纳米锰氧化物超级电容器电极材料的制备与性能

采用模板和液相沉淀两种方法制备了锰的氧化物,XRD的测试结果表明,两种方法制备的锰氧化物分别为MnO2和Mn3O4。从TEM图可以看出,模板法制备的MnO2为直径为5~8nm左右的颗粒,而用液相沉淀制备的Mn3O4形貌为直径约为10nm左右的纤维棒。循环伏安和充放电测试结果都表明MnO2是更好的超电容器的电极材料。MnO2和Mn3O4在200mA·g-1电流密度下的放电比电容分别为157.5和145.0F·g-1,经过500次充放电后比电容分别为132.5和125.0F·g-1,充放电效率分别为64.9%和63.7%。     

Nanocomposites of manganese oxides and carbon nanotubes for aqueous supercapacitor stacks

Symmetrical supercapacitors and their serially connected two-cell stacks via a bipolar electrode were constructed with nanocomposites of manganese oxides and carbon nanotubes (MnO_x/CNTs) as the electrode materials. Nanocomposites with different contents of MnO_x were synthesised through the redox reaction between KMnO₄ and CNTs in aqueous solutions. The nanocomposites were characterised by scanning and transmission electron microscopy, BET nitrogen adsorption and X-ray diffraction before being examined in a three-electrode cell with a novel trenched graphite disc electrode by electrochemical means, including cyclic voltammetry, galvanostatic charging-discharging, and electrochemical impedance spectroscopy. The nanocomposites demonstrated capacitive behaviour in the potential range of 0-0.85 V (vs Ag/AgCl) in aqueous KCl electrolytes with less than 9% capacitance decrease after 9000 charging-discharging cycles. Symmetrical supercapacitors of identical positive and negative MnO_x/CNTs electrodes showed capacitive performance in good agreement with the individual electrodes (e.g. 0.90 V, 0.53 F, 1.3 cm²). The bipolarly connected two-cell stacks of the symmetrical cells exhibited characteristics in accordance with expectation, including a doubled stack voltage and reduced internal resistance per cell.     

高循环稳定性碳化钛/氧化石墨烯复合超级电容

二维材料碳化钛(Ti₃C₂T_x)因具有高导电性和大比表面积的特点,在作为超级电容电极材料时,可以实现较高的能量密度。然而,Ti₃C₂T_x在储能过程中会出现不可逆的氧化失活反应,而且它与基底间的结合力较差,这将导致碳化钛超级电容的循环稳定性欠佳,极大地阻碍了其作为电极材料的广泛应用。将Ti₃C₂T_x作为活性层与氧化石墨烯(GO)分层复合制作成超级电容电极,覆盖在Ti₃C₂T_x薄膜之上的GO层可以削弱氧化失活反应。同时,对电极的热处理可提升Ti₃C₂T_x对基底的附着力。这使得Ti₃C₂T_x/GO复合电极的充放电循环稳定性明显改善,在5 000次循环之后其容量仍高于初始容量。该设计可为制备高循环稳定性超...     

Effect of conductive layer on the performance of gel electrolyte-based supercapacitors

Solid-state electrolytes such a further novel finding is going to have great importance because of the disadvantages of liquid electrolytes such as electrochemical instability, low ion selectivity, and interface contact. It is anticipated that the use of solid-state electrolytes including supercapacitors (SCs) will become widespread with decreasing self-leakage and environmental damage more than liquid electrolytes. In this study, SCs with graphene/PEDOT: PSS coated electrodes and binary PVA gel electrolytes with a conductive layer were designed and the electrochemical performance of the configurations was characterized. The effects of the conductive layer between binary electrolytes and the concentration of the KOH solution in the electrolytes were studied. It was observed that the conductive layer used between the gel electrolytes causes additional charging at the electrolyte/conductive layer interface and behaves like a serially connected capacitor to the double-layer capacitor. Interestingly, at a slow sweep rate (5 mV/s), the specific capacitance values of the assembled SCs decreased when a conductive layer was used but it increased when the sweep rate was fast (100 mV/s).     

Electrospun porous carbon nanofibers derived from bio-based phenolic resins as free-standing electrodes for high-performance supercapacitors

Phenolic resins were employed to prepare electrospun porous carbon nanofibers with a high specific surface area as free-standing electrodes for high-performance supercapacitors. However, the sustainable development of conventional phenolic resin has been challenged by petroleum-based phenol and formaldehyde. Lignin with abundant phenolic hydroxyl groups is the main non-petroleum resource that can provide renewable aromatic compounds. Hence, lignin, phenol, and furfural were used to synthesize bio-based phenolic resins, and the activated carbon nanofibers were obtained by electrospinning and one-step carbonization activation. Fourier transform infrared and differential scanning calorimetry were used to characterize the structural and thermal properties. The results reveal that the apparent activation energy of the curing reaction is 89.21 kJ·mol^–1 and the reaction order is 0.78. The activated carbon nanofibers show a uniform diameter, specific surface area up to 1100 m²·g^–1, and total pore volume of 0.62 cm³·g^–1. The electrode demonstrates a specific capacitance of 238 F·g^–1 (0.1 A·g^–1) and good rate capability. The symmetric supercapacitor yields a high energy density of 26.39 W·h·kg^–1 at 100 W·kg^–1 and an excellent capacitance retention of 98% after 10000 cycles. These results confirm that the activated carbon nanofiber from bio-based phenolic resins can be applied as electrode material for high-performance supercapacitors.     

Microporous activated carbons from used coffee grounds for application to electric double‐layer capacitors

Electrochemical double‐layer capacitors (EDLCs) are devices that store enormous amounts of charge electrostatically when a potential is applied between electrodes of very high surface area (typically made of porous carbon) and an electrolyte. Wider commercialization of this technology has been held back by the lack of ultralow‐cost electrode materials. We demonstrate that used coffee grounds can be processed to form low‐cost electrodes. The surface and electrochemical characteristics of microporous activated carbons from used coffee grounds (CGCs) were measured. First, optimal times and temperatures for carbonization and activation were identified on the basis of Brunauer–Emmett–Teller (BET) surface area, pore volume, and pore size distribution. Second, CGCs were used as polarized electrodes in EDLCs, whose capacitances were evaluated using cyclic voltammetry. The results show that carbonization for 1 h at 600 °C with a heating rate of 300 °C/h, followed by CO₂ activation for 2 h at 1000 °C, affords the highest BET surface area (1867 m²/g) compared to other works. The produced CGCs have many micropores of less than 2 nm across, which contribute to the formation of an electric double layer. Capacitors made using these CGCs show the highest capacitance (103 F/g) in 0.8 M (C₂H₅)₄NBF₄/PC as an organic electrolyte, which is much higher than the ∼80 F/g typically used in organic‐electrolyte‐based commercial EDLCs, suggesting that coffee grounds are a useful electrode material. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

ZIF-8衍生柔性多孔炭材料的制备及其电容性能研究

随着柔性可穿戴电子器件的迅速发展,柔性储能电极材料引起众多学者们的广泛关注。金属有机框架结构（MOFs）衍生物具有优异的储能性能,但其本征无柔性的物理特性亟需解决。采用静电纺丝技术将ZIF-8结构单元嵌入纤维结构中,获得高电容性能柔性多孔炭纤维。同时,探究了ZIF-8的嵌入量（CF-ZIF-8-1.2）对柔性多孔炭纤维结构及电容性能的影响。实验结果表明：柔性多孔炭纤维CF-ZIF-8-1.2的比电容可以达到425.5 F?g^-1（电流密度为1 A?g^-1）,并呈现出较小的电荷转移电阻（R_s=0.06 Ω）和接触电阻（R_ct=2.31 Ω）,这主要归因于CF-ZIF-8-1.2具有较大的比表面积（212.83 m²?g^-1）、相对丰富的孔隙结构和丰富的N和O原子共掺杂。随后,进一步将其组装成对称柔性超级电容器（CF-ZIF-8-1.2//CF-ZIF-8-1.2）,其能量密度高达7.6 Wh?kg^-1（功率密度为250 W?kg^-1）,在不同弯曲角度和扭曲下呈现出优异的电容保持率（97%以上）,说明柔性多孔炭纤维电极材料具有优异的柔性和稳定性。因此,CF-ZIF-8-1.2柔性多孔炭纤维材料具有潜在应用前景。     

电化学双电层电容器的研制

通过催化裂解法制备了碳纳米管并进一步制备了碳纳米管薄膜电极。基于该种材料的超电容器电极比容量达到36 F/g并表现出良好的功率特性。本文采用多种研究方法对基于该种材料的双电层电容器进行了详细的研究。     

Nitrogen‐Doped Carbon Encapsulated Mesoporous Vanadium Nitride Nanowires as Self‐Supported Electrodes for Flexible All‐Solid‐State Supercapacitors

Flexible 3D nanoarchitectures have received tremendous interest recently because of their potential applications in flexible/wearable energy storage devices. Herein, 3D intertwined nitrogen‐doped carbon encapsulated mesoporous vanadium nitride nanowires (MVN@NC NWs) are investigated as thin, lightweight, and self‐supported electrodes for flexible supercapacitors (SCs). The MVN NWs have abundant active sites accessible to charge storage, and the N‐doped carbon shell suppresses electrochemical dissolution of the inner MVN NWs in an alkaline electrolyte, leading to excellent capacitive properties. The flexible MVN@NC NWs film electrode delivers a high areal capacitance of 282 mF cm⁻² and exhibits excellent long‐term stability with 91.8% capacitance retention after 12 000 cycles in a KOH electrolyte. All‐solid‐state flexible SCs assembled by sandwiching two flexible MVN@NC NWs film electrodes with alkaline poly(vinyl alcohol) (PVA), sodium polyacrylate, and KOH gel electrolyte boast a high volumetric capacitance of 10.9 F cm⁻³, an energy density of 0.97 mWh cm⁻³, and a power density of 2.72 W cm⁻³ at a current density of 0.051 A cm⁻³ based on the entire cell. By virtue of the excellent mechanical flexibility, high capacitance, and large energy/power density, the self‐supported MVN@NC NWs paper‐like electrodes have large potential applications in portable and wearable flexible electronics.