Platinum Oxide Research Articles

Aerobic oxidation of primary aliphatic alcohols over bismuth oxide supported platinum catalysts in water

Catalytic oxidation of non-activated aliphatic alcohols with molecular oxygen is rather challenging, especially in an aqueous medium in the absence of an additional base. Bismuth is usually used as a promoter of platinum-based catalysts. In this work, bismuth oxide was explored as a support, and Pt0 nanoparticles supported on bismuth oxide (Pt/Bi2O3) exhibited high activity for aerobic oxidation of n-butanol using water as a solvent in the absence of an additional base under optimized conditions. Besides n-butanol, liquid primary aliphatic alcohols with low solubility in water could also be smoothly oxidized into the corresponding carbonyl compounds with molecular oxygen. Pt/Bi2O3 reduced by H2 at about 200 °C showed the highest activity for aerobic oxidation of n-butanol. At this temperature, platinum oxide was reduced to Pt0 and bismuth oxide could be reduced partially which might change the surface property of bismuth oxide.

Eletrodegradação de Ponceau 2R utilizando ânodos dimensionalmente estáveis e Ti/Pt

This paper reports the electrochemical degradation of the azo dye Ponceau 2R under galvanostatic electrolysis in the 1 to 200 mA cm-2 range at room temperature using dimensionally-stable anodes of oxygen (DSA-O2), chlorine (DSA-Cl2) and a titanium electrode of platinum coated with platinum oxide (Ti/Pt). The methodology applied was efficient for removing the color of the Ponceau 2R and the highest percentage removal of total organic carbon was obtained at 200 mA cm-2. Despite not having been observed complete mineralization, approximately80% removal of aromatic rings was estimated, resulting in drastic reduction of toxicity of the sample.

An Experimental Study of the Effects of Operational History on Activity Changes in a PEMFC

The accurate evaluation of the activation overpotential of a membrane electrode assembly (MEA) is essential for fuel cell design. We have developed a new method of precisely determining the activity of cathode catalyst layer in MEA by maintaining the effect of platinum oxides at a constant level and have subsequently studied activity changes resulting from various operational histories. Cyclic voltammetry was used to quantitatively correlate activity changes in the cathode catalyst layer with various operational conditions and demonstrated that activity decreased after low humidity operation and recovered after high humidity operation in a N2 atmosphere at potentials below 0.2 V. The activity changes were found to be very slow and a span of more than 8 hours was required for the activity to reach the steady state. This phenomenon is presumably caused by the adsorption/desorption of ionomer sulfonate groups on the Pt surface, based on observations that the activity changes are consistent with sulfonate group adsorption and dependent on the ionomer structure. Oxygen transport resistance in the catalyst layer also varied in conjunction with the activity changes. Two possible Pt/ionomer interface models are proposed in an attempt to explain the above observations.

1573KにおけるFeOx- SiO<sub>2 </sub>系スラグの白金の溶解度

There is an increasing trend in the copper smelters to recycle electronic materials, which contain relatively high concentration of platinum group metals. Platinum group metals lost in the slag is increasing with increasing of treated scrap amount. To determine the portion of the platinum group metals chemically dissolved in the slag will be a key factor to improve the recovery of those metals. An experimental study was carried out to determine the solubility of platinum in FeOx-SiO2 slag equilibrated with a pure platinum and the liquid Pt-Cu alloy at 1573 K and the range of oxygen partial pressure from 10-9 to 10-6. The solubility of platinum in the slag tends to increase with increasing oxygen partial pressure and content of copper in the slag. Based on the measured platinum solubility, activity coefficients of platinum oxide in the FeOx-SiO2 slag were derived. The activity coefficients decrease by increasing copper contents in slag. Therefore, lower copper content in the slag tend to lower precious metals dissolution in the slag.

Dynamic Stress Analysis Applied to (111)-Textured Pt in HClO4 Electrolyte

Dynamic stress analysis (DSA) was performed on Pt cantilever electrodes immersed in 0.1 mol/L HClO4 electrolyte. DSA combines elements of electrochemical impedance spectroscopy (EIS) and cantilever curvature. In this paper DSA is used to determine the relationship between surface stress f and charge density q for (111)-textured Pt as a function of steady state potential. The parameter of merit is the stress-charge coefficient, ξ, a complex number, which is obtained from the product of the electrochemical impedance Ze and the stress admittance Ys. The magnitude and sign of ξr, the real component of ξ, quantifies how the surface responds to changes in charge density. Three regions of stress-charge behavior have been identified at potentials bound by hydrogen adsorption and platinum oxide formation. In the hydrogen adsorption region, stress and charge are in phase, resulting in a positive value of ξr. In the double layer region the surface stress and the charge density are 180° out of phase, yielding a negative value of ξr. The actual potential at which this phase angle transition occurs may vary by as much as 0.3 V, depending on electrode history. At more positive potential ξr remains negative in the early oxide region, where the reversible adsorption of O occurs. Only at more positive potential, where place exchange between Pt and O occurs and the surface layer of PtO becomes fully formed, does ξr transition back to a positive value. The experimental methods described in this work provide a means to probe the dynamic behavior of surface stress.

Methanol Oxidation Activity and Chemical State of Platinum Oxide Thin Film Treated by Electrochemical Reduction

The methanol oxidation activity of Pt oxide can be significantly improved by heat reduction in a H2 atmosphere or by electrochemical reduction using a cathodic current. Therefore, the Pt oxide is expected to be a novel anode catalyst for DMFC. In this study, measurement of the electrochemical active surface area by CO stripping voltammetry, analysis of the chemical bonding state by XPS and determination of the O/Pt atomic ratio by EPMA were carried out to investigate the cause of the improvement in the methanol oxidation activity of the Pt oxide by the reduction treatment. Although the methanol oxidation current remarkably increased by electrochemical reduction treatment of the Pt oxide thin film prepared by reactive sputtering in 100% O2, the effect of the reduction on the methanol oxidation activity was not recognized at all for the Pt thin film prepared in 100% Ar. For the Pt oxide thin films, it was shown that there was a close correlation between the methanol oxidation current and the electrochemically active surface area obtained by CO stripping voltammetry. Moreover, the quantitative analysis by EPMA clearly showed that the O/Pt atomic ratio of the Pt oxide thin film having a high activity for the methanol oxidation reaction decreased to about 0.1 by the electrochemical reduction. These results together with the XPS analysis suggested that the residual oxygen related to the Pt­O bond was activating the methanol oxidation for the electrochemically reduced Pt oxide thin films. [doi:10.2320/matertrans.MBW201215]

Pt–Al2O3 dual layer atomic layer deposition coating in high aspect ratio nanopores

Functional nanoporous materials are promising for a number of applications ranging from selective biofiltration to fuel cell electrodes. This work reports the functionalization of nanoporous membranes using atomic layer deposition (ALD). ALD is used to conformally deposit platinum (Pt) and aluminum oxide (Al2O3) on Pt in nanopores to form a metal–insulator stack inside the nanopore. Deposition of these materials inside nanopores allows the addition of extra functionalities to nanoporous materials such as anodic aluminum oxide (AAO) membranes. Conformal deposition of Pt on such materials enables increased performances for electrochemical sensing applications or fuel cell electrodes. An additional conformal Al2O3 layer on such a Pt film forms a metal–insulator–electrolyte system, enabling field effect control of the nanofluidic properties of the membrane. This opens novel possibilities in electrically controlled biofiltration. In this work, the deposition of these two materials on AAO membranes is investigated theoretically and experimentally. Successful process parameters are proposed for a reliable and cost-effective conformal deposition on high aspect ratio three-dimensional nanostructures. A device consisting of a silicon chip supporting an AAO membrane of 6 mm diameter and 1.3 μm thickness with 80 nm diameter pores is fabricated. The pore diameter is reduced to 40 nm by a conformal deposition of 11 nm Pt and 9 nm Al2O3 using ALD.

Effect of noble metals on activity of MnOx/γ-alumina catalyst in catalytic ozonation of toluene

This work addresses effect of addition of two noble metals, platinum or palladium (1wt.%), on performance of alumina-supported manganese oxides (10wt.%) in catalytic ozonation of toluene in the range of 22–100°C. Catalysts were characterized by ICP-MS, BET, X-ray diffraction (XRD), hydrogen temperature programmed reduction (H2-TPR) and X-ray absorption spectroscopy (XAS) including quantitative X-ray absorption near edge structure (XANES) and qualitative extended X-ray absorption fine structure (EXAFS). It was found that addition of platinum improves activity of manganese oxides leading to complete conversion of toluene at 70°C. Palladium was found to be ineffective in enhancing activity of manganese oxides mainly because of lack of atomic interaction between Pd and Mn. Pt and Mn XANES and EXAFS spectra changed after addition of Pt to manganese oxides implying an atomic interaction between platinum and manganese oxides. It is proposed that the interaction between Pt and Mn occurs via surface oxygen of manganese oxide clusters increasing dispersion of Pt atoms in the presence of Mn. This interaction could increase electron occupancy of Mn 3d orbital which is more favorable in decomposition of ozone and consequently oxidation of toluene.

Growth of nano-porous Pt-doped cerium oxide thin films on glassy carbon substrate

Abstract Glassy carbon (GC) substrates were treated by the oxygen plasma over several periods of time. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM) study showed the dramatic influence of oxygen plasma on the morphology of glassy carbon. The treatment leads to the formation of nanostructured surface, which consists of well separated rod-like nanostructures oriented perpendicularly to the substrate surface. The surface roughness was found to increase with increasing treatment time. By using magnetron co-sputtering of platinum and cerium oxide we can prepare oxide layers continuously doped with Pt atoms during the growth. This technique combines etching of the carbon substrate and growth of the deposit. This leads to the formation of high surface area catalyst which makes this method promising for production of thin film catalysts.

Nonanal gas sensing properties of platinum, palladium, and gold-loaded tin oxide VOCs sensors

We have investigated the nonanal sensing properties of Pt-, Pd-, and Au-loaded SnO2 (Pt, Pd, Au/SnO2) thick films. These films show a higher response to nonanal than a non-loaded SnO2 film, can detect several tens of ppb of nonanal and exhibit fast response and recovery times. Their nonanal sensing ability is improved by pretreatments, such as annealing temperature and aging. The resistance of these films in pure air depends on the working temperature, but the resistance in nonanal gas depends mainly on the film thickness. We suggest nonanal detection models for Pt, Pd, Au/SnO2 films with different film thicknesses, and determine the optimum film thickness for nonanal detection.

Electrochemical Oxidation of Size-Selected Pt Nanoparticles Studied Using in Situ High-Energy-Resolution X-ray Absorption Spectroscopy

High-energy-resolution fluorescence-detected X-ray absorption spectroscopy (HERFD-XAS) has been applied to study the chemical state of ∼1.2 nm size-selected Pt nanoparticles (NPs) in an electrochemical environment under potential control. Spectral features due to chemisorbed hydrogen, chemisorbed O/OH, and platinum oxides can be distinguished with increasing potential. Pt electro-oxidation follows two competitive pathways involving both oxide formation and Pt dissolution.

Relieving Steric Strain at Octahedral Platinum(IV): Isomerization and Reductive Coupling of Alkyl and Aryl Chlorides

Oxidation of monocyclometalated platinum(II) complexes results in octahedral platinum(IV) complexes. Depending on the substitution, two different reactions occur: either a simple isomerization, resulting in the exchange of ligand positions, or a reductive coupling of aryl chloride. With a doubly cyclometalated complex, stability of the oxidized form is dependent on isomeric form: whereas the trans isomer is robust, being manipulable in air at room temperature, the cis isomer decomposes at -20 °C and above. Reductive coupling at this cis isomer is 100% selective for alkyl chloride over aryl chloride and is suggested to be a concerted process. © 2012 American Chemical Society.

Study of bactericidal properties of carbohydrate-stabilized platinum oxide nanoparticles

Platinum oxide nanoparticles were prepared by a simple hydrothermal route and chemical reduction using carbohydrates (fructose and sucrose) as the reducing and stabilizing agents. In comparison with other metals, platinum oxide has less environmental pollution. Therefore, Pt is considered an appropriate candidate to deal with environmental pathogens. The crystallite size of these nanoparticles was evaluated from X-ray diffraction, atomic force microscopy, and transmission electron microscopy (TEM) and was found to be 10 nm, which is the demonstration of EM bright field and transmission electron microscopy. The effect of carbohydrates on the morphology of the nanoparticles was studied using TEM. The nanoparticles were administered to the Pseudomonas stutzeri and Lactobacillus cultures, and the incubation was done at 37°C for 24 h. The nanocomposites exhibited interesting inhibitory as well as bactericidal activity against P. stutzeri and Lactobacillus species. Incorporation of nanoparticles also increased the thermal stability of the carbohydrates. The results of this paper showed that carbohydrates can serve as a carrier for platinum oxide nanoparticles, and nanocomposites can have potential biological applications.

Structures of Platinum Oxide Clusters in the Gas Phase

The structures of small gas-phase Pt(n)O(2m)(+) (n = 1-6, m = 1, 2) cluster cations have been investigated in a combined infrared multiple photon dissociation (IRMPD) spectroscopy and density functional theory (DFT) study. On the basis of the infrared spectra obtained, it is concluded that in most clusters oxygen is bound dissociatively, preferring 2-fold bridge binding motifs, sometimes combined with singly coordinated terminal binding. Comparison of the oxide cluster structures with those of bare cationic platinum clusters reported previously reveals major structural changes induced in the platinum core upon oxygen binding. For some cluster sizes the presence of the Ar messenger atom(s) is found to induce a significant change in the observed cluster structure.

Functional Effects of the Deposition Substrate on the Electrochemical Behavior of Platinum Particles

In the present work, polytyramine (PTy) and cobalt oxide (Co3O4) were used as substrates for platinum electrodeposition, in order to obtain electrode systems with electrocatalytic properties. PTy and Co3O4 were previously electrochemically deposited on graphite and boron-doped diamond (BDD) supports, respectively. Anodic oxidation of methanol was used as a test-reaction for assessing possible functional effects of the substrate on the electrochemical behavior of the Pt particles. It was found that, when deposited on PTy or cobalt oxide, the electrocatalyst exhibits higher activity and is less susceptible to fouling, via strong adsorption of reaction intermediates. X-ray photoelectron spectroscopy (XPS) measurements suggested that these features can be ascribed to the presence of –OH functional groups at the surface of the Pt particles. It was also found that electrodeposition of platinum on BDD resulted only in metallic Pt and Pt(OH)2, whereas when graphite was used as substrate the presence of platinum oxides was also evident. During prolonged anodic oxidation of methanol, a higher stability of the –OH groups from the platinum surface was observed for graphite-supported Pt particles, compared to the case when bare BDD was used as support.

Photocatalytic water splitting to produce hydrogen using multi-junction solar cell with different deposited thin films

Multi-junction solar cell (MJSC) was integrated into an H-type reactor system to carry out water-splitting reaction without external circuit and bias. In the H-type reactor, hydrogen and oxygen could be evolved separately. Different kinds of materials were deposited on the bottom cell to prevent corrosion. These materials include silver, platinum, and iron oxide layers which were prepared via an electron beam-induced deposition (EBID) method. Under visible-light irradiation, hydrogen production was achieved by using the MJSC; however, only a small amount of oxygen was evolved. The photogenerated holes may oxidize the photoelectrode instead of water, meaning that Ge subcell or the deposited thin film was oxidized during the photoreaction. The thin films ranked from highest hydrogen evolution to lowest are: Pt> bare Ge> Fe3O4> Ag. The photoelectrode deposited with metal thin film showed better activity due to its higher conductivity, except Ag. The poor performance of photoelectrode with silver thin film was due to the formation of silver oxide during photoreaction which may trap electrons, lowering the amount of electrons available to carry out water reduction. The chemical bias for H-type reactor system was eliminated by using sodium sulfate as the electrolyte. The ratio of evolved hydrogen to oxygen was near 2:1, suggesting that real water-splitting reaction can be achieved by using the MJSC incorporated H-type reactor system without chemical bias.

Influences of pH value in deposition-precipitation synthesis process on Pt-doped TiO2 catalysts for photocatalytic oxidation of NO

This work has been undertaken to study the influences of pH value on the characteristics and activity of photocatalyst by deposition-precipitation method during its preparation process. A series of Pt-modified TiO2 were prepared by deposition-precipitation method at different pH values as well as wet impregnation method, and characterized by XRD, XPS, TEM, UV-Vis and photoluminescence (PL). It was found that the catalysts had the highest photocatalytic activity for NO conversion when pH value was kept at around 7. And the sample prepared by deposition-precipitation method showed higher activity than that by impregnation method. This was mainly due to their high value in highly-dispersed platinum oxides (PtOx) content on the surface of the catalysts. The results from UV-Vis absorption showed that highest absorbance was obtained for Pt/TiO2 prepared at pH values of around 7. And PL spectra results indicated that the recombination rate of photogenerated electrons and holes of the samples prepared by deposition-precipitation method was lower than that prepared by impregnation method. And in the zeta potential study, the pH values for the isoelectric point of the preparing slurry of 0.05 wt.%Pt/TiO2 and 0.5 wt.%Pt/TiO2 were determined to be 6.5−8.5, which further confirmed the enrichment of PtOx dopants for the catalysts repapered when pH value was around 7.

Dynamic impedance study of ethanol and acetaldehyde oxidation at platinum in acid solutions

Ethanol and acetaldehyde oxidation at polycrystalline platinum electrode in 0.5M sulfuric acid were studied using cyclic voltammetry and dynamic electrochemical impedance spectroscopy and different concentrations of electroactive species. It was found that sharp peaks on cyclic voltammograms of ethanol observed by various authors were related to the appearance of negative resistances. The simplest electrical equivalent circuits explaining the impedance were found. Double layer capacitance measurements revealed that hydrogen underpotential deposition exists at the least positive potentials. In the potential range 0.3–0.7V low capacitance of ∼10μFcm−2 was observed due to strong adsorption of organic fragments and increased upon platinum oxidation. These results were reproducible upon cycling. In the potential zone of the formation of the first anodic peak the logarithmic slopes of dE/dRct were larger for the positive sweep than for the negative sweep. The zones of the negative resistances were identified.

The effect of Platinum Oxide Growth on Platinum Stability in PEMFCs

not Available.

Platinum oxidation responsible for degradation of platinum–cobalt alloy cathode catalysts for polymer electrolyte fuel cells

Platinum oxidation of Pt–Co alloy catalysts for polymer electrolyte fuel cells was investigated for a series of Pt–Co alloy catalysts with different specification. The chemical state of platinum evaluated by soft X-ray photoemission spectroscopy was compared with the electrochemical properties to elucidate the origin of catalyst degradation. Increase in the particle size of Pt–Co alloy catalysts caused the decrease in the concentration of platinum hydroxide and improved the catalyst durability. Applying potential cycling below 1.0 V, only platinum hydroxide was observed, while platinum oxides, PtO and PtO2, appeared after potential cycling up to 1.2 V. The peak shift of Pt 4f spectra after the potential cycling implies that these platinum hydroxide and oxide are dissolved and deposited on another platinum catalyst in a reduced metallic state, which causes the catalyst degradation.