal capacitance of 41 mF cm−2 at 1 mA cm−2. Similarly, a thin film-based Bi2MoO6 ǁ PVA-KOH ǁ Bi2MoO6 SSD attained a maximum specific areal capacitance of 13.33 mF cm−2. Further, the assembled BiMnxOy ǁ PVA-KOH ǁ Bi2MoO6 TFHSC device delivers a voltage of 1.6 V and the TFHSC device exhibited a maximum specific areal capacitance of 52 mF cm−2 at a fixed current density of about 2 mA cm−2. The BiMnxOy ǁ PVA-KOH ǁ Bi2MoO6 TFHSC device shows outstanding stability performances such as 99 % of capacitance retention as well as 93 % of coulombic efficiency after 25,000 charge/discharge cycles. Additionally, the TFHSC device delivers a maximum areal energy density and power density of 18.5 μWh.cm−2, and 978.7 μW cm−2, respectively.

Self-assembled architecture of 2D layered double hydroxide pillared with 0D polyoxomolybdate anions: High-performance redox-type cathode for solid-state hybrid supercapacitor

Herein, mesoporous self-assembled architecture of two-dimensional (2D) nickel chromium-layered double hydroxide (NiCr–LDH) monolayers pillared with 0D polyoxomolybdate anions (NCMo) was prepared via a lattice engineering rapid exfoliation–restacking synthesis route. The self-assembled 2D-0D NCMo architecture exhibited expanded surface area, porous interconnected nanosheet morphology, flexible chemical composition, layer-by-layer stacking structure, and excellent electrochemical activity. The NCMo architecture exhibited promising electrochemical performance with a large specific capacity of 567 C g−1 at a current density of 1 A g−1, and an excellent cyclic retention of 89 % after 5000 charge–discharge cycles. Additionally, an all-solid-state hybrid supercapacitor (HSC) device was assembled using NCMo architecture as the redox-type cathode, reduced graphene oxide (rGO) as the EDLC-type anode, and PVA-KOH gel as the electrolyte. The NCMo-2//PVA-KOH//rGO HSC device exhibited a high specific capacitance (171.8 F g−1 at 10 A g−1), decent cycling stability (91 % after 10,000 cycles), and a high energy/power density (61.1 Wh kg−1/6.7 W kg−1). The findings of this study demonstrate that the intercalation of polyoxomolybdate is an effective lattice-engineered method for improving the electrode functionality of self-assembled LDH-based architectures.

Carbon nanofiber-supported elongated square bipyramid-like MnWO4 composite electrodes for high-performance battery-type supercapacitors: Enhanced electrochemical performance via synergistic effect

Battery-type electrode materials known for high electrochemical performance are commonly paired with carbon-based materials, which have recently gained attention for their potential application in supercapacitors. These carbon-based materials offer the potential for comprehensive energy storage properties along with excellent cycle life. In this study, a carbon nanofiber (CNF)-based elongated square bipyramid-like manganese tungstate (MnWO4; MnW) composite was synthesized via a simple and cost-effective solid-state reaction followed by an impregnation method. The main objective was to understand the synergistic effects of varying the content of CNF in the reaction on the formation of two different composites (MnW-CNF@L and MnW-CNF@H) and their physicochemical and electrochemical properties were thoroughly examined and compared to those of the MnW. Pure composites have a high crystalline nature with bipyramid-shaped microstructures anchored on the one-dimensional (1D) tubular CNF backbone, as confirmed by the structural and morphological analysis. In the context of the battery-type supercapacitor, the specific capacity is 2-fold higher for MnW-CNF@L (235.3 mAh g−1/848.1 C g−1) and 4-fold higher for MnW-CNF@H (451.3 mAh g−1/1624 C g−1) compared to the MnW (11.8 mAh g−1/402.6 C g−1) electrode at a current density of 1 A g−1. In addition, the MnW-CNF@H composite electrode delivered 96% capacity retention when current density increased 20-fold and exhibited outstanding cyclic stability of 95% initial capacity retention after 5,000 cycles. A solid-state hybrid supercapacitor was fabricated using the battery-type MnW-CNF@H composite electrode as the cathode and activated carbon (AC) as the anode. The MnW-CNF@H//AC HSC device configuration resulted in remarkable performance metrics, displaying a high energy density of 48.9 Wh kg−1 at 1018.2 W kg−1. The exceptional performance of this composite can be attributed to the synergistic effect among redox centres of Mn, W, and CNF. This work broadcasts a simple and cost-effective approach for designing high-performance supercapacitors, contributing to the development of sustainable energy storage systems.

Investigation on two-dimensional molybdenum oxide-graphitic carbon nitride (MoO3-g-C3N4) heterostructures based hybrid electrodes for the fabrication of high energy density solid state supercapacitors

BackgroundThe fabrication of high-performance supercapacitor electrodes has been extensively investigated for future high power storage applications. Molybdenum trioxide (MoO3) was synthesized and the graphitic carbon nitride have been introduced with the MoO3 to enhance the electrochemical performance by synergistic effect. MethodsMoO3-gC3N4 Nanocomposite (NC) was synthesized by thermal treatment followed by sonication process and can be utilized as active material for the preparation of supercapacitor electrode. The solid-state hybrid supercapacitor device (SHSC) is fabricated with MoO3-gC3N4 NC as cathode, activated carbon as anode, and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) ionic liquid as an ionogel electrolyte to perform the electrochemical studies. Significant findingsCyclic voltammetry (CV) revealed that the synthesized composite delivers higher specific capacity of 520. 97 C/g at 10 mV/s. The electrochemical impedance spectroscopy (EIS) of MoO3-g-C3N4 NC reveals lower solution (Rs) and charge transfer resistance (Rct) of 0.05 and 3.14 Ω respectively. The fabricated MoO3-g-C3N4//AC SHSC delivers high energy density of 59.75 Wh/kg and a high-power density of 1125 W/kg. Furthermore, the SHSC exhibits superior cyclic stability of 86.1% even after 6000 consecutive charge-discharge cycles.

Development of binder-free, amorphous nickel vanadate cathodes by SILAR method for hybrid supercapacitors: Exploiting surface area by monitoring growth rate

Developing self-supported electrode material in the absence of electro-inert binders considering the effortless transfer of charges and manipulating physicochemical properties of electrodes in energy storage devices is essential. Hence, the present attempt emphasizes the facile synthetic strategy of successive ionic layer adsorption and reaction (SILAR) for controlled nickel vanadate (NV) growth over the conducting plate. In SILAR synthesis, the growth rate is monitored by rinsing and adsorption/reaction time variation to tune the surface area, mesoporous structure, and surface morphology of NV thin films. As a result, the formation of mesoporous, amorphous, hydrous nanoparticles of NV over the stainless-steel substrate is affirmed by structural analysis. Furthermore, alteration in specific surface area with variation in growth rate is observed in BET analysis. As a result, the optimal NV(1:2) thin film electrode exhibited the highest specific capacity (capacitance) of 355C g−1 (710 F g−1) at 1 A g−1 current density. Moreover, the fabricated aqueous hybrid supercapacitor device (NV(1:2)//rGO) delivered 109 F g−1 specific capacitance at 1.3 A g−1 current density, and the device exhibited a maximum specific energy (SE) of 44 Wh kg−1 at a particular specific power (SP) of 1.14 kW kg−1. Furthermore, the solid-state hybrid supercapacitor (NV(1:2)//PVA-KOH//rGO) device conferred a specific capacitance of 89 F g−1 at 0.5 A g−1 current density and an SE of 36 Wh kg−1 at 0.482 kW kg−1 SP. This research paved an avenue to the binder-free, scalable synthesis of NV electrodes and employed them as a cathode in practical applications of hybrid energy storage devices.

Defective core–shell NiCo2S4/MnO2 nanocomposites for high performance solid-state hybrid supercapacitors

The roles of oxygen vacancies to enhance the electrochemical performance were not clearly explained in comprehensive research. Herein, the vertically oriented NiCo2S4/MnO2 core–shell nanocomposites are in situ grown on the nickel foam (NF) surface and activated by oxygen vacancy engineering via a chemical reduction method. The scanning electron microscope (SEM) and transmission electron microscope (TEM) results show the shell-MnO2 is well coated on the core-NiCo2S4. The hierarchical core–shell nanostructures synergistically increase conductivity and provide rich faradaic redox chemical reactions. Moreover, the density functional theory (DFT) calculations further indicate that the electronic properties and structure properties in NiCo2S4/MnO2 electrode of reduction for 60 min (NiCo2S4/MnO2-60) are effectively adjusted by introducing oxygen vacancies. Impressively, the NiCo2S4/MnO2-60 electrode delivers substantially appreciable areal capacity of 2.13 mAh·cm−2 couple with superior rate capability. The as-prepared high-performance electrode material can assemble into solid-state hybrid supercapacitor. The fabricated NiCo2S4/MnO2-60//AC device exhibits an exceptional energy density of 43.16 Wh·kg−1 at a power density of 384.21 W·kg−1 and satisfactory cyclic stability of 92.1 % at current density of 10 mA·cm−2 after 10,000 cycles. In general, the work demonstrates the significance of NiCo2S4/MnO2-60 as a highly redox active electrode material for future practical application in supercapacitors.

A homologous strategy to parallelly construct doped MOFs-derived electrodes for flexible solid-state hybrid supercapacitors

A homologous strategy to parallelly construct doped MOFs-derived electrodes for flexible solid-state hybrid supercapacitors

Design and fabrication of nickel lanthanum telluride microfibers for redox additive electrolyte-based flexible solid-state hybrid supercapacitor

In this article, we describe the design of a flexible solid-state hybrid supercapacitor (FSSHSC) using mixed metal telluride NiLaTe microfibers (MFs) atop Ni foam (NF). The goal of the study is to examine the effect of counter metal ions Ni and La, in addition to Te, in the formation of longer one-dimensional (1-D) architecture. The NiTe MFs and La2Te3 microrods (MRs) were synthesized and compared with bimetallic telluride. La exhibit's slower reaction kinetics than Ni when reacting with Te due to the different crystal structural stability of La2Te3 (cubic phase) and Te (hexagonal phase). Three-electrode investigations incorporating aqueous potassium ferrocyanide (KFC) reveal that the electrochemical performance of NiLaTe MFs is doubled compared to the typical aqueous KOH electrolyte alone. The presence of the redox pair [Fe(CN)6]3−/[Fe(CN)6]4− allows for faster ion transport inside the active electrode surface, which improves electrochemical performance. The FSSHSC device was fabricated, comprising NiLaTe as the positive, activated carbon (AC) as the negative electrode, and PVA-KOH-KFC gel, which acts as an electrolyte and a separator. The device performance was compared to that of a liquid system as well as one without a redox additive gel system. The significance of polymer-based gel and KFC for device construction is briefly reviewed. The final built device NiLaTe//AC in gel + KFC system has a maximum areal capacity of 65.6 μAh cm−2 (60.0 mA h g−1) at a current density of 2 mA cm−2, a maximum energy density of 45.5 Wh Kg−1 (52.36 μWh cm−2), and a maximum power density of 5488.7 W Kg−1(6312.0 μW cm−2). Furthermore, the device outperforms the cyclic stability for 10,000 cycles with an 80.1 % capacity retention and exhibits excellent flexibility at different bending angles. The assembled FSSHSCs device successfully illuminates an LED bulb for 70 s.

High ionic conductivity and toughness hydrogel electrolyte for high-performance flexible solid-state zinc-ion hybrid supercapacitors enabled by cellulose-bentonite coordination interactions

The lamellar structure of BT and coordination interaction with cellulose make cellulose hydrogel electrolytes have both high ionic conductivity and mechanical strength, and assembled ZHSCs can be applied in the field of wearable electronic devices.

Metal silicates for supercapacitors derived from the multistep treatment of natural green algaes

Natural green algaes (GAs) was treated with NaCl solution to prepare metal- silicates (S-C-FeSi-3 and S-C-CuSi-3) with high electrochemical performance. Then, the as-synthesized samples were soaked in NaOH solution to obtain etched metal silicates (e-S-C-FeSi-3 and e-S-C-CuSi-3). This novel method was used to generate a more porous structure with a higher specific surface area. In the three-electrode system, e-S-C-FeSi-3 and e-S-C-CuSi-3 showed the best electrochemical performance (476 F g−1 and 458 F g−1 at 0.5 A g−1, 96 % and 97% after 10,000 cycles, respectively). The solid-state hybrid supercapacitor (HSC) devices (denoted as e-S-C-FeSi-3//AC and e-S-C-CuSi-3//AC), manufactured by metal- silicates and activated carbon (AC), were tested in a two-electrode system. e-S-C-MSi-3//AC exhibited much better electrochemical properties such as areal specific capacitances (603 and 615 mF cm−2 at 2 mA cm−2), energy densities (4.57 and 4.43 Wh m−2 at the power density of 19.2 and 21.0 W m−2) and cycle performances (74.5 % and 76.3 % after 6,000 cycles) than those of C-MSi-3//AC, e-C-MSi-3//AC and S-C-MSi-3//AC (M = Fe and Cu). This study confirms that supercapacitors with excellent electrochemical performance can be prepared by naturally polluted GAs. Furthermore, treatment with porogens is shown to be an effective method to enhance the electrochemical properties of metal- silicates and to prepare electrode materials applied for high-performance supercapacitors.

In-situ construction of carbon cloth-supported amorphous/crystalline hybrid NiCo-sulfide with permeable concrete-like morphology for high-performance solid-state hybrid supercapacitors

Constructing the amorphous/crystalline hybrid materials has been proved to be an effective strategy to boost the specific capacity, rate capability, and cycle durability of supercapacitors. Presently, the amorphous/crystalline hybrid materials are generally constructed by simply overlaying one amorphous material on or under another crystalline material. In this work, we successfully constructed carbon cloth-supported amorphous/crystalline hybrid NiCo-sulfide with a permeable concrete-like morphology (NiCo-sulfide@CCH) by in-suit partially converting the crystalline NiCo-sulfide into the amorphous phase in a specially-made quartz reactor. The obtained NiCo-sulfide@CCH material exhibits a high specific capacity of 250.16 mAh/g (1801.13F g−1 or 900.6C g−1) at 1 A/g, outstanding cycle stability, and good rate capability. The solid-state hybrid supercapacitor (SSHSC) device based on the prepared NiCo-sulfide@CCH material delivers high specific energy of 57.71 Wh kg−1 at a specific power of 1.56 kW kg−1 with remarkable specific energy retention of 97.9 % after 5000 cycles. The developed scheme is expected to promote the application of the amorphous/crystalline hybrid materials in high-performance supercapacitors.

Facile synthesis of hierarchical core–shell heterostructured ZnO/SnO2@NiCo2O4 nanorod sheet arrays on carbon cloth for high performance quasi-solid-state asymmetric supercapacitors

We synthesized the hierarchical ZnO/SnO2@NiCo2O4 core–shell nanorod sheet arrays (NRSAs) grown on a flexible conductive carbon cloth (CC) substrate by a hydrothermal method. The amalgamation and formation mechanism were proposed. The as obtained ZnO/SnO2@NiCo2O4 core–shell heterostructures is investigated using X-ray diffraction, X-ray photoelectron spectroscopy, high resolution transmission electron microscopy, field emission scanning electron microscopy, and nitrogen adsorption and desorption isotherm analysis. The SnO2 layer which is conducting between ZnO and NiCo2O4 may effectively boost the electrical conductivity of the electrodes and also defend the ZnO from corrosion in the alkaline solution. Benefitting from the core–shell heterostructure formation, the hybrid ZnO/SnO2@NiCo2O4//CC electrode delivered a high specific capacity of 244.5 mA h/g, enhanced cycling stability with a 94.5% retention in specific capacitance even after 10,000 continuous charge–discharge cycles and good rate capability. To utilize the high specific capacity and ultra-long cycling stability, the PVA-KOH gel electrolyte based solid-state hybrid supercapacitor device was assembled with AC//CC as a negative electrode and ZnO/SnO2@NiCo2O4//CC as a positive electrode. The fabricated HSC device delivered a specific capacitance of 117.5 F/g with high energy density (41.7 Wh/kg) and power density (6400 W/kg) along with the outstanding capacitance retention of 94.6% even after 10,000 continuous charging and discharging cycles. With exceptional electrochemical performance, a facile and cost-effective preparation, such ZnO/SnO2@NiCo2O4//CC core–shell heterostructured electrode show a great potential for high-performance electrochemical supercapacitor applications in future.

Ultrasonically dispersed multi-composite strategy of NiCo2S4/Halloysite nanotubes/carbon: An efficient solid-state hybrid supercapacitor and hydrogen evolution reaction material

Herein, we have developed a novel hybrid material based on NiCo 2 S 4 (NCS), halloysite nanotubes (HNTs), and carbon as promising electrodes for supercapacitors (SCs). Firstly, mesoporous NCS nanoflakes were prepared by co-precipitation method followed by physically mixing with HNTs and carbon, and screen printed on nickel foam. After ultrasonication, a uniform distribution of the Carbon/HNTs complex was observed, which was confirmed by surface morphological analysis. When used as electrode material, the NCS/HNTs/C hybrid displayed a maximum specific capacity of 544 mAh g −1 at a scan rate of 5 mV s −1 . Later, a solid-state hybrid SCs was fabricated using activated carbon (AC) as the negative and NCS/HNTs/C as the positive electrode (NCS/HNTs/C//AC). The device delivers a high energy density of 42.66 Wh kg −1 at a power density of 8.36 kW kg −1 . In addition, the device demonstrates long-term cycling stability. Furthermore, the optimized NCS, NCS/HNTs, and NCS/HNTs/C nanocomposites also presented superior hydrogen evolution reaction (HER) performance of 201, 169, and 116 mV in the acidic bath at a current density of 10 mA cm −2 , respectively. Thus, the synthesis of NCS/HNTs/C nanocomposite as positive electrodes for hybrid SCs opens new opportunities for the development of next-generation high energy density SCs. • Synthesis of novel hierarchical NiCo 2 S 4 nanoflakes using a simple co-precipitation method with high electrochemical performance. • Preparation of final NiCo 2 S 4 /HNTs/C composite electrode by screen-printing method on Ni foam. • Improved the supercapacitor capacitive properties than the NiCo 2 S 4 /HNTs/C then the NiCo 2 S 4 and NiCo 2 S 4 /HNTs composite. • A novel NiCo 2 S 4 /HNTs/C//AC constructed solid-state hybrid device. • SSHSc shows a high energy density of 42.66 Wh kg −1 at a power density of 8.36 kW kg −1 .

Butterfly-like metal-silicates derived from natural green algaes for supercapacitors with enhanced electrochemical properties by alkali etching

The 3D N, S, P-doped C-metal-silicates (C-MSi, M = Ni, Co and Ni/Co) are derived from green algaes (GAs) calcined by N2. Then the alkali etching technique is used to treat the as-synthesized C-MSi by 3 M NaOH aqueous solution for 12 h (e-C-MSi). The electrochemical performance can be significantly improved due to the acquisition of the more hierarchical pores and larger specific surface area by alkali etching. In detail, the e-C-NiSi-3, e-C-CoSi-3 and e-C-NiCoSi-3 show higher specific capacitances and cycling performances than those of C-MSi in the three-electrode system. The solid-state hybrid supercapacitor (HSC) devices (C-MSi//AC and e-C-MSi//AC, M = Ni, Co and Ni/Co) are fabricated by the metal-silicates and activated carbon (AC). The e-C-MSi//AC HSC devices exhibit better electrochemical properties than those of C-MSi//AC in the two-electrode system: higher specific capacitances, larger energy densities and better cycle performance. For instance, e-C-NiCoSi-3//AC HSC device (479 mF cm−2 at 2 mA cm−2, 3.97 W h m−2 at 2.31 W m−2, 92 % after 5000 cycles) is superior to C-NiCoSi-3//AC HSC device (432 mF cm−2 at 2 mA cm−2, 3.15 W h m−2 at 2.14 W m−2, 87 % after 5000 cycles). These results demonstrate that the high-performance supercapacitors can be prepared by the natural GAs using simple method. Alkali etching technique can be used as a conventional and positive method to improve the electrochemical performance of metal-silicates, and can provide electrodes for applying to high-performance SCs.