Platinum Oxide Research Articles

Drying Techniques Affecting Structure‐Reactivity of Pt/Cr‐Ta : SrTiO3 Catalysts in Visible Light‐Irradiated Water Splitting Reaction

AbstractIn this study, the effect of drying techniques on properties of Pt/Cr−Ta : SrTiO3 catalysts in photocatalytic water splitting reaction were investigated. Drying techniques directly affected platinum particle size, which influenced the Pt phases and optical properties, all of which impact the activity of photocatalysts. The performances of Pt/Cr−Ta : SrTiO3 catalysts were in the following order: microwave>infrared>sonication>rotary evaporation>hot‐air oven. Among these techniques, microwave drying was the most efficient, providing high surface area, small platinum particle size and high percentage of platinum (II) oxide, which in turn led to the outstanding apparent quantum yield of H2 per energy consumption (22.4 %/KWh), which was 5.7, 5.7, 44.8 and 9.3 times higher than that of infrared, sonication, rotary evaporation and hot‐air oven, respectively. This result indicated that microwave technique provided efficient rapid and uniform heating rate with low energy consumption, leading to lowering the operating time period and cost.

Study on the dissolution of hollow mesoporous silica nanosphere-supported nanosized platinum oxide in biorelevant media for evaluating its potential as chemotherapeutics

Platinum oxide (PtOx) nanoparticles (NPs) have been shown to possess anticancer activity by releasing ionic Pt species under biological conditions. However, the dissolution kinetics and the changes in the chemical state of Pt during PtOx dissolution have not yet been studied. To fill this gap, we prepared a composite (designated as PtOx@MMT-2) containing PtOx NPs on hollow mesoporous silica nanospheres and studied the dissolution of the material in different biorelevant media. We found that the release of Pt was retarded due to the adsorption of biomolecules on PtOx NPs during the degradation of host silica. The biomolecules adsorption also lowered the accessibility of PtOx NPs, resulting in the reduced catalase-like activity of the NPs. In line with the results, the cytotoxicity of PtOx@MMT-2, which was positively correlated to the amount of Pt uptake, was reduced by biomolecules adsorption. Our findings should be applicable to other metal (oxide) NPs under biological conditions and may provide implications for the design of nanomaterials for practical therapeutic applications.

Optimization of Platinum dioxide properties by plasma oxidation of sputtered PtOx

We have previously used reactively sputtered Platinum oxide thin film as DNA sensing element. In this work, we subject the reactively sputtered Platinum oxide thin films to an additional RIE step for 3, 6 and 9 min and carry out a detailed comparative study of the material and electrical properties of these films. XRD and XPS analysis revealed that when the reactively sputtered Platinum oxide film was subjected to RIE step for longer periods of time, it became progressively α-PtO2 in nature. Activation energies of 0.24 eV, 0.26 eV, 0.29 eV and 0.31 eV were obtained for the as deposited film and the films subjected to RIE step for 3, 6 and 9 min respectively. The Hall mobility of the as deposited Platinum oxide film was found to be 32.15 cm2V−1s−1 at room temperature. However, when the as deposited film was subjected to RIE step for 9 min the mobility value rises to as high as 136.13 cm2V−1s−1 at room temperature.

Influence of doped platinum nanoparticles on photocatalytic performance of CuO–SiO2 for degradation of Acridine orange dye

Preparation of cupric oxide-silicon dioxide nanoparticles was carried out using a sol-gel method. Cupric oxide-silicon dioxide nanoparticles were decorated by different weight percent of platinum (0.5, 1.0, 3.0 and 5.0 wt %) using method of photoassisted deposition. XRD remarks revealed that XRD patterns for all samples are composed of cupric oxide. Therefore, silicon dioxide is amorphous and decoration of cupric oxide-silicon dioxide nanoparticles by platinum has no effect on the formed phase. Also, due to low percent of platinum there are no peaks for platinum oxide or platinum. Cupric oxide has bandgap energy absorb in visible region but has high e-h recombination rate. Decoration of cupric oxide-silicon dioxide nanoparticles by platinum was decreased bandgap energy from 2.38 to 1.91 eV and also decrease rate of e-h recombination rate. The photocatalytic activity of platinum decorated cupric oxide-silicon dioxide nanoparticles was measured under visible light for Acridine orange dye degradation. 100% of Acridine orange dye can be degraded using 3.0 wt % of platinum decorated cupric oxide-silicon dioxide photocatalyst, 1.2 g/L dose of platinum decorated cupric oxide-silicon dioxide photocatalyst and 30 min reaction time. 3.0 wt % of platinum decorated cupric oxide-silicon dioxide photocatalyst has photocatalytic stability for five times.

Synthesis and Properties of a Carbon Monoxide Oxidation Catalyst Based on Platinum and Plasma-Chemical Titanium Nitride

A CO oxidation catalyst that includes Pt clusters applied on nanosized TiN supports with a particle size of 18 and 36 nm has been synthesized. The catalyst has been studied using TEM, X-ray powder diffraction, and XPS methods. It has been found that platinum clusters formed on the support surface are covered with a mixture of platinum and platinum oxide. The coherent scattering range of the Pt cluster is close to 8 nm on a support with titanium nitride particles of 18 nm. The catalytic properties in the reaction of CO oxidation at 295 K and low CO concentrations (<100 mg/m3) have been examined. It has been found that when the platinum content in the catalyst is 9 to 15 wt %, the CO oxidation rate is 120 times higher than that on platinum black with a specific surface area of 30 m2/g. The catalysts are promising for use in catalytic systems for air purification.

Between Physical Complexity and Simplicity: Nailing Down the Cathodic Activation Overpotential in a Small-Scale PEM Fuel Cell

Understanding the kinetics of polymer electrolyte fuel cells (PEFC) remains a key issue for the optimization of the catalyst layer structure with respect to fuel cell performance and ageing. In this study, firstly the impact of hydrogen crossover from anode to cathode through the membrane on the measurable open circuit voltage (OCV) is analyzed extensively. For this purpose, all the other parasitic reactions like platinum oxide formation or carbon corrosion are neglected in a first approach and the influences of the operating conditions on the crossover flux by means of voltammetry measurements and also mass spectrometry in the cathode exhaust gas are examined. These experimental results yield an efficient parameterization of the crossover rate. Incorporated into a physical 1D through-plane cell simulation model, it allows for consistent predictions at and close to OCV conditions. Subsequently, the activation overpotential is parameterized experimentally thanks to electrochemical impedance spectroscopy on a 25 cm2 cell with a straight parallel channel flowfield under differential conditions. Therefore, spectra are recorded for a large range of conditions (Fig. 1a) and the distribution of relaxation times (DRT) is evaluated (Fig. 1b). As a result, an equivalent circuit is set up. Hence, it is possible to fit the experimental data and to extract the kinetic parameters for our model, as functions of electrical load, oxygen partial pressure and temperature. We finally use this extensive dataset for comparing different approaches for modelling the oxygen reduction reaction (ORR) on platinum, ranging from single-step Butler-Volmer kinetics to advanced microkinetic models that take into account the intermediates of the ORR and thereby also the potential dependent surface coverage of the electrode [1-2].

Construction of Porphyrin-Sensitized Solar Cells Containing Toray™/TGP-H-060 Carbon - Based Cathodes

In this work, we present the construction and photovoltaic response of porphyrin-sensitized solar cells containing TorayTM/TGP-H-060 carbon – modified indium-doped tin oxide (ITO) cathodes (ITO/C), as a viable alternative for substituting platinum oxides – modified ITO cathodes (ITO/PtOx), which are traditionally employed for designing dye-sensitized solar cells. In this case, a binary mixture (75:25) of propylene carbonate (PC) : 3-methoxypropionitrile (MPN), containing 0.015M I2 plus 0.285M LiI was employed as electrolyte for filling the photo-cells. On one hand, our experimental results demonstrated that both cathodic systems, ITO/C and ITO/PtOx, had a very comparable electron transfer kinetics when studied the cathodic semi-reaction I3 - + 2e­ - --> 3I- at these electrode surfaces. Table 1. Electron transfer constants (k°) and cathodic transfer coefficients (∝c) obtained for the semi-reaction I3 - + 2e­ - --> 3I- at ITO/C and ITO/PtOx cathodes. Electrolyte: 0.015M I2 plus 0.285M LiI contained in a binary mixture 75:25 of PC:MPN at 25°C. A polycrystalline Pt cathode was also employed for comparison purposes. cathode Electron transfer kinetic parameters k°/10-4 (cm/s) and ∝ c Pt 5.31 0.27 ITO/PtOx 3.35 0.26 ITO/C 2.70 0.23 On the other hand, a detailed revision of Table 2 reveals that the photovoltaic responses of porphyrin-sensitized solar cells containing ITO/C and ITO/PtOx cathodes were comparable under simulated solar light (AM1.5, 100mW/cm2). These interestingly results confirmed that TorayTM/TGP-H-060 carbon – modified ITO cathodes are promising to substitute those PtOx – modified ITO cathodes typically employed for constructing dye-sensitized solar cells. Table 2. Photovoltaic responses obtained for porphyrin-sensitized solar cells containing ITO/C and ITO/PtOx cathodes, where: Eoc, jsc, ff and ξ are open-circuit potential, short-circuit photocurrent, fill-factor and global conversion efficiency, respectively, under simulated solar light (AM1.5, 100mW/cm2). cathode Eoc (V) jsc (m A/cm2) ff ξ(%) ITO/PtOx -0.30 1.23 0.39 0.17 ITO/C -0.35 1.18 0.40 0.19 References U.López-García, O.A.Castellanos, L.A.Godínez, J.Manríquez, “Electrophoretically-Assisted Deposition of Mesoporphyrin IX on Nanoparticulate TiO2 Films for Constructing Efficient Dye-Sensitized Solar Cells”, Journal of The Electrochemical Society, 158 (2011) F100-F105.

Mechanism Investigation of Hydrocarbon Emissions from the In-Cylinder Post-Injection Effect on NO Oxidation over a Diesel Oxidation Catalyst.

The purpose of this study was to investigate hydrocarbon emissions from the in-cylinder post-injection effect on NO oxidation over a diesel oxidation catalyst (DOC) with various feed mixtures. In the temperature ramp experiments with varying C3H6 concentrations in NO/O2 and NO/O2/H2 mixtures, addition of C3H6 was observed to inhibit NO oxidation by delaying the ignition temperature of NO. Furthermore, NO2 production was decreased with an increase in the feed C3H6 concentration. NO was able to reduce platinum oxide and produce NO2 at 200 °C. Experimental results with C3H6 switching in/out at 350 °C indicated that the introduction of 1.1% C3H6 clearly increased the catalyst temperature and decreased the NO2 field. Feeding in H2 led to a higher NO2 field and a lower NO2 field drop. The decline in the NO2 concentration can be attributed to platinum passivation caused by H2 in the NO/O2/H2 mixture.

Highly dispersed platinum supported catalysts – Effect of properties on the electrocatalytic activity

This work addresses scientific issues regarding the most challenging component of PEM fuel cells, the electrocatalyst, and explores a new approach to exploit the differentiations induced to the metal by the surface chemistry of the support. The study focuses on the development of Pt based electrocatalysts supported on pyridine modified carbon nanotubes with different Pt loadings, their thorough characterization and parallel comparison with non-modified or conventional carbon supports. The aim is the interpretation of the catalyst electrochemical behavior through a structural and physicochemical characterization study. The introduction of pyridines can differentiate the metal deposition, in terms of dispersion, nanoparticle properties, platinum oxidation state and metal-support interactions. Moreover, the substrate can play a decisive role on the size and functionality of the electrochemical interface. This approach constitutes a promising route for developing materials with innovative features aiming to a serious reduction in the Pt loads through increased activity and metal utilization.

Controllable Anomalous n- and p-Type Photothermoelectric Effects of Platinum Oxide and Tungsten Trioxide Layers with and without Chromic Reaction

We attempted to develop both n-type and p-type anomalous photothermoelectric (photo-TE) effects, which are of interest for developing practical applications of TE devices for energy harvesting usin...

Synthesis, Alkylation and Reduction of 4‐Aryl‐2H‐1,2,3‐benzothiadiazine 1,1‐dioxides

Abstractortho‐(2‐Aryl‐1,3‐dioxolan‐2‐yl)benzenesulfonyl chlorides obtained from benzophenone ketals by directed ortho‐lithiation chemistry were cyclized either with hydrazine monohydrate or with acetohydrazide to furnish variously substituted 4‐aryl‐2H‐1,2,3‐benzothiadiazine 1,1‐dioxides. Alkylation of benzothiadiazine dioxides with alkyl iodides under basic conditions was elaborated, revealing significant differences compared to the reactivity of 4‐unsubstituted ones. Hydrogenation of the C=N double bond in the presence of platinum(IV) oxide is also described. Detailed NMR studies and DFT calculations supported the structure elucidation of the compounds.

Development of tungsten doped Ni-Zn nano-ferrites with fast response and recovery time for hydrogen gas sensing application

This paper reports on the study of series of tungsten doped Ni0.5Zn0.5WxFe2−xO4 (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) ferrites synthesized by a co-precipitation scheme. The crystallite size varies from 62 to 49 nm and the scanning electron microscope (SEM) images show the spinel cubic structure of the powder sample. Energy Dispersive X-ray Fluorescence Spectroscopy (EDXRF) confirms the presence of Ni, Zn, W and Fe elements in the prepared samples. The specific surface areas of the Ni0.5Zn0.5W0.2Fe1.8O4, Ni0.5Zn0.5W0.4Fe1.6O4 and Ni0.5Zn0.5W0.6Fe1.4O4 samples calculated from Brunauer-Emmett-Teller (BET) method are 18.9 m2/g, 21.5 m2/g and 24.6 m2/g, respectively. The metal oxide pellet type resistive sensor was made for gas sensor application. These sensors are selective for hydrogen (H2) gas. The performance of these sensors for sensing hydrogen gas at a concentration of 1000 ppm in the temperature range 80–300 °C has been investigated. Platinum electrodes were deposited on all the pellets by RF sputtering technique. The subsequent decomposition of platinum oxides on the metal oxide pellet surface results in an increase in surface roughness and electrical resistivity. The sensor shows a change in resistance from 1.21 × 105 Ω to 7.83 × 104 Ω in the presence of H2 gas even at alow temperature. The composition with x = 0.2 at an optimum temperature of 180 °C showed a fast response (14 s) and recovery time (20 s). High sensitivity, low cost, long term stability, high selectivity and fast response at low temperature makes this sensor useful for industrial applications.

Oxidation and Corrosion of Platinum–Nickel and Platinum–Cobalt Nanoparticles in an Aqueous Acidic Medium

We report on the synthesis, characterization, and corrosion behavior of randomly oriented platinum–nickel and platinum–cobalt nanoparticles (PtNi-NPs, PtCo-NPs). Unsupported and carbon-supported nanocatalysts were synthesized using the “water-in-oil” microemulsion method. X-ray diffraction (XRD) was used to examine their average crystallite size, which was 2.3 nm in both cases. The shape, size, and size distribution of the nanoparticles were evaluated using transmission electron microscopy (TEM); they were determined to be spherelike with an average size of 3.3 and 3.2 nm for PtNi-NPs and PtCo-NPs, respectively, and a narrow size distribution. Comparison of the XRD and TEM data indicated that the nanocatalysts were polycrystalline in nature. Thermogravimetric analysis (TGA) measurements were carried out to evaluate the metal loadings of the carbon-supported nanocatalysts, which were 38.1 wt % for PtNi-NPs and 40.8 wt % for PtCo-NPs. Static Density Functional Theory (DFT) calculations were performed to ana...

Processing Strategies for High-Performance Schottky Contacts on n-Type Oxide Semiconductors: Insights from In2O3

Preparation of rectifying Schottky contacts on n-type oxide semiconductors, such as indium oxide (In2O3), is often challenged by the presence of a distinct surface electron accumulation layer. We investigated the material properties and electrical transport characteristics of platinum contact/indium oxide heterojunctions to define routines for the preparation of high-performance Schottky diodes on n-type oxide semiconductors. Combining the evaluation of different Pt deposition methods, such as electron-beam evaporation and (reactive) sputtering in an (O and) Ar atmosphere, with oxygen plasma interface treatments, we identify key parameters to obtain Schottky-type contacts with high electronic barrier height and high rectification ratio. Different photoelectron spectroscopy approaches are compared to characterize the chemical properties of the contact layers and the interface region toward In2O3, to analyze charge transfer and plasma oxidation processes as well as to evaluate the precision and limits of different methodologies to determine heterointerface energy barriers. An oxygen-plasma-induced passivation of the semiconductor surface, which induces electron depletion and generates an intrinsic interface energy barrier, is found to be not sufficient to generate rectifying platinum contacts. The dissolution of the functional interface oxide layer within the Pt film results in an energy barrier of ∼0.5 eV, which is too low for an In2O3 electron concentration of ∼1018 cm-3. A reactive sputter process in an Ar and O atmosphere is required to fabricate rectifying contacts that are composed of platinum oxide (PtOx). Combining oxygen plasma interface oxidation of the semiconductor surface with reactive sputtering of PtOx layers results in the generation of a high Schottky barrier of ∼0.9 eV and a rectification ratio of up to 106. An additional oxygen plasma treatment after contact deposition further reduced the reverse leakage current, likely by eliminating a surface conduction path between the coplanar Ohmic and Schottky contacts. We conclude that processes that allow us to increase the oxygen content in the interface and contact region are essential for fabrication of device-quality-rectifying contacts on various oxide semiconductors.

Platinum Electrocatalysts Deposited onto Composite Carbon Black–Metal Oxide Support

New nanostructured Pt/(SnO2/C)-electrocatalyst (20 wt % Pt) is synthesized via platinum chemical deposited onto composite SnO2/C-support microparticles (4 wt % Sn). The composite support was prepared beforehand using unique method of the tin electrochemical deposition onto disperse carbon black particles. It was shown by X-ray diffraction and transmission electron microscopy that the platinum and tin oxide nanoparticles distributed over the carbon surface are sized 2.4 and 2.9 nm, respectively. Electrochemical measurements showed the obtained catalyst to approach the commercial Pt/C HiSPEC 3000 catalyst (20 wt % Pt) with respect to its mass-activity in the oxygen electroreduction reaction and to be superior thereto as for the electrochemically active surface area, stability in stress test, and activity in methanol electrooxidation reaction. The peculiarities in electrochemical behavior of the synthesized Pt/(SnO2/C)-electrocatalyst can be explained by the SnO2 nanoparticle effect on the platinum nanoparticle nucleation/growth, as well as presence of Pt–SnO2–C triple junction nanostructure at the surface. The Pt/SnO2 contact provides stable platinum-to-support adhesion and asserts bifunctional catalysis mechanism of the methanol electrooxidation. And the Pt/C junctions provide for electron supplying/retraction to or from the platinum nanoparticles.

Oxide formation as probe to investigate the competition between water and alcohol molecules for OH species adsorbed on platinum

The creation of defects on the surface of Pt(111) and Pt(100) and the dissolution of Pt were used as probes to investigate the oxidation of the surface in the absence and in the presence of methanol, ethanol, glycerol and ethylene glycol. Electrochemical and Graphite Furnace Atomic Absorption Spectrometry showed that in the presence of ethanol, glycerol and ethylene glycol, in the same potential window, the formation of defects is decreased in comparison to the oxidation of platinum in the absence of these alcohols. Since both the oxidation of the alcohols and the oxidation of the surface depend on PtOH formation, the competition for this species can displace the potential at which the oxidation of the surface oxidation to PtO is favored in the presence of ethanol, glycerol and ethylene glycol. On the other hand, the presence of methanol does not influence the oxidation and subsequent disordering of the surface, possibly because this reaction takes place in parallel with platinum oxidation to PtO.

Ruthenium Nanoparticles for Catalytic Water Splitting.

Both global warming and limited fossil resources make the transition from fossil to solar fuels an urgent matter. In this regard, the splitting of water activated by sunlight is a sustainable and carbon-free new energy conversion scheme able to produce efficient technological devices. The availability of appropriate catalysts is essential for the proper kinetics of the two key processes involved, namely, the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). During the last decade, ruthenium nanoparticle derivatives have emerged as true potential substitutes for the state-of-the-art platinum and iridium oxide species for the HER and OER, respectively. Thus, after a summary of the most common methods for catalyst benchmarking, this review covers the most significant developments of ruthenium-based nanoparticles used as catalysts for the water-splitting process. Furthermore, the key factors that govern the catalytic performance of these nanocatalysts are discussed in view of future research directions.

In-situ local phase-transitioned MoSe2 in La0.5Sr0.5CoO3-\u03b4 heterostructure and stable overall water electrolysis over 1000 hours

Developing efficient bifunctional catalysts for overall water splitting that are earth-abundant, cost-effective, and durable is of considerable importance from the practical perspective to mitigate the issues associated with precious metal-based catalysts. Herein, we introduce a heterostructure comprising perovskite oxides (La0.5Sr0.5CoO3–δ) and molybdenum diselenide (MoSe2) as an electrochemical catalyst for overall water electrolysis. Interestingly, formation of the heterostructure of La0.5Sr0.5CoO3–δ and MoSe2 induces a local phase transition in MoSe2, 2 H to 1 T phase, and more electrophilic La0.5Sr0.5CoO3–δ with partial oxidation of the Co cation owing to electron transfer from Co to Mo. Together with these synergistic effects, the electrochemical activities are significantly improved for both hydrogen and oxygen evolution reactions. In the overall water splitting operation, the heterostructure showed excellent stability at the high current density of 100 mA cm−2 over 1,000 h, which is exceptionally better than the stability of the state-of-the-art platinum and iridium oxide couple.

Hot Electron Transport on Three-Dimensional Pt/Mesoporous TiO2 Schottky Nanodiodes.

We present the design of a three-dimensional Pt/mesoporous TiO2 Schottky nanodiode that can capture hot electrons more effectively, compared with a typical two-dimensional Schottky diode. Both chemically induced and photon-induced hot electrons were measured on the three-dimensional Pt/mesoporous TiO2 Schottky nanodiode. An increase in the number of interfacial sites between the platinum and support oxide affects the collection of hot electrons generated by both the catalytic reaction and light injection. We show that hot electrons flowing 2.5 times higher are detected as the current in the mesoporous system, compared with typical two-dimensional nanodiode systems that have a planar Schottky junction. Identical trends for the chemicurrent and photocurrent in the mesoporous system demonstrate that the enhanced hot electrons are attributed to the larger interface area between the metal and the mesoporous TiO2 support fabricated by the anodization process. This three-dimensional Schottky nanodiode can provide insights into hot electron generation on a practical catalytic device.

The Oxidation of Platinum under Wet Conditions Observed by Electrochemical X-ray Photoelectron Spectroscopy.

During the electrochemical reduction of oxygen, platinum catalysts are often (partially) oxidized. While these platinum oxides are thought to play a crucial role in fuel cell degradation, their nature remains unclear. Here, we studied the electrochemical oxidation of Pt nanoparticles using in situ XPS. When the particles were sandwiched between a graphene sheet and a proton exchange membrane that is wetted from the back, a confined electrolyte layer was formed, allowing us to probe the electrocatalyst under wet conditions. We show that the surface oxide formed at the onset of Pt oxidation has a mixed Ptδ+/Pt2+/Pt4+ composition. The formation of this surface oxide is suppressed when a Br-containing membrane is chosen due to adsorption of Br on Pt. Time-resolved measurements show that oxidation is fast for nanoparticles: even bulk PtO2·nH2O growth occurs on the subminute time scale. The fast formation of Pt4+ species in both surface and bulk oxide form suggests that Pt4+-oxides are likely formed (or reduced) even in the transient processes that dominate Pt electrode degradation.