High-performance Hybrid Supercapacitors Research Articles

High-performance Zn-ion hybrid supercapacitors enabled by rationally designed hierarchical SiC@C quasi-aligned nanoarrays

In the present work, we report the exploration of rationally designed electrodes based on quasi-aligned nanoarrays composited by the cores of SiC nanowires and shells of sulfur-doped porous carbons (SiC@PC-S), which are directly employed as the free-standing electrodes for Zn-ion hybrid supercapacitors. They behave an ultrahigh areal capacitance of 38.24 mF/cm2 at a scan rate of 10 mV/s, with an exceptional rate capability (~20.67 mF/cm2 even at 1000 mV/s). The as-constructed hybrid supercapacitors deliver a remarkable energy of 10.6 μWh/cm2, which is the highest one among SiC-based supercapacitors ever reported. Moreover, such hybrid devices exhibit a high power density of 7.2 mW/cm2 and a robust cycle stability with ~97 % capacitance retention after 5000 cycles at 2 mA/cm2, representing their promising practical applications.

Triple-shelled nickel-cobalt-manganese sulfides hollow spheres for advanced hybrid supercapacitors

To design high-performance hybrid supercapacitors, positive and negative electrode materials with superior electrochemical features are needed. This paper proposes the fabrication of a hybrid supercapacitor using hollow ternary mixed metal sulfides as a positive electrode and iron oxide-decorated nitrogen-doped reduced graphene oxide (Fe3O4/N-rGO) as the negative electrode. Triple-shelled hollow spheres of nickel-cobalt-manganese-sulfides (NCMS) are synthesized using an optimum calcination temperature, followed by post-sulfurization. As the positive electrode, NCMS produced at 350 °C (NCMS-350) displays a high specific capacity of 797 C g−1 (1885 F g−1) at 1 A g−1 with excellent rate capability (79.5% at 20 A g−1). On the other hand, the negative Fe3O4/N-rGO electrode is synthesized hydrothermally without post-calcination and exhibits a maximum specific capacity of 454 C g−1 (378 F g−1) at 1 A g−1. Moreover, the NCMS-350//Fe3O4/N-rGO hybrid device delivers an impressive energy density of 67.9 Wh kg−1 at 474 W kg−1. These promising electrochemical performances provide a facile strategy for optimizing and integrating electrode materials to develop high-performance hybrid supercapacitors for efficient energy storage.

Optimized Synthesis of Nanostructured Trimetallic Mn–V–Fe Selenides with Battery-Type Behavior for High-Performance Hybrid Supercapacitors

The design and synthesis of innovative materials with a specific architecture are necessary to advance the supercapacitor industry. Recently, transition metal selenides have been identified as an auspicious type of material for energy storage devices due to their enormous electronic conductivity and high theoretical capacitance. Consequently, mono- and diselenides have been extensively investigated. Trimetallic selenides, however, are infrequently reported, and their charge storage mechanism is still not fully understood. Herein, earth-abundant trimetallic Mn–V–Fe selenide (MVF-Se) is successfully fabricated via a two-step hydrothermal approach. The chemical composition, structure, and morphology of the as-synthesized material have been thoroughly characterized. The electrochemical tests revealed that the MVF-Se electrode possesses a high areal capacitance of 16,212.88 mF cm–2 at 1 mA cm–2 in the three-electrode configuration. In addition, the assembled asymmetric supercapacitor device by coupling MVF-Se and activated carbon as the positive and negative electrodes, respectively, demonstrates a desirable 0.56 mWh cm–2 energy density at a 1.0 mW cm–2 power density. After 17,000 charge/discharge cycles, the device exhibits robust cyclic stability with a 95% capacitance retention.

2D coordination unsaturated Ni-MOFs hierarchical nanosheets with internal electric fields for high-performance hybrid supercapacitors

The poor intrinsic electronic conductivity and low-exposure electroactive sites of MOFs limit their practical application in energy storage. Herein, the coordination unsaturated nickel-based metal organic frameworks (Ni-MOFs) were prepared by one-step solvothermal method via adjusting the molar ratio of metal salts to organic ligands (RM/L). The coordination unsaturated degree and morphology of the materials can be controlled by adjusting RM/L. When the RM/L is 2, the obtained Ni-MOF 2:1 is a two-dimensional (2D) hierarchical nanosheets made of interwoven ultra-thin nanoribbons. The 2D hierarchical nanosheets structure of Ni-MOF 2:1 can not only expose more electroactive sites, but also promote ions diffusion. The density functional theory (DFT) simulations reveal that the coordination unsaturated centers can narrow the band gap, thus resetting the internal electric field and improving the conductivity of Ni-MOF 2:1. Benefit from abundant electroactive sites, rapid ions diffusion and improved electrical conductivity, the Ni-MOF 2:1 shows a high specific capacity of 746 C g−1 at 1 A g−1 and excellent cycling stability of 89.7 % capacity retention after 10,000 cycles at 10 A g−1. The hybrid supercapacitor (HSC) assembled with Ni-MOF 2:1 as cathode and activated carbon (AC) as anode has a maximum energy density of 53.1 Wh Kg−1 at 799.9 W Kg−1. This work provides a promising strategy for the rational design of MOFs-based electrode materials for high performance HSC. Moreover, compared with the studies using MOFs derivatives as electrode materials, the direct use of Ni-MOFs as electrode materials in this study is of great significance to avoid energy waste and maintain the inherent advantages of MOFs.

High-performance hybrid supercapacitors with N and O codoped mesoporous carbon-supported NiCo2S4 electrodes

High-capacitance electrode materials are extremely useful in high-performance supercapacitors. Here, an N and O codoped mesoporous carbon (MPC) material is reported. The MPC-3 exhibited a substantial capacitance of 306.6 F g−1 at 1 A g−1. NiCo2S4 grown in situ on the MPC-3 formed the composite material (NCS/MPC). This composite material, 0.4-NCS/MPC-3, showed a specific capacitance of 551.8C g−1 at 1 A g−1; cyclic capacity was exceptional 95.9%, after 10,000 cycles. A 0.4-NCS/MPC-3//MPC-3 HSC device exhibited an energy density of 57.6 Wh kg−1 at a power density of 750 W kg−1. The device displayed a stable capacity of 90.2% after 10,000 cycles. This process is inexpensive and simple, highlighting value in the field of energy storage.

Block Copolymer-Directed Facile Synthesis of N-Doped Mesoporous Graphitic Carbon for Reliable, High-Performance Zn Ion Hybrid Supercapacitor.

Ordered mesoporous carbons (OMCs) are promising materials for cathode materials of a Zn ion hybrid capacitor (Zn HC) due to their high surface area and interconnected porous structure. Graphitization of the framework and nitrogen doping have been used to improve the energy storage performance of the OMCs by enhancing electrical conductivity, pseudocapacitive reaction sites, and surface affinity toward aqueous electrolytes. Thus, when both methods are simultaneously implemented to the OMCs, the Zn HC would have improved energy storage performance. Herein, we introduce a facile synthetic method for N-doped mesoporous graphitic carbon (N-mgc) by utilizing polystyrene-block-poly(2-vinlypyridine) copolymer (PS-b-P2VP) as both soft-template and carbon/nitrogen sources. Co-assembly of PS-b-P2VP with Ni precursors for graphitization formed a mesostructured composite, which was converted to N-doped graphitic carbon through catalytic pyrolysis. After selective removal of Ni, N-mgc was prepared. The obtained N-mgc exhibited interconnected mesoporous structure with high nitrogen content and high surface area. When N-mgc was employed as a cathode material in Zn ion HC, excellent energy storage performance was achieved: a high specific capacitance (43 F/g at 0.2 A/g), a high energy density of 19.4 Wh/kg at a power density of 180 W/kg, and reliable cycle stability (>3000 cycles).

High-valent bimetal Ni2P/Co2P heterostructures induced by Mo doping as an advanced electrode for hybrid supercapacitors

The development of advanced electrode materials with fast reaction kinetics and optimized morphology is key to achieving high-performance hybrid supercapacitors with high energy density and outstanding cycling performance. Herein, an ingenious strategy is developed to prepare M doped Ni2P/Co2P (M = Cu, Zn, Mo) bimetallic phosphide electrode materials with heterostructure. For the Mo-doped Ni2P/Co2P, the unique morphology of hollow nanocubes consisting of ultrathin nanosheets facilitates the availability of more electrochemical active sites and relieves the deformational effects. In addition, the formation of heterogeneous structures modulates the electronic structure and the causes redistribution of interfacial charges, while the introduction of Mo cation can promote the formation of more high-valent Ni/Co sites, which synergistically accelerate reaction kinetics. Consequently, the Mo-Ni2P/Co2P hollow nanocubes with heterogeneous interfaces exhibit an optimal specific capacitance of 2300 F g−1 at 1 A g−1. In addition, when combined with activated carbon (AC) as a hybrid supercapacitor (HSC), the Mo-Ni2P/Co2P //AC device displays an energy density of 35.56 Wh kg−1 at a splendid power density of 800.0 W kg−1 and a remarkable cycling performance (the capacitance retention of 84.83% after 15,000 cycles). This study reveals that the introduction of Mo cation induces the formation of high-valence Ni/Co, providing a meaningful reference for the construction of high-performance metal phosphides with unique morphology and massive phase boundaries.

Enhanced performance with ionic and organic redox-couple electrolytes on MTMO anchored CQD nanocomposites and renewable carbon-based asymmetric flexible supercapacitor

The work utilizes a hybrid approach at electrode and electrolyte systems to fabricate a high-energy density supercapacitor. Hybrid nanocomposite electrodes were fabricated using a facile hydrothermal synthesis. The kinetics were studied by preparing in-situ and ex-situ nanocomposites. The in-situ preparation delivers a homogeneous flower petal-like interconnected porous morphology with an appreciable BET surface area of 97 m2 g−1. The actual electrochemical performance was analyzed by accounting for discharge area instead of discharge time to avoid discrepancies related to hybrid energy storage systems. The three-electrode measurement suggests that the electrode delivers an excellent specific capacitance of 3802 F g−1 at 1 A g−1. In the asymmetric configuration, the device reveals excellent actual specific capacitance of 292 F g−1 at 1 A g−1. However, upon adding 0.02 M KI as redox mediators in a traditional electrolyte (6 M KOH), a ∼37% increase in specific capacitance is achieved without the degradation in the device stability. The nanoarchitecture porous morphology and modification in traditional electrolyte enables a high-performance device having an energy density of 165 Wh kg−1 at a power density of 1000 W kg−1, which retain till 50 Wh kg−1 at 25 kW kg−1. The nanocomposite also shows excellent compatibility in a flexible device assembly, delivering a specific capacitance of 192 mF cm−1 at 1 mA cm−1 without deteriorating its performance upon different bending angles. The study claims the design of a low-cost, environmentally benign, and facile approach for developing a high-performance hybrid supercapacitor.

Structurally stable Fe–Ni–Co phosphide/graphene and nitrogen-doped carbon/graphene constructed by atomic layer deposition for high-performance hybrid supercapacitor

Constructing high-volume hybrid supercapacitors (HSCs) based on transition metal phosphides (TMPs) cathode and porous carbon anode is an effective way to promote energy density of supercapacitors (SCs). Herein, FeNiCoP nanoneedles are uniformly and stably coated on reduced graphene oxide (FeNiCoP/rGO) by atomic layer deposition technology. The synergistic effect between the large surface area of rGO and high specific capacity of TMP improves electrode reaction kinetics by fully exposing the active sites of FeNiCoP/rGO and shortening the ion/electron transport path. Therefore, FeNiCoP/rGO reveals a high specific capacitance (184.8 mAh/g at 1 A/g), favorable rate performance (151.1 mAh/g at 10 A/g) and excellent structural stability. To better exploit the advantages of the performance of the FeNiCoP/rGO, an anode of porous nitrogen-doped carbon/rGO (N–C/rGO) was prepared. Benefitting from the rich void structure and the nitrogen doping, N–C/rGO delivers a specific capacitance of 240 F/g at 1 A/g. The HSC device assembled by them exhibits the maximum energy and power densities of 52.9 Wh/kg and 8579.5 W/kg. Moreover, the device maintains 82.8% specific capacity after 5000 cycles.

Nickel selenide nano-cubes anchored on cadmium selenide nanoparticles: First-ever designed as electrode material for advanced hybrid energy storage applications

The rational design and impressive performance of the desired electrode material are one of the top priorities in the field of the supercapacitor era. Chalcogenides are functional materials that attracted tremendous research due to their great electrochemical activity, non-toxicity, high theoretical capacities, low cost, high environmental safety, and tunable electronic configurations. Combining two different materials (compositing strategy) is a popular route to develop novel, robust, and highly efficient electrodes for high capacity, energy, and power delivery with good durability. Herein, for the first time, a high-performance hybrid supercapacitor is developed based on NiSe2, and CdSe and their composites, e.g., NiSe2/CdSe (denoted as CN-1, CN-2, and CN-3) via hydrothermal via ex-situ wet-chemical method. By changing the stoichiometry of the host compounds (e.g., NiSe2, CdSe), various nanocomposites take birth, such as; CN-1, CN-2, and CN-3. Notably, their capacitive performance was measured and compared in an aqueous alkaline media in KOH with three milli molar concentration. Subsequently, the CN-2 electrode displayed a good electrochemical energy storage performance of 358C/g capacity and lower overall resistance, which promotes the fast diffusion of electrolyte kinetics; hence, optimized electrochemical properties prove its importance for the fabrication of full cell development. More strikingly, the CN-2//AC hybrid supercapacitor revealed a high capacitance of 90 F/g, 40.5 Wh/kg energy density, and a maximum power of 7161.2 W/kg coupled with a high stability of 87.6 % (20 A/g) when repeatedly tested for long-term 15,000 cycling. The proposed method portrays a cost-effective and appealing runner for high-energy hybrid supercapacitors in future energy storage applications.

MOF-derived (Ni, Co)Se2 @CoP/CNFs@CF with enhanced reaction kinetics by heterointerface engineering for high-performance hybrid supercapacitors

Ni/Co selenide (NCSe), which has a high theoretical capacity and a lot of redox activity, is a candidate for high-performance supercapacitor electrode materials. With its poor reaction kinetics, it performs electrochemically much less efficiently than it should. Herein, we first synthesized MOF-derived zero-dimensional (0D)/two-dimensional (2D) (Ni, Co)Se2 @CoP/CNFs@CF (carbon and nitrogen framework) hierarchical heterogeneous nanosheet arrays. The charge transport is accelerated by the Coulomb forces of the built-in electric field created by the electron rearrangement at the heterointerface of (Ni, Co) Se2 @CoP/CNFs@CF. Moreover, the 0D/2D micro-nanostructure promotes interlayer shuttling and the penetration of electrolyte ions while combining the benefits of 0D and 2D materials. The two synergistically accelerate the reaction kinetics of the electrode. As expected, (Ni, Co)Se2 @CoP/CNFs@CF has an excellent specific capacity (431.7 mAh g−1, 1 A g−1). In addition, the hybrid supercapacitor (Ni, Co)Se2 @CoP/CNFs@CF//AC (activated carbon) has an ultra-high energy density (85.31 Wh kg−1, 800 W kg−1) and cycling stability (10,000 cycles, 113.72%). This is the P/Se hybrid metal compound electrode's best electrochemical performance to date. This work offers a method for fabricating electrodes with heterostructures for high energy density hybrid supercapacitors by enhancing the attributes of the electrode structure and interface.

Interface engineered hydrangea-like ZnCo2O4/NiCoGa-layered double hydroxide@polypyrrole core-shell heterostructure for high-performance hybrid supercapacitor

Rationally constructing advanced battery-type electrodes with hierarchical core–shell heterostructure is essential for improving the energy density and cycling stability of hybrid supercapacitors. Herein, this work successfully constructs hydrangea-like ZnCo2O4/NiCoGa-layered double hydroxide@polypyrrole (denoted as ZCO/NCG-LDH@PPy) core–shell heterostructure. Specifically, the ZCO/NCG-LDH@PPy employs ZCO nanoneedles clusters with large open void space and rough surfaces as the core, and NCG-LDH@PPy composite as the shell, comprising hexagonal NCG-LDH nanosheets with rich active surface area, and conductive PPy films with different thicknesses. Meanwhile, density functional theory (DFT) calculations authenticate the charge redistribution at the heterointerfaces between ZCO and NCG-LDH phases. Benefiting from the abundant heterointerfaces and synergistic effect among different active components, the ZCO/NCG-LDH@PPy electrode acquires an extraordinary specific capacity of 381.4 mAh g−1 at 1 A g−1, along with excellent cycling stability (89.83% capacity retention) after 10,000 cycles at 20 A g−1. Furthermore, the prepared ZCO/NCG-LDH@PPy//AC hybrid supercapacitor (HSC) exhibits a remarkable energy density (81.9 Wh kg−1), an outstanding power density (17,003.7 W kg−1), and superior cycling performance (a capacitance retention of 88.41% and a coulombic efficiency of 93.97%) at the end of the 10,000th cycle. Finally, two ZCO/NCG-LDH@PPy//AC HSCs in series can light up a LED lamp for 15 min, indicating its excellent application prospects.

Self-assembled hierarchical porous nanoarchitectured 2,6-diaminopyridine decorated N-doped reduced graphene oxide as advanced electrode for high-performance aqueous Zn-ion hybrid supercapacitors

2,6-diaminopyridine (DAP), an active organic molecule containing amino groups and pyridine N is expected to be an attractive material for energy storage due to its fast and reversible proton-involved redox activity. Herein, the novel N-doped (or CNTs) and DAP organic molecules double-modified reduced graphene oxide nanocomposites with hierarchical porous nanoarchitectures were successfully designed and synthesized by a simple solvothermal method. Benefiting from the advantages of the three components and the positive synergistic enhancement between them, the newly synthesized N-RGO/DAP and CNTs/RGO/DAP nanocomposites exhibit excellent electrochemical properties, such as high specific capacitance, excellent rate capability and cycling stability. Furthermore, the Zn-ion hybrid supercapacitor further assembled with the optimal N-RGO/DAP as cathode delivers excellent Zn-ion energy storage performance in aqueous electrolyte, with a high specific capacitance (capacity) of 320.2 F g−1 (158.3 mAh g−1), excellent energy density of 140.9 Wh kg−1 at a power density of 534 W kg−1, and an ultra-long durability of 95.3% capacitance retention after 16,000 cycles at a large current of 100 mV s−1. This paper provides a novel strategy and advanced electrode nanocomposite with excellent electrochemical properties, which shows great promise in high-performance energy storage devices with high-flexibility, light-weight and sustainability.

Preparation of two-dimensional sodium-boron phosphide nanosheets used for Na-ion hybrid supercapacitor devices

The development of high-performance sodium-ion hybrid supercapacitors (NISCs) are assembled using facile bulk preparations of sodium boron phosphide (Na-BP) nanosheets as the negative electrode (battery type) and mesocarbon microbeads (MCMB) as the positive electrode (capacitor type). The Na-BP is optimized through different annealing temperatures ranging from 700 to 900 °C under an inert atmosphere. The structural and morphological characterization of the as-prepared materials were investigated by XRD, micro-laser RAMAN, FE-SEM and FE-TEM. The hybrid NISCs were assembled with an Na-BP-700//MCMB, Na-BP-800//MCMB and Na-BP-900//MCMB device configuration with a wide potential of 1–4 V vs. (Na/Na+) and their revealed a gravimetric specific capacitance (Csp) of 48.66 F/g, 83.33 F/g and 125 F/g @ 0.1 A/g, respectively. Finally, Na-BP-900//MCMB device is exhibiting excellent capacity retention of 73.52% even after 10,000 cycles at 0.3 A/g. Moreover, sodium boron phosphide (Na-BP) facile preparations by annealing method and efficient scaleable process for preparing without pre-sodiations for future hybrid supercapacitor devices.

Dual N-doped porous carbon derived from pyrolytic carbon black and critical PANIs constructing high-performance Zn ion hybrid supercapacitor

In view of massive accumulation of pyrolytic carbon black (CBp) from waste tires with low quality, it is urgent to explore its application in electrochemical energy storage to realize the high-value utilization of carbon resources and reduce the cost of supercapacitors. Herein, in-situ polymerization of aniline monomers on activated CBp (ACBp) with the introduction of o-phenylenediamine (OPD) for enhanced N content was first performed to prepare the composite of CBp and polyaniline (PANI), denoted as ACBp-oPANI, and then a dual N-doped material (ACBp-oN) was obtained via direct activation of ACBp-oPANI. The ACBp-oN product shows satisfactory specific capacitance of 335 F g−1 (1 A g−1) with superior rate performance as well as long cycle life in three-electrode system. The investigated charging/discharging kinetics reveal rapid electron transport and ion diffusion, which are attributed to its doped N and enriched channel structure. Besides, the assembled Zn ion hybrid supercapacitor (Zn|C), including ACBp-oN cathode and electrodeposited Zn anode, delivers an amazing energy density of 68.9 Wh kg−1 which is almost 4 times higher than that of conventional symmetrical supercapacitor (C|C), demonstrating more practicality. The research provides new perception into the high-value utilization of waste CBp resources in energy field and strategy for the boosted electrochemical properties of carbon-based materials via the suggested Zn|C energy storage system.

CoNi bimetallic engineering on porous carbon for high energy density hybrid supercapacitors

Rationally designed, structurally stable, and high-capacity transition metal alloy decorated carbon composites have attracted considerable attention as electrode materials for high-performance hybrid supercapacitors (HSCs). A unique electrode material composed of mixed transition metals (Co and Ni) on fryums-derived porous carbon was synthesized using a facile one-step pyrolysis approach. The CoNi@C composite exhibited rich redox kinetics and good electrochemical performance in an aqueous alkaline electrolyte. In particular, the CoNi@C composite delivered a maximum specific capacity of 390 mA h g−1 at 1 A g−1 with good capacitance retention of 91 % over 5000 cycles. The gravimetric specific capacity of the CoNi@C composite was 1.3 times better than that of the single alloy composite. Moreover, the HSC fabricated with CoNi@C, and activated carbon electrodes exhibited a high energy density of 57.6 Wh kg−1 at a power density of 742 W kg−1 and good cycling stability with a low-capacity loss of 8 % after 5000 cycles. Utilizing high-voltage and energy density, the HSCs can power light-emitting diodes of different wavelengths, demonstrating its practical applicability in energy storage technologies. The structural verification of fryum-derived carbon revealed a good graphitization degree, ensuring its remarkable adaptability for device fabrication.

Explosive effect-assisted synthesis of hierarchical porous carbon for high-performance aqueous Zn-ion hybrid supercapacitors with commercial level mass loading

Aqueous Zn-ion hybrid supercapacitors (AZHCs) are potential types of energy storage applications that combine the advantages of supercapacitors and batteries. The low mass loading and poor rate performance of cathodes, however, severely limits their practical application. Herein, an explosive effect assisted strategy is reported for the efficient synthesis of N, O co-doped porous carbon nanosheets (NPCNs) by synergistic activation of high-quality soft carbon precursor perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) with KOH and Zn(NO3)2. Benefiting from the comprehensive modulation of the morphology, pore structure, and surface chemistry, the obtained NPCNs show the significant enhancement in diffusion kinetics. Consequently, the as-fabricated AZHCs exhibited remarkably improved Zn-ion storage capability (189.3 mAh g−1 at 0.1 A g−1, 96.7 mAh g−1 at 20 A g−1) and long-term cycling stability at 20 A g−1 (∼ 92.5 % retention upon 6000 cycles). Moreover, NPCNs also deliver a superb areal capacity of 1.6 mAh cm−2 with a mass loading of 15.4 mg cm−2. Most importantly, we demonstrate that such porous carbon framework with competent electrochemical properties can be easily produced from diverse soft carbon precursor. This work thus introduces a universal and efficient strategy to produce high-performance porous carbon electrode materials for AZHCs.

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

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

Mesoporous Cobalt Oxide (CoOx) Nanowires with Different Aspect Ratios for High Performance Hybrid Supercapacitors.

Cobalt oxide (CoOx) nanowires have been broadly explored as advanced pseudocapacitive materials owing to their impressive theoretical gravimetric capacity. However, the traditional method of compositing with conductive nanoparticles to improve their poor conductivity will unpredictably lead to a decrease in actual capacity. The amelioration of the aspect ratio of the CoOx nanowires may affect the pathway of electron conduction and ion diffusion, thereby improving the electrochemical performances. Here, CoOx nanowires with various aspect ratios were synthesized by controlling hydrothermal temperature, and the CoOx electrodes achieve a high gravimetric specific capacity (1424.8 C g-1) and rate performance (38% retention at 100 A g-1 compared to 1 A g-1). Hybrid supercapacitors (HSCs) based on activated carbon anode reach an exceptional specific energy of 61.8 Wh kg-1 and excellent cyclic performance (92.72% retention, 5000 cycles at 5 A g-1). The CoOx nanowires exhibit great promise as a favorable cathode material in the field of high-performance supercapacitors (SCs).

Heterogeneous Ni–Co phosphide/phosphate with a specific hollow sea-urchin-like structure for high-performance hybrid supercapacitor and alkaline zinc-metal battery applications

Constructing well-defined nanostructures consisting of the multiple components with distinctive features are a promising but challenging strategy to develop advanced electroactive materials for energy storage applications. Herein, heterogeneous Ni–Co phosphide/phosphate with a specific hollow sea-urchin-like structure has been synthesized as advanced electroactive materials for both hybrid supercapacitor (HSC) and alkaline zinc-metal battery (AZB) applications. The heterogeneous Ni–Co phosphide/phosphate combines the merits of improved electrolyte interfacial property from the specific hollow sea-urchin-like structure, high electron-conductivity of phosphide, and better ion adsorption and solid diffusion property of phosphate. As a result, the Ni–Co phosphide/phosphate achieves a high capacity to 180.7 mA h g−1 at 1 A g−1, excellent rate capability of 51% capacity retention when the specific current increases by 50 times, and stable cycling stability of 85% capacity retention when cycled for 1000 cycles. Ex situ test was conducted to investigate the formation mechanism for the hollow and sea-urchin-like structure, which can be ascribed to the anion exchange reaction between pre-formed hydroxide and CO32– ions. When used to assemble HSCs with reduced graphene oxide (RGO), the HSCs exhibit a high specific energy of 49.4 W h kg−1, an ultrahigh specific power to 11.7 kW kg−1, and an eminent cycling stability over 10,000 cycles. Meanwhile, Ni2Co–P/POx-based AZB also achieves both high-energy and high-power performance with the specific energy of 308.0 W h kg−1 at 828.4 W kg−1 and 117.4 W h kg−1 at 30.8 kW kg−1. These results above suggest that heterogeneous Ni–Co phosphide/phosphate has great potential to be used as a candidate for both HSC and AZB applications.