Anode For Asymmetric Supercapacitors Research Articles

Envisaging quantum capacitance in modified germanene: a first principle investigation

Two-dimensional (2D) nanomaterials with enhanced quantum capacitance have been in high demand over the past few years due to super capacitors application. A number of 2D nanosheet, including MoS2, arsenene, antimonene, and germanene, have also been explored for the same reason. The present investigation aims to explore modified germanene such as monovacant germanene/divacant germanene(MVG/DVG) and their derivatives, such as Ns substituted MVG/DVG and transition metal incorporated MVG. It is observed that 1N-MVG/3N-MVG shows the characteristics of a p-type semiconductor, while 3N-MVG/4N-DVG is considered as semiconductor. A robust binding of under-coordinated Ge to transition metals (TMs) at MVG surfaces suggests such functionalization can be accomplished. Except Ti and Co other studied TMs-MVG show metallic nature. Furthermore, it is revealed that there is an asymmetric CQ dispersion in 1N-MVG, 2N-MVG, 3N-MVG, and 4N-DVG, as opposed to the pristine germanene/MVG/DVG. Additionally, it is predicted that TMs such as Ti, V, Cr, Mn, Fe and Co incorporated MVG can provide high quantum capacitance (CQ). Enormous amount of CQ is noticed for 3N-MVG with maximum of 726 μF cm−2 in the positive biased region. Among TM-MVG, V-MVG and Mn-MVG are well suited to serve as anodes for asymmetric super capacitors due to their CQ peak of 978 μF cm−2 and 1180 μF cm−2, respectively, in negative bias region.

Fabrication of Co1.5Ni1.5S4 and Prussian blue analogues composites with yolk-shell heterostructures as cathode and biomass derived carbon as anode for asymmetric supercapacitors

As highly efficient electrode materials for supercapacitors, the clean production of transition metal sulfide and biomass-derived carbon played an important role in promoting the practical process. In this work, Prussian blue analogues were grown in situ on glycerate precursors through a simple ion-exchange process, followed by sulfidation to obtain the Co1.5Ni1.5S4 and Prussian blue analogues composite microspheres with yolk-shell structures. Thanks to the unique micro-nano structure and multi-element synergy, composites exhibited excellent specific capacitance (up to 2388.7 F g−1 at 1 A g−1), rate performance (55.0 % capacitance retention at 30 A g−1), and cycling stability (capacitance maintained at 81.5 % after 5000 cycles). In addition, Nitrogen-doped sunflower seed shell derived carbon, prepared by two pyrolysis and salt-activation processes, could attain a specific capacitance of 347.1 F g−1 at 1 A g−1 and an almost undiminished capacity of 5000 cycles. With Co1.5Ni1.5S4 and Prussian blue analogues composites as cathode and derived carbon as anode, the assembled hybrid supercapacitor exhibited an eminent energy density of 82.2 Wh kg−1 (at a power density of 904.9 W kg−1) and stable cycling characteristics (only 16.7 % loss of capacitance after 10,000 cycles). This work provided a feasible scheme for the structure regulation of sulfides and the defect construction of porous carbon.

High-performance CF/MXene/β-PbO2 materials as anodes for asymmetric supercapacitors

MXene has excellent capacitive properties as a two-dimensional material, but its cycling stability is poor. β-PbO2 is one of the common crystalline forms of lead dioxide, and it has excellent electrochemical properties and cyclic stability and has potential as a capacitor electrode material. However, the capacitive performance of β-PbO2 as a capacitor electrode material is not ideal. Therefore, CF/MXene/β-PbO2 (CMP) composites were prepared in this study by combining β-PbO2 with CF/MXene (CM) using a constant current electrodeposition method, and their electrochemical energy storage properties were investigated. The ordered structure of interwoven CF is used to fix MXene, which has metallic properties and large layer spacing, as the matrix material. This utilization enables faster ion transport and electron storage. The electrochemical advantages of β-PbO2 and CM can be unified by the synergistic effect of the composites, which results in a high specific capacity (399.42 F g−1) of the CMP electrode at 0.2 A g−1. In addition, the CM//CMP asymmetric supercapacitor constructed in 1 M Na2SO4 solution has a wide potential window of 2.0 V and a high specific capacitance of 193.8C g−1, and the capacity remains 54.3% of the initial value after 5000 cycles at a charge/discharge rate of 40 mA g−1. This work provides important research ideas and clues for the application of β-PbO2 composite electrode materials in supercapacitors.

Electrochemical performance of MoO3-RuO2/Ti in H2SO4 electrolyte as anodes for asymmetric supercapacitors

Based on the corrosion and low decomposition voltage of acid solutions, many electrodes are limited in the fields of supercapacitors. MoO3 has a wide potential window from -1.0 to 0.8 V in acid solution in theory. But there are very few reports of MoO3 used as anode due to its poor cycle stability and low electrochemical performance under a negative potential in most electrolyte solutions. The MoO3-RuO2/Ti was prepared by thermal decomposition. The phase structure, pore size, microstructure and capacitive characteristics of the MoO3-RuO2/Ti with different content of RuO2 were analyzed in detail by XRD, SEM, EDS, XPS, BET and electrochemical tests. The amorphous RuO2 was evenly distributed in MoO3. Remarkably, a high surface area and total pore volume were achieved by adding 5mol% RuO2 into MoO3, which resulted in a specific capacity of 639 C g–1 at 1A g–1. The poor cycle stability and electrochemical performance of MoO3 under a negative potential were greatly improved by adding RuO2. MoO3-RuO2/Ti used as anode in H2SO4 electrolyte was firstly discussed. The working voltage of MoO3-RuO2/Ti for anode was -0.35 to 0 V and had an excellent specific electrochemical performance. Asymmetric supercapacitor (ASC) was constructed using the MoO3-RuO2/Ti as anode and the IrO2-ZnO/Ti as cathode in H2SO4 electrolyte, which could be run under the potential range from 0 to 1.5 V. When the power density of asymmetric supercapacitor was 932 W kg–1 and 6580 W kg–1, the energy density was 80.5 Wh kg–1 and 57.4 Wh kg–1, respectively. Asymmetric supercapacitor with the MoO3-RuO2/Ti as anode and the RuO2-ZnO/Ti as cathode was also successfully assembled.

High-performance battery-type Fe1-xS@CFs anode for all-solid-state battery-type asymmetric supercapacitor with high energy density and wide working temperature range

Pseudo-capacitive materials with high performance are always combined with carbon-based materials applying for supercapacitors, which can realize satisfactory properties of energy storage while excellent cycle life. Enhancing electrochemical performance of anodes following the method is an effective method to get high energy densities. Herein, Fe1-xS grown on carbon nanofibers (Fe1-xS/CFs) through electrospinning and calcination approach, possesses excellent electrochemical properties when it serves as the anode for asymmetric supercapacitors. The specific capacity of which can reach up to 238 mAh g−1 (1 A g−1) while remain 95.3 mAh g−1 at 15 A g−1. The retention rate of the anode can retain 78.5% after 5000 cycles. Considering high performance of anode, NiCo2S4/NCTs with a high specific capacity of 203 mAh g−1 (1 A g−1) was selected as the cathode applying for all-solid-state battery-type asymmetric supercapacitor to get high energy density. Benefitting from excellent properties of both anode and cathode, as-fabricated all-solid-state battery-type asymmetric supercapacitor possesses high energy density of 55.4 Wh kg−1 at the power density of 882 W kg−1 with remarkable cyclic performance (80.6% after 5000 cycles). More important, all-solid-state battery-type asymmetric supercapacitor NiCo2S4/NCTs//Fe1-xS/CFs-5 can work with a wide temperature range (−10 to 60 °C), which can display a specific capacity of 40.4 mAh g−1 at 1 A g−1 in −10 °C and 112.3 mAh g−1 in 60 °C. All these results indicate that as-fabricated NiCo2S4/NCTs//Fe1-xS/CFs-5 battery-type asymmetric supercapacitor possesses great potential for future applications.

Polyoxometalates-Based Metal-Organic Frameworks Made by Electrodeposition and Carbonization Methods as Cathodes and Anodes for Asymmetric Supercapacitors.

Hybrid materials have obtained well-deserved attention for energy storage devices, because they show high capacitances and high energy densities induced by the synergistic effect between complementary components. Polyoxometalate-based metal-organic frameworks (POMOFs) possess the abundant redox-active sites and ordered structures of polyoxometalates (POMs) and metal-organic frameworks (MOFs), respectively. Here, an asymmetric supercapacitor (ASC) NENU-5/PPy/60//FeMo/C was fabricated in which both its electrodes are prepared from POMOF precursors. A typical POMOF material, NENU-5, was first connected with polypyrrole (PPy) through electrodeposition to form the cathode material NENU-5/PPy. Another representative POMOFs material, PMo12 @MIL-100, was carbonized to obtain the anode material FeMo/C. Cathode NENU-5/PPy exhibited an extraordinary capacitance of 508.62 F g-1 (areal capacitance: 2034.51 mF cm-2 ). In addition, anode FeMo/C shows excellent cyclic stability attributed to its unique structure. Finally, benefiting from the outstanding capacitances and structural merits of the anode and cathode, assembled asymmetric supercapacitor NENU-5/PPy/60//FeMo/C achieves an energy density of 1.12 mWh cm-3 at a power density output of 27.78 mW cm-3 , as well as a notable life of 10 000 cycles with an capacity retention of 80.62 %. Thus, the unique ASC is strongly competitive in high capacitance, long cycle life, and high energy-required energy storage devices.

Three-dimensional iron oxyhydroxide/reduced graphene oxide composites as advanced electrode for electrochemical energy storage

Three-dimensional (3D) electrodes hold great potential for supercapacitors (SCs) due to their unique architectures and prominent electrochemical properties. Herein, a kind of 3D FeOOH/reduced graphene oxide/Ni foam (FeOOH/rGO/NF) electrode with remarkable capacitive performance has been developed as a new anode for asymmetric supercapacitors (ASCs). Benefiting from the improved conductivity and increased surface area, the as-prepared 3D FeOOH/rGO/NF electrode exhibits a high areal capacitance of 406.5 mF cm−2 at 10 mV s−1. Moreover, when using the as-prepared 3D FeOOH/rGO/NF electrode as anode, a high-performance ASC device with a maximum volumetric energy density of 0.48 mWh cm−3 and excellent cycling stability is achieved.