Graphene oxide with improved electrical conductivity for supercapacitor electrodes

Predominant few-layer graphene (FLG) sheets of high electrical conductivity have been synthesized by a multi-step intercalation and reduction method. The electrical conductivity of the as-synthesized FLG is measured to be ∼3.2 × 10⁴ S m⁻¹, comparable to that of pristine graphite. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman analysis reveal that the as-synthesized FLG sheets have large areas with single and double layers. The specific capacitance of 180 F g⁻¹ is obtained for the FLG in a 1 M Na₂SO₄ aqueous electrolyte by integrating the cyclic voltammogram. The good capacitive behavior of the FLG is very promising for the application for next-generation high-performance electrochemical supercapacitors.     

Fe-MOF电极材料的合成及电性能

通过溶剂热法合成出Fe-MOF材料并进行了XRD表征,结果显示Fe-MOF的XRD衍射峰位置和强度都与已知同类型的MOF结构相似,且没有其他晶相出现;在不同扫描速率下测得的循环伏安具有明显的还原电流峰和氧化电流峰,表现出典型的法拉第氧化还原特性;随着扫描速率的增大,比电容急速下降,Fe-MOF结构可能发生扭曲;500次循环实验结果表明,Fe-MOF比容量没有出现明显的衰减,具有良好的循环寿命.     

Electrochemical properties of Mn-doped activated carbon aerogel as electrode material for supercapacitor

Carbon aerogel (CA) was prepared by a sol-gel polymerization of resorcinol and formaldehyde, and it was activated with KOH to obtain activated carbon aerogel (ACA). Specific capacitance of carbon aerogel and activated carbon aerogel was measured by cyclic voltammetry and galvanostatic charge/discharge methods in 6 M KOH electrolyte. Activated carbon aerogel showed higher specific capacitance than carbon aerogel (136 F/g vs. 90 F/g). In order to combine excellent electrochemical performance of activated carbon aerogel with pseudocapacitive property of manganese oxide, 7 wt% manganese oxide was doped on activated carbon aerogel by an incipient wetness impregnation method. For comparison, 7 wt% manganese oxide was also doped on carbon aerogel by an incipient wetness impregnation method. It was revealed that 7 wt% Mn-doped activated carbon aerogel (Mn/ACA) showed higher specific capacitance than 7 wt% Mn-doped carbon aerogel (Mn/CA) (168 F/g vs. 98 F/g). The enhanced capacitance of 7 wt% Mn-doped activated carbon aerogel was attributed to the outstanding electric properties of activated carbon aerogel as well as the faradaic redox reactions of manganese oxide.     

γ-Ray-induced synthesis and electrochemical properties of a mesoporous layer-structured α-Co(OH)2 for supercapacitor applications

α-Cobalt hydroxide is synthesized through a novel radiation-induced route using a cobalt nitrate hexahydrate isopropanol solution by irradiating ⁶⁰Co γ-rays. The as-prepared product shows a layer-structured mesoporous morphology with an average size of 250 nm. Crystalline property analysis exhibits the presence α-Co(OH)₂ as a predominant phase with a tiny amount of secondary phases of β-Co(OH)₂ and CoO. X-ray photoelectron spectroscopy discloses the existence of Co as Co(OH)₂ and CoO with a stoichiometric ratio of 76.7:23.3. In addition, the supercapacitive properties of the product are investigated using cyclic voltammetry and impedance spectroscopy in 1M KOH aqueous solution, showing a maximum capacitance value of 246.7 F g⁻¹ at a scan rate of 5 mV s⁻¹.     

聚苯胺纳米刺/掺氮空心碳球复合材料的制备及电容性能

以掺氮空心碳球（N-HCS）为骨架,通过化学氧化聚合法制备了聚苯胺纳米刺/掺氮空心碳球复合材料（PANI/N-HCS）,采用扫描电子显微镜、透射电子显微镜和红外光谱仪等对样品的形貌、结构等进行了表征. 采用循环伏安、计时电位和交流阻抗等方法在1 mol/L H₂SO₄水溶液中考察了材料的电化学性能. 结果表明,PANI/N-HCS具有良好的电化学性能,在0.5 A/g电流密度下,PANI/N-HCS的比电容达346 F/g;当电流密度为20 A/g时,PANI/N-HCS比电容值为228 F/g,电容保持率为66%;在5 A/g电流密度下,经1000次充放电循环后,电容保持率为76%.     

Supercapacitor Performance of Hollow Carbon Spheres by Direct Pyrolysis of Melamine-formaldehyde Resin Spheres

The nitrogen and oxygen co-doped hollow carbon spheres(HCSs) were prepared via a simple pyrolysis of solid melamine-formaldhyde resin spheres. The carbonization temperature has an important influence on the specific surface area, pore-size distribution and heteroatom contents of HCSs. The synergistic effects of those physical and chemical properties on supercapacitor performance were systematically investigated. Among the HCSs obtained at different temperatures, HCSs-800(co-doped HCSs at 800 ℃) exhibits the best reversible specific capacitance in 2 mol/L H₂SO₄ electrolyte and meanwhile maintains a high-class capacitance retention capability. The nitrogen heteroatoms were confirmed to play a crucial role in improving capacitance in an acid medium. This kind of nitrogen doped HCSs is a potential candidate for an efficient electrode material for supercapacitors.     

Preparation and Supercapacitive Properties of Fe2O3/Active Carbon Nanocomposites

Fe₂O₃/active carbon(Fe₂O₃/AC) nanocomposites were readily fabricated by pyrolyzing Fe³⁺ impregnated active carbon in a nitrogen atmosphere. The as-prepared composites were studied by X-ray powder diffraction(XRD), X-ray photoelectron spectroscopy(XPS) and transmission electron microscopy(TEM). The capacitive property of the composites was investigated by cyclic voltammetry(CV) and galvanostatic charge-discharge test. Physical characterizations show that the γ-Fe₂O₃ fine grains dispersed in the AC well, with a mean size of 21.24 nm. Electrochemical tests in 6 mol/L KOH solutions indicate that the as-prepared nanocomposites exhibited improved capacitive properties. The specific capacitance(SC) of Fe₂O₃/AC nanocomposites was up to 188.4 F/g that was derived from both electrochemical double-layer capacitance and pseudo-capacitance, which was 78% larger than that of pristine AC. A symmetric capacitor with Fe₂O₃/AC nanocomposites as electrode showed an excellent cycling stability. The SC was only reduced by a factor of 9.2% after 2000 cycles at a current density of 1 A/g.     

Electrodeposited ruthenium oxide thin films for supercapacitor: Effect of surface treatments

Amorphous and porous ruthenium oxide thin films have been deposited from aqueous Ru(III)Cl₃ solution on stainless steel substrates using electrodeposition method. Cyclic voltammetry study of a film showed a maximum specific capacitance of 650 F g⁻¹ in 0.5 M H₂SO₄ electrolyte. The surface treatments such as air annealing, anodization and ultrasonic weltering affected surface morphology. The supercapacitance of ruthenium oxide electrode is found to be dependent on the surface morphology.     

Synthesis and characterization of ZnCo2O4 nanomaterial for symmetric supercapacitor applications

ZnCo₂O₄ nanomaterial was prepared by co-precipitation method and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), cyclic voltammetry (CV), and galvanostatic charge–discharge tests at various current densities. It is shown that the crystal structure and surface morphology play an important role in the enhancement of the specific capacitance. The TEM results clearly indicate that the prepared material shows aggregated particles. The particle size powder was about 50 nm, and SEM pictures indicate a porous morphology. The electrochemical behavior of ZnCo₂O₄ was characterized by mixing equal proportion of carbon nanofoam (CNF). From CV, it is concluded that the combination of redox and pseudo-capacitance increases the specific capacitance up to 77 F g⁻¹ at 5 mV s⁻¹ scan rate. The ZnCo₂O₄-based supercapacitor cell has good cyclic stability and high coulombic efficiency.     

Electrochemical properties of polyaniline in p-toluene sulfonic acid solution

Polyaniline was deposited potentiodynamically on a stainless steel substrate in the presence of an inorganic acids (sulfuric acid). The electrochemical characterization of the electrode was carried out by means of cyclic voltammetry and electrochemical impedance spectroscopy in the organic acids (p-toluene sulfonic acid) solution. The results show that polyaniline has a high specific capacitance of 431.8 F g⁻¹ at 1 mV s⁻¹, high coulombic efficiency of 95.6% at 20 mV s⁻¹, and exhibits a high reversibility. This indicates the promising feasibility of the polyaniline used as an electrochemical capacitor material in the electrolyte of p-toluene sulfonic acid solution especially at high charge–discharge process.