Nora A. Garcia-Gomez

Enhancement of electrochemical properties on TiO2/carbon nanofibers by electrospinning process

In the present work, we report the preparation of TiO2–carbon/carbon dual nanofibers using an electrospinning technique. The dual nanofibers were synthesized using a modified side-by-side spinneret, which allowed the fabrication of the desired dual nanofiber architecture in a one-step process. A subsequent heat treatment permitted the control on the crystal structure of the synthesized dual nanofibers. Scanning electron microscopy and transmission electron microscopy results confirmed the continuity and duality of the obtained nanofibers. The difference in composition between the fibers composing the dual fibers was clearly observed by energy dispersive X-ray spectroscopy. The effect of heat treatment on crystallinity was evident on the results obtained from the X-ray diffraction and selected area electron diffraction studies; where, depending on the heat treatment conditions, clear signals for anatase and rutile phases of TiO2 were observed. Electrochemical studies suggest an improvement on the conduction properties of TiO2–carbon/carbon dual nanofibers compared to single TiO2–carbon nanofibers, attributed to the carbon nanofiber contribution attached to the TiO2 nanofibers. Based on the morphological and structural features of this novel nanostructured material, and to the electrochemical performance observed, it has a wide range of potential applications.

Fabrication and characterization of a nanostructured TiO2/In2S3-Sb2S3/CuSCN extremely thin absorber (eta) solar cell

In this work we report the successful assembly and characterization of a TiO2/In2S3-Sb2S3/CuSCN extremely thin absorber solar cell. Nanostructured TiO2 deposited by screen printing on an ITO substrate was used as an n-type electrode. An ~80 nm extremely thin layer of the system In2S3-Sb2S3 deposited by successive ionic layer adsorption and a reaction (silar) method was used as an absorber. The voids were filled with p-type CuSCN and the entire assembly was completed with a gold contact. The solar cell fabricated with this heterostructure showed an energy conversion efficiency of 4.9%, which is a promising result in the development of low cost and simple fabrication of solar cells.

Ultrasonic irradiation-assisted synthesis of Bi2S3 nanoparticles in aqueous ionic liquid at ambient condition

In this work, an easy, fast and environmentally friendly method to obtain Bi2S3 nanostructures with sphere-like morphology is introduced. The promising material was successfully synthesized by a sonochemical route in 20% 1-ethyl-3-methylimidazolium ethyl sulfate [EMIM][EtSO4] ionic liquid solution (IL). Morphological studies by electron microscopy (SEM and TEM) show that the use of IL in the synthesis of Bi2S3 favors the formation of nanocrystals non-agglomerated. Micro Raman and energy dispersive X-ray spectroscopy (EDXS) were used to determine the composition and purity of the synthesized material. X-ray powder diffraction (XRD) and selective area electron diffraction (SAED) revealed that ultrasonic radiation accelerated the crystallization of Bi2S3 into orthorhombic bismuthinite structure. The band gap calculated from the diffuse reflectance spectra (DRS) was found to be 1.5eV.

Electrochemical study of TiO 2 modified with silver nanoparticles upon CO 2 reduction

A systematic cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) study on titanium dioxide (TiO2) and silver–TiO2 surfaces was performed in order to decouple electrochemical reduction processes of carbon dioxide in aqueous solutions. CV studies indicate cathodic current increase on Ag–TiO2 compared to bare TiO2 surfaces. An equivalent circuit based on transmission line model was applied in order to adjust EIS data, and a modification of this model was made to account for Ag particle interaction with the electrolyte solution. Electrochemical processes were then decoupled upon applied potential where the role of TiO2 surface states was identified and separated from (a) silver reduction, (b) electronic transport on TiO2, and (c) charge transfer on TiO2 and Ag surfaces. The Ag–electrolyte interface impedance has considerably lower values than the TiO2–electrolyte interface, suggesting that the silver particles may be considered as favorable reaction sites for the electrochemical reduction of water and carbon dioxide.

Oxidation behaviour of amorphous steel: impact on electromagnetic properties

Purpose High silicon amorphous steels are gaining preference as the material of choice for the fabrication of the core of low and medium power electrical transformers because they present a better electromagnetic behaviour compared to that offered by common grain-oriented and non-oriented high silicon steels. This study aims to investigate the effects that the environmental conditions present during the high temperature annealing of cores exert on the surface oxidation and electromagnetic changes experienced by a commercial amorphous steel alloy. Design/methodology/approach The effect of environmental impact on the correct development of annealing practices during the manufacture process of amorphous steel cores used in distribution transformers was studied by the development of an oxidation reactor. With this installation, it was possible to simulate environmental conditions that could affect the surface of magnetic cores made from amorphous steel. Findings It was found that: the surface oxidation of amorphous steels affects their electromagnetic behaviour, environmentally induced surface degradation can be modelled at laboratory scale and oxide formation does not affect the amorphous condition of the alloy. Originality/value The effect of surface oxidation induced by the existence of water vapour in the annealing process of cores made from amorphous steels and its impact on the electromagnetic behavior of these alloys has been barely studied.

Simultaneous intercalated assembly for mesostructured hybrid carbon nanofiber/reduced graphene oxide and its use in electrochemical sensing.

Polyacrylonitrile nonwovens intercalated with graphene oxide (GO) sheets were prepared by a simultaneous electrospinning-spray deposition system. These hybrid nonwovens were carbonized in a two-stage process to obtain a mesostructured hybrid carbon containing carbon nanofibers (CNF) and reduced GO sheets (CNF/RGO). During the carbonization process, the CNF act as spacers between the RGO layers to prevent their compactation and restacking resulting in a three-dimensional structure. The presence of RGO increases the electrical conductivity in the CNF/RGO material. The resulting hybrid carbon is nitrogen-doped as indicated by x-ray photoelectron spectroscopy and Fourier transformed infrared spectroscopy. This N-doped porous carbon was used to prepare electrodes with improved sensitivity for the electrochemical detection of L-cysteine.