Decomposition Of Polymeric Precursors Research Articles

Phase Formation in Copper and Calcium Titanate Dielectric Ceramic Obtained by Polymeric Precursor Method

The polycrystalline ceramic named calcium and copper titanate is a dielectric ceramic with very high dielectric constant applicable in several electronic devices. The powder form for that advanced ceramic can be synthesized through chemical route, like the Polymeric Precursor Method at relative lower temperatures the presence of alkaline earth cations harms the structural homogenization during the crystallization process. In this work, the calcium and copper titanate powder was obtained by Polymeric Precursors Method by imposing a slow thermal decomposition of polymeric precursor and several crushing steps before the calcination at 800 °C for 4 hours. The entire process was observed by thermogravimetric analysis and FTIR spectrometry, including the nitrogen adsorption-desorption isotherms and X-ray diffractometry techniques for calcined power samples. It was observed the crystallization of the cubic Im-3 Ca1/4Cu3/4TiO3phase only starts after organics removal and full calcium carbonate elimination above 700 oC, which is followed by pore elimination and particle sintering. The chemical synthetic route used in this work shows the ability to prepare CCT powders sample with very structural homogeneity, which characteristics are required to manufacturing many electronic devices.

Effect of Iron and Vanadium on the Phase Transition of Titanium Dioxide Obtained by Polymeric Precursor Method

The titanium dioxide phase formation is dependent on the synthesis method, temperature of calcination and modifiers insertion. By using chemical methods, such as Polymeric Precursor Method, the organic impurities or extrinsic defects caused by doping play an important rule on the formation of precursor structure before the phase crystallization above 500 oC. Some dopants can change the decomposition mechanism of the precursor, which affects the anatase-rutile phase transition. In this work, the Polymeric Precursor Method was used to synthesize titanium dioxide powder samples in order to investigate the effects of iron (III) and vanadium (V) dopants on the phase formation. Through thermal analysis of polymeric precursors and X-ray diffractometry for calcined powder samples it was possible to show the existence of antagonistic effects for both investigated dopants. While the iron doping reduces the anatase phase tetragonality and delays the rutile phase conversion, the vanadium one changes the mechanism of decomposition of polymeric precursor and leads to more amount of rutile phase.

Effect of Adding a Third Metal to Carbon-Supported PtSn-Based Nanocatalysts for Direct Ethanol Fuel Cell in Acidic Medium

We prepared different PtSnX (X = Ni, Ru, Rh, Pd, and W) nanocatalysts supported on Vulcan carbon XC-72 with 40 wt% metal loading by thermal decomposition of polymeric precursors (DPP) and tested their activity in the electrooxidation of ethanol in acidic medium (0.05 mol L−1 H2SO4). We characterized the nanoparticles by EDX and XRD, which revealed 64% atomic ratio of Pt in an fcc structure with crystallite sizes of 4 to 10 nm. Electrochemical tests in the presence of ethanol showed that the addition of Ni to the PtSn/C nanocatalysts enhanced ethanol electrooxidation. The composition Pt66Sn11Ni23/C presented mass activity of 3.5 A gPt−1 and power density of 25 mW cm−2 in a direct ethanol fuel cell test. The Ni effect on the PtSn nanocatalyst prompted us to synthesize and test other compositions containing this metal and use them in a direct ethanol fuel cell station. The Pt82Sn09Ni09/C nanocatalyst delivered the best power density value (45 mW cm−2).

An optimization study of PtSn/C catalysts applied to direct ethanol fuel cell: Effect of the preparation method on the electrocatalytic activity of the catalysts

The aim of this work was to perform a systematic study of the parameters that can influence the composition, morphology, and catalytic activity of PtSn/C nanoparticles and compare two different methods of nanocatalyst preparation, namely microwave-assisted heating (MW) and thermal decomposition of polymeric precursors (DPP). An investigation of the effects of the reducing and stabilizing agents on the catalytic activity and morphology of Pt75Sn25/C catalysts prepared by microwave-assisted heating was undertaken for optimization purposes. The effect of short-chain alcohols such as ethanol, ethylene glycol, and propylene glycol as reducing agents was evaluated, and the use of sodium acetate and citric acid as stabilizing agents for the MW procedure was examined. Catalysts obtained from propylene glycol displayed higher catalytic activity compared with catalysts prepared in ethylene glycol. Introduction of sodium acetate enhanced the catalytic activity, but this beneficial effect was observed until a critical acetate concentration was reached. Optimization of the MW synthesis allowed for the preparation of highly dispersed catalysts with average sizes lying between 2.0 and 5.0 nm. Comparison of the best catalyst prepared by MW with a catalyst of similar composition prepared by the polymeric precursors method showed that the catalytic activity of the material can be improved when a proper condition for catalyst preparation is achieved.

Development of plurimetallic electrocatalysts prepared by decomposition of polymeric precursors for EtOH/O2 fuel cell

This work aimed to develop plurimetallic electrocatalysts composed of Pt, Ru, Ni, and Sn supported on C by decomposition of polymeric precursors (DPP), at a constant metal:carbon ratio of 40:60 wt.%, for application in direct ethanol fuel cell (DEFC). The obtained nanoparticles were physico-chemically characterized by X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX). XRD results revealed a face-centered cubic crystalline Pt with evidence that Ni, Ru, and Sn atoms were incorporated into the Pt structure. Electrochemical characterization of the nanoparticles was accomplished by cyclic voltammetry (CV) and chronoamperometry (CA) in slightly acidic medium (0.05 mol L-1 H2SO4), in the absence and presence of ethanol. Addition of Sn to PtRuNi/C catalysts significantly shifted the ethanol and CO onset potentials toward lower values, thus increasing the catalytic activity, especially for the quaternary composition Pt64Sn15Ru13Ni8/C. Electrolysis of ethanol solutions at 0.4 V vs. RHE allowed determination of acetaldehyde and acetic acid as the main reaction products. The presence of Ru in alloys promoted formation of acetic acid as the main product of ethanol oxidation. The Pt64Sn15Ru13Ni8/C catalyst displayed the best performance for DEFC.

XAS characterization of the RuO 2–Ta 2O 5 system local (crystal) structure

The influence of the preparation method on the structural properties of the RuO 2–Ta 2O 5 system was investigated. Both thin films on Ti substrates and powder samples of nominal composition Ti/RuO 2–Ta 2O 5 (Ru:Ta = 100:0, 90:10, 80:20, 30:70, and 0:100 at.%) were prepared through thermal decomposition of polymeric precursors (DPP). The thin films and powder samples were investigated using X-ray absorption spectroscopy (XAS). XANES analyses showed that Ru and Ta are present in the Ru(IV) and Ta(V) oxidation states. EXAFS signals of all the samples were analyzed, to obtain the average bond length ( r), coordination number, and the Debye–Waller factor ( σ 2) for each Ru–O, Ru–Ru, Ta–O nearest-neighbor. The first shell Ru–O distance was found at 1.91–1.92 Å with coordination number of 1.8–2.1, and at 2.01–2.02 Å with coordination number of 3.9–4.1. The Ta–O distance obtained for all the samples and in both modes (transmission and fluorescence) had significantly different values from the theoretical ones. The results revealed that the local structure around both the Ru and Ta sites are similar, and that they consist of distorted M–O 6 octahedra (where M = Ru or Ta).

Oxygen Reduction Reaction on Pt–NiO x /C, Pt–CoO x /C, and Pt–SnO2/C Electrodes in the Presence of Ethanol

Pt–NiO x /C, Pt–CoO x /C, and Pt–SnO2/C catalysts, prepared by thermal decomposition of polymeric precursors, are characterized for the oxygen reduction reaction in the presence of ethanol, and their tolerance to the presence of alcohol is determined. The electrocatalytic activities of Pt–NiO x /C, Pt–CoO x /C, and Pt–SnO2/C in the absence of ethanol are similar to those of the Pt/C catalysts or lower, depending on electrode composition. However, these catalysts present higher catalytic activity for the oxygen reduction reaction in the presence of ethanol, compared with the Pt/C catalyst. This makes Pt–NiO x /C, Pt–CoO x /C, and Pt–SnO2/C potentially applicable as cathodes in direct ethanol fuel cells, thereby reducing the effect of ethanol crossover.

Effect of the preparation methodology on some physical and electrochemical properties of Ti/IrxSn(1−x)O2 materials

The aim of this work was to prepare electrodes based on the Ti/IrxSn(1−x)O2 composition, as well as test their stability toward the chlorine evolution reaction (ClER). To this end, two different preparation routes were investigated: thermal decomposition of polymeric precursors (DPP) and standard decomposition using isopropanol as solvent (SD/ISO). A systematic investigation of the structural, morphological, and electrochemical properties of the anodes with a nominal composition of Ti/IrxSn(1−x)O2, prepared through the two different methodologies, was carried out. The oxide layer surface morphology, microstructure, and composition were investigated by Energy Dispersive X-ray Spectroscopy (EDS) and Scanning Electron Microscopy (SEM) techniques prior to and after accelerated life tests. EDS analyses following total deactivation of the electrode gave evidence of a relatively large content of Ir in the coating. XRD results showed there was formation of solid solution between IrO2 and SnO2, and the degree of miscibility of these solutions is controlled by the preparation method. Thus, the DPP method led to phase separation and large interval of immiscibility between the oxides analyzed. On the other hand, the SD/ISO method led to formation of solid solution for all the investigated compositions. The SD/ISO method produced materials rich in Ir, so the electrode lifetime was much longer if compared with the DPP counterparts.

Methanol electro-oxidation at Ptx Ru(1–x)Oy electrodes — An in situ FTIR study

In this work we investigated the nature of the intermediates adsorbed during the electrooxidation of methanol on PtxRu(1–x)Oy electrodes, where 0.5 < x < 0.9, prepared by the decomposition of polymeric precursors. Thin layer electrodes with different compositions were prepared directly on a gold substrate by thermal decomposition of ethylene glycol – citric acid solutions containing the precursor salts at 400 °C. In situ IR reflectance spectra were obtained using the SPAIRS (single potential alteration infrared reflectance spectroscopy) and SNIFTIRS (subtractively normalized interfacial Fourier transform IR reflectance spectroscopy) techniques. For all the investigated compositions, the SNIFTIRS and SPAIRS spectra displayed three main bands, which were attributed to CO species in the linear (COL) and bridged (COB) forms adsorbed over Pt and linearly adsorbed over Ru. Formation of CO2 carbonyl species was also detected. The spectra features were analyzed in terms of the applied potential and they were compared with those reported for Pt–Ru electrodes prepared by other methods.Key words: methanol, electrocatalytic oxidation, in situ infrared reflectance spectroscopy, PtxRu(1–x)Oy, adsorption

Preparation of Ir0.3Sn(0.7-x)Ti x O2 Electrodes by the Polymeric Precursor Method: Characterization and Lifetime Study

Thin film electrodes of nominal composition Ir0.3Sn(0.7-x)Ti x O2 (0 ≤ x ≤ 0.7) were prepared by decomposition of polymeric precursors. The solutions used to prepare the electrodes were obtained by mixing of the precursor salts with a mixture of ethylene glicol and citric acid. The films were burned at 400 °C and characterized by X-ray diffraction, scanning electronic microscopy, energy dispersive X-ray spectroscopy and cyclic voltammetry. The electrodes were submitted to high anodic current density in order to evaluate their lifetime in perchloric acid solution. Results show that the electrodes present compositions similar to that of the precursor solutions, suggesting that there is no loss of tin during the calcination step. The electrodes had large surface area and higher lifetime in comparison with electrodes of similar composition prepared by other methods. The possible mechanisms involved in deactivation of the electrodes are discussed.

Electrooxidation of methanol on PtM yO x (M = Sn, Mo, Os or W) electrodes

In this paper, we have studied the electrooxidation of methanol on PtM y O x (M = Sn, Mo, Os or W) electrodes prepared by the decomposition of polymeric precursors. The PtM y O x materials were prepared on Ti plates and were characterized by SEM and EDX. The electrodes presented compositions very similar to the nominal ones, except for the electrodes containing Os, which presented high Os loss. The electrodes catalytic activity in the electrooxidation of methanol was studied by cyclic voltammetry and chronoamperometry. The electrodes containing tin in their compositions presented the highest electroactivity. The possible mechanisms involved in activity enhancement are discussed.

Atividade eletrocatalítica de eletrodos compostos por Pt, RuO2 e SnO2 para a eletrooxidação de formaldeído e ácido fórmico

A atividade eletrocatalítica para a oxidação de ácido fórmico e formaldeído em eletrodos binários de Pt e SnO2 e ternários de Pt, RuO2 e SnO2 em diferentes composições, foi investigada através das técnicas de voltametria cíclica e cronoamperometria. Os materiais foram preparados por decomposição térmica de precursores poliméricos na temperatura de 400°C. Os experimentos de voltametria cíclica mostraram que os eletrodos mistos proporcionaram uma diminuição de ~100 mV (ERH) no potencial de pico de oxidação das moléculas orgânicas em relação ao eletrodo contendo somente Pt e indicaram que a composição Pt0,6Ru0,2Sn0,2Oy possui maior densidade de corrente de oxidação em potenciais inferiores ao potencial de pico. Os experimentos de cronoamperometria confirmam a contribuição da adição de SnO2 e RuO2 para o aumento da atividade catalítica em menores valores de potencial.

Preparation of Strontium Titanate Powders by Decomposition of Polymeric Precursors

ABSTRACTThe effects of substituting poly(acrylic acid), PAA, and mucic acid for citric acid in the standard Pechini powder synthesis process was studied. Strontium titanate was chosen as the model system for this study. Powders were prepared from precursor solutions in which PAA (average molecular weight = 2,000 and 5000) was substituted for citric acid (up to 70% by weight), and with reduced weight of total organic reagents (50% reduction). The powders prepared with a 30% substitution of PAA for citric acid produced weakly agglomerated submicron particles after calcining. These powders contained a larger fraction of weak agglomerates than the powders prepared by the original Pechini process. As such, the PAA derived powder could be easily fractionated and dispersed with greater than 70% of the calcined powder having particle sizes less than 0.5 μm