The hierarchical and porous MnO sub(2)-modified diatomite structures are prepared for the first time by a one-pot hydrothermal method. The morphology and structure of MnO sub(2)-modified diatomite ...hierarchical structures are examined by focus ion beam scanning electron microscopy (FIB/SEM) and X-ray diffraction spectroscopy (XRD). The results show that Birnessite-type MnO sub(2) nanosheets are observed to grow vertically on the purified diatomite, thus building hierarchical architecture. Furthermore, the electrochemical properties of the MnO sub(2)-modified diatomite electrodes are elucidated by cyclic voltammograms, galvanostatic charge/discharge tests and electrochemical impedance spectroscopy in 1 M Na sub(2)SO sub(4) electrolyte. The electrochemical results demonstrate that the MnO sub(2)-modified diatomite electrode exhibits highly reversible features and good rate abilities, respectively. Significantly, it exhibits the specific capacitance of 202.6 F g super(-1) for the MnO sub(2)-modified diatomite and 297.8 F g super(-1) for the MnO sub(2) nanostructures after etching the diatomite. The capacitance retention of 95.92% over 5000 cycles further indicates the suitability of the low-cost MnO sub(2)-modified diatomite structure as a potential electrode material for supercapacitors.
High specific surface area carbon has been modified with para-benzoquinone (p-BQ) via Friedel-Crafts reaction catalyzed by Iron(III) chloride followed by oxidation, in order to explore alternative ...strategies for obtaining high energy density supercapacitor materials by the combination of the double layer capacitance of carbons with the redox pseudocapacitance of the organic redox couple added on the carbon surface. Suitable structural and physicochemical characterization proved the formation of covalent bonds between carbon and p-BQ, and the electrochemical characterization showed a significant increase in gravimetric capacitance values after the addition of p-BQ which is maintained even after many cycles. This gravimetric capacitance increase was not only due to the redox reactions of p-BQ, but also to an increased double layer capacitance after p-BQ modification even when the BET surface area decreases after modification. A correlation with the pore structure of carbons showed that the increased double layer capacitance can be attributed to a better matching of carbon pore size with the size of electrolyte ions after p-BQ addition. Thus, this new addition strategy opens the way for the development of carbon-based materials for supercapacitors with higher energy densities coming from both increased pseudocapacitive reactions and increased double layer capacitance.
Poly3,4-(ethylenedioxy)thiophene (PEDOT) nanocomposites (NCs) reinforced by varying titanium(IV)-doped iron(III) nano oxide (NITO) particles have been fabricated in dodecylbenzene sulphonic acid by ...in situ polymerization process using ammonium perdisulfate as initiator. The samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, electron microscopy, BET surface analysis etc. followed by subsequent evaluation of thermal properties, temperature-dependent 3D electrical transport. Thermal stability of the NCs increased with increasing NITO amount in PEDOT matrix. Electrical conductivity of the NCs increased significantly with increasing NITO content (0.45a67.73 S cm-1) and also with the temperature (50a300 K). 3D variable range hopping conduction mechanism explained the conduction pathways. Specific capacitance of NCs are enhanced with higher NITO content in polymer from 107 F ga1 (pristine PEDOT) to 158 F ga1 (NC) owing to the development of mesoporous (pore size: 4.1 nm and cylindrical pore volume: 0.103 cm3 ga1) structure and high specific surface area (~104 m2 ga1).
A novel reduced graphene oxide (RGO)-Cu(2)O-TiO(2) ternary nanocomposite was successfully fabricated via a facile one-step solution-phase method. The synthesized RGO-Cu(2)O-TiO(2) nanocomposite was ...characterized by X-ray powder diffraction, transmission electron microscopy, atomic force microscopy and Raman spectroscopy, and its electrochemical properties as an active electrode material for supercapacitors were investigated through cyclic voltammetry (CV) and galvanostatic charge/discharge measurements in a 6 M KOH aqueous electrolyte. The obtained RGO-Cu(2)O-TiO(2) nanocomposite exhibits a specific capacitance of 80 F g(-1) at a current density of 0.2 A g(-1) in the 6 M KOH electrolyte, nearly twice the value of 41.4 F g(-1) for the RGO-Cu(2)O nanocomposite and 2.5 times the value of 32.7 F g(-1) for the RGO-TiO(2) nanocomposite. Furthermore, the specific capacitance of RGO-Cu(2)O-TiO(2) increases from 80 to 91.5 F g(-1) after 1000 cycles, which can be said the least that the capacitance has not changed within error, while the specific capacitances of RGO-Cu(2)O and RGO-TiO(2) decrease from 41.4 to 34.5 F g(-1) and from 32.7 to 25.2 F g(-1), respectively.
Improving the capacitance of carbon materials for supercapacitors without sacrificing their rate performance, especially volumetric capacitance at high mass loadings, is a big challenge because of ...the limited assessable surface area and sluggish electrochemical kinetics of the pseudocapacitive reactions. Here, it is demonstrated that “self‐doping” defects in carbon materials can contribute to additional capacitance with an electrical double‐layer behavior, thus promoting a significant increase in the specific capacitance. As an exemplification, a novel defect‐enriched graphene block with a low specific surface area of 29.7 m2 g−1 and high packing density of 0.917 g cm−3 performs high gravimetric, volumetric, and areal capacitances of 235 F g−1, 215 F cm−3, and 3.95 F cm−2 (mass loading of 22 mg cm−2) at 1 A g−1, respectively, as well as outstanding rate performance. The resulting specific areal capacitance reaches an ultrahigh value of 7.91 F m−2 including a “self‐doping” defect contribution of 4.81 F m−2, which is dramatically higher than the theoretical capacitance of graphene (0.21 F m−2) and most of the reported carbon‐based materials. Therefore, the defect engineering route broadens the avenue to further improve the capacitive performance of carbon materials, especially for compact energy storage under limited surface areas.
Owing to the significantly improved double‐layer capacitance originating from the “self‐doping” defects, defective graphene blocks with high defect density (ID/IG = 2.16), high packing density (0.917 g cm–3), and low specific surface area (29.7 m2 g–1) show an integration of high gravimetric, volumetric, and areal capacitances for supercapacitors.
Noticeable pseudo‐capacitance behavior out of charge storage mechanism (CSM) has attracted intensive studies because it can provide both high energy density and large output power. Although cyclic ...voltammetry is recognized as the feasible electrochemical technique to determine it quantitatively in the previous works, the results are inferior due to uncertainty in the definitions and application conditions. Herein, three successive treatments, including de‐polarization, de‐residual and de‐background, as well as a non‐linear fitting algorithm are employed for the first time to calibrate the different CSM contribution of three typical cathode materials, LiFePO4, LiMn2O4 and Na4Fe3(PO4)2P2O7, and achieve well‐separated physical capacitance, pseudo‐capacitance and diffusive contributions to the total capacity. This work can eliminate misunderstanding concepts and correct ambiguous results of the pseudo‐capacitance contribution and recognize the essence of CSM in electrode materials.
Well‐separated physical capacitance, pseudo‐capacitance, and diffusive capacity are achieved from the CV curves of typical electrode materials for metal‐ion batteries after three successive treatments including de‐polarization, de‐residual and de‐background as well as non‐linear fitting calculation, offering a more rational and reliable method to calculate the pseudo‐capacitance contribution.
In order to describe the influence of Pr sub(6)O sub(11) on thermal and electrochemical performance of polyaniline (PANI), PANI/Pr sub(6)O sub(11) composites were synthesized by in situ ...polymerization in the presence of sulfosalicylic acid (as dopant). The composites obtained was characterized by scanning electron microscope, Fourier transform infrared spectra, and X-ray diffraction. The thermal stability of the composites was investigated by thermogravimetry and derivative thermogravimetry. Finally, the comparative analysis on the electrochemical properties of PANI/Pr sub(6)O sub(11) composites electrodes, such as cyclic voltammetry, electrochemical impedance spectroscopy, and constant current charge-discharge test, was conducted under similar conditions. Scanning electron microscope, infrared, and X-ray diffraction results show that interaction exists between PANI and Pr sub(6)O sub(11), and the composites are more crystalline than pure PANI. Thermogravimetry and derivative thermogravimetry analyses indicate that PANI/Pr sub(6)O sub(11) composites and pure PANI have similar thermal stability. Moreover, the studies regarded to capacitive properties show that the electrochemical performance of the composites is improved greatly when Pr sub(6)O sub(11) is added in small amount. However, with increasing the amount of Pr sub(6)O sub(11), the electrochemical performance of the composites become worse, which indicates a large amount of Pr sub(6)O sub(11) has a negative effect on the capacitance. These results suggest that PANI is still in the conductive form after inserting the Pr sub(6)O sub(11), and the capacitance performance of PANI can be improved only by a low percentage of Pr sub(6)O sub(11). Copyright copyright 2013 John Wiley & Sons, Ltd.
For the proliferation of the supercapacitor technology, it is essential to attain superior areal and volumetric performance. Nevertheless, maintaining stable areal/volumetric capacitance and rate ...capability, especially for thick electrodes, remains a fundamental challenge. Here, for the first time, a rationally designed porous monolithic electrode is reported with high thickness of 800 µm (46.74 mg cm−2, with high areal mass loading of NiCo2S4 6.9 mg cm−2) in which redox‐active Ag nanoparticles and NiCo2S4 nanosheets are sequentially decorated on highly conductive wood‐derived carbon (WC) substrates. The hierarchically assembled WC@Ag@NiCo2S4 electrode exhibits outstanding areal capacitance of 6.09 F cm−2 and long‐term stability of 84.5% up to 10 000 cycles, as well as exceptional rate capability at 50 mA cm−2. The asymmetric cell with an anode of WC@Ag and a cathode of WC@Ag@NiCo2S4 delivers areal/volumetric energy density of 0.59 mWh cm−2/3.93 mWh cm−3, which is much‐improved performance compared to those of most reported thick electrodes at the same scale. Theoretical calculations verify that the enhanced performance could be attributed to the decreased adsorption energy of OH− and the down‐shifted d‐band of Ag atoms, which can accelerate the electron transport and ion transfer.
High conductivity wood‐based carbon WC@Ag@NiCo2S4 thick composite electrodes show high areal/volumetric energy density. The electrode exhibits outstanding areal capacitance of 6.09 F cm−2 and supercapacitance retention of 84.5% up to 10 000 cycles (50 mA cm−2). The assembled asymmetric supercapacitor with WC@Ag anode and WC@Ag@NiCo2S4 cathode delivers areal and volumetric energy density of 0.59 mWh cm−2 and 3.93 mWh cm−3, respectively.
The interwinding parasitic capacitance of transformers and the parasitic capacitance between semiconductor switches and the ground are two major contributors to the common-mode (CM) noise currents in ...switched mode power converters. In this paper, a generalized CM current cancelation approach is proposed for the reduction of CM noise in isolated power converters. The approach is demonstrated in a forward converter. In this approach, the total effect of the two parasitic capacitances on CM noise is represented with an equivalent parasitic capacitance (EPC) at low frequencies. With this EPC, different CM current cancelation techniques can be efficiently organized to simultaneously cancel the low-frequency CM noise caused by these two parasitic capacitances. Furthermore, the EPC can be used to evaluate and quantify the performance of CM noise reduction techniques. Both theoretical analysis and experimental results show that the proposed approach is easy to implement and can significantly attenuate low frequency CM noise and therefore greatly reduce CM filter size and cost.
This article presents a continuous-time (CT) delta-sigma (<inline-formula> <tex-math notation="LaTeX">\Delta \Sigma </tex-math></inline-formula>) capacitance-to-digital converter (CDC) intended for ...use in applications with high capacitance resolution (tens of aF), and a large parasitic capacitance <inline-formula> <tex-math notation="LaTeX">{C}_{P} </tex-math></inline-formula> (<inline-formula> <tex-math notation="LaTeX">> </tex-math></inline-formula>400 pF). It consists of a current conveyor (CC) front-end and a CT <inline-formula> <tex-math notation="LaTeX">\Delta \Sigma </tex-math></inline-formula> modulator. The CC-based front-end isolates <inline-formula> <tex-math notation="LaTeX">{C}_{P} </tex-math></inline-formula> from the first integrator of the modulator, and the CC's output current is directly coupled to the CT <inline-formula> <tex-math notation="LaTeX">\Delta \Sigma </tex-math></inline-formula> modulator. The CC uses a class-AB configuration, which enables to maintain energy efficiency and its capacitance resolution even with <inline-formula> <tex-math notation="LaTeX">{C}_{P} </tex-math></inline-formula>. The proposed CDC is fabricated in a 110-nm CMOS process and occupies only 0.033 mm 2 . It achieves a capacitance resolution of 21.5-59 aF with an input range of 0.2-1.5 pF. This corresponds to an effective resolution of 14.3 bits in a conversion time of 1.2 ms, while drawing only 120 <inline-formula> <tex-math notation="LaTeX">\mu \text{W} </tex-math></inline-formula> from a 1.5-V supply. It also achieves a capacitance resolution of 119.4 aF with <inline-formula> <tex-math notation="LaTeX">{C}_{P} </tex-math></inline-formula> of 480 pF, offering robust capacitance resolution with external noise interference (10 <inline-formula> <tex-math notation="LaTeX">{V}_{\text {PP}} </tex-math></inline-formula>).
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