Laser Induced Temperature Perturbation on Ultramicroelectrodes: Unsupported Solutions in Nonaqueous Methanol

Temperature dependence studies of electrochemical parameters provide insight into electron transfer processes. In cases where adding excess electrolyte experimental causes complications colloidal systems, organic or biological samples it is preferable to deal with the high resistivity of the medium. We validate the use of unsupported and weakly supported solutions in thermoelectrochemical experiments. The temperature dependence of the diffusion coefficient allows calibration of the steady-state current to measure changes when a continuous wave (CW) ultraviolet laser, λ=325 nm, illuminates an ultramicroelectrode (UME) from the front. Calibrating the steady-state current ratios before and after heating with a thermostatic bath allows temperature measurements within an accuracy of 0.6 K. The solutions are without supporting electrolytes in methanol, a volatile solvent, and we use a model that accurately describes the viscosity and temperature dependence of the solvent. We calculated the temperature and derived an equation to estimate the temperature measurement error. A numeric method yields satisfactory results, considering the changes for both diffusion coefficients and viscosity explicitly, and predict the thermostatic temperature bath, agreeing with the theoretical model's error. In unsupported solutions, the ferrocene diffusion coefficient and the iodide apparent diffusion coefficient follow the expected increase with temperature. Under CW laser illumination ΔT=4±1 K.

Active Damping Injection Output Voltage Control with Dynamic Current Cut-off Frequency for DC/DC Buck Converters

With regard to DC/DC buck converter applications, the objective of this study is to expand the admissible range of the output voltage cut-off frequency while lowering the steady-state current cut-off frequency as possible. This study fortifies the inner loop by incorporating the novel subsystems such as an auto-tuner (for the dynamic current cut-off frequency) and active damping injection invoking the pole-zero cancellation nature with the particular designed feedback gain structure. The outer loop active damping control renders the closed-loop speed transfer function to be a first-order low-pass filter with the cooperation of the specially structured design parameters; in addition, it provides time-varying disturbance attenuation. The experimental results obtained for a 3-kW buck converter validate the feasibility of the proposed technique by showing a 34% performance enhancement (at least) compared with the recent active damping controller.

Effect of Single Walled Carbon Nanotubes on the Series Resistance and Trap Energy of Malachite Green Dye Based Organic Device

In this paper, we have estimated the series resistance (Rs) and the trap energy (Ec) of the sandwiched type Malachite Green (MG) dye-based organic device and have also observed the influence of single-walled carbon nanotubes (SWCNT) on both of these parameters. To form the organic device, we have used Indium Tin Oxide (ITO) coated glass as the front electrode and Aluminium (Al) as a back electrode by using the spin coating technique. The values of series resistance are measured from both I-V characteristics and by utilizing Cheung Function due to the non ideal behavior of organic devices. We have also extracted the values of Rs by using H (I) versus I plot and verified the values with the measured values of Rs from the Cheung function. The extracted values of series resistance using these three processes remain consistent with each other in showing that the values of series resistance have been reduced considerably in the presence of SWCNT. The trap energy has been estimated from the steady-state current-voltage characteristics. There is a significant correlation in between series resistance and the trap energy of the organic device. The presence of Single-Walled Carbon Nanotubes reduces the trap energy from 0.086 eV to 0.057 eV. Lowering of the trap energy of the metal-organic layer interface in presence of Single Walled Carbon Nanotubes attributes to the reduction of the value of the series resistance. The extracted value of Rs decreases from 0.154 MΩ to 0.0389 MΩ in presence of SWCNT. Decrease in the value of both of these parameters in the presence of SWCNT will definitely improve the charge transport mechanism of the organic device and thereby the conductivity.

Synthesis and Characterization of PdAgNi/C Trimetallic Nanoparticles for Ethanol Electrooxidation

The direct use of ethanol in fuel cells presents unprecedented economic, technical, and environmental opportunities in energy conversion. However, complex challenges need to be resolved. For instance, ethanol oxidation reaction (EOR) requires breaking the rigid C–C bond and results in the generation of poisoning carbonaceous species. Therefore, new designs of the catalyst electrode are necessary. In this work, two trimetallic PdxAgyNiz/C samples are prepared using a facile borohydride reduction route. The catalysts are characterized by X-ray diffraction (XRD), Energy-Dispersive X-ray spectroscopy (EDX), X-ray photoelectron Spectroscopy (XPS), and Transmission Electron Microscopy (TEM) and evaluated for EOR through cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS). The XRD patterns have shown a weak alloying potential between Pd, and Ag prepared through co-reduction technique. The catalysts prepared have generally shown enhanced performance compared to previously reported ones, suggesting that the applied synthesis may be suitable for catalyst mass production. Moreover, the addition of Ag and Ni has improved the Pd physiochemical properties and electrocatalytic performance towards EOR in addition to reducing cell fabrication costs. In addition to containing less Pd, The PdAgNi/C is the higher performing of the two trimetallic samples presenting a 2.7 A/mgPd oxidation current peak. The Pd4Ag2Ni1/C is higher performing in terms of its steady-state current density and electrochemical active surface area.

Bimetallic Pd-Co Nanoparticles Supported on Nitrogen-Doped Reduced Graphene Oxide as Efficient Electrocatalysts for Formic Acid Electrooxidation

In this work, bimetallic PdxCoy nanoparticles supported on nitrogen-doped reduced graphene oxide catalysts were synthesized and tested for formic acid oxidation as potentially efficient and durable electrocatalysts. Graphene oxide was nitrogen doped through hydrothermal chemical reduction with urea as a nitrogen source. The PdxCoy nanoparticles were deposited on the nitrogen-doped graphene oxide support using the impregnation-reduction method with sodium borohydride as a reducing agent and sodium citrate dihydrate as a stabilizing agent. The structural features, such as phases, composition, oxidation states, and particle sizes, of the nanoparticles were characterized using X-ray diffraction, transmission electron microscopy, scanning electron microscopy–energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The Pd nanoparticle sizes in Pd1Co1/N-rGO, Pd/N-rGO, and Pd1Co1/CNT were 3.5, 12.51, and 4.62 nm, respectively. The electrochemical performance of the catalysts was determined by CO stripping, cyclic voltammetry, and chronoamperometry. Pd1Co1/N-rGO showed the highest mass activity of 4833.12 mA–1 mg Pd, which was twice that of Pd1Co1/CNT. Moreover, Pd1Co1/N-rGO showed a steady-state current density of 700 mA–1 mg Pd after 5000 s in chronoamperometry carried out at +0.35 V. Apart from the well-known bifunctional effect of Co, nitrogen-doped graphene contributed to the performance enhancement of the Pd1Co1/N-rGO catalyst.

Transient Current Density in a Pair of Long Parallel Conductors

Two infinitely long parallel conductors of arbitrary cross section connected to a voltage source form a loop. If the source voltage depends on time, then due to induction there is no constant current density in the loop conductors. It is only recently that a method has been published for accurately calculating current density in a group of long parallel conductors. The method has thus far been applied to the calculation of steady-state current density in a loop connected to a sinusoidal voltage source. In the present article, the method is used for an accurate calculation of transient current using transient current density. The transient current is analysed when connecting and short-circuiting the sources of sinusoidal, constant and sawtooth voltages. For circular cross section conductors, the dependences of maximum current density, maximum current and the time of achieving steady state on the source frequency, the distance of the conductors and their resistivity when connecting the source of sinusoidal voltage are examined.

Effect of Polypyrrole-Fe3O4 Composite Modified Anode and Its Electrodeposition Time on the Performance of Microbial Fuel Cells

Anode modification is a useful method to increase the performance of microbial fuel cells (MFCs). By using the electrochemical deposition method, Fe3O4 and polypyrrole (PPy) were polymerized on a carbon felt anode to prepare Fe3O4-PPy composite modified anodes. In order to ascertain the effect of electrodeposition time on characteristics of the modified electrode, the preparation time of the modified electrode was adjusted. The modified anodes were used in MFCs, and their performances were evaluated by analyzing the electricity generation performance and sewage treatment capacity of MFCs. Experimental results indicated that the Fe3O4-PPy composite modified anodes could enhance the power production capacity and sewage treatment efficiency of MFC effectively. In particular, when the deposition time was 50 min, the modified anode could significantly improve the MFC performance. In this case, the steady-state current density of MFC increased by 59.5% in comparison with that of the MFC with an unmodified carbon felt anode, and the chemical oxygen demand (COD) removal rate was 95.3% higher than that of the unmodified anode. Therefore, the Fe3O4-PPy composite is an effective material for electrode modification, and a good anode modification effect can be obtained by selecting the appropriate electrodeposition time.