Performance Asymmetric Supercapacitors Research Articles

Asymmetric Supercapacitors Based on ZnCo2O4 Nanohexagons and Orange Peel Derived Activated Carbon Electrodes.

Herein, the performance of asymmetric supercapacitors (ASC) fabricated using ZnCo2O4 (ZCO) nano-hexagons and orange peel-derived activated carbon (OPAC) as electrodes was studied. ZCO was prepared by a double hydroxide method and OPAC was prepared from orange peel followed by KOH activation. For ZCO, the calcination temperature was determined using TGA analysis. The XRD showed the presence of a cubic spinel structure. The chemical structure was analyzed using XPS, FTIR, and Raman spectroscopy respectively. For OPAC, the presence of an amorphous nature was inferred; FTIR and Raman studies indicate the presence of functional groups and defect structure in the material. The presence of ZCO nano-hexagons was observed from SEM and TEM respectively. For OPAC, an interconnected pore structure was observed from the SEM image. The specific capacitance for ZCO and OPAC was found to be 194 F.g-1 and 159 F.g-1 at a current density of 0.25 A.g-1. Further, an ASC was fabricated using ZCO as a positive and OPAC as a negative electrode in 2M KOH-soaked separator. A cell voltage of 1.2 V was achieved and the specific capacitance was calculated to be 64 F.g-1 at 0.25 A.g-1. Further, the cyclic stability and the changes at the electrode/electrolyte interface were studied.

Novel isostructural iron‐series‐MOF calcined derivatives as positive and negative electrodes: A new strategy to obtain matched electrodes in a supercapacitor device

AbstractThe performance of asymmetric supercapacitors (ASCs) is strongly restricted by the capacity gap between the positive and negative electrodes. To address this issue, two new electrode materials deriving from Co‐ and Fe‐based metal–organic frameworks (MOFs, Co‐TAMBA‐d, and Fe‐TAMBA‐d) through a single‐step sintering method have been developed by considering the superiorities of the derivatives of MOFs including large surface areas, sufficient metal‐atom‐doping content, and extreme surface wettability to the bath solution. The as‐prepared Co‐TAMBA‐d as a positive electrode delivers typical pseudocapacitive behavior with the improvement of capacity, which is better than those of pristine MOF materials, while Fe‐TAMBA‐d as negative electrodes displays better electrochemical behavior than those of activated carbon. ASCs based on these two electrodes exhibits excellent energy density and power density of 47 W h/kg and 1658 W/kg, respectively, where this device can maintain prominent cycling stability with capacity retention after 5000 cycles being about 75%. Furthermore, the capacity can feed a series of red light‐emitting diodes, which gives solid evidence of the potential utilization. These results can afford the feasibility of isostructural MOF derivatives as promising electrodes in novel ASCs.

Effect of dealloying the r edox‐active zinc‐based electrodes on the performance of asymmetric supercapacitors

Effect of dealloying the r <scp>edox‐active</scp> zinc‐based electrodes on the performance of asymmetric supercapacitors

Hollow C-LDH/Co9S8 nanocages derived from ZIF-67-C for high- performance asymmetric supercapacitors

The design of supercapacitor electrode materials greatly depends on the rational construction of nanostructures and the effective combination of different active materials. Due to the poor electrical conductivity and mechanical strength, nickel-cobalt double hydroxide (NiCo-LDH) cannot reach the theoretical high specific capacitance value, while Co9S8 shows many interesting features, such as excellent electrochemical properties, high conductivity, and greatly improved redox reactions. Therefore, we prepared ZIF-67-C derived hollow NiCo-LDH (C-LDH)/Co9S8 nanocages containing two components of Co9S8 and NiCo-LDH through a multistep transformation method. The prepared C-LDH/Co9S8 nanoparticles showed a hollow rhomboid dodecahedron structure, and many NiCo-LDH nanosheets were reasonably distributed on the surface. In the three-electrode test, it can be obtained that its specific capacitance is 1654 F·g−1 when current density is 2 A·g−1 and 82.5% capacitance retention after 5000 cycles. Moreover, asymmetric supercapacitors (ASCs) prepared with C-LDH/Co9S8 as cathode and AC as anode can achieve a large energy density of 47.3 Wh·kg−1 under the condition of high power density of 1505 W·kg−1. After 10,000 cycles, capacitance retention rate is 80.9%, exhibit excellent cycle performance, suggesting the great potential of hollow C-LDH/Co9S8 nanocages in the application of supercapacitors.

A high-performance asymmetric supercapacitor-based (CuCo)Se2/GA cathode and FeSe2/GA anode with enhanced kinetics matching.

The performance of asymmetric supercapacitors (ASCs) is limited by the poorly matched electrochemical kinetics of available electrode materials, which generally results in reduced energy density and inadequate voltage utilization. Herein, a porous conductive graphene aerogel (GA) scaffold was decorated with copper cobalt selenide ((CuCo)Se2) or iron selenide (FeSe2) to construct positive and negative electrodes, respectively. The (CuCo)Se2/GA and FeSe2/GA electrodes exhibited high specific capacitances of 672 and 940 F g-1, respectively, at 1 A g-1. The capacitance contributions from the Co3+/Co2+ and Fe3+/Fe2+ redox couple for the positive and negative electrodes were determined to elucidate the energy storage mechanism. Furthermore, the kinetics study of the two electrodes was performed, revealing b values ranging between 0.7 and 1 at various scan rates and demonstrating that the surface-controlled processes played the dominant role, leading to fast charge storage capability for both electrodes. Fabrication of an ASC device with a configuration of (CuCo)Se2/GA//FeSe2/GA resulted in a voltage of 1.6 V, a high energy density of 39 W h kg-1, and a power density of 702 W kg-1. The excellent electrochemical performances of the (CuCo)Se2/GA and FeSe2/GA electrodes demonstrate their potential applications in energy storage devices.

Vital effect of sufficient vulcanization on the properties of Ni-Co-S/graphene composites for supercapacitor

Ni-Co-S/graphene-based composites have a broad prospect in the application of supercapacitors. Whether the vulcanization process is sufficiently performed seriously affect the performance of the composites. Here, a series of transition metal sulfide/graphene composites is synthesized through a two-step hydrothermal method by introducing different sulfur sources selected from organic (thiourea and thioacetamide) to inorganic (sodium sulfide and sodium thiosulfate). Both thioacetamide and sodium sulfide can vulcanize Ni-Co hydroxy-carbonate precursor to form the Ni-Co sulfide, but the other two cannot. And the Ni-Co-S/graphene composites synthesized by using sodium sulfide as sulfur source possess the best performance in asymmetric supercapacitor with an initial specific capacitance of 178.1 F g−1, and a capacitance retention of 89.47% after 10,000 cycles at 10 A g−1. The excellent stability is related to the ideal hollow structure with rich electrochemical active sites, and dispersed constituents of the Ni-Co-S on the surface of rGO.

Synthesis of nanoporous graphene and their electrochemical performance in a symmetric supercapacitor

The present work finds a new method for the synthesis of nanoporous graphene and its applications in high energy density supercapacitor. The synthesis of nanoporous graphene by wet chemical method using Mg/Zn strip as a reducing agent has been reported by many researchers, but its application of supercapacitor is not yet reported. The nanoporous graphene exhibited variations in structure, morphology, and electrochemical properties as compared to chemical reduction by sodium borohydride. In contrast, the formation of nanoporous graphene using Mg/Zn, it’s much faster than the chemical reduction by sodium borohydride. However, a significant improvement in the supercapacitor performance was observed upon Mg/Zn reduction method. In addition, the high electrical conductivity, improved higher surface area, better cyclability and typical electrochemical property enables one of the best high-rate performances studied for electrochemical supercapacitors: specific capacitance of 204 Fg−1 obtained at 10 Ag−1 with capacitance retention of 95% after 20000 cycles of charge-discharge.

Performance of asymmetric supercapacitor using CoCr-layered double hydroxide and reduced graphene-oxide

Cobalt chromium-layered double hydroxides (CoCr-LDHs) were electrodeposited on to carbon paper by potentiostatic method from the respective cobalt and chromium ion sources. The electrodeposited CoCr-LDHs were characterized by x-ray diffraction (XRD), Fourier transferred infrared (FT-IR) spectroscopy, scanning electron microscope (SEM), energy-dispersive x-ray analysis (EDX) and x-ray fluorescence (XRF) elemental mapping. The XRD and IR data confirmed that the deposits were CoCr-LDH with carbonate and nitrate ions in the basal space. The SEM observations confirmed that the CoCr-LDH surface had distinct morphology consisting of aggregate size of about 100 nm. For the first time, the supercapacitor characteristics of the CoCr-LDHs were assessed in three-electrode configuration in 1 M KOH or two-electrode (asymmetric capacitor device with reduced graphene-oxide (RGO)). It turned out that the asymmetric capacitor consisted of the CoCr-LDH and the RGO exhibited higher energy density with excellent power density. The higher energy density and power density of the asymmetric capacitor device is believed to be due to the unique LDH morphology in addition to the Faradaic and non-Faradaic contributions. It was demonstrated that the two asymmetric capacitor devices connected in series could light an LED bulb.