Josimar Ribeiro

Characterization of RuO2 ­ Ta2 O 5 Coated Titanium Electrode Microstructure, Morphology, and Electrochemical Investigation

A systematic investigation of the structural, morphological, and electrochemical properties of anodes with a nominal composition of Ti/RuO 2 -Ta 2 O 5 (Ru:Ta = 10:90; 30:70; 50:50 and 80:20 atom %) was performed. The oxide layer surface morphology, microstructure, and composition were investigated prior to and after accelerated life test through energy dispersive X-ray spectroscopy (EDS) and scanning electron microscopy. EDS analyses following total deactivation of the electrode showed a relatively large content of Ru in the coating. X-ray diffraction results showed the formation of a solid solution between RuO 2 and Ta 2 O 5 . Cyclic voltammograms of this system were registered in acidic solutions (H 2 SO 4 0.5 mol dm -3 ) and they presented a well-defined peak attributed to the Ru(III)/Ru(IV) solid-state redox transition. The electrocatalytic activity shows a strong dependence on the RuO 2 content in the film. The stability of the electrodes toward oxygen evolution reaction was evaluated at 0.5 mol dm -3 H 2 SO 4 , using a current density of 750 mA cm -2 and a temperature of 80°C. A direct dependence between the electrode lifetime (LT) and RuO 2 present in the coating was observed. Upon changing TiO 2 for Ta 2 O 5 (Ru = 50 atom %) a considerable improvement (average of 54%) in the LT values of these oxides was obtained. This result is a good indication that the Ru/Ta system might be a promising coating to operate under severe conditions.

Development of ternary and quaternary catalysts for the electrooxidation of glycerol.

This work consisted in the preparation of platinum-based catalysts supported on carbon (Vulcan XC-72) and investigation of their physicochemical and electrochemical properties. Catalysts of the C/Pt-Ni-Sn-Me (Me = Ru or Ir) type were prepared by the Pechini method at temperature of 350°C. Four different compositions were homemade: C/Pt60Sn10Ni30, C/Pt60Sn10Ni20Ru10, C/Pt60Sn10Ni10Ru20, and C/Pt60Sn10Ni10Ir20. These catalysts were electrochemically and physically characterized by cyclic voltammetry (CV), chronoamperometry (CA) in the presence of glycerol 1.0 mol dm−3, X-ray diffraction (XRD), and high-resolution transmission electron microscopy (HRTEM). XRD results showed the main peaks of face-centered cubic Pt. The particle sizes obtained from XRD and HRTEM experiments were close to values ranging from 3 to 8.5 nm. The CV results indicate behavior typical of Pt-based catalysts in acid medium. The CV and CA data reveal that quaternary catalysts present the highest current density for the electrooxidation of glycerol.

Electrochemical and Morphological Investigations of Ga Addition to Pt Electrocatalyst Supported on Carbon

This paper is consisted in the synthesis of platinum-based electrocatalysts supported on carbon (Vulcan XC-72) and investigation of the addition of gallium in their physicochemical and electrochemical properties toward ethanol oxidation reaction (EOR). PtGa/C electrocatalysts were prepared through thermal decomposition of polymeric precursor method at a temperature of 350°C. Six different compositions were homemade: Pt50Ga50/C, Pt60Ga40/C, Pt70Ga30/C, Pt80Ga20/C, Pt90Ga10/C, and Pt100/C. These electrocatalysts were electrochemically characterized by cyclic voltammetry (CV), chronoamperometry (CA), chronopotentiometry (CP), and electrochemical impedance spectroscopy (EIS) in the presence and absence of ethanol 1.0 mol L−1. Thermogravimetric analysis (TGA), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and transmission electron microscopy (TEM) were also carried out for a physicochemical characterization of those materials. XRD results showed the main peaks of face-centered cubic Pt. The particle sizes obtained from XRD and TEM analysis range from 7.2 nm to 12.9 nm. The CV results indicate behavior typical of Pt-based electrocatalysts in acid medium. The CV, EIS, and CA data reveal that the addition of up to 31% of gallium to the Pt highly improves catalytic activity on EOR response when compared to Pt100/C.

Raman Spectroscopy and Electrochemical Investigations of Pt Electrocatalyst Supported on Carbon Prepared through Plasma Pyrolysis of Natural Gas

Physicochemical and electrochemical characterisations of Pt-based electrocatalysts supported on carbon (Vulcan carbon, C1, and carbon produced by plasma pyrolysis of natural gas, C2) toward ethanol electrooxidation were investigated. The Pt20/C180 and Pt20/C280 electrocatalysts were prepared by thermal decomposition of polymeric precursors at 350°C. The electrochemical and physicochemical characterisations of the electrocatalysts were performed by means of X-ray diffraction (XRD), transmission electron microscope (TEM), Raman scattering, cyclic voltammetry, and chronoamperometry tests. The XRD results show that the Pt-based electrocatalysts present platinum metallic which is face-centered cubic structure. The results indicate that the Pt20/C180 electrocatalyst has a smaller particle size (10.1–6.9 nm) compared with the Pt20/C280 electrocatalyst; however, the Pt20/C280 particle sizes are similar (12.8–10.4 nm) and almost independent of the reflection planes, which suggests that the Pt crystallites grow with a radial shape. Raman results reveal that both Vulcan carbon and plasma carbon are graphite-like materials consisting mostly of sp2 carbon. Cyclic voltammetry and chronoamperometry data obtained in this study indicate that the deposition of Pt on plasma carbon increases its electrocatalytic activity toward ethanol oxidation reaction.