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To obtain fundamental insights into the performance of polymer electrolyte membrane (PEM) fuel cells, we perform a parallel investigation of the influence of platinum surface oxide (PtO) formation on the electrocatalytic activity toward the oxygen reduction reaction (ORR) for a polycrystalline platinum electrode in comparison with a commercial PEM fuel cell. PtO is formed by holding both systems at a constant potential for a given period of time. Conditioning potentials between 0.5 and 1.0 V versus SHE and conditioning times from 5 s up to 10 h are explored, respectively. We find that the voltage difference of the ORR between the oxidized and oxide‐free states depends on both the conditioning potential as well as the conditioning time at a given potential and furthermore increases with the applied target current. The change of the voltage loss over time, the so‐called voltage loss rate α, shows a maximum at potentials between 0.85 and 0.9 V and increases with increasing current density. We discuss various hypotheses to explain these findings obtained by linear voltammetry, Tafel slope analysis, Auger electron spectroscopy, and atomic force microscopy experiments. Finally, we conclude that the voltage loss rate is influenced by changes in the relative electrocatalytic activity of different crystal facets for the ORR as the oxide coverage varies. [ABSTRACT FROM AUTHOR]

Plasmonic optical trapping is a new approach that can potentially overcome some of the limitations associated with conventional optical trapping. Plasmonic tweezers generate heat because of the absorption of light at the surface of metals, and this is one of the contributions to the failure of stable trapping. Heating problems and the trapping forces tend to differ with the geometry of the plasmonic structures. Nanodisk structures can generally deliver stronger trapping forces than nanohole structures. However, the nanodisk structures also lead to greater heat generation, which can cause the medium to boil and eventually produce bubbles that can potentially push trapped particles away from the trap. Concentrated local heat can also melt the plasmonic features or instantaneously vaporize the medium. In this paper, we have closely examined this heat generation problem for two typical plasmonic structures, nanodisks and nanoholes, and provided a detailed analysis. For identical force generations, it is shown that the nanohole structures exhibit less heat generation. [ABSTRACT FROM AUTHOR]

We investigated the influence of compressive surface strain on the progression of oxygen reduction reaction (ORR) on Pt(111) surface using the density functional theory (DFT) calculation method. Specifically, we calculated the binding energies of all the chemical species possibly involved in ORR and the reaction energies (heat of reaction and activation energy) of all the possible ORR elementary reactions on the Pt(111) surfaces with - 2% and - 3% strain. Our DFT results indicate that all the ORR species bind more weakly on the compressively strained surfaces than on an unstrained surface owing to strain-induced d-electron band broadening. Our DFT calculations further predict that both OOH dissociation and HOOH dissociation pathways could be active for ORR on the Pt(111) surface with compressive strain between - 2% and -3%. Moreover, the activation energies of the ORR ratedetermining steps on the compressively strained Pt(111) surfaces were found to be lower than that on the unstrained Pt(111) surface. It was thus inferred that a - 2% to - 3% surface strain could lead to enhanced ORR activity on the Pt(111) catalysts. Consequently, our study suggests that tuning surface strain is an effective way to improve the performance of Pt-based electrocatalysts for ORR. [ABSTRACT FROM AUTHOR]

We report on density functional theory (DFT)-GGA (generalized gradient approximation) computed adsorption energetics of water and the water-related fragments OH, O, and H on stepped Pt surfaces in the low coverage limit. The Pt(100) step edge as encountered on Pt(533) shows increased binding for all species studied, while the Pt(110) step edge, as found on Pt(553) shows only significantly enhanced binding for O and OH. Comparing these results to ultra high vacuum experiments reveals that DFT can explain the main experimental trends semiquantitatively. [ABSTRACT FROM AUTHOR]

The surface morphology of chemisorbed N on the Pt(111) surface has been studied at the atomic level with low temperature scanning tunneling microscopy (STM). When N is coadsorbed with O on the surface, they form a mixed (2 × 2)-N+O structure. When the surface is covered with N atoms only, isolated atoms and incomplete (2 × 2) patches are observed at low coverages. In a dense N layer, two phases, ( √ 3 × √ 3)R30°-N and p(2 × 2)-N, are found to coexist at temperatures between 360 and 400 K. The ( √ × × √ 3)R30° phase converts to the (2 × 2) phase as temperature increases. For both phases, nitrogen occupies fcc-hollow sites. At temperatures above 420 K, nitrogen starts to desorb. The p(2 × 2)-N phase shows a honeycomb structure in STM images with three nitrogen and three platinum atoms forming a six-membered ring, which can be attributed to the strong nitrogen binding to the underlying Pt surface. [ABSTRACT FROM AUTHOR]

The adsorption of the chiral molecule lactate on the intrinsically chiral noble metal surfaces Pt(321), Au(321), and Ag(321) is studied by density functional theory calculations. We use the oPBE-vdW functional which includes van der Waals forces on an ab initio level. It is shown that the molecule binds via its carboxyl and the hydroxyl oxygen atoms to the surface. The binding energy is larger on Pt(321) and Ag(321) than on Au(321). An analysis of the contributions to the binding energy of the different molecular functional groups reveals that the deprotonated carboxyl group contributes most to the binding energy, with a much smaller contribution of the hydroxyl group. The Pt(321) surface shows considerable enantioselectivity of 0.06 eV. On Au(321) and Ag(321) it is much smaller if not vanishing. The chiral selectivity of the Pt(321) surface can be explained by two factors. First, it derives from the difference in van der Waals attraction of L- and D-lactate to the surface that we trace to differences in the binding energy of the methyl group. Second, the multi-point binding pattern for lactate on the Pt(321) surface is sterically more sensitive to surface chirality and also leads to large binding energy contributions of the hydroxyl group. We also calculate the charge transfer to the molecule and the work function to gauge changes in electronic structure of the adsorbed molecule. The work function is lowered by 0.8 eV on Pt(321) with much smaller changes on Au(321) and Ag(321). [ABSTRACT FROM AUTHOR]

• Pt{1 1 0}-(1 × 1) site identified as most active for nitrate reduction. • Linear correlation between nitrate reduction current density and number of Pt{1 1 0}-(1 × 1) active sites. • Correlation may be used to estimate number of Pt{1 1 0}-(1 × 1) sites present at polycrystalline and nanoparticle Pt surfaces. • Pt{1 1 0} structure highly sensitive to ambient cooling conditions. • CO cooling favours formation of Pt{1 1 0}-(1 × 1). • Argon, nitrogen, hydrogen and oxygen cooling favour mixed (1 × 1)/(1 × 2) disordered phases. The electrochemical reduction of nitrate anions in aqueous 0.1 M perchloric acid has been studied using Pt(S)-[n{1 1 0} × {1 1 1}] and Pt(S)-[n{1 1 0} × {1 0 0}] single crystal electrodes. It is demonstrated that the presence of Pt{1 1 0} adsorption sites is associated with a single, broad nitrate reduction peak centred at 0.18 V (RHE). Moreover, depending on the cooling environment used after flame-annealing (CO, H 2 , Ar, air, nitrogen), the surface concentration of such sites varies which in turn regulates the nitrate reduction current density achievable for a given stepped Pt{ h k l } electrode. The origin of this phenomenon is the propensity of the clean Pt{1 1 0} basal plane (and vicinal surfaces containing this plane) to reconstruct towards a stable (1 × 2) phase with strong CO chemisorption favouring formation of larger Pt{1 1 0}-(1 × 1) domains. In contrast, argon/air-cooling appears to promote the development of a largely (1 × 2) reconstructed surface which is much less active for nitrate reduction since the surface density of Pt{1 1 0}-(1 × 1) terrace sites is significantly diminished. Interestingly, hydrogen-cooling affords nitrate reduction activity intermediate between these two extremes. We suggest that under this particular preparation condition, a partially deconstructed (1 × 1) phase forms containing the "excess" 50% of surface atoms (originating from the (1 × 2) phase) sitting proud of the surface in the form of small (1 × 1) islands, together with residual (1 × 2) missing row regions. Hence, after hydrogen cooling, the nominal Pt{1 1 0} surface plane is speculated to exhibit a wider distribution of smaller terrace widths than found with CO cooling together with residual areas of (1 × 2). The weaker chemisorption of hydrogen apparently limits the size of the Pt{1 1 0}-(1 × 1) domains achievable and consequently, nitrate reduction activity is diminished. Based on these findings, it is proposed that nitrate reduction may be used as a quantitative electrochemical probe of Pt{1 1 0}-(1 × 1) sites at Pt nanoparticles in an analogous fashion to the method of ammonia electrooxidation presently used to quantify the surface abundance of Pt{1 0 0} sites. [ABSTRACT FROM AUTHOR]

Surface plasmon resonance spectroscopy (SPRS) provides insight into interfacial chemical or electrochemical processes regarding surface composition, thickness or reactivity, but is typically limited to Au, Ag or Cu surfaces that satisfy the surface plasmon resonance conditions. Here, we provide a quantitative electrochemical and SPRS study of sputtered thin film Au/Pt surfaces that allows designing hybrid films optimized for stable electrochemical Pt behavior and efficient Au plasmonic excitation. Simulations show that for a given Au layer thickness, there is an optimal Pt layer thickness that makes the corresponding Au∖Pt film perform best in the sense of SPRS angular resolution. Cyclic voltammetry data suggests that a minimum of 3 nm Pt layer thickness is required to form a pinhole-free adlayer on Au that shows Pt-like surface reactivity. As a result, the optimum Au∖Pt layer thickness combination lies in the range of 27∖3 nm for SPRS experiments on surfaces exhibiting Au optical and Pt (electro)chemical properties. The combined experimental and modelling approach paves the way for predictive design of optimized transition/nobel metal hybrid thin films for plasmon-based spectroelectrochemical applications. [ABSTRACT FROM AUTHOR]

Abstract Peroxodisulfate (PDS) reduction has been investigated by electrochemical and FTIR techniques in a wide pH range, on platinum stepped single crystals electrodes vicinal to the (111) pole. PDS reduction is a structure-sensitive reaction and proceeds on well differentiated potential regions for terrace and step sites. This fact allows gaining local information about the individual behavior of those sites. The reaction proceeds at appreciable rate in a narrow potential range, being inhibited in the low and high potential regions of the voltammogram. The inhibition of the reaction at low potentials is most likely associated with a change in the sign of the charge on the electrode, from positive to negative. Therefore, PDS reduction gives an approximate indication of the position of the potential of zero free charge (pzfc). In this way, two local values of pzfc, associated with terrace and steps sites, can be determined. Such values of local pzfc are compared with the local values of potential of maximum entropy (pme) of double layer formation deduced from laser induced T-jump experiment. Good agreement between both magnitudes is found, especially for terraces. The local pzfc on terraces shifts to more positive potentials as the terrace length diminishes, while the local pzfc for steps remains constant. The inhibition of PDS reduction at high potentials can also be related with a second inversion in the sign of the electrode charge. Therefore, PDS reduction can be used to determine a second pzfc on the (111) terraces at high potentials, revealing a non-monotonic charge – potential relationship. Spectroscopic experiments allow the identification of the species involved in PDS reduction. Highlights • Peroxodisulfate reduction is investigated on platinum stepped single crystal surfaces. • This reaction is sensitive to the crystallographic structure of the surface. • The rate of the reaction is sensitive to the local nature of the charge on the surface. • This allows detection of local values of the potential of zero free charge. • The dependence of local values of potential of zero charge on terrace length is investigated. [ABSTRACT FROM AUTHOR]

This article report microwave assisted green method for the synthesis of silver nanoparticle from Brassica oleracea var. Italica (BI) extract. The synthesized silver nanoparticle (AgNP-BI) was characterized by various analytical techniques. Here we are reporting three methods for the sensing of Ni (II) from the synthesized AgNP-BI. First one is the detection of Ni (II) ion based on changes in the absorbance resulting from the complex formation of the Ni (II) ion with AgNP-BI. The second one is the fluorescent sensing of Ni (II) ion using AgNP-BI by the changes in the fluorescence intensity. The third one is the electrochemical sensing of Ni (II) ion in which silver nanoparticle attached to the platinum electrode surface. The above-mentioned methods exhibit outstanding selectivity towards Ni (II) ion. The practical application of the AgNP-BI was also carried out for the trace determination of Ni (II) ions. The limit of detection was found to be 0.932 µM using differential pulse voltammetry (DPV). [ABSTRACT FROM AUTHOR]

Highlights • CO molecule is stably adsorbed on top of a Pt atom on the (111) Pt surface according to our DFT calculation. • The experimentally observed order of site preference for CO adsorption is reproduced in this DFT calculation. • Inclusion of van der Waals interaction is necessary for obtaining the correct order of adsorption site preference. • The calculated adsorption energy agrees very well with experimentally measured one when CO is adsorbed on top of a Pt atom. • The vdW-DF and vdW-DF2 functionals give the best results for CO adsorption on Pt(111), in terms of adsorption energy and site preference. ABSTRACT Adsorption of CO on Pt (111) surface is a well known problem due to the fact that theoretical calculations based on standard Density functional theory (DFT) fail to predict the adsorption site and energy in agreement with the experimental results. Here, we investigate the role of van der Waals interaction on the CO/Pt (111) system, using different functionals of the vdW-DF family. Our calculations show that the optimized vdW functionals such as optPBE-vdW, optB88-vdW and optB86b-vdW give a wrong order of site preference and tend to overestimate adsorption energies. We find that vdW-DF and vdW-DF2 functionals predict stable adsorption at atop site. Both these functionals give adsorption energy values and order of site preference that agree well with the experimental results. Our results demonstrate that the nature of vdW functional plays an important role in obtaining a correct description of adsorption in the CO/Pt (111) system. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

The formation of N-heterocyclic carbenes on a platinum surface is demonstrated. Surface vibrational spectroscopy measurements isolate steps in the transformation from 1,3-diisopropylbenzimidazolium hydrogen carbonate to surface carbene. As the temperature is further increased, the reactive metal transforms the isopropyl groups leading to the effective formation of a new surface carbene. [ABSTRACT FROM AUTHOR]

Highlights • KEYNOTE-021 A-C evaluated pembrolizumab + platinum chemotherapy in advanced NSCLC. • No dose-limiting toxicity occurred in any cohort at pembrolizumab 2 or 10 mg/kg. • Evidence of antitumor activity in all 3 cohorts at both pembrolizumab doses. • Pembrolizumab + platinum chemotherapy is a feasible front-line treatment strategy. Abstract Objectives Platinum-based chemotherapy for advanced non–small-cell lung cancer (NSCLC) has modest benefit overall, but has the potential to amplify immune responses. In cohorts A-C of the multicohort phase 1/2 study KEYNOTE-021 (Clinicaltrials.gov, NCT02039674), we evaluated combinations of platinum-doublet chemotherapy with the anti–programmed death 1 monocloncal antibody pembrolizumab. Materials and methods Patients with previously untreated, advanced NSCLC without EGFR / ALK aberrations were randomized to pembrolizumab 2 or 10 mg/kg Q3W plus carboplatin area under the serum concentration-time curve (AUC) 6 mg/mL/min plus paclitaxel 200 mg/m2 (cohort A, any histology), carboplatin AUC 6 mg/mL/min plus paclitaxel 200 mg/m2 plus bevacizumab 15 mg/kg (cohort B, non-squamous), or carboplatin AUC 5 mg/mL/min plus pemetrexed 500 mg/m2 (cohort C, non-squamous) for 4 cycles followed by maintenance pembrolizumab (cohort A), pembrolizumab plus bevacizumab (cohort B), or pembrolizumab plus pemetrexed (cohort C). Response was assessed by blinded independent central review. Results Overall, 74 patients were randomized; median follow-up was 21.4, 16.4, and 17.4 months in cohorts A, B, and C, respectively. No dose-limiting toxicities occurred in any cohort at either pembrolizumab dose. Most frequent treatment-related adverse events (AEs) were alopecia, fatigue, and nausea. Treatment-related grade 3/4 AEs occurred in 40%, 42%, and 46% of patients in cohorts A, B, and C, respectively; AEs with possible immune etiology occurred in 24%, 50%, and 38% of patients, respectively. Objective response rates were 48%, 56%, and 75% in cohorts A, B, and C, respectively. Conclusion Pembrolizumab in combination with carboplatin-paclitaxel and with pemetrexed-carboplatin yielded encouraging antitumor activity and toxicity consistent with known toxicities of platinum-based chemotherapy or pembrolizumab monotherapy. [ABSTRACT FROM AUTHOR]

The computational study of chemisorption of atoms and gases intends to provide a great insight in the developing of an up‐to‐date elusive assessment of a correct choice of the site for the adsorption on platinum surfaces i. e. a key step for many chemical processes in catalysis and surface sciences. A density functional theory (DFT) calculation using generalized gradient approximation (GGA) scheme and supercell model with the inclusion of modified dispersion correction (DFT−D2) has been performed to explore the adsorption trends and evaluate adsorption energies of H, C, N, O, and S (atoms) and H2, C2, N2, O2, and S2 (homonuclear diatomic molecules) on Pt(111) and Pt(100) surfaces for multiple sites, in search of the most active catalytic site. Our chemisorption data revealed that the incorporation of DFT−D2 correction strengthens the adsorption energy by the amount of 0.05 eV to 0.67 eV for atoms and gases. Finally, this study focuses on unveiling catalytic activity of the two seemingly simplest electrochemical reactions; the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) on numerous sites of Pt surfaces using the adsorption strength of H and O with the inclusion of DFT−D2 correction, which shows the good consistency with the results of standard DFT calculations. The highest catalytic activity towards HER is shown by Pt(100) in contrast to the best OER catalytic activity by Pt(111) surface with their respective most favorable 4fh and top sites. Shedding light on site‐selective binding mechanism of adsorbates on platinum surfaces with their benchmarking HER and OER catalytic activity. [ABSTRACT FROM AUTHOR]

Because of scaling effect, phase change behaviors of nano-liquid films on solid surfaces display distinct features from macroscale pool boiling. In this work, evaporation and explosive boiling of nano-liquid argon films with various film thicknesses on hydrophilic or hydrophobic platinum surfaces are investigated via molecular dynamics simulations. The simulations show that the onset of explosive boiling closely depends on the film initial thickness on both the hydrophilic and hydrophobic surfaces, and the onset temperature for explosive boiling significantly reduces with the increase of the film thickness. In addition, the simulations also demonstrate that, with the same film thickness and the same wall superheat, explosive boiling is triggered on the hydrophilic surface, while only evaporation is observed on the hydrophobic surface, indicating that a high surface wettability reduces the onset temperature, which is opposite to the prediction by classical nucleation theory and the observation in pool boiling experiments. For a thicker film and a higher surface wettability, it is found that a larger temperature gradient is generated along the film thickness direction due to the heat accumulation effect, which leads to a very high temperature occurring at the film bottom and thereby is responsible for the lower onset temperature for explosive boiling on these circumstances. [ABSTRACT FROM AUTHOR]

In this study, the interactions between H atoms and the (100), (110), and (111) surfaces of platinum have been investigated by using the London-Eyring-Polanyi-Sato (LEPS) potential function. The adsorption zones (sites) and LEPS energy values of these sites have been determined theoretically. In addition, the potential-energy surfaces for each Pt surface have been obtained in detail. Further, the adsorption sites on the surface, scattering from the surface, diffusion paths on the surface, and transition regions to the subsurface, have been determined and the differences have been examined in detail among the surfaces. From these results, it is found that an H atom has the lowest binding energy at the hollow sites on the Pt (100) and Pt (111) surfaces and that it has the lowest binding energy at the long-bridge sites on the Pt (110) surface. It has also been determined that the hollow sites on the three surfaces are the regions through which H atoms can penetrate into the subsurface. In addition, it has also been found that, for each of the three Pt surfaces, the diffusion of an H atom across the surface may follow a bridge-hollow-bridge pathway. These results are in agreement with previous experimental and theoretical results. Besides, the adsorption and diffusion manners of hydrogen atoms on each of the Pt surfaces have been analyzed deeply. [ABSTRACT FROM AUTHOR]

Although the modified Young’s equation is frequently applied to evaluate the line tension of droplets, debate concerning the value and even the sign of the line tension is ongoing. The reason for this is that the line tension defined in the modified Young’s equation is not a pure line tension but an apparent line tension, which includes the effects of the Tolman length and the stiffness coefficients. In this paper, we employ molecular dynamics (MD) to simulate three-dimensional water nanodroplets on platinum surfaces and determine their apparent line tensions by applying a linear fit to the relation of the cosine of the contact angle to the curvature of the contact line. The effects of the Tolman length and the position of the solid-liquid dividing interface on the measured line tension are investigated. On the one hand, our results elucidate the reason why MD results for line tensions are so scattered and also lend numerical support to Schimmele et al.’s theoretical predictions [“Conceptual aspects of line tensions,” J. Chem. Phys. 127, 164715 (2007)]. On the other hand, our MD simulation results demonstrate that the modified Young’s equation is a useful tool to predict the macroscopic contact angle based on a linear fit of the measured contact angles at the nanoscale. The apparent line tension is, however, sensitive to the chosen position of the solid-liquid dividing interface. [ABSTRACT FROM AUTHOR]

Galvanic exchange involving dissolution of iron and the simultaneous growth of platinum onto 316 L stainless steel was investigated for specimens manufactured by 3D-printing, and the behavior was compared to conventional stainless steel. Novel phenomena associated with the 3D-printed steel, but not conventional steel, reacting in three distinct phases were observed: first, with low platinum loading, a bright etching pattern linked to the laser-manufacturing process is revealed at the steel surface; second, a nanostructured pore pattern with platinum nano-deposits forms; and third, a darker platinum film coating of typically 500-nm thickness forms and then peels off the steel surface with further platinum growth underneath. Unlike the conventional steel (and mainly due to residual porosity), 3D-printed steel supports well-adhered platinum films for potential application in electrocatalysis, as demonstrated for alkaline methanol oxidation.ᅟ [ABSTRACT FROM AUTHOR]

The introduction of stabilizing elements, such as Au, has been recognized as an effective approach to increasing the durability of Pt electrocatalysts toward oxygen reduction reaction (ORR). However, significant tensile strain involved in this system leads to an undesirable decrease of its intrinsic ORR activity as compared to the native Pt, due to a ∼3.8% tensile strain of Pt layer on Au core. In this work, we demonstrate that for a core-shell structured Pt monolayer on nanoporous gold (NPG), electrochemical potential-cycling can induce PtAu surface alloy formation, which results in unexpected improvement of its ORR activity. Theoretical calculations suggest that PtAu surface alloys possess more suitable configurations that give relatively low changes of free energy for the corresponding overpotential-determining step during ORR relative to Pt monolayer on Au. The improved ORR performance and high utilization of Pt make the nanoporous metal-based electrodes promising for green energy technologies. [ABSTRACT FROM AUTHOR]

In this paper, the bubble nucleation of ultra-thin liquid argon film on a platinum surface is studied by molecular dynamics simulation. In the simulations, the liquid is heated by the middle part and cooled by the two sides of the platinum surface. Observation of bubble nucleation is performed after increasing the temperature of heating zone. The space and time evolution of argon density distribution and the size of bubble are monitored to investigate the nucleation processes above surfaces with and without nanostructures. The results illustrate that nanostructure surface increases the solid-liquid contacting area and the degree of surface temperature non-uniformity, which results in the enhancement of heating intensity and higher rate of nucleation. Comparisons are made among surfaces with different nanostructures, with which it is further found that the heat flux increases with the height of nanostructures. Higher nanostructure reduces nucleation duration. [ABSTRACT FROM AUTHOR]

A nanoscale thin film of niobium oxide on a platinum substrate was evaluated for its influence on the electronic and chemical properties of the underlying platinum towards the oxygen reduction reaction with applications to proton exchange membrane fuel cells. The nanoscale thin film of niobium oxide was deposited using atomic layer deposition onto the platinum substrate. A film of niobium oxide is a chemically stable and electronically insulating material that can be used to prevent corrosion and electrochemical degradation when layers are several nanometers thick. These layers can be insulating if sufficiently thick and may not be sufficient to protect the platinum from corrosion if too thin. An ∼3 nm thin film of niobium oxide was fabricated on the platinum surface to determine its influence on the electronic and chemical properties at the interface of these materials. The atomic layer deposition process enabled a precise control over the material composition, structure, and layer thickness. The niobium oxide film was evaluated using cyclic voltammetry and electrochemical impedance spectroscopy to evaluate whether a balance could be found between the inhibition of platinum degradation and electronic insulation of the platinum for use in proton exchange membrane fuel cells. The 3 nm thin niobium oxide film was found to be sufficiently thin to permit electronic conductivity while reducing the incidence of platinum dissolution. [ABSTRACT FROM AUTHOR]

First-principles density functional calculations are performed to study the adsorption behavior of Pt monolayer on the stoichiometric BiFeO 3 (0001) polar surfaces. According to our results, the Pt monolayer adsorbed on the negative BiFeO 3 (0001) surface behaves as a satisfactory epitaxial layer, while the Pt monolayer on the positive surface exhibits no epitaxial relation with the BiFeO 3 substrate. In either case, the Pt adatoms can be classified into two types: One type is the Pt adatom which binds directly to the low-lying O anion and exhibits cationic feature, the other type of Pt adatom displays anionic character with Bi or Fe cation as its nearest neighbor. Besides the distinct charge transfer effect and orbital hybridization behavior, we also predict that these two types of Pt adatoms have different effects on the surface magnetic properties. Our results provide significant implications for the magnetoelectric devices and heterogeneous catalysis based on the metal/BiFeO 3 interfaces. [ABSTRACT FROM AUTHOR]

A new iridium-based planar pH sensor for bioanalytical purposes is introduced. The fabrication of the sensor was carried out by a two-stage coating process of different iridium solutions on a platinum thick film surface. The pH response behaviour and the Nernstian characteristics of the double-layer electrode exhibited better results than the single iridium depositions. An almost theoretical Nernstian slope could be obtained as well as a pH response time of about 3 to 5 min in a pH range of 4.01 to 9.18. Furthermore, a biofilm growth of different microorganisms onto the iridium-coated electrodes could be achieved. Afterwards, the viability of the microorganisms was demonstrated via cell plating studies. [ABSTRACT FROM AUTHOR]

The nature of hydrated protons formed at water/metal interfaces is one of the most intriguing research questions in the field of interfacial chemistry. We prepared coadsorption layers of hydrogen and water on a Pt(111) surface in ultrahigh vacuum and studied the ionization of adsorbed hydrogen atoms to H+ ions by employing a combined experimental and theoretical approach. Spectroscopic evidence obtained by mass spectrometry and reflection absorption infrared spectroscopy as well as corresponding density functional theory calculations consistently show that adsorbed hydrogen atoms ionize into multiply hydrated proton species (H5O2+, H7O3+, and H9O4+) on the surface, rather than H3O+. Then, upon addition of a water overlayer, the metal-bound hydrated protons spontaneously evolve into three-dimensional fully hydrated proton structures through proton transfer along the water overlayer. The stability of hydrated protons on the Pt surface and their bulk dissolution behavior suggest the possibility that surface hydrated protons are a key intermediate in electrochemical interconversion between adsorbed H atoms and H+(aq) in water electrolysis and hydrogen evolution reactions. [ABSTRACT FROM AUTHOR]

We summarize our recent results on the oxidation of platinum surfaces, stressing the close connection between theory and experiment. The present theoretical approach is based on ab-initio quantum mechanics methods, such as density functional theory (DFT), ab-initio atomistic thermodynamics, Monte-Carlo methods and reactive molecular dynamics (RMD). Experimentally, photoelectron spectroscopy (XPS) under UHV and in-situ conditions (NAP-XPS) provides most of the discussed results. The oxidation of an extended variety of platinum surfaces is reviewed, starting from atomically flat Pt(111) over stepped surfaces to regularly shaped nanoparticles, under conditions ranging from UHV through ambient pressures up to electrochemical interfaces. [ABSTRACT FROM AUTHOR]

A Sn4+-doped double-shelled Pt/TiO2 hollow nanocatalyst (DHS-SnPt) with excellent photocatalytic H2 production efficiency was prepared successfully via a facile hydrothermal method. In the catalytic system, Pt active sites were in situ reduced by Sn2+ and showed an enhanced interaction with Sn species. The enhanced SnO2/Pt interface could accelerate the migration rate of e− from SnO2 to Pt, improving the charge separation efficiency of h+ and e−. The as prepared DHS-SnPt contained a very low Pt content (0.24 wt%) and showed the highest photocatalytic H2 production efficiency (ca. 18 496 μmol g−1 within 3 h), nearly 5.8 and 1.678 times as high as that of a pure double-shelled Pt/TiO2 hollow nanocatalyst and the traditional Sn4+ doped counterpart, respectively, demonstrating the significantly improved Pt atom utilization of DHS-SnPt in photocatalytic H2 evolution activity. On the basis of experimental results, a possible photocatalytic H2 production mechanism was proposed to explain the excellent H2 production efficiency of DHS-SnPt. [ABSTRACT FROM AUTHOR]

We have studied the adsorption of benzene on three low index surfaces of platinum using plane-wave Density Functional Theory (DFT) calculations, taking into consideration van der Waals (vdW) interaction. Experimentally, it is known that benzene adsorbs at the bridge site on the (111) surface, but in case of (110) and (100), this is not known yet. Our calculations show that benzene preferably adsorbs on bridge position on Pt(111) surface, whereas on Pt(110) and Pt(100) surfaces, the hollow position is energetically more favoured. The structural and electronic modifications of molecule and the surfaces are also examined. In all cases, adsorption-induced distortions of adsorbate-substrate complex are found to be modest in character, but relatively maximum in case of the (110) facet. The molecule is bound most strongly to the (110) surface. Importantly, we find that adsorption at bridge and atop positions are energetically feasible on the (110) surface, with the canting of benzene ring at a small angle from the metal plane. We study changes in electronic structure and the net charge transfer upon adsorption of benzene on all three low index planes. Inclusion of vdW interactions is important for obtaining realistic adsorption strengths for benzene on various Pt facets. [ABSTRACT FROM AUTHOR]

Platinum is a metal utilized in many applications. Its catalytic activity can be decreased due to chemical poisoning caused e.g. by phosphorus. To gain more understanding of its poisoning, we present a study of phosphorus adsorption on a platinum (110) single crystal surface. Using X-ray photoelectron spectroscopy, we have found that the adsorbate coverage saturates at around 3 monolayers. Annealing the phosphorus-covered platinum surface at 750 °C gives rise to three different ordered adlayer structures, with symmetries of 2 × 3, 11 × 4 and 2 × 1 , from the lowest to the highest coverage, detected with low-energy electron diffraction. We have studied the sample topography with scanning tunnelling microscopy. We also present a tentative model for the observed structures and their evolution. [ABSTRACT FROM AUTHOR]

Pulsed laser irradiation-induced reflectivity decrease of metal surfaces is a well-established phenomenon, which is extensively utilized in numerous applications. Since the stability of these black surfaces is often a demand, we investigated the resistance of darkened copper and titanium surfaces against optical and mechanical damages. For optical stability studies, samples were irradiated by a probe laser beam ( λ = 775 nm, FWHM = 150 fs, f = 1 kHz) at different fluences (0-300 mJ/cm), while the mechanical stability was studied with scratch test using 2.5 µm radius tip and applying normal force in 29.4-147 µN range. The observed reflectivity and morphological changes indicated that the optical damage threshold fluence is 130 and 160 mJ/cm for copper and titanium surfaces, respectively. Mechanical damage only in case of copper could be detected in the applied parameter range indicating a scratch hardness of 21.5 MPa. [ABSTRACT FROM AUTHOR]

Nanoparticles of Ni(OH) 2 surrounded with ultra-low Pt content and supported on functionalized carbon were prepared by a scalable synthesis method and investigated as electrocatalysts for the oxygen reduction reaction (ORR) in acidic media. The effect of altering the Pt surface composition on the Ni(OH) 2 nanoparticle core was investigated as a route to simultaneously increase the ORR activity and stability. Modifying the Pt surface composition resulted in both structural and electronic changes. Decreasing the Pt surface composition resulted in stronger Pt-Pt compressive strain and decrease in the occupancy of d-band vacancies per atom. The correlation of strain and d-vacancies with ORR activity and stability showed a Volcano-type tendency, with the 6 wt. % Pt sample showing the highest activity and stability. The electrochemical results obtained using rotating disk electrode (RDE) tests showed an enhancement of about six times higher surface and mass-normalized activity as well as improved durability compared to commercial Pt/C. These improvements were further corroborated by single cell membrane electrode assembly (MEA) tests where similar trends were observed, showing higher power densities with lower Pt loadings, in comparison with commercial Pt/C. These results show that new electrocatalysts with higher activity and stability can be obtained through precise control of the atomic-level catalyst structure. [ABSTRACT FROM AUTHOR]

In this paper, we describe the design, fabrication, and characterization of a flexible platinum temperature sensor embedded in polyimide (PI) films for temperature monitoring applications on curved surfaces, such as the skin of a human body, and various tubes and pipes. In order to optimize and enhance the properties of the flexible temperature sensors, we investigated the effects of the designed thickness (0.5, 1.0, and 1.5 µm) and length (10, 50, 100, and 150 mm) of Pt thin-film electrodes embedded in PI films on the temperature coefficient of resistance (TCR) properties and sensitivities. The average TCRs for flexible temperature sensors with different lengths but identical thicknesses of Pt thin-film electrodes were 0.0027, 0.0029, and 0.0030 °C-1 for designed thicknesses of 0.5, 1.0, and 1.5 µm of Pt thin-film electrodes, respectively. The TCRs slightly increased when the thickness of the Pt electrodes increased. Meanwhile, thinner or longer Pt electrodes led to higher sensitivity for the temperature sensors. The highest sensitivity of a fabricated flexible temperature sensor was 15.59 Ω·°C-1 in the device with a length of 150 mm and thickness of 0.5 µm. The bending effect on the change in the TCR of flexible temperature sensors, with radii of curvature of 5, 10, and 15 mm, was small. In order to confirm the performance of the fabricated flexible temperature sensor, actual skin temperatures of the palm and back of the hand were measured. [ABSTRACT FROM AUTHOR]

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To obtain a microscopic explanation on the difference of oxygen reduction reaction activity on different Pt low index surfaces, we simulated competitive adsorptions of O 2 and OH on four Pt low index surfaces. Firstly, all possible chemical adsorption configurations of the O 2 and OH molecules on the three surfaces were acquired through density functional theory. The distribution of these configurations on the different surfaces was collected from Monte Carlo simulations. Our results demonstrated that the adsorption energy order of O 2 on different surfaces was (110)(1 × 2) > (110) > (100) > (111) and that the adsorption energy order of the OH molecules on Pt surfaces was the same. Considering the competitive adsorption of O 2 and OH on Pt surfaces, the final O 2 adsorption efficiencies order of three surfaces was (111) > (110) > (100) > (110)(1 × 2), which was consistent with the experimental activities of oxygen reduction. Our study provided theoretical references for previous experimental studies and had important significance for the understanding of oxygen adsorption on Pt surfaces. [ABSTRACT FROM AUTHOR]

The modification of heterogeneous catalysts through the chemisorption of chiral molecules is a method to create catalytic sites for enantioselective surface reactions. The chiral molecule is called a chiral modifier by analogy to the terms chiral auxiliary or chiral ligand used in homogeneous asymmetric catalysis. While there has been progress in understanding how chirality transfer occurs, the intrinsic difficulties in determining enantioselective reaction mechanisms are compounded by the multisite nature of heterogeneous catalysts and by the challenges facing stereospecific surface analysis. However, molecular descriptions have now emerged that are sufficiently detailed to herald rapid advances in the area. The driving force for the development of heterogeneous enantioselective catalysts stems, at the minimum, from the practical advantages they might offer over their homogeneous counterparts in terms of process scalability and catalyst reusability. The broader rewards from their study lie in the insights gained on factors controlling selectivity in heterogeneous catalysis. Reactions on surfaces to produce a desired enantiomer in high excess are particularly challenging since at room temperature, barrier differences as low as ~2 kcal/mol between pathways to R and S products are sufficient to yield an enantiomeric ratio (er) of 90:10. Such small energy differences are comparable to weak interadsorbate interaction energies and are much smaller than chemisorption or even most physisorption energies. In this Account, we describe combined experimental and theoretical surface studies of individual diastereomeric complexes formed between chiral modifiers and prochiral reactants on the Pt(111) surface. Our work is inspired by the catalysis literature on the enantioselective hydrogenation of activated ketones on cinchona-modified Pt catalysts. Using scanning tunneling microscopy (STM) measurements and density functional theory (DFT) calculations, we probe the structures and relative abundances of non-covalently bonded complexes formed between three representative prochiral molecules and (R)-(+)-1-(1-naphthyl)ethylamine ((R)-NEA). All three prochiral molecules, 2,2,2-trifluoroacetophenone (TFAP), ketopantolactone (KPL), and methyl 3,3,3-trifluoropyruvate (MTFP), are found to form multiple complexation configurations around the ethylamine group of chemisorbed (R)-NEA. The principal intermolecular interaction is NH...O H-bonding. In each case, submolecularly resolved STM images permit the determination of the prochiral ratio (pr), pro-R to pro-S, proper to specific locations around the ethylamine group. The overall pr observed in experiments on large ensembles of KPL-(R)-NEA complexes is close to the er reported in the literature for the hydrogenation of KPL to pantolactone on (R)-NEA-modified Pt catalysts at 1 bar H2. The results of independent DFT and STM studies are merged to determine the geometries of the most abundant complexation configurations. The structures reveal the hierarchy of chemisorption and sometimes multiple H-bonding interactions operating in complexes. In particular, privileged complexes formed by KPL and MTFP reveal the participation of secondary CH...O interactions in stereocontrol. State-specific STM measurements on individual TFAP-(R)-NEA complexes show that complexation states interconvert through processes including prochiral inversion. The state-specific information on structure, prochirality, dynamics, and energy barriers delivered by the combination of DFT and STM provides insight on how to design better chiral modifiers. [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) calculations were performed to investigate hydrogen adsorption on Pt(1 0 0), (1 1 0) and (1 1 1) surfaces at different coverages. It is found that each surface has different hydrogen adsorption strength and saturated coverages, and Pt(1 1 1) surface has the weakest adsorption as well as smallest saturated coverage. Thermodynamics method was applied to include the effects of temperature and hydrogen partial pressure on the stable hydrogen coverage, where the built phase diagram clearly revealed the reaction condition dependent H concentration on the surface. The theoretically predicted hydrogen desorption temperatures are in nice agreement with available experimental results. Interestingly, the adsorption of hydrogen was also found to be able to modify the morphology of Pt catalyst based on Wulff constructions. All these calculations provide very useful information for reaction mechanism calculations, especially for the hydro-treating reactions, where hydrogen coverage on the surface has very important roles in determining the adsorption configurations of the reactants as well as the final reaction mechanisms. [ABSTRACT FROM AUTHOR]

O2 adsorption on Pt surfaces is of great technological importance owing to its relevance to reactions for the purification of car exhaust gas and the oxygen reduction on fuel-cell electrodes. Although the O2/Pt(111) system has been investigated intensively, questions still remain concerning the origin of the low O2 sticking probability and its unusual energy dependence. We herein clarify the alignment dependence of the initial sticking probability ( S0) using the single spin-rotational state-selected [( J, M)=(2,2)] O2 beam. The results indicate that, at low translational energy ( E0) conditions, direct activated chemisorption occurs only when the O2 axis is nearly parallel to the surface. At high energy conditions ( E0>0.5 eV), however, S0 for the parallel O2 decreases with increasing E0 while that of the perpendicular O2 increases, accounting for the nearly energy-independent O2 sticking probability determined previously by a non-state-resolved experiment. [ABSTRACT FROM AUTHOR]

Local activity of oxygen reduction reaction (ORR) at the middle of the (111)-terraces on n(111) × (111) Pt surfaces (n = 6, 8, 10, 12 and ∞) are examined by using a DFT-based kinetic mean field model. Calculations indicate that solvation stabilization energies of all related reaction intermediates, O, OH and HO 2 adsorbates, decrease with the decrease in the terrace width n, and their formation rates are decelerated by the destabilizations while their removals are accelerated. Because of the trade-off relationship between the formation and removal rates, the local ORR activity exhibits a maximal point versus the terrace width n, and the trend can be summarized in a volcano-plot versus the OH formation potential similarly to the ORR activity on alloy surfaces. The theoretically-obtained results qualitatively agree with the experiments and indicate the significance of solvation effects for designing highly active and durable cathode catalysts for polymer electrolyte fuel cells. [ABSTRACT FROM AUTHOR]

Detailed knowledge of the structure and degree of oxidation of platinum surfaces under operando conditions is essential for understanding catalytic performance. However, experimental investigations of platinum surface oxides have been hampered by technical limitations, preventing in situ investigations at relevant pressures. As a result, the time-dependent evolution of oxide formation has only received superficial treatment. In addition, the amorphous structures of many surface oxides have hindered realistic theoretical studies. Using near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) we show that a time scale of hours ( t≥4 h) is required for the formation of platinum surface oxides. These experimental observations are consistent with ReaxFF grand canonical Monte Carlo (ReaxFF-GCMC) calculations, predicting the structures and coverages of stable, amorphous surface oxides at temperatures between 430-680 K and an O2 partial pressure of 1 mbar. [ABSTRACT FROM AUTHOR]

It is well-known that hydrogen adsorption/desorption on Pt open surfaces sites (110 and 100) shows a dependence on the pH below a pure Nernstian shift. Also, it is recognized that the oxidation of CO (and organic molecules) on Pt open surface electrodes occurs at more negative potentials in alkaline media than in acidic solutions. In contrast, both electrochemical processes develop a pure Nernstian behavior at the close-packed Pt(111) over the whole pH range. The current work employs experimental results of hydrogen desorption and carbon monoxide oxidation on Pt electrodes with different surface orientations over a wide pH range to reveal that the unusual Nernstian behavior observed at open surface sites is linked to an electrochemical process for both reactions, owing to the fact that similar absolute values are detected. Furthermore, the nature and concentration of alkali cations appear to play an important role in the mutual electrochemical process. [ABSTRACT FROM AUTHOR]

The layer-by-layer (LbL) sequential adsorption of oppositely charged polyelectrolytes leads to the formation of multilayered films (Polyelectrolyte Multilayer, PEM). Such systems may find application as ultrathin membranes with controlled properties. In this paper we examine different polyelectrolyte multilayers formed from poly-L-lysine (PLL), polyethyleneimine (PEI), poly(sodium 4-styrenesulfonate) (PSS) and alginate (ALG) polyelectrolytes. Film thicknesses for the PLL/PSS, PLL/ALG and PEI/PSS combinations showed similar values of up to 14 nm on mica and ca. 22 nm on platinum surfaces. The PEI/ALG combination formed thicker films with thicknesses of up to 90 nm on mica and ca. 140 nm on platinum surfaces. For the prepared films, the electroactive behavior towards [Fe(CN) 6 ] 3−/4− and [Ru(NH 3 ) 6 ] 3+/2 ions was monitored. We found that the oxidation/reduction current of [Fe(CN) 6 ] 3−/4− ions showed three different modes of behavior which can be described as non-permeability, permeability and accumulation of ions. For [Ru(NH 3 ) 6 ] 3+/2+ such a relation was not observed and all of the films remained permeable. The permeability of the thin PEMs seems to depend more strongly on the film composition than the film thickness. The best candidate for encapsulation purposes is proposed. [ABSTRACT FROM AUTHOR]

Microkinetic models of methane steam reforming (MSR) over bare platinum and rhodium (111) surfaces are analyzed in present work using calculated rate constants. The individual rate constants are classified into three different sets: (i) rate constants of adsorption and desorption steps of CH 4 , H 2 O, CO and of H 2 ; (ii) rate constants of dissociation and formation of A–H bonds (A = C, O, and H), and (iii) rate constants of dissociation and formation of C–O bond. The rate constants of sets (i) and (iii) are calculated using transition state theory and published thermochemical data. The rate constants of H-dissociation reactions (set (ii)) are calculated in terms of a previously-developed approach that accounts for thermal metal lattice vibrations and for H tunneling through a potential barrier of height which depends on distance of AH from a surface. Pre-exponential factors of several group (ii) steps were calculated to be usually lower than the traditional k B T / h due to tunneling effect. Surface composition and overall MSR rates over platinum and rhodium surfaces are compared with those over nickel surface showing that operating conditions strongly affect on the activity order of the catalysts. [ABSTRACT FROM AUTHOR]

An interconnected framework of reduced graphene oxide/phenyl formaldehyde polymer composites was synthesized by a one-pot hydrothermal reaction followed by carbonizing under different conditions. Then, the obtained porous materials with varied surface properties were used to disperse ultrasmall Pt nanoparticles. The catalyst with the optimized support demonstrates superior achievements to methanol oxidation reaction (MOR): distinctive improved mass activity (MA) and specific activity at both forward peak position and at the potential range near the operation of fuel cells, best antipoisonous ability revealed by 17 times MA and 7 times the retaining rate of commercial Pt/C in chronoamperometric evaluations, and outstanding long-term stability verified by 3-4 times MA and the retaining rate of Pt/C in the accelerated duration tests. By analyzing the performances of all studied catalysts, we proposed that fruitful oxygen groups and defects on the surface of supporting materials play a key role in boosting the MOR fulfillments through strengthening the Pt-substrate interaction or facilitating the removal of CO from the Pt surface. Elimination of surface oxygen groups and defects may promote the conductivity and mechanical strength of the catalysts but could result in a serious deterioration of antipoisonous ability, which means that only if the deliberate balance is achieved in the preparation of supporting materials can the MOR performances of Pt be improved synergistically. [ABSTRACT FROM AUTHOR]

Kinetics of electrocatalytic oxidation of arsenite ions has been investigated at a Pt disk electrode using cyclic voltammetry, convolution potential sweep voltammetry and electrochemical impedance spectroscopy. A complimentary environment pertaining to oxidation reactions of arsenite ions is attained in the acidic medium compared to a neutral or basic medium. It is suggested that in the neutral and basic media, direct electron transfer from the solution to electrode instigate the oxidation process without any pre adsorption. Meanwhile, in the acidic medium, prior to oxidation, arsenite ions are adsorbed on the Pt surface and a stepwise reaction mechanism is involved. Using impedance analysis, it is suggested that different forms of surface oxides at various pH values control the oxidation kinetics. [ABSTRACT FROM AUTHOR]

Stepped Pt surfaces having different width (1 1 1) terraces interrupted by (1 1 0) or (1 0 0) monoatomic steps were employed to evaluate the catalytic activity toward CO oxidation at Pt specific sites in HClO 4 , H 2 SO 4 , and H 3 PO 4 solutions, as well as in phosphate buffer and alkaline solution. The catalytic activity at the (1 1 1) terraces was sensitive to the nature of the anions derived from the electrolyte dissociation, while no effect on activity was detected at the monoatomic steps. A change in solution pH, passing from acid to alkaline solutions, had contrasting effects on catalytic activity at the (1 1 1) terraces and the step sites, with the catalytic activity of the (1 1 1) terraces improving, while activity at the step sites deteriorated. During the CO adlayer oxidation, the release of surface sites occurred preferentially from the (1 1 1) terraces of the Pt(s) − [( n − 1)(1 1 1) × (1 1 0)] surfaces, while from Pt(s) − [( n )(1 1 1) × (1 0 0)] surfaces, (1 1 1) terrace and (1 0 0) step sites were released simultaneously. [ABSTRACT FROM AUTHOR]

Binuclear C^C* cyclometalated NHC platinum(II) compounds with bridging amidinate ligands were synthesized to evaluate their photophysical properties. Their three-dimensional structures were determined by a combination of 2D NMR experiments, mass spectrometry, DFT calculations, and solid-state structure analysis. The bridging amidinate ligands enforce short distances between the platinum centers of the two cyclometalated structures, which gives rise to extraordinary photophysical properties. [ABSTRACT FROM AUTHOR]

Alkene-based self-assembled monolayers grafted on oxidized Pt surfaces were used as a scaffold to covalently immobilize oxidase enzymes, with the aim to develop an amperometric biosensor platform. NH 2 -terminated organic layers were functionalized with either aldehyde (CHO) or N-hydroxysuccinimide (NHS) ester-derived groups, to provide anchoring points for enzyme immobilization. The functionalized Pt surfaces were characterized by X-ray photoelectron spectroscopy (XPS), static water contact angle (CA), infrared reflection absorption spectroscopy (IRRAS) and atomic force microscopy (AFM). Glucose oxidase (GOX) was covalently attached to the functionalized Pt electrodes, either with or without additional glutaraldehyde crosslinking. The responses of the acquired sensors to glucose concentrations ranging from 0.5 to 100 mM were monitored by chronoamperometry. Furthermore, lactate oxidase (LOX) and human hydroxyacid oxidase (HAOX) were successfully immobilized onto the PtOx surface platform. The performance of the resulting lactate sensors was investigated for lactate concentrations ranging from 0.05 to 20 mM. The successful attachment of active enzymes (GOX, LOX and HAOX) on Pt electrodes demonstrates that covalently functionalized PtOx surfaces provide a universal platform for the development of oxidase enzyme-based sensors. [ABSTRACT FROM AUTHOR]

The surface pressure solely by hydrogen species at polycrystalline and single crystalline platinum is calculated from a modified Gibbs-Lippmann Equation taking the contributions of electrode potential and hydrogen coverage in perchloric acid. Hydrogen surface pressures at reference surface coverages are rather low for Pt(100) and Pt(110), i.e., 20–35 μN cm − 1 , but 5-fold larger for Pt(111) due the formation of long range water-hydrogen layers on trigonal sites. Surface tensions also follow the same tendencies. On polycrystalline platinum they are sensibly inferior to those obtained on single crystals but similar in magnitude for both types of hydrogens indicating that the presence of water in weakly bound hydrogen responds to a slight interaction (not bound to platinum atoms). Free energy of adsorption for hydrogen ad-atoms on polycrystalline platinum is reported here at experimentally found reference coverages, i.e. − 29 and − 14 kJ mol − 1 for both kinds of hydrogens in perchloric acid. The interaction/heterogeneity factor of the Frumkin/Temkin isotherm, which are similar (ca. 11–12 kJ mol − 1 ) for both types of hydrogens, again verifies that water interaction is not straight to platinum atoms. On single crystalline surfaces, the most favorable value of adsorption energy was found on Pt(100) and the lowest on Pt(111). The three single crystals exhibit positive interaction/heterogeneity factors (from 11 to 18 kJ mol − 1 ) being the greatest on Pt(110) as a consequence of being the most disordered surface. [ABSTRACT FROM AUTHOR]

The hydrogenation of C 2 molecules formed on the Pt(111) surface through acetylene exposure at 750 K was monitored in-situ with reflection absorption infrared spectroscopy (RAIRS) in the presence of up to 10 Torr of H 2 . The coverage of post-reaction surface carbon was measured with Auger electron spectroscopy. The RAIR spectra show that C 2 is hydrogenated to an ethylidyne intermediate. The hydrogenation of ethylidyne was also monitored at 400 K for H 2 (g) pressures of 1.0 × 10 − 2 to 10 Torr. At H 2 (g) pressures greater than 1.0 Torr, ethylidyne is completely hydrogenated. In an attempt to probe the nature of the C 2 adsorption sites, RAIR spectra of coadsorbed CO were obtained. It is found that while C 2 does not block CO adsorption, the spectra indicate that the surface carbon is free of hydrogen. In contrast, ethylidyne blocks CO adsorption sites. In the presence of coadsorbed CO, complete hydrogenation of ethylidyne occurs at 450 K versus 400 K in the absence of CO. [ABSTRACT FROM AUTHOR]

The preferred binding site of H/Pt(111) has been shown to be change from the on-top to FCC as the Pt(111) surface goes approximately from a state of compressive to tensile strain. A chemical analysis of the system has shown that for both FCC and on-top bound cases the H s Pt s and H s Pt d interactions have a similar importance in determining the preferred binding position. It has been seen that FCC-bound H forms a distinct state below the Pt d-band, whereas the on-top bound H does not. [ABSTRACT FROM AUTHOR]

Activation of C-H bonds in the sequential reactions of Pt+ + x(CH4/CD4), where x = 1-4, have been investigated using infrared multiple photon dissociation (IRMPD) spectroscopy and theoretical calculations. Pt+ cations are formed by laser ablation and exposed to controlled amounts of CH4/CD4 leading to [Pt,xC,(4x-2)H/D]+ dehydrogenation products. Irradiation of these products in the 400-2100 cm-1 range leads to CH4/CD4 loss from the x = 3 and 4 products, whereas PtCH2+/PtCD2+ products do not decompose at all, and x = 2 products dissociate only when formed from a higher order product. The structures of these complexes were explored theoretically at several levels of theory with three different basis sets. Comparison of the experimental and theoretical results indicate that the species formed have a Pt(CH3)2+(CH4)x-2/Pt(CD3)2+(CD4)x-2 binding motif for x = 2-4. Thus, reaction of Pt+ with methane occurs by C-H bond activation to form PtCH2+, which reacts with an additional methane molecule by C-H bond activation to form the platinum dimethyl cation. This proposed reaction mechanism is consistent with theoretical explorations of the potential energy surface for reactions of Pt+ with one and two methane molecules. [ABSTRACT FROM AUTHOR]