AC Asymmetric Supercapacitor Device Research Articles

High‐Performance NiCo2O4/Graphene Quantum Dots for Asymmetric and Symmetric Supercapacitors with Enhanced Energy Efficiency

AbstractFor the sustainable growth of future generations, energy storage technologies like supercapacitors and batteries are becoming more and more common. However, reliable and high‐performance materials’ design and development is the key for the widespread adoption of batteries and supercapacitors. Quantum dots with fascinating and unusual properties are expected to revolutionize future technologies. However, while the recent discovery of quantum dots honored with a Nobel prize in Chemistry, their benefits for the tenacious problem of energy are not realized yet. In this context, herein, chemical‐composition tuning enabled exceptional performance of NiCo2O4(NCO)/graphene quantum dots (GQDs) is reported, which outperform the existing similar materials, in supercapacitors. A comprehensive study is performed on the synthesis, characterization, and electrochemical performance evaluation of highly functional NCO/GQDs in supercapacitors delivering enhanced energy efficiency. The high‐performance, functional NCO/GQDs electrode materials are synthesized by the incorporation of GQDs into NCO. The effect of variable amount of GQDs on the energy performance characteristics of NCO/GQDs in supercapacitors is studied systematically. In‐depth structural and chemical bonding analyses using X‐ray diffraction (XRD) and Raman spectroscopic studies indicate that all the NCO/GQDs composites crystallize in the spinel cubic phase of NiCo2O4 while graphene integration evident in all the NCO/GQDs. The scanning electron microscopy imaging analysis reveals homogeneously distributed spherical particles with a size distribution of 5–9 nm validating the formation of QDs. The high‐resolution transmission electron microscopy analyses reveal that the NCOQDs are anchored on graphene sheets, which provide a high surface area of 42.27 m2g−1 and high mesoporosity for the composition of NCO/GQDs‐10%. In addition to establishing reliable electrical connection to graphene sheets, the NCOQDs provide reliable 3D‐conductive channels for rapid transport throughout the electrode as well as synergistic effects. Chemical‐composition tuning, and optimization yields NCO/GQDs‐10% to deliver the best specific capacitance of 3940 Fg−1 at 0.5 Ag−1, where the electrodes retain ≈98% capacitance after 5000 cycles. The NCO/GQD‐10%//AC asymmetric supercapacitor device demonstrates outstanding energy density and power density values of 118.04 Wh kg−1 and 798.76 W kg−1, respectively. The NCO/GQDs‐10%//NCO/GQDs‐10% symmetric supercapacitor device delivers excellent energy and power density of 24.30 Wh kg−1 and 500 W kg−1, respectively. These results demonstrate and conclude that NCO/GQDs are exceptional and prospective candidates for developing next‐generation high‐performance and sustainable energy storage devices.

Microwave-assisted hydrothermal synthesis of NiO/Co3O4 nanosheets decorated on three-dimensional porous graphene for supercapacitors

Electrode material is the key part of capacitor, which seriously affects the electrochemical performance of supercapacitor. NiO/Co3O4 nanosheets decorated on three-dimensional porous graphene (NiO/Co3O4/3DGN) have been prepared though a microwave-assisted hydrothermal method. It is found that NiO can affect the crystallinity and morphology of Co3O4 in the composites. The composites possess excellent electrochemical performance with the special capacity of 1303.9 F g−1 (at 1 A g−1). The assembled NiO/Co3O4/3DGN//AC asymmetric supercapacitor device achieved an energy density of 18.8 Wh kg−1 at a power density of 750.4 W kg−1 and maintained 92.7% of the initial capacitance after 10,000 cycles. The excellent capacitance and rate capability of the composites can be attributed to its unique structural features. The large surface area and the rich porosity provide more activate sites and facilitate the fast diffusion of electrolyte during the charge/discharge process. The direct contact between NiO/Co3O4 nanosheets and 3DGN ensures effective charge transport.

Effect of fluoride (CoF2) based electrode material for high energy and power density asymmetric flexible supercapacitors

Herein, an asymmetric supercapacitor (ASC) device was assembled by employing the pristine CoF2 as active positive electrode material and activated carbon (AC) as negative electrode material. The CoF2 electrode exhibited an outstanding electrochemical behavior with enhanced specific capacitance (Cs) of 872 F/g at 1 A/g current density in three electrode configurations. The reversible Faradaic redox reactions in CoF2 instigate the formation of cobalt-oxyfluorides and generating the mixed valence state of Co (Co2+ and Co3+) which improves its electrical conductivity and electrochemical behaviors. Furthermore, the room temperature paramagnetic nature of CoF2 increases the gradient force of ions which could possibly increase the redox reactions at the electrolyte/electrode interface. The constructed asymmetric device structure of CoF2//AC revealed a quasi-rectangular shaped cyclic voltametric curve and symmetrical semi-triangular shaped galvanostatic charge-discharge profiles, respectively, which affirms the combined electric double layer capacitance and pseudocapacitive nature by its hybrid assembly. Hence, the constructed CoF2//AC ASC demonstrated a remarkable specific capacitance of 141 F/g, energy density of 44.06 Wh.Kg−1, and power density of 422.97 W.Kg−1 at 1 A/g with the high cell voltage of 1.5 V. The CoF2//AC ASC device retained c.a. 92 % of its initial capacitance and attained over 96 % of Coulombic efficiency after 2000 cycles of charge-discharge profiles at 1 A/g, which suggests the high electrochemical stability. This admirable electrochemical performance and the origin towards the magneto-capacitance of CoF2 could pave a new way to explore next generation high-performance supercapacitors.

Zn2+ doped Ni3(NO3)2(OH)4 nanoflower spheres for electrochemical applications

In this present work, Ni3(NO3)2(OH)4 doped with Zn2+ ions are prepared by a solvothermal method using Ni(NO3)2·6H2O, Zn(NO3)2·6H2O, C16H33(CH3)3NBr (CTAB) and C2H5OH as raw materials. Characterization methods such as X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) are used to analyze the materials. Cyclic voltammetry (CV) and galvanostatic charge–discharge curves (GCD) are employed to compare the electrochemical performance of materials with different doping amounts. The electrochemical test results show that doping with Zn2+ significantly enhances the poor electrical conductivity of Ni3(NO3)2(OH)4. Electrochemical tests reveal that the doping amount of 0.4 mmol has the best electrochemical performance with a mass-specific capacitance of 1832 F·g−1 at a current density of 1 A·g−1 in the three-electrode system which is much higher than that of undoping sample (771 F·g−1). Additionally, the assembled NiZn-0.4//AC asymmetric supercapacitor device (ASC) has an energy density of 61.9 Wh·kg−1 at a power density of 747.8 W·kg−1. The Coulombic efficiency retention of the ASC device remains at 98 % after 2000 galvanostatic charge–discharge circles, and the specific capacitance retention is 91 % of the initial value. The doping of Zn2+ provides a valuable approach for enhancing the conductivity and specific capacitance of nickel-based supercapacitor electrode materials.

Amorphous-crystalline CoMoS4 with high mass loading for high-performance asymmetric supercapacitors

CoMoS4 as electrode material in supercapacitors is attributable to the high theoretical capacitance of CoSx and MoS2. However, there is still room for improvement in its capacitive performance. Besides, electrode material possessing good electrochemical properties is usually restricted to low mass loading. In this work, four amorphous-crystalline CoMoS4 materials were obtained by a precipitation process through altering additive in a mixed solution and subsequent by a thermal treatment process. As-synthesized four CoMoS4 materials consist of numerous amorphous phase accompanying with a very few crystalline phase as well as display different morphology and structure. All CoMoS4 materials with high mass loading achieve high specific capacitance. At 0.5 A g−1, CoMoS4–1, CoMoS4–2, CoMoS4–3, and CoMoS4–4 possess a specific capacitance of 1720.9, 2560.6, 1914.5, and 2498.7 F g−1, respectively. Amongst the four CoMoS4, CoMoS4–2 delivers the highest specific capacitance at 0.5∼4 A g−1. However, the specific capacitance of CoMoS4–3 reaches the largest value at 8∼16 A g−1. CoMoS4–3 and CoMoS4–1 exhibit good rate capability, much better than those of CoMoS4–2 and CoMoS4–4. CoMoS4–3 owns good comprehensive supercapacitive performances related to its optimum amorphous-crystalline ratio, suitable morphology and structure. The assembled CoMoS4–3//AC asymmetric supercapacitor (ASC) using CoMoS4–3 as the positive electrode and activated carbon (AC) as the negative electrode provides a superior energy density (59.2 Wh kg−1 at 425 W kg−1), which is superior to those of previously reported CoMoS4-based ASC devices. In addition, the ASC device displays a satisfactory cycle stability of 85.5% after 2000 cycles at 2 A g−1. This work shows a promising material applied in supercapacitors.

Electrochemically enhanced battery-type Ni substituted CaMo-MOF electrodes: Towards futuristic energy storage system

Constructing a physiochemically proficient electrode for energy application is of pioneer in commercializing electronic devices. In that view, we engineered the nickel-incorporated calcium molybdate (NCMF) metal-organic framework (MOFs) with nanosheets in 3D floral morphology using the facile hydrothermal method. The floral structured NCMF0.5 MOFs when employed as the electrode in supercapacitor (SC) application exhibit impressive electrocatalytic performance. The advantage of a well-defined arrangement of petal-like sheets hierarchically, makes the KOH electrolyte access the inner area of the electrode resulting in a distinguished specific capacitance value of 822 F/g at 1 A/g current density. The fabricated NCMF0.5||AC asymmetric supercapacitor device (ASC) on account of the high specific surface area with more metal active sites contributes to achieving excellent energy and power density of 45 Wh/kg and 750 W/kg at the current density of 1 A/g. The stability and reproducibility of the constructed ASC device were 84 % and 99.4 %, respectively. Hereby, our findings clearly elucidate the substantial prospects attained by the synergistic effect in NCMF0.5 MOFs, which could be beneficial for developing sophisticated energy storage devices.

Battery-type WS2 decorated WO3 nanorods for high-performance supercapacitors

Active sites enriched WS2 quantum dot decorated WO3 electrode was designed for supercapacitor application, using hydrothermal and sonication techniques. The WS2/WO3 electrode exhibited a specific capacitance of 570.1 F/g at 1 A/g due to numerous active sites, and facile electrolyte accessibility. The battery-type WS2/WO3//AC asymmetric supercapacitor device achieved an energy and power density of 55.6 Wh/kg and 1335 W/kg, and a notable retention capacitance and columbic efficiency of 87.4 % and 99.8 % for 5000 cycles at 6A/g, respectively. The results highlight WS2/WO3 as a promising electrode for supercapacitors.

Ni-foam modified binder-free Ni3S2 electrode for improved cyclic performance in asymmetric supercapacitors

The rising interest in binder-free electrode supercapacitors can be attributed to their outstanding electrochemical performance and seamless compatibility with a diverse range of electronic devices. This study show cases the successful development of a binder-free electrode, facilitating the direct growth of Ni3S2 nanostructures on Ni foam substrate, resulting in the development of high-performance supercapacitors. The formation of 0.5@Ni3S2, 1@Ni3S2, 2@Ni3S2, and 3@Ni3S2 with a heazle-woodite-phase structure was confirmed through X-ray diffraction, grown by the direct sulfurization of the Nickel foam surface into Ni3S2 using a straightforward one-step hydrothermal process with varying quantities of sulfur source. Field emission scanning electron microscopy (FESEM) was employed to visualize the continuous porous micro-networks on Ni foam surface. In a three-electrode system, the supercapacitor exhibited a capacitance of 418.46 F/g at 2 A/g. Furthermore, the Ni3S2//AC asymmetric supercapacitor device demonstrated remarkable performance with a specific capacitance of 192.24 F/g, an energy density of 65.42 Wh/kg, and a power density of 2966.14 W/kg @ 1 A/g. Impressively, even after undergoing 8000 charge-discharge cycles, these devices retained 51% of their initial capacitance.

A novel mesoporous CoMn2O4@rGO composite as an electrode material for hybrid supercapacitor for energy storage device applications

Cobalt‑manganese spinel oxide (CoMn2O4) was hybridized with reduced graphene oxide (rGO) via a facile hydrothermal process and a highly porous three-dimensional (3D) structure was constructed. The phase structure, chemical bands, morphology and chemical state of the synthesized powders were investigated by X-ray diffraction (XRD), Raman spectroscopy, field emission secondary electron microscopy (FE-SEM) and X-ray photoelectron spectroscopy (XPS). CoMn2O4@rGO electrode delivered high specific capacitance of 1578 Cg−1at 1 Ag−1 in 1.0 M KOH electrolyte and an outstanding cycling stability with 94.2 % retention over 5000 cycles, suggesting the great potential application of this material in advanced energy storage device. The rGO makes great contributions to hybrid through supplying a conductive support for CoMn2O4, resulting in the prominent specific capacitances and outstanding cycle stability. Besides, the assembled CoMn2O4@rGO//AC asymmetric supercapacitor (ASC) displays the maximum energy density of 35.6 Whkg−1 at a power density of 8916.9 Wkg−1. Significantly, an ultralong cycling life of 98.2 % capacitance retention is achieved for the ASC device after 10,000 charge/discharge cycles at 1 Ag−1.

Ultrafine nanoparticles of tin-cobalt-sulfide decorated over 2D MXene sheets as a cathode material for high-performance asymmetric supercapacitor

The design of electrode materials for improved electrochemical properties and stable geometric configuration is known as effective research in developing the electrochemical capability of supercapacitors (SCs). However, there is a difficulty in designing innovative composite material with excellent electrical conductivity and superior specific capacity by way of low cost and easy synthesis process. Herein, for the first time, a stable Sn-Co-S/MXene hybrid material is fabricated through the electrochemical assembly by combining positively charged ultrafine Sn-Co-S nanoparticles (NPs) and negatively charged 2D Ti3C2Tx (MXene) sheets due to electrostatic interaction. The Sn-Co-S/MXene hybrid material has displayed excellent electrochemical performance with an ultrahigh specific capacity of 305.71 mA h gm−1 at 1 A g−1 and capacity retention of 94.8% after 10, 000 charge–discharge cycles. The Sn-Co-S/MXene hybrid material of high electrochemical performance has improved charge transfer kinetics during the charge–discharge process, due to the synergistic coupling effect between ultrafine Sn-Co-S nanoparticles and MXene sheets. Furthermore, the Sn-Co-S/MXene//activated carbon (AC) asymmetric supercapacitor (ASC) device has been configured with the assistance of Sn-Co-S/MXene as cathode and AC as anode materials. The Sn-Co-S/MXene//AC ASC device exhibits a stable potential window of 1.7 V, a high specific capacitance of 108.50F g−1 at 1 A g−1, and an energy density of 43.55Wh kg−1 at a power density of 0.83 kW kg−1. This study validates the design and application of highly electroactive Sn-Co-S/MXene hybrid electrode material for ultrastable asymmetric supercapacitors.

RGO‐Wrapped Hexagonal WO3 Nanorod as Advanced Electrode Material for Asymmetric Electrochemical Supercapacitors

The multiple oxidation states of redox‐active materials enable them to store high‐energy better than the commonly used carbon‐based electrode materials. Accounting for these advantages, designing asymmetric supercapacitors by coupling redox‐active materials as positive electrodes with carbon‐based negative electrodes becomes a very attractive strategy. Herein, reduced graphene oxide‐wrapped hexagonal WO3 nanorod (rGO‐WO3 NR) by simple hydrothermal synthesis method is synthesized. Because of improved reaction kinetics resulting from the close contact between rGO and WO3 NRs, rGO‐WO3 NR demonstrates superior electrochemical properties than pure WO3. Motivated by the very high areal capacitance (2.5 F cm−3 at the applied current of 30 mA cm−2), an asymmetric SC device by combining rGO‐WO3 NR with activated carbon is assembled. The as‐assembled rGO‐WO3 NR//activated carbon asymmetric supercapacitor device demonstrates outstanding electrochemical performance in an operating voltage window of 1.2 V, admirable cycling stability of ≈95% (even after 14 000 cycles), with an energy density of 24.1 Wh Kg−1 at a power density of 1532.6 W Kg−1. These demonstrate the combination of redox‐active materials with high energy density can importantly boost the energy storage capacity of a supercapacitor.

Construction of Three-Dimensional Co(PO3)2/Cu3P Heterostructure for High-Rate Supercapacitors

The exploration for pseudocapacitive materials that employ surface Faradaic reactions to store charges in supercapacitors is highly desirable. However, the traditional transition metal oxides with poor electronic conductivity and sluggish reaction kinetics lead to a poor rate capability. In this study, a Co(PO3)2/Cu3P heterostructure is fabricated by a facile in situ phosphorization process. Benefiting from the formation of heterojunctions and modified electronic structures, the electronic transfer and ionic diffusion kinetics have been significantly improved. Specifically, the Co(PO3)2/Cu3P heterostructure electrode exhibits a capacitance of 787.1 F g–1 at 1.0 A g–1 and a superior rate capability of 78.4% capacitance retention at 20.0 A g–1. The fabricated Co(PO3)2/Cu3P//AC asymmetric supercapacitor device with this Co(PO3)2/Cu3P heterostructure as the positive electrode shows an excellent energy density of 39.8 Wh kg–1 at a power density of 936.7 W kg–1 and satisfactory cyclic stability. This design of a metaphosphate based heterostructure provides a path to explore electrode materials with both high capacitance and superior rate capability.

Phosphorus doped molybdenum disulfide regulated by sodium chloride for advanced supercapacitor electrodes.

As a pseudocapacitor electrode material, molybdenum disulfide (MoS2) usually shows inferior capacity, rate capability and cyclability. Structural regulation and heteroatom doping are the available methods to ameliorate the electrochemical properties of MoS2. Herein, phosphorus doped molybdenum disulfide regulated by sodium chloride (SP-MoS2) is successfully synthesized using phosphomolybdate acid as a molybdenum source and an in situ dopant and sodium chloride (NaCl) as a structural regulator. Under the structural regulation of NaCl, the SP-MoS2 nanosheets exhibit an interweaved architecture with a large interlayer spacing of 0.68 nm. Owing to the in situ P doping and large specific surface area (21.0 m2 g-1), the SP-MoS2 electrode possesses a maximum capacity of 564.8 F g-1 at 1 A g-1 and retains 56.3% of the original capacity at 20 A g-1. Density functional theory (DFT) calculations indicate that SP-MoS2 displays a high K+ average adsorption energy of -3.636 eV. In addition, the fabricated SP-MoS2//AC asymmetric supercapacitor device displays an energy density of 22.8 W h kg-1 at 759 W kg-1.

Outstanding energy storage performance in Co[sbnd]Fe bimetallic metal-organic framework spindles via decorating with reduced graphene oxide nanosheets

Reduced graphene oxides (rGOs; 3 and 5 wt%) decorated on CoFe bimetallic metal-organic framework (CoFe-MOF) have been synthesized by the ultrasonic-assisted solvothermal method. XRD patterns did not show any significant amendment in crystalline structure of MIL-88A and 3 % rGO@CoFe-MOF revealed better crystallinity than other samples. TEM and FESEM images clearly demonstrated that the rGO nanosheets are coated on the CoFe-MOF spindles. BET and BJH analyzes showed that the 3 % rGO@CoFe-MOF composite had the highest specific surface area (149 m2 g−1) and mean pore size (1.79 nm) compared to the other samples. The MOF and rGO decorated on MOF samples were deposited on Ni foam (NF) and their electrochemical performance as binder-free electrodes was evaluated in 3 M KOH electrolyte. The 3 % rGO@CoFe-MOF/NF electrode exhibits outstanding specific capacitance of 2069.1 F g−1 at a current density of 0.5 A g−1 and good cycling stability with 91.3 % capacitance retention at a high current density of 10 A g−1 after 5000 cycles. The assembled 3 % rGO@CoFe-MOF//activated carbon asymmetric supercapacitor device delivers a maximum energy density of 75.8 Wh kg−1 at a power density of 700 W kg−1. The results exhibit that the 3 % rGO@CoFe-MOF can be a propitious electrode material in energy storage devices.

Morphology-controlled synthesis of metal-organic frameworks derived hollow nanostructures for supercapacitor application

The design and construction of nanostructured electrode materials are regarded as a key factor for the supercapacitor. In this paper, we demonstrated a self-templated method which hollow structure with different morphologies derived from ZIF-67 (Zeolitic imidazolate frameworks-67) as electrode materials can be synthesized. By the assistance of surfactant and proper sulfurization, the hollow cobalt sulfides with dodecahedron, cube, and plate-like morphologies can be obtained. The optimized hollow cobalt sulfide dodecahedron electrode displayed a high specific capacitance of 684.08 F g−1 at a scan rate of 5 mV s−1, while the hollow cobalt sulfide nanoplate, in contrast, showed a highest capacitive retention. Also, they were further employed as the positive electrode in asymmetric supercapacitors. The assembled hollow cobalt sulfide dodecahedron//activated carbon asymmetric supercapacitor device exhibited a maximum operating potential window of 1.5 V, high volumetric capacitance of 3511 mF cm−3, the maximum energy density of 1.17 Wh cm−3 and the maximum power density of 0.697 W cm−3. This part of the result revealed the relationship of different morphologies-hollow metal−organic framework structures with the electrochemical performance in supercapacitor application.

Hierarchical Fe2O3 hexagonal nanoplatelets anchored on SnO2 nanofibers for high-performance asymmetric supercapacitor device

Metal oxide heterostructures have gained huge attention in the energy storage applications due to their outstanding properties compared to pristine metal oxides. Herein, magnetic Fe2O3@SnO2 heterostructures were synthesized by the sol–gel electrospinning method at calcination temperatures of 450 and 600 °C. XRD line profile analysis indicated that fraction of tetragonal tin oxide phase compared to rhombohedral hematite was enhanced by increasing calcination temperature. FESEM images revealed that hexagonal nanoplatelets of Fe2O3 were hierarchically anchored on SnO2 hollow nanofibers. Optical band gap of heterogeneous structures was increased from 2.06 to 2.40 eV by calcination process. Vibrating sample magnetometer analysis demonstrated that increasing calcination temperature of the samples reduces saturation magnetization from 2.32 to 0.92 emu g-1. The Fe2O3@SnO2-450 and Fe2O3@SnO2-600 nanofibers as active materials coated onto Ni foams (NF) and their electrochemical performance were evaluated in three and two-electrode configurations in 3 M KOH electrolyte solution. Fe2O3@SnO2-600/NF electrode exhibits a high specific capacitance of 562.3 F g-1 at a current density of 1 A g-1 and good cycling stability with 92.8% capacitance retention at a high current density of 10 A g-1 after 3000 cycles in three-electrode system. The assembled Fe2O3@SnO2-600//activated carbon asymmetric supercapacitor device delivers a maximum energy density of 50.2 Wh kg-1 at a power density of 650 W kg-1. The results display that the Fe2O3@SnO2-600 can be a promising electrode material in supercapacitor applications.

Promoting the cyclic and rate performance of nickel hydroxide with ZnO via electrodeposition for supercapacitor

A novel Ni(OH)2/ZnO hydrangea-like structure is prepared via a facile electrodeposition strategy with the Ni(OH)2 flower-like particles growing on the ZnO layered carrier. This flower-like structure can take advantage of both ZnO and Ni(OH)2, leading to a fast ion/electron transport speed and structural stability, finally, attaining an outstanding specific capacitance (2264.55 F g−1 at 0.5 A g−1), excellent rate performance (601.09 F g−1 at 30 A g−1) and cycle stability (maintain 94.9% specific capacitance after 5000 cycles). The Ni-OH/ZnO//AC asymmetric supercapacitor device achieves a high energy density of 68.44 Wh kg−1 at a power density of 400 W kg−1, demonstrating great potential as an electrode material for energy storage devices. The mechanism of synergistic effect of Ni(OH)2 and ZnO mutually supporting composite structure to improve electrochemical properties is innovatively proposed.

Fe incorporated ternary layered double hydroxides with remarkably improved electrochemical performance towards asymmetric supercapacitors

A nanocomposite composed of ternary NiCo2Fex layered double hydroxide (LDH) anchored to g-C3N4 was prepared for high-performance supercapacitor. In this novel material, Fe played an important part in enhancing the energy storage performance of the NiCo2Fex-LDH. Density functional theory calculations on this material showed that Fe improved the Fermi level of NiCo2Fex-LDH, moreover, the stability of the N–Ni bonds were formed after combining NiCo2Fex-LDH with g-C3N4. The electrochemical test results for this material showed that the NiCo2Fe1.0-LDH@g-C3N4 electrode yielded an extremely high specific capacitance of 1550 F g−1 at a current density of 1 A g−1, which was far superior to that of the NiCo2-LDH@g-C3N4 electrode. An assembled NiCo2Fe1.0-LDH@g-C3N4//AC asymmetric supercapacitor device delivered an impressive specific capacitance of 129.64 F g−1, in addition, the device yielded the energy density of up to 35 Wh kg−1 at the corresponding power density of 701 W kg−1 with superior cycling performance (92.7% capacitance retention after 5000 cycles). The NiCo2Fe1.0-LDH@g-C3N4//AC asymmetric supercapacitors easily powered a blue LED. The results of this work provide a promising research path for constructing high-performance of NiCo2-LDH-based nanostructured electrodes materials, which can be employed in new energy storage devices.

Synchronous Defect and Interface Engineering of NiMoO4 Nanowire Arrays for High-Performance Supercapacitors.

Developing high-performance electrode materials is in high demand for the development of supercapacitors. Herein, defect and interface engineering has been simultaneously realized in NiMoO4 nanowire arrays (NWAs) using a simple sucrose coating followed by an annealing process. The resultant hierarchical oxygen-deficient NiMoO4@C NWAs (denoted as “NiMoO4−x@C”) are grown directly on conductive ferronickel foam substrates. This composite affords direct electrical contact with the substrates and directional electron transport, as well as short ionic diffusion pathways. Furthermore, the coating of the amorphous carbon shell and the introduction of oxygen vacancies effectively enhance the electrical conductivity of NiMoO4. In addition, the coated carbon layer improves the structural stability of the NiMoO4 in the whole charging and discharging process, significantly enhancing the cycling stability of the electrode. Consequently, the NiMoO4−x@C electrode delivers a high areal capacitance of 2.24 F cm−2 (1720 F g−1) at a current density of 1 mA cm−2 and superior cycling stability of 84.5% retention after 6000 cycles at 20 mA cm−2. Furthermore, an asymmetric super-capacitor device (ASC) has been constructed with NiMoO4−x@C as the positive electrode and activated carbon (AC) as the negative electrode. The as-assembled ASC device shows excellent electrochemical performance with a high energy density of 51.6 W h kg−1 at a power density of 203.95 W kg−1. Moreover, the NiMoO4//AC ASC device manifests remarkable cyclability with 84.5% of capacitance retention over 6000 cycles. The results demonstrate that the NiMoO4−x@C composite is a promising material for electrochemical energy storage. This work can give new insights on the design and development of novel functional electrode materials via defect and interface engineering through simple yet effective chemical routes.

Double metal ions synergistic effect in the Ni-doped Co(OH)(BA) nanobelts for enhanced supercapacitor performance

In this work, we report the synthesis and energy storage application of a Ni-doped hybrid inorganic-organic cobalt hydroxide ultrathin nanobelt with benzoate anion intercalation. The sample was prepared by a one-step hydrothermal method without any surfactants and adhesives. The layered cobalt hydroxide intercalated with benzoate anion is a promising cathode material due to the large interlayer distance, which improves ion flow efficiency. Importantly, Ni-doped Co(OH)(BA) enhances the electrochemical performance of supercapacitors, thereby achieving an ultra-high specific capacitance of 1664 F/g at 5 A/g, outstanding rate performance of 32.5% from 5 to 50A/g, low RESR of 4.8 Ω, and long capacity retention rate of 83% after 8000 cycles. Meanwhile, the combined Ni–Co(OH)(BA)//AC asymmetric supercapacitor device provides a high energy density of 47.5 Wh/kg at a power density of 850 W/kg with a long capacity retention of 91% after 8000 cycles.