Surfaces Of Pb Research Articles

A Machine Learning Model for Adsorption Energies of Chemical Species Applied to CO2 Electroreduction

Machine learning methods are applied to obtain adsorption energies of different chemical species on (100), (111), and (211) FCC surfaces of several transition metals and Pb. Based on information available in databases containing adsorption energies obtained via first-principles calculations, we implemented MLPRegressor, XGBRegressor, Support Vector Regressor, and Stacking machine learning models. The fourth model is created from the combination of the previous three through a Stacking technique. In a broader context, our results showed the robustness of machine learning models and the ability of these methods to speed up the screening materials to specific goals, at a low computational cost. We emphasize the ability of our models to predict the adsorption energy for different systems. Due to their generality of them, we were able to make ion predictions on metallic surfaces, taking into account the influence of different functionals. This capability is of special significance due to the difficulty of calculating the correct energy for charged systems by traditional atomistic simulations. From then on, we made predictions for important chemical species in the CO2 electroreduction process, such as the radical anion CO2 −•, an important intermediary for obtaining new products in view of a negative carbon footprint.

Collective excitations and quantum size effects on the surfaces of Pb(111) films: An experimental study* *Project supported by the National Natural Science Foundation of China (Grant Nos. 11874404 and 11634016), the National Key Research and Development Program of China (Grant Nos. 2016YFA0302400, 2016YFA0202300, and 2017YFA0303600), and the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDB33000000). Xuetao

Pb(111) film is a special system that exhibits strong quantum size effects in many electronic properties. The collective excitations, i.e., plasmons, in Pb(111) films are also expected to show signatures of the quantum size effect. Here, using high-resolution electron energy loss spectroscopy, we measured the plasmons on the surface of Pb(111) films with different film thicknesses and analyzed the plasmon dispersions. One surface plasmon branch exhibits prominent damping in the small momentum range, which can be attributed to the interaction between the top and bottom interfaces of the Pb(111) films. With the film thickness increasing, the critical momentum characterizing the damping in Pb(111) films decays not only much slower in Pb(111) films than in other metal films, and even in films with the thickness up to 40 monolayers the damping still exists. The slow decay of the surface plasmon damping, manifesting the strong quantum size effect in Pb(111) films, might be related to the strong nesting of the Fermi surface along the (111) direction.

Experimental search for the origin of low-energy modes in topological materials

Point-contact spectroscopy of several non-superconducting topological materials reveals a low temperature phase transition that is characterized by a Bardeen-Cooper-Schrieffer-type of criticality. We find such a behavior of differential conductance for topological surfaces of non-magnetic and magnetic Pb$_{1-y-x}$Sn$_y$Mn$_x$Te. We examine a possible contribution from superconducting nanoparticles, and show to what extent our data are consistent with Brzezicki's et al. theory [arXiv:1812.02168], assigning the observations to a collective state adjacent to atomic steps at topological surfaces.

Mechanistic Insights into Furfural Reduction on Transition Metals Electrodes from First-Principles Methods

Furfural is a significant platform compound derived from biomass. Electrocatalytic reduction of furfural on transition metals emerges as a sustainable approach compared to heterogeneous catalysis to obtain valuable chemicals and fuels, such as furfuryl alcohol (FA) and 2-methylfuran (MF). Although the product selectivity was shown to be strongly depended on the intrinsic properties of the transition metal electrodes, similar as CO2 reduction, the complex chemical nature of furfural presents challenges to investigate the reaction mechanisms, which are still under debate. Density functional theory (DFT) calculations have been performed for electrocatalytic reduction of furfural to FA and MF on the close-packed (111) and stepped (211) surfaces of Cu, Ag, Pb, and Ni electrodes. The elementary reaction steps have been evaluated based on computational hydrogen electrode (CHE) model. A novel Brønsted–Evans–Polanyi (BEP) relationship has been established for C-O bond cleavage which is necessary for MF production. On Cu, Ag, Pb, and Ni, at both terrace and stepped sites, the first hydrogenation step of C=O, leading to mh6 or mh7 formation, influences the overall reaction activity and product selectivity. It has been found that the pathway via mh6 is more competitive than that via mh7 for FA formation on Cu, Ag, and Pb, whereas on Ni, both mh6 and mh7 routes are competitive due to strong interactions between the furan ring and the substrate. The C-O bond cleavages of furfural, the partially hydrogenated intermediates (mh6 and mh7) and FA were considered as the parallel pathways to produce MF besides FA formation pathways. It is well-known that solvation can facilitate the hydrogenation reactions involving proton-electron pairs. In this work, solvation was confirmed to decrease the C-O bond cleavage energy barriers, which could boost MF production and potentially tune the product selectivity on transition metal electrodes.

Ab initio study of intrinsic profiles of liquid metals and their reflectivity

The free surfaces of liquid metals are known to exhibit a stratified profile that, in favourable cases, shows up in experiments as a peak in the ratio between the reflectivity function and that of an ideal step-like profile. This peak is located at a wave-vector related to the distance between the layers of the profile. In fact the surface roughness produced by thermally induced capillary waves causes a depletion of the previous so called intrinsic reflectivity by a damping factor that may hinder the observation of the peak. The behaviour of the intrinsic reflectivity below the layering peak is however far from being universal, with systems as Ga or In where the reflectiviy falls uniformly towards the q → 0 value, others like Sn or Bi where a shoulder appears at intermediate wavevectors, and others like Hg which show a minimum. We have performed extensive ab initio simulations of the free liquid surfaces of Bi, Pb and Hg, that yield direct information on the structure of the profiles and found that the macroscopic capillary wave theory usually employed in order to remove the capillary wave components fails badly in some cases for the typical sample sizes affordable in ab initio simulations. However, a microscopic method for the determination of the intrinsic profile is shown to be succesful in obtaining meaningful intrinsic profiles and corresponding reflectivities which reproduce correctly the qualitative behaviour observed experimentally.

Effect of phosphoric acid concentration on conductivity of anodic passive film formed on surface of lead–indium alloy

The addition of phosphoric acid into sulfuric acid solution is mentioned to be helpful in the reduction of sulfation after deep discharge of lead-acid battery. The anodic behavior of Pb and Pb–In alloys was studied in pure phosphoric acid and sulfuric acid containing various concentrations of phosphoric. The electrochemical measurements were performed using potentiodynamic, potentiostatic and cyclic voltammetric techniques. The composition and morphology of passive layer formed on the surfaces of Pb and Pb–In alloys were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy analysis (EDX) and scanning electron microscopy (SEM). The potentiodynamic study shows that the passive current density increases with increasing the indium content in the alloy in the examined solutions. The addition of 0.1 mol/L H3PO4 into the electrolyte is more effective to decrease the thickness of passive film on the surface of alloys containing higher indium content (10% and 15%). The XRD, EDX and SEM data reveal that the formation of PbSO4 and PbO on the surface decreases with increasing the indium level in the alloy and is completely prevented at higher indium content (15%) in mixed acid.

Mechanism of action of electrochemically active carbons on the processes that take place at the negative plates of lead-acid batteries

It is known that negative plates of lead-acid batteries have low charge acceptance when cycled at high rates and progressively accumulate lead sulphate on high-rate partial-state-of-charge (HRPSoC) operation in hybrid-electric vehicle (HEV) applications. Addition of some carbon or graphite forms to the negative paste mix improves the charge efficiency and slows down sulfation of the negative plates. The present investigation aims to elucidate the contribution of electrochemically active carbon (EAC) additives to the mechanism of the electrochemical reactions of charge of the negative plates. Test cells are assembled with four types of EAC added to the negative paste mix in five different concentrations. Through analysis of the structure of NAM (including specific surface and pore radius measurements) and of the electrochemical parameters of the test cells on HRPSoC cycling, it is established that the electrochemical reaction of charge Pb 2+ + 2e − → Pb proceeds at 300–400 mV lower over-potentials on negative plates doped with EAC additives as compared to the charge potentials of cells with no carbon additives. Hence, electrochemically active carbons have a highly catalytic effect on the charge reaction and are directly involved in it. Consequently, the reversibility of the charge/discharge processes is improved, which eventually leads to longer battery cycle life. Thus, charging of the negative plates proceeds via a parallel mechanism on the surfaces of both Pb and EAC particles, at a higher rate on the EAC phase. Cells with EAC in NAM have the longest cycle life when their NAM specific surface is up to 4 m 2 g −1 against 0.5 m 2 g −1 for the lead surface. The proposed parallel mechanism of charge is verified experimentally on model Pb/EAC/PbSO 4 and Pb/EAC electrodes. During the charge and discharge cycles of the HRPSoC test, the EAC particles are involved in dynamic adsorption/desorption on the lead sulfate and lead surfaces. Another effect of electrochemically active carbons is also evidenced namely that, above a definite concentration, some EAC forms reduce the mean pore radius of NAM. When it diminishes to less than 1.5 μm, access of sulfuric acid into the pores is impeded and PbO forms instead of PbSO 4 in the pores of NAM during discharge. Thus, it may be presumed that electrochemically active carbons change the overall electrochemical reaction of charge and discharge of lead-acid cells when operated under HRPSoC cycling conditions.

Study on the structure and property of lead tellurium alloy as the positive grid of lead-acid batteries

A series of novel Pb–Te binary alloys with different contents of tellurium (0.01–1.0 wt.%) were investigated as the positive grid of a lead acid battery. The microstructure of Pb–Te alloys was observed using a polarizing microscope. The morphology of the corrosion layers and corroded surfaces of Pb and Pb–Te alloy electrodes were analyzed by scanning electron microscopy (SEM) following the corrosion test. The electrochemical properties of Pb–Te alloys and Pb–Te–Sn alloy in sulfuric acid solution were investigated by cyclic voltammetry (CV), open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), alternating current voltammetry (ACV), and linear sweeping voltammetry (LSV). The results indicate that the introduction of tellurium results in grain refinement, increased corrosion resistance, and an accelerated oxygen evolution reaction for the Pb–Te binary alloys. The passive films formed on Pb–Te–Sn alloy shows improved performances in comparison to those on Pb–Ca–Sn alloy.

Phase transformation in unpoled bulk Pb(Zn1∕3Nb2∕3)O3–8%PbTiO3 single crystals revealed by the fracturing technique

Polished-and-annealed surfaces of bulk Pb(Zn1∕3Nb2∕3)O3–PbTiO3 (PZN-PT) single crystals were covered with a deformed layer and, hence, were unsuitable for structural study by means of x-ray diffraction technique. In contrast, fractured surfaces of bulk single crystals were relatively strain-free giving rise to distinctive diffraction patterns. Using the fracturing technique and high-resolution synchrotron x-ray diffraction, the present work shows that unpoled (annealed) PZN-8%PT single crystal undergoes a (MC)-T-C transformation upon heating under zero field condition, where T and C are the tetragonal and cubic phases, respectively. The symbol (MC) indicates an “apparent” type-C monoclinic phase, which in fact may be a rhombohedral phase of complicated domain structures.

Calculation of the surface energy of fcc metals with modified embedded-atom method

The surface energies for 38 surfaces of fcc metals Cu, Ag, Au, Ni, Pd, Pt, Al, Pb, Rh and Ir have been calculated by using the modified embedded-atom method. The results show that, for Cu, Ag, Ni, Al, Pb and Ir, the average values of the surface energies are very close to the polycrystalline experimental data. For all fcc metals, as predicted, the close-packed (111) surface has the lowest surface energy. The surface energies for the other surfaces increase linearly with increasing angle between the surfaces (hkl) and (111). This can be used to estimate the relative values of the surface energy.

Calculation of the surface energy of FCC metals with modified embedded-atom method

The surface energies for 38 surfaces of FCC metals Cu, Ag, Au, Ni, Pd, Pt, Al, Pb, Rh and Ir have been calculated by use of the modified embedded-atom method. The results show that, for all FCC metals, as predicted, the close-packed (111) surface has the lowest surface energy. The surface energies for the other surfaces increase linearly with increasing angle between the surfaces (hkl) and (111). This can be used to estimate the relative values of the surface energy.

Analysis for electrolytic oxidation and reduction of PbSO 4/Pb electrode by electrochemical QCM technique

In situ observations of the mass change were carried out using the electrochemical quartz crystal microbalance (EQCM) technique for the active materials in a lead–acid battery during charge–discharge. Lead sulfate was formed on the surfaces of the pure Pb and Pb–Ca–Sn alloys immersed in 4.50 kmol m −3 H 2SO 4 solution at 298 K. The rates of PbSO 4 formation on the Pb–0.08 mass% Ca–Sn alloys, which are the choice materials for grids in the valve-regulated lead–acid battery (VRLA), were inhibited by the presence of Sn. This fact observed by the EQCM technique was in good agreement with the results determined by the prolonged corrosion test of 604.8 ks at 348 K. This state, in which the PbSO 4 exists in the surface and the underlying Pb is not thoroughly reacted, corresponds to the state of active materials after discharge. During electrolytic oxidation, i.e. the charging of the positive electrode, the reaction of PbSO 4→PbO 2 could take place to decrease the electrode mass when the current density exceeded a critical value. On the other hand, the reaction of PbSO 4→Pb could readily proceed at just one-fourth the current density of the electrolytic oxidation during the electrolytic reduction of the PbSO 4/Pb electrode, i.e. the charging of the negative electrode.

Ion-induced spike effects on metal surfaces

The effects of single Xe ion impacts on the surfaces of Au, Ag, In and Pb have been studied using in-situ transmission electron microscopy. Individual ion impacts produce surface craters with associated expelled material. The cratering efficiency scales with the density of the irradiated metal. Calculation indicates that, when collision cascades occur near surfaces (within about 5 nm) with energy densities sufficient to cause local melting, craters will occur. Crater formation occurs as a result of the explosive outflow of material from the hot molten core of the cascade. This would appear to indicate that, although the number of atoms in a spike is small and its duration short, it is reasonable to use macroscopic concepts such as vibrational temperature, melting and flow to describe spike effects.

Identification of LEIS contributions observed in the ion kinetic energy distributions collected on a cameca IMS-3f SIMS instrument

Kinetic energy distributions of the secondary ions and scattered ions of O + , Cs + and Ar + (bombardment with primary ions of O-, O 2+, Cs + and Ar + was utilized) were obtained from the elemental surfaces of Mg, Al, Si, Ag and Pb using a modified Cameca IMS-3f magnetic sector mass spectrometer. In addition, the distributions of O + were acquired for O 2+ ion surface bombardment of several standard reference materials (Ti-base alloys of SRM648 and SRM649) and geological samples [pyrrhotite (Fe (1-x) S) and arsenopyrite (FeAsS)]. Distinct features attributable to elastic binary projectile/target backscattering collisions were found to be superimposed in the data. Hence, a full characterization of these kinetic ion energy distributions could be made. As a result it is possible to identify both the secondary ion and scattered ion contributions present in the collected kinetic energy distributions and to perform low-energy primary ion surface scattering (LEIS) experiments combined with in situ secondary ion mass spectrometry (SIMS) analysis, albeit to a reduced sensitivity and resolution compared to those possible on dedicated LEIS instruments.

Hydrothermally stable bonding of silicone rubber to titanium.

WE HAVE published experimentally determined lifetimes of lap-shear adhesive joints, periodically subjected to a test force and submerged in boiling buffer solution between tests (DONALDSON and AYLETT, 1995). The adhesive used was Dow Coming (DC) 3140, a flowable single-part silicone rubber, unusual in that it does not evolve acetic acid upon cure. The adherends were metal-oxide surfaces of Ag, Cr, Cu, Fe, Ni, Pb, Si, Sn, Ti and Zr. In these tests, the performance of titanium/silicone rubber joints was disappointing. Consideration of the iso-electric potential for the titanium oxide surface leads to expectations of a submerged joint life of about 90 days at pH 7. The mean life obtained in practice was only 34 days. Consideration of the Slater potentials for the oxides leads to the expectation that the joint durabilities will be ranked as follows:

Jump to contact and neck formation between Pb surfaces and a STM tip

We present a study of the interaction of a W STM tip and the (110) and (111) surfaces of Pb. Atomic resolution has been obtained at room temperature on Pb(110) and up to 330 K on Pb(111). At higher temperatures the surfaces can jump to mechanical contact with the STM tip, resulting in the formation of a connecting neck of Pb between tip and surface. As the tip is retracted, the neck elongates and finally breaks. The dependence of the maximum neck size on the temperature and the tip retraction speed indicates that surface diffusion is responsible for the neck build-up. When the surface is partially oxidized the maximum neck size is reduced. We derive a scaling relation between the maximum neck size, the retraction speed and the surface diffusion coefficient. With this relation and the temperature dependence of the maximum neck size we obtain activation energies for the neck build-up of 1.3 and 0.9 eV respectively for necks on Pb(110) and Pb(111). When a neck breaks, either a crater or a hillock is left on the surface.

Dynamics of formation of the liquid-drop phase of laser erosion jets near the surfaces of metal targets

An investigation was made of laser erosion jets formed at 0.1–1.5 mm above the surfaces of Pb, Co, Ni, Sn, and Zn targets. A neodymium laser emitting rectangular pulses of 400 μs duration and of energy up to 400 J was used. The diameters, as well as the number density and volume fraction of the metal particles present in the jet, were measured. An analysis of the results showed that the metal liquid drops broke up near the surface and experienced additional evaporation because of their motion opposite to the laser beam.

Ion bombardment induced topography evolution on low index crystal surfaces of Cu and Pb

(100), (110) and (111) oriented single crystal surfaces of Cu and Pb have been bombarded with inert gas ions, self ions, ions of the other substrate species and Bi in the energy range 50–150 keV and in the fluence range 10 15–10 18 ions cm 2. The evolving surface topography was observed by scanning electron microscopy. This topography was observed to be strongly influenced by ion species and surface orientation but the habit of the topography was delineated at low fluences and the features increased in size and density with increasing fluence with some mutation to the more stable of the features. As an example Bi and Pb bombardment of (100) Cu leads to little topographic evolution, (110) Cu develops a system of parallel ridges with (100) facets and (111) Cu develops a prismatic surface, each prism possessing (100) facets. These, and the more general, results cannot be explained by surface erosion by sputtering theory alone (this predicts surface stability of the lowest sputtering yield orientation (110), nor by surface free energy density minimisation criteria (this predicts stability of (111) surfaces). It is proposed that the observed topography is most strongly related to the crystallographic form of precipitates of implanted species.

Premelting at the (110) surface of Al and Pb. What do we understand today?

In this paper I review the experimental efforts to obtain microscopic information on the surface disordering process on the (110) surfaces of Al and Pb, thereby focussing in particular onto glancing angle X-ray scattering experiments. The results will be discussed in view of the concept of “surface melting”.

Chemical Activities of Fresh Surfaces of 1B-4B Metals and Alloys.

Chemical activities of fresh surfaces of Cu, Zn, Al, Sn and Pb and copper-base alloys were investigated at room temperature. The fresh surfaces were formed by scratching under high vacuum conditions. Fresh copper surfaces exhibited the highest chemical activity among 1B∼4B metals used. On the other hand, no organic compound chemisorbed on fresh lead surfaces. Judging from the chemisorption activities of organic compounds, the activities of fresh metal surfaces decreased in the following order; Pb < Sn< Al< Zn< Cu. The order of the adsorption activity of organic compounds on the fresh copper surfaces was : ether < sulfide <oleffin and benzene < iodide. The order can be explained in terms of softness of functional groups. XPS measurements revealed that lead was concentrated on scratched surface of Cu-Pb alloys. Chemical activity of Cu-Pb alloy was similar to that of Pb. This can be explained by the concentrated Pb on the fresh surface. The chemical activity of copper-alloys for propyl iodide decreased by the addition of zinc or tin to copper. It was concluded that the chemical activity of fresh surfaces was controlled by chemical properties of metals and the functional groups to be adsorbed.