Supercapacitive Properties Research Articles

A dual-acetate synchronous catalysis-activation strategy towards regulable porous graphitic carbon for high-energy supercapacitor with acetate water-in-salt electrolyte

Supercapacitors are one of the most extensively studied energy storage devices due to their many unique advantages. The design of electrode material and electrolyte is the key to building high-performance supercapacitors. In this work, high-energy aqueous supercapacitors are constructed by optimizing these two factors. On the one hand, a dual-acetate (nickel/potassium acetates) synchronous catalysis-activation strategy is developed for the first time to prepare porous graphitic carbon from commercial super absorbent polymer as electrode material. Compared with the porous carbon activated by potassium acetate alone and the graphitic carbon catalyzed by nickel acetate alone, the porous graphitic carbon shows much more remarkable electrochemical performance. On the other hand, the impacts of water-in-salt and salt-in-water electrolytes of aqueous potassium acetate on energy storage properties of supercapacitors are investigated comparatively. The water-in-salt electrolyte of 22 M potassium acetate has a significant effect in broadening voltage window up to 2.95 V. When the operating voltage window is extended from 1.6 to 2.2 V, the energy density can be increased from 17.1 to 40.6 Wh kg−1. Moreover, both the porous graphitic carbon electrode and potassium acetate water-in-salt electrolyte are conducive to the slow self-discharge capability.

Supersonically Sprayed Flexible ZnO/PVDF Composite Films with Enhanced Piezoelectricity for Energy Harvesting and Storage

A flexible piezoelectric nanogenerator (PENG) was developed to convert ambient mechanical energy into electrical energy. Highly crystalline template-free zinc oxide (ZnO) microrods were prepared using a wet chemical method at a low temperature. As-synthesized ZnO microrods were blended with polyvinylidene fluoride (PVDF) to prepare a piezoelectric composite film using the supersonic spraying method. A PENG electrode comprising ZnO microrods (0.5 g) produced 15.2 V under a tapping force of 20 N at 5 Hz. In addition, an output current of 32 μA was produced with a maximum power density of 12.5 μW cm–2. The output voltage considering various body movements was investigated to demonstrate the flexibility and durability of the proposed PENG. Furthermore, the supercapacitive properties of ZnO/reduced graphene oxide were studied.

Hierarchical spinel NiMn2O4 nanostructures anchored on 3-D nickel foam as stable and high-performance supercapacitor electrode material

A simple hydrothermal route has been used to synthesize NiMn2O4 nanostructures (NSs) on nickel foam. The electrochemical investigation shows how annealing temperature affects its supercapacitive properties. The NMO@500-Ni-foam electrode shows a high specific capacitance of 930 Fg−1 at a constant scan rate of 5 mVs−1 in 1 M KOH electrolyte. Additionally, the corresponding symmetric supercapacitor device (SSCs) has a superior cyclic span with 93.7 % capacitance retention even after 5000 cycles, excellent electrochemical performance with a specific capacitance of 72.9 Fg−1, specific energy of 11 Whkg−1, and specific power of 857 Wkg−1. The exceptional results suggest that NiMn2O4 grown on Ni-foam might be a promising candidate for electrochemical energy storage applications.

A self-sacrificing template strategy: In-situ construction of bimetallic MOF-derived self-supported CuCoSe nanosheet arrays for high-performance supercapacitors

Transition metal selenides (TMSs) are viewed as a prospective high-capacity electrode material for asymmetric supercapacitors (ASCs). However, the inability to expose sufficient active sites due to the limitation of the area involved in the electrochemical reaction severely limits their inherent supercapacitive properties. Herein, a self-sacrificing template strategy is developed to prepare self-supported CuCoSe (CuCoSe@rGO-NF) nanosheet arrays by in situ construction of copper-cobalt bimetallic organic framework (CuCo-MOF) on rGO-modified nickel foam (rGO-NF) and rational design of Se2- exchange process. Nanosheet arrays with high specific surface area are considered to be ideal platforms for accelerating electrolyte penetration and exposing rich electrochemical active sites. As a result, the CuCoSe@rGO-NF electrode delivers a high specific capacitance of 1521.6 F/g at 1 A/g, good rate performance and an excellent capacitance retention of 99.5% after 6000 cycles. The assembled ASC device has a high energy density of 19.8 Wh kg−1 at 750 W kg−1 and an ideal capacitance retention of 86.2% after 6000 cycles. This proposed strategy offers a viable strategy for designing and constructing electrode materials with superior energy storage performance.

Study on Electrochemical Performance of MnO@rGO/Carbon Fabric-Based Wearable Supercapacitors.

In this work, we reported the electrochemical performance of a type of carbon fabric-based supercapacitor by coating MnOx@rGO nanohybrids on carbon fabric with a simple one-step hydrothermal method. We studied the mass ratio of MnOx to rGO on the electrochemical properties of the carbon fabric-based supercapacitors. We found that as the mass ratio is 0.8:1 for MnO@rGO, the supercapacitor with a loading of 5.40 mg cm-2 of MnO@rGO nanohybrids on carbon fabric exhibits a specific capacitance of 831.25 mF cm-2 at 0.1 mA cm-2 current density. It also shows long-term cycling capacitance retention of 97.2% after 10,000 charge-discharge cycles at a current density of 0.4 mA cm-2. We speculate that the high electrochemical performance results from the strong interfacial bonding between the hierarchical architecture of MnO@rGO nanohybrids and carbon fabric.

Experimental and Theoretical Insights of Anion Regulation in MOF-Derived Ni-Co-Based Nanosheets for Supercapacitors and Anion Exchange Membrane Water Electrolyzers.

The anionic components have a significant role in regulating the electrochemical properties of mixed transition-metal (MTM)-based materials. However, the relationship between the anionic components and their inherent electrochemical properties in MTM-based materials is still unclear. Herein, we report the anion-dependent supercapacitive and oxygen evolution reaction (OER) properties of in situ grown binary Ni-Co-selenide (Se)/sulfide (S)/phosphide (P) nanosheet arrays (NAs) over nickel foam starting from MOF-derived Ni-Co layered double hydroxide precursors. Among them, the Ni-Co-Se NAs exhibited the best specific capacity (289.6 mA h g-1 at 4 mA cm-2). Furthermore, a hybrid device constructed with Ni-Co-Se NAs delivered an excellent energy density (74 W h kg-1 at 525 W kg-1) and an ultra-high power density (10 832 W kg-1 at 46 W h kg-1) with outstanding durability (∼94%) for 10 000 cycles. Meanwhile, the Ni-Co-Se NAs showed superior electrocatalytic OER outputs with the lowest overpotential (235 mV at 10 mA cm-2) and Tafel slope. In addition, Ni-Co-Se NAs outperformed IrO2 as an anode in an anion exchange membrane water electrolyzer at a high current density (>1.0 A cm-2) and exhibited a stable performance up to 48 h with a 99% Faraday efficiency. Theoretical analyses validate that the Se promotes OH adsorption and improves the electrochemical activity of the Ni-Co-Se through a strong electronic redistribution/hybridization with an active metal center due to its valence 4p and inner 3d orbital participations. This study will provide in-depth knowledge of bifunctional activities in MTM-based materials with different anionic substitutions.

Introducing non-conjugated ionic spacer in metallo-supramolecular polymer: Generation of nanofibers for high-performance electrochromic supercapacitor

The use of indicative electrochromic (EC) supercapatteries is gaining significant attention for their ability to indicate their charging and discharging status through optical color changes and their high energy and power densities, making them a promising renewable alternative energy source. In this study, we performed molecular engineering to prepare a non-conjugated pyridinium cation-containing bisterpyridine ligand (TpyNTpy) and its metallo-supramolecular polymer (MSP), Fe-TpyNTpy. The MSP was thoroughly characterized through spectroscopic, morphological, and structural studies, revealing a homogeneous nanofiber morphology with good thermal stability. The gel-state EC devices, fabricated using Fe-TpyNTpy as the active layer, demonstrated EC color changes from purple to dirty white, with a large optical contrast of 47% at 570 nm, fast coloration (1.5 s) and bleaching (2.4 s) times, high coloration efficiency of 312.8 cm2C-1, longer optical memory, and extremely high EC cycle stability. Incorporating nonconjugated and ionic ligands helped address the opposite electrochemical behaviors, such as EC fastness and optical memory. The Fe-TpyNTpy film showed good supercapacitive properties in solution electrolytes, and the energy storage behavior was correlated with EC transmittance/color change. The energy storage properties were evaluated by preparing a hybrid ESD. The Fe-TpyNTpy and Prussian blue containing hybrid ESD exhibited an improved volumetric capacitance of 73 ± 2F/cm3 with low iR drop, high energy storage capacity (energy density 61 mWh/cm3 at a power density of 8.5 W/cm3), and 95% retention of initial volumetric capacitance after 10,000 charge–discharge cycles. The hybrid ESD can illuminate a single LED, demonstrating the practical applicability of the ESD.

Tapping the supercapacitive properties of porous activated carbon from expired white chickpeas

With an insight of clean and sustainable energy from green renewable waste, porous activated carbon was prepared by direct carbonization and activation of expired dried chickpeas with ZnCl2 for supercapacitor application. The expired chickpeas were powdered and mixed with zinc chloride in different ratios and pyrolyzed at high temperatures and the structural, morphological, and electrochemical analysis were studied. The pore size distribution of the carbonized samples was dominated by micropores and mesopores, with specific surface area in the range of 865.002 m2/g to 1094.638 m2/g and pore volume in the range of 0.618 cc/g to 0.739 cc/g. The as-fabricated symmetric device exhibited a specific capacitance of 204.6 F/g at 5 mV/s, the energy density of 11.732 Wh/kg and power density of 266.196 W/kg at 1 A/g with a capacitive retention of 97.48 % for 3000 cycles. Thus, the heterogeneous porous structure and excellent surface area helps in boosting the electrochemical behaviour of the expired white chickpea as waste derived carbon samples.

One-Step Microwave-Assisted Hydrothermal Preparation of Zn-ZnO(Nw)-rGO Electrodes for Supercapacitor Applications.

Zn-ZnO(Nw)-rGO hybrid electrodes for supercapacitor applications were successfully prepared in situ by a one-step microwave-assisted hydrothermal method by deposition of reduced graphene oxide (rGO) on the structure of ZnO nanowires grown on the Zn foil. During the hydrothermal treatment, two processes occur the reduction of graphene oxide (GO) and the deposition of rGO on the Zn-ZnO(Nw) support. The growth of ZnO nanowires was achieved by thermal oxidation below the melting point of the Zn foil in a controlled atmosphere. The as-obtained electrodes were assessed for structural, optical, and morphological properties by X-ray diffraction, Raman spectroscopy, ultraviolet-visible spectroscopy, SEM microscopy, and EDX analysis. The supercapacitor properties of the Zn-ZnO(Nw)-rGO hybrid electrodes were investigated by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge-discharge analysis. The CV curve reveals that the Zn-ZnO(Nw)-rGO hybrid structures work as negative electrodes and exhibit a non-ideal rectangle-like shape, suggesting that the as-synthesized structure behaves as a pseudo-capacitor. A maximum capacitance was determined to be 395.79 mF cm-2 at a scan rate of 5 mV s-1. Based on GCD analysis, the maximum specific capacitance of 145.59 mF cm-2 was achieved at a low power density of 2 mA cm-2. The cycle life assessment of the Zn-ZnO(Nw)-rGO hybrid electrode over a 250-cycle number was performed by CV and GCD analysis. The maximum retention rate of 120.86% was achieved from GCD analysis over 250 cycles for the Zn-ZnO(Nw)-rGO hybrid electrode.

Ni3S4 combined hydrophilic hydroxylated MWCNTs for high performance asymmetric supercapacitors

A composite material (Ni3S4-Q) of Ni3S4 combined with hydrophilic hydroxylated multi-walled carbon nanotubes (MWCNTs) was prepared by one-step method in the reactor. For comparison, hydrophilic MWCNTs were replaced by hydrophobic MWCNTs (Ni3S4-S), and pure Ni3S4 was synthesized without adding MWCNTs, so as to study the influence of the hydrophilicity and hydrophobicity of MWCNTs on the capacitive performance of Ni3S4. The contact Angle analysis shows that Ni3S4-Q has better hydrophilicity. The electrochemical cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy show that Ni3S4-Q has the highest specific capacitance and the lowest ion diffusion resistance. In addition, the asymmetric supercapacitor assembled by Ni3S4-Q and activated carbon has a maximum energy density of 51 Wh kg−1. This work strongly validated that hydrophilicity can improve the electrochemical properties of supercapacitors.

Excellent electrochemical performance of porous carbon by in situ nitrogen-doped derived from polyurethane

In this work, the application of high specific surface area nitrogen-doped porous carbon prepared from polyurethane (TPUC) as a supercapacitor electrode is reported. Five samples are prepared with KOH as activator at different activation temperatures and applied to research the electrochemical properties of supercapacitor. The problems of uneven distribution and loss of nitrogen atoms are solved by in situ doping. The conductivity and wettability of activated carbon are improved by nitrogen-doped. The maximum specific capacitance (up to 527 F g−1 at 0.5 A g−1) and outstanding cycling stability (up to 342 F g−1 after 10,000 cycles) are obtained by the TPUC-800 sample (specific surface area of 3575 m2 g−1). These features are explained for the improvement of the effective specific surface area and the shortened ion diffusion distance in carbon electrode due to nitrogen-doped and the enhancement of hydrophilicity of carbon surface. The results reveal that such a simple strategy of nitrogen-doped polyurethane is an efficient way to prepare promising nitrogen-doped porous carbons for supercapacitor with good performance.

The influence of ethylene glycol-based solvents on the morphological and supercapacitive properties of hydrothermalized δ-Bi2O3 with additional Bi2O2CO3

The influence of ethylene glycol-based solvents on the morphological and supercapacitive properties of hydrothermalized δ-Bi2O3 with additional Bi2O2CO3

Studies on Dielectric, Super-Capacitive and Photoluminescence Properties of Metal Organic Frameworks Subjected to Varying Temperature and Frequencies

Metal organic frameworks when subjected to varying temperatures and frequencies. The analysis indicate the presence of guest molecules enhance the dielectric constant. The dielectric constant increase to a limit with the rise in temperature but it reduces gradually. The increase in frequencies enhance the peaks of permittivity towards higher temperatures. Shortening of ion diffusion also enhances the capacitance and a better contact between the electrode and active substance increases the electrochemical performance. Luminescence, the color depends on particle size, the structure and intermolecular packing of atoms in material. This paper gives an overview of MOFs studied based on their dielectric, super-capacitive and photo-luminescence when subjected to varying temperatures and frequencies.

Biomass-derived hierarchically porous carbon-supported MnOx enable fast ion/electron transport at high operating voltages

Metal oxide/carbon composite systems have been investigated extensively for fabrication of supercapacitors. To obtain high capacitance, a thick pseudocapacitive layer loaded on a conventional carbon support inevitably leads to high dead volume and poor rate/power characteristics. Herein, we propose a strategy with biomass-derived hierarchical porous carbon as supports to bridge two critical but mutually exclusive properties of supercapacitors: high capacitance and rapid ion/charge transport. Highly dispersed deposition of nanosized MnO2 and MnO on hierarchically porous carbon were achieved through slow redox reaction controlled by gradual hydrolysis of fibrous polymers remaining in the hydrothermal carbon. High surface area, ultrathin pseudocapacitance layer, and wide voltage window (1.6–2 V) improve the synergy between the high energy density of MnOx and the high power density of porous carbon. The maximum energy density of 40.95 Wh kg−1 (at 180 W kg−1) and power density of 9000 W kg−1 (at 23.85 Wh kg−1) was realized for the assembled asymmetric/symmetric supercapacitors in aqueous electrolytes. More importantly, a cycle life comparable to that of carbon-based double-layer capacitors (95.6% capacitance retention after 10,000 charge/discharge cycles) could be achieved. Furthermore, density functional theory (DFT) was also conducted to elaborate the differences between manganese valence states for in-depth understanding. The characteristics of low cost, environmental friendliness, and excellent performance highlight the great promise of biomass waste in designing carbon supports for electrochemical applications.

Effect of intercalated anion in nickel-cobalt-layered double hydroxide on its supercapacitive properties

Layered double hydroxides (LDHs), a class of 2D lamellar intercalating materials, is a promising candidate for high-performance supercapacitors, while its poor cycling stability has always been its Achille’s heel. Although doping metal ions into the host layer is proved to be an effective way to improve the weakness, the effects of intercalated anions on cycling performance have been rarely studied and highly underestimated. In this paper, we prepared a group of NiCo-LDHs with different intercalated anions, including NO3−, Cl−, SO42−, MoO42− and WO42−, which expand the interlayer spacing from 0.73 to 1.07 nm. Interestingly, although expanding the interlayer spacing could increase the specific capacity by providing more electrochemical active sites, it could not guarantee the improvement in cycling performance and rate capability. The correlation between interlayer spacing and cycling performance exhibits a “volcano” plot. The MoO42− intercalated NiCo-LDH with a 0.96 nm interlayer spacing delivers a high specific capacity of 795 C g−1 and the best cycling stability with 80% capacity retention after 20,000 cycles, which is better than NiCo-LDH-NO3 (0.73 nm, 50% after 3000 cycles) and NiCo-LDH-WO4 (1.07 nm, 64% after 20,000 cycles). By combining the results with the DFT method, the effects of intercalated anion on cycling performance are illustrated. In addition, the asymmetric supercapacitor also exhibits an excellent cycling stability with ∼100% capacity retention after 10,000 cycles. This study provides new insight to the compositional design of LDH-based electrodes for long-lifespan supercapacitors.

Observation of synergistic effects in multiphase tungsten oxide (WO3) nanocomposite and its role in enhanced supercapacitive and photoluminescence properties

Herein we report the synthesis of metal (W) and multiphase metal oxide (orthorhombic, tetragonal, and hexagonal-phase of WO3) nanocomposites through a simple hydrothermal process and the electrochemical performance of this composite displays enormous specific capacitance (CS) of 1885 F/g in 1 M H2SO4. The distinct phases of the metal tungsten and WO3 nanoplates have been identified by XRD, FTIR and Raman spectra. This study also demonstrates how the different intercalated ionic radius significantly alters the electrochemical performance with the W–O bond length and displays moderately higher CS in 1 M H2SO4 (1885 F/g) compared to 2 M KOH (821 F/g) electrolytes at 1 mV/s scan rate. The proton (H+ and K+) insertion dynamics is also explored by galvanostatic charge-discharge (GCD), scan rate-dependent electrochemical analysis and electrochemical impedance spectroscopy (EIS). The enhanced W5+ to W6+ intercalation efficiency of the individual phase of WO3 has been demonstrated by three imperfectly resolved arcs with slopes line in acidic solution of EIS spectrum, whereas a single arc with slope in the KOH solution indicates less reaction kinetics in base solution. Moreover, multiphase WO3 nanoplates show outstanding 96.6% capacitance retention in 1 M H2SO4 compared to 2 M KOH (86.2%) solution after 900 cycles at a 10 A/g current density. Based on W-WO3 nanoparticle's improved three-electrode activity, we have constructed a solid-state asymmetric supercapacitor (ASC), and it exhibits energy densities of 76.3 Wh/kg and 86.8 Wh/kg at power densities of 1125 W/kg in KOH and H2SO4 soaked devices, respectively. Linear dependence of the excitation-dependent luminance spectra (250 nm–300 nm) and clean PL spectra at the lowest excitation (1.5 W) make these multiphase WO3 nanoplates a promising candidate as UV-B detector materials. So the multifunctionality of the WO3 nanostructures makes it a potential candidate as a future-generation integrated device materials.

Fabrication of MnCoS Thin Films Deposited by the SILAR Method with the Assistance of Surfactants and Supercapacitor Properties

Compact MnCoS thin films on a nickel foam (NF) substrate were prepared by successive ionic layer adsorption and a reaction (SILAR) method, and two surfactants (SDS and CTAB) were used to improve the wettability of the NF. The MnCoS thin films were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The supercapacitive properties were evaluated by cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and impedance spectroscopy (EIS). The results show that while the NF was first dipped in surfactant solution, followed by a mixture of Mn2+ and Co2+ or a Na2S solution, the load and density of the MnCoS on the NF’s surface significantly increased and delivered a much higher specific capacitance than that of the MnCoS thin film formed without the assistance of surfactants, which were 2029.8 F g−1 (MnCoS-CTAB), 1500.3 F g−1 (MnCoS-SDS), and 950.4 F g−1 (MnCoS-H2O) at a current density of 1 A g−1 in 3 M KOH aqueous solution. When the current density increased to 10 A g−1, the MnCoS-CTAB with the highest specific capacitance exhibited a capacitance of 1371.9 F g−1, with a 71% capacity retention up to 1000 cycles, showing a good rate performance and cycle stability.

B and N Co-Doped Wood Scrap Charcoal for Decorated Supercapacitor with High Conductivity

The optimization of supercapacitive properties in carbon materials derived from cheap and sustainable wood scraps exhibits great application potential. Herein, in support of interfacial groups, polyaniline nanospheres were in situ constructed in the internal pore structure of wood scraps; further, the B and N elements were imported by carbonized and hydrothermal methods. The doped B regulated the species of N doping to improve the electrical conductivity of carbonized wood scraps, and it endowed a certain pseudo-capacitance. Coupled with the fine double-layer capacitance from the hierarchical structures constructed by carbonized nanospheres and wood scrap channels, a high specific capacitance of 406 F g−1 at 0.5 A g−1, high energy density (17.71 Wh kg−1 at 250 W kg−1) and cycle stability (93.04% capacitance retention after 10,000 cycles) were performed simultaneously. This study provided a new strategy to improve the supercapacitive performance of bio-carbon materials in terms of structure and conductance.

Preparation of Polyindole-MnO2/Reduced Graphene Oxide-based Ternary Composite System for Supercapacitive Application

ABSTRACT A polyindole-MnO2 (PIn-MnO2)/reduced graphene oxide (RGO)-based ternary composite system has been assembled by an in-situ polymerization. In this system, the concentration of RGO has been varied by the interval of 0.25 wt.% in fixed quantity of PIn-MnO2 system. The mean crystallite size of RGO was observed to be 6.64 nm calculated by using Debye–Scherrer formula. This study demonstrates the dispersion of RGO nanoparticles in PIn-MnO2 system to optimize the supercapacitive properties. As expected, the supercapacitive properties of PIn-MnO2-RGO composites were influenced by the addition of RGO nanoparticles and it is optimized for 0.5 wt.% of RGO concentration. The 0.5 wt.% RGO-loaded PIn-MnO2-RGO composite shows specific capacitance of the order 1750 Fg−1 at a scan rate of 50 mV s−1. The main accomplishment of present work is that the 0.5 wt.% RGO-loaded composite shows long-term stability, which is capacitance retention up to 6000 cycles. Similarly, galvanostatic charge/discharge curves of 0.5 wt.% RGO-loaded composite show long and nearly symmetric behavior, which is suitable for range of practical applications.

Hyper-conjugated polyaniline delivering extraordinary electrical and electrochemical properties in supercapacitors

Conjugated polymers promise extremely-high theoretical supercapacitance to develop large capacitive storage devices. Existing conjugated polymers commonly realize their < 20% supercapacitance due to inferior electronic and electrochemical activities. Here we report hyper-conjugated effect to minimize energy level difference and carrier migration barrier in copolymerized polyaniline (PANI), a typical supercapacitive material. The hyper-conjugated effect efficiently promotes the elongation of conjugation system and the delocalization of π electrons. The largely increased number of free carriers in combination with the expanded range of carrier mobility guarantee 800% increments in electrical conductivity. Tests of symmetric supercapacitors with hyper-conjugated PANI show a high specific capacitance of 512 F g−1, excellent rate-capability and long-term cyclability. This work paves the way for designing conjugated polymers with remarkable electronic and electrochemical properties.