Oxidation Of Pt Research Articles

Improved catalytic NO oxidation over Pt supported on sulfuric acid treated TiO2

Promoting the formation of metallic Pt over the catalysts is the key to improving the NO reactivity. In general, TiO2 suppresses the oxidation of Pt by surface acidity and induces the formation of the metallic phase of Pt by Pt-Ti interaction. However, the limited number of acidic sites (–OH) contributes to the formation of large Pt particles, which may lead to the formation of Pt2+ or Pt4+, resulting in performance degradation. In this study, we further formulated the acidic sites of the TiO2 with sulfuric acid treatment (SA-TiO2) to improve catalytic NO oxidation. During the SA treatment, the TiO2 surface is positively charged by the low pH, providing an environment for well-distributed sulfate. In the subsequent introduction of Pt, the increase in acidic sites for Pt adsorption greatly enhanced the dispersion of Pt. During this process, Pt formed bonds with sulfate as [Pt(NH3)4]-SO4. The surface species combined with SO4 and NH3 were decomposed during the calcination process, thereby inhibiting the oxidation of Pt, which promotes the formation of metallic Pt. As a result, highly reactive Pt0 and Pt2+ were further formulated by increasing the acidic sites of SA-TiO2, where the low-temperature NO oxidation performance was improved, regardless of the Pt loading (0.3 to 3 wt.%).

Co-effect of perchlorate anions and hydrated protons on the electrochemical formation of Adams’ catalyst

The structure and morphology of oxide on the metal electrodes are strongly linked with the activity and stability of the electrocatalysts. Herein, the novel co-effect of anion and hydrated proton on structure of PtO2 formation is observed during the oxidation of water on Pt(100) preferentially oriented nanoparticles with in situ Raman spectroscopy and XPS. Higher concentrations (≥1.5 M) of non-specifically adsorbed perchlorate in 0.1 M perchloric acid solution facilitated the formation of crystalline α−PtO2 during the electro−oxidation of Pt(100), and no crystalline α−PtO2 was obtained without acid. Higher acidity electrolyte solution favors the formation of crystalline α–PtO2, indicating that proton plays a key role since specifically adsorbed sulfate without sulfuric acid did not lead to the formation of crystalline α–PtO2. A model containing anions, protons, and water molecules co-adsorbed on the Pt surface is constructed during density functional theory (DFT) calculations, which well explains the formation of crystalline α–PtO2 depending on anion and proton. The study findings provide an alternate approach for environmentally friendly and controllable preparation of Adams’ catalyst and an atomic–level understanding of oxide formation on Pt electrodes, which is essential for developing the next–generation electro-catalyst with exceptional performance and stability.

Localized Surface Modification during Alternating Current Scanning Electrochemical Microscopy: Origin and Mechanism

In the current study, we report for the first time the observation of unintended localized surface modification on commercially pure aluminum (Al) during an alternating current scanning electrochemical microscopy (AC-SECM) analysis, its origin, and the probable mechanism responsible for it. Application of an AC perturbation potential (∼100 mV amplitude at ∼100 kHz frequency) to the Platinum ultramicroelectrode (Pt UME), during AC-SECM in acidic, neutral chloride, tap water, and alkaline electrolytes was found to cause surface modification on the scanned region of Al. An increase in the local pH of the electrolyte between the UME and the Al substrate, irrespective of the electrolyte pH (3–11) and UME biasing conditions, led to the local surface modification. The reason for the enhancement of local pH is attributed to the occurrence of higher rates of cathodic reduction reactions than that of anodic oxidation reactions. The reduction of dissolved oxygen/protons/water in the electrolytes led to the generation or consumption of OH−/H+ ions, respectively, and thus increased the pH, whereas the oxidation of Pt UME/Al surfaces decreased the pH with the generation of H+ or consumption of OH− ions. These results contribute significantly to accurately analyzing Al and its alloys using the AC-SECM technique.

Surface Extraction Process During Initial Oxidation of Pt(111): Effect of Hydrophilic/Hydrophobic Cations in Alkaline Media.

The surface oxidation states of the metal electrodes affect the activity, selectivity, and stability of the electrocatalysts. Oxide formation and reduction on such electrodes must be comprehensively understood to achieve next-generation electrocatalysts with outstanding performance and stability. Herein, the initial electrochemical oxidation of Pt(111) in alkaline media containing hydrophilic and hydrophobic cations is investigated by X-ray crystal truncation rod (CTR) scattering, infrared (IR) spectroscopy, and nanoparticle-based surface-enhanced Raman spectroscopy (SERS). Structural determination using X-ray CTR revealed surface buckling and Pt extraction at the initial stage of surface oxidation, depending on the cationic species. Vibrational spectroscopy is performed to identify the potential- and cation-dependent formation of three oxide species (IR-active OHad, Raman-active OHad/Oad(H2O), and Raman-active Oad). Hydrophilic alkali metal cations (Li+) inhibit surface roughening via irreversible oxide formation. Hydrophilic Li+ can strongly stabilize IR-active OHad, hindering the extraction of Pt surface atoms. Interestingly, bulky hydrophobic cations such as tetramethylammonium (TMA+) cation also reduce the extent of irreversible oxidation despite the absence of IR-active OHad. Hydrophobic TMA+ inhibits the formation of Raman-active OHad/Oad(H2O) associated with Pt extraction. In contrast, the moderate hydrophilicity of K+ has no protective effect against irreversible oxidation. Moderate hydrophilicity enables the coadsorption of Raman-active OHad/Oad(H2O) and Raman-active Oad. The electrostatic repulsion between Raman-active OHad/Oad(H2O) and neighboring Raman-active Oad promotes Pt extraction. These results provide insights into controlling the surface structures of electrocatalysts using cationic species during the oxide formation and reduction processes.

Low platinum loading electrocatalyst supported on a carrier derived from carbon dots doped ZIF-67 for the ORR and zinc-air batteries.

The development of economical and efficient platinum-based catalysts for the oxygen reduction reaction (ORR) is considered the most promising strategy for the widespread application of clean energy conversion devices. Herein, Co nanoparticles encapsulated in N-doped carbon carriers, CoCN(CDs-X), were constructed by pyrolyzing carbon dots (CDs) doped ZIF-67 and further used to anchor Pt to prepare low Pt loading catalysts, PtCoCN(CDs-X). The introduction of CDs not only improves the conductivity for efficient electron transfer, but also regulates the interaction between Pt and the CoCN(CDs-X) support and alleviates the oxidation of Pt. The optimized PtCoCN(CDs-0.10) displays decent ORR behavior with onset and half-wave potentials of 0.95 V and 0.83 V, respectively, in alkaline media and superior catalytic stability and methanol tolerance. While employing PtCoCN(CDs-0.10) as a cathode catalyst for an as-assembled zinc-air battery (ZAB), it delivers an excellent power density of 194.2 mW cm-2 and exceptional operation stability, which is indicated by a voltage efficiency loss of only 7.7% after a long cycle life of 100 h, demonstrating its great potential applications.

Exploring the Degradation Mechanism on PtxCoy Alloy Catalysts for Oxygen Reduction Reaction by Operando X-Ray Absorption Spectroscopy

At present, alloying the Pt with 3d-transition metal, such as Co, has been demonstrated as an efficacious approach in enhancing the activity of the cathodic catalysts and diminishing the cost of Pt through ligand effect and strain effect. However, these catalysts were facing with a substantial challenge of the limited durability, primarily attributed to the leaching of the 3d-transition metal under the rigorous electrochemical conditions for the proton exchange membrane fuel cells (PEMFCs)[1]. Herein, we applied both operando conventional XAS and high energy resolution fluorescence detection (HERFD) XAS to identify the electro-chemical behaviors of subsize (about 2.5 nm) PtxCoy alloy catalysts with different Co content and associated with the Pt1Co3@Pt core-shell (CS) nanostructure catalysts obtained by simple displacement reaction. We find that the introduction of Co helps to modify the structure of PtCo alloy catalysts and benefit the activity, however, the increase content of Co brings to the heavier oxidation of Pt, which accelerate the degradation of the PtCo alloy catalysts. While the structure with Pt-rich shell suggested a high tolerance to the Pt oxidation which benefits both stability and activity. Based on these findings, we demonstrate the significance of designing PtCo CS nanostructure with high Co content to achieve optimal performance in PEMFCs. Our research provides valuable insights in designing the catalysts combined with operando XAS analysis and paves the way for the development for the large-scale application for PEMFCs. For the typical synthesis of PtCox alloy catalysts, the Pt(acac)2 and Co(acac)3 were used as Pt and Co precursors. 4mL ethanol was added to the pre-mixed Pt and Co precursors and heated up to 60 °C with magnetic stirring. After the precursors completely dissolved, certain amount of Vulcan 72 was added into the solution. Then repeat ultrasonication and magnetic stirring in 60 °C until the solution converted into slurry statement, dried the product in 30 °C over night. Next, the above well-milled products were treated at 700 °C for 2h in Ar atmosphere to transfer into alloy particles. According to the introduced ratio between Pt and Co, the catalysts were noted as Pt3Co1, Pt1Co1, and Pt1Co3. The contribution of CS nanostructure of Pt1Co3 was applied by simple displacement reaction using H2PtCl6 solution as Pt source. The production was annealed in H2 for 30 min. Operando conventional XAS (at BL36XU in Spring 8) was performed to investigate the electronic statement and structure changes during the operation. Operando HERFD XAS (at BL39XU in Spring 8) further identified the formation of metal Pt with chemisorbed O and Pt oxidation during the polarization varying different Co content and Pt-rich shell. The electronic performance of PtCo alloy catalysts was evaluated in rotating disk electrode, gas diffusion electrode, and membrane electrode assembly, which exhibited a higher performance (about 5 times higher than Pt/C) for Pt1Co3@Pt catalyst. Fig. 1a shows the STEM mapping results for Pt1Co3@Pt catalysts, the linear scanning profile is shown in the mix-image, and the signal intensity between the Pt L-edge and Co K-edge indicates the Pt-rich shell and Pt and Co core structure, which suggested the successful synthesis of Pt-rich shell with high Co content. To further analyze the electronic-behavior for the catalysts, the operando HERFD-XAS analysis was performed on Pt1Co3 and Pt1Co3@Pt catalysts, which provides a higher signal-to-noise ratio and detailed information about the electronic statement of Pt atom[2]. As shown in Figure 1b and c, the main Pt L3-edge white line intensity continuously increased and positively shifted, which suggested the increasing coverage of chemisorbed O or OH onto the Pt surface and the generation of oxidic component at high polarization potential for Pt1Co3 catalyst. While less changes were shown in Pt1Co3@Pt catalyst, which implied the formation of Pt-rich shell could help to suppress the oxidation of Pt in PtCo alloy catalysts and benefit the catalytic performance.

Effect of Electrolyte Ions on Crystalline/Amorphous α-PtO2 Formation in the Electrocatalytic Oxidation of Pt(100) Preferentially Oriented Nanoparticles

Effect of Electrolyte Ions on Crystalline/Amorphous α-PtO₂ Formation in the Electrocatalytic Oxidation of Pt(100) Preferentially Oriented Nanoparticles

Local environmental engineering for highly stable single-atom Pt1/CeO2 catalysts: first-principles insights

Single-atom Pt1/CeO2 catalysts may cope with the high cost and durability issues of fuel cell electrocatalysts. In the present study, the stability and underlying interaction mechanisms of the Pt1/CeO2 system are systematically investigated using first-principles calculations. The Pt adsorption energy on CeO2 surfaces can be divided into chemical interaction and surface deformation parts. The interaction energy, mainly associated with the local chemical environment, i.e. the number of Pt-O bonds, plays a major role in Pt1/CeO2 stability. When forming a Pt-4O configuration, the catalytic system has the highest stability and Pt is oxidized to Pt2+. An electronic metal-support interaction mechanism is proposed for understanding Pt1/CeO2 stability. In addition, our calculations show that the Pt1/CeO2(100) system is dynamically stable, and the external O environment can promote the further oxidation of Pt to Pt n+ (2 ≤ n < 4). The present study provides useful guidance for the experimental development of highly stable and efficient electrocatalysts for fuel cell applications.

A Structural Model for Transient Pt Oxidation during Fuel Cell Start-up Using Electrochemical X-Ray Photoelectron Spectroscopy

Potential spikes during the start-up (SU) and shutdown (SD) of fuel cells are a major cause of platinum (Pt) electrocatalyst degradation, which limits the lifetime of the device. The electrochemical oxidation of Pt that occurs on the cathode during the potential spikes plays a key role in this degradation process. However, the composition of the oxide species formed, as well as their role in catalyst dissolution remains unclear. In this study, we employ a special arrangement of XPS (X-ray Photoelectron Spectroscopy), in which the Pt electrocatalyst is covered by graphene, making the in situ examination of the Pt oxidation/reduction under wet conditions possible. We use this assembly to investigate oxidation state changes of Pt within fuel cell relevant potential window. We show that above 1.1 VRHE, a mixed Ptδ+/Pt2+/Pt4+ surface oxide is formed, with an average oxidation state that gradually increases as the potential is increased. By comparing a model based on the XPS data to the oxidation charge measured during potential spikes, we show that our description of Pt oxidation is also valid during the transient conditions of fuel cell SU/SD. This is due to the rapid Pt oxidation kinetics during the pulses. As a result of the irreversibility of Pt oxidation, some remnants of oxidized Pt remain at typical fuel cell operating potentials after a pulse. Figure 1

Pt-based Rare Earth Alloy as Efficient and Robust Electrocatalyst for High-temperature Proton Exchange Membrane Fuel Cells.

High-temperature proton exchange membrane fuel cells (HT-PEMFCs) are crucial in future energy system. However, the activity and stability of the electrocatalysts are severely restricted by high temperature and phosphoric acid poisoning. Herein, PtCe alloy as oxygen reduction reaction (ORR) electrocatalyst for HT-PEMFCs exhibits fantastic performance. Ce can increase the electronic density of Pt weakening phosphoric acid poisoning and improving ORR activity. The optimized electronic structure can also reduce the dipole effect between Pt and O, which suppresses the irreversible oxidation of Pt. Additionally, the dramatically negative heat of formation in PtCe catalyst brings high kinetic barrier of metal diffusion and dissolution. With this electrocatalyst, the HT-PEMFCs show a preeminent peak power of 605 mW cm-2 with 0.3 mgPt cm-2. After 30000 cycles of accelerated stability test, the peak power density only decreases by 31.6 %, achieving the goal of Department of Energy in 2020 (＜40 % loss).

Synergistic Au passivation and prolonged aging optimization enhance the long-term catalytic stability of porous YSZ/Pt electrodes

The catalytic activity of an oxygen-pumping electrode is very important to the performance of amperometric NOx (NO and NO2) sensors. To enhance the stability of electrochemical NOx sensors based on Pt electrodes, we fabricated sensitive electrodes of Pt-based materials doped with small and different Au contents on 8% mol Y2O3-stabilized ZrO2 (8YSZ) solid electrolyte substrates by screen printing and high-temperature co-firing. The effects of Au on the porous Pt electrode’s catalytic activity and long-term stability were investigated, and the results are as follows. First, the catalytic capacity of the Pt–Au alloy electrode decreases with increasing Au content due to the inhibition of the oxygen adsorption on Au, which decreases the amount of oxygen participating in the reaction at triple-phase boundaries (TPBs). Second, the catalytic ability of the alloy electrode decreases exponentially with aging time due to the reduction in the length of TPBs caused by the significant reduction in the number of holes in the electrode, and the oxidation of Pt. In addition, the conductivity decay rate of the electrode decreases with increasing Au doping. This indicates that Pt-based electrodes doped with varying Au contents, long-term, and high-temperature aging have notably regular effects on the catalytic activity of oxygen-pumping electrodes, for which we have developed a model of Au passivation and the synergistic effect of aging time on the activity of Pt-based oxygen-pumping electrodes.

Anchoring a Pt-based alloy on oxygen-vacancy-defected MXene nanosheets for efficient hydrogen evolution reaction and oxygen reduction reaction.

Rational design and controllable synthesis of Pt-based materials with intimate interfacial contact open up the possibility for boosting the performance of the ORR (oxygen reduction reaction) and HER (hydrogen evolution reaction). However, it is still challenging to prevent the oxidation of Pt during the formation of alloys and to clarify the interfacial synergistic effects on the catalytic performance between Pt alloys and the dispersed substrate. Herein, the wet chemical stripping and intercalation methods were employed to synthesize a two-dimensional (2D) MXene with abundant defect sites, which can anchor Pt3Co/Pt3Ni nanoparticles and prevent the oxidation of Pt during the process of atomic rearrangement at high temperatures. The obtained Pt3Co/MXene and Pt3Ni/MXene displayed different phase compositions and alloying degrees on adjusting the annealing temperature. Electrochemical test results showed that the optimized HER and ORR electrocatalytic activities occurred at 700 °C. Compared with Pt3Ni/MXene-700, Pt3Co/MXene-700 exhibited an HER overpotential of 1.3 mV at a current density of 10 mA cm-2, and a Tafel slope of 27.11 mV dec-1 in 0.1 M HClO4 solution. Furthermore, Pt3Co/MXene-700 exhibited an ORR half-wave potential of 0.897 V, and a mass activity of 241.1 mA mg-1Pt in 0.1 M HClO4 solution. This can be attributed to the formation of intermetallic compounds in Pt3Co/MXene. The electronic structure analysis showed that the enhanced performance could be assigned to the electron-capturing capability of the MXene, less oxidation of Pt and synergistic interactions between the Pt alloy and the MXene substrate. These findings provide a new strategy for the synthesis of highly active HER/ORR catalysts and broaden the way for the design of MXene-based catalysts.

Unraveling the role of introduced W in oxidation tolerance for Pt-based catalysts via on-line inductive coupled plasma-mass spectrometry

Water electrolysis cells and fuel cells have attracted considerable attention because they provide renewable and sustainable energy conversion and storage systems. Pt is the best catalyst for these two devices. However, cathodic Pt dissolution can occur after the oxidation of Pt, degrading the Pt catalyst. We report a PtW/C catalyst with high oxidation tolerance under repeated reverse-potential tests. The prepared PtW/C catalyst possesses higher oxidation tolerance than does the commercial Pt/C catalyst under repeated reverse-potential tests while showing comparable catalytic activity. From a combination of on-line inductively coupled plasma-mass spectrometry (ICP-MS) and ex-situ spectroscopy, we suggest that cathodic Pt dissolution is significantly inhibited because the introduced W suppresses the oxidation of Pt in PtW/C. However, W is dissolved in PtW/C rather than in Pt, indicating the need for further research. Our study demonstrates a new perspective for developing Pt-based catalysts with high oxidation tolerance by reducing cathodic Pt dissolution.

Improved immunotherapy for gastric cancer by nanocomposites with capability of triggering Dual-Damage of Nuclear/Mitochondrial DNA and cGAS/STING-Mediated innate immunity

Immune checkpoint inhibitors-based cancer immunotherapy is yielding great clinical benefit, but its efficacy is limited in gastric cancer (GC) by the lack of T-cell infiltration in the tumor microenvironment. Notably, activating the DNA-sensitive cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS/STING) signaling pathway could trigger innate immunity and recruitment of tumor-infiltrating lymphocytes. Herein, we constructed co-loaded platinum nanoparticles (Pt-NPs; chemo-prodrugs) and IR820 (photosensitizer) into hollow mesoporous organosilica nanoparticles (termed as HMON@IR820/Pt-NPs). The HMON@IR820/Pt-NPs exhibit appropriate size distribution, good biocompatibility, and generate reactive oxygen species under mild near infrared irradiation (0.7 W cm−2). Importantly, HMON@IR820/Pt-NPs efficiently enter GC cells and release loaded drugs. Pt-NPs can trigger H2O2 decomposition to O2, enhancing photodynamic efficiency. Furthermore, IR820 could enter into mitochondria, then induce mitochondria oxidative stress disorder, resulting in the releasing of oxidative mitochondrial DNA (mitoDNA). Meanwhile, this oxidative process also allowed for oxidation of Pt(0) to cytotoxic Pt(II), resulting in the dysfunction of nuclear DNA (nDNA). Dual-damage to nDNA and mitoDNA activates the c-GAS/STING pathway, stimulating innate immunity, including a primary anti-tumor effect and recruitment of CD8+ T cells, enhancing cross-presentation inside dendritic cells, and sustaining lethality in distant tumors. In summary, HMON@IR820/Pt-NPs have the potential to improve immunotherapy efficacy in GC.

Hydroxylation of Platinum Surface Oxides Induced by Water Vapor.

With its high stability and well-tuned binding strength for adsorbates, platinum is an excellent catalyst for a wide range of reactions. In applications like car exhaust purification, the oxidation of hydrocarbons, and fuel cells, platinum is exposed to highly oxidizing conditions, which often leads to the formation of surface oxides. To reveal the structure of these surface oxides, the oxidation of Pt in O2 has been widely studied. However, in most applications, H2O is also an important or even dominant part of the reaction mixture. Here, we investigate the interaction of H2O with Pt surface oxides using near-ambient-pressure X-ray photoelectron spectroscopy. We find that reversible hydroxylation readily occurs in H2O/O2 mixtures. Using time-resolved measurements, we show that O–OH exchange occurs on a time scale of seconds.

Electrochemical oxidation of Pt(111) beyond the place-exchange model

Oxide formation plays an important role in the degradation of Pt electrocatalysts. However, the exact oxide structure and reaction mechanism are not fully understood. Here, we used in situ surface X-ray diffraction experiments to resolve the oxide formation at a Pt(111) model electrode at potentials near the onset of the oxygen evolution reaction. Fast experiments are possible by using X-ray photons with a high kinetic energy in combination with a large 2D detector. By employing very low potential sweep rates we obtain a more ordered oxidized surface compared to literature data from potential step experiments. This demonstrates that the oxidation process is strongly governed by the reaction kinetics. The increased surface order enables us to disentangle two subsequent oxidation process; initially the place-exchange process, followed by the formation of a partially disordered oxide in which still 50% of the surface atoms reside on sites commensurate to the Pt(111) surface. The reduction experiments indicate that the place-exchange process is structurally reversible, whereas the disordered oxide causes the surface roughening observed during potential cycling. Despite the increased surface order, oxide superstructures are not observed. These results provide important insights in the oxidation and degradation process of Pt(111), which are valuable for the design of improved electrocatalysts and they rationalize operating procedures.

Evaluation of functional layers thinning of high temperature polymer electrolyte membrane fuel cells after long term operation.

The operation related degradation processes of high temperature polymer electrolyte membrane fuel cell operated with hydrogen-rich reformate gas are studied. CO impurities from the reformate gas are strongly adsorbed by the catalyst surface, leading to poisoning and thus, reduction of the overall performance of the cell. Most of the studies are performed in a laboratory set-up by applying accelerated stress tests. In the present work, a high temperature polymer electrolyte membrane fuel cell is operated in a realistic configuration for 12 000 h (500 days). The fuel cell contains as electrocatalyst Pt in the cathode and a Pt-Ru alloy in the anode. The study of the degradation occurring in the functional layers, i.e. in different regions of cathode, anode and membrane layer, is carried out by scanning electron microscopy, (scanning) transmission electron microscopy and energy dispersive X-ray spectroscopy. We observed a thinning of the functional layers and a redistribution of catalyst material. The thinning of the cathode side is larger compared to the anode side due to harsher operation conditions likely causing a degradation of the support material via C corrosion and/or due to a degradation of the catalyst via oxidation of Pt and Ru. A thinning of the membrane caused by oxidation agents is also detected. Moreover, during operation, catalyst material is dissolved at the cathode side and redistributed. Our results will help to design and develop fuel cells with higher performance.

Pt Deposits on Bi-Modified Pt Electrodes of Nanoparticle and Disk: A Contrasting Behavior of Formic Acid Oxidation

This work presents a contrasting behavior of formic acid oxidation (FAO) on the Pt and Bi deposits on different Pt substrates. Using irreversible adsorption method, Bi and Pt were sequentially deposited on Pt electrodes of nanoparticle (Pt NP) and disk (Pt disk). The deposited layers of Bi and Pt on the Pt substrates were characterized with X-ray photoelectron spectroscopy, transmission microscopy and scanning tunneling microscopy. The electrochemical behaviors and FAO enhancements of Pt NP and Pt disk with deposited Bi only (i.e., Bi/Pt NP and Bi/Pt disk), were similar to each other. However, additional deposition of Pt on Bi/Pt NP and Bi/Pt disk (i.e., Pt/Bi/Pt NP and Pt/Bi/Pt disk) changed the electrochemical behavior and FAO activity in different ways depending on the shapes of the Pt substrates. With Pt/Bi/Pt NP, the hydrogen adsorption was suppressed and the surface oxidation of Pt was enhanced; while with Pt/Bi/Pt disk, the opposite behavior was observed. This difference was interpreted as a stronger interaction between the deposited Bi and Pt on Pt NP than that on Pt disk. The FAO performance on Pt/Bi/Pt NP is much better than that on Pt/Bi/Pt disk, most likely due to the difference in the interaction between the deposited Pt and Bi depending on the shapes of Pt substrates. In designing FAO electrochemical catalysts using Pt and Bi, the shape of a Pt substrate was concluded to be critically considered.

Ceria supported platinum catalyst for CO oxidation reaction: Importance of metallic active species ― Commemorating the 100th anniversary of the birth of Academician Guangxian Xu

Ceria supported platinum catalyst has now been widely studied due to its excellent activity for CO oxidation. However, the electron state of active metal center is still an open question. In this work, a ceria nanorod support was prepared and platinum (Pt) with 0.9 at% was deposited using an impregnation method to obtain Pt/CeO2 catalyst. With the help of “light-off” experiment and temperature-programmed reduction under CO (CO-TPR) test, the conclusion is proposed that the process of hydrogen reduction can enhance the activity of CO oxidation reaction for the generation of optimal active Pt site. An innovative near-situ X-ray absorption fine structure (XAFS) technique was used to investigate the chemical state of central Pt atom during the reaction process, clearly demonstrating that the high oxidized state of Pt does harm to the activity for CO oxidation while the relatively reductive Pt exhibits high activity, and the different oxidized state and chemical environment of Pt during every process has been identified. Furthermore, the activity of our Pt/CeO2 catalyst is superior to that of most of the previous reports about CO catalytic oxidation by Pt based catalyst. Moreover, the optimal active species (Pt–O4) have been identified after hydrogen reduction, which could be a possible key strategy to control the oxidation of Pt.

The Cyclic Hot Corrosion Behavior of Pt–Al–7%YSZ Coating

In this study, the microstructure and cyclic oxidation of Pt–Al–7%YSZ thermal barrier coating applied on Rene-80 superalloy were investigated after Type I hot corrosion. The field emission scanning electron microscope and X-ray diffraction were used to evaluate the microstructure and phase identification, respectively. Na2SO4 was added to the surface of the coating for hot corrosion tests. The tests were carried out by the repeated cycles of heating at 900 °C for 30 and 60 min and rapid cooling to 400 °C in 10 min. Before the cyclic hot corrosion test, the specimens were coated with the platinum electroplating, high-activity low-temperature aluminizing, and the thermal spray of 7% yttria-stabilized zirconia (YSZ), respectively. The results showed that the cyclic hot corrosion mechanisms were the basic fluxing of primary thermally grown oxide (TGO), the formation of chromia, spinel and nickel oxides (C.S.N oxides) and Ni–Cr perovskites on the oxide scale. The type I cyclic hot corrosion resistance of Pt–Al–7%YSZ coating decreased with the number of thermal cycles due to a decrease in Al, an increase in Cr concentration, and increase in the volume fraction of C.S.N oxides and Ni–Cr perovskites in the oxide scale. As the number of thermal cycles increased, the oxide scale growth stresses and thermal mismatch stresses increased, leading to TBC degradation by the rumpling and ratcheting mechanisms in the Pt–Al/TGO interface. However, in lower thermal cycles, internal hot corrosion, and the formation of Kirkendall pores at the substrate/Pt–Al interface caused TBC degradation.