Finite Size Effects in Submonolayer Catalysts Investigated by CO Electrosorption on PtsML/Pd(100)

Electrochemiluminescence of Ultrasmall Silica Nanoparticles from Size Modulation and Multipath Surface State Adjustment for Ultrasensitive HIV-DNA Fragment Detection

Here, ultrasmall SiO2 nanoparticles (u-SiO2 NPs, <5 nm) with obvious electrochemiluminescence (ECL) phenomenon, which was absent for conventional silica nanoparticles (c-SiO2 NPs), were reported. In a finite ultrasmall volume, the u-SiO2 NPs exhibited increasing ground state energy and higher optical absorption strength due to the electron-hole confinement model and favored catalyzing the reaction through the rapid diffusion of bulk charge, resulting in apparent ECL emission. Then, Zn2+-induced u-SiO2 nanoaggregates (Zn/u-SiO2-Ov nAGG) were synthesized and exhibited improved ECL performance via multipath surface state adjustment of u-SiO2 from several aspects, including aggregation-induced ECL, the generation of oxygen vacancy (Ov), and more positive surface charge. In addition, an ECL biosensor was constructed for ultrasensitive human immunodeficiency virus-related deoxyribonucleic acid detection from 100 aM to 1 nM with a low limit of 50.48 aM, combining the ECL luminescence of Zn/u-SiO2-Ov nAGG with three-dimensional DNA nanomachine-mediated multioutput amplification for enhanced accuracy and sensitivity compared to the single-output method. Therefore, exploring the ECL of ultrasmall nanoparticles via the adjustment of size and surface state provided a valuable indication to a wider investigation and application of novel ECL materials for clinical diagnostic.

Adsorption and solar light activity of noble metal adatoms (Au and Zn) on Fe(111) surface: a first-principles study

Noble metals such as gold (Au), zinc (Zn), and iron (Fe) are highly significant in both fundamental and technological contexts owing to their applications in optoelectronics, optical coatings, transparent coatings, photodetectors, light-emitting devices, photovoltaics, nanotechnology, batteries, and thermal barrier coatings. This study presents a comprehensive investigation of the optoelectronic properties of Fe(111) and Au, Zn/Fe(111) materials using density functional theory (DFT) first-principles method with a focus on both materials' spin orientations. The optoelectronic properties were obtained employing the generalized gradient approximation (GGA) and the full-potential linearized augmented plane wave (FP-LAPW) approach, integrating the exchange-correlation function with the Hubbard potential U for improved accuracy. The arrangement of Fe(111) and Au, Zn/Fe(111) materials was found to lack an energy gap, indicating a metallic behavior in both the spin-up state and the spin-down state. The optical properties of Fe(111) and Au, Zn/Fe(111) materials, including their absorption coefficient, reflectivity, energy-loss function, refractive index, extinction coefficient, and optical conductivity, were thoroughly examined for both spin channels in the spectral region from 0.0 eV to 14 eV. The calculations revealed significant spin-dependent effects in the optical properties of the materials. Furthermore, this study explored the properties of the electronic bonding between several species in Fe(111) and Au, Zn/Fe(111) materials by examining the density distribution mapping of charge within the crystal symmetries.

Surface coverage dynamics for reversible dissociative adsorption on finite linear lattices

Dissociative adsorption onto a surface introduces dynamic correlations between neighboring sites not found in non-dissociative absorption. We study surface coverage dynamics where reversible dissociative adsorption of dimers occurs on a finite linear lattice. We derive analytic expressions for the equilibrium surface coverage as a function of the number of reactive sites, N, and the ratio of the adsorption and desorption rates. Using these results, we characterize the finite size effect on the equilibrium surface coverage. For comparable N's, the finite size effect is significantly larger when N is even than when N is odd. Moreover, as N increases, the size effect decays more slowly in the even case than in the odd case. The finite-size effect becomes significant when adsorption and desorption rates are considerably different. These finite-size effects are related to the number of accessible configurations in a finite system where the odd-even dependence arises from the limited number of accessible configurations in the even case. We confirm our analytical results with kinetic Monte Carlo simulations. We also analyze the surface-diffusion case where adsorbed atoms can hop into neighboring sites. As expected, the odd-even dependence disappears because more configurations are accessible in the even case due to surface diffusion.

The enhancement in the performance of ultra-small core-shell Au@AuPt nanoparticles toward HER and ORR by surface engineering

In this work, ultra-small core-shell (USCS) Au_38.4@Au_4.1Pt_57.5 nanoparticles (NPs) with an optimal Pt-to-Au ratio were successfully prepared by the optimal etching treatment of USCS Au@AuPt NPs by Fe(III) ions to remove some exposed Au atoms on their outermost surfaces. The as-prepared USCS Au_38.4@Au_4.1Pt_57.5 NPs with Fe(III)-etching treatment for 2 h loaded on carbon black as catalysts (USCS^2h Au_38.4@Au_4.1Pt_57.5-NP/C catalysts) exhibit superior electrocatalytic activity and durability for both the hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) in acidic media. For instance, the overpotential of USCS^2h Au_38.4@Au_4.1Pt_57.5-NP/C catalysts toward the HER is 13 mV at a current density of -10 mA cm^-2 (η₁₀ = 13 mV), which is much better than that of commercial Pt/C catalysts (η₁₀ = 31 mV). Moreover, their mass activity (63.8 A mg_Pt^-1) is about 16.4 times larger than that of commercial Pt/C catalysts (3.9 A mg_Pt^-1). In addition, they also present better long-term stability. Furthermore, they also show an improved activity toward the ORR in terms of the half-wave potential (E_1/2) (0.89 V vs. RHE), which is more positive by about 38 mV than commercial Pt/C catalysts (0.852 V). In addition, they also show a higher kinetic current density (14.22 mA cm^-2 at 0.85 V) and better long-term durability. This etching-treatment strategy can be extended to further improve the catalytic performance of ultra-small Au-based bimetallic or multi-metallic NPs by surface engineering.

Atomic Structures of Single-Layer Nanoislands of Ni, Cu, Rh, Pd, Ag, Ir, Pt, Au Supported on Au(111) from Density Functional Theory Calculations

We have used density functional theory calculations to study the atomic structure of single-layer nanoislands of metal M (M=Ni, Cu, Rh, Pd, Ag, Ir, Pt, Au) supported on M(111) and Au(111) surfaces. Nanoislands of Cu, Pd, Ag, Pt, and Au have planar structures on Au(111), while nanoislands of Ni, Rh, and Ir are nonplanar. The calculations also show that nanoislands of Cu, Pd, Pt, and Au on Au(111) with a diameter below 3 nm can have one of several atomic structures. Two of these structures have atoms at the edges of the nanoislands located near bridge sites on Au(111), and the other structures have atoms at the edges and center of the nanoislands located near bridge sites. The relative stability of these atomic structures depends on the size and nature of the Au-supported nanoparticles. Our findings provided computational support for the work of Liao and Ya [J. Phys. Chem. C. 121 (2017) 19218-19225] reporting the formation of two phases of Pt nanoislands on Au(111). These findings also reveal the rich and complex atomic structures of small single-layer metal nanoislands supported on metal surfaces.

Simulation of Metal-Supported Metal-Nanoislands: A Comparison of DFT Methods

We have evaluated various density functional theory (DFT) methods to simulate geometric, energetic, electronic, and hydrogen adsorption properties of metal-nanoparticles supported on metal surfaces. We used Pt and Pd nanoislands on Au(111) as model systems. The evaluated DFT methods include GGA (PW91, PBE, RPBE, revPBE, and PBESol), GGA with van der Waals (vdW) corrected (PBE-D3), GGA with optimized vdW functionals (revPBE-vdW), meta-GGA (SCAN and MS2), and the machine learning-based method BEEF-vdW. The results show that the various DFT methods yield similar geometric and electronic properties for Pt (or Pd) nanoislands on Au(111). The DFT methods also produce similar relative energetics for small Pt (or Pd) clusters with different conformations on Au(111). The results show that a triatomic cluster of Pt on Au(111) is more stable with a linear conformation. In contrast, a triatomic cluster of Pd is more stable with a triangular conformation. For clusters with four or more atoms, Pt and Pd clusters on Au(111) prefer non-linear conformation. We found that the various DFT methods yield different results only for the adsorption energy of hydrogen.

The use of amino-based functional molecules for the controllable synthesis of noble-metal nanocrystals: a minireview

Controlling the morphologies and structures of noble-metal nanocrystals has always been a frontier field in electrocatalysis. Functional molecules such as capping agents, surfactants and additives are indispensable in shape-control synthesis. Amino-based functional molecules have strong coordination abilities with metal ions, and they are widely used in the morphology control of nanocrystals. In this minireview, we pay close attention to recent advances in the use of amino-based functional molecules for the controllable synthesis of noble-metal nanocrystals. The effects of various amino-based molecules on differently shaped noble-metal nanocrystals, including zero-, one-, two-, and three-dimensional nanocrystals, are reviewed and summarized. The roles and mechanisms of amino-based small molecules and long-chain ammonium salts relating to the morphology-control synthesis of noble-metal nanocrystals are highlighted. Relationships between shape and electrocatalytic properties are also described. Finally, some key prospects and challenges relating to the controllable synthesis of noble-metal nanocrystals and their electrocatalytic applications are proposed.

Hydrogen Adsorption on Au-Supported Pt and Pd Nanoislands: A Computational Study of Hydrogen Coverage Effects

We have studied the dissociative adsorption of hydrogen under high coverage conditions of adsorbed hydrogen on Pd and Pt nanoislands supported on Au(111) using Density Functional Theory calculations. The results reveal that for Pd/Au(111), the free energy of hydrogen adsorption ΔG is close to 0 kJ/mol when the coverage of adsorbed hydrogen is near 1 ML, where the available catalytic sites are located at the edges of the Pd nanoislands. In the case of Pt/Au(111), ΔG ≈ 0 kJ/mol under a broad range of hydrogen coverage conditions, from 1 ML to 3 ML, depending on the size of the Pt nanoislands. This is the case because the available catalytic sites are located at both the steps and terraces of Pt nanoislands. These findings indicate that Au surfaces with Pd or Pt nanoislands offer catalytic sites with ΔG ≈ 0 for hydrogen reactions, one key factor for an ideal electrocatalyst for hydrogen reactions.

Strain and Low-Coordination Effects on Monolayer Nanoislands of Pd and Pt on Au(111): A Comparative Analysis Based on Density Functional Results

Recent experiments demonstrated that the catalytic centers for the hydrogen evolution reaction (HER) are different on Pd and Pt nanoislands on Au(111). Inspired by these experiments, we examined the geometric, energetic, electronic and hydrogen adsorption properties of monolayer model nanoislands of Pd and Pt supported on Au(111) with density functional theory calculations. Accordingly, Au-tensile strain effects can be nearly 50% larger on the geometric structure of nanoislands of Pd on Au(111) than their Pt analogs, resulting on different electronic properties for these nanoislands. Despite these differences between Pd and Pt nanoisland on Au(111), our computational modelling of the hydrogen adsorption suggests that the unique catalytic centers for the HER on Pd and Pt nanoislands supported on Au(111) derive from the existence of low-coordinated adsorption sites and the intrinsic properties of Pd and Pt, but not from Au-tensile strain effects.

Shape Control of Monodispersed Sub-5 nm Pd Tetrahedrons and Laciniate Pd Nanourchins by Maneuvering the Dispersed State of Additives for Boosting ORR Performance

It is a great challenge to simultaneously control the size, morphology, and facets of monodispersed Pd nanocrystals under a sub-5 nm regime. Meanwhile, quantitative understanding of the thermodynamic and kinetic parameters to maneuver the shape evolution of nanocrystals in a one-pot system still deserves investigation. Herein, a systematic study of the density functional theory (DFT)-calculated adsorption energy, thermodynamic factors, and reduction kinetics on Pd growth patterns is reported by combining theory and experiments, with a focus on the dispersed state of additives. As pure models, monodispersed Pd tetrahedrons enclosed by (111) facets with a narrow size distribution of 4.9 ± 1 nm and a high purity approaching 98% can be obtained when using 1,1'-binaphthalene (C₂₀ H₁₄ ) +2NH₃ as additives. Specifically, laciniate Pd nanourchins (Pd LUs) can evolve via anisotropic growth when replacing additive with dose-consistent 1,1'-binaphthyl-2,2'-diamine (C₂₀ H₁₆ N₂ , two NH₂ binding in C₂₀ H₁₄ ). Catalytic investigations show that the sub-5 nm Pd tetrahedrons exhibit higher activity in both the oxygen reduction (E_onset = 1.025 V, E_1/2 = 0.864 V) and formic acid oxidation reaction with respect to the Pd LUs and Pd black, which represents a great step for the development of well-defined Pd nanocrystals with size in the sub-5 nm regime as non-Pt electrocatalysts.