Modification and photovoltaic properties of reduced graphene oxide/acetylene black composite electrode

A simple and high efficient reduced graphene oxide/acetylene black (rGO/ACET) nano-composite electrode was prepared as the substitute of high-cost Pt counter electrode in dye-sensitized solar cells (DSSCs). Surface-modified method called solvent-substituting (SS) was firstly used to avoid agglomeration of rGO sheets. The Brunner-Emmet-Teller (BET)-specific surface area of rGO was increased from 195.823 to 355.210 m²/g after modifying with ethanol. Then ACET particles were introduced between rGO layers to improve the electronic transportation properties. The chemical compositions, microstructures, and pore size distributions of rGO/ACET composites were investigated. Electrochemical impedance spectroscopy (EIS) indicated that rGO/ACET counter electrode had a lower charge transfer resistance (R_ct) and its S-shaped current–voltage curves disappeared obviously. The highest power conversion efficiency up to 6.62% was achieved for the DSSCs with rGO/ACET nano-composite counter electrode.     

Electrical impedance spectroscopy of ionic liquid 1-ethyl-3-methylimidazolium methanesulfonate (ECOENG™ 110)

Ionic liquid “ECOENG? 110”, a promising electrolyte for electrochemical devices, was investigated by impedance spectroscopy. Metallic electrodes (Pt, Cu, Ag, and Mo) as well as carbon were used for the electrochemical characterization. The dependences of the real and imaginary impedance, polarization resistance and electrochemical capacity of the double layer on the electrode potential were investigated using electrical equivalent circuits of R₁(QR₂) and R₁[Q(R₂W)] types.     

真空热处理碳纳米管的储氢性能研究

研究了真空热处理对多壁碳纳米管(MWNTs)电化学储氢性能的影响.采用化学气相沉积法(CVD)制备碳纳米管，碳纳米管与LaNi₅储氢合金按质量比1∶10混合，制作成CNTs-LaNi₅电极.电解池采用三电极体系，6mol/L KOH为电解液，Ni(OH)₂为正极，Hg/HgO为参比电极.实验结果表明，在相同的充放电条件下，850℃时CNTs-LaNi₅电极的储氢性能最好，克容量最大为503.6mAh/g，相应的平台电压高达1.18V.从500—850℃随着温度升高，放电量有较大幅度的增加，但到950℃时放电量反而下降.由此可见，碳纳米管的热处理温度对碳纳米管的电化学储氢性能有着较大的影响. 关键词： 碳纳米管(CNTs) 储氢性能 5合金')" href="#">LaNi₅合金 化学气相沉积法(CVD法)     

Electrochemical impedance spectroscopic study of the rate-determining step of Li ion intercalation and deintercalation in LixNiO2 cathodes

The rate-determining step of the intercalation and deintercalation process of lithium ions in Li_xNiO₂ cathodes was studied by electrochemical impedance spectroscopic (EIS) analysis. EISs of the electrode process are composed of two semicircles. The higher frequency semicircle is related to the charge transfer resistance (R_ct) and the double layer capacitance (C_dl), while the lower frequency semicircle results from ion incorporation impedance (R_lattice) and space charge capacitance (C_sc). The assignment of the latter capacitance is discussed. It is found that R_lattice is 1000 times larger than R_ct. Accordingly, in most cases the ion incorporation into the lattice dominates the kinetic behavior. But for the ideal hexagonal phase, in the deintercalated state the Warburg impedance becomes important. As a result, the ion diffusion in the lattice is the rate-determining step. Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Italy, Sept. 15–22, 1996     

Facile preparation of SGC composite as anode for lithium-ion batteries

The silicon/graphite/carbon (SGC) composite was successfully prepared by ball-milling combined with pyrolysis technology using nanosilicon, graphite, and phenolic resin as raw materials. The structure and morphology of the as-prepared materials are characterized by X–ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscope (TEM). Meanwhile, the electrochemical performance is tested by constant current charge–discharge technique, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) measurements. The electrodes exhibit not only high initial specific capacity at a current density of 100 mA g^?1, but also good capacity retention in the following 50 cycles. The EIS results indicate that the electrodes show low charge transfer impedance R_sf?+?R_ct. The results promote the as-prepared SGC material as a promising anode for commercial use.     

Electrochemical properties of modified acetylene black/sulfur composite cathode material for lithium/sulfur batteries

Lithium/sulfur (Li/S) batteries have a high theoretical specific capacity of 1672 mAh g^?1. However, the insulation of the elemental sulfur and polysulfides dissolution could result in poor cycling performance of Li/S batteries, thus restricting the industrialization process. Here, we prepared sulfur-based composite by thermal treatment. The modified acetylene black (H-AB) was used as a carrier to fix sulfur. The H-AB could interact with polysulfides and reduce the dissolution of polysulfides in the electrolyte. Nonetheless, the conductivity of H-AB relatively reduced. So the conductivity of the sulfur electrode would be improved by the addition of the conductive agent (AB). In this paper, the different content of conductive agent (AB) in the sulfur electrode was studied. The electrochemical tests indicate that the discharge capacity of the sulfur electrode can be increased by increasing the conductive agent (AB) content. The H-AB@S composite electrode with 30 wt.% conductive agent has the best cycle property. The discharge capacity still remains at 563 mAh g^?1 after 100 cycles at 0.1 C, which is 71% retention of the highest discharge capacity.     

Electrooxidation of hydrazine in alkaline medium at carbon paste electrode decorated with poly(<Emphasis Type="Italic">P</Emphasis>-phenylendiamine/ZnO) nanocomposite

In this study, poly(P-phenylenediamine/ZnO) (PpPD/ZnO) nanocomposite (NC) under ultrasonic conditions was synthesized and characterized. The presence of zinc oxide nanoparticles changed the morphology of PpPD considerably as confirmed by SEM observations. Hydrazine electrooxidation at novel modified carbon paste electrodes (CPE) with supported NC was investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronoamperometry (CA) techniques. Obtained results showed that the NC increases the surface catalytic activity of CPE toward hydrazine electrooxidation. The electrocatalytic current density increased linearly with hydrazine concentration, and the detection limit and sensitivity are determined to be 24 μM and 0.172 mA cm^?2 mM^?1, respectively. As revealed by the EIS measurements, the increased conductivity and decreased R _ct are owing to the presence of ZnO NPs in the PpPD matrix. The CA results indicated that hydrazine electrooxidation results in higher steady-state current density on CPE/PpDP/ZnO electrode system compared to the CPE/PpDP and CPE electrodes.     

Influences on power performances of metal oxide additives for LiFePO4 electrodes

Metal oxide additives are added into LiFePO₄ electrodes attempting to improve cell power performances. Electrochemical performances are tested with 5 wt% different sizes of neutral alumina, nano Al₂O₃, and nano MgO individually comparing with those with 5 wt% more active LiFePO₄ and acetylene black. The polarization between charge and discharge plateaus is reduced not only by adding more conductive acetylene black, but also by adding all these insulated metal oxide additives. Adding natural alumina and nano MgO can significantly increase rate capacities. This might be because of their “lithium ion saver” effect.     

Synthesis and electrochemical properties of SnS as possible anode material for lithium batteries

Tin monosulfide, SnS particles were synthesized at 950 °C using a simple melt mixing. The as prepared materials were subjected to XRD, SEM and EDAX analyses. The CR 2032-type coin cell composed of Li/SnS was assembled and its cycling profile was examined. The cell delivered an initial discharge capacity of 956 mAh/g at its first cycle and fades subsequently in the following cycles. The formation of Li₂CO₃ in the solid electrolyte interface (SEI) was identified by FT-IR analysis. Impedance spectroscopic study on Li/SnS cells revealed an increase in the value of charge transfer resistance “R_ct” upon cycling and is attributed to the breaking of inter-particle contact caused by the volume expansion.     

Effect of mesoporous carbon containing binary conductive additives in lithium ion batteries on the electrochemical performance of the LiCoO2 composite cathodes

Binary conductive additives (BCA), formed by sonication of mesoporous carbon (MC) and acetylene black (AB), were used as conductive additives to improve the electrochemical performance of a LiCoO₂ composite cathode. The electrochemical performance of the LiCoO₂ composite cathode dispersed with BCA was investigated. The results showed that the electrochemical performance (including the discharge capacity, the discharge voltage and the total internal resistance) of a BCA loaded LiCoO₂ composite cathode was better than that of a cathode loaded with AB. The possible mechanism is that the MC in BCA can adsorb and retain electrolyte solution, which allows an intimate contact between the lithium ions and the cathode active material LiCoO₂ due to its large mesopore specific surface area. A simplified model was also proposed.     

New insight on nanostructure assembling of high-performance electrode materials: synthesis of surface-modified hexagonal β-Ni(OH)<Subscript>2</Subscript> nanosheets as an example

Hexagonal β-Ni(OH)₂ nanosheets with thickness of ～12 nm were synthesized by a hydrothermal method at 150 °C using nickel chloride as nickel source and morpholine as alkaline. Electrodes for application in pseudocapacitor were assembled through a traditional technique: pressing a mixture of β-Ni(OH)₂ nanosheets and acetylene black onto nickel foam. Due to the hexagonal shape of rigid β-Ni(OH)₂ nanosheet and the mediation of surface-modified glycerol during electrochemical charge–discharge cycles, a nanostructure of electrode material with facile interior pathway for the transfer of electrolyte was formed. As a result, the as-formed electrodes presented high specific capacitance of 1,917 F g^?1 at current density of 1.6 A g^?1 in 3 mol L^?1 KOH solution. At high charge and discharge current density of 31.3 A g^?1, the electrodes still remained a high specific capacitance of 1,289 F g^?1. The interesting results obtained from this investigation may provide a new insight for the synthesis of electrode materials with high electrochemical performance.     

Impedance spectroscopy of Na+ conducting zeolite ZSM-5

The electrochemical impedance of Na⁺ ion conducting zeolite Na-ZSM-5 contacted with gold electrodes is measured. Complementary impedance measurements of the same material contacted with Na⁺ ion conducting Na₂CO₃ enabled the separation of volume and electrode parts of the impedance. Both volume and electrode impedances consisted of multiple components. Possible underlying mechanisms are discussed in view of the application of zeolites as sensitive materials in solid-state ionic gas sensors.     

Preparation of MnO<Subscript>2</Subscript>/WMNT composite and MnO<Subscript>2</Subscript>/AB composite by redox deposition method and its comparative study as supercapacitive materials

The manganese oxide/multi-walled carbon nanotube (MnO₂/MWNT) composite and the manganese oxide/acetylene black (MnO₂/AB) composite were prepared by translating potassium permanganate into MnO₂ which formed the above composite with residual carbon material using the redox deposition method and carbon as a reducer. The products were characterized by X-ray diffraction, Fourier transform infrared, and scanning electron microscope. Electrochemical properties of both the MnO₂/MWNT and MnO₂/AB electrodes were studied by using cyclic voltammetry, electrochemical impedance measurement, and galvanostatic charge/discharge tests. The results show that the MnO₂/MWNT electrode has better electrochemical capacitance performance than the MnO₂/AB electrode. The charge–discharge test showed the specific capacitance of 182.3 F·g⁻¹ for the MnO₂/MWNT electrode, and the specific capacitance of 127.2 F·g⁻¹ for the MnO₂/AB electrode had obtained, within potential range of 0–1 V at a charge/discharge current density of 200 mA·g⁻¹ in 0.5 mol·L⁻¹ potassium sulfate electrolyte solution in the first cycle. The specific capacitance of both the MnO₂/MWNT and MnO₂/AB electrodes were 141.2 F·g⁻¹ and 78.5 F·g⁻¹ after 1,200 cycles, respectively. The MnO₂/MWNT electrode has better cycling performance. The effect of different morphologies was investigated for both MnO₂/MWNT and MnO₂/AB composites.     

Effect of electrode microstructure on gas-phase diffusion in solid oxide fuel cells

The relation between electrode microstructure and gas diffusion has been investigated with different morphologies of Pt electrodes by using AC impedance techniques. The measurements were carried out at temperatures of 873–1273 K and oxygen partial pressure (P_O2) of 0.01–1 atm.Gas-phase diffusion was observed only for high-performance electrodes at the high-temperature (1073–1273 K) and low-oxygen-partial-pressure regions (<0.1 atm P_O2). Considering the physical and electrochemical characteristics of impedance arcs, it was found that the arc at the frequency of below 1 Hz was related to gas conversion resistance, while the arc at the frequency of around 10 Hz represented pore diffusion resistance through the current-collecting part. For a thick electrode with a low porosity, however, gas diffusion resistance through pores of an electrode was observed at a frequency of around 100 Hz.From the results of a comparison of electrode performances with different electrode microstructures, electrochemical reaction sites (ERS) are supposed to be located at the peripheral line of Pt and YSZ as well as the Pt/YSZ interfaces where reaction gas can easily diffuse.     

Kinetic study on LiFePO<Subscript>4</Subscript>-positive electrode material of lithium-ion battery

LiFePO₄-positive electrode material was successfully synthesized by a solid-state method, and the effect of storage temperatures on kinetics of lithium-ion insertion for LiFePO₄-positive electrode material was investigated by electrochemical impedance spectroscopy. The charge-transfer resistance of LiFePO₄ electrode decreases with increasing the storage temperatures. This suggests that it has a high electrochemical activity at high temperature. The diffusion coefficient of lithium ion is greatly increased with increasing the storage temperatures, indicating that the kinetics of Li⁺ and electron transfer into the electrodes were much fast at high storage temperature.     

Sensitive voltammetric determination of diclofenac using room-temperature ionic liquid-modified carbon nanotubes paste electrode

An ionic liquid-modified carbon nanotubes paste electrode (IL/CNTPE) has been fabricated using hydrophilic ionic liquid (n-hexyl-3-methylimidazolium hexafluoro phosphate) as a binder. This electrode showed enhanced electrochemical response and strong analytical activity towards the direct electrochemical oxidation of diclofenac (DCF). The electron transfer coefficient, α, and charge transfer resistance (R _ct) of DCF at the modified electrode were calculated. Under optimal conditions at pH 7.0, the anodic peak currents increased linearly with the concentration of DCF in the range of 0.5–300 μmol L^?1 with a detection limit of 0.2 μmol L^?1 (3σ). The interferences of foreign substances were investigated. Differential pulse voltammetry was used to check the applicability of the proposed sensor to the determination of DCF in real samples with satisfactory results.     

Flexible polyethylene terephthalate (PET) electrodes based on single-walled carbon nanotubes (SWCNTs) for supercapacitor application

Flexible polyethylene terephthalate (PET) electrodes based on pristine single-walled carbon nanotubes (SWCNTs) and acid-treated single-walled carbon nanotubes (A-SWCNTs) were prepared by spray coating technique. Flexible A-SWCNTs electrodes showed enhanced electrochemical properties compared to the pristine SWCNTs electrodes. The electrochemical properties of the flexible A-SWCNTs electrodes were optimized with various types of aqueous electrolytes including sulfuric acid (H₂SO₄), sodium sulfate (Na₂SO₄), potassium chloride (KCl), sodium hydroxide (NaOH), and potassium hydroxide (KOH). The electrochemical performance of the A-SWCNTs electrodes as a function of bending to 30° were evaluated using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge/discharge (GCD) measurements in 1 M H₂SO₄. The specific capacitance value of the unbent A-SWCNTs electrode was 67 F g^?1, which decreased to 63 F g^?1 (94% retention) after 1000 GCD cycles. Interestingly, the specific capacitance of the unbent A-SWCNTs electrode with application of the 1000 GCD cycles was retained even after 500 bending to 30° with 6000 GCD cycles.     

Electrochemical and surface characterisation of carbon-film-coated piezoelectric quartz crystals

The electrochemical properties of carbon films, of thickness between 200 and 500 nm, sputter-coated on gold- and platinum-coated 6 MHz piezoelectric quartz crystal oscillators, as new electrode materials have been investigated. Comparative studies under the same experimental conditions were performed on bulk electrodes. Cyclic voltammetry was carried out in 0.1 M KCl electrolyte solution, and kinetic parameters of the model redox systems Fe(CN)₆^3−/4− and [Ru(NH₃)₆]^3+/2+ as well as the electroactive area of the electrodes were obtained. Atomic force microscopy was used in order to examine the surface morphology of the films, and the properties of the carbon films and the electrode-solution interface were studied by electrochemical impedance spectroscopy. The results obtained demonstrate the feasibility of the preparation and development of nanometer thick carbon film modified quartz crystals. Such modified crystals should open up new opportunities for the investigation of electrode processes at carbon electrodes and for the application of electrochemical sensing associated with the EQCM.     

An electrochemical cell with sapphire windows for operando synchrotron X‐ray powder diffraction and spectroscopy studies of high‐power and high‐voltage electrodes for metal‐ion batteries

A new multi‐purpose operando electrochemical cell was designed, constructed and tested on the Swiss–Norwegian Beamlines BM01 and BM31 at the European Synchrotron Radiation Facility. Single‐crystal sapphire X‐ray windows provide a good signal‐to‐noise ratio, excellent electrochemical contact because of the constant pressure between the electrodes, and perfect electrochemical stability at high potentials due to the inert and non‐conductive nature of sapphire. Examination of the phase transformations in the Li_1–xFe_0.5Mn_0.5PO₄ positive electrode (cathode) material at C/2 and 10C charge and discharge rates, and a study of the valence state of the Ni cations in the Li_1–xNi_0.5Mn_1.5O₄ cathode material for Li‐ion batteries, revealed the applicability of this novel cell design to diffraction and spectroscopic investigations of high‐power/high‐voltage electrodes for metal‐ion batteries.     

Microstructure and electrode properties of La0.6Sr0.4Co0.2Fe0.8O3-δ spin-coated on Ce0.8Sm0.2O2?δ electrolyte

Fine and uniform La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ powder was synthesized by a glycine–nitrate combustion process. La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ electrodes were prepared on dense Ce_0.8Sm_0.2O_2−δ electrolyte substrates using a spin-coating technique by sintering at 900–1,000 °C. The electrode properties of La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ were investigated by electrochemical impedance spectroscopy and chronopotentiometry techniques with respect to preparation conditions and the resulting microstructures. The results indicate a significant effect of the microstructure on the electrode processes and polarization characteristics. The oxygen adsorption and dissociation process acted as a larger contribution to the overall electrode polarization R _p in magnitude compared with the charge transfer process due to relatively low porosity levels of the electrodes. It was detected that the grain size of the electrodes exhibited a crucial role on the electrocatalytic reactivity. At 800 °C, the electrode sintered at 950 °C attained a polarization resistance of 0.18 Ω cm², an overpotential of 27 mV at a current density of 200 mA cm⁻², and an exchange current density of 308 mA cm⁻².