SnO2-decorated multiwalled carbon nanotubes and Vulcan carbon through a sonochemical approach for supercapacitor applications

Multiwalled carbon nanotubes (MWCNTs) and Vulcan carbon (VC) decorated with SnO₂ nanoparticles were synthesized using a facile and versatile sonochemical procedure. The as-prepared nanocomposites were characterized by means of transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier transform infra red spectroscopy. It was evidenced that SnO₂ nanoparticles were uniformly distributed on both carbon surfaces, tightly decorating the MWCNTs and VC. The electrochemical performance of the nanocomposites was evaluated by cyclic voltammetry and galvanostatic charge/discharge cycling. The as-synthesized SnO₂/MWCNTs nanocomposites show a higher capacity than the SnO₂/VC nanocomposites. Concretely, the SnO₂/MWCNTs electrodes exhibit a specific capacitance of 133.33 F g⁻¹, whereas SnO₂/VC electrodes exhibit a specific capacitance of 112.14 F g⁻¹ measured at 0.5 mA cm⁻² in 1 M Na₂SO₄.     

Rechargeability improvement of δ-type chemical manganese dioxide with the co-doping of Bi and Ni in alkaline electrolyte

δ-MnO₂ with the doping of Ni and Bi was prepared through a simple chemical precipitation/oxidation method. Its structure was confirmed by the X-ray diffraction tests. The results of cyclic voltammetry and galvanostatic charge–discharge tests showed that both the doping of Bi and Ni benefited the electrochemical activity of the MnO₂ electrode. Compared to the un-doped electrode, the Bi-doped one showed larger discharge capacity and the Ni-doped one showed higher discharge potential and better cycleability. With the co-doping of 5 wt% Bi and 10 wt% Ni, the discharge capacity of the MnO₂ electrode reached 252 mA h g^?1 at a 0.2C rate and 116 mA h g^?1 at a 1C rate, respectively. Its capacity remained in 105 mA h g^?1 after 50 cycles at a 1C rate, but the capacity of a commercial electrolytic MnO₂ electrode was only 37 mA h g^?1.     

Galvanostatically deposited Fe: MnO2 electrodes for supercapacitor application

The present investigation describes the addition of iron (Fe) in order to improve the supercapacitive properties of MnO₂ electrodes using galvanostatic mode. These amorphous worm like Fe: MnO₂ electrodes are characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDAX), Fourier transform infrared spectroscopy (FTIR) and wettability test. The supercapacitive properties of MnO₂ and Fe: MnO₂ electrodes are investigated using cyclic voltammetry, chronopotentiometry and impedance techniques. It is seen that the supercapacitance increases with increase in Fe doping concentration and achieved a maximum of 173 F g^?1 at 2 at% Fe doping. The maximum supercapacitance obtained is 218 F g^?1 for 2 at% Fe: MnO₂ electrode. This hydrous binary oxide exhibited ideal capacitive behavior with high reversibility and high pulse charge–discharge property between ?0.1 and +0.9 V/SCE in 1 M Na₂SO₄ electrolyte indicating a promising electrode material for electrochemical supercapacitors.     

Facile synthesis of low-dimensional SnO2 nanostructures: An investigation of their performance and mechanism of action as anode materials for lithium-ion batteries

Owing to high-energy density of rechargeable lithium-ion batteries (LIBs), they have been investigated as an efficient electrochemical power sources for various energy applications. High theoretical capacities of tin oxide (SnO₂) anodes have led us a path to meet the ever-growing demands in the development of high-performance electrode materials for LIBs. In this paper, a facile approach is described for the synthesis of porous low-dimensional nanoparticles and nanorods of SnO₂ for application in LIBs with the help of Tween-80 as a surfactant. The SnO₂ samples synthesized at different reaction temperatures produced porous nanoparticles and nanorods with average diameters of ~7–10 nm and ~70–110 nm, respectively. The SnO₂ nanoparticle electrodes exhibit a high reversible charge capacity of 641.1 mAh/g at 200 mA/g after 50 cycles, and a capacity of 340 mAh/g even at a high current density of 1000 mA/g during the rate tests, whereas the porous nanorod electrodes delivers only 526.3 mAh/g at 200 mA/g after 50 cycles and 309.4 mAh/g at 1000 mA/g. It is believed that finer sized SnO₂ nanoparticles are much more favorable to trap more Li⁺ ion during electrochemical cycling, resulting in a large irreversible capacity. In contrast, rapid capacity fading was observed for the porous nanorods, which is the result of their pulverization resulting from repeated cycling.     

Current transport mechanism and photovoltaic properties of photoelectrochemical cells of ITO/TiO2/PVC–LiClO4/graphite

This paper deals with the current transport mechanism of solid state photoelectrochemical cells of ITO/TiO₂/PVC–LiClO₄/graphite as well as the physical properties of a component of a device affecting its performance. The principle of operation and a schematic energy level diagram for the materials used in the photoelectrochemical cells are presented. The device makes use of ITO films, TiO₂ films, PVC–LiClO₄ and graphite films as photoanode, photovoltaic material, solid electrolyte and counter electrode, respectively. The device shows rectification. The J_sc and V_oc obtained at 100 mW cm⁻² were 0.95 μAcm⁻² and 180 mV, respectively.     

Thermal stabilities of metal bottom electrodes for Ta2O5 metal-oxide-metal capacitor structure

Thermal stabilities of various metal bottom electrodes were examined by using a Ta₂O₅ metal-oxide-metal (MOM) capacitor structure. After depositing 10-nm thick Ta₂O₅ on metal-electrode/poly-Si, we performed rapid thermal oxidation (RTO) at 850 °C for 60 s in an O₂ ambient. A chemical-vapor-deposition (CVD) WSi₂ electrode showed satisfactory thermal stability after the RTO, while other examined electrode materials exhibited thermal degradation caused by oxidation failure or interfacial reaction between the substrate poly-Si and the Ta₂O₅. After post-annealing at 650 °C for 30 min (in N₂ condition) with CVD TiN top electrode, an effective oxide thickness (T_ox) of ∼32 Å and a leakage current density of ∼10⁷ A/cm² at 1.25 V were obtained from the MOM capacitor with the WSi₂ bottom electrode. Other electrode materials, such as TiN, TiSi_x, WN_x, W, and Ta, were severely oxidized during the RTO in the MOM structures, and very poor capacitor properties were obtained in terms of T_ox and leakage current.     

Combined XPS,electrochemical and Kelvin probe measurements of NaY zeolite

In the present study X-ray Photoelectron Spectroscopy (XPS) combined with in situ electrochemical and Kelvin probe measurements was used in order to get a deeper insight on the mechanism of the cation transport through NaY zeolite and the charge transfer through the Au electrode/zeolite interface. It is shown that by imposing a potential gradient across the NaY powder which is sandwiched between two electrodes, Na⁺ ions can be electrically transferred to or from the Au working electrode area, following the direction of the applied potential between the two electrodes. Two peaks corresponding to sodium species were detected by means of in situ XPS investigation during potential application. The first peak of Na1s photoelectrons with binding energy at 1072.2 ± 0.2 eV is attributed to Na adsorbed on the grounded Au electrode with its coverage remaining unchanged upon potential imposition. The second peak is directly associated with Na present in the zeolite and upon potential application its binding energy varies proportionally with the variation of the surface potential measured by Kelvin probe. Upon varying the potential from − 4 to + 4 V between the working and counter electrode, the Na⁺ concentration decreases by ca30% at the Au/zeolite interface. However the invariant amount of Na on the Au electrode under vacuum shows that the variation in Na⁺ concentration is not due to ionic transfer onto the Au surface but instead Na⁺ accumulation can be assumed at the Au/zeolite interface. On the other hand, current or potential application under O₂ atmosphere promotes the electrocatalytic reaction of Na⁺ towards the formation of Na₂O on the Au electrode surface.     

Internal evaluation of impregnation treatment of waterlogged wood; relation between concentration of internal materials and relaxation time using magnetic resonance imaging

The purpose of this study is to clarify the degree of impregnation resulting from treatment of internal waterlogged wood samples using MRI. On a 1.5 T MR scanner, T₁ and T₂ measurements were performed using inversion recovery and spin-echo sequences, respectively. The samples were cut waterlogged pieces of wood treated with various impregnation techniques which were divided into different concentrations of trehalose (C₁₂H₂₂O₁₁) and polyethylene glycol (PEG; HO-(C₂H₄O)_n-H) solutions. Then these samples underwent impregnation treatment every two weeks. From the results, we found that the slope of the T₁-concentration curve using linear fitting showed the value of the internal area for PEG to be higher than the external area; internal, − 2.73 ms/wt% (R² = 0.880); external, − 1.50 ms/wt% (R² = 0.887). Furthermore, the slope of the T₁-concentration curve using linear fitting showed the values for trehalose to have almost no difference when comparing the internal and the external areas; internal, − 2.79 ms/wt% (R² = 0.759); external, − 3.02 ms/wt% (R² = 0.795). However, the slope of the T₂-concentration curve using linear fitting for PEG showed that there was only a slight change between the internal and the external areas; internal, 0.26 ms/wt% (R² = 0.642); external, 0.18 ms/wt% (R² = 0.920). The slope of the T₂-concentration curve did not show a change in linear relationship between the internal and the external areas; internal, 0.06 ms/wt% (R² = 0.175); external, − 0.14 ms/wt% (R² = 0.043). In conclusion, using visualization of relaxation time T₁, it is possible to obtain more detail information noninvasively concerning the state of impregnation treatment of internal waterlogged wood.     

Electrode reaction of Sr1−xLaxCo0.8Fe0.2O3−δ with x = 0.1 and 0.6 on Ce0.9Gd0.1O1.95 at 600 ≤ T ≤ 800 °C

The electrode reaction of the perovskite phases Sr_1−xLa_xCo_0.8Fe_0.2O_3−δ (x = 0.1 and 0.6) on Ce_0.9Gd_0.1O_1.95 has been investigated by impedance spectroscopy in the temperature range 600 ≤ T ≤ 800 °C. Thick porous electrodes (t ∼ 20 μm) were sprayed on Ce_0.9Gd_0.1O_1.95 and ac impedance spectra were recorded on symmetrical cells at the equilibrium. The analysis of the complex impedance diagrams clearly indicates the presence of two contributions. The low frequency one was assigned to the gas phase oxygen diffusion through the porous electrode and a finite length diffusion (Warburg) impedance was used to describe the high frequency (HF) data. The polarization resistance of the HF impedance contribution (R_w) is higher for x = 0.1 while the activation energy of R_w is higher for x = 0.6. The variations of R_w versus the La content, temperature and thickness indicate that the Warburg-type impedance contains information of both bulk oxygen diffusion and surface processes.     

Improving La0.6Sr0.4Co0.2Fe0.8O3 − δ cathode performance by infiltration of a Sm0.5Sr0.5CoO3 − δ coating

La_xSr_1 ? xCo_yFe_1 ? yO_3 ? δ (LSCF) represents one of the state-of-the-art cathode materials for solid oxide fuel cells (SOFCs) due primarily to its high ionic and electronic conductivity. In this study, a one-step infiltration process has been developed to deposit, on the surface of a porous LSCF cathode, a thin film (50–100 nm) of Sm_0.5Sr_0.5CoO_3 ? δ (SSC), which is catalytically more active for oxygen reduction. Electrochemical impedance spectroscopy reveals that the SSC coating has dramatically reduced the polarization resistance of the cathode, achieving area-specific resistances of 0.036 Ω cm² and 0.688 Ω cm² at 750 °C and 550 °C, respectively. It has also maintained the stability of LSCF cathodes. In particular, the peak power densities are increased by ~ 22% upon the infiltration of SSC onto the porous LSCF cathodes of our best performing cells. These results demonstrate that a conductive backbone (e.g., LSCF) coated with a catalytic film (e.g., SSC) is an attractive approach to achieving an active and stable SOFC cathode for low-temperature solid oxide fuel cells.     

Characterization of doped La0.7A0.3Cr0.5Mn0.5O3 − δ (A = Ca,Sr, Ba) electrodes for solid oxide fuel cells

Doped lanthanum manganese chromite based perovskite, La_0.7A_0.3Cr_0.5Mn_0.5O_3 ? δ (LACM, A = Ca, Sr, Ba), on yttria-stabilized zirconia (YSZ) electrolyte is investigated as potential electrode materials for solid oxide fuel cells (SOFCs). The electrical conductivity and electrochemical activity of LACM depend on the A-site dopant. The best electrochemical activity is obtained on the La_0.7Ca_0.3Cr_0.5Mn_0.5O_3 ? δ/YSZ (LCCM/YSZ) composite electrodes. The conductivity of LCCM is 29.9 S cm^? 1 at 800 °C in air, and the electrode polarization resistance (R_E) of the LCCM/YSZ composite cathode for the O₂ reduction reaction is 0.5 Ω cm² at 900 °C. The effect of Gd-doped ceria (GDC) impregnation on the LCCM cathode polarization resistances is also studied. GDC impregnation significantly enhances the electrochemical activity of the LCCM cathode. In the case of the 6.02 mg cm^? 2 GDC-impregnated LCCM cathode, R_E is 0.4 Ω cm² at 800 °C, ~ 60 times smaller than 24.4 Ω cm² measured on a LCCM cathode without the GDC impregnation. Finally the electrochemical activities of the doped lanthanum manganese chromites for the H₂ oxidation reaction are also investigated.     

Kinetic studies of the electrochemical nitrogen reduction and incorporation into yttria stabilized zirconia

The kinetics of the electrochemical reduction of molecular nitrogen at gold micro electrodes on yttria stabilized zirconia (YSZ) solid oxide electrolyte is studied by steady state polarization measurements. From the η / lg i plot for both cathodic and anodic polarization the apparent transfer coefficients α_a and α_c are evaluated. The sum of α_a + α_c exceeds unity and thus a multistep electron transfer process is suggested. The concept of the stoichiometric number is applied to the electrode reaction N₂ + 6e⁻ = 2N³⁻ supposing that the overall process involves at least two intermediate species. On the basis of the evaluation of the experimental results the reaction N₂⁻ + e⁻ ⇌ N₂²⁻ is suggested as the rate determining reaction step for the cathodic nitrogen reduction and nitride formation.     

High surface area monodispersed Fe3O4 nanoparticles alone and on physical exfoliated graphite for improved supercapacitors

Highly conductive, unsophisticated and easy to be obtained physical exfoliated graphite (PHG) supporting well dispersed magnetite, Fe₃O₄/PHG nanocomposite, has been prepared by a one-step chemical strategy and physico-chemical characterized. The nanocomposite, favoured by the a-polar nanoparticles (NPs) capping, results in a self-assembled monolayer of monodispersed Fe₃O₄, covering perfectly the hydrophobic surfaces of PHG. The nanocomposite as an electrode material was fabricated into a supercapacitor and characterized by cyclic voltammetry (CV) and galvanostatic charge–discharge measurements. It shows, after a suitable annealing, significant electrochemical properties (capacitance value of 787 F/g at 0.5 A g⁻¹ and a Fe₃O₄/PHG weight ratio of 0.31) and good cycling stability (retention 91% after 30,000 cycles). Highly monodispersed very fine Fe₃O₄ NPs, covered by organic chains, have been also synthesized. The high surface area Fe₃O₄ NPs, after washing to leave a low content of organic chains able to avoid aggregation without excessively affecting the electrical properties of the material, exhibit remarkable pseudocapacitive activities, including the highest specific capacitance over reported for Fe₃O₄ (300 F/g at 0.5 A g⁻¹).     

Sonoelectrochemical degradation of triclosan in water

The sonoelectrochemical degradation of triclosan in aqueous solutions with high-frequency ultrasound (850 kHz) and various electrodes was investigated. Diamond coated niobium electrode showed the best results and was used as standard electrode, leading to effective degradation and positive synergistic effect. The influence of different parameters on the degradation degree and energy efficiency were evaluated and favorable reaction conditions were found. It could be shown that 92% of triclosan (1 mg L⁻¹ aqueous solution) was degraded within 15 min, following pseudo-first order kinetics.     

I–V characteristics of a methanol concentration sensor for direct methanol fuel cell (DMFC) by using catalyst electrode of Pt dots

In this work, the methanol sensors were fabricated by using Pt dot catalyst electrode and the level of electrochemical response was analyzed. This kind of sensors can be applicable to sensing the methanol concentration in real-time. When we measured the methanol sensor with 5 nm of Pt dot, we could get 2.00 × 10⁻⁶, 3.06 × 10⁻⁶ and 6.25 × 10⁻⁶ A of electric current value for the methanol concentration of 1, 2 and 3 mole, respectively. The measured voltage was 1 V. To optimize the sensitivity level of Pt dot catalyst electrode, the electrodes were made in H-grid shape. The distance between electrode branches was designed to be 80, 150 and 300 μm, respectively. When we measured the electric current–voltage characteristics of methanol sensor with 2 M of methanol, it was 3.06 × 10⁻⁶, 2.02 × 10⁻⁶ and 1.50 × 10⁻⁶ A, for 80, 150 and 200 μm, respectively. Thus it is suggested that more efficient response of methanol sensing is possible when the distance between electrodes is reduced.     

A preliminary study on a new LiBOB/acetamide solid phase transition electrolyte

New solid electrolytes containing acetamide and lithium bioxalato borate (LiBOB) with different molar ratios have been investigated. Their melting points (T_m) are around 42 °C. The ionic conductivities and activation energies vary drastically below and above T_m, indicating a typical feature of phase transition electrolyte. The ionic conductivity of the LiBOB/acetamide electrolyte with a molar ratio of 1:8 is 5 × 10^? 8 S cm^? 1 at 25 °C but increases to 4 × 10^? 3 S cm^? 1 at 60 °C. It was found that anode materials, such as graphite and Li₄Ti₅O₁₂, could not discharge and charge properly in this electrolyte at 60 °C due to the difficulty in forming a stable passivating layer on the anodes. However, a Li/LiFePO₄ cell with this electrolyte can be charged properly after heating to 60 °C, but cannot be charged at room temperature. Although the LiBOB/acetamide electrolytes are not suitable for Li-ion batteries due to poor electrode compatibility, the current results indicate that a solid electrolyte with a slightly higher phase transition temperature than room temperature may find potential application in stationary battery for energy storage where the electrolyte is at high conductive liquid state at elevated temperature and low conductive solid state at low temperature. The interaction between acetamide and LiBOB in the electrolyte is also studied by Raman and FTIR spectroscopy.     

Studies on the percolation limit of Ce0.9Gd0.1O1.95 in La0.6Sr0.4Co0.2Fe0.8O3−δ–Ce0.9Gd0.1O1.95 nanocomposites for solid oxide fuel cells application

A large difference in thermal expansion coefficient of electrode and electrolyte leads to imperfect electrode/electrolyte interface and hence significant polarization losses in solid oxide fuel cells. To overcome the difficulties associated with electrode and electrode/electrolyte interface, there is need to fabricate the composite cathode. Thus the present paper deals with study of La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ(LSCF)–Ce_0.9Gd_0.1O_1.95(GDC) nanocomposite with different fractions of GDC obtained by physical mixing of combustion synthesized nanopowders. No secondary phases were observed upon sintering at 1100 °C for 2 h affirming the chemical compatibility between LSCF and GDC. The composites with relatively high GDC% have higher density as a consequence of rapid grain growth and less conductivity. The nanocomposite with 50% of GDC showed electric conductivity of 30 Scm⁻¹ at 500 °C and low area specific resistance of 106 Ω cm² with 10 μs relaxation time at 200 °C.     

Improved efficiency of dye-sensitized solar cells applied with nanostructured N–F doped TiO2 electrode

Dye-sensitized solar cells (DSSCs) were fabricated with N–F-doped TiO₂ electrodes. The XRD pattern of the N–F-doped TiO₂ is almost the same as that of pure TiO₂, showing that N and F doping has little influence on the formation of anatase titania. The influence of dopant N and F on band energetics and photoelectrochemical properties of nanostructured TiO₂ electrodes were investigated. Compared with pure TiO₂ electrodes, the E_fb of N–F-doped TiO₂ electrodes shifted a little in electrolytes containing LiClO₄. However the total trap densities were remarkably decreased as TiO₂ electrodes were doped with N and F. Finally the N–F-doped TiO₂ electrodes were sensitized with N3 and their photoelectrochemical properties were studied. Experimental results showed that the photoelectric conversion efficiency of N3 sensitized N–F-doped TiO₂ electrodes was 8.61% under irradiation of 100 mW cm^?2 white light, about 17.1% higher than that of a pure TiO₂ electrode.     

EHD atomization characteristics of a point-plate system with a porous point electrode

An electrohydrodynamic (EHD) atomization from a point-to-plate system, with a wet porous point as a corona electrode, has been studied. And the atomized water droplets from the wet porous point, as well as the water droplet traces, the water droplet charge-to-mass ratios, and the water droplet number concentrations, were investigated. It was observed that the wet porous point can atomize abundant amounts of water droplet, 2.8, 2.6 and 2.2 mg/min for negative, AC and positive corona, respectively. The migrated water droplet traces were observed. The positive wet porous point atomized very fine water droplets than those obtained with the negative wet porous point. Moreover, the water droplets atomized from the AC corona showed granular-like larger traces. A weak corona discharge can atomize water droplets very effectively. On the other hand, an intensive corona discharge can eject more water droplets. As a result with the wet porous point, the maximum corona-current-based and corona-power-based water droplet atomization yields of Y_C = 3.34, 3.32 and 3.25 μg/μAs and Y_P = 0.35, 0.40 and 0.27 mg/Ws have been obtained for the negative, AC and positive corona discharges.     

High room-temperature pyroelectric response of MgO-modified Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3 ceramics

The dielectric and pyroelectric responses of MgO-modified Pb_0.99(Zr_0.95Ti_0.05)_0.98Nb_0.02O₃ ceramics were investigated near F_R(LT)–F_R(HT) phase transition. It was found that MgO additive reduced the F_R(LT)–F_R(HT) phase transition temperature from 41 °C to room temperature (24 °C). Superior room-temperature pyroelectric properties were obtained in the composition of 0.10 wt% MgO addition without DC bias. The largest pyroelectric coefficient, 65 × 10⁻⁸ C cm⁻² K⁻¹, was detected. Accordingly, the detectivity figures of merit F_d had maximum values of 20 × 10⁻⁵ Pa^−1/2, and especially the voltage responsivity F_v = 0.91 m²C⁻¹ is the highest value reported so far among all pyroelectric materials. It shows promising potential for application in uncooled pyroelectric infrared detector.