Preparation and electrochemical performance of novel ruthenium-manganese oxide electrode materials for electrochemical capacitors

A series of novel ruthenium-manganese oxide (denoted as Ru_nMn_1−nO_x) has been formed by oxidative co-precipitating. The precursor was obtained by mixing Mn(VII) (potassium permanganate), Mn(II) (manganese acetate) and Ru(III) (ruthenium chloride) in neutral aqueous solution at room temperature. The powder of Ru_nMn_1−nO_x was obtained by calcinating the precursor at appropriate temperature. The crystalline structure and electrochemical performance of the powder have been studied as a function of the calcination temperature. At appropriate calcination temperature (e.g. 170 °C), the powder is in hydrous amorphous phase with a high specific capacitance. When the calcination temperature reaches up to 350 °C, the crystal form of α-MnO₂ is formed, but the ruthenium oxide still keeps amorphous structure, which will lead to the decrease of specific capacitance of the composite electrode materials. The X-ray photoelectron spectroscopy (XPS) analysis shows that the powder of Ru_nMn_1−nO_x prepared in this study belongs to the composite of RuO₂-MnO₂. The results from cyclic voltammetry (CV), chronopotentiometry and electrochemical impedance spectroscopy (EIS) indicate that the ruthenium weight density of 9 wt% in Ru_nMn_1−nO_x can improve the cost-performance of ruthenium-manganese composite electrode.     

Highly amorphous PbO2 as an electrode in hybrid electrochemical capacitors

This paper presents a synthesis and characterizes highly amorphous lead dioxide and its use in hybrid electrochemical capacitor C/PbO₂. Highly amorphous lead dioxide with a small amount of β-PbO₂ was synthesized by galvanostatic deposition from acetate solution. The hybrid supercapacitor was constructed with PbO₂ as the positive electrode whereas activated carbon as the negative electrode. The morphology of materials was examined by scanning electron microscopy and their structure was characterized by means of an X-ray diffraction technique. The electrochemical performance of hybrid electrochemical capacitor with synthesized PbO₂ was studied by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. To indicate that the amorphous form of lead dioxide was predominant, results were compared to highly crystalline β-PbO₂. The hybrid electrochemical capacitor with synthesized material exhibits a much greater specific capacitance, higher specific energy and power than the highly crystalline one. The specific capacitance values obtained for the supercapacitor rose more than twice in favour of amorphous PbO₂. Also, long cycling did not influence any of the electrochemical properties of this hybrid electrochemical capacitor, which makes it an interesting energy storage device.     

Preparation and electrochemical properties of mesoporous Co3O4 crater-like microspheres as supercapacitor electrode materials

Mesoporous Co₃O₄ microspheres with unique crater-like morphology were obtained by utilizing the mesoporous silica material MCM-41 as a template. The analysis results of N₂ adsorption–desorption measurement indicate that the product has a large Brunauer–Emmett–Teller (BET) surface area of 60 m² g⁻¹ and a narrow pore size distribution centering around 3.7 nm. Its electrochemical properties were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements. The findings reveal that this novel morphology material has a smaller inner resistance of about 0.4 Ω and a higher onset frequency of 550 Hz. This material can provide a high specific capacitance of 102 F g⁻¹ and a large capacity retention of 74% in 500 continuous cycles test at a sweep rate of 3 mV s⁻¹. More significantly, the mass loading of electroactive species can reach as large as 2 mg cm⁻², which is one order of magnitude larger than common amount used.     

氮掺杂碳气凝胶电极材料的制备及性能

以三聚氰胺（M）、间苯二酚（R）和甲醛（F）为原料,经溶胶-凝胶法、超临界干燥和高温碳化制备了系列的氮掺杂碳气凝胶（NCAs）。X射线光电子能谱(XPS)分析表明,氮元素成功地引入到碳气凝胶中,并且可以通过调节三聚氰胺掺杂量来控制氮掺杂量;扫描电子显微镜（SEM）和N2吸附测试显示出不同氮掺杂量的碳气凝胶的微观结构差异较大,随着氮含量的增加,比表面积有先减后增的趋势;在6 mol/L KOH溶液中进行的恒流充放电和循环伏安测试表明,引入氮元素能够极大地改善碳气凝胶的电化学性能,最高比电容量达176 Fg-1,并且凝胶具有良好的电容特性和可逆性。     

Preparation and physical/electrochemical characterization of carbon nanotube-chitosan modified pencil graphite electrode

In this work, preparation and characterization of single-walled carbon nanotube-chitosan (SWNT-chitosan) modified disposable pencil graphite electrode (PGE) was carried out. Firstly, commercial single-walled carbon nanotube was purified and characterized using thermal gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and energy dispersive analysis of X-ray (EDX) for this purpose. Purified SWNT was mixed with chitosan polymer for preparing their composite. Then, PGE was modified with this composite. The characterization of the modified electrode was carried out using atomic force microscopy (AFM). The electrochemical behaviour of the obtained electrode was investigated and compared with the electrochemical behaviour of chitosan modified and unmodified PGEs using cyclic voltammetry (CV), differential pulse voltammetry (DPV) and alternative current (AC) impedance spectroscopy. In order to obtain more sensitive electrochemical signals, the effect of SWNT concentration was studied. This modified electrode also showed electrocatalytic effect for hydrogen evolution.     

Electrosynthesis and characterization of poly aniline/garnet nanoparticles for high-performance electrochemical capacitors

In this work, supercapacitive performance of polyaniline/yttrium aluminum garnet (YAG: Y₃Al₅O₁₂) nanoparticles (PANI/YAGNPs) was studied. YAG nanoparticles were synthesized by pulse electro-deposition method and after that, PANI/YAGNPs electrodeposited on the surface of glassy carbon electrodes through cyclic voltammetry. Morphological studies show that YAG nanoparticles were distributed in the structure of PANI filaments uniformly. XRD and FTIR were used to perform a structural study of materials. Different electrochemical techniques such as cyclic voltammetry (CV), galvano static charge discharge (CD), and impedance spectroscopy (EIS) were used to evaluate the applicability of using PANI/YAGNPs as an active material for supercapacitors. The specific capacitance (SC) of PANI and PANI YAG NPs electrodes calculated using CV technique are 240 and 440 F/g, respectively. Increasing the conductivity and stability of composite electrodes during continuous CD cycles compared to PANI ones are some features of using YAG NPs in the structure of polymer electrodes. Stability of composite electrodes remains about 98% through 1000 continuous cycles whereas the polymeric electrode loses about 91% of its capacitance during this time range.     

Nickel, cobalt, and manganese oxide composite as an electrode material for electrochemical supercapacitors

A composite material, Ni_1/3Co_1/3Mn_1/3(OH)₂, is synthesized by chemical precipitation method for supercapacitors' electrode material. Physical characterizations using x-ray diffraction, energy-dispersive x-ray, and scanning electron microscopy show that Ni_1/3Co_1/3Mn_1/3(OH)₂ possesses an amorphous structure and higher specific surface area (268.5 m²?g^?1), which lead to a high initial specific capacitance of 1,403 F?g^?1 in the potential window of 0–1.5 V. It may be a potential electrode material for future supercapacitor when its cycling stability and rate performance are addressed.     

Excellent long-term electrochemical performance of graphite oxide as cathode materials for lithium-ion batteries

A facile, scalable route has been adopted to synthesize graphite oxides with different degrees of oxidation. Subsequently, graphite oxides with rationally designed functional groups have been utilized as cathode materials for lithium-ion batteries (LIBs). The electrodes deliver the initial and second discharge capacities of 332 and 172 mAh g^?1 at a current density of 0.1 A g^?1, respectively. More importantly, a remarkable long-term cycling performance of 130 mAh g^?1 after 800 cycles has been gathered, with an ultralow capacity fading of 0.03% per cycle from the second cycle. The root cause of excellent cycling stability should be ascribed to the admirable reversibility of epoxy and carbonyl groups in graphite oxides during the Li-cycling. Meanwhile, the deep study has provided a novel way to avoid complex and expensive post-treatment process of graphite oxides, whose synthesis conditions are also optimized. Those striking features make graphite oxides as promising cathode materials for lithium-ion batteries.     

MgO-templated carbon as a negative electrode material for Na-ion capacitors

In this study, MgO-templated carbon with different pore structures was investigated as a negative electrode material for Na-ion capacitors. With increasing the Brunauer–Emmett–Teller surface area, the irreversible capacity increased, and the coulombic efficiency of the 1st cycle decreased because of the formation of solid electrolyte interface layers. MgO-templated carbon annealed at 1000 °C exhibited the highest capacity and best rate performance, suggesting that an appropriate balance between surface area and crystallinity is imperative for fast Na-ion storage, attributed to the storage mechanism: combination of non-faradaic electric double-layer capacitance and faradaic Na intercalation in the carbon layers. Finally, a Na-ion capacitor cell using MgO-templated carbon and activated carbon as the negative and positive electrodes, respectively, exhibited an energy density at high power density significantly greater than that exhibited by the cell using a commercial hard carbon negative electrode.     

Anchoring alpha-manganese oxide nanocrystallites on multi-walled carbon nanotubes as electrode materials for supercapacitor

The partial coverage of manganese oxide (MnO₂) particles was achieved on the surfaces of multi-walled carbon nanotubes (MWCNTs) through a facile hydrothermal process. These particles were demonstrated to be alpha-manganese dioxide (α-MnO₂) nanocrystallites, and exhibited the appearance of the whisker-shaped crystals with the length of 80–100 nm. In such a configuration, the uncovered CNTs in the nanocomposite acted as a good conductive pathway and the whisker-shaped MnO₂ nanocrystallites efficiently increased the contact of the electrolyte with the active materials. Thus, the highest specific capacitance of 550 F g⁻¹ was achieved using the resulting nanocomposites as the supercapacitor electrode. In addition, the enhancement of the capacity retention was observed, with the nanocomposite losing only 10% of the maximum capacity after 1,500 cycles.     

Preparation and electrochemical performance of bramble-like ZnO array as anode materials for lithium-ion batteries

A bramble-like ZnO array with a special three-dimensional (3D) nanostructure was successfully fabricated on Zn foil through a facile two-step hydrothermal process. A possible growth mechanism of the bramble-like ZnO array was proposed. In the first step of hydrothermal process, the crystal nucleus of Zn(OH) ₄ ^2? generated by the zinc atoms and OH^? ions fold together preferentially along the positive polar (0001) to form the needle-like ZnO array. In the second step of hydrothermal process, the crystal nuclei of Zn(OH) ₄ ^2? adjust their posture to keep their c-axes vertical to the perching sites due to the sufficient environmental force and further grow preferentially along the (0001) direction so as to form bramble-like ZnO array. The electrochemical properties of the needle- and bramble-like ZnO arrays as anode materials for lithium-ion batteries were investigated and compared. The results show that the bramble-like ZnO material exhibits much better lithium storage properties than the needle-like ZnO sample. Reasons for the enhanced electrochemical performance of the bramble-like ZnO material were investigated.     

碳气凝胶及活化碳气凝胶电极材料制备与性能

以间苯二酚(R)-甲醛(F)为原料,制备了有机气凝胶和碳气凝胶,并对其进行二氧化碳活化。X射线衍射(XRD)测试表明,二氧化碳渗入到碳气凝胶网络结构发生反应,造成(002)峰和(100)峰减弱;扫描电子显微镜(SEM)测试表明,活化没有破坏碳气凝胶的骨架结构,而是增加了大量的nm尺度微孔,从而大大提高了碳气凝胶的比表面积和微孔比例。在1 mol/L KOH电解液中进行了循环伏安和计时电位扫描测试,电极材料电化学性能稳定,具有较好的可逆性,在1 mA/s电流密度下进行充放电测试,得到活化前电极比电容为103 F/g,活化后由于比表面积的增加,比电容达到371 F/g,是一种理想的电化学电极材料。     

碳气凝胶及活化碳气凝胶电极材料制备与性能

 以间苯二酚(R)-甲醛(F)为原料,制备了有机气凝胶和碳气凝胶,并对其进行二氧化碳活化。X射线衍射(XRD)测试表明,二氧化碳渗入到碳气凝胶网络结构发生反应,造成(002)峰和(100)峰减弱;扫描电子显微镜(SEM)测试表明,活化没有破坏碳气凝胶的骨架结构,而是增加了大量的nm尺度微孔,从而大大提高了碳气凝胶的比表面积和微孔比例。在1 mol/L KOH电解液中进行了循环伏安和计时电位扫描测试,电极材料电化学性能稳定,具有较好的可逆性,在1 mA/s电流密度下进行充放电测试,得到活化前电极比电容为103 F/g,活化后由于比表面积的增加,比电容达到371 F/g,是一种理想的电化学电极材料。     

Ageing of solid electrolytes and electrode materials in electrochemical devices

The ageing behavior reported in this work concerns the consequences of the matter transport processes on the cationic sublattice which occur in solid electrolytes, mixed ionic conducting compounds and semiconducting oxides subjected to a chemical potential gradient, an applied electrical field or a mechanical stress gradient. The principle of the kinetic demixing under a “generalized” thermodynamic potential gradient is reviewed. Available experimental results concerning yttria-doped zirconia and iono-covalent oxides are reported. The results are discussed in relation with the microstructure and composition evolution of the surfaces and the electrode resistance. Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998.     

New counter electrode prepared as vanadium oxide and V/Ce oxide films: preparation and characterization

Vanadium oxide and mixed V/Ce-oxide films at 78, 55, 38, 32 atomic % of V were prepared via the sol-gel route from an aqueous colloidal solution of inorganic precursors. The influence of the added cerium precursor on their electrochemical, optical and structural properties was investigated by cyclic voltammetry (CV), X-ray analysis, IR spectroscopy and UV-VIS techniques. The electrochemical stability of films was tested by CV measurements in 1 M LiClO₄ in propylene carbonate electrolyte. The addition of CeO₂ improved the poor stability of vanadium oxide films and enhanced their ion-charge capacity up to 30 mC/cm² for thicknesses about 300 nm. The intercalation of Li⁺ ions in vanadium oxide and V/Ce-oxide films was followed by FT-IR spectroscopy performed at near-grazing incidence angle (NGIA) conditions in combination with CV measurements at potentials of −1.5 V and +2.0 V (vs. Ag/AgCl). The observed shift of V–O_v vibrations in the IR spectra confirmed the intercalation of Li⁺ ions.     

Synthesis of graphene/nickel oxide composite with improved electrochemical performance in capacitors

A novel reduced graphene oxide/NiO nanosheet composite (r-GO/NiO) (ca. 75 % NiO in weight) was synthesized by a facile two-step method, where the NiO nanosheets were decorated with some voids. The composite was characterized by using X-ray diffraction, transmission electron microscopy, thermal gravimetric analysis, and Raman spectroscopy. The electrochemical properties of the composite were investigated by cyclic voltammetry, galvanostatic charge, and discharge measurements. The results show that the r-GO/NiO composite exhibits a stable average specific capacitance of ca. 1,139 F g^?1 (at 0.5 A g^?1) during 1,000 charge–discharge cycles, suggesting that the r-GO/NiO composite is a potential supercapacitor material. The main correlation between the electrochemical performance and the structure of the materials was studied, and the formation process of the composite was also discussed.     

Fabrication of electrode Pt nanotubes for semiconductor capacitors

Template-wetting process was used to fabricate Pt electrode nanotubes for the further application in 3D nanotube capacitors. Anodic alumina oxide (AAO) was used as a template, which can be fabricated by means of two-step anodization process. After the wetting process, released Pt nanotubes have been obtained by selective etching of the template using KOH solution. Pt nanotubes formation and tube walls morphology were investigated by FE-SEM technique. Furnace annealing (FA) effects at temperatures ranging from 200 to 600 °C with 100^oC step on nucleation and crystal growth condition of Pt nanotubes have been examined. Crystallization of the Pt nanotube inside the template has been examined by step-by-step annealing at different temperatures, and confirmed by XRD.     

Synthesis and electrochemical properties of three-dimensional graphene/polyaniline composites for supercapacitor electrode materials

To improve the specific capacitance and rate capability of electrode material for supercapacitors, a three-dimensional graphene/polyaniline(3DGN/PANI) composite is prepared via in situ polymerization on GN hydrogel. PANI grows on the GN surface as a thin film, and its content in the composite is controlled by the concentration of the reaction monomer. The specific capacitance of the 3DGN/PANI composite containing 10 wt% PANI reaches 322.8 F·g-1at a current density of1 A·g-1, nearly twice as large as that of the pure 3DGN(162.8 F·g-1). The capacitance of the composite is 307.9 F·g-1at 30 A·g-1(maintaining 95.4%), and 89% retention after 500 cycles. This study demonstrates the exciting potential of3DGN/PANI with high capacitance, excellent rate capability and long cycling life for supercapacitors.     

Hydrothermal synthesis of single crystal MoO3 nanobelts and their electrochemical properties as cathode electrode materials for rechargeable lithium batteries

Orthorhombic phase MoO₃ (α-MoO₃) nanobelts with uniform diameter are successfully prepared through a hydrothermal synthesis route at a low temperature (180 °C) in the presence of cetyltrimethylammonium bromide (CTAB) using saturated solution of ammonium molybdate tetrahydrate (AHM) as well as nitrate as raw materials, and are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. The CTAB plays a key role in the formation of α-MoO₃ nanobelts and the aspect ratio of nanobelts significantly varies with quality of CTAB. The nanobelts with rectangular cross-sections have single crystalline orthorhombic phase structure, preferentially grow in [001] direction. Raman shifts of the α-MoO₃ nanobelts are fully consistent with that of flaky structure; however, intensity ratio of peaks 818.3 cm^?1 and 991.2 cm^?1 of α-MoO₃ nanobelts remarkably changes comparing with that of lamellar MoO₃. Electrochemical properties of α-MoO₃ single crystal nanobelts synthesized as cathode electrode materials for rechargeable lithium batteries are also measured. It indicates that the α-MoO₃ nanobelts exhibit a better performance than MoO₃ micro flakes.     

Nano-composite LiMnPO4 as new insertion electrode for electrochemical supercapacitors

Nano-composite olivine LiMnPO₄ (nC-LMP) was found to exhibit facile pseudo-capacitive characteristics in aqueous as well as non-aqueous electrolytes. We demonstrated employing nC-LMP as positive electrode in hybrid electrochemical capacitors namely Li-Ion hybrid capacitors (LIC). Adapting a simple CVD technique, nano-crystallites of LiMnPO₄ were coated with carbon monolayers of ∼2 nm thick to circumvent its poor intrinsic electronic conductivity. The novelty is that the single crystallites were intimately covered with carbon ring and networked to the neighboring crystallites via the continuous carbon wire-like connectivity as revealed from HRTEM analysis. Single electrode faradic capacitance of 3025 Fg⁻¹ (versus standard calomel reference electrode) was deduced for carbon coated LMP, the highest reported hitherto in Li⁺ aqueous electrolytes. Employing nC-LMP as working electrode versus an activated carbon (AC), we obtained a high specific energy of 28.8 Wh kg⁻¹ with appreciable stability in aqueous electrolytes whereas in nonaqueous electrolyte there is an obvious increase in energy density (35 Wh kg⁻¹) due to wider potential window. That is, a full cell version of LIC, AC|Li⁺|LMP, was fabricated and demonstrated its facile cycling characteristics via removal/insertion of Li⁺ within nC-LMP (positive electrode) and the electrosorption of Li⁺ into mesoporous carbon (AC) (negative electrode). Such cells ensured a typical battery-like charging and EDLC-like discharging characteristics of LIC type electrochemical capacitors (ECs) which are desired to enhance safety and energy densities.