Project description:One-dimensional (1D) yarn or fiber-based supercapacitors that have small diameter, volume and high mechanical strength are needed due to the demands on power source for wearable electronics, micro-devices, and implantable medical devices. The composite sheath is fabricated on a commercially available CNT yarn substrate by alternating depositions of MnO2 and Ag layers. Synergistic effect of high loading level of pseudocapacitive MnO2 and reasonably improved rate-capability are achieved. In the composite sheath, the interconnected networks provide electrical contact between MnO2 aggregates and adjacent Ag layer. The conductive Ag inter layers shorten the solid-state charge diffusion length in the MnO2. Moreover, generated electrons during the charge/discharge process can be collected rapidly by the adjacent Ag layer, therefore, the great extents of MnO2 could be loaded onto the surface of CNT core fiber electrode without a significant rate-capability degradation. Due to the high MnO2 loading level, the composite sheath-core yarn supercapacitor showed excellent specific areal capacitance (322.2 mF/cm2) and according energy density (18.3 µWh/cm2).
Project description:In this study, α-MnO2 and Fe2O3 nanomaterials are prepared on a carbon fiber modified with carbon nanotubes to produce the nonbinder core-shell positive (α-MnO2@CNTs/CC) and negative (Fe2O3@CNTs/CC) electrodes that can be operated in a wide voltage window in ultrafast asymmetrical flexible supercapacitors. MnO2 and Fe2O3 have attracted wide research interests as electrode materials in energy storage applications because of the abundant natural resources, high theoretical specific capacities, environmental friendliness, and low cost. The electrochemical performance of each electrode is assessed in 1 M Na2SO4 and the energy storage properties of the supercapacitors consisting of the two composite electrodes are determined in Na2SO4 and EMImBF4 electrolytes in the 2 V and 4 V windows. The 2 V supercapacitor can withstand a large scanning rate of 5000 mV S-1 without obvious changes in the cyclic voltammetry (CV) curves, besides showing a maximum energy density of 57.29 Wh kg-1 at a power density of 833.35 W kg-1. Furthermore, the supercapacitor retains 87.06% of the capacity after 20,000 galvanostatic charging and discharging (GCD) cycles. The 4 V flexible supercapacitor shows a discharging time of 1260 s and specific capacitance of 124.8 F g-1 at a current of 0.5 mA and retains 87.77% of the initial specific capacitance after 5000 GCD cycles. The mechanical robustness and practicality are demonstrated by physical bending and the powering of LED arrays. In addition, the contributions of the active materials to the capacitive properties and the underlying mechanisms are explored and discussed.
Project description:Transition metal oxides are known as the active materials for capacitors. As a class of transition metal oxide, Magnéli phase TiO x is particularly attractive because of its excellent conductivity. This work investigated the electrochemical characteristics of TiO x and its composite with reduced graphene oxide (rGO). Two types of TiO x , i.e. low and high reduction extent, were employed in this research. Electrochemical impedance spectroscopy revealed that TiO x with lower reduction extent delivered higher electro-activity and charge transfer resistance at the same time. However, combining 10% of low-reduction state TiO x and rGO using a simple mixing process delivered a high specific capacitance (98.8 F g-1), which was higher than that of standalone rGO (49.5 F g-1). A further improvement in the specific capacitance (102.6 F g-1) was given by adding PEDOT:PSS conductive polymer. Results of this research gave a basic understanding in the electrochemical behavior of Magnéli phase TiO x for the utilization of this material as supercapacitor in the future.
Project description:MnO2-MWNT-Ni foam supercapacitor electrodes were developed based on directly grown multiwalled carbon nanotubes (MWNTs) and hydrothermal MnO2 nanostructures on Ni foam substrates. The electrodes demonstrated excellent electrochemical and battery properties. The charge transfer resistance dropped 88.8% compared with the electrode without MWNTs. A high specific capacitance of 1350.42 F·g-1 was reached at the current density of 6.5 A·g-1. The electrode exhibited a superior rate capability with 92.5% retention in 25,000 cycles. Direct MWNT growth benefits the supercapacitor application for low charge transfer resistance and strong MWNT-current collector binding.
Project description:Manganese dioxide and its derivatives are widely used as promising electrode materials for supercapacitors. To achieve the environmentally friendly, simple, and effective material synthesis requirements, the laser direct writing method is utilized to pyrolyze the MnCO3/carboxymethylcellulose (CMC) precursors to MnO2/carbonized CMC (LP-MnO2/CCMC) in a one-step and mask-free way successfully. Here, CMC is utilized as the combustion-supporting agent to promote the conversion of MnCO3 into MnO2. The selected materials have the following advantages: (1) MnCO3 is soluble and can be converted into MnO2 with the promotion of a combustion-supporting agent. (2) CMC is an eco-friendly and soluble carbonaceous material, which is widely used as the precursor and combustion-supporting agent; (3) the redundant part of the MnCO3/CMC precursor can be removed by deionized water, which is simple and convenient. The different mass ratios of MnCO3 and CMC-induced LP-MnO2/CCMC(R1) and LP-MnO2/CCMC(R1/5) composites are investigated in the electrochemical performance toward electrodes, respectively. The LP-MnO2/CCMC(R1/5)-based electrode showed the high specific capacitance of 74.2 F/g (at the current density of 0.1 A/g) and good electrical durability for 1000 times charging-discharging cycles. Simultaneously, the sandwich-like supercapacitor which was assembled by LP-MnO2/CCMC(R1/5) electrodes presents the maximum specific capacitance of 49.7 F/g at the current density of 0.1 A/g. Moreover, the LP-MnO2/CCMC(R1/5)-based energy supply system is used to light a light-emitting diode, which demonstrates the great potential of LP-MnO2/CCMC(R1/5)-based supercapacitors for power devices.
Project description:Nitrogen-doped multiwalled carbon nanotubes (N-MWCNTs) have been used to fabricate nanostructured materials for various energy devices, such as supercapacitors, sensors, batteries, and electrocatalysts. Nitrogen-doped carbon-based electrodes have been widely used to improve supercapacitor applications via various chemical approaches. Based on previous studies, CuO@MnO2 and CuO@MnO2/N-MWCNT composites were synthesized using a sonication-supported hydrothermal reaction process to evaluate their supercapacitor properties. The structural and morphological properties of the synthesized composite materials were characterized via Raman spectroscopy, XRD, SEM, and SEM-EDX, and the morphological properties of the composite materials were confirmed by the nanostructured composite at the nanometer scale. The CuO@MnO2 and CuO@MnO2/N-MWCNT composite electrodes were fabricated in a three-electrode configuration, and electrochemical analysis was performed via CV, GCD, and EIS. The composite electrodes exhibited the specific capacitance of ~ 184 F g-1 at 0.5 A g-1 in the presence of a 5 M KOH electrolyte for the three-electrode supercapacitor application. Furthermore, it exhibited significantly improved specific capacitances and excellent cycling stability up to 5000 GCD cycles, with a 98.5% capacity retention.
Project description:Commercial application of supercapacitors (SCs) requires high mass loading electrodes simultaneously with high energy density and long cycle life. Herein, we have reported a ternary multi-walled carbon nanotube (MWCNT)/MnO2/reduced graphene oxide (rGO) nanocomposite for SCs with commercial-level mass loadings. The ternary nanocomposite was synthesized using a facile ultrasound-assisted one-pot method. The symmetric SC fabricated with ternary MWCNT/MnO2/rGO nanocomposite demonstrated marked enhancement in capacitive performance as compared to those with binary nanocomposites (MnO2/rGO and MnO2/MWCNT). The synergistic effect from simultaneous growth of MnO2 on the graphene and MWCNTs under ultrasonic irradiation resulted in the formation of a porous ternary structure with efficient ion diffusion channels and high electrochemically active surface area. The symmetric SC with commercial-level mass loading electrodes (∼12 mg cm-2) offered a high specific capacitance (314.6 F g-1) and energy density (21.1 W h kg-1 at 150 W kg-1) at a wide operating voltage of 1.5 V. Moreover, the SC exhibits no loss of capacitance after 5000 charge-discharge cycles showcasing excellent cycle life.
Project description:Three kinds of MnO₂/Ni foam composite electrode with hierarchical meso-macroporous structures were prepared using potentiodynamic (PD), potentiostatic (PS), and a combination of PS and PD(PS + PD) modes of electrodeposition. The electrodeposition mode markedly influenced the surface morphological, textural, and supercapacitive properties of the MnO₂/Ni electrodes. The supercapacitive performance of the MnO₂/Ni electrode obtained via PS + PD(PS + PD(MnO₂/Ni)) was found to be superior to those of MnO₂/Ni electrodes obtained via PD and PS, respectively. Moreover, an asymmetric supercapacitor device, activated carbon (AC)/PS + PD(MnO₂/Ni), utilizing PS + PD(MnO₂/Ni) as a positive electrode and AC as a negative electrode, was fabricated. The device exhibited an energy density of 7.7 Wh·kg-1 at a power density of 600 W·kg-1 and superior cycling stability, retaining 98% of its initial capacity after 10,000 cycles. The good supercapacitive performance and excellent stability of the AC/PS + PD(MnO₂/Ni) device can be ascribed to its high surface area, hierarchical structure, and interconnected three-dimensional reticular configuration of the nickel metal support, which facilitates electrolyte ion intercalation and deintercalation at the electrode/electrolyte interface and mitigates volume change during repeated charge/discharge cycling. These results demonstrate the great potential of the combination of PS and PD modes for MnO₂ electrodeposition for the development of high-performance electrodes for supercapacitors.
Project description:Mesoporous Mn1.5Co1.5O₄ (MCO) spinel films were prepared directly on a conductive nickel (Ni) foam substrate via electrodeposition and an annealing treatment as supercapacitor electrodes. The electrodeposition time markedly influenced the surface morphological, textural, and supercapacitive properties of MCO/Ni electrodes. The (MCO/Ni)-15 min electrode (electrodeposition time: 15 min) exhibited the highest capacitance among three electrodes (electrodeposition times of 7.5, 15, and 30 min, respectively). Further, an asymmetric supercapacitor that utilizes (MCO/Ni)-15 min as a positive electrode, a plasma-treated activated carbon (PAC)/Ni electrode as a negative electrode, and carboxymethyl cellulose-lithium nitrate (LiNO₃) gel electrolyte (denoted as (PAC/Ni)//(MCO/Ni)-15 min) was fabricated. In a stable operation window of 2.0 V, the device exhibited an energy density of 27.6 Wh·kg-1 and a power density of 1.01 kW·kg-1 at 1 A·g-1. After 5000 cycles, the specific energy density retention and power density retention were 96% and 92%, respectively, demonstrating exceptional cycling stability. The good supercapacitive performance and excellent stability of the (PAC/Ni)//(MCO/Ni)-15 min device can be ascribed to the hierarchical structure and high surface area of the (MCO/Ni)-15 min electrode, which facilitate lithium ion intercalation and deintercalation at the electrode/electrolyte interface and mitigate volume change during long-term charge/discharge cycling.