Noble Metal Materials Research Articles

High-efficiency broadband perfect absorber based on a multilayered pyramid structure

In this paper, an ultra-broadband perfect absorber based on a four-layer pyramid metamaterial and a metal insulator metal (MIM) structure has been demonstrated and investigated. Finite-difference time-domain (FDTD) results indicate that the absorption originates from localized surface plasmons and waveguide mode resonance effect. An average absorption of 96.18 % with bandwidth ranging from 308 nm to 2387 nm was achieved, and the average absorption in the entire wave band (200–2800 nm) was approximately 94.64%. The results of the impedance matching theory are consistent with the FDTD simulation. Polarization insensitivity was investigated by studying the absorption characteristic of TE and TM polarizations. The effect of top and bottom materials was investigated and compared in detail. Moreover, by adjusting the geometrical size, the absorption performance can be fine- tuned. In addition, the proposed broadband absorber exhibited excellent absorption stability and environmental refractive index tolerance. Without noble metal materials, the proposed structure can reduce the fabrication costs. We believe that the proposed broadband absorber has potential applications in solar cells, infrared imaging, and thermal emitters.

Highly dispersed CoPx nanoparticles supported on carbon cloth for the enhanced catalytic performance of methanol electro-oxidation

Direct methanol fuel cell (DMFC) is a potential commercial fuel cell technology that is presently hindered by the expensive noble metal materials of the anode. Developing a method to obtain a uniformly dispersed metal phosphide catalyst with narrow size distribution is still a challenge. In this work, cobalt oxide was deposited on carbon cloth (CC) through atomic layer deposition (ALD), then cobalt phosphide was obtained after the phosphorization process. By changing the number of ALD-based ozone pulses (ALD-O3) for CC, the nucleation and growth modes of cobalt oxide (ALD-CoOx) on the CC were regulated, and CoPx nanoparticles with small particle size and uniform distribution were obtained. The optimized CoPx-based catalyst with 40 cycles of ALD-O3 treatment (CoPx/40-CC) exhibits excellent activity (153 mA/cm2) toward methanol electrocatalytic oxidation reaction in the alkaline solution, which is higher than the catalyst prepared by impregnation (Imp-CoPx/CC), although the CoPx loading of CoPx/40-CC is lower than that of Imp-CoPx/CC. The results indicate that the enhanced activity benefits from the small particle size and the uniform CoPx distribution, which promote the electron-transfer and mass transport kinetics of the methanol electro-oxidation process.

Strategies to improve the catalytic activity and stability of bioinspired Cu molecular catalysts for the ORR

The oxygen reduction reaction (ORR) is essential for energy conversion devices such as fuel cells and metal-air batteries. The use of expensive and scarce noble metal materials to catalyze the ORR is a limitation for the massification of these energy conversion technologies. Copper molecular catalysts that mimic the active sites of metalloenzymes such as laccase are under continuous development. In this minireview, we present the strategies to increase the activity and stability of the copper catalysts for the ORR. The flexibility, lability, and electronic character of the ligands are crucial to promote the ORR. In addition, the use of polymers as backbone for multicopper catalysts and the synthesis of copper carbon-based pyrolyzed catalysts present remarkable results with promissory applications. • The rational design of bioinspired Cu-catalysts should focus on the ligand structure. • Ligands' flexibility and lability in Cu-catalysts are crucial to promoting the ORR. • Multicopper catalysts present higher ORR catalytic activity than mononuclear ones. • The stability of multicopper catalysts should be improved. • Multicopper polymeric or pyrolyzed catalysts show remarkable ORR catalytic activity.

Ultrastable Anti-Acid "Shield" in Layered Silver Coordination Polymers.

Surface passivation technology provides noble-metal materials with limited chemical stability, especially under highly acidic condition. To design effective strategy to enhance stability of noble-metal particles, an understanding of their surface anticorrosion mechanism at the atomic level is desirable by using two-dimensional (2D) noble-metal coordination polymer (CP) as an ideal model for their interfacial region. With the protection of 2-thiobenzimidazole (TBI), we isolated two Ag-based 2D CPs, {Ag14 (TBI)12 X2 }n (S-X, where S denotes sheet and X=Cl or Br). These compounds exhibited excellent chemical stability upon immersion in various common solvents, boiling water, boiling ethanol, 10 % hydrogen peroxide, concentrated acid (12 M HCl), and concentrated alkali (19 M NaOH). Systematic characterization and DFT analyses demonstrate that the superior stability of S-X was attributed to the hydrophobic organic shell and dynamic proton buffer layer acting as a double protective "shield".

Wavelength-Dependent Nonlinear Absorption in Platinum Nanoparticles at Off-Resonant Wavelength

In order to obtain optical nonlinear materials with high transparency and low propagation loss in the visible and infrared range, noble metal materials in the off-resonant band have become a hot spot in the optical field in recent years. Therefore, the nonlinear absorption characteristics of platinum nanoparticles (PtNPs) with the surface plasmon resonance (SPR) in the ultraviolet band were investigated with multi-wavelength (500–700 nm) nanosecond Z-scan technology. The measurement results showed that the SPR wavelength of PtNPs was far away from the excitation wavelength, but there were still the saturated absorption (SA) and the reverse saturated absorption (RSA) phenomena, and the size of nonlinear absorption was related to the excitation wavelength and the excitation energy. When the excitation wavelength was constant, with the increase in excitation energy, PtNPs converted from SA to RSA. When the excitation energy was constant, with the excitation wavelength approaching SPR, PtNPs also converted from SA to RSA. The SA and RSA phenomena in the off-resonant region were complementary to the systematic study of the nonlinearity of PtNPs.

Double-Base Plate Cooperative Assembly Strategy for the Construction of Ordered Macro-/Mesoporous Noble-Metal Materials for Enhanced Electrochemical Oxidation of Formic Acid

Herein, we propose a general and mild double-base plate cooperative assembly strategy to synthesize the three-dimensional ordered macro-/mesoporous (3DOM/m) noble-metal materials (including Pd, Pt, and Ru), in which the unique double-base plate can play the role of restricting growth area and effectively stabilizing the porous structure of the noble-metal material. In this synthesis process, poly(styrene-b-acrylic acid) (PS-b-PAA) micelles and polymer colloidal crystals are used as templates for the construction of mesopores and macropores, respectively. By adjusting the particle size of polymer colloidal nanospheres, the size of three-dimensional ordered macropores can be precisely adjusted from 160 to 320 nm. Benefiting from the synergistic effect of hierarchical pore structures, the as-prepared 3DOM/m Pd film exhibits outstanding electrocatalytic performance for formic acid oxidation. These results provide an effective and universal method for the designed synthesis of the three-dimensional hierarchical architecture of high-catalytic-activity noble-metal materials.

Bimetallic Boron Phosphide Ni‐2Fe‐BP as an Active Water‐Splitting Catalyst

AbstractThe increasing development of hydrogen energy requires us to continuously update the technology of hydrogen production and promote the more rapid development of hydrogen energy. Among them, the electrolysis of water to produce hydrogen is the current research hotspot. In this paper, a simple synthesis method is used to prepare amorphous nano‐scale monometallic Ni and bimetallic Ni, Fe boron phosphides, which are used as electrocatalysts to catalyze water splitting. We explored the best ratio of B to P in monometallic boron phosphides, and the optimal ratio of Ni and Fe in the bimetallic boron phosphide. It shows that when the ratio of B to P is 1 : 5 and the iron content is 0.2 in the Ni‐Fe‐BP, the catalytic performance of the material is optimal. It shows outstanding performance of 310 mV overpotential at a current density of 20 mA cm−2, and its hydrogen evolution reaction overpotential is only 258 mV, which is better than noble metal materials. At the same time, it maintains excellent stability for 12 h at a constant potential. This work provides a better choice for subsequent research on non‐precious metal catalyst materials.

Sensitive detection of As(III) on Fe3O4/MoS2 through interfacial engineering to accelerate the Fe2+/Fe3+ cycle: Identifying the dominant role of electron transfer induced by valence change in synergistic electroanalysis

Fe-based metal oxide nanomaterials have attracted significant attention as the electroanalytical sensing for heavy metal ions (HMIs) detection. It is recently found that their activities should be mainly ascribed to their valance change behavior (i.e. the Fe2+/Fe3+ cycle). However, how to promote the Fe2+/Fe3+ cycle to further increase their detection performance is highly desired yet challenging. Herein, the nanocomposite of Fe3O4/MoS2 is developed as a sensing for the electrochemical detection of the highly toxic As(III). Through a series of characterizations including the XPS and DFT, the Fe3O4/MoS2 shows an accelerated electron transfer induced by the valence change of Fe2+/Fe3+ cycle. The active Mo4+ on MoS2 can serve as electron doner to reduce the Fe3+ to Fe2+ on Fe3O4, and thus promotes the Fe2+/Fe3+ cycle. Moreover, the synergistic effect between the excellent adsorption ability of Fe3O4 towards As(III) and the good conductivity of MoS2 will further benefit to the detection. As expected, the Fe3O4/MoS2 reflects an outstanding detection performance to As(III) with a sensitivity of 4.16 μA•ppb–1, which even much outperforms than that of noble-metal materials. Overall, these discoveries are expected to drive great advances in the application of the accelerated valence change behavior for electroanalysis.

Defect-engineered MXene monolith enabling interfacial photothermal catalysis for high-yield solar hydrogen generation

Solar-driven formic acid dehydrogenation shows great potential for sustainable hydrogen utilization. Nevertheless, photothermal catalytic materials that are essential to dehydrogenation not only exhibit limited solar absorption and large heat loss but also heavily rely on noble metals, limiting efficient and low-cost hydrogen generation. Here, we report a porous MXene monolith that enables interfacial heat localization and propose a defect-engineering strategy for MXenes to realize the coordinated regulation of photothermal property and catalytic activity, which is further evidenced by density functional theory calculations. As a result, this design achieves a hydrogen generation rate of 401 mmol g −1 h −1 with an H 2 selectivity of 100% and catalytic stability over 45 h of operation, significantly surpassing many state-of-the-art, Pd-based noble metal materials. The work provides new insight into the design of photothermal catalytic MXenes and may open a new application toward solar hydrogen generation. • A defective MXene monolith enables both interfacial photothermal and catalysis • Defect engineering guides solar energy capture and intermediate conversion • A high hydrogen generation rate with long-term stability is presented Zhang and co-authors design a porous MXene monolith that enables interfacial heat localization and propose a defect-engineering strategy for MXenes to realize the coordinated regulation of photothermal and catalytic properties. The design may offer advantages over noble metals in solar fuel generation to concurrently realize high efficiency and cost effectiveness.

Electrocatalytic Hydrogen Oxidation in Alkaline Media: From Mechanistic Insights to Catalyst Design.

With the potential to circumvent the need for scarce and cost-prohibitive platinum-based catalysts in proton-exchange membrane fuel cells, anion-exchange membrane fuel cells (AEMFCs) are emerging as alternative technologies with zero carbon emission. Numerous noble metal-free catalysts have been developed with excellent catalytic performance for cathodic oxygen reduction reaction in AEMFCs. However, the anodic catalysts for hydrogen oxidation reaction (HOR) still rely on noble metal materials. Since the kinetics of HOR in alkaline media is 2-3 orders of magnitude lower than that in acidic media, it is a major challenge to either improve the performance of noble metal catalysts or to develop high-performance noble metal-free catalysts. Additionally, the mechanisms of alkaline HOR are not yet clear and still under debate, further hampering the design of electrocatalysts. Against this backdrop, this review starts with the prevailing theories for alkaline HOR on the basis of diverse activity descriptors, i.e., hydrogen binding energy theory and bifunctional theory. The design principles and recent advances of HOR catalysts employing the aforementioned theories are then summarized. Next, the strategies and recent progress in improving the antioxidation capability of HOR catalysts, a thorny issue which has not received sufficient attention, are discussed. Moreover, the significance of correlating computational models with real catalyst structure and the electrode/electrolyte interface is further emphasized. Lastly, the remaining controversies about the alkaline HOR mechanisms as well as the challenges and possible research directions in this field are presented.

Refractive Index Sensing Simulations of CsPbBr3 Quantum Dots/Gold Bilayer Coated Triangular-Lattice Photonic Crystal Fibers

With the incorporation of noble metal materials, photonic crystal fibers (PCFs) could be performed as an effective platform for refractive index sensing of the filling analytes. Furthermore, by coating functional dielectric layers upon the metal surfaces, the resonance energy transfer is modulated from the core mode of the PCFs towards the surface plasmon resonance mode of the metals, and the sensing performance could be boosted. Here, considering that the exciton-plasmon coupling is efficient between perovskite quantum dots (QDs) and gold, a kind of CsPbBr3 QDs/Au bilayer coated triangular-lattice PCFs has been simulated numerically as the refractive index sensors. With the optimization of the QDs and gold layer thicknesses, together with the variation of the central hole size of the PCFs, in the refractive index (RI) region of 1.26 to 1.34, a rather narrow full width at half maximum (FWHM) of the loss spectra was achieved as 13.74nm when the central hole size was 1.28 µm and the highest figure of merit was 63.79RIU (the central hole size was 1.53 µm). This work demonstrates that the analyte identification accuracy was enhanced by FWHM narrowing of the loss spectra; in addition, taking the abundance of the material choice of perovskite QDs into consideration, more analytes could be detected effectively. Moreover, by adopting asymmetric structures, the sensitivity of the PCFs based refractive index sensors could be further improved.

Amorphous/Crystalline Heterophase Ruthenium Nanosheets for pH‐Universal Hydrogen Evolution

To design and synthesize heterophase noble-metal materials is of crucial importance owing to their unique structure and apparent properties. Ruthenium (Ru) is one of the most active candidates for hydrogen evolution reaction because of its low price compared with other precious metals, which is favorable for industrial hydrogen cycle operation. In this study, free-standing amorphous/crystalline Ru nanosheets are facilely synthesized through a controlled annealing method. Charge redistribution occurs at the phase interface because of the work function difference between amorphous and crystalline domains. The resulting structure and property are conductive to the adsorption and dissociation of water molecules, associated with optimized hydrogen interaction and enhanced binding between Ru atoms. Accordingly, electrochemical measurements demonstrate that the amorphous/crystalline heterophase Ru exhibits improved hydrogen evolution efficiency as compared with pure amorphous Ru and pure crystalline Ru, at pH-universal conditions. Specifically, only 16.7mV overpotential is required to reach 10mA cm-2 in 1.0 m KOH. Meanwhile, the heterophase structure displays a higher stability during operation than pure amorphous and crystalline structures. This study demonstrates the importance of phase engineering, broadens the Ru-based material family, and provides more insights for developing efficient metal materials.

The ultrathin palladium nanosheets for sensitive and visual Hg2+ detection in the food chain

The detection of mercury, one of the ten most dangerous chemicals, is significant to provide helpful information for assessing mercury toxicity and health risks. However, it is a challenge to explore simple, sensitive, accurate, and cheap Hg2+ detection methods. Noble metal nanomaterials are used for Hg2+ detection by the colorimetric method widely. Still, the pure noble metal materials’ detection limit of Hg2+ is high, and sensitivity enhancement usually requires further complex modification. Here, we use a facile one-step route to synthesize ultra-thin two-dimensional palladium nanosheets (PdNS), which have high selectivity and sensitivity for Hg2+ detection by colorimetric method with a low detection limit (0.55 ppb). The detection of Hg2+ by PdNS involves multiple mechanisms, including the formation of amalgam and PdO to improve the peroxidase-mimic activity of PdNS and PdNS motor function to increase its collision probability with the detection reactant. The PdNS can be used to detect Hg2+ in various actual samples. The detection results are highly consistent with the data obtained by the atomic fluorescence spectrometer (AFS). Then, we developed a Hg2+ detection kit, which can realize simple, sensitive, and accurate Hg2+ detection by naked eye or cellphone at a meager cost (0.3 dollars each sample).

Facile synthesis of low-dimensional PdPt nanocrystals for high-performance electrooxidation of C 2 alcohols

Low-dimensional noble-metal materials (LDNMs) with different structural advantages have been considered as the high-performance catalysts for C2 alcohol electrooxidation. However, it is still a great challenging to precisely construct nanomaterials with low-dimensional composite structure thus to take advantages of various dimension, especial without the surfactant participation. Most studies focus on the modulation of the single dimensional nanocatalysts, the correlation between electrocatalytic performances and low-dimension composite have been rarely reported. Herein, we engineered a simple one-step approach to design multi-low-dimensional PdPt nanomaterials by using different Pd precursors. The low-dimensional PdPt nanocrystals (NCs) composed of zero dimension (0D) dendrite-like nanoparticles and two dimension (2D) nanosheets were obtained by using Pd(OAc)2, and meanwhile the 2D PdPt nanosheet assemblies (NAs) were synthesized by the introduction of NaPdCl4. Specifically, benefitting from the unique low-dimension structures with fast electron/mass transfer, and optimized electronic and synergistic effect, the multi-low-dimensional 0D-2D PdPt NCs showed the highest ethanol oxidation reaction (EOR)/ethylene glycol oxidation reaction (EGOR) mass activities, which were much higher than 2D PdPt NAs. The 0D-2D PdPt NCs also exhibited the highest structural stability. Generally, this work could inspire more advanced designs for surfactant-free synthesis and promote the fundamental engineering on nanocatalysts with low-dimension composite structure for electrocatalytic fields.

Dicobalt Nickel Oxides With a Sugar-Based Carbon Precursor for Water Splitting Applications

In order to effectively reduce carbon emissions and achieve the goal of providing alternate energy sources hydrogen energy has high hopes as a representative of new energy. According to current research compounds of cobalt and nickel have been widely studied as alternative noble metal materials as catalysts for electrolysis of water. Based on other research reports, a simple hydrothermal method is proposed to grow cobalt-nickel oxide on nickel foam that has been pre-carbonized with a glucose source in advance. In order to compare the modification results of the materials by different activation methods high-temperature treatment and sulfurization of the materials were carried out. Among them, the sulfurized material not only has a relatively good performance in the catalytic reaction of hydrogen evolution and oxygen evolution but also has a good performance as an energy storage material for supercapacitors.

Amorphous Ni(OH)2 nanocages as efficient SERS substrates for selective recognition in mixtures

Surface-enhanced Raman scattering (SERS) technology has become one of the most powerful tools for identifying trace analytes due to its outstanding merit of fingerprint spectrum. It has been found that noble metal (Ag, Au) materials can produce obvious surface plasmon resonance under visible light illumination, which can bring out a strong SERS effect. However, due to poor stability and non-selectivity, its practical applications are seriously hindered, especially for the detection of polluted water contaminating mixture organic pollutants. Herein, we designed an amorphous Ni(OH)2 nanocages (a-Ni(OH)2 NCs) substrate that exhibits an excellent SERS performance with good spectral stability and selectivity, which is attributed to the strong interfacial photo-induced charge transfer (PICT) mechanism between a-Ni(OH)2 NCs and molecules. Due to the effective vibrational coupling of a-Ni(OH)2 NCs and molecule under laser irradiation, the PICT transitions between a-Ni(OH)2 NCs and molecules evidently increase the molecular polarizability tensor and magnify molecular Raman scattering cross-section, resulting in a remarkable SERS activity. Besides, in wastewater containing several nitrogen and phosphorus pollutants, we successfully identified methylene blue and crystal violet molecules by using a-Ni(OH)2 NCs due to their selective recognition function. This research points out a new application direction for SERS technology in water pollution detection based on non-metal substrates, which widely broadens application prospects of SERS spectroscopy.

Ternary NiO/Ag/reduced graphene oxide nanocomposites as, a sensitive electrochemical sensor for nanomolarity detection of sunset yellow in soft drinks

NiO nanoparticles (NPs) with small Ag NPs loading supported on reduced graphene oxide nanosheets (ternary NiO/Ag/RGO nanocomposites) were synthesized via a hydrothermal process followed by high-temperature calcination, extending the synergistic effects among noble metal, metal oxide and carbon materials. Based on ternary NiO/Ag/RGO nanocomposites, a new electrochemical sensor was fabricated for the detection of sunset yellow (SY) in soft drinks through cyclic voltammetry, Tafel plot and differential pulse voltammetry. The experimental conditions were optimized and kinetic parameters studied. Due to the synergistic effect of the ternary components, the prepared sensor exhibited superior electroanalytical performance toward SY detection, including wide linear range from 0.1 to 50 μM and from 50 to 450 μM, low detection limit of 13 nM, excellent specificity against various interfering colorants, good reproducibility and stability. Importantly, the electrochemical sensors was successfully employed for quantitative SY analysis in soft drinks with satisfactory recoveries, where the analyzed results were also in agreement with LC/MS analysis.

Spin Hall effect of light based on a surface plasmonic platform

Abstract In recent years, the spin Hall effect of light (SHE), also called the photonic spin Hall effect has received extensive research attention, and a series of interesting results have been achieved. This phenomenon has potential applications in nanooptics, quantum information, and optoelectronic devices. In contrast to the pure photon SHE, the photonic spin Hall effect in the surface plasmonic platform exhibits unique properties due to the surface plasmon resonance effect of noble metal material and establishes the connection between photons and electrons. Therefore, the SHE of light in a surface plasmonic platform is expected to be applied to integrated optical devices to create a novel means of developing communication devices. In this paper, we review the progress on the SHE of light based on the plasmonic platform in recent years, and we discuss the future directions of research and prospects for its applications.

Ag/TiO2 nanocomposites as a novel SERS substrate for construction of sensitive biosensor

Abstract In this work, the Ag/TiO2 nanocomposites was fabricated by catalytic hairpin assembly (CHA) strategy to construct surface-enhanced Raman scattering (SERS) biosensor for sensitive detection of uracil DNA glycolase (UDG), which could achieve greater Raman enhancement of methylene blue by the surface plasmon resonance (SPR) of Ag nanocubes (Ag NCs) and the charge transfer (CT) effect of TiO2 compared with traditional noble metal material. Impressively, the Pb2+ assisted DNAzyme cleavage reaction was introduced to convert the trace target UDG into great number of trigger DNA for improving the sensitivity of this method. Thus, the SERS biosensor demonstrated excellent performance for sensitive detection of UDG with a low detection limit of 1.2 × 10−5 U mL-1. This proposed assay offered a new strategy to design SERS substrate for analysis of biomolecule and disease diagnosis.

In Search of Excellence: Convex versus Concave Noble Metal Nanostructures for Electrocatalytic Applications.

Controlling the shape of noble metal nanoparticles is a challenging but important task in electrocatalysis. Apart from hollow and nanocage structures, concave noble metal nanoparticles are considered a new class of unconventional electrocatalysts that exhibit superior electrocatalytic properties as compared with those of conventional nanoparticles (including convex and flat ones). Herein, several facile and highly reproducible routes for synthesizing nanostructured concave noble metal materials reported in the literature are discussed, together with their advantages over noble metal nanoparticles with convex shapes. In addition, possible ways of optimizing the synthesis procedure and enhancing the electrocatalytic characteristics of concave metal nanoparticles are suggested. Nanostructured noble metals with concave features are found to show better catalytic activity and stability hence improve their practical applicability in electrocatalysis.