Noble Metals Au Research Articles

Genetic-algorithm-aided ultra-broadband perfect absorbers using plasmonic metamaterials.

Complete absorption of electromagnetic waves is paramount in today's applications, ranging from photovoltaics to cross-talk prevention into sensitive devices. In this context, we use a genetic algorithm (GA) strategy to optimize absorption properties of periodic arrays of truncated square-based pyramids made of alternating stacks of metal/dielectric layers. We target ultra-broadband quasi-perfect absorption of normally incident electromagnetic radiations in the visible and near-infrared ranges (wavelength comprised between 420 and 1600 nm). We compare the results one can obtain by considering one, two or three stacks of either Ni, Ti, Al, Cr, Ag, Cu, Au or W for the metal, and poly(methyl methacrylate) (PMMA) for the dielectric. More than 1017 configurations of geometrical parameters are explored and reduced to a few optimal ones. This extensive study shows that Ni/PMMA, Ti/PMMA, Cr/PMMA and W/PMMA provide high-quality solutions with an integrated absorptance higher than 99% over the considered wavelength range, when considering realistic implementation of these ultra-broadband perfect electromagnetic absorbers. Robustness of optimal solutions with respect to geometrical parameters is investigated and local absorption maps are provided. Moreover, we confirm that these optimal solutions maintain quasi-perfect broadband absorption properties over a broad angular range when changing the inclination of the incident radiation. The study also reveals that noble metals (Au, Ag, Cu) do not provide the highest performance for the present application.

Fabrication of noble metal (Au, Ag, Pt)/polythiophene/reduced graphene oxide ternary nanocomposites for NH3 gas sensing at room temperature.

Room temperature NH3 gas sensors composed of noble metal (Au, Ag or Pt)/polythiophene/reduced graphene oxide (Au, Ag or Pt/PTh/rGO) ternary nanocomposite films were fabricated using a simple one-pot redox reaction. The surface morphology and composition of Au, Ag or Pt/PTh/rGO ternary nanocomposite films were analyzed using Fourier transform infrared spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). Compared with Ag/PTh/rGO and Pt/PTh/rGO ternary nanocomposite films, obviously bright Au nanoparticles were observed on the surface of the massive lamination PTh film which wrapped the rGO, and encapsulated Au nanoparticles were observed in the Au/PTh/rGO film. Comparative gas sensing results showed that the Au/PTh/rGO ternary nanocomposite film had the highest response compared with Ag/PTh/rGO and Pt/PTh/rGO ternary nanocomposite films at room temperature, especially when the testing concentration of NH3 gas was below 5 ppm. The Au/PTh/rGO ternary nanocomposite film also had a fast response time and good reproducibility. The combination of the high catalytic activity of naked Au nanoparticles and the formation of effective carrier transfer channels by encapsulated Au nanoparticles was responsible for the improved response of the Au/PTh/rGO ternary nanocomposite film.

Effect of Au loading on Schottky barrier height in TiO2 + Au plasmonic photocatalysts

Composites of TiO2 and different amounts of plasmonic noble metal Au (0.25–2 wt%) were synthesized by employing the wet impregnation technique. The results of SEM, TEM, XRD and N2 physisorption analyses reveal that the morphologies of the prepared composites are similar to the morphology of bare TiO2 support and are not influenced by the increasing amount of deposited Au nanoparticles. On the other hand, the size of Au ensembles in the TiO2 + Au composites increased from 27.1 to 54.9 nm with the increasing amount of Au. With the increase of the diameter of Au ensembles, the intensity of the surface plasmon resonance (SPR) effect of Au ensembles in the UV–Vis diffuse reflectance spectra of the composites increased. The X-ray photoelectron spectroscopy (XPS) analysis of the valence band maxima (VBM) of the investigated photocatalysts revealed that the height of the Schottky barrier (SBH) at the Au/TiO2 junction in the investigated TiO2 + Au composites decreased from 0.4 to 0.15 eV with the increasing amount of Au (and their size). Therefore, the visible-light-generated “hot electrons” in Au ensembles of TiO2 + 2% Au composite have to overcome a lower energy barrier during the injection into the conduction band (CB) of the TiO2 support than “hot electrons” in the Au ensembles in the TiO2 + 0.25% Au composite. This makes the “hot electrons” in the TiO2 + 2% Au composite less accessible for the recombination with the visible-light generated holes, as the “hot electrons” do not agglomerate at the Schottky barrier (SB). This phenomenon was well expressed in the results of electrochemical impedance spectroscopy (EIS) analysis: under visible-light illumination, the TiO2 + 2% Au composite generated the highest amount of charge carriers among all investigated photocatalysts. The beneficial effect of the low SBH in the TiO2 + 2% Au solid was also expressed in the photoluminescence (PL) emission spectra, where the TiO2 + 2% Au composite showed the lowest charge carrier recombination rate. Further, the TiO2 + 2% Au composite expressed the highest visible-light triggered photocatalytic activity in the hydroxyl radical (OH·) generation and water-dissolved bisphenol A (BPA) oxidation test.

Photo-assisted sequential assembling of uniform metal nanoclusters on semiconductor support

SummaryDispersing metal nanoclusters on the oxide supports is attracting close attention in heterogeneous catalysis, but great challenges still lie in controlling the size and dispersion of nanoclusters due to the inevitable agglomeration. Here, we propose a sequential photochemical deposition strategy named “first store, and then release” to uniformly fabricate the size-controlling noble metal nanoclusters on semiconductor oxides. Using the typical semiconductor TiO2, the photoexcited electrons can be first stored as reduced species (e.g. Ti3+) under irradiation and the Ti3+ species can optimize both the nucleation and growth processes in dark reaction, resulting in a uniform dispersing of various noble metals (Au, Pt, Ag etc.) with size diameters of ∼1 nm. The nanoclusters catalysts exhibited superior performance in catalytic oxidation of HCHO compared with that of nanoparticles. This work brings a new and useful strategy to construct size-controlling noble metals on the oxide supports for heterogeneous catalysis and the related fields.

Adsorption Performance of Noble-Metal Decorated InN Monolayer to CO: A Computational Study

In this paper, based on density functional theory (DFT), the adsorption properties of four noble metal(Au, Ag, Pd and Rh) decorated InN monolayers to CO were investigated. The results indicate that the decorated InN monolayers with Pd, Ag and Au dopant have excellent adsorption capacities for CO, and the adsorption energies are −1.366, −0.948 and −1.318 eV, respectively. Density of states (DOS) and deformation charge density (DCD)analysis were adopted to further analysis of the electronic structure of the adsorption system. Besides, the change in the band gap of each system before and after adsorption was calculated based on the frontier orbital theory and desorption time of CO from each decorated InN monolayer was estimated to evaluate its potential applications in the sensor field.

Hydrogen photo-production from glycerol on platinum, gold and silver-modified TiO2-USY62 catalysts

In this work, photocatalysts consisting of TiO2 supported on zeolite (USY62) were synthesized by sol-gel method and, subsequently, a noble metal (Pt, Au, or Ag) was incorporated by impregnation or photodeposition. Zeolite-TiO2 composites were characterized by SEM, TEM, XRD, N2 adsorption-desorption, Raman and UV–vis spectroscopy, and well-dispersed anatase TiO2 particles (ca. 10 nm) that exhibited a blue-shift in the UV–vis absorption due to the size quantization effect were produced. The photocatalytic activity of all zeolite-TiO2 composites was examined by the photoreforming of aqueous glycerol solution (10% w/w) under UV and solar-simulated radiation. The activity of the zeolitic photocatalysts decreased in the order Pt > Au > Ag, being catalysts prepared by photodeposition more active than those prepared by impregnation. Moreover, Zeolite-supported TiO2, led to a TiO2 with smaller deactivation in H2 production than unsupported TiO2, which can be ascribed to the small TiO2 particle size or an interaction zeolite-TiO2. All in all, a photocatalyst (USY-Ti-PPt) with TiO2 up to four times more active than unsupported TiO2 under UV radiation was prepared.

Porous-coral-like cerium doped tungsten oxide/graphene oxide micro balls: A robust electrochemical sensing platform for the detection of antibiotic residue

Metal oxides decorated carbon nanomaterials, as an electrode material have been well explored in the field of electrochemical sensor. However, instead of using the high concentration of graphene oxide (GO), we try to explore the influence of minimum quantity of GO in material synthesis. Here we demonstrate the hydrothermal synthesis of low-cost cerium (Ce)-doped tungsten oxide/graphene oxide (CeW/GO) composite for the precise electrochemical detection of antibiotic drug furazolidone (FUZ). For the synthesis of composite, 40 μg/mL concentration of GO has been utilized. Then, several physicochemical and electrochemical techniques were used to examine the morphological, structural, and electrochemical characteristics of the CeW/GO composite. Interestingly, the composite material has a porous-coral-like structure, which is being described here for the first time. The GO nanosheets cover the CeW and make the smooth surface and lead to the porous structure. Then we looked into the analytical behavior of CeW/GO composite modified glassy carbon electrode for the application towards the electrochemical detection of the FUZ using the voltammetric technique. The effect of experimental conditions, including loading concentration of active material, pH, scan rate, accumulation time, and concentration of FUZ, were analyzed with respect to the reduction peak current response of FUZ. At the optimum conditions, the fabricated sensor has a low detection limit (0.054 μM), appreciable sensitivity (2.5 μA μM −1 cm −2 ) with a wide linear range (1–260 μM), and the decent anti-interference ability for FUZ detection. Furthermore, the developed sensor was successfully used to assess the FUZ concentration in the human urine samples, yielding satisfactory results. • porous-coral-like CeW/GO micro balls composite material was designed for the first time. • The CeW/GO composite was employed as a novel electrocatalyst to detect the furazolidone (antibiotic drug). • A detailed study was made on electrochemical performance of the developed sensor. • The performance of CeW/GO/GCE was comparable with the noble metals (Pt, Re, and Au) based modified electrodes.

Bi2O3@Bi nanoparticles for ultrasensitive electrochemical determination of thiourea: monitoring towards environmental pollutants

Thiourea and other sulphur containing organic molecules are commonly present in industrial waste water and because of their toxic nature are environmental pollutants. Thiourea oxidation constructed on cost effective and proficient catalyst to substitute/alternative with noble metals (Pt, Au, Ir, Rh, Pd and others) based electrodes. Herein, this report for the synthesis of Bi2O3@Bi (∼ 4-5 nm) nanoparticles by using polyfunctional citric acid is a surface protecting molecule for electrocatalytic thiourea oxidation reactions as a one of the environmental hazardous monitoring system at room temperature. These as-synthesized nanoparticles were well characterized by scanning electron microscopy (SEM), Furrier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA) and further studied for electrochemical determination of thiourea (TU). These structural and morphological studies were further confirms the rhombohedral crystal structure with thermogravimetric analysis (TGA) shows 20 wt% citrate molecules on the surface of Bi2O3@Bi nanoparticles. The electrochemical studies on Bi2O3@Bi nanoparticle reveals that, it's having ultra-low detection limit, higher sensitivity and better activity at ultralow potential for a current density of 11.2 mA/cm2 for oxidation of thiourea (TU). Moreover, chronoamphrometric (i-t) measurement shows proposed Bi2O3@Bi based system is having stable and long term current performance at a potential of 0.85 V vs. SCE towards the TU oxidation. This work affords with noble metal free electrocatalyst for novel appliance and remarkable consequence as a thiourea determination and conversion as a part of waste management.

A Nanocluster [Ag307Cl62(SPhtBu)110]: Chloride Intercalation, Specific Electronic State, and Superstability

The controlling synthesis of novel nanoclusters of noble metals (Au, Ag) and the determination of their atomically precise structures provide opportunities for investigating their specific properties and applications. Here we report a novel silver nanocluster [Ag307Cl62(SPhtBu)110] (Ag307) whose structure is determined by X-ray single crystal diffraction. The structure analysis shows that nanocluster Ag307 contains a Ag167 core, a surface shell of [Ag140Cl2S110], and a Cl60 intermediate layer located between Ag167 and [Ag140Cl2S110]. It is a first example that such many chlorides are intercalated into a Ag nanocluster. Chlorides are released in situ from solvent CHCl3. Nanocluster Ag307 exhibits superstability. Differential pulse voltammetry experiment reveals that Ag307 has continuous charging/discharging behavior with a capacitance value of 1.39 aF, while the Ag307 has a surface plasmonic feature. These characteristics show that Ag307 is of metallic behavior. However, its electron paramagnetic resonance (EPR) spectra display a spin magnetic behavior which could be originated from the unpassivated dangling bonds of surface atoms. The direct capture of EPR signals can be attributed to the Cl- intercalating layer which partly suppresses the electronic interactions between core and surface atoms, resulting in the relatively independent electronic states for core and surface atoms.

Characterization and Structural Insights of the Reaction Products by Direct Leaching of the Noble Metals Au, Pd and Cu with N,N'-Dimethyl-piperazine-2,3-dithione/I2 Mixtures.

In the context of new efficient and safe leaching agents for noble metals, this paper describes the capability of the Me2pipdt/I2 mixture (where Me2pipdt = N,N′-dimethyl-piperazine-2,3-dithione) in organic solutions to quantitatively dissolve Au, Pd, and Cu metal powders in mild conditions (room temperature and pressure) and short times (within 1 h in the reported conditions). A focus on the structural insights of the obtained coordination compounds is shown, namely [AuI2(Me2pipdt)]I3 (1), [Pd(Me2pipdt)2]I2 (2a) and [Cu(Me2pipdt)2]I3 (3), where the metals are found, respectively, in 3+, 2+ and 1+ oxidation states, and of [Cu(Me2pipdt)2]BF4 (4) and [Cu(Me2dazdt)2]I3 (5) (Me2dazdt = N,N′-dimethyl-perhydrodizepine-2,3-dithione) compared with 3. Au(III) and Pd(II) (d8 configuration) form square–planar complexes, whereas Cu(I) (d10) forms tetrahedral complexes. Density functional theory calculations performed on the cationic species of 1–5 help to highlight the nature of the bonding in the different complexes. Finally, the valorization of the noble metals-rich leachates is assessed. Specifically, gold metal is quantitatively recovered from the solution besides the ligands, showing the potential of these systems to promote metal recycling processes.

Investigation of Interaction of Noble Metals (Cu, Ag, Au, Pt and Ir) with Nanosheets.

Two-dimensional nanomaterials, such as graphene and hexagonal boron nitride nanosheets, have attracted tremendous interest in the research community and as a starting point for the development of nanotechnology. Using classical applied mathematical modeling, we derive explicit analytical expressions to determine the binding energies of noble metals, including copper, silver, gold, platinum and iridium (Cu, Ag, Au, Pt and Ir) atoms, on graphene and hexagonal boron nitride nanosheets. We adopt the 6–12 Lennard–Jones potential function, together with the continuous approach, to determine the preferred minimum energy position of an offset metal atom above the surface of the graphene and hexagonal boron nitride nanosheets. The main results of this study are analytical expressions of the interaction energies, which we then utilize to report the mechanism of adsorption of the metal atoms on graphene and hexagonal boron nitride surfaces. The results show that the minimum binding energy occured when Cu, Ag, Au, Pt and Ir were set at perpendicular distances in the region from 3.302 Å to 3.683 Å above the nanosheet surface, which correspond to adsorption energies in the region ranging from 0.842 to 2.978 (kcal/mol). Our results might assist in providing information on the interaction energies between the metal atoms and the two-dimensional nanomaterials.

Hot-Electron Injection and Charge Carrier Lifetime Prolongation Enhance the Photoelectrochemical Performance of a Plasmonic CdS/Au Photoanode

The utilization of the surface plasmon resonance effect of plasmonic noble metal Au or Ag nanostructures is an effective paradigm for increasing the photoelectrochemical performance of photoelectro...

Relaxation dynamics of hot electrons in the transition metals Au, Ag, Cu, Pt, Pd, and Ni studied by ultrafast luminescence spectroscopy

The ultrafast relaxation dynamics of photoexcited electrons in six transition metals, Au, Ag, Cu, Pt, Pd, and Ni, were investigated using femtosecond luminescence spectroscopy in the infrared region between 0.4 and 1.05 eV. The behaviors of the time-resolved spectra are significantly different between group 11 noble metals (Au, Ag, and Cu) and group 10 transition metals (Pt, Pd, and Ni), which are neighbors in the periodic table of elements. In the latter group, the instantaneous luminescence intensities are one order of magnitude lower and the lifetimes (around 200 fs) are far shorter than those of the group 11 metals (typically 700 fs). The time-resolved spectra, decay profiles, and excitation power dependence were analyzed using a phenomenological model that considers both the nonthermal and thermal electrons. It was found that the nonthermal component is remarkably small in the group 10 transition metals. These systematic differences between group 10 and 11 metals are ascribed to the differences in their electron band structures and/or electron–phonon coupling strengths.

Carbon Nanotube Assemblies for Neuroscience Applications

Assembling carbon nanotubes (CNTs) into macroscopic materials allows multiple applications that takes advantage of their physical properties. Specifically, the synthesis, fiber assembly, polymer coating and application of CNTs as microelectrodes has allowed us explore physiological applications as well as sensor development. This talk will summarize our research in CNT microelectrode development, neural recording and stimulation, and neurotransmitter detection and quantification through voltammetric techniques. Recordings and stimulations of neuronal electrical activity is a topic of great interest in neuroscience. Current commercial electrodes for transferring charges from solid electrode materials to and from biological tissue still have some limitations. A microelectrode that is flexible, chemically inert, electrically conducting, and preferentially transfers electrons via capacitive charge-injection is needed to treat multiple neurological disorders. This talk will compare charge transport capabilities from carbon nanotube fibers, noble metals Au and Ag wire microelectrodes to biological tissue. The recording ability of microelectrodes is demonstrated through Electroretinography (ERG) on Sarcophaga bullata fly eyes, where light stimulation generates potential changes that were detected by our microelectrodes. Stimulation is demonstrated through Au wire and carbon nanotube fiber implants in Madagascar hissing cockroach (Gromphadorhina portentosa) antennas to control their locomotion directions. In addition, CNT microelectrodes has been found to detect neurotransmitters dopamine (DA), serotonin (5-HT), epinephrine (Epn) and nor-epinephrine (Nor-epn) using voltammetric techniques with excellent limits of detection in the range of ~10-11 M. For practical applicability, the electrodes can detect in real time DA release from culture rat pheochromocytoma (PC12) cells upon concentrate K+stimulation.

One‐Step Formation of Hybrid Nanocrystal Gels: Deposition of Metal Domains on CdSe/CdS Nanorod and Nanoplatelet Networks

AbstractHybrid semiconductor‐based nanocrystals (NCs) are generally synthesized in organic media prior to their assembly into catalytically promising nanostructures via multistep methods. Here, a tunable, easy‐to‐adapt and versatile approach for the preparation of hybrid nanoparticle networks from aqueous nanocrystal solutions is demonstrated. The networks consist of interconnected semiconductor NC backbones (made of CdSe/CdS dot‐in‐rods or core/crown nanoplatelets) decorated with noble metal (Au and Pt) or with metal‐based domains (Co2+ and Ni2+) demonstrating a powerful synthetic control over a variety of hybrid nanostructures. The deposition of the domains and the formation of the network take place simultaneously (one‐step method) at room temperature in dark conditions without any external trigger. Beside the in‐depth structural characterization of the gel‐like hybrid networks, the wavelength‐dependent optical features are studied to reveal an efficient charge carrier separation in the systems and a controllable extent of fluorescence quenching through the domain sizes. Photoluminescence quantum yields and decay dynamics highlight the importance of fine‐tuning the conduction band/Fermi level offset between the semiconductors and the various deposited metals playing central role in the electron–hole separation processes. This procedure provides a novel platform toward the preparation of photo(electro)catalytically promising hybrid nanostructures (acetogels and xerogels) without the need of presynthetic hybrid particle design.

Ab initio theory of the Drude plasma frequency

We derive a theoretical expression to calculate the Drude plasma frequency ω D based on quantum mechanical time-dependent perturbation theory in the long-wavelength regime. We show that, in general, ω D 2 should be replaced by a second-rank tensor, the Drude tensor D , which we relate to the integral over the Fermi surface of the convective momentum flux tensor divided by the magnitude of the Fermi velocity and which is amiable to analytical and numerical evaluation. We also obtain an expression in terms of the average inverse mass tensor. For Sommerfeld’s model of metals, our expression yields the ubiquitous plasma frequency ω D 2 = 4 π n e e 2 / m e . We compare our expressions with those of previous theories. The Drude tensor takes into account the geometry of the unit cell and may be calculated from first principles for isotropic as well as anisotropic metallic systems. We present results for the noble metals Ag, Cu, and Au without stress and subject to isotropic and uniaxial strains; we also compare the results with those available from experiments. We show that, within density functional theory, nonlocal potentials are necessary to obtain an accurate Drude tensor.

Investigation of doping effects of different noble metals for ethanol gas sensors based on mesoporous In2O3

Elaborating the sensitization effects of different noble metals on In2O3 has great significance in providing an optimum method to improve ethanol sensing performance. In this study, long-range ordered mesoporous In2O3 has been fabricated through replicating the structure of SBA-15. Different noble metals (Au, Ag, Pt and Pd) with the same doping amount (1 at%) have been introduced by an in situ doping routine. The results of the gas sensing investigation indicate that the gas responses towards ethanol can be obviously increased by doping different noble metals. In particular, the best sensing performance towards ethanol detection can be achieved through Pd doping, and the sensors based on Pd-doped In2O3 not only possess the highest response (39.0–100 ppm ethanol) but also have the shortest response and recovery times at the optimal operating temperature of 250 °C. The sensing mechanism of noble metal doped materials can be attributed to the synergetic effect combining ‘catalysis’ and ‘electronic and chemical sensitization’ of noble metals. In particular, the chemical state of the noble metal also has a great influence on the gas sensing mechanism. A detailed explanation of the enhancement of gas sensing performance through noble metal doping is presented in the gas sensing mechanism part of the manuscript.

Versatile Mesoporous Nanoparticles for Cell Applications.

Mesoporous silica nanostructures are emerging as a promising platform able to deal with challenges of many different applications in fields such as biomedicine and nanotechnology. The versatile physical and functional properties of these materials like high specific surface area, ordered porosity, chemical stability under temperature and pH variations, and biocompatible performance, offers new approaches to many biomedical applications ranging from drug delivery systems to biosensing, cell applications and tissue engineering. Their morphology, size and textural properties can be easily tailored by means of chemical control, giving rise to a variety of nanostructures with hexagonal (SBA15, MCM41) or cubic (SBA16) arrangement of channels and pore size ranging from 1.3 to 10 nm. Based on the versatility of their silane surface, a plethora of hybrid mesoporous matrices can be prepared incorporating new functionalities like contrast enhancement for magnetic resonance imaging, magnetic/plasmonic hyperthermia, drug delivery or cell applications by the simple grafting of superparamagnetic metal oxides (Fe₃O₄, transition metal ferrites) nanoparticles, noble metal (Au, Ag) nanoparticles, fluorescent moieties (fluorescein, rhodamine) or biological agents (mAb, mRNA, etc). The goal of this work is to present the development, by a facile soft template method, of size tailored mesoporous silica nanospheres from 20 to 350 nm (by means of chemical control), and highlight its versatility for surface grafting (with rhodamine and polydopamine) and their biological compatibility and efficient uptake by cultured HeLa cells. The combined, physicochemical and biological, properties indicate that MSNs are good candidates for cell tagging, gene transfer or targeted therapies.

Plasmon-Driven Chemistry on Mono- and Bimetallic Nanostructures.

ConspectusHot carriers are highly energetic species that can perform a large spectrum of chemical reactions. They are generated on the surfaces of nanostructures via direct interband, phonon-assisted intraband, and geometry-assisted decay of localized surface plasmon resonances (LSPRs), which are coherent oscillations of conductive electrons. LSPRs can be induced on the surface of noble metal (Ag or Au) nanostructures by illuminating the surfaces with electromagnetic irradiation. These noble metals can be coupled with catalytic metals, such as Pt, Pd, and Ru, to develop bimetallic nanostructures with unique catalytic activities. The plasmon-driven catalysis on bimetallic nanostructures is light-driven, which essentially enables green chemistry in organic synthesis. During the past decade, surface-enhanced Raman spectroscopy (SERS) has been actively utilized to study the mechanisms of plasmon-driven reactions on mono- and bimetallic nanostructures. SERS has provided a wealth of knowledge about the mechanisms of numerous plasmon-driven redox, coupling, and scissoring reactions. However, the nanoscale catalytic properties of both mono- and bimetallic nanostructures as well as the underlying physical cause of their catalytic reactivity and selectivity remained unclear for decades.In this Account, we focus on the most recent findings reported by our and other research groups that shed light on the nanoscale properties of mono- and bimetallic nanostructures. This information was revealed by tip-enhanced Raman spectroscopy (TERS), a modern analytical technique that has single-molecule sensitivity and subnanometer spatial resolution. TERS findings have shown that plasmonic reactivity and the selectivity of bimetallic nanostructures are governed by the nature of the catalytic metal and the strength of the rectified electric field on their surfaces. TERS has also revealed that the catalytic properties of bimetallic nanostructures directly depend on the interplay between the catalytic and plasmonic metals. We anticipate that these findings will be used to tailor synthetic approaches that are used to fabricate novel nanostructures with desired catalytic properties. The experimental and theoretical results discussed in this Account will facilitate a better understanding of TERS and explain artifacts that could be encountered upon TERS imaging of a large variety of samples. Consequently, plasmon-driven chemistry should be considered as an essential part of near-field microscopy.

Constructing a Multifunctional Interface between Membrane and Porous Transport Layer for Water Electrolyzers.

The cell performance and durability of polymer electrolyte membrane (PEM) water electrolyzers are limited by the surface passivation of titanium-based porous transport layers (PTLs). In order to ensure stable performance profiles over time, large amounts (≥1 mg·cm-2) of noble metals (Au, Pt, Ir) are most widely used to coat titanium-based PTLs. However, their high cost is still a major obstacle toward commercialization and widespread application. In this paper, we assess different loadings of iridium, ranging from 0.005 to 0.05 mg·cm-2 in titanium PTLs, that consequently affect the investment costs of PEM water electrolyzers. Concerning a reduction in the precious metal costs, we found that Ir as a protective layer with a loading of 0.025 mg·cm-2 on the PTLs would be sufficient to achieve the same cell performance as PTLs with a higher Ir loading. This Ir loading is a 40-fold reduction over the Au or Pt loading typically used for protective layers in current commercial PEM water electrolyzers. We show that the Ir protective layer here not only decreases the Ohmic resistance significantly, which is the largest part of the gain in performance, but moreover, the oxygen evolution reaction activity of the iridium layer makes it promising as a cost-effective catalyst layer. Our work also confirms that the proper construction of a multifunctional interface between a membrane and a PTL indeed plays a crucial role in guaranteeing the superior performance and efficiency of electrochemical devices.