The demand for a new generation of flexible, portable, and high‐capacity power sources increases rapidly with the development of advanced wearable electronic devices. Here we report a simple process for large‐scale fabrication of self‐standing composite film electrodes composed of NiCo2O4@carbon nanotube (CNT) for supercapacitors. Among all composite electrodes prepared, the one fired in air displays the best electrochemical behavior, achieving a specific capacitance of 1,590 F g−1 at 0.5 A g−1 while maintaining excellent stability. The NiCo2O4@CNT/CNT film electrodes are fabricated via stacking NiCo2O4@CNT and CNT alternately through vacuum filtration. Lightweight, flexible, and self‐standing film electrodes (≈24.3 µm thick) exhibit high volumetric capacitance of 873 F cm−3 (with an areal mass of 2.5 mg cm−2) at 0.5 A g−1. An all‐solid‐state asymmetric supercapacitor consists of a composite film electrode and a treated carbon cloth electrode has not only high energy density (≈27.6 Wh kg−1) at 0.55 kW kg−1 (including the weight of the two electrodes) but also excellent cycling stability (retaining ≈95% of the initial capacitance after 5000 cycles), demonstrating the potential for practical application in wearable devices.
Manganese oxides of different structures, especially α-MnO 2 , have been extensively studied as electrodes for pseudocapacitors. However, the poor stability associated with intercalation of proton has been the main obstacle to their commercial applications. To effectively mitigate this problem, it is necessary to fully understand the energy storage mechanism of the MnO 2 phases. In this study, δ phase MnO 2 has been synthesized through controllable electroplating on architectural Ga-doped ZnO (GZO) bones, demonstrating a high specific capacitance of 1,068 F g -1 and high stability (slight performance drop focus on the first 2,000 cycles and then remained relatively constant in the subsequent 13,000 cycles). The charge storage mechanism of the δ-MnO 2 coated GZO has been carefully investigated at this limiting reaction 2 condition. Results suggest that the amount of charge stored in the electrode material correlates well with the amount of Na + inserted into the electrode material from the electrolyte. It is also noted that no spectral features corresponding to H + insertion were detected during cycling when the sample was probed using in operando Raman spectroscopy. Therefore, for layered δ-MnO 2 , a charge storage mechanism of Na + intercalation/deintercalation dominated, accompanied by interlayer spacing expansion/contraction, is proposed. Moreover, theoretical calculations also confirmed that the insertion of Na + is more energetically favorable than H + at all sites of the interlayer in δ-MnO 2 , offering a rational explanation of the proposed mechanism and the observed excellent stability.
With the development of smart grid, demand-side resources (DSR) will play an increasingly important role in the power balance of supply and demand. In addition, the requirement of a low-carbon smart grid means some policy backgrounds, such as carbon emissions trading (CET), should not be ignored. Under these circumstances, it is a good idea to construct a novel unit commitment (UC) model. This paper proposes a model that not only takes advantage of various resources on the demand side, such as electric vehicles, demand response, and distributed generation, but also reflects the effects of CET on generation schedule. Then, an improved particle swarm optimization (IPSO) algorithm is applied to solve the problem. In numerical studies, we analyze the impacts of DSR and CET on the results of UC, respectively. In addition, two meaningful experiments are conducted to study the approaches to allocate emission quotas and the effects of price transmission mechanism.
Index Terms-Carbon emission quotas, carbon emissions trading (CET), demand response (DR), distributed generation (DG), electric vehicle (EV), improved particle swarm optimization (IPSO), smart grid, unit commitment (UC).
Index bIndex of bus. i Index of generating unit. j Index of electric vehicle (EV). t Index of hour. Variables and Functions DGa t Distributed generation (DG) used by its owners at time t. DGb t Output of grid-connected DG at time t. DGC Total cost (TC) of DG. DRC TC of demand response (DR). Emission of unit i at time t. E V2G,t Emission of vehicle-to-grid (V2G) at time t. FC i Fuel cost of unit i. I i,t On/off status of unit i at time t. Iter Current number of iteration. pc Probability of crossover. P i,t Output of unit i at time t. pm Probability of mutation. SC i,t Start-up cost of unit i at time t. SoC t,j State of charge of EV j at time t. TC TC of unit commitment (UC). V2GC TC of V2G. V2G t Output of V2G at time t. V2G t,j Output of V2G of EV j at time t. X on i,t , X off i,t Duration of continuously on/off of unit i at time t. η t Penetration rate of DG at time t.
α-Fe2O3 and reduced
graphene oxide (rGO) composites, α-Fe2O3/rGO, have been synthesized via a simple hydrothermal method accompanied
by surface potential tuning. The obtained samples exhibit good electrochemical
performance with a wide negative potential window of −1–0.2
V vs Ag/AgCl when serving as supercapacitor electrodes. There is only
about 10% decay after 11 000 cycles of galvanostatic charge–discharge
(GCD) test. After a few tens of cycles of cycling activity, the capacitance
achieved a stable value of 255 F g–1 at 0.5 A g–1 and 174 F g–1 at 5 mV s–1; 75% of the capacitance was retained when the scan rate increased
to 200 mV s–1, indicating satisfactory power density.
Most attractively, along with cycling, the α-Fe2O3 particles begin to be well-wrapped by rGO gradually from
prior stacked structure, which is supposed to be the key factor for
the exceptional high cycling stability.
Self-standing and flexible films worked as pseudocapacitor electrodes have been fabricated via a simple vacuum-filtration procedure to stack δ-MnO2@carbon nanotubes (CNTs) composite layer and pure CNT layer one by one with CNT layers ended. The lightweight CNTs layers served as both current collector and supporter, while the MnO2@CNTs composite layers with birnessite-type MnO2 worked as active layer and made the main contribution to the capacitance. At a low discharge current of 0.2 A g(-1), the layered films displayed a high areal capacitance of 0.293 F cm(-2) with a mass of 1.97 mg cm(-2) (specific capacitance of 149 F g(-1)) and thickness of only 16.5 μm, and hence an volumetric capacitance of about 177.5 F cm(-3). Moreover, the films also exhibited a good rate capability (only about 15% fading for the capacitance when the discharge current increased to 5 A g(-1) from 0.2 A g(-1)), outstanding cycling stability (about 90% of the initial capacitance was remained after 5,000 cycles) and high flexibility (almost no performance change when bended to different angles). In addition, the capacitance of the films increased proportionally with the stacked layers and the geometry area. E.g., when the stacked layers were three times many with a mass of 6.18 mg cm(-2), the areal capacitance of the films was increased to 0.764 F cm(-2) at 0.5 A g(-1), indicating a high electronic conductivity. It is not overstated to say that the flexible and lightweight layered films emerged high potential for future practical applications as supercapacitor electrodes.
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