High Mass Specific Capacitance Research Articles

Designing chemical bonds between active materials and current collectors for packaging a high-performance supercapacitor

Clarifying the interaction between active materials and current collectors of the same electrode is crucial for understanding the electrochemical energy storage mechanism and designing high-performance supercapacitors. The interaction mechanism is mainly due to the evolution of chemical bonding. Here, we explore the chemical bonding evolution between cobalt-nickel layered double hydroxide and carbon fiber paper by using ex situ x-ray photoelectron spectroscopy during redox reaction. The results reveal that chemical bonding corresponds to more ionic states at the lowest potential and more covalent states at the highest potential. Attributed to the formation of C–O-Metal (Co, Ni) chemical bonds, high capacitance with enhanced stability and rate capability is obtained. The Co–Ni layered double hydroxide electrode exhibits a high areal and mass specific capacitance of 0.55 and 952 F g−1 at a low mass loading of 0.58 mg cm−2. At a high mass loading of 3.59 mg cm−2, high areal and mass specific capacitance of 3.24 F cm−2 and 811 F g−1 are obtained. Based on this, a hybrid supercapacitor is fabricated with high-mass-loading Co–Ni layered double hydroxide and active carbon as positive and negative electrodes, respectively. As a result, this device delivers a prominent energy density of 20.9 Wh cm−3 at a power density of 0.12 W cm−3.

Nitrogen and sulfur co-doped porous carbon fibers film for flexible symmetric all-solid-state supercapacitors

Abstract Flexible supercapacitors have drawn tremendous attention resulting from the rapid development of wearable electronic devices. Herein, we develop an effective and facile two-step approach to prepare high content nitrogen, sulfur co-doped porous carbon nanofibers film as electrodes of flexible supercapacitors. Benefiting from the high specific surface area and rich nitrogen/sulfur content, nitrogen and sulfur co-doped porous carbon fibers film (N, S co-doped PCFF) electrodes exhibit a high mass specific capacitance of 307.8 F g−1, and the capacitance retains 98% of initial capacitance after 5000 cycles in a three-electrode system. The as-assembled flexible supercapacitor devices with polyvinyl alcohol/KOH gel electrolyte demonstrate a highest mass specific capacitance of single electrode of 183.9 F g-1 at the scan rate of 2 mV s-1, which is better than that of other heteroatom doping carbon materials. In addition, the energy density reaches as high as 16.35 Wh kg−1 with the power density of 147 W kg−1 and retains as 5.34 Wh kg−1 with higher power density of 2402 W kg−1. Furthermore, the flexible devices show good cycling stability, superior flexibility and stable electrochemical performance.

Capacitance characteristic of PEDOT electrodeposited on different substrates

Poly(3,4-ethylenedioxythiophene) (PEDOT) has been electrochemically deposited on carbon paper (CP), stainless steel mesh (SSM), stainless steel (SS), and indium tin oxide (ITO) by unipolar-pulsed method. The surface morphology, micro-structure, and electrochemical capacitance for PEDOT/substrates were characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), and electrochemical techniques. The electrochemical capacity measurements of the PEDOT/CP electrode in 0.5 M H2SO4 shows high mass-specific capacitance of 126.24 F/g at a 1 mA/cm2, which is consistent with the specific capacitance of 126.75 F/g at 5 mV/s. Compared with PEDOT/SSM, PEDOT/SS, and PEDOT/ITO, PEDOT/CP electrode shows better capacitive performance, which presents good rate performance of 76.78% at 5 mA/cm2 and charge-discharge stability with the capacitance retention rate of 80.57% for 5000 cycles. SEM result shows PEDOT maintained the spindle-like structure along with the threads of each carbon fiber, which are densely packed and randomly oriented forming the porous structure.

High-performance solid state asymmetric supercapacitor based on electrochemically decorated 3D network-like Co3O4 architecture on NiO nanoworms

The unique 3D network-like cobalt oxide architecture was electrochemically deposited on nickel oxide nanoworms (NiONWs) with nickel foil (NF) substrate. After the anodic polarization of NF and its activation, a very thin film of NiO nanoworms with the average diameter of 30 nm and the length of 100 nm was successfully grown on anodized Ni foil (a-NF) by using a facile hydrothermal method under the mild conditions including a saturated alkaline solution of Ni2+ at 65 °C to prepare a-NF/NiONWs. Then, 3D network-like Co3O4 nanosheets with the average thickness of 25 nm were directly electrodeposited on a-NF/NiONWs by using cyclic voltammetry under the optimized experimental conditions. The morphologies and detailed geometrical structures of the electrodes were conducted by FE-SEM. The fabricated a-NF/NiONWs/Co3O4 electrode provides a high areal specific capacitance of 1320 mF cm-2 at a current density of 4 mA cm−2 and high mass specific capacitance of 2000 F g−1 at the current density of 6 A g−1. By using a-NF/NiONWs/Co3O4 as a positive electrode and reduced graphene oxide-deposited NF (RGO/NF) as a negative electrode, a solid-state asymmetric a-NF/NiONWs/Co3O4//RGO/NF supercapacitor was assembled and it exhibited a high specific capacitance of 471.4 mF cm-2 at a current density of 3 mA cm−2. The fabricated solid-state supercapacitor also showed good rate capacity and long-term cycling performance of 2000 cycles.

Hydrothermally controlled synthesis of α-MnO2, γ-MnOOH, and Mn3O4 nanomaterials with enhanced electrochemical properties

In this work, a facile hydrothermal method was used to obtain various manganese oxides nanomaterials including α-MnO2, γ-MnOOH, and Mn3O4 with different morphology based on the direct reaction between Mn(CH3COO)2·4H2O and NaOH. Gelatin and cetyltrimethylammonium bromide were adopted as dispersants to decrease the size and inhibit agglomeration of nanomaterials in the synthesis process. It is significant that the chemical composition and morphology of as-prepared materials can be controlled by solely tuning the hydrothermal time. All the findings of morphological and structural studies on α-MnO2, γ-MnOOH, and Mn3O4 nanomaterials show the regular shapes, pure crystal phases, and high specific surface areas (51.6–67.2 m2 g−1). Furthermore, those nanomaterials were applied as electrode materials in the presence of Na2SO4 electrolyte that exhibited the satisfactory electrochemical performances such as excellent redox reversibility, high mass specific capacitance, and eminent capacitance retention with minor loss after long-term cycles, which confirms that these manganese oxides nanomaterials are outstanding candidates of supercapacitors electrode materials.

Facile preparation of porous carbon nanomaterials for robust supercapacitors

Abstract

MnO2 Nanosheets Grown on Internal Surface of Macroporous Carbon with Enhanced Electrochemical Performance for Supercapacitors

Supercapacitor performance is strongly dependent on the utilization rate of electrode materials. In this paper, MnO2 nanosheets (MONSs) have been grown on the inner surface of macroporous carbon (MPC) for increasing the utilization rate. The MPC is prepared from luffa sponge fibers. The MPC possesses closely arranged straight channels at the micrometer scale, which makes the MONSs be able to grow on the inner surface. Because of sufficient exposure toward electrolyte, the MONSs exhibit high mass specific capacitance at different loadings such as 1332 F/g (150 μg/cm2) and 354 F/g (5690 μg/cm2). Because of the presence of the large pores allowing the electrolyte solution to access easily, the active materials are capable of working at high loadings, obtaining areal specific capacitance as high as 2.9 F/cm2. The assembled supercapacitors show a high specific energy of 194 μWh/cm2 at the specific power of 4.5 mW/cm2. As the luffa sponge is abundant and pollution-free in production, the MONSs/MPC is of high pr...

Growth of NiCo2O4@MnMoO4 Nanocolumn Arrays with Superior Pseudocapacitor Properties.

Three-dimensional heterostructured NiCo2O4@MnMoO4 nanocolumn arrays (NCAs) on Ni foam were first fabricated through an improved two-step hydrothermal process associated with a successive annealing treatment. The hybrid NiCo2O4@MnMoO4 electrode exhibited remarkable pseudocapacitor property with high initial mass specific capacitance of 1705.3 F g(-1) at 5 mA cm(-2), and retained 92.6% after 5000 cycles, compared to the bare NiCo2O4 electrode with 839.1 F g(-1) and 90.9%. The excellent capacitive property of the NiCo2O4@MnMoO4 hydrid was attributed to its high-electron/ion-transfer rate, large electrolyte infiltrate area, and more electroactive reaction sites.

Pseudocapacitive Hausmannite Nanoparticles with (101) Facets: Synthesis, Characterization, and Charge‐Transfer Mechanism

Hausmannite Mn3 O4 octahedral nanoparticles of 18.3 ± 7.0 nm with (101) facets have been prepared by an oxygen-mediated growth. The electrochemical properties of the Mn3 O4 particles as pseudocapacitive cathode materials were characterized both in half-cells and in button-cells. The Mn3 O4 nanoparticles exhibited a high mass-specific capacitance of 261 F g(-1), which was calculated from cyclic voltammetry analyses, and a capacitive retention of 78% after 10,000 galvanostatic charge-discharge cycles. The charge-transfer mechanisms of the Mn3 O4 nanoparticles were further studied by using synchrotron-based in situ X-ray absorption near edge spectroscopy and XRD. Both measurements showed concurrently that throughout the potential window of 0-1.2 V (vs. Ag/AgCl), a stable spinel structure of Mn3 O4 remained, and a reversible electrochemical conversion between tetrahedral [Mn(II) O4 ] and octahedral [Mn(III) O6 ] units accounted for the redox activity. Density functional theory calculations further corroborated this mechanism by confirming the enhanced redox stability afforded by the abundant and exposed (101) facets of Mn3 O4 octahedra.

Facile fabrication of multiwalled carbon nanotube/α-MnOOH coaxial nanocable films by electrophoretic deposition for supercapacitors

Multiwalled carbon nanotube (MWCNT)/α-MnOOH coaxial nanocable (MMCNC) films are successfully fabricated by a simple and low-cost electrophoretic deposition (EPD) process. The as-prepared MMCNC films exhibit three-dimensional (3D) nanoporous network structure. A possible mechanism is proposed to explain the formation of the MMCNC films. Electrochemical test results show that the films exhibit superior capacitive behaviors and cycle stability in 0.1 M Na2SO4 aqueous solution. The thickness, mass loading and capacitive performance of the MMCNC films can be easily and continuously tuned by varying the deposition time. A relatively high mass specific capacitance of 327 F g−1 is obtained from the films with relatively low mass loading of 0.05 mg cm−2, while, a relatively high areal capacitance of 0.2 F cm−2 is achieved when the mass loading was increased to 1.38 mg cm−2. The superior capacitive performances can be attributed to the unique structure advantages of the MMCNC films. On one hand, the one-dimensional (1D) coaxial nanocable structure works, with MWCNT core serving as high electronic conductive frame and α-MnOOH sheath providing high pseudocapacitance. On the other hand, the 3D nanoporous network structure can facilitate fast ions transportation.

High total-electrode and mass-specific capacitance cellulose nanocrystal-polypyrrole nanocomposites for supercapacitors

For practical applications, new supercapacitor electrode materials need to exhibit a high mass-specific capacitance (CM/F g−1), a high total-electrode capacitance (CE/F cm−2), and high stability during charge–discharge cycling. Very often, newly developed materials display high CM values for thin films (nm or μm thickness) but these rapidly drop off in the thicker electrode structures needed for commercial devices. In this work, we describe the fabrication of thick nanocomposites of polypyrrole (PPY) and cellulose nanocrystals (CNXLs) with consistently high capacitance (CM = 240 F g−1) and performance. CE of the PPY-CNXL nanocomposite increased linearly with increasing film thickness up to a value of 1.24 F cm−2 and this increased to a maximum of 1.54 F cm−2 for even thicker films where non-linear CE increases were due to electrolyte diffusion limitations. Testing of a symmetric supercapacitor with these high CE electrodes showed that it retained half of its initial capacity after 50 000 charge–discharge cycles, demonstrating the excellent stability of PPY-CNXL supercapacitor electrode materials.

Fabrication of manganese oxide electrodes by radio frequency sputtering for electrochemical capacitors

Manganese oxide thin films were sputtered on graphite foils by radio frequency (RF) sputtering. At the 1,000th cycle of potential cycling, maximum mass specific capacitance of 341 F g−1 was obtained in 0.5 M LiCl and with optimum sputtering conditions (5 sccm of oxygen, 20 mTorr, and 70 W) as well as annealing temperature (150 °C). These show its high electrochemical stability and good mass specific capacitance at a higher sweep rate of 100 mV s−1. In addition, the higher the volume flow rates of oxygen, the larger the amount of trivalent manganese oxide and the higher the surface roughness, the higher the mass specific capacitance at lower volume flow rates of oxygen, but the amounts of trivalent manganese oxide were almost the same and the mass specific capacitance decreased due to decreasing surface roughness at higher volume flow rates of oxygen. Furthermore, the geometric specific capacitance increases with increasing sputtering pressure and power.

Synthesis of mesoporous carbon as electrode material for supercapacitor by modified template method

The pore structures and electrochemical performances of mesoporous carbons prepared by silica sol template method as electrode material for supercapacitor were investigated. The mean pore size and mass specific capacitance of the mesoporous carbons increase with the increase of mass ratio of silica sol to carbon source (glucose). A modified template method, combining silica sol template method and ZnCl2 chemical activation method, was proposed to improve the mass specific capacitance of the mesoporous carbon with an improved BET surface area. The correlation of rate capability and pore structure was studied by constant current discharge and electrochemical impedance spectroscopy. A commercially available microporous carbon was used for comparison. The result shows that mesoporous carbon with a larger pore size displays a higher rate capability. Mesoporous carbon synthesized by modified template method has both high mass specific capacitance and good rate capability.