三元合金氧还原电催化剂

质子交换膜燃料电池作为重要的电化学能源转换装置,在提高能量转换效率、减少环境污染等方面具有诱人的前景.然而,阴极氧还原过电位较大、活性较低、稳定性差,且铂基催化剂昂贵,使该燃料电池难以商业化.纳米结构电催化剂的发展有望解决此难题。对纳米合金电催化剂其组分和结构的设计是开发高活性、高稳定性和低成本的燃料电池电催化剂的重要因素.本文综述了近期由分子设计和热化学控制处理法制备的三元纳米合金电催化剂对燃料电池氧还原反应催化性能的最新进展.该方法可控制纳米合金的尺寸、组成以及二元和三元纳米催化剂的合金化程度.以高活性的三元纳米合金催化剂PtNiCo/C为例,综述了在设计燃料电池电催化剂时结构和组成的纳米级调优的重要性.PtNiCo/C电催化剂的质量比活性远高于其二元合金催化剂和Pt/C商业电催化剂.三元电催化剂的催化活性可通过控制其组成来调节.文章还讨论了三元纳米合金催化剂的结构及其协同效应对增强其电催化性能的影响.     

Composition-Controlled Laser-Induced Alloying of Colloidal Au–Cu Hetero Nanoparticles

Due to their optical properties (localized surface plasmon resonance, LSPR), colloidally dispersed metal nanoparticles are well suited for selective heating by high-energy laser radiation above their melting point without being limited by the boiling point of the solvent, which represents an excellent complement to wet-chemical nanoparticle synthesis. By combining wet-chemical synthesis and postsynthesis laser treatment, the advantages of both methods can be used to specifically control the properties of nanoparticles. Especially in the colloidal synthesis of nanoalloys consisting of two or more metals with different redox potentials, wet-chemical synthesis quickly reaches its limits in terms of composition control and homogeneity. For this reason, the direct synthesis path is divided into two parts to take the strengths of both methods. After preparing Au–Cu hetero nanoparticles by wet-chemical synthesis, nanoalloys with previous adjusted composition can be formed by postsynthesis laser treatment. The formation of these nanoalloys can be followed by different characterization methods, such as transmission electron microscopy (TEM), where the fusion of both metal domains and the formation of spherical and homogeneous Au–Cu nanoparticles can be observed. Moreover, the alloy formation can be followed by different shifts of X-ray diffraction (XRD) reflections and LSPR maxima depending on the composition.     

Total Integration of the Sample Injection,Microdroplet Reaction,Phase Separation,Real-Time Optical Detection,and Recovery of Diverse Silver–Gold Bimetallic Nanoalloys in a Continuous Process

Microfluidic droplet generators have garnered great attention due to the uniformity, high-throughput capability, and facile experimental setup. To maximize the potentials of droplet technology as a chemical/biological nanoliter-scale reactor, the downstream processes such as separation of the aqueous and oil phase, real-time monitoring of the products formed in droplets, and the final product recovery from the droplets is necessary. In this study, the droplet is utilized as a chemical reactor to synthesize a variety of Ag and Au bimetallic nanoalloys in a fully integrated microsystem including sample injection, a T-junction droplet generator, droplet reaction, water–oil phase separation, real-time UV–vis absorbance detection, and product recovery. The flow rate of the Ag nanoparticle (NP) solution and the HAuCl₄ solution was tuned to generate different molar ratios of Ag and Au components. The in-line UV–vis absorbance spectrometer displays a peak shift of the Ag/Au bimetallic alloys depending on the molar ratio of Ag/Au in the continuous process, enabling to judge the kind of the Ag/Au alloys in situ and collect a variety of Ag/Au nanoalloys. Thus, the desired nanomaterials can be obtained with minimal trial and error, saving time and cost.     

Tuning the Selectivity of AuPd Nanoalloys towards Selective Dehydrogenative Alkyne Silylation

The cross-dehydrogenative coupling of terminal alkynes and hydrosilanes catalyzed by AuPd nanoalloys is described. Metal nanoparticles are readily prepared in 15 minutes from commercially available and cheap starting materials by using a photochemical approach. The ratio of Au and Pd in the alloys heavily influences their reactivity. These cooperative nanoalloy catalysts tolerate a large number of functional groups (e.g., free amines and acids), operate at room temperature under air atmosphere at low loading (2 mol %), and the cross-dehydrogenative coupling can easily be scaled up.     

Heating rate effects for the melting transition of Pt-Ag-Au nanoalloys

The classical molecular dynamics simulations in canonical NVT ensemble conditions are used to investigate the melting transition in different heating rates of Pt-Ag-Au ternary nanoalloys. In order to obtain the initial configurations used in the molecular dynamics simulations, optimizing the chemical ordering of Pt₁₃Ag_nAu_42-n (n=0-42) ternary nanoalloys was performed using the Basin-Hopping algorithm which would not allow changes in the icosahedron structure. The Gupta many-body potential was used to model interatomic interactions in both molecular dynamics simulations and optimization simulations. The melting transitions of selected Pt-Ag-Au nanoalloys were explored using caloric curves and Lindemann parameters. There have been two identified types of melting mechanisms, one includes sudden jump behavior in the caloric curve and the other is an isomerization while melting transition. The temperature range in which the isomerization takes place depends on the heating rate value.     

Gold Doping of Silver Nanoclusters: A 26‐Fold Enhancement in the Luminescence Quantum Yield

A high quantum yield (QY) of photoluminescence (PL) in nanomaterials is necessary for a wide range of applications. Unfortunately, the weak PL and moderate stability of atomically precise silver nanoclusters (NCs) suppress their utility. Herein, we accomplished a ≥26‐fold PL QY enhancement of the Ag₂₉(BDT)₁₂(TPP)₄ cluster (BDT: 1,3‐benzenedithiol; TPP: triphenylphosphine) by doping with a discrete number of Au atoms, producing Ag_29?xAu_x(BDT)₁₂(TPP)₄, x=1–5. The Au‐doped clusters exhibit an enhanced stability and an intense red emission around 660 nm. Single‐crystal XRD, mass spectrometry, optical, and NMR spectroscopy shed light on the PL enhancement mechanism and the probable locations of the Au dopants within the cluster.     

Precision Polyolefin Nanoalloy Polypropylene/Poly(ε‐caprolactone)

This communication reports the first example of precision polyolefin nanoalloys where an exotic immiscible polymer is nanometrically dispersed with stability in a polyolefin matrix in a highly controlled mode. Following the preparation of polypropylene/multiwalled carbon nanotubes nanocomposites (PP/MWCNTs) by in situ Ziegler‐Natta polymerization, the hydroxyl groups on the surfaces of individual MWCNTs are used to initiate ring‐opening polymerization of ε‐caprolactone, resulting in PP/poly(ε‐caprolactone) (PCL) alloy with PCL grafted on MWCNTs. Upon phase formation, the PP/MWCNTs‐g‐PCL alloys exhibit a unique PCL dispersion morphology, which is stable and solely governed by PCL molecular weight.