Thermal Decomposition Of Polymeric Precursors Research Articles

PdAg/C Electrocatalysts Synthesized by Thermal Decomposition of Polymeric Precursors Improve Catalytic Activity for Ethanol Oxidation Reaction

An efficient ethanol oxidation reaction (EOR) is required to enhance energy production in alcohol-based fuel cells. The use of bimetallic catalysts promises decreasing reliance on platinum group metal (PGM) electrocatalysts by minimizing the use of these expensive materials in the overall electrocatalyst composition. In this article, an alternative method of bimetallic electrocatalyst synthesis based on the use of polymeric precursors is explored. PdAg/C electrocatalysts were synthesized by thermal decomposition of polymeric precursors and used as the anode electrocatalyst for EOR. Different compositions, including pristine Pd/C and Ag/C, as well as bimetallic Pd80Ag20/C, and Pd60Ag40/C electrocatalysts, were evaluated. Synthesized catalysts were characterized, and electrochemical activity evaluated. X-ray diffraction showed a notable change at diffraction peak values for Pd80Ag20/C and Pd60Ag40/C electrocatalysts, suggesting alloying (solid solution) and smaller crystallite sizes for Pd60Ag40/C. In a thermogravimetric analysis, the electrocatalyst Pd60Ag40/C presented changes in the profile of the curves compared to the other electrocatalysts. In the cyclic voltammetry results for EOR in alkaline medium, Pd60Ag40/C presented a more negative onset potential, a higher current density at the oxidation peak, and a larger electrically active area. Chronoamperometry tests indicated a lower poisoning rate for Pd60Ag40/C, a fact also observed in the CO-stripping voltammetry analysis due to its low onset potential. As the best performing electrocatalyst, Pd60Ag40/C has a lower mass of Pd (a noble and expensive metal) in its composition. It can be inferred that this bimetallic composition can contribute to decreasing the amount of Pd required while increasing the fuel cell performance and expected life. PdAg-type electrocatalysts can provide an economically feasible alternative to pure PGM-electrocatalysts for use as the anode in EOR in fuel cells.

Development of palladium catalysts modified by ruthenium and molybdenum as anode in direct ethanol fuel cell

Physical and electrochemical properties of Pd catalysts combined with Ru and Mo on carbon support were investigated. To this end, Pd, Pd1.3Ru1.0, Pd3.2Ru1.3Mo1.0 and Pd1.5Ru0.8Mo1.0 were synthesized on Carbon Vulcan XC72 support by the method of thermal decomposition of polymeric precursors and then physically and electrochemically characterized. The highest reaction yields are obtained for Pd3.2Ru1.3Mo1.0/C and Pd1.5Ru0.8Mo1.0/C and, as demonstrated by thermal analysis, they also show the smallest metal/carbon ratio compared the other catalysts. XRD (X-ray Diffraction) and Raman analyses show the presence of PdO and RuO2 for the Pd/C and the Pd1.3Ru1.0/C catalysts, respectively, a fact not observed for the Pd3.2Ru1.3 Mo1.0 /C and the Pd1.5Ru0.8Mo1.0/C catalysts. The catalytic activities were tested for the ethanol oxidation in alkaline medium. Cyclic voltammetry (CV) shows Pd1.3Ru1.0/C exhibiting the highest peak of current density, followed by Pd3.2Ru1.3Mo1.0/C, Pd1.5Ru0.8Mo1.0/C and Pd/C. From, chronoamperometry (CA), it is possible to observe the lowest rate of poisoning for the Pd1.3Ru1.0/C, followed by Pd3.2Ru1.3Mo1.0/C, Pd1.5Ru0.8Mo1.0/C and Pd/C. These results suggested that catalytic activity of the binary and the ternary catalysts are improved in comparison with Pd/C. The presence of RuO2 activated the bifunctional mechanism and improved the catalytic activity in the Pd1.3Ru1.0/C catalyst. The addition of Mo in the catalysts enhanced the catalytic activity by the intrinsic mechanism, suggesting a synergistic effect between metals. In summary, we suggest that it is possible to synthesize ternary PdRuMo catalysts supported on Carbon Vulcan XC72, resulting in materials with lower poisoning rates and lower costs than Pd/C.Graphic abstract

Catalysts of PtSn/C Modified with Ru and Ta for Electrooxidation of Ethanol

PtSn/C-type catalysts modified with Ta and Ru were prepared by the thermal decomposition of polymeric precursors with the following nominal compositions: Pt70Sn10Ta20/C, Pt70Sn10Ta15Ru5/C, Pt70Sn10Ta10Ru10/C and Pt70Sn10Ta5Ru15/C. The physicochemical characterization was performed by X-ray diffraction (XRD) and energy dispersive X-ray (EDX). The electrochemical characterization was performed using cyclic voltammetry, chronoamperometry and fuel cell testing. PtSnTaRu/C catalysts were characterized in the absence and presence of ethanol in an acidic medium (H2SO4 0.5 mol L−1). All the catalysts showed activity for the oxidation of ethanol. The results indicated that the addition of Ta increased the stability and performance of the catalysts, as the Pt70Sn10Ta20/C catalyst had the maximum power density of 27.3 mW cm−2 in an acidic medium. The results showed that the PtSn/C-type catalysts modified with Ta and Ru showed good performance against alcohol oxidation, representingan alternative to the use of direct ethanol fuel cells.

NiO-promoted Pt electrocatalysts prepared by thermal decomposition of polymeric precursors for oxidation of glycerol in alkaline medium

We have investigated the electrocatalytic behavior of PtxNi(1-x)Oy/Ti electrodes during the oxidation of glycerol in alkaline medium. The catalysts were prepared by thermal decomposition of polymeric precursors, and characterized by scanning electron microscopy, energy-dispersive X-ray, and X-ray diffraction. According to cyclic voltammetry and chronoamperometry experiments, mixed catalysts with different metal compositions and high electrochemical surface area, prepared by thermal decomposition of polymeric precursors, afford higher current densities at low values of potential as compared to the PtOy/Ti electrocatalyst. In addition, the onset potential for the oxidation of glycerol shifts toward less positive values, showing that the mixed electrodes facilitate oxidation as compared to the PtOy/Ti electrocatalyst. Among the tested metal compositions, the Pt0.8Ni0.2Oy/Ti and the Pt0.9Ni0.1Oy/Ti electrocatalysts display the highest electroactivity.

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.

Addition of iron oxide to Pt-based catalyst to enhance the catalytic activity of ethanol electrooxidation

Iron oxide is largely used as catalyst in many industrial processes such as the synthesis of ammonia, the conversion of carbon monoxide into carbon dioxide, and the dehydrogenation of different organic substrates. For this reason and based on previous results obtained with iron as co-catalyst for the electrooxidation of ethanol, we have investigated how iron oxide as support for Pt-based catalysts affects the oxidation of this alcohol. For this purpose, we deposited Pt and PtSn over iron oxide-C and compared the catalytic activity of these materials with the catalytic activity of Pt/C and PtSn/C. Iron oxide-C, mainly in the form of γ-Fe2O3-C, was obtained by thermal decomposition of polymeric precursors, which was followed by deposition of Pt and PtSn on the γ-Fe2O3-C substrate by the microwave-assisted method. γ-Fe2O3-C positively affected the activity of Pt/C and PtSn/C in the electrooxidation of ethanol. Therefore, the addition of γ-Fe2O3-C improves the activity of the well-known catalyst Pt3Sn in the oxidation of ethanol

Study of the Oxygen Evolution Reaction on Ta/RuO2-Ta2O5-TiO2 Type Electrodes

This paper aimed to prepare electrodes DSA ® -type (dimensionally stable anode) consisting of transition metal oxides such as ruthenium, titanium and tantalum with the following nominal compositions: TiO 2 (100 %); RuO 2 -TiO 2 - Ru:Ti = 30:70 % atomic; RuO 2 -TiO 2 -Ta 2 O 5 - Ru:Ti:Ta = 30:40:30 % atomic; Ta 2 O 5 (100 %); RuO 2 -Ta 2 O 5 - Ru:Ta = 30:70 % atomic e RuO 2 -Ta 2 O 5 -TiO 2 - Ru:Ta:Ti = 30:40:30 % atomic. The electrodes were obtained from the thermal decomposition of polymeric precursors (MPP). The morphology and elemental composition were analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) techniques. The results showed that the thin films of oxides formed on the metal surface is typically mud-crack with morphology, crevices and cracks of the order of 1-3 ? m, and films without ruthenium oxide have large plates between cracks. The crystalline structure of the material was analyzed by X-ray diffraction, and data shows that the ruthenium and titanium oxides presents tetragonal form and tantalum oxide in the orthorhombic form. The results obtained by electrochemical analyses, such as cyclic voltammetry and Tafel showed that electrodes that have pentoxide tantalum in its composition or that it had the titanium base replacement by tantalum showed improvements in the electrochemical properties those electrodes.

Kinetic analysis on the synthesis of Mg0.95Zn0.05TiO3 microwave dielectric ceramic by polymeric precursor method

Thermo gravimetric-differential scanning calorimetry (TG-DSC) was used to analyze the thermal decomposition of polymeric precursor of Mg0.95Zn0.5TiO3 at different heating rates in the flow of air atmosphere. The kinetic parameters of the reaction were calculated using isoconversional methods. Three dimensional diffusion reaction (Jander); g(α)=[1−(1−α)1/3]2 was proposed mechanism function for the reaction. By using Flynn–Wall–Ozawa model the calculated values of the average activation energy, pre-exponential factor and order of the reaction were found to be 129.33kJ/mol, 1.04×108min−1, and 2.00, respectively. Whereas in the Kissinger–Akahira–Sunose model corresponding values were 123.88kJ/mol, 2.95×107min−1, and 2.09, respectively. The thermodynamic parameters such as enthalpy, Gibbs free energy and entropy of activation calculated at the peak temperature were noted to be 120.46kJ/mol, 228.69kJ/mol, and −146.63J/molK, respectively. Moreover, phase, microstructure and microwave dielectric properties of Mg0.95Zn0.5TiO3 are discussed.

High Electrocatalytic Activity of the Pt-Based Catalyst Supported on Carbon Prepared Using a Plasma Torch and Natural Gas

Physicochemical and electrochemical characterisations of Pt-based electrocatalysts supported on carbon (Vulcan® XC72, C1 and carbon produced using a plasma torch from natural gas vehicles, C2) toward ethanol electrooxidation were investigated. The Pt/C1 and Pt/C2 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), 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 Pt/C1 electrocatalyst has a smaller particle size (10.1 – 6.9) compared with the Pt/C2 electrocatalyst; however, the Pt/C2 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 showed that all the materials are composed of randomly oriented structural units varying from 50 to 80 Å in size. Cyclic voltammetry and chronoamperometry data obtained in this study indicate that the deposition of Pt on carbon plasma increases its electrocatalytic activity toward ethanol oxidation. AcknowledgmentsFAPES, CAPES, FINEP, PETROBRAS, LMC and CNPq.

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/C180and Pt20/C280electrocatalysts 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/C180electrocatalyst has a smaller particle size (10.1–6.9 nm) compared with the Pt20/C280electrocatalyst; however, the Pt20/C280particle 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 sp2carbon. 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.

Influence of metallic oxides on ethanol oxidation

An improvement in ethanol oxidation electrocatalysis is possible with multifunctional Pt-based combinations. Thus, the addition to Pt of Sn, Ir or Ni enhances the ethanol oxidation reaction (EO) and shifts the onset oxidation potential to lower values. It has been suggested that metallic oxides in the vicinity of Pt have the capacity of promoting the oxidation of residues coming from alcohol oxidative adsorption. In order to get a deeper knowledge on the ethanol oxidation catalysis, supported catalysts prepared either by thermal decomposition of polymeric precursors (PP) or by microwave assisted poliol reduction (MW) methodology are studied to determine the role of the catalyst components and its oxides on the improvement of ethanol oxidation. The catalysts are physically and electrochemically characterized. According to the synthesis method, the amount of SnO2 in the catalyst varies. Faceted particle structures for the microwave-synthesized catalysts are observed. By employing electrochemical techniques it is concluded that the catalyst with the highest amount of SnO2 has the best catalytic behaviour for EO.

Synthesis of RuxIr1-xO2 Anode Electrocatalysts for Proton Exchange Membrane Water Electrolysis

Ru and Ir based materials were prepared by the thermal decomposition of polymeric precursor's method. The anode catalysts free from carbon substrate were obtained by tailoring the reaction process to avoid occurrence of CO2 formation during water electrolysis. Various Ir contents were added in the Ru catalytic compositions for improving the oxidation-resistance of RuO2 which was the best metallic oxide in H2O splitting. Their physical characterizations revealed the presence of agglomerates due probably to the heat treatment process consisting in the removal of organic carbon at 400 ºC. The prevalent existence of RuO2 and IrO2 in the anode materials was confirmed by XPS experiments and the electrochemical measurements enabled to show that RuxIr1-xO2 materials were more active towards water oxidation than IrO2 catalyst. The O2 evolution process started at 1.45 V with Ru0.9Ir0.1O2 in the anodic compartment of a 25 cm2 Proton Exchange Membrane Water Electrolyzer at 60ºC.

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).

Evaluation of Ni and Ti Addition in PtSn/C Catalysts for Ethanol and Glycerol Electrooxidation

Electrocatalysts of type PtSnNiTi/C were prepared by thermal decomposition of polymeric precursors. The physico-chemical and electrochemical characterization of the electrocatalysts was performed by different techniques: X-ray diffraction, transmission electron microscopy, cyclic voltammetry and chronoamperometry. The XRD results showed that the electrocatalysts comprise mainly Pt metal with face-centered cubic crystal structure. The electrocatalysts were evaluated in the absence and presence of ethanol and glycerol in sulfuric acid medium. All showed activity toward alcohols oxidation. Furthermore, the Pt50Sn20Ni25Ti5/C electrocatalyst showed the best results of cyclic voltammetry and chronoamperometry in presence of glycerol and ethanol, respectively. Cyclic voltammetry data obtained in this study indicate that the addition of Ni and Ti in PtSn electrocatalysts increases its electrocatalytic activity toward alcohols oxidation. For alcohol (ethanol and glycerol) electrooxidation, high performance liquid chromatography (HPLC) was carried out after electrolysis, for determination of the products generated from alcohol consumption. The main product found after electrolysis was acetaldehyde.

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.

An Optimization Study of PtSn/C Nanocatalysts Prepared by Microwave-assisted Heating and Their Application in Direct Ethanol Fuel Cell: A Comparative Study of PtSn/C Nanocatalysts

Direct Alcohol Fuel Cells (DAFCs) have become a more and more attractive energy source for portable devices. Nevertheless, one of the major drawbacks for its implementation is high catalysts cost. For operation at low temperatures (50-90 ºC), these cells require electrode materials with high catalytic activity, which calls for the use of precious metals like Pt associated with Sn, Ru, and other metals on the electrode. 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 and thermal decomposition of polymeric precursors.

Investigation on the Stability of Pt/C and Pt-RuOx/C Catalysts

Electrode electroactivity depends directly on its nature, morphology, and structure. These parameters, in turn, are related to the preparation method, which will influence the cell performance and electrode stability. Thermal decomposition of polymeric precursors is among the several proposed methods for catalyst preparation. In this work, the effect of modifications to this method during the synthesis of Pt-RuOx/C electrocatalysts on the composition and electrochemically active surface area of electrode catalysts were monitored. To this end, the prepared electrodes were subjected to a large number of potential scans and to constant potential for a prolonged time period in sulfuric acid 0.5 mol L-1 and methanol 0.1 mol L-1 solution

Effect of Ni on Pt/C and PtSn/C prepared by the Pechini method

Different compositions of Pt, PtNi, PtSn, and PtSnNi electrocatalysts supported on carbon Vulcan XC-72 were prepared through thermal decomposition of polymeric precursors. The nanoparticles were characterized by morphological and structural analyses (XRD, TEM, and EDX). XRD results revealed a face-centered cubic structure for platinum, and there was evidence that Ni and Sn atoms are incorporated into the Pt structure. The electrochemical investigation was carried out in slightly acidic medium (H2SO4 0.05 mol L−1), in the absence and in the presence of ethanol. Addition of Ni to Pt/C and PtSn/C catalysts significantly shifted the onset of ethanol and CO oxidations toward lower potentials, thus enhancing the catalytic activity, especially in the case of the ternary PtSnNi/C composition. Electrolysis of ethanol solutions at 0.4 V vs. RHE allowed for determination of acetaldehyde and acetic acid as the reaction products, as detected by HPLC analysis. Due to the high concentration of ethanol employed in the electrolysis experiments (1.0 mol L−1), no formation of CO2 was observed.

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.