As-prepared Asymmetric Supercapacitor Research Articles

Binder free cobalt Manganese layered double hydroxide anode conjugated with bioderived rGO cathode for sustainable, high-performance asymmetric supercapacitors

Metal-organic frameworks (MOFs) possessmultifunctional characteristicssuch as tuneable pore structure and high specific surface area and are being designed with great interest to enhance the electrochemical properties of current energy storage devices. In this aspect, MOFs-derived layered double hydroxides (LDHs) are important candidates for advanced supercapacitors due to their high electrochemical activity and electric conductivity. Herein, we report synthesis of Cobalt Manganese layered double hydroxides (CoMn LDH) utilising Co MOF as a precursor via ion exchange method, while optimising the dosage of Mn to achieve the best possible structural outcome. The unique structure of CoMn LDH expressed high electrochemical parameters possessing specific capacitance of 1305F/g at 1 A/g. Afterwards, an asymmetric supercapacitor device was fabricated employing CoMn LDH as cathode and coffee grounds derived rGO (reduced graphene oxide) as anode. The as-prepared asymmetric supercapacitor device demonstrated a maximum working potential window of 1.2 V with energy and power density of 23.8 Wh/kg and 0.30 kW/Kg respectively. The device also exhibits superiorcoulombic efficiency and capacitance retention of 71.11 % and 82.7 % respectively over 3010 charge–discharge cycles that represents an effectiveapproach towards sustainable and effectiveenergy storage devices. In a nutshell, our study centred on adjusting composition, engineering structures, and assembling devices.

Highly scalable and low cost binder free electrode of Zinc modified NiO nanofoam for dual role of supercapacitor and its free radical scavenging activity

In this study, pristine nickel oxide (NiO) and Zinc modified NiO nanofoams were prepared by green approach using camellia sinensis leaves extract. Pristine nickel oxide and Zn2+ modified NiO nanofoam were characterized by XRD, FTIR, FL, UV and FESEM. FE-SEM micrographs were clearly shows that the synthesised porous nanofoam with spherical shaped were constant distribution. The as prepared foam electrodes showed excellent supercapacitive behaviour with increase in specific capacitance with decrease in scan rate. The maximum specific capacitance 1530, 1706 and 1847Fg-1 was obtained at scan rate of 10 mVs-1 for increasing the Zn concentrations. After 3,000 cycles at 1 A g−1, the cyclic stability remains excellent at 88.1% of the initial capacitance. Moreover, the as-prepared asymmetric supercapacitor exhibits a high energy density of 30.6 W h·kg−1 at power density of 398 W kg−1. This study is expected to provide new insights into exploring the potential mechanism of catalyst action. These findings show that Zinc @ NiO nanofoam could be a potentially useful electrode material for energy storage devices.

Tuning parallel manganese dioxide to hollow parallel hydroxyl oxidize iron replicas for high-performance asymmetric supercapacitors

A novel and facile strategy is developed to tune parallel manganese dioxide (MnO2) to hollow parallel hydroxyl oxidize iron (FeOOH) replicas, which can exactly keep its original morphology. The key factors leading to the morphology-preserved transformation are the low-temperature and dropwise strategy via a serial of controlled experiments. Benefiting from the characteristics of parallel and hollow structures, the FeOOH replica delivers remarkable specific capacitance of 186.8F g−1 at 0.5 A g−1. The electrochemical performances delivered by the asymmetric supercapacitor (parallel MnO2//hollow parallel FeOOH) are much superior to those where conventional activated graphene or FeOOH nanoneedles are used as negative electrode materials. This can be attributed to the advantages of parallel nanostructure and high electrochemical matching effect of positive and negative electrode materials. The energy density is recorded up to 46.8 Wh kg−1 at the power density of 0.5 kW kg−1, while it still remains 20.7 Wh kg−1 with the maximum power density of 10 kW kg−1. Furthermore, this strategy shows great universality and can be broadened to almost all MnO2 related researches to synthesize ideal negative electrode materials with high structural and electrochemical matching effect, thus further enhances the electrochemical performances of as-prepared asymmetric supercapacitor devices.

An in situ growth strategy of NiCo-MOF nanosheets with more activity sites for asymmetric supercapacitors

NiCo layered double hydroxides (LDHs) for supercapacitors have been studied by virtue of the high specific capacitance theoretical values. However, less active sites limit the further increase of their specific capacitances. Metal-organic framework (MOF), as a promising material, has attracted intense attention with enormous specific area and adjustable structure. Herein, a practical strategy was designed to improve the active sites of the binder-free electrode by potentiostatic deposition and soaking NiCo-LDHs in 2-methylimidazole for in situ growth of MOF. This layered NiCo-MOF was obtained at room temperature which can retain more active sites to enhance capacitive properties. In particular, the prepared layered NiCo-MOF obtained a superior capacitance (1289 F g−1 at 0.5 A g−1), along with a remarkable rate capability (767 F g−1 at 20 A g−1). In addition, the as-prepared asymmetric supercapacitor exhibited a maximum specific energy of 57.8 Wh kg−1 at 748.7 W kg−1 (at a working potential of 1.5 V), and it retained 71.40% capacitance after 6000 cycles. All of these findings suggest that this work gives a practical way to synthesize NiCo-MOF nanosheets, and it exhibits excellent prospect in further energy field.

Super-conductive silver nanoparticles functioned three-dimensional CuxO foams as a high-pseudocapacitive electrode for flexible asymmetric supercapacitors

Copper oxide has aroused great concern in energy storage fields due to its properties of high theoretical capacitance, low cost and mild toxicity. However, its wide application still remains challenges owing to its poor electrical conductivity and unstable cycling life. Binder-free foam electrodes possess abundant porous structures and high specific surface area, which could get good contact with electrolyte. Herein, we demonstrate Ag nanoparticles decorated CuxO nanowires grown spontaneously on copper foam (CF) electrode for asymmetric supercapacitor. The skeleton structure of CF provides large amounts of active sites for the growth of CuxO nanowires. Moreover, Ag nanoparticles further decrease the internal resistance and enhance the electrochemical performance. Ag/CuxO/CF-40 electrode presents a high area specific capacitance of 1192 mF cm−2 at 2 mA cm−2 and the influence of surface capacitance-dominated process and diffusion-controlled process are discussed in detail. Besides, the energy density of the as-prepared asymmetric supercapacitor (ASC) reaches 46.32 μWh cm−2 at a power density of 3.00 mW cm−2. A 2V LED is lighted successfully by two ASC in series. This work provides a new strategy to prepare low internal resistance and binder-free flexible Ag/CuxO/CF electrode, which demonstrates a good potential application in flexible supercapacitors or other wearable electronic devices.

Rational design of cobalt–nickel double hydroxides for flexible asymmetric supercapacitor with improved electrochemical performance

Rational design of micro-nano morphology and suitable crystalline structure are highly desired for metal hydroxides to achieve overall high-performance in the advanced electrodes for flexible supercapacitors. Herein, a novel wisteria flower-like microstructure of cobalt–nickel double hydroxide (CoNi-DH) is successfully constructed on carbon cloth (CC) using an in-situ hydrolysis-induced exchange process between hydroxide ions and organic ligands of the Co-MOF in four different kinds of solutions containing Ni2+. The as-prepared wisteria flower-like microstructure grown on CC shows vertically aligned arrays with high specific area and abundant active sites, which not only guarantee the CoNi-DH active materials to be thoroughly exposed in the electrolyte, resulting in highly effective pseudocapacitive energy storage, but also are beneficial to rapid and reversible redox kinetics and thus give rise to high-rate capability. In addition, compared to Ni(NO3)2, NiCl2, and Ni(CH3COO)2 solutions, the Ni2SO4 solution is found to facilitate the formation of the most regular morphology and the largest interlayer spacing on (003) plane of the layered nickel hydroxide phase in the resultant CoNi-DH. As a result, the optimal CoNi-DH-S@CC (CoNi-DH prepared in Ni2SO4) serves as an advanced electrode to show high-rate capability (only 13% Cs decay after a 15-fold current elevation) and a superior specific capacity (Cs) of 929.4 C g−1, which remarkably exceeds those of CoNi-DH-N (823.1 C g−1, in Ni(NO3)2), CoNi-DH-Cl (798.4 C g−1, in NiCl2), CoNi-DH-C (803.8 C g−1, in Ni(CH3COO)2), and other similar metal hydroxides. Moreover, with this CoNi-DH-S electrode as the positive electrode, the as-prepared asymmetric supercapacitor (ASC) delivers an impressive capacity of 204.8 C g−1, a superior energy density of 42.5 Wh kg−1, and satisfactory cycle life (81.5% reservation after 7500 cycles). As a proof-of-concept application, a quasi-solid-state ASC is further successfully fabricated based on the CoNi-DH-S electrode to exhibit encouraging application potential.

Ultrathin porous Mn(PO3)2 nanosheets and MoO2 nanocrystal arrays on N, P-dual-doped graphene for high-energy asymmetric supercapacitors

Recently, heteroatom doped graphene based architectures exhibit promising prospects in the commercial application of supercapacitors because of their higher electrical conductivity and a wider potential window. Herein, we report on ultrathin porous nanosheets Mn(PO3)2 and MoO2 nanocrystal array on N, P dual-doped graphene (NPG) framework and study their supercapacitor properties. The irregularly overhead Mn(PO3)2 present a unique structure, which provide clear electron/ion transport channels to accelerate charge transfer together with the three-dimensional NPG structure. The obtained Mn(PO3)2/NPG hybrid electrode exhibit an extraordinary specific capacity (2073.4F g−1, 1 A g−1) and good rate performance (capacity retention rate of 77.8% from 1 A g−1 to 20 A g−1). In addition, the 3D NPG coated with MoO2 nanocrystal have also made a great progress in electrochemical performance of large capacitance and merely 5.54% fading capacitance after 10,000 cycles. Subsequently, the asymmetric supercapacitor (ASC) hybrid devices based on Mn(PO3)2/NPG as the positive electrode and MoO2/NPG as the negative electrode has a wide voltage range of 0 ~ 1.8 V, delivers an excellent CF value of 213.8F g−1 and keeps 91.5% initial capacitance retention after 10,000 cycles. Furthermore, the as-prepared ASC also obtains an outstanding energy density of 96.2 W h kg−1 at a power performance of 726.73 W kg−1, which demonstrate that the reasonable conductive network of Mn(PO3)2/NPG//MoO2/NPG devices can greatly increase the utilization of active substances, improve the performance in all aspects and open up new avenues of the future application and development of supercapacitors.

Confining Redox Electrolytes in Functionalized Porous Carbon with Improved Energy Density for Supercapacitors.

It is a big challenge to improve the energy density of the carbon-based supercapacitors for wide applications. In this work, considering the properties of redox electrolytes, functionalized porous carbon has been synthesized with interconnected pores and oxygen functional groups, which is employed to well hold the redox electrolyte ions. As a result, the functionalized porous carbon shows a high capacitance of 454 F g-1 at a current density of 1 A g-1 and can maintain 88% of the initial capacitance after 10 000 charge-discharge cycles at 10 A g-1. Especially, the as-prepared asymmetric supercapacitor obtains high energy density of 36.9 W h kg-1 at the power density of 225 W kg-1. This new design strategy by coordinating carbon materials with the redox electrolytes will guide the development of high-energy density supercapacitors.

Core-shell structured ZnCo2O4@ZnWO4 nanowire arrays on nickel foam for advanced asymmetric supercapacitors

One of the most effective tactics to promote the electrochemical performance of supercapacitors is to design and synthesize hybrid binder-free electrodes with core-shell structures. In this work, hierarchical ZnCo2O4@ZnWO4 core-shell nanowire arrays grown on nickel foam are successfully fabricated via a facile two-step hydrothermal route and subsequent thermal treatment. The ZnCo2O4 nanowire arrays supported on nickel foam serve as the backbone for anchoring ZnWO4 nanosheets. When tested as binder-free electrodes for supercapacitors, the as-prepared ZnCo2O4@ZnWO4 hybrid electrode exhibits an ultrahigh specific areal capacitance of 13.4 F cm−2 at a current density of 4 mA cm−2 and superb cycling stability (98.5% retention after 5000 continuous cycles at a current density of 100 mA cm−2). Furthermore, an asymmetric supercapacitor based on ZnCo2O4@ZnWO4//active carbon is successfully designed. The as-designed asymmetric supercapacitor can achieve a maximum energy density of 24 Wh kg−1 at a power density of 400 W kg−1. Moreover, two as-prepared asymmetric supercapacitor devices in a series connection are able to light up a white light-emitting diode over 30 min. The outstanding electrochemical properties of the hybrid electrode demonstrate that it holds great potential for next generation energy storage applications.

Green Fabrication of Ultrathin Co3O4 Nanosheets from Metal-Organic Framework for Robust High-Rate Supercapacitors.

Two-dimensional cobalt oxide (Co3O4) is a promising candidate for robust electrochemical capacitors with high performance. Herein, we use 2,3,5,6-tetramethyl-1,4-diisophthalate as a recyclable ligand to construct a Co-based metal-organic framework of UPC-9, and subsequently, we obtain ultrathin hierarchical Co3O4 hexagonal nanosheets with a thickness of 3.5 nm through a hydrolysis and calcination process. A remarkable and excellent specific capacitance of 1121 F·g-1 at a current density of 1 A·g-1 and 873 F·g-1 at a current density of 25 A·g-1 were achieved for the as-prepared asymmetric supercapacitor, which can be attributed to the ultrathin 2D morphology and the rich macroporous and mesoporous structures of the ultrathin Co3O4 nanosheets. This synthesis strategy is environmentally benign and economically viable due to the fact that the costly organic ligand molecules are recycled, reducing the materials cost as well as the environmental cost for the synthesis process.

Synthesis of Capsule-like Porous Hollow Nanonickel Cobalt Sulfides via Cation Exchange Based on the Kirkendall Effect for High-Performance Supercapacitors.

To construct a suitable three-dimensional structure for ionic transport on the surface of the active materials for a supercapacitor, porous hollow nickel cobalt sulfides are successfully synthesized via a facile and efficient cation-exchange reaction in a hydrothermal process involving the Kirkendall effect with γ-MnS nanorods as a sacrificial template. The formation mechanism of the hollow nickel cobalt sulfides is carefully illustrated via the tuning reaction time and reaction temperature during the cation-exchange process. Due to the ingenious porous hollow structure that offers a high surface area for electrochemical reaction and suitable paths for ionic transport, porous hollow nickel cobalt sulfide electrodes exhibit high electrochemical performance. The Ni(1.77)Co(1.23)S4 electrode delivers a high specific capacity of 224.5 mAh g(-1) at a current density of 0.25 A g(-1) and a high capacity retention of 87.0% at 10 A g(-1). An all-solid-state asymmetric supercapacitor, assembled with a Ni(1.77)Co(1.23)S4 electrode as the positive electrode and a homemade activated carbon electrode as the negative electrode (denoted as NCS//HMC), exhibits a high energy density of 42.7 Wh kg(-1) at a power density of 190.8 W kg(-1) and even 29.4 Wh kg(-1) at 3.6 kW kg(-1). The fully charged as-prepared asymmetric supercapacitor can light up a light emitting diode (LED) indicator for more than 1 h, indicating promising practical applications of the hollow nickel cobalt sulfides and the NCS//HMC asymmetric supercapacitor.

Template-free hydrothermal synthesis of nickel cobalt hydroxide nanoflowers with high performance for asymmetric supercapacitor

In this work, various nickel cobalt double hydroxide nanoflowers with different Ni/Co ratios (denoted as NixCo(1−x)(OH)2), assembled by filmy nanoflakes, are prepared via a facile template-free hydrothermal process. The sizes of these nanoflowers are easily tuned by the Ni/Co ratio in the precursors. The formation mechanism of flower-like nickel cobalt hydroxide, based on the synergistic effect of ammonia complexation, Ni/Co ratios, precipitators and solvents in the template-free hydrothermal system, is demonstrated in detail. As the battery materials, the as prepared flower-like nickel cobalt double hydroxides exhibit excellent specific capacities and high rate performance. Ni0.28Co0.72(OH)2 displays the highest capacity of 206.7mAhg−1 at 1mVs−1 and 174.3mAhg−1 at 1Ag−1, respectively. The capacity retention of Ni0.28Co0.72(OH)2 is 59.1% (from 206.7 to 122.2mAhg−1) at the potential scan rate from 1 to 25mVs−1. Due to the high rate performance corresponding to high power energy, Ni0.28Co0.72(OH)2 is used as positive material to assemble the hybrid device (asymmetric supercapacitor) with activated carbon as negative material. The as-prepared asymmetric supercapacitor exhibits 19.4Whkg−1 at 80.5Wkg−1, and even 20.6Whkg−1 at 3.93kWkg−1.

Hydrothermal synthesis of a flower-like nano-nickel hydroxide for high performance supercapacitors

To construct suitable nanostructures for electronic and ionic transport in the electrode of a supercapacitor, a flower-like nanostructured nickel hydroxide (Ni(OH)2) was synthesized by a facile hydrothermal process in this study. For comparison, an additional two Ni(OH)2 samples were synthesized to investigate the formation mechanism of the flower-like Ni(OH)2. Physicochemical characterizations indicate that the Ni(OH)2 nanoflower was formed by stacked hexagonal β-phase of the Ni(OH)2 nanoflakes. The dissolution-recrystallization of Ni(OH)2 and the stacking of nanoflakes play important roles in the formation of Ni(OH)2 nanoflowers. Due to the higher conductivity and the suitable macropores for ionic transport, the nanoflower-like Ni(OH)2 exhibits a high specific capacitance of 2653.2Fg−1 at 2Ag−1 and 1998.5Fg−1 at 40Ag−1. An asymmetric supercapacitor, which was assembled with Ni(OH)2 as the positive material and HNO3-treated activated carbon as the negative material, exhibited a high cell voltage of 1.6V. Due to the high specific capacitance and high cell voltage, the as-prepared asymmetric supercapacitor exhibited a high energy density of 32.7Whkg−1 at 71.5Wkg−1 and 25.5Whkg−1 at 1.28kWkg−1.