As-fabricated Asymmetric Supercapacitor Research Articles

Preparation of Spherical δ-MnO2 Nanoflowers by One-Step Coprecipitation Method as Electrode Material for Supercapacitor.

Spherical δ-MnO2 nanoflower materials were synthesized via a facile one-step coprecipitation method through adjusting the molar ratio of KMnO4 to MnSO4. The influence of the molar ratio of the reactants on the crystal structure, morphology, and electrochemical performances was investigated. At a molar ratio of 3.3 for KMnO4 to MnSO4, the spherical δ-MnO2 nanoflowers composed of nanosheets with the highest specific surface area (228.0 m2 g-1) were obtained as electrode materials. In the conventional three-electrode system using 1 M Na2SO4 as an electrolyte, the specific capacitance of the spherical δ-MnO2 nanoflowers reached 172.3 F g-1 at a current density of 1 A g-1. Moreover, even after 5000 cycles at a current density of 5 A g-1, the GCD curves remained essentially unchanged, and the specific capacitance still retained 86.50% of the maximum value. The kinetics of the electrode reaction were preliminarily studied through the linear potential sweep technique to observe diffusion-controlled contribution toward total capacitance. For the spherical δ-MnO2 nanoflower electrode material, diffusion-controlled contribution accounted for 65.1% at low scan rates and still remained significant at high scan rates (100 mV s-1), indicating excellent utilization efficiency of the bulk phase. The as-fabricated asymmetric supercapacitor HFC-7//MnO2-3.3-ASC presented a prominent specific energy of 16.5 Wh kg-1 at the specific power of 450 W kg-1. Even when the specific power reached 9.0 kW kg-1, the energy density still retained 9.5 Wh kg-1.

Construction of core-shell coordination polymers@layered double hydroxides microspheres via ions-exchanging strategy for enhanced supercapacitor performances

Coordination polymers (CPs) are gained numerous investigations due to their structure talents, such as ultrahigh high specific area, abundant pores or channels, and diverse and adjustable composition in energy storage area. However, their application on supercapacitor devices is restricted by low conductivity and lack of stability. In this work, a Co- and benzenetricarboxyl-based CPs (Co-BTC) is selected as precursor, and then used as template to fabricate a layer-double-hydroxide-covered core-shell structure (noted as Co-BTC@LDH) using a cation/anion co-exchanging process. This fine tune nanomaterial is achieved by, which demonstrates a remarkable specific capacitance of 1226 F g−1 at a current density of 1 A g−1, and outstanding ratio performance of maintaining 86.79% initial capacitance even as the current density elevates tenfold to 10 A g−1. Moreover, the as-fabricated asymmetric supercapacitor based on Co-BTC@LDH and active carbon (AC), displays an energy density of 58.70 Wh kg−1 at the power density of 0.36 kW kg−1 and an impressive cycle stability of retaining 98.2 % initial capacity even after 9000 cycles.

Cellulose graphitic carbon directed iron oxide interfaced polypyrrole electrode materials for high performance supercapacitors

The rising demand for green and clean energy urges the enlargement of economical and proficient electrode materials for supercapacitors. Herein, we designed a novel electrode material by porous cellulose graphitic carbon (CC) derived from bio-waste cornhusk via the pyrolysis route, and α-Fe2O3 decorated nanostructure with CC (CCIO) was achieved in situ pyrolysis of corn-husk and Fe(NO3)3·9H2O metal salt followed by a coating of polypyrrole (CCIOP). The CC, CCIO, and CCIOP nanocomposite electrodes were characterized by XRD, Raman, FTIR, FE-SEM/EDX, FE-TEM, XPS, and BET analysis. The CCIOP nanocomposite electrode exhibits an enhanced specific capacitance (Csp) of 290.9 F/g, which is substantial to its pristine CC (128.3 F/g), PPy (140.3 F/g), and CCIO (190.7 F/g). The Csp of CCIOP in a three-electrode system, using 1 M Na2SO4 electrolyte exhibits excellent capacity retention of 79.1 % even at a high current density of 10 A/g. The as-fabricated asymmetric supercapacitor (ASC) delivered a remarkable capacity retention of 88.7 % with a coulombic efficiency of 98.8 % even after 3000 cycles. The study shows successful utilization of cellulose from bio-waste cornhusk into a substantial template applicable in future alternative energy storage devices.

Fabrication of Hierarchical MOF-Derived NiCo2S4@Mo-Doped Co-LDH Arrays for High-Energy-Density Asymmetric Supercapacitors.

The rational fabrication of composite structures made of mixed components has shown great potential for boosting the energy density of supercapacitors. Herein, an elaborate hierarchical MOF-derived NiCo2S4@Mo-doped Co-LDH arrays hybrid electrode was fabricated through a step-wise method. By leveraging the synergistic effects of a uniform array of NiCo2S4 nanowires as the core and an MOF-derived porous shell, the NiCo2S4@Mo-doped Co-LDH hybrid electrode demonstrates an exceptional specific capacitance of 3049.3 F g-1 at 1 A g-1. Even at a higher current density of 20 A g-1, the capacitance remains high at 2458.8 F g-1. Moreover, the electrode exhibits remarkable cycling stability, with 91% of the initial capacitance maintained after 10,000 cycles at 10 A g-1. Additionally, the as-fabricated asymmetric supercapacitor (ASC) based on the NiCo2S4@Mo-doped Co-LDH electrode achieves an impressive energy density of 97.5 Wh kg-1 at a power density of 835.6 W kg-1. These findings provide a promising approach for the development of hybrid-structured electrodes, enabling the realization of high-energy-density asymmetric supercapacitors.

Fabrication of High-Performance Asymmetric Supercapacitors Using Rice Husk-Activated Carbon and MnFe2O4 Nanostructures

To meet the growing demand for efficient and sustainable power sources, it is crucial to develop high-performance energy storage systems. Additionally, they should be cost-effective and able to operate without any detrimental environmental side effects. In this study, rice husk-activated carbon (RHAC), which is known for its abundance, low cost, and excellent electrochemical performance, was combined with MnFe2O4 nanostructures to improve the overall capacitance of asymmetric supercapacitors (ASCs) and their energy density. A series of activation and carbonization steps are involved in the fabrication process for RHAC from rice husk. Furthermore, the BET surface area for RHAC was determined to be 980 m2 g−1 and superior porosities (average pore diameter of 7.2 nm) provide abundant active sites for charge storage. Additionally, MnFe2O4 nanostructures were effective pseudocapacitive electrode materials due to their combined Faradic and non-Faradic capacitances. In order to assess the electrochemical performance of ASCs extensively, several characterization techniques were employed, including galvanostatic charge –discharge, cyclic voltammetry, and electrochemical impedance spectroscopy. Comparatively, the ASC demonstrated a maximum specific capacitance of ~420 F/g at a current density of 0.5 A/g. The as-fabricated ASC possesses remarkable electrochemical characteristics, including high specific capacitance, superior rate capability, and long-term cycle stability. The developed asymmetric configuration retained 98% of its capacitance even after 12,000 cycles performed at a current density of 6A/g, demonstrating its stability and reliability for supercapacitors. The present study demonstrates the potential of synergistic combinations of RHAC and MnFe2O4 nanostructures in improving supercapacitor performance, as well as providing a sustainable method of using agricultural waste for energy storage.

Asymmetric Supercapacitors Using Porous Carbons and Iron Oxide Electrodes Derived from a Single Fe Metal-Organic Framework (MIL-100 (Fe)).

MOF-derived carbon (MDC) and metal oxide (MDMO) are superior materials for supercapacitor electrodes due to their high specific capacitances, which can be attributed to their high porosity, specific surface area (SSA), and pore volume. To improve the electrochemical performance, the environmentally friendly and industrially producible MIL-100 (Fe) was prepared using three different Fe sources through hydrothermal synthesis. MDC-A with micro- and mesopores and MDC-B with micropores were synthesized through carbonization and an HCl washing process, and MDMO (α-Fe2O3) was obtained by a simple sintering in air. The electrochemical properties in a three-electrode system using a 6 M KOH electrolyte were investigated. These novel MDC and MDMO were applied to an asymmetric supercapacitor (ASC) system to overcome the disadvantages of traditional supercapacitors, enhancing energy density, power density, and cyclic performance. High SSA materials (MDC-A nitrate and MDMO iron) were selected for negative and positive electrode material to fabricate ASC with KOH/PVP gel electrolyte. As-fabricated ASC resulted in high specific capacitance 127.4 Fg-1 at 0.1 Ag-1 and 48.0 Fg-1 at 3 Ag-1, respectively, and delivered superior energy density (25.5 Wh/kg) at a power density 60 W/kg. The charging/discharging cycling test was also conducted, indicating 90.1% stability after 5000 cycles. These results indicate that ASC with MDC and MDMO derived from MIL-100 (Fe) has promising potential in high-performance energy storage devices.

Electrodeposited CuxFe3-xSe4 nanoheterostructure arrays on carbon cloth as a binder-free faradaic negative electrode for asymmetric supercapacitors

Extensive research is being conducted worldwide to design and develop novel high-performance electrodes for supercapacitors (SCs) being a viable alternative to fossil fuels, dealing with the challenges of looming energy crisis and environmental issues globally. Herein, the design and synthesis of novel binder-free CuxFe3-xSe4@carbon cloth (CFS@CC) nanoheterostructure array electrode materials with tunable copper (Cu)/iron (Fe) stoichiometric ratios are demonstrated via a one-step room-temperature chronoamperometric (potentiostatic) electrodeposition process and their electrochemical characteristics as a promising faradaic negative electrode for SCs are explored systematically. The effect of Cu/Fe stoichiometric ratios on the morphological property and electrochemical performance of different CFS@CC array electrodes is thoroughly investigated to realize the sufficiently reaping synergistic benefits of Cu and Fe ions. Moreover, following a kinetic matching strategy, the optimized CFS@CC arrays as a negative electrode are assembled with the faradaic Ni3Se2/NiSe2@CC nanosheet arrays as a positive electrode to fabricate a novel asymmetric supercapacitor (ASC) device (Ni3Se2/NiSe2@CC//CFS-1.5@CC) which is operable in a large and stable potential window of 1.6 V and exhibits a high energy density of 84.8 Wh kg−1 at a power density of 664 W kg−1 with an excellent long-term electrochemical cycling stability. Some real-life applications of the as-fabricated ASC device are displayed to ensure its practicality.

Heterostructures of MoO3 nanobelts assembled on delaminated V4C3Tx MXene nanosheets for supercapacitors with excellent room/high temperature performance

A novel flexible delaminated vanadium carbide MXene (d-V4C3Tx) and molybdenum trioxide (MoO3) are promising electrode materials. However, the re-stacking of the d-V4C3Tx nanosheets and the poor conductivity and cyclic stability of MoO3 seriously restrict their development for supercapacitors application. Constructing heterostructures to obtain a synergistic property enhancement is an effective strategy to solve it. Herein, the free-standing d-V4C3Tx/MoO3 heterostructure composite films are fabricated by combining hydrothermal, electrostatic assembly with vacuum-assisted filtration methods, and the energy storage mechanism is dominated by diffusion-controlled process. Results indicate that the as-prepared composite film electrode has high specific capacity of 645 0 C g−1 at current density of 1 A g−1. Even at 40 °C, it also has 639.2 C g−1 at a scan rate of 2 mV s−1. This impressive electrochemical performance can be attributed to the enhanced conductivity and high pseudocapacitance offered by the heterostructures. The as-fabricated asymmetric supercapacitor (ASC), in which the d-V4C3Tx/MoO3 composite film is used as negative electrode and the active carbon (AC) is used as positive electrode, exhibits maximum energy density of 22.2 Wh kg−1 and maximum power density of 5289.9 W kg−1, and the capacity retention rate can still up to 97.0% even after 10,000 cycles at a current density of 10 A g−1. Furthermore, the assembled ASC device successfully drives the small alarm clock and lights the light emitting diode (LED), which facilitates the development of applications for such high-performance supercapacitors.

Effect of Electrolytic Cations on a 3D Cd-MOF for Supercapacitive Electrodes

A cadmium-based metal-organic framework (Cd-MOF) is synthesized in a facile manner at ambient temperature by an easy slow diffusion process. The three-dimensional (3D) structure of Cd-MOF is authenticated by single-crystal X-ray diffraction studies and exhibits a cuboid-shaped morphology with an average edge length of ∼1.13 μm. The prepared Cd-MOF was found to be electroactive in nature, which resulted in a specific capacitance of 647 F g-1 at 4 A g-1 by maintaining a retention of ∼78% over 10,000 successive cycles in the absence of any binder. Further, to distinguish the efficiency of Cd-MOF electrodes, different electrolytes (NaOH, KOH, and LiOH) were explored, wherein NaOH revealed a higher capacitive response due to its combined effect of ionic and hydrated ionic radii. To investigate the practical applicability, an asymmetric supercapacitor (ASC) device is fabricated by employing Cd-MOF as the positive electrode and activated carbon (AC) as the negative electrode, enabling it to light a commercial light-emitting diode (LED) bulb (∼1.8 V). The as-fabricated ASC device delivers comparable energy density and power density.

Interconnected plate-like NiCo2O4 microstructures for supercapacitor application

The precise synthesis of interconnected and porous microstructured electrode materials for supercapacitor application is always challenging to obtain maximum surface area for electrode–electrolyte interaction. Herein, the interconnected microstructured morphology of NiCo2O4 is synthesized via an inexpensive chemical route viz hydrothermal method. Synthesized NiCo2O4 nanomaterial is characterized for structural, morphological, electrochemical characteristics by XRD, SEM, CV, GCD, and EIS measurements. The XRD pattern reveals that nanostructured material is polycrystalline with a cubic phase. The average crystallite size of NiCo2O4 is 10.85 nm. The SEM analysis confirms interconnected plates microstructures with surface aea of 34 m2g−1. The NiCo2O4 electrodes are fabricated and their specific capacitance was measured using CV and GCD data. The maximum specific capacitance of the NiCo2O4 electrode is 550 F/g. Furthermore, an as-fabricated asymmetric supercapacitor (ASC) has an energy density of 3.81 Wh/kg, a power density of 789 W/kg at 4 mAcm−2, and capacitance retention of 87% after 2,000 cycle. An interconnected plate-like microstructure of NiCo2O4 material is a potential candidate for energy storage application.

3D self-supported hierarchical lettuce-like Ni3S2 super architecture with an internal nanowire network for high-performance supercapacitors

Tremendous efforts are devoted to the rational design of self-supported hierarchical architectures that are capable of delivering ultrahigh areal capacitance, and that are essential for miniaturized energy storage devices. Herein we propose a one-step-solvothermal approach for the hierarchical advancement in the morphology of the Ni3S2 on Ni foam from one-dimensional (1D) nanowires to a three-dimensional lettuce-like architecture with an internal nanowire network and corals at the edges. As the formation of this unique 3D lettuce-like architecture has resulted from the integration of 2D sheets with internal 1D nanowires, the combined features make it possible to realize ultra-high capacitance. This 3D architecture Ni3S2 electrode efficiently offers ultrahigh areal capacitance of 14.64 F cm−2, five times higher than that of nanowire arrays of 2.82 F cm−2 at the higher current density of 10 mA cm−2. A high value of 5.90 F cm−2 achieved, even at a larger current density of 50 mA cm−2, and retention of about 93% of the original capacitance over 7500 charge–discharge cycles when the applied current density is 150 mA cm−2, makes it a potential electrode material for large-scale energy storage devices with confined areas, like micro-supercapacitors. In addition, an as-fabricated asymmetric supercapacitor (ASC) exhibits areal capacitance of 597 mF cm−2, an energy density of 0.21 mWh cm−2, and a power density of 4.44 mW cm−2 at 10 mA cm−2, with high rate capability and capacitance retention of 79.5% over 10,000 cycles.

MnO2 nanosheets synthesized on nitrogen-doped vertically aligned carbon nanotubes as a supercapacitor electrode material

In the present study, nitrogen-doped vertically aligned carbon nanotubes (N-VACNTs) were synthesized on carbon cloth (CC) using the floating catalyst chemical vapor deposition (FCCVD) method, and MnO2 nanosheets were grown on them using the hydrothermal method to produce an N-VACNT@MnO2 nanocomposite structure. In this structure, a synergistic effect was obtained by combining N-VACNTs, which allow high electrical conductivity and fast ion transfer. In the galvanostatic charge-discharge (GCD) measurements performed separately in a three-electrode test cell using 1 M of Na2SO4 electrolyte, the specific capacitance of the N-VACNTs was found to be 53.7 F g−1 at a current density of 0.5 A g−1, and the specific capacitance of the N-VACNT@MnO2 electrode structure was found to be 497 F g−1. In addition, after 10,000 charge-discharge cycles at a current density of 10 A g−1, the N-VACNT electrode retained 99 % of its initial specific capacitance, while the N-VACNT@MnO2 electrode exhibited outstanding cyclic stability with 76 % of its initial specific capacitance. Moreover, in the as-fabricated asymmetric supercapacitor (ASC) using N-VACNTs and N-VACNTs@MnO2, the negative and positive electrodes achieved a stable voltage window of 0–1.7 V, with a specific capacitance of 59.4 F g−1 at a current density of 1 A g−1. Additionally, this ASC showed good cycling stability retaining 84 % of its specific capacitance at the end of 10,000 cycles. Therefore, this ASC structure with an energy density of 24.7 Wh kg−1 and a power density of 15.7 kW kg−1 are promising electrode materials for energy storage.

Amorphous V-doped Co3S4 yolk-shell hollow spheres derived from metal-organic framework for high-performance asymmetric supercapacitors

Metal-organic frameworks (MOFs) have appeared as a new option for constructing various functional materials for energy storage applications. In this work, a novel amorphous vanadium doped Co3S4 (V-CS) hollow sphere is synthesized through a facile method. Due to the unique structure, the amorphous V doped Co3S4 provides large amount of active sites for better storage energy. A remarkable specific capacitance of 1725 F g−1 at the current density of 0.3 A g−1 was achieved for this electrode. Further, the as-fabricated asymmetric supercapacitor device contains the V-CS electrode and activated carbon electrode (positive and negative, respectively) lead to outstanding performance with maximum energy and power densities of 88.29 Wh kg−1 and 486 W kg−1, respectively, that is better than traditional supercapacitors. In addition, the fabrication process illustrated in this article is facile, controllable, and economical, offering a viable method for fabricating the next generation of high-performance energy storage devices.

Structuring graphene quantum dots anchored CuO for high-performance hybrid supercapacitors

Pseudocapacitive materials with multiple oxidation/reduction modes can deliver an improved specific capacity and energy density owing to their reversible Faradic redox reactions. Also, ingeniously integrating a conductive carbon material and a pseudocapacitive transition metal to develop reactive compounds with a high conductivity is a plausible solution to make up for the deficiencies of individual oxides and hydroxides. In this study, we rationally design graphene quantum dots decorated CuO nanoframework (GQDs/CuO) for high-performance supercapacitors. Specifically, the Cu-MOF template as the precursor with a confined porosity and skeleton as well as Cu2+ as the central atoms is converted into CuO by in-situ growth and annealing. Afterward, the negatively charged GQDs can adsorb and uniformly anchor on the CuO surface via electrostatic and coordination interactions by a subsequent hydrothermal treatment. The deposited GQDs with carboxyl functional groups not only increase the surface area for electrochemical reactions but also modulate the conductivity and reduce interfacial resistance by allowing effective paths for electron transportation, leading to better redox reaction kinetics. As a supercapacitor cathode material, the integrated GQDs/CuO electrode affords a high specific capacitance of 729 F g−1 at a current density of 1 A g–1 and good-rate capability together with an improved cyclic performance (82.2% retention after 3000 cycles). Moreover, the as-fabricated asymmetric supercapacitor (ASC) with a large output voltage window of 1.5 V realizes an energy density of 32.2 W h kg–1 at power density of 748.9 W kg–1 with an enhanced cyclability over 8000 cycles, benefiting from the enriched electrochemical active sites and intimated connection between Cu species and doped GQDs. Thus, the adopted strategy may demonstrate an effective opportunity to explore high-performance electrode materials for energy harvesting.

Tunable agglomeration of Co3O4 nanowires as the growing core for in-situ formation of Co2NiO4 assembled with polyaniline-derived carbonaceous fibers as the high-performance asymmetric supercapacitors

Cobalt-based multicomponent oxides nanocomposites deliver extraordinary rate capabilities and electrochemical capacitance owing to the fast reaction kinetics, regarded as advanced electrodes for novel renewable energy harvest and conversion with great attention recently. Herein, by manipulating the concentration of fluoride ions (F−), the in-situ agglomeration states of cobalt oxides nanowires on 3D Ni Foam are investigated systemically, which benefiting the further growth of novel spinel Co2NiO4 through electrochemical routine. Acting as the positive electrode for supercapacitor, Co2NiO4@Co3O4 composite exhibits the specific capacitance as high as 1241.8 F g−1, together with the excellent rate capabilities of 92.83% retention with a 20-fold specific current increase. Based on the kinetics analysis, the capacitive contribution achieves 83.3% at the scan rates of 50 mV s−1. Matching core-shell like Co2NiO4@Co3O4 composites with self N,O-doped conducting polymers derived carbon, as-fabricated asymmetric supercapacitor (ASC) devices could deliver an energy density of 85.97 Wh kg−1 at the power density of 0.8 W kg−1. Taking advantage of Faradic redox electrodes couple with pseudocapacitive ones can be proved as a promising way to obtain high performance energy storage devices.

Design and optimization of asymmetric supercapacitors assembled by Platanus acerifolia seeds and ZIF-67 as precursors

Effective utilization of waste biomass has been a fascinating topic for the development of sustainable energy. An effective alkaline hydrothermal/pyrolysis process was designed to prepare highly porous carbons noted as HK-PSC800 using waste Platanus acerifolia seeds as precursors. A symmetric supercapacitor (SSC) device based the same two HK-PSC800 electrodes owns the high specific energy density (30.9 Wh kg−1 at a low power density of 500 W kg−1) with excellent rate capability. To further optimize the energy density of the device, two types of asymmetric supercapacitors (ASC) with a working potential window of 1.5 V are designed and assembled by using HK-PSC800 and Co3O4 derived from zeolitic imidazolate framework-67 as electrode materials. The specific energy density of as-fabricated ASC (Co3O4//HK-PSC800) with pure Co3O4 materials as the positive electrode is nearly the same as the SSC (HK-PSC800//HK-PSC800). However, the specific energy density of the other ASC (Co3O4@HK-PSC800//HK-PSC800) can be improved by 18.8% when 28 wt% Co3O4 is in-situ grown in HK-PSC800 as the positive electrode. This research proves that the suitable composition of ASC electrode materials helps us to develop biomass based carbons materials for application in the high-voltage and high-energy devices.

Controllable synthesis of Ni1-xCoxMoO4 with tunable morphologies for high-performance asymmetric supercapacitors

Recently, elemental doping has proven to be an efficient method to improve the electrochemical performance of nanomaterials. In this work, we successfully synthesized Ni1-xCoxMoO4 with tunable morphologies through Co-doping by a facile chemical co-precipitation method, among which Ni0.85Co0.15MoO4 displays an excellent specific capacitance (1301 F g−1 at 1 A g−1), which is higher than NiMoO4 electrode (1050.4 F g−1 at 1 A g−1) and Ni0.7Co0.3MoO4 electrode (755.2 F g−1 at 1 A g−1). In addition, Ni0.85Co0.15MoO4 electrode shows excellent cycling stability with 86% retention of its original capacitance after 3000 cycles. Additionally, an asymmetric supercapacitor (ASC) device can be fabricated using Ni0.85Co0.15MoO4/nickel foam (Ni0.85Co0.15MoO4/NF) as positive electrode and active carbon/nickel foam (AC/NF) as negative electrode. The as-fabricated ASC achieves a high energy density of 37.26 Wh kg−1 at the power density of 400 W kg−1, highlighting its potential application for the efficient energy storage devices.

High energy-density supercapacitor based on a novel conjugated poly (1, 5-diaminoanthraquinone)/intercalated graphene composite system

In this work, we select a novel multi-redox poly (1, 5-diaminoanthraquinone) (PDAAQ) as electroactive material and Cetyltrimethylammonium bromide (CTAB) modified graphene oxide (CGO) as conductive substrate. Benefit from the excellent dispersion of CGO in organic polymerization medium and the abundant functional groups on the surface of CGO, 1, 5-diaminoanthraquinone (DAAQ) monomers may covalently graft on the conducting substrates and realize the directional growth of PDAAQ via the in-situ chemical oxidative polymerization. In three-electrode system, the optimization of PDAAQ/CGO electrode exhibits a high specific capacitance of 760 F g−1 at 1 A g−1 and superior electrochemical stability of 90.4% after 10 000 cycles. Most importantly, the electrochemical kinetic behavior of PDAAQ/CGO electrode is studied in detail. The result indicates that the energy storage process of PDAAQ/CGO is a synergistic result of diffusion-controlled process and capacitive effects, and the latter one is dominant. According to the simulation calculation of kinetic model, the capacitive contribution ratio of PDAAQ/CGO can be as high as 80.6% at a scan rate of 50 mV s−1. Finally, the as-fabricated asymmetric supercapacitor (ASC) can deliver an energy density up to 41.1 W h kg−1 at a power density of 1000 W kg−1, indicating a great potential application in high performance supercapacitors.

Boosted charge transfer in p-n heterojunctions LaMoO3/GQDs negative electrode for all-solid-state asymmetric supercapacitor

The low energy density of asymmetric supercapacitor (ASC) is limited by the negative electrodes; thus, to further increase the energy density of ASCs, it is necessary to optimize the design of the negative electrode and the device. Constructing p-n heterojunctions may be a viable approach for enhancing the performance of the negative electrode, as it enhances the driving force for the built-in charge transfer and thereby it is beneficial for the charge transfer dynamics. Herein, we attempted to configure graphene quantum dots (GQDs) and LaMoO3 as a p-n heterojunction via one-step hydrothermal method, which shows outstanding capacitance performance. The specific capacitance of the LaMoG-3 (1396 F g−1 at 1 A g−1) was higher than the theoretical value for molybdenum trioxide (1256 F g−1). Moreover, the ASC is successfully assembled all-solid-state ASC with GQDs/Mn3O4 as the positive electrode and LaMoG-3 as the negative electrode. The as-fabricated ASC exhibited an ultra-high density of 235.8 Wh kg−1 and a power density of ~1000 W kg−1. One device can light the LED indicator for more than 11 min after only charging for 5 min. The above-mentioned results will open up promising research pathways for achieving excellent energy density and high power density.

Complexing of NixMny sulfides microspheres via a facile solvothermal approach as advanced electrode materials with excellent charge storage performances

Mixed metal sulfides with high specific capacitances and superior rate capabilities can meet the need of new materials for technological advancement of energy storage systems. We demonstrate in this study a facile fabrication of microspheres-like NixMny sulfides with different molar ratios of metallic salts through a one-step solvothermal route. The hierarchical NixMny sulfides-based compounds feature spherical architectures with relatively rough surfaces and assembled from ultrasmall and self-aggregated nanoprimary crystals. Especially, the NixMny sulfide (x/y = 1:1) presents an excellent battery-like performance with a high specific capacitance (219.4 mAh g−1 at current density of 1 A g−1) and a good rate capability (123 mAh g−1 at 50 A g−1), benefiting from the greatly improved faradaic redox processes boosted by the synergistic effect of Ni and Mn electroactive components and as well as fast mass transfer. Furthermore, the as-fabricated asymmetric supercapacitor based on NixMny sulfide (x/y = 1:1) presents a maximum energy density of 34 W h kg−1 at a power density of 868.1 W kg−1 with both superior rate and long-term cycling stabilities. In view of low cost and improved electrochemical performance, such integrated compound proposes a new and feasible pathway as a potential electrode configuration for energy storage devices.