Bimetallic Films Research Articles

Heterostructured Pd/Ti/Pd Thin Films as Highly Efficient Catalysts for Methanol and Formic Acid Oxidation.

Finding a highly efficient catalyst for proton exchange membrane fuel cells is still the subject of extensive research. This article describes heterostructured Pd/Ti/Pd bimetallic thin films prepared using a strain-release technology as electrocatalysts for fuel cells. With their particular structure, these materials exhibit intriguing electrocatalytic activity toward the oxidation of both methanol and formic acid, yielding current densities of 0.17 and 0.56 A mg-1Pd, much superior to that of the commercial Pd black catalyst. Moreover, the Pd/Ti/Pd thin films display a low onset oxidation potential and extremely high current retention in both acidic and alkaline media. The carbon monoxide poisoning resistance is also significantly enhanced, thus contributing to ultrahigh stability in the long-term electrocatalytic processes. Their encouraging performance implies that such composites could be potential materials for energy conversion in the fuel cell field.

CO and H2 adsorption on Au-Ni bimetallic surfaces: a combined experimental and DFT theoretical study

Au-Ni bimetallic thin films were grown on refractory metal substrates. CO and H2 adsorption on Au-Ni bimetallic surfaces have been studied by a combination of in situ polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS), temperature-programmed desorption (TPD), and density functional theory (DFT) calculations. It is found CO desorption peak shifts from 413 K on pure Ni surfaces to 293 K on the isolated Ni atoms formed by alloying with Au atoms. The sharp decrease of CO desorption temperature on Au-Ni surfaces with increasing Au coverage is caused by the change of the favored CO adsorption sites from bridge/hollow sites on pure Ni surfaces to Ni top sites on Au-Ni bimetallic surfaces. In situ PM-IRRAS shows two CO adsorption bands on Au sites at 2119 cm−1 and 2103 cm−1 on Au-Ni surfaces at 80 K, which are due to CO bound on under-coordinated Au atoms and electron negatively charged Au sites modified with nearby Ni atoms, respectively. Even with the Au-Ni surface temperature at as low as 100 K, CO adsorption induced Ni surface segregation has been observed by in situ PM-IRRAS. Furthermore, DFT calculation results discover the adsorption energy of CO on Ni top sites continues to decrease with increasing Au coverage due to the geometric ensemble effect and the lowered d-band center after Ni alloying with Au. H2 desorption temperature decreases from 363 K on pure Ni thin films to 302 K with increasing Au coverage to 0.6 ML. A new H2 peak appears at around 170 K on the Au-Ni surfaces with Au coverages between 0.6 ML and 0.9 ML. This new H2 TPD peak is assigned to H2 desorption from the totally isolated Ni sites. With Au coverage above 1.5 ML, there is no any H2 desorption detected. The combined surface science studies and DFT calculations provide new insights into the surface structure-activity correlation of Ni-base bimetallic surface alloys.

Photochemical synthesis of bimetallic gold/silver nanoparticles in polymer matrix with tunable absorption properties: Superior photocatalytic activity for degradation of methylene blue

Bimetallic nanoparticles are widely used in chemical catalysis. Their practical performance can be better exploited through morphological control by adjusting the synthetic strategy. Herein, a photochemical synthesis route was used to achieve the controlled preparation of bimetallic Au/Ag BNps. Size and shape control is achieved depending on the type of initiating radical therefore synthesized new one-component Type II photoinitiator, namely 2-thioxanthone thioacetic acid-dioxide was employed for the synthesis of Au/Ag BNp both in solution and polymer matrix. The effect of the gold/silver ratio on the nanoparticle size, shape and distribution was investigated, and the characterization of the obtained nanoparticles was performed by UV–Vis spectrophotometry, DLS and SEM techniques. Additionally, photocatalytic oxidative degradation of methylene blue was achieved with the prepared Au/Ag bimetallic nanocomposite films. By evaluating the photocatalytic oxidation degradation of methylene blue under UV–Vis light irradiation, 2:1 ratio of Au/Ag nanoparticles containing nanocomposite film exhibit the best activity compared with other composition of Au/Ag. The size and high SPR absorption band are thought to be responsible for superior photocatalytic activity.

Determination of the homogeneity of the Ag-Au bimetallic alloy thin films by means of a micro beam X-Ray fluorescence setup with using elemental composition

The goal of this work is to research the effect of different Au-Ag ratios on the homogeneity of Au-Ag bimetal alloys. Thin films of silver (Ag)-gold (Au) bimetal alloy were produced using Vaksis Thermal Evaporator system and quartz crystal microbalance detector at different gold (Au) additive ratios. Micro beam X-Ray fluorescence spectrometer system was used to calculate the homogeneity of bimetallic Ag-Au alloy thin films and to calculate production Au-Ag ratios with different concentration values. It is seen that the calculated ratios and production value are in good agreement.

Electroformation of Pd‐modified Thin Film Electrocatalysts Using E‐ALD Technique

AbstractElectrochemical atomic layer deposition was used to form bimetallic (BiPd, CuPd) and trimetallic (CuBiPd) thin films via surface‐confined reactions. Pd thin films were characterized by cyclic voltammetry, scanning electron microscopy (SEM) and the alloy formation with preferred Au/Pd(111) orientation was confirmed by XRD. AFM revealed uniform grain distribution, with 3D islands growing on CuBiPd. EDX verified the presence of all deposited elements. Compared to other prepared catalysts, CuBiPd catalyst showed higher activity and stability towards the ethanol oxidation reaction (EOR), as confirmed by the peak current and onset potential trends, respectively: CuBiPd (1.35 mA, −0.450 V)>CuPd (0.6016 mA, −0.442 V)>BiPd (0.275 mA, −0.384 V)>Pd (0.186 mA, −0.350 V). The EOR current on CuBiPd improved by 2.5 folds relative to Pd. The results show that CuBiPd electrocatalyst is a promising material for EOR with enhanced catalytic properties for direct ethanol fuel cell

Fluorescence Based on Surface Plasmon Coupled Emission for Ultrahigh Sensitivity Immunoassay of Cardiac Troponin I.

This work demonstrates the quantitative assay of cardiac Troponin I (cTnI), one of the key biomarkers for acute cardiovascular diseases (the leading cause of death worldwide) using the fluorescence-based sandwich immune reaction. Surface plasmon coupled emission (SPCE) produced by non-radiative coupling of dye molecules with surface plasmons being excitable via the reverse Kretschmann format is exploited for fluorescence-based sandwich immunoassay for quantitative detection of cTnI. The SPCE fluorescence chip utilizes the gold (2 nm)-silver (50 nm) bimetallic thin film, with which molecules of the dye Alexa 488 (conjugated with detection antibodies) make a near field coupling with the plasmonic film for SPCE. The experimental results find that the SPCE greatly improves the sensitivity via enhancing the fluorescence signal (up to 50-fold) while suppressing the photo-bleaching, permitting markedly enhanced signal-to-noise ratio. The limit of detection of 21.2 ag mL−1 (atto-gram mL−1) is obtained, the lowest ever reported to date amid those achieved by optical technologies such as luminescence and label-free optical sensing techniques. The features discovered such as ultrahigh sensitivity may prompt the presented technologies to be applied for early diagnosis of cTnI in blood, particularly for emergency medical centers overloaded with patients with acute myocardial infarction who would suffer from time-delayed diagnosis due to insufficient assay device sensitivity.

Enhanced electrocatalytic performance of mesoporous Au-Rh bimetallic films for ammonia synthesis

Electrocatalysis nitrogen reduction reaction (NRR) is expected to achieve sustainable clean and sustainable NH3 production. Owing to the chemical inertness of N2, the design of efficient catalysts is a critical issue. In this work, we propose micelle-assisted replacement method to in situ synthesize mesoporous Au3Rh film on Ni foam (mAu3Rh/NF). Because of the bimetallic mesoporous and binder-free structures, mAu3Rh/NF obtains high Faraday efficiency of 23.84% and NH3 yield of 26.29 μg h−1 mg-1cat. for NRR in 0.1 M Na2SO4 at − 0.1 V, outperforming other counterparts with different Au/Rh ratios. This micelle-assisted synthesis method is universal to synthesize high-efficiency mesoporous noble films for NRR and beyond.

Glassy carbon electrode modified by Pd–Cu bimetallic nano-dendrites film decorated on the reduced graphene oxide using galvanic replacement as a low-cost anode in methanol fuel cells

Glassy carbon electrode (GCE) modified by reduced graphene oxide Cu–Pd nano-dendrimer (Pd-CuNDs-RGO/GCE) was prepared using electro-deposition and spontaneous displacement methods. Graphene oxide was put on the surface of GCE by drop-casting, then a thin film of reduced graphene oxide (RGO) was formed by electro-reduction at −0.9 V. The copper nano-dendrimers (CuNDs) were electro-plated on RGO/GCE surface. Finally, Pd-CuNDs-RGO/GCE was prepared by the spontaneous replacement of CuNDs with palladium nanoparticles (PdNPs) in a dilute solution of palladium. The electrode surface was characterized using field-emission scanning electron microscopy (FESEM), X-ray energy diffraction (EDX) spectroscopy, and electrochemical techniques. The electrochemical behavior of the modified electrode in the oxidation of alkaline solution of methanol was investigated. The experimental conditions affecting the performance of the modified electrode in the methanol oxidation were studied and optimized. Finally, the proposed electrode has the onset potential of −0.5 V and the ratio of if/ib equal to 2.2, which confirms the high catalytic activity. The electrode has appropriate stability and shows about 86% of initial activity after 100 times testing.

Optical properties of thin Ag - In films prepared by interdiffusion in bimetallic nanolayered stacks

The present work reports on the preparation, structural and optical properties of thin bimetallic films from the Ag-In system. Thin films with required compositions were prepared by annealing of Ag/In stacks. The chemical and phase composition, as well as the surface morphology of thin films were analyzed by energy dispersive X-ray microanalysis, X-ray diffraction and atomic force microscopy, respectively. The optical properties of the thin film coatings were characterized by spectroscopic ellipsometry. The increase of the indium content increases the values of the imaginary part of the complex permittivity in the visible spectral region and decreases them in the ultraviolet spectral region. As a result, a shift of the plasmonic activity towards higher photon energies was achieved.

Structural, Wetting and Magnetic Properties of Sputtered Fe70Pd30 Thin Film with Nanostructured Surface Induced by Dealloying Process

FePd alloys in the thin film form represent a multipurpose and versatile material with relevant chemical and physical properties studied in different research fields. Moreover, the ability to manipulate and fine-tune the film surface with nanometric scale precision represents a degree of freedom useful to adapt these thin film properties to the demands of different desired applications. In this manuscript, Fe70Pd30 (at. %) thin films are prepared with a thickness of 50 and 200 nm by means of the widely used co-sputtering deposition technique. Subsequently, selective removal of the iron element from the alloy and the consequent surface diffusion of the palladium was induced by a dealloying treatment under free corrosion conditions in hydrochloric acid. The size and shape of the grains of the as-deposited thin films determine the dissolution rate of the iron element with a direct consequence not only on the surface morphology and the stoichiometry of the alloy but also on the wetting and magnetic properties of the sample. X-ray diffraction, Scanning Electron Microscopy (SEM) images, contact angle and magnetic measurements have been performed to provide a thorough characterisation of the fundamental properties of these nanostructured bimetallic thin films.

Investigation of charge transfer interaction in heterometallic precursors to control their surface reactivity for MOCVD of Pd-Cu alloy films

The work aims to study main factors determining surface reactions mechanism of the heterometallic MOCVD precursors for multicomponent inorganic films. A set of theoretical and experimental techniques is proposed to investigate the electronic structure of the copper-palladium precursor to control its surface reactivity in MOCVD of Pd-Cu alloy films. The surface and bulk charge distribution in the heterometallic precursors CuPdL4 (1) and Cu(hfa)2PdLF2 (2) and parent monometallic complexes was carried out using both experimental X-ray photoelectron (XPS) and X-ray emission (XES) spectroscopies and theoretical techniques (DFT calculations and NBO analysis). Comparison of calculated and experimental atomic charges for monometallic and heterometallic complexes revealed the electronic density redistribution on oxygen and metal atoms due to electronic charge transfer interaction between monometallic fragments in the heterocomplex, which was confirmed by NBO analysis. The charge transfer intensity appeared to be stronger for the fluorinated precursor 2, indicating its greater resistance to thermal dissociation into monometallic fragments compared to 1, which was confirmed by the data on the bimetallic films composition. Thus, the evidenced charge transfer interaction can be altered by changing the composition of the precursors to control their surface reactivity and films composition.

Bimetallic mesoporous RhRu film for electrocatalytic nitrogen reduction to ammonia

Bimetallic mesoporous RhRu film on Ni foam has been prepared for the efficient electrosynthesis of ammonia.

Film Fabrication and Composition Control of Transition Metal Oxide Nanoparticles for Oxygen Evolution Catalysts

Development of highly efficient oxygen evolution reaction (OER) catalysts is necessary for commercial implementation of water electrolysis due to overcome slow kinetics of OER. Noble metal based electrocatalysts such as Ir and Ru demonstrate high performance for OER in acidic media. In contrast, the first-row transition metal oxides such as Ni, Co, and Fe oxides show the high catalytic activity and stability in alkaline media. In this work, the composition of bimetallic metal oxide NPs was tuned and their electrochemical performance was analyzed. Furthermore, the electrophoretic deposition (EPD) technique was utilized for the efficient fabrication of NP thin film electrode. The bimetallic transition metal oxide NPs were synthesized by using Ni(acac)2 as Ni precursor and Fe(acac)3 as Fe precursor, leading to the phase control of bimetallic Ni-Fe oxide NPs. As Fe precursor amount was gradually increased compared to that of Ni, the particle size of Ni-Fe oxide NPs was increased, and the shape of NPs was transformed from spherical to irregular shape. The magnetic property of Ni-Fe oxide NPs was also analyzed by vibrating sample magnetometer. The saturation magnetization (Ms) of bimetallic metal oxide was increased and the magnetic coercivity was decreased when the Fe composition was increased. For the electrochemical analysis for OER, the overpotential of bimetallic metal oxide NPs catalysts was highly influenced by the composition of bimetallic metal oxide NPs. Higher Fe contents than Ni in the NPs led to high performance as OER catalysts. The EPD technique was introduced to manufacture the uniform NP films with improved catalytic activity. The catalyst film formed through EPD technique was prepared under the applied voltage of 500 V for 10 minutes. The film of Ni-Fe oxide NPs was well covered on the substrate of the Ti foil. The overpotential of the bimetallic metal oxide NP film fabricated by EPD was decreased from 510 mV to 400 mV at 10 mA/cm2 compared to the films fabricated by drop casting. These results provide useful insights not only for understanding the catalytic activity of bimetallic metal oxide NPs in OER but also for suggesting the film fabrication method for enhancing the catalytic activity.

Antimicrobial Cellulose Nanocomposite Films with In Situ Generations of Bimetallic (Ag and Cu) Nanoparticles Using Vitex negundo Leaves Extract

Antimicrobial cellulose nanocomposite films with in situ synthesized bimetallic nanoparticles were developed by a three-step process. These antimicrobial cellulose nanocomposite films with in situ synthesized bimetallic, silver (Ag) and copper (Cu) nanoparticles (NPs) through the apozem of medicinal important plant Vitex negundo (Vavili) leaves, and which is acts as a bio-reductant and stabilizing agent. Through a three-step process, the cellulose films were prepared via a solution casting method and loaded with the apozem of V. negundo (Vavili) leaves via the swelling process. The resulted nanocomposite films were characterized by XRD, UV, FTIR, SEM/EDAX, TGA, UTM and antibacterial measurements. The XRD studies confirm that the presence of AgNPs and CuNPs in the cellulose matrix. The formation Ag/Cu, bimetallic nanoparticles were observed by the change of the color of the cellulose films. The presence of UV absorption peaks at around ~ 415 (Ag) and ~ 570 nm (Cu) confirms the formation of bimetallic cellulose nanocomposite films. The SEM and EDAX spectrum confirmed the presence of Ag, Cu, and Ag/Cu elements. The average size of the Ag–Cu, Ag, and Cu nanoparticles generated were ~ 60, ~ 67, and ~ 74 nm, respectively. The UTM and TGA studies revealed that bimetallic nanocomposites have high strength and stability than monometallic nanocomposite films. The nanocomposites have shown good antibacterial activities towards gram-positive and gram-negative bacteria. These cellulose nanocomposite films stand as good candidature for food, medical, and disinfection packaging materials.

Tunable surface plasmon resonance of Al-Cu bimetallic nanoparticles thin films induced by pulsed-laser

Al-Cu bimetallic nanoparticles (NPs) thin film was fabricated by Nd:YAG fiber pulsed-laser irradiation of Al/Cu bilayers at ambient conditions. The effects of laser irradiation on the morphology, structure, composition and optical properties of the samples were investigated. The tunability of both localized surface plasmon resonance (LSPR) wavelength and intensity were realized by varying the pulse shot or relative thickness of Al/Cu bilayers. The SEM analysis with EDS results further revealed that the obtained particles consisted of a mean diameter of 36–80 nm bimetallic NPs system, being dependent on the Cu proportion. In addition, Surface-enhanced Raman spectroscopy (SERS) measurement and corresponding finite-difference time-domain (FDTD) simulation of before and after laser irradiation samples were discussed to verify the LSPR properties.

Thermal annealing induced tunable localized surface plasmon resonance of Au/Ag bimetallic thin film

Abstract Tunable localized surface plasmon resonance (LSPR) was achieved on thermally annealed thin films composed of Au deposited on Ag. Characterization of the crystallographic structure, morphology, and optical properties of the thin films was done by X-ray diffraction (XRD), scanning electron microscope (SEM), atomic force microscopy (AFM), UV–VIS-NIR double-beam spectrometer, and Raman system. The XRD results confirmed that thermal annealing improved the grain growth and orientation of Au/Ag bimetallic thin films. AFM and SEM results showed that Au/Ag bimetallic thin films transformed into Au/Ag ellipsoid nanoparticles (NPs) on thermal annealing. The LSPR wavelength of Au/Ag NPs could be tuned between 500 nm and 342 nm. Additionally, the Raman scattering could be adjusted by increasing the thickness of Ag in the Au/Ag bimetallic composite structure.

Coherently coupled quantum-well states in bimetallic Pb/Ag thin films

It has been well established that the presence of quantum-well states in metal thin films plays an essential role in determining the thickness dependence of many physical properties. Oscillatory features in these properties are often observed and attributed to the energy variations of these quantum-well states near the Fermi level. Modern film growth capability has made it possible to create composite metal thin films in which one metal thin film is stacked on top of a dissimilar one with precise control of individual thickness. How the original quantum-well states evolve in the composite film becomes a critical issue in understanding the electronic structure of these new complex thin-film systems. In this paper we present first-principles calculations and measurements by angle-resolved photoemission spectroscopy for electronic states in a bimetallic film composed of ten layers of Pb and nine layers of Ag in the [111] direction on a Si substrate. It is found that the original quantum-well states in individual Pb and Ag films evolve into a new set of states in the bimetallic film by extending into the additional space, instead of directly coupling with each other as one would have expected. The new set of quantum-well states therefore has modified effective masses and energy values compared with the parent ones. Even though the Pb/Ag interface is incommensurate, the coherently coupled electronic states across the whole bimetallic film are verified by supercell configurations with different rotational arrangements in the calculation. The excellent agreement between theory and experiment in the energy dispersion of the quantum-well states in this bimetallic film confirms the physical picture proposed in this work, which could form the basis for exploring the electronic structure in multiple stacked thin films with more complicated designs.

All nitride asymmetric supercapacitors of niobium titanium nitride-vanadium nitride

Metal nitrides are potential electrode materials for supercapacitors because of their high conductivity, high capacitance and good corrosion resistance. Herein, we present a general strategy to prepare self-standing bimetallic nitride thin film nanostructures using magnetron co-sputtering and further to boost their electrochemical performance for supercapacitors. Using niobium titanium nitride (TiNbN) as an example, we show that the synergy of Ti and Nb greatly boosts the capacitive performance to a high specific capacitance of up to 59.3 mF cm−2 at 1.0 mA cm−2, along with outstanding cycling stability for at least 20000 cycles. We further demonstrate an all metal nitride based asymmetric device by combing TiNbN with a vanadium nitride (VN) negative electrode. The asymmetric device operates at a voltage window of 1.6 V and achieves a maximum energy density 74.9 mWh cm−3 at a power density of 8.8 W cm−3. Our work not only presents a first demonstration of employing TiNbN as supercapacitor electrode material, but also opens up new possibility for the rational construction of all nitride based high performance asymmetric supercapacitors.

Synergistic effects in bimetallic Pd\u2013CoO electrocatalytic thin films for oxygen evolution reaction

Bimetallic catalysts due to the synergistic effects often outperform their single-component counterparts while exhibiting structure and composition-dependent enhancement in active sites, thereby having the potential to improve the current density and over-potential parameters in the water oxidation reaction. Herein, we demonstrate a simple and rapid, yet highly efficient method to fabricate Pd–CoO films of immaculate homogeneity as characterized using different imaging and spectroscopic techniques. The SEM images revealed that the films were composed of bimetallic spherical granules wherein both metals were uniformly distributed in an atomic ratio of ~ 1:1. The time-dependent investigations of the film fabrication behavior demonstrated that the films formed in shorter deposition times (1–2 h) display more porous character, allowing better access to the reaction centers. This character was transcribed into their enhanced electrocatalytic performance toward the oxygen evolution reaction (OER). Using this specific bimetallic formulation, we could attain a low over-potential of 274 mV for a current density of 10 mA cm−2, whereas the high current density value of > 200 mA cm−2 was achieved while still under 600 mV of over-potential. The cycling and current generation stability was also found to be sufficiently high, which can only be attributed to the facile electron transfer processes and a higher number of active sites available in homogeneous bimetallic films.

Photoinduced Charge Transfer and Bimetallic Bond Dissociation of a Bi-W Complex in Solution.

Organometallic complexes including metal carbonyls have been widely utilized in academic and industrial settings for purposes ranging from teaching basic catalytic reactions to developing state-of-the-art electronic circuits. Characterization of these materials can be obtained via steady-state measurements; however, the intermediate photochemical events remain unclear, hindering effective and rational molecular engineering methods for new materials. We employed femtosecond transient absorption (fs-TA) and ground-state femtosecond stimulated Raman spectroscopy (FSRS) on triphenylbismuth-tungsten pentacarbonyl complex, a solution precursor for bimetallic oxide thin films. Upon 280 nm excitation into a charge-transfer band, an ultrafast bimetallic bond dissociation occurs within ∼140 fs. The subpicosecond nondiffusive solvation events are followed by ∼10 ps (15 ps) methanol (ethanol) complexation of the nascent tungsten pentacarbonyl intermediate, which mainly undergoes vibrational relaxation after crossing into a hot ground state. The trans ligand to axial CO is revealed to play a key role in the electronic and vibrational structure and dynamics of the complex. These findings could power rational design of bimetallic and functional solution precursors for the light-driven nanopatterning of thin films.