Anode Materials For Asymmetric Supercapacitors Research Articles

Amplified Response of Nickel Oxide-Decorated Lanthanum Phosphate Composite as an Anode Material for Asymmetric Supercapacitors

Amplified Response of Nickel Oxide-Decorated Lanthanum Phosphate Composite as an Anode Material for Asymmetric Supercapacitors

Fe3O4 nanoparticles anchored on carbon nanotubes as high-performance anodes for asymmetric supercapacitors

Fe3O4/CNT composites are synthesized with ethylene glycol as solvent by a one-step solvothermal method and used as anode materials for asymmetric supercapacitors (ASC). An appropriate amount of water in ethylene glycol can accelerate the formation of Fe3O4 and reduce the average size of Fe3O4 to around 20 nm. However, spherical Fe3O4 particles larger than 100 nm will form in pure ethylene glycol for long reaction time. The Fe3O4/CNT composite with small Fe3O4 nanoparticles exhibits a high specific surface area, promoted electron transfer ability, as well as a high utilization rate of active materials. The optimized electrode shows a high specific capacity of 689 C g−1 at 1 A g−1, and remains 443 C g−1 at 10 A g−1. The inferior long-term cycling stability is due to the phase transition of Fe3O4 and a reductive effect to form metallic Fe. An ASC using Fe3O4/CNT and NiCoO2/C composites as anode and cathode, respectively, delivers a high energy density of 58.1 Wh kg−1 at a power density of 1007 W kg−1 in a voltage window of 1.67 V and has a capacity retention of 63% after 5000 cycles. The self-discharge behavior of the ASC is also investigated.

Direct Ink Writing (DIW) printed high-performance asymmetric supercapacitor based on 0D@2D silver-nanoparticles@MXene as anode and 0D@2D MnO2-nanoparticles@MXene as cathode materials

The electrochemical performance of printed asymmetric supercapacitors can be improved by designing and implementing properly engineered anode and cathode electrode materials with enriched redox kinetics. However, the development of high-performance printed anode/cathode electrodes with three-dimensional (3D) structures is crucial task. Direct Ink Writing (DIW) is a versatile advanced manufacturing technology for developing 3D complex electrode architectures for efficient energy storage devices. In addition, replacing conventional electric double-layer capacitors as anode materials with redox-driven electrodes can significantly improve the specific capacitance and energy density of asymmetric supercapacitors. Herein, for the first time, we report a 0D@2D silver-nanoparticles@Ti3C2 DIW printed anode material for asymmetric supercapacitors. The Ag-NPs@Ti3C2 hybrid material contributes a high-specific capacitance of 368.56 F g−1 at a current density of 1 A g−1 with a minimum specific capacitance of 233.84 F g−1 at 10 A g−1. To assemble the asymmetric supercapacitor device, 0D@2D MnO2@Ti3C2 DIW printed cathode is implemented, which displays excellent electrochemical performance in terms of specific capacitance (474.45 F g−1 at 1 A g−1). In the existence of all-printed advanced anode (Ag@Ti3C2) and cathode (MnO2@Ti3C2) materials, the asymmetric supercapacitor device shows a maximum energy density of 38.16 Wh kg−1 at a power density of 800 W kg−1, with a capacitance retention of up to 91.27 % after 5000 cycles. Thus, the application of DIW printed electrode materials with optimum electrochemical contributions provides new avenues for the development of high-performance energy storage devices.

Theoretical investigation of quantum capacitance of Co-doped α-MnO2 for supercapacitor applications using density functional theory.

The rapid depletion of fossil fuels and ever-growing energy demand have led to a search for renewable clean energy sources. The storage of renewable energy calls for immediate attention to the fabrication of efficient energy storage devices like supercapacitors (SCs). As an electrode material for SCs, MnO2 has gained wide research interest because of its high theoretical capacitance, variable oxidation state, vast abundance, and low cost. However, the low electric conductivity of MnO2 limits its practical application. The conductivity of MnO2 can be enhanced by tuning the electronic states through substitution doping with cobalt. In the present work, first principles analysis based on density functional theory (DFT) has been used to examine the quantum capacitance (CQC) and surface charge (Q) of Co-doped MnO2. Doping enhanced the structural stability, electrical conductivity, potential window, and quantum capacitance of α-MnO2. The shortened band gap and localized states near the Fermi level improve the CQC of α-MnO2. For the narrow potential range (-0.4 to 0.4 V), the CQC is observed to increase with doping concentration. The highest CQC value at +0.4 V is observed to be 2412.59 μF cm-2 for Mn6Co2O16 (25% doping), five times higher than that of pristine MnO2 (471.18 μF cm-2). Mn6Co2O16 also exhibits better CQC and 'Q' at higher positive bias. Hence, it can be used as an anode material for asymmetric supercapacitors. All these results suggest better capacitive performance of Co-doped α-MnO2 for aqueous SCs and as an anode material for asymmetric supercapacitors.

Freestanding vanadium nitride nanowire/nitrogen-doped graphene paper with hierarchical pore structure for asymmetric supercapacitor anode

Vanadium nitride (VN) is a promising anode material for asymmetric supercapacitors (ASCs) owing to its high theoretical pseudocapacitance and high electrical conductivity. However, the instability of VN in aqueous electrolytes hinders practical applications. In this study, VN nanowires (VNNWs) were hybridized with nitrogen-doped graphene (NG) to fabricate a freestanding VNNW/NG porous paper electrode. The prepared paper electrode exhibited excellent electrochemical performance with an outstanding specific capacitance of 244.7 F·g−1 at 0.5 A·g−1 and a rate capability of 70.7% capacitance retention as the current density increased from 1 to 10 A·g−1. Moreover, the VNNW/NG anode presented remarkable cycling stability of 87% capacitance retention over 10,000 cycles at 5 A·g−1. Encapsulation with NG significantly improved the stability of VNNWs, overcoming their major drawbacks (i.e., low cycling stability). Also, the hierarchical pore structure of the VNNG/NG could facilitate high energy and power density capabilities. An ASC assembled with VNNW/NG anode and nickel oxide/reduced graphene oxide (NiO/rGO) cathode presented high energy density of 20.2 Wh·kg−1 at power density of 850.0 W·kg−1. Thus, we suggest that the design strategy of the fabricated porous paper electrode could be utilized to produce high-performance anode materials for application in supercapacitors.

Design and synthesis of MOF-derived CuO/g-C3N4 composites with octahedral structures as advanced anode materials for asymmetric supercapacitors with high energy and power densities

Two-component composites consisting of transition metal copper oxide (CuO) and graphite carbon nitride (g-C3N4) were successfully synthesized. This CuO/g-C3N4 displays a high reversible specific capacity (1530.4 F g−1, 2 A g−1) as an anode material.

A facile synthesis strategy of fungi-derived porous carbon-based iron oxides composite for asymmetric supercapacitors

Transition metal oxides (TMOs) have been considered as potential anode materials for asymmetric supercapacitors due to their high theoretical capacities. However, undesirable electric conductivity limits the further application in future energy storage. Here, a honeycomb-like architecture of FeOx embedded in the fungi-derived porous carbon-based material (FeOx/C) for asymmetric supercapacitor was reported. The facile synthesis strategy of fungi-derived porous carbon-based iron oxides was using the carbon derived from fungi and the process of carbothermal reduction to form the iron oxide compound. This carbon-encapsulated iron oxide compound provides highly specific surface area (The specific surface area of Fe–O–C-650 was largest (up to 219.0905 m2/g) compared with samples of Fe–O–C-550(144.0304 m2/g), Fe–O–C-750(201.7352 m2/g), Fe–O–C-850(163.2206 m2/g).), an abundance of redox sites, sufficient efficient channels for fast transportation of ions, excellent electrical conductivity, and stable skeleton. Under the three-electrode test system, the FeOx/C electrode delivers excellent specific capacitance of 565F/g at 1 mV/s and impressive cycling performance with capacitance retention of 100% after 3000 cycles. And the NiO electrode delivers a high specific capacitance of 425 F/g at a high current density of 5 mV/s. In addition, the FeOx/C//NiO asymmetric supercapacitor was assembled which exhibits remarkable specific capacitance of 111F/g at 10 mV/s and gravimetric energy density of 36 Wh/kg as well as gravimetric power density of 800W/kg with capacitance retention of 100% after 20,000 cycles, approaching those of ions capacitors.

Iron oxide encapsulated in nitrogen-doped carbon as high energy anode material for asymmetric supercapacitors

A new strategy is proposed for the preparation of Fe3O4 encapsulated in N-doped carbon (denoted as Fe3O4@NC) through a self-assembly of the colloidal FeOOH with polyaniline (PANI) and then a subsequent pyrolysis. Benefiting from the well-designed heterostructure, the resultant Fe3O4@NC shows an ultra-high gravimetric capacitance of 313 F g−1 at 1 A g−1 and still delivers 193 F g−1 at a high current density of 15 A g−1, demonstrating an excellent rate performance. In addition, it has an outstanding volumetric capacitance of 20.25 F cm−3 at 1 A g−1. The asymmetric supercapacitors (ASCs) are constructed by using Fe3O4@NC as anode and layered double hydroxides (LDHs) as cathode, respectively. Due to the enlarged voltage window and matched capacity and kinetics, the obtained CoMn-LDH//Fe3O4@NC ASC device shows a remarkable electrochemical performance with a large energy density up to 35 Wh·kg−1 at a power density of 900 W kg−1 and a high energy density of 24 Wh·kg−1 at a power density of 13.5 kW kg−1 as well as an excellent rate capability and a good cycling stability. The present work may provide an insight into the design of novel anode materials for high-performance ASCs.

Fe2O3-decorated millimeter-long vertically aligned carbon nanotube arrays as advanced anode materials for asymmetric supercapacitors with high energy and power densities

An asymmetric supercapacitor with extremely high energy and power densities has been developed by using the novel Fe2O3/VACNTs anode.

Facile low-temperature synthesis of hematite quantum dots anchored on a three-dimensional ultra-porous graphene-like framework as advanced anode materials for asymmetric supercapacitors

Hematite quantum dots anchored on a 3D ultraporous graphene-like framework as anode materials showed superior electrochemical performance for asymmetric supercapacitors.

Hierarchical Fe₃O₄@Fe₂O₃ Core-Shell Nanorod Arrays as High-Performance Anodes for Asymmetric Supercapacitors.

Anode materials with relatively low capacitance remain a great challenge for asymmetric supercapacitors (ASCs) to pursue high energy density. Hematite (α-Fe2O3) has attracted intensive attention as anode material for ASCs, because of its suitable reversible redox reactions in a negative potential window (from 0 V to -1 V vs Ag/AgCl), high theoretical capacitance, rich abundance, and nontoxic features. Nevertheless, the Fe2O3 electrode cannot deliver large volumetric capacitance at a high rate, because of its poor electrical conductivity (∼10(-14) S/cm), resulting in low power density and low energy density. In this work, a hierarchical heterostructure comprising Fe3O4@Fe2O3 core-shell nanorod arrays (NRAs) is presented and investigated as the negative electrode for ASCs. Consequently, the Fe3O4@Fe2O3 electrode exhibits superior supercapacitive performance, compared to the bare Fe2O3 and Fe3O4 NRAs electrodes, demonstrating large volumetric capacitance (up to 1206 F/cm(3) with a mass loading of 1.25 mg/cm(2)), as well as good rate capability and cycling stability. The hybrid electrode design is also adopted to prepare Fe3O4@MnO2 core-shell NRAs as the positive electrode for ASCs. Significantly, the as-assembled 2 V ASC device delivered a high energy density of 0.83 mWh/cm(3) at a power density of 15.6 mW/cm(3). This work constitutes the first demonstration of Fe3O4 as the conductive supports for Fe2O3 to address the concerns about its poor electronic and ionic transport.

Facile Synthesis of Hematite Quantum‐Dot/Functionalized Graphene‐Sheet Composites as Advanced Anode Materials for Asymmetric Supercapacitors

For building high‐energy density asymmetric supercapacitors, developing anode materials with large specific capacitance remains a great challenge. Although Fe2O3 has been considered as a promising anode material for asymmetric supercapacitors, the specific capacitance of the Fe2O3‐based anodes is still low and cannot match that of cathodes in the full cells. In this work, a composite material with well dispersed Fe2O3 quantum dots (QDs, ≈2 nm) decorated on functionalized graphene‐sheets (FGS) is prepared by a facile and scalable method. The Fe2O3 QDs/FGS composites exhibit a large specific capacitance up to 347 F g−1 in 1 m Na2SO4 between –1 and 0 V versus Ag/AgCl. An asymmetric supercapacitor operating at 2 V is fabricated using Fe2O3/FGS as anode and MnO2/FGS as cathode in 1 m Na2SO4 aqueous electrolyte. The Fe2O3/FGS//MnO2/FGS asymmetric supercapacitor shows a high energy density of 50.7 Wh kg−1 at a power density of 100 W kg−1 as well as excellent cycling stability and power capability. The facile synthesis method and superior supercapacitive performance of the Fe2O3 QDs/FGS composites make them promising as anode materials for high‐performance asymmetric supercapacitors.

Novel iron oxyhydroxide lepidocrocite nanosheet as ultrahigh power density anode material for asymmetric supercapacitors.

A simple one-step electroplating route is proposed for the synthesis of novel iron oxyhydroxide lepidocrocite (γ-FeOOH) nanosheet anodes with distinct layered channels, and the microstructural influence on the pseudocapacitive performance of the obtained γ-FeOOH nanosheets is investigated via in situ X-ray absorption spectroscopy (XAS) and electrochemical measurement. The in situ XAS results regarding charge storage mechanisms of electrodeposited γ-FeOOH nanosheets show that a Li(+) can reversibly insert/desert into/from the 2D channels between the [FeO6 ] octahedral subunits depending on the applied potential. This process charge compensates the Fe(2+) /Fe(3+) redox transition upon charging-discharging and thus contributes to an ideal pseudocapacitive behavior of the γ-FeOOH electrode. Electrochemical results indicate that the γ-FeOOH nanosheet shows the outstanding pseudocapacitive performance, which achieves the extraordinary power density of 9000 W kg(-1) with good rate performance. Most importantly, the asymmetric supercapacitors with excellent electrochemical performance are further realized by using 2D MnO2 and γ-FeOOH nanosheets as cathode and anode materials, respectively. The obtained device can be cycled reversibly at a maximum cell voltage of 1.85 V in a mild aqueous electrolyte, further delivering a maximum power density of 16 000 W kg(-1) at an energy density of 37.4 Wh kg(-1).

High-performance asymmetric supercapacitors based on MnFe2O4/graphene nanocomposite as anode material

MnFe2O4/graphene nanocomposite is synthesized and demonstrated as promising anode material for asymmetric supercapacitors. An asymmetric supercapacitor operating at 1.8V is fabricated using MnFe2O4/graphene as anode and MnO2/carbon nanotube as cathode. The asymmetric supercapacitor shows an energy density of 25.9Whkg−1 at a power density of 225Wkg−1 and an energy density of 18.1Whkg−1 at a power density of 14.4kWkg−1, indicating an excellent power capability.

Preparation and characterization of ramsdellite Li 2Ti 3O 7 as an anode material for asymmetric supercapacitors

Ramsdellite Li 2Ti 3O 7 was first synthesized via sol–gel process with good crystallity of an average particle size of 0.175 μm. The product was thoroughly investigated as a lithium intercalation compound, and as an active anode material in asymmetric supercapacitors coupling with activated carbon as cathode. Lithium intercalation reactions were found occurring at 1.32 and 1.62 V versus Li/Li +, respectively. A reversible specific capacity of 150 mA h g −1 at 1 C was obtained on Li 2Ti 3O 7 electrode in a nonaqueous electrolyte. The charge current was found to strongly influence the anodic discharge capacity in the asymmetric cell. The capacity retention at 10 C charge–discharge rate was found to be 75.9% in comparison with that at 1 C.