R. Antaño-López

Hydrogen-gas sensors based on graphene functionalized palladium nanoparticles: impedance response as a valuable sensor

Palladium–graphene (PdGO) nanostructures with high-quality-graphene layers and well monodispersed palladium nanoparticles (PdNPs) were synthesized by the hydrothermal microwave exfoliation method. The structural and morphological characteristics of PdGO were investigated, and the results indicate that the hydrothermal-microwave method allows both the reduction of metal precursors and their anchorage on highly exfoliated graphene layers. The synthesized PdGO nanostructures were then deposited as active layers for sensing hydrogen gas (H2). PdGO-based sensors with gas concentrations from 0.01 to 5 vol% in air exhibited a very reproducible performance with fast response times (∼30 s) and recovery behavior at room temperature. Measurement of impedance response serves as a highly sensitive feasible sensor technique. Our results show that it is feasible to obtain an efficient H2-sensor with reliable and reproducible sensing properties by means of a simple and cost-effective preparation method under real atmospheric conditions.

Zn Electrodeposition from an Acidic Chloride Bath Containing Polyethyleneglycol (Mw 200) and Benzylideneacetone as Additives

The influence of Polyethylene Glycol 200 (PEG200) or a PEG200/benzylideneacetone (BDA) mixture on the mechanism of Zn deposition and nucleation kinetics was studied by voltammetry, chronoamperometry and atomic force microscopy (AFM). The addition of PEG200 or PEG200/BDA to the solution partially inhibited the reduction of Zn(II) at E ¼� 1.135 V vs. SCE. In the presence of PEG200/BDA, an additional reduction process was observed at E ¼� 1.24 V vs. SCE. Analysis of the nucleation processes indicated that, in all systems studied, the initial stage of Zn deposition was dominated by 3D diffusion-controlled nucleation. At E ¼� 1.132 V vs. SCE, the addition of PEG200 caused a reduction in the nucleation rate constant (A) and the number density of active sites (N0) with respect to the values obtained without additives. AFM analysis of coatings obtained at E ¼� 1.132 V vs. SCE, showed the formation of Zn clusters with different sizes distributed randomly on the surface. At E ¼� 1.243 V vs. SCE, both A and N0were higher for the solution containing the PEG200/BDA mixture than for the systems with PEG200 alone or without additives. AFM analysis revealed the formation of similarly sized Zn clusters uniformly distributed on the surface.

Electrochemical glucose oxidation using glassy carbon electrodes modified with Au-Ag nanoparticles: influence of Ag content

This paper describes the application of glassy carbon modified electrodes bearing Aux-Agy nanoparticles to catalyze the electrochemical oxidation of glucose. In particular, the paper shows the influence of the Ag content on this oxidation process. A simple method was applied to prepare the nanoparticles, which were characterized by transmission electron microscopy, Ultraviolet-Visible spectroscopy, X-ray diffraction spectroscopy, and cyclic voltammetry. These nanoparticles were used to modify glassy carbon electrodes. The effectiveness of these electrodes for electrochemical glucose oxidation was evaluated. The modified glassy carbon electrodes are highly sensitive to glucose oxidation in alkaline media, which could be attributed to the presence of Aux-Agy nanoparticles on the electrode surface. The voltammetric results suggest that the glucose oxidation speed is controlled by the glucose diffusion to the electrode surface. These results also show that the catalytic activity of the electrodes depends on the Ag content of the nanoparticles. Best results were obtained for the Au80-Ag20 nanoparticles modified electrode. This electrode could be used for Gluconic acid (GA) production.

Estimation of Intrinsic Rate Constants of Electrochemical Adsorption-Desorption Processes from AC Impedance Data

A method to estimate the single rate constants of adsorption and desorption from electrode impedance data is proposed. This method is based on fitting the data with an equivalent circuit but then comparing the fit with a mechanistic reaction model. The theoretical framework was developed from the classical adsorption impedance theory, together with electrokinetics concepts. The proposed method can help to elucidate the elementary steps in adsorption-desorption processes.