Platinum Oxide Research Articles

Experimental analysis of recoverable performance loss induced by platinum oxide formation at the polymer electrolyte membrane fuel cell cathode

Unrecoverable and recoverable performance degradation is a major issue hindering commercialization of polymer electrolyte membrane fuel cells. The recoverable losses, caused for example by a contaminant adsorption, catalyst flooding, ionomer dehydration, and platinum oxidation, can be reversed, usually following an interruption in the cell operation. In order to elucidate the link between platinum oxidation and recoverable performance loss, three MEAs were characterized in this work. They involved catalysts with different nanoparticle sizes and loadings tested using a combination of the electrochemical impedance spectroscopy, constant-voltage, constant-current and potential controlled techniques, before and after electrocatalyst aging. Experimental results indicate that a decrease in specific activity over time is not affected by nanoparticle size or aging. Nevertheless, linear sweep voltammetry, which is adopted to reduce platinum oxide and as diagnostics for oxide composition, reveals that a change in composition is observed in correlation with catalyst morphology and catalyst aging. The formation of the platinum oxide associated with the peak at 0.61 VRHE in the voltammetry is found to decrease the catalyst's specific activity more than oxides associated with peaks at higher potentials. This indicates that the recoverable performance loss due to the platinum oxide formation depends on the oxide composition.

Impact of Shutdown Procedures on Recovery Phenomena of Proton Exchange Membrane Fuel Cells

AbstractThe paper presents the obtained measurement and analysis results of the accelerated stress test protocols consisting of voltage cycling, designed to target electrocatalyst degradation, with the intentional recovery periods (so‐called soak time steps) every 2,500 voltage cycles on an already conditioned 50 cm2 (single) fuel cell provided by ElringKlinger. Before and after every intentional stop, a series of diagnostic methods (polarization curves, electrochemical impedance spectroscopy, cyclic voltammetry, linear sweep voltammetry) were performed. During the conducted durability test, different shutdown procedures, as well as different duration of the soak time period were tested with their impact on performance recovery phenomenon. The results suggest that cause of the reversible degradation could be accumulated water within the cell and/or presence of oxygen within the catalyst layer leading to formation of platinum oxides on the catalyst surface. The prolonged soak time step reduces recovery effect, while rapid reduction of the cell temperature with ice proved to be counterproductive for performance recovery. Shutdown procedure without shortly‐connected resistor has shown no effect on recovery. Shutdown procedure without nitrogen purge proved to be the most effective for performance recovery.

Time and Size-dependent Biogenically Synthesized Nanoparticles Using Fungus Fusarium Oxysporum: A Review on their Preparation, Characterization and Biological Activities

In recent time, green synthesis of Metal Nanoparticles (MNPs) is the latest developing technology and received exceptional interest because it is simple, eco-friendly, pollutant-free, nontoxic, and a low-cost approach. Green route of biogenic synthesis of metal nanoparticles via microbes (bacteria, fungi, virus, yeast, algae etc.) has the potential to deliver clean manufacturing technology. Fungi are in the great use for the synthesis of nanoparticles and are more advantageous as compared with other microorganisms in several ways. Fungi grow in the form of a group of mycelia, which helps them to withstand flow pressure and agitation and various other conditions to which microbes are subjected to in a bioreactor, used for large-scale production. This review has its major focus on fungus Fusarium oxysporum, which is capable of synthesizing a large number of different types of nanoparticles such as titanium, magnesium, platinum, silver, gold, zirconium, and strontium, titania and silica oxide and many more. Biogenically synthesized nanoparticles are characterized by different techniques and exhibited biological activity. The fungi with metabolic capabilities can effectively synthesize a large number of nanoparticles both extracellularly and intracellularly. The biologically synthesized nanoparticles have wide ranges of applications especially in agricultural and medicinal industries.

Predictive system-level modeling framework for transient operation and cathode platinum degradation of high temperature proton exchange membrane fuel cells

High temperature proton exchange membrane fuel cells (HT-PEMFCs) are a promising and emerging technology, which enable highly efficient, low-emission, small-scale electricity and heat generation. The simultaneous reduction in production costs and prolongation of service life are considered as major challenges toward their wider market adoption, which calls for the application of predictive virtual tools during their development process. To present significant progress in the addressed area, this paper introduces an innovative real-time capable system-level modeling framework based on the following: (a) a mechanistic spatially and temporally resolved model of HT-PEMFC operation, and (b) a degradation modeling framework based on interacting individual cathode platinum degradation mechanisms. Additional innovative contributions arise from a consistent consideration of the varying particle size distribution in the transient fuel cell operating regime. The degradation modeling framework interactively considers the carbon and platinum oxidation phenomena, and platinum dissolution, redeposition, detachment, and agglomeration; hence, covering the entire causal chain of these phenomena. Presented results confirm capability of the modeling framework to accurately simulate the platinum particle size redistribution. Results clearly indicate more pronounced platinum particle growth towards the end of the channel since humidity is the main precursor of oxidation reactions. In addition, innovative modeling framework elucidate contributions of agglomeration, which is more pronounced at voltage cycling, and Ostwald ripening, which is more pronounced at higher voltages, to the platinum particles growth. These functionalities position the proposed modeling framework as a beyond state-of-the-art tool for model-supported development of the advanced clean energy conversion technologies.

Exchange Bias in FePt-FePt3 Thin Films by Controlled Phase Transition of Blended Nanoparticle Building Blocks.

Nanostructured composite thin films showing magnetic exchange coupling at the material interface have attracted great interest for the development of electronic components such as spin-valves. Besides the commonly performed fabrication of multilayer systems, the utilization of nanoparticle building blocks holds great potential for thin films with tailored magnetic properties and allows the facile but controlled combination of materials with complementary magnetic characteristics. In this work, we present the use of prefabricated highly crystalline iron platinum (fcc-FePt) and iron oxide (FexOy) nanoparticles for the preparation of nanocomposite thin films with varying compositions by wet processing from mixed dispersions. The resulting multiphase coatings showed high homogeneity, low surface roughness, and superparamagnetic behavior. By the variation of the amount of incorporated iron oxide, a precise adjustment of the magnetization at high field strength could be achieved. Furthermore, calcination under inert gas atmosphere resulted in a controlled phase transition of the magnetic phases and thus, in purely metallic coatings composed of ferromagnetic fct-FePt and antiferromagnetic fcc-FePt3, a decrease in surface roughness as well as high magnetic coercivity at room temperature. Field-cooling below the Néel temperature of fcc-FePt3 led to an exchange bias effect with a strong increase in coercivity and the characteristic hysteresis shift. In comparison to the literature, our nanocomposite thin films showed fully ordered phases without the occurrence of phase impurities, a distinctly higher coercivity, and an exchange bias shift of 38.7 mT.

Pt-O bond as an active site superior to Pt0 in hydrogen evolution reaction

The oxidized platinum (Pt) can exhibit better electrocatalytic activity than metallic Pt0 in the hydrogen evolution reaction (HER), which has aroused great interest in exploring the role of oxygen in Pt-based catalysts. Herein, we select two structurally well-defined polyoxometalates Na5[H3Pt(IV)W6O24] (PtW6O24) and Na3K5[Pt(II)2(W5O18)2] (Pt2(W5O18)2) as the platinum oxide model to investigate the HER performance. Electrocatalytic experiments show the mass activities of PtW6O24/C and Pt2(W5O18)2/C are 20.175 A mg−1 and 10.976 A mg−1 at 77 mV, respectively, which are better than that of commercial 20% Pt/C (0.398 A mg−1). The in situ synchrotron radiation experiments and DFT calculations suggest that the elongated Pt-O bond acts as the active site during the HER process, which can accelerate the coupling of proton and electron and the rapid release of H2. This work complements the knowledge boundary of Pt-based electrocatalytic HER, and suggests another way to update the state-of-the-art electrocatalyst.

Communication—Electrocatalytic Coupling of Methane at Platinum Oxide Electrodes in Superacids

Electrochemical oxidation of methane in the absence of chemical oxidants offers the potential to directly synthesize high value hydrocarbons at low temperatures. Experimental results demonstrate methane oxidization at oxidized Pt electrodes in liquid superacid electrolytes. Ethane and ethylene are observed as products under chronoamperometric experiments at room temperature. Faradaic efficiencies for C2 products range from 5% to 25% at anodic potentials between 0.8 to 1.4 V vs RHE. A generalized Lewis-acid Pt2+ mechanism including methylidene coupling is proposed.

Communication—Platinum and Tin Oxide Dispersed in a Fluffy TiO2 Nanolayer for Electrocatalytic Reduction of Oxygen

Pt catalysts perform well in the oxygen reduction reaction (ORR), but they suffer weak bonding with carbon supports, leading to catalyst degradation. We introduce a fluffy titanium dioxide (TiO2) nanolayer with a very high specific surface area as support, made possible with a new condensed layer deposition technique. When Pt and SnO2 were incorporated in it as co-catalyst, a remarkable improvement in ORR onset potential was achieved at 930 mV vs RHE in sulfuric acids. The mass activity was 2.66 times that of Pt/C at 900 mV. The fluffy layer stabilized SnO2 and together, they enabled a pronounced ligand effect.

HOR Activity of Pt-TiO2-Y at Unconventionally High Potentials Explained: The Influence of SMSI on the Electrochemical Behavior of Pt

The formation of strong metal support interactions (SMSI) is known for many metal/metal oxide systems and its consequences are well established in the field of heterogeneous catalysis, but this knowledge has only been recently transferred to the field of electrocatalysis. In this study, Pt was deposited via atomic layer deposition (ALD) onto TiO2−Y, which allowed a good control of the particle size through the number of ALD cycles. During the ALD process, a thin-film of reduced titania is formed on the Pt surface, which leads to SMSI effects. With increasing Pt particle size, the fraction of the titania-covered Pt surface decreases. As a result, the extent of platinum oxide formation in cyclic voltammetry (CV) measurements scales with the size of the Pt particles. The influence of these thin titanium oxide films, which cover the Pt surface, on the catalytic behavior with respect to oxygen reduction reaction (ORR), hydrogen oxidation reaction (HOR), CO oxidation and oxygen evolution reaction (OER) is investigated by using an RDE setup. The covering TiOX thin-films reduce the ability to catalyze ORR, OER and CO oxidation, while it does not influence the HOR and Pt H-UPD formation. These findings indicate that proton and hydrogen transport are possible through the thin TiOX film, while oxygenated species suffer from transport limitations through the thin-film. Due to this selective permeability, these materials are able to oxidize hydrogen well beyond 1.2 VRHE.

Trans-Platinum(iv) pro-drugs that exhibit unusual resistance to reduction by endogenous reductants and blood serum but are rapidly activated inside cells: 1H NMR and XANES spectroscopy study.

Recent results have confirmed that protection of transplatin from reactions on the path to cancer cells substantially increases their activity, suggesting that such complexes have greater potential than previously thought. In this study we have investigated the use of the platinum(iv) oxidation state and the tetracarboxylate coordination sphere to determine whether these features could impart the same stability to trans-diammineplatinum complexes that they do to cis-diam(m)ineplatinum complexes. The cis complexes exhibit resistance to reduction by l-ascorbate and human blood serum, but are readily reduced inside cancer cells. Studies of reduction monitored by 1H NMR revealed that oxidation of trans-diammineplatinum(ii) complexes does not always result in significant stabilisation, but the complexes trans, trans, trans-[Pt(OAc)4(NH3)2] (OAc = acetate) and trans, trans, trans-[Pt(OPr)2(OAc)2(NH3)2] (OPr = propionate) exhibit second order half-lives of 33 h and 5.9 days respectively in the presence of a ten-fold excess of l-ascorbate. XANES spectroscopy studies of reduction in blood models showed that trans, trans, trans-[Pt(OAc)4(NH3)2] is stable in blood serum for at least 24 hours, but is reduced rapidly in whole blood and was observed to have a half-life of approximately 4 hours in DLD-1 colon cancer cells. Consequently, the tetracarboxylatoplatinum(iv) moiety has the properties required to enable the delivery of trans-diammine platinum complexes to cancer cells.

Imaging dose of cone-beam computed tomography in nanoparticle-enhanced image-guided radiotherapy: A Monte Carlo phantom study

Using kilovoltage cone-beam computed tomography (kV-CBCT) and heavy-atom radiosensitizers in image-guided radiotherapy (IGRT) can provide numerous benefits, such as image contrast enhancement in radiation dose delivery. However, the increased use of kV-CBCT for daily imaging procedures may inevitably deposit certain amount of radiation dose to the patient, especially when nanoparticles used as radiosensitizers are involved. In this study, we use Monte Carlo simulation to evaluate the imaging dose escalation due to nanoparticle addition with varying nanoparticle material, nanoparticle concentration and photon beam energy. A phantom was used to determine the relationships between the imaging dose enhancement ratios (IDERs) and different concentrations (3–40 mg/ml) of gold (Au), platinum (Pt), iodine (I), silver (Ag) and iron oxide (Fe2O3) nanoparticles, under the delivery of 120–140 kVp photon beams from the CBCT. It is found that gold and platinum nanoparticles of 40 mg/ml concentration had the highest IDER (∼1.6) under the 120 kVp photon beam. This nanoparticle addition resulted in a 0.63% increase of imaging dose based on a typical dose prescription of 200 cGy per fraction in radiotherapy, and is within the standard uncertainty of ±5% in radiation dose delivery. This study proves that the incorporation of higher concentration nanoparticles under lower photon beam energy could increase the imaging dose. The results from this study can enable us to understand more about the incorporation of heavy-atom nanoparticles in IGRT systems.

The origin of the hysteresis in cyclic voltammetric response of alkaline methanol electrooxidation.

The mechanism of the alkaline methanol electrooxidation reaction on platinum is complex and not fully understood. However, a better understanding will facilitate reaching the theoretical performance of an alkaline methanol fuel cell. Cyclic voltammetry is an often used method to investigate the mechanism of electrochemical reactions. The cyclic voltammogram of methanol electrooxidation shows a hysteresis in potential between the oxidation peaks in the forward and backward scans. The origin of this hysteresis has not been fully clarified. By means of parameter variations, such as the upper potential or the starting point of the CV measurements, and by physicochemical modeling, we investigate the formation of platinum oxides as a possible cause of this behaviour. The experiments show that the formation of platinum oxides is more likely to cause the hysteresis than the strongly adsorbed intermediates, which are formed during the forward scan. The simulation includes the formation of platinum oxide species and supports the experimental results that the hysteresis is due to the formation and reduction of platinum oxides. Besides, the simulation reveals that in the investigated potential area, different oxide forms are present.

Performance-Enhanced Non-Enzymatic Glucose Sensor Based on Graphene-Heterostructure.

Non-enzymatic glucose sensing is a crucial field of study because of the current market demand. This study proposes a novel design of glucose sensor with enhanced selectivity and sensitivity by using graphene Schottky diodes, which is composed of graphene (G)/platinum oxide (PtO)/n-silicon (Si) heterostructure. The sensor was tested with different glucose concentrations and interfering solutions to investigate its sensitivity and selectivity. Different structures of the device were studied by adjusting the platinum oxide film thickness to investigate its catalytic activity. It was found that the film thickness plays a significant role in the efficiency of glucose oxidation and hence in overall device sensitivity. 0.8–2 μA output current was obtained in the case of 4–10 mM with a sensitivity of 0.2 μA/mM.cm2. Besides, results have shown that 0.8 μA and 15 μA were obtained by testing 4 mM glucose on two different PtO thicknesses, 30 nm and 50 nm, respectively. The sensitivity of the device was enhanced by 150% (i.e., up to 30 μA/mM.cm2) by increasing the PtO layer thickness. This was attributed to both the increase of the number of active sites for glucose oxidation as well as the increase in the graphene layer thickness, which leads to enhanced charge carriers concentration and mobility. Moreover, theoretical investigations were conducted using the density function theory (DFT) to understand the detection method and the origins of selectivity better. The working principle of the sensors puts it in a competitive position with other non-enzymatic glucose sensors. DFT calculations provided a qualitative explanation of the charge distribution across the graphene sheet within a system of a platinum substrate with D-glucose molecules above. The proposed G/PtO/n-Si heterostructure has proven to satisfy these factors, which opens the door for further developments of more reliable non-enzymatic glucometers for continuous glucose monitoring systems.

Platinum Oxide Nanoparticles for Electrochemical Hydrogen Evolution: Influence of Platinum Valence State

Electrochemical hydrogen generation is a rising prospect for future renewable energy storage and conversion. Platinum remains a leading choice of catalyst, but because of its high cost and low natural abundance, it is critical to optimize its use. In the present study, platinum oxide nanoparticles of approximately 2 nm in diameter are deposited on carbon nitride (C3N4) nanosheets by thermal refluxing of C3N4 and PtCl2 or PtCl4 in water. These nanoparticles exhibit apparent electrocatalytic activity toward the hydrogen evolution reaction (HER) in acid. Interestingly, the HER activity increases with increasing Pt4+ concentration in the nanoparticles, and the optimized catalyst even outperforms commercial Pt/C, exhibiting an overpotential of only -7.7 mV to reach the current density of 10 mA cm-2 and a Tafel slope of -26.3 mV dec-1 . The results from this study suggest that the future design of platinum oxide catalysts should strive to maximize the Pt4+ sites and minimize the formation of the less active Pt2+ species.

In Situ AFM Imaging of Platinum Electrode Surface during Oxidation–Reduction Cycles in Alkaline Electrolyte

The development of energy conversion systems depends strongly on our fundamental understanding of the electrochemical interface of the electrocatalyst. Here, we study the changes in the surface morphology of a platinum polycrystalline electrode during oxidation-reduction cycles in a wide potential window (0.05-2.0 V) in sodium hydroxide by in situ atomic force microscopy. Platinum nanoparticles are observed on the surface after cycling due to the redeposition of dissolved platinum ions. The influence of scan rate on platinum redeposition is studied by applying asymmetric potential sweep programs. The negative-going scan rate is the key factor here, as it controls the reduction of platinum oxide, as well as the redeposition of platinum. Moreover, it is found that chloride ions in the electrolyte impede the redeposition by complexing with platinum. This investigation enables us to reveal the surface roughening processes on platinum electrode in alkaline electrolyte and assists in understanding the fundamentals of the stability of platinum-containing energy conversion systems.

Deactivation of a Pd/Pt Bimetallic Oxidation Catalyst Used in a Biogas-Powered Euro VI Heavy-Duty Engine Installation

The reduction of anthropogenic greenhouse gas emissions is crucial to avoid further warming of the planet. We investigated how effluent gases from a biogas powered Euro VI heavy-duty engine impact the performance of a bimetallic (palladium and platinum) oxidation catalyst. Using synthetic gas mixtures, the oxidation of NO, CO, and CH4 before and after exposure to biogas exhaust for 900 h was studied. The catalyst lost most of its activity for methane oxidation, and the activity loss was most severe for the inlet part of the aged catalyst. Here, a clear sintering of Pt and Pd was observed, and higher concentrations of catalyst poisons such as sulfur and phosphorus were detected. The sintering and poisoning resulted in less available active sites and hence lower activity for methane oxidation.

Physical Modeling of Catalyst Degradation in Low Temperature Fuel Cells: Platinum Oxidation, Dissolution, Particle Growth and Platinum Band Formation

The loss of electrochemical active surface area (ECSA) at the cathode is one of the main causes of performance degradation in Polymer Electrolyte Membrane Fuel Cells (PEMFCs). In order to investigate the catalyst degradation and the influence of the operating conditions we develop a multiscale degradation model which includes the formation and reduction of platinum oxides, platinum dissolution, particle growth due to Ostwald ripening, platinum ion transport through the ionomer and platinum band formation in the membrane. This degradation model is coupled with a 2D PEMFC performance model and predictions regarding ion concentration, ECSA evolution and particle growth are validated with dedicated experiments and literature data. Degradation under several AST protocols and under steady state operation are compared and discussed. The importance of a spatially resolved catalyst degradation model is conveyed by the occurrence of a depletion zone in the catalyst layer close to the membrane due to the platinum migration into the membrane. By comparing the correlation between platinum mass loss in the catalyst layer and the ECSA loss we conclude that catalyst degradation under AST conditions with nitrogen is not representative for the degradation under normal operation.

Stomatocyte structural color-barcode micromotors for multiplex assays.

Artificial micromotors have a demonstrated value in the biomedical area. Attempts to develop this technology tend to impart micromotors with novel functions to improve the values. Herein, we present novel structural color-barcode micromotors for the multiplex assays. We found that, by rapidly extracting solvent and assembling monodispersed nanoparticles in droplets, it could form stomatocyte colloidal crystal clusters, which not only showed striking structural colors and characteristic reflection peaks due to their ordered nanoparticles arrangement, but also provided effective cavities for the integration of functional elements. Thus, the micromotors with catalysts or magnetic elements in their cavities, as well as with the corresponding structural color coding, could be achieved by using the platinum and ferric oxide dispersed pre-gel to fill and duplicate the stomatocyte colloidal crystal clusters. We have demonstrated that the self-movement of these structural color-barcode micromotors could efficiently accelerate the mixing speed of the detection sample and greatly increase the probe–target interactions towards faster and more sensitive single or multiplex detection, and the magnetism of these barcode micromotors enables the flexible collection of the micromotors, which could facilitate the detection processes. These features make the stomatocyte structural color-barcode micromotors ideal for biomedical applications.

Mixed Platinum–Nickel Catalysts of Oxygen Reduction

A mixed catalyst based on platinum and nickel oxide was obtained as a result of the synthesis and subsequent alkaline hydrolysis of thin polymer films of poly[Ni(Salen)] with platinum nanoparticles previously electrodeposited in its pores. The efficiency of catalyst operation was tested in oxygen electroreduction in an alkaline medium. A distinction of the catalyst is its high activity and tolerance to methanol impurities compared with commercial analogs.

Study on the Gilbert damping of polycrystalline YIG films with different capping layers

This paper describes the effect of 5-nm thick platinum (Pt), aluminum (Al) and silicon oxide (SiOx) capping layers on the static and dynamic magnetic properties of 400-nm thick polycrystalline YIG films deposited on a Pt buffer layer. Both static and dynamic magnetic properties of Pt capped YIG film are totally different among all YIG films. Namely, the squareness of the magnetization curve for Pt capped YIG film increases, indicating that Pt capped YIG film is magnetically softer than other YIG films. Interestingly, the effective Gilbert damping parameter of Pt capped YIG films is about four times as large as those of other YIG films, and its value is approximately 9.52 × 10−4. However, the value of Gilbert damping is 2.55 × 10−4, 3.46 × 10−4 and 3.85 × 10−4 respectively for no capping, SiOx capping and Al capping samples respectively. This huge change in Gilbert damping parameter is mainly originating from the spin pumping effect, which arises at the interface of a material having strong spin orbit interaction such as Pt. Moreover, the enourmous increase in the value of effective anisotropic field and decrese in effective saturation magnetization indicates interface anisotropy is induced in Pt capped sample. These results suggest that the static and dynamic magnetic properties of YIG film can be controlled by selecting an appropriate capping layer.