Metal Overlayers Research Articles

Deciphering NonCubic Phases in Au Microcrystallites via Under Potential Cu Deposition and Selective Growth of Noble Metal and Sulfide Overlayers

Deciphering <i>NonCubic</i> Phases in Au Microcrystallites via Under Potential Cu Deposition and Selective Growth of Noble Metal and Sulfide Overlayers

Exploring Pd-Ag/Cu electrodes in electrochemical CO2 reduction: Insights into C1, C2, and C3+ chemistry

Bimetallic alloy electrodes have been extensively investigated, with multiple metal elements emerging as candidates for developing practical electrodes in electrochemical (EC) CO2 reduction. Understanding C1 chemistry, C–C coupling leading to C2 and C3+ products, and electrode development is crucial for this purpose. In this study, Pd-Ag/Cu electrodes were prepared through the co-sputter deposition of Pd and Ag. These electrodes were tested in EC CO2 reduction to examine the products associated with C1, C2, and C3+, along with exploring their relationships over the Pd-Ag modification. In three different electrolytes—KHCO3, phosphate, and KOH—the presence of overlayer metals enhanced the production of CH4, C2H4, C3+ hydrocarbons, and propanol, while inhibiting ethanol and formate. These outcomes were found to be highly dependent on applied potential and recycling processes. The production mechanisms for CH4 and C2H4 appeared distinct from those of C2H6 and C3+ hydrocarbons, which were elucidated through Fischer-Tropsch (FT) chemistry and Anderson-Schulz-Flory equation analysis. EC CO reduction predominantly led to FT chemistry. These studies offer deeper insights into the interconnected C1, C2, and C3+ chemistry in EC CO2 reduction, contributing to enhanced understanding and potential advancements in alloy electrode development.

Development of a constructive solution of wood columns and crossbars interfaces on metal overlays and screws

Development of a constructive solution of wood columns and crossbars interfaces on metal overlays and screws

Effect of Travel Speed on the Properties of 5087 Aluminum Alloy Walls Produced by Wire and Arc Additive Manufacturing

An innovative Wire and Arc Additive Manufacturing combines the well-studied process of arc welding with direct energy deposition. Effect of travel speed 5.0 and 7.5 mm/s on the microstructure and mechanical properties of 5087 aluminum alloy was investigated. Five thousand eighty-three aluminum alloy was used as a substrate material and 5087 aluminum alloy was utilized as a filler material for the walls fabrication. The presence of pores reducing the strength of the overlay weld metal was detected on both overlay welds. The lower welding speed (5 mm/s) resulted in the smaller amount of porosity in comparison to higher welding speed (7.5 mm/s). Average pore area of wall No. 1 was 0.66% and wall No. 2 was 1.13%. It was found that higher welding speed affected the wall width and overlay weld bead geometry. Increase in welding speed led to a narrowing of wall width from 10.23 to 8.44 mm. The microstructure of weld metal matrix consisted of a α-Al substitution solid solution. The tensile strength of parallel to welding direction removed samples exceeded the tensile strength of perpendicular removed samples. It is a result of the cohesion of the layers in the overlay welding direction compared to the non-uniformity of the layers in the perpendicular direction. Furthermore, the tensile strength was higher in the case of travel speed of 5 mm/s in comparison to that of 7.5 mm/s.

Ultraviolet Light-Assisted Decontamination of Chemical Warfare Agent Simulant 2-Chloroethyl Phenyl Sulfide on Metal-Loaded TiO2/Ti Surfaces.

The application of ultraviolet (UV) light for the decontamination of chemical warfare agents (CWAs) has gained recognition as an effective method, especially for treating hard-to-reach areas where wet chemical methods are impractical. In this study, TiO2/Ti was employed as a model catalyst, which was contaminated with 2-chloroethyl phenyl sulfide (CEPS), and subjected to photocatalytic decontamination using both UVB and UVC light. Additionally, photocatalytic decontamination efficiency by introducing Au, Pt, and Cu onto the TiO2/Ti surface was explored. During the photodecomposition process under UVC light, at least eight distinct secondary byproducts were identified. It was observed that the introduction of overlayer metals did not significantly enhance the photodecomposition under UVC light instead overlaid Au exhibited substantially improved activity under UVB light. Whereas, photodecomposition process under UVB light, only five secondary products were detected, including novel compounds with sulfoxide and sulfone functional groups. This novel study offers valuable insights into the generation of secondary products and sheds light on the roles of overlayer metals and photon wavelength in the photodecontamination process of CWA.

Impact of heat guide structure on the power generation performance of integrated cavity-free micro thermoelectric generators

The performance of a cavity-free micro thermoelectric generator (TEG) consisting of Si nanowires (Si-NWs) is investigated in this research. In the cavity free structure, one side of TEG is heated by a structure of a metal overlayer, called the Heat Guide (HG), to supply heat selectively to specific microregions within the device. Thus, heat energy flows in the perpendicular direction, which forms steep a temperature gradient in the NWs. However, the performance can be varied by varying the thickness of the HG. In this work, the impact of the HG structure of an integrated TEG upon the power generation performance was experimentally demonstrated. Higher metal HG thickness and thick interlayer dielectric (ILD) thickness show higher power generation performance with the integrated device.

Transition metal nitride catalysts for selective conversion of oxygen-containing molecules.

Earth abundant transition metal nitrides (TMNs) are a promising group of catalysts for a wide range of thermocatalytic, electrocatalytic and photocatalytic reactions, with potential to achieve high activity and selectivity while reducing reliance on the use of Pt-group metals. However, current fundamental understanding of the active sites of these materials and the mechanisms by which selective transformations occur is somewhat lacking. Recent investigations of these materials from our group and others have utilized probe molecules, model surfaces, and in situ techniques to elucidate the origin of their activity, strong metal-support interactions, and unique d-band electronic structures. This Perspective discusses three classes of reactions for which TMNs have been used as case studies to highlight how these properties, along with synergistic interactions with metal overlayers, can be exploited to design active, selective and stable TMN catalysts. First, studies of the reactions of C1 molecules will be discussed, specifically highlighting the ability of TMNs to activate CO2. Second, the upgrading of biomass and biomass-derived oxygenates over TMN catalysts will be reviewed. Third, the use of TMNs for H2 production via water electrolysis will be discussed. Finally, we will discuss the challenges and future directions in the study of TMN catalysts, in particular expanding on opportunities to enhance fundamental mechanistic understanding using model surfaces, the elucidation of active centers via in situ techniques, and the development of efficient synthesis methods and design principles.

Two-dimensional topological insulators: past, present and future

Two-dimensional (2D) topological insulators (TIs) are special quantum conductors that possess an insulating bulk but metallic edge with quantized charge and spin conductance protected by electron band topology. The concept of topology and TI has not only renewed our fundamental understanding of electronic properties of solid materials, but also opened an exciting avenue towards potential applications of topological quantum devices with minimized heat dissipation and robustness against disorder. In this video article, I will first introduce and review the concept of TIs within the context of transport properties of solid-state materials. I will then use two examples, the organic 2D TIs and the surface-based 2D topological states, to recap the rapid theoretical and experimental developments made in this emerging field. The existence of quantized edge conductance and topological edge states of 2D TIs has been so far confirmed experimentally in several systems, such as semiconductor quantum wells, 2D transition metal dichalcogenides, metallic overlayer of bismuth on a semiconductor surface. However, discovery of high-temperature 2D TIs and construction of functional TI-based quantum devices remain largely elusive. At the end of this video article, I will offer briefly my personal perspective and possible future directions in low-dimensional topological materials.

Unlocking long-chain hydrocarbons (C2–7) via direct electrochemical CO2 and CO reduction on balanced Au/Ni electrodes

Electrochemical (EC) CO2 reduction method has been widely used as a green energy and environmental solution strategy. The use of Au/Ni electrodes was introduced to showcase a new concept of the direct EC Fischer-Tropsch (dEC F-T) synthesis pathway. This pathway involves the combination of electrodes that produce H2 and CO (syngas) during electrochemical CO2 reduction. The introduction of Au on the Ni electrode surface led to an increase in CO production and a gradual decrease in H2 production. When the interface was balanced, a pronounced F-T synthesis pathway was observed, resulting in the production of a series of hydrocarbons (CnH2n and CnH2n+2, n = 2–7). The dEC F-T synthesis was evaluated under different conditions, including electrolytes, concentrations, metal supports (Co and Fe), various overlayer metals (Ag and Cu), light irradiation, and isotope effects. The process was elucidated through surface C−C coupling polymerization reactions based on Anderson-Schulz-Flory weight distribution analysis. Additionally, the F-T synthesis was demonstrated through EC CO reduction via direct CO and H adsorption. The dEC F-T path provides a novel strategy for energy and environment by producing high-value long-chain hydrocarbons.

Effect of material chemical composition on oxidation and stress corrosion cracking of the submerged arc welding Alloy 52M overlay in a simulated PWR primary water

Compact tension (CT) specimens from submerged arc welding Alloy 52 M overlay are used to determine the stress corrosion cracking (SCC) resistance of the dilution zones and bulk overlay metal on the 52 M side in a simulated pressurized water reactor (PWR) primary water. SEM-EDS and X-ray fluorescence spectroscopy (XRF) results show three dilution zones (DZs) on the 52 M side. Oxidation test results show that the thickness of the compact oxide layer and maximum local oxidation penetration depth decrease for 1st DZ, 2nd DZ, and bulk 52 M, which are consistent with the average SCC growth rate and the number of local intergranular SCC cracks in these regions. The dilution zones with low Cr but high Fe content possess lower oxidation and SCC resistance than the bulk 52 M.

Catalytic Properties of Nanometric Metal Overlayers with Two‐Dimensional Structures

AbstractAlthough most of the currently used solid catalysts possess a three‐dimensional structure of nanoparticles dispersed on a porous support, the nanoparticle structure should not be considered the optimal structure for all catalytic reactions due to some disadvantages such as thermal instability and catalyst poisoning. Herein, we present the unique catalytic performance of a two‐dimensional metal foil‐supported nanometric Rh thin film, referred to as the “Rh overlayer”, for a catalytic CO−NO reaction and a stoichiometric three‐way catalytic reaction under practical conditions. The extremely high turnover frequency for NO reduction using two‐dimensional Rh is a key to understanding this phenomenon, the detailed mechanism of which can be explained by theoretical calculations.

Nanometric Metal Overlayer Catalysts: Fundamental Aspects and Applications

Nanometric metal overlayer catalysts have been developed as novel catalyst structures with high three-way catalytic performance for practical applications. The metal overlayer is prepared via a dry process using pulsed arc plasma deposition, unlike wet coating processes for conventional powder catalysts containing nanoparticles. The key point to achieving high performance is the extremely high turnover frequencies for specific chemical reactions catalyzed by a large two-dimensional surface compared with metal nanoparticles. This overview study presents the preparation, structure, performance, reaction mechanism, and thermal stability of metal overlayer catalysts, focusing on rhodium (Rh) and catalytic conversion of nitric oxide (NO). Rh plays a pivotal role in the reduction of NO to N2 in automotive three-way catalytic converters. The potential benefit of the overlayer structure is the minimum loading of precious metal, such as Rh, which is limited and expensive.

Photonic Applications for Restoration and Conservation of 19th Century Polychrome Religious Wooden Artworks

The present paper reports the multi-analytical approach for the removal of thick layers of metallic overpaints from a Brancovan iconostasis of the “Holy Trinity” church in Măgureni, România, which was built in 1694. After a restoration procedure at the beginning of the 20th century, the polychrome sculpture of the frame, which was initially gilded with a thin silver foil, was covered with a thick metallic overpaint layer imitating silver and gold. Currently, the conservation project of the church is focused on restoring the original aspect; thus, the overpainting that presented strong oxidation and soiling was removed. The adopted conservation methodology involved physicochemical characterization of the pictorial layers via optical microscopy, laser-induced breakdown spectroscopy, and Fourier-transform infrared spectroscopy, followed by the removal of the overpaints. The cleaning tests were performed by evaluating several methods in order to find the proper regime that would help preserve as much of the underlying polychrome layers as possible. Based on the tests, it was decided that the best solution was to use laser cleaning for the rough removal of the metallic paint overlayers and finalizing with chemical cleaning.

Electrochemical CO2 reduction over surface-modified Cd-based electrodes and reaction paths for long-chain hydrocarbons

Using an electrocatalyst to convert CO2 into useful chemicals is a promising strategy for sustainable energy and environmental solutions. In this study, cadmium (Cd) was modified with different transition metals (Ti, Zr, Au, Cu, and Pt) and used as an electrode for electrochemical CO2 reduction. The resulting chemicals produced, such as CO, H2, and formate, were dependent on various factors, including the applied potential, electrolyte concentration, and overlayer metal. By increasing the NaHCO3 concentration, the production of CO and formate decreased, but long-chain hydrocarbons (CnH2n and CnH2n+2, n = 2–6) were produced. These hydrocarbons were further increased by sputter deposition of Zr and Ti on the Cd electrode, which followed a Fischer-Tropsch synthesis mechanism. Despite the low production efficiency, the results obtained provide significant insights into the mechanisms underlying C–C coupling and the electrochemical generation of long-chain hydrocarbons. By modifying the Cd surface with other metals (Au, Cu, and Pt), the resulting chemicals were compared, and Cd was found to recrystallize to CdCO3 cuboid/cube morphology after electrochemistry. These results provide valuable insights for the development of surface-modified Cd-based electrocatalysts and long-chain hydrocarbon productions for energy and the environment.

Large Anomalous Frequency Shift in Perpendicular Standing Spin Wave Modes in BiYIG Films Induced by Thin Metallic Overlayers.

Interface-driven effects on magnon dynamics are studied in magnetic insulator-metal bilayers using Brillouin light scattering. It is found that the Damon-Eshbach modes exhibit a significant frequency shift due to interfacial anisotropy generated by thin metallic overlayers. In addition, an unexpectedly large shift in the perpendicular standing spin wave mode frequencies is also observed, which cannot be explained by anisotropy-induced mode stiffening or surface pinning. Rather, it is suggested that additional confinement may result from spin pumping at the insulator-metal interface, which results in a locally overdamped interface region. These results uncover previously unidentified interface-driven changes in magnetization dynamics that may be exploited to locally control and modulate magnonic properties in thin-film heterostructures.

Pt overlayer for direct oxidation of CH4 to CH3OH

Highly selective conversion of methane (CH4) to methanol (CH3OH) is an emerging attractive but challenging process for future development of hydrogen economy, which requires efficient catalysts. Herein, we systematically explore the catalytic properties of Pt(111) overlayer on transition metal oxides (TMOs) for CH4 conversion by first principles calculations. The Pt(111) monolayer supported by Ce-terminated CeO2(111) substrate exhibits high activity and selectivity for CH4 conversion to CH3OH, with the kinetic barrier of rate-limiting step of 1.05 eV. Intriguingly, the surface activity of Pt overlayer is governed by its d-band center relative to the energy of bonding states of adsorbed molecules, which in turn depends on the number of charge transfer between Pt(111) monolayer and underlying TMOs substrates. These results provide useful insights in the design of metal overlayers as catalysts with high-ultra performance and atomic utilization.

Surface Hydroxyl-Determined Migration and Anchoring of Silver on Alumina in Oxidative Redispersion

Hydroxyl (OH) groups are widely present on an oxide surface, which have been recognized as a key factor affecting surface properties of the oxide and interaction of the metal overlayer with the oxide. Here, γ-alumina (γ-Al2O3) supports with different OH contents are prepared by calcinating pseudo-boehmite (AlOOH) at different temperatures. The surface OH effect on oxidative redispersion of supported Ag nanoparticles including surface migration and anchoring of Ag species has been explored using in situ X-ray diffraction and UV–visible spectroscopy, as well as ex situ X-ray photoelectron spectroscopy and transmission electron microscopy. We reveal that the dispersion capacity, i.e., the amount of anchored Ag species associated with the steady dispersion state is thermodynamically determined by the surface OH contents, while the dispersion rate related to the surface migration process is kinetically limited by surface OH densities at low Ag loading. The higher dispersion ability is observed on the support with higher OH contents, and the quicker dispersion occurs on the support with higher OH densities. The results reveal that both OH contents and OH densities are critical in the redispersion of metal particles on oxide surfaces, which can be used to manipulate the Ag-catalyzed CO oxidation reaction.

Electronic Perturbation of Platinum Alloy By Transition Metal-Doping Towards Improved ORR Activity and Stability

As of today, Pt-based catalysts are the predominant ORR catalysts that meet the desired activity requirements of ORR in fuel cells. However, their broader applications are still challenging due to highly sluggish ORR kinetics, limited stability and higher cost of Pt. In order to develop novel electrocatalyst materials, herein we report surface tuning of binary PtCo alloy through transition metal doping, which reveals superior ORR activity achieving a mass activity of 2.07 A mgPt -1 at 0.9 V vs. reversible hydrogen electrode (RHE) and excellent durability with minor degradation after 30000 cycles. The ternary PtCoMn@NGNS alloy prepared through facile molten salt pyrolysis reveals a strong metal-support interaction via metal-nitrogen-graphene coordination.Furthermore, Mn dopants alter the electronic structure of Pt alloy, which improves the oxygen-intermediate binding energy on the interface and suppress the Co dissolution through unique configuration, resulting in enhanced activity and durability of the catalyst. According to the DFT calculations, the surface Mn extensively adsorbs an OH, resulting in increased surface Co stability and overall ORR catalytic performance. Therefore, it is understandable that the development of ternary Pt alloy results in considerable changes in the structural and electrical characteristics of metal overlayer, which varies dramatically from monometallic surfaces.Our experimental results corroborated by theoretical calculations show that electronic perturbation of PtCo by Mn doping stabilizes the Co and causes significant strain in the Pt(111), which accounts for the increased ORR performance. The strained lattice of Pt caused by Co alloying and surface segregation of Mn both play important roles in the increased ORR activity. Similarly, the Pt3CoMn-OH configuration diminishes Co dissolution and improves overall stability. It is anticipated that such a facile preparation of high-performance electrocatalysts will advance the practical applications of ORR catalysts.Figure 1: Figure 1

Electrochemical Epitaxy: Perspective and Applications

Properties of heteroepitaxial thin films are often dependent on the method and conditions for deposition[1]. In that respect, the electrochemical growth represents energetically different approach as compared to conventional vacuum deposition methods. It offers unique advantages, which can be exploited to get high quality ultra-thin films. The obvious one is that process occurs at an ambient temperature, which allows growth of heteroepitaxial metal overlayers while preserving the integrity of the interface. In recent years, significant progress has been made in controlling the thin film growth modes[2],[3],[4]. Various approaches to manipulate growth kinetics and enhance the evolution of atomically flat epitaxial overlayers were discovered[5],[6],[7]. Some of these findings were successfully implemented in electrochemical epitaxial growth resulting in development of deposition protocols such as Defect Mediated Growth (DMG)[8],[9], Surfactant Mediated Growth (SMG)[10] and growth via Surface Limited Redox Replacement (SLRR)[11],[12] with its sub-derivatives such as SEBALD, ECALD, ECALE, E-less ALD. These methods are used extensively by practitioners in different areas to synthesize monolayer or nanocluster catalysts and ultra-thin films with different compositions and applications.In this talk, we will review current perspective and progress on electrochemical epitaxial growth. Discussion will focus on fundamental and practical details of the relevant phenomena about UPD, SMG, DMG, SLRR and E-less ALD using examples and challenges that are facing researchers in these areas. If time allowed, some out of the box idea will be posted opening podium for discussion.

The Influence of Graphene on the Electrodeposition of Metals

Electrodeposition of metals with controlled crystallography and grain structure is critical for applications including batteries, electronic circuit fabrication, and industrial coating processes. For metal-anode-based batteries in particular, it is important to understand how the electrode surface affects the crystallography of electrodeposited metals. Graphene and other 2D materials have recently been shown to exhibit strong effects on metal crystallography during electrodeposition, but it is unclear the extent to which graphene is affecting epitaxy, and further understanding of the 3D metal/2D material interface is crucial for advancing interfacial electrodeposition control. In this work, we study the influence of graphene and the underlying Cu substrate on the crystal structure and morphology of electrodeposited metals. Based on extensive electrochemical testing and electron backscatter diffraction (EBSD), we find that the orientation of the substrate underneath graphene (usually copper) exerts a controlling crystallographic influence on the electrodeposited metal overlayer, rather than the graphene layer itself. Further transmission electron microscopy (TEM) and Raman spectroscopy investigations are used to probe the nature of the interface and the graphene layer. These findings are important because they show that graphene can potentially be used as an interlayer to enable high-quality remote epitaxy between a variety of metals that normally exhibit inhibited epitaxy because of surface oxide layers.