Site-selective Cu deposition on Pt dendrimer-encapsulated nanoparticles: correlation of theory and experiment

The voltammetry of Cu underpotential deposition (UPD) onto Pt dendrimer-encapsulated nanoparticles (DENs) containing an average of 147 Pt atoms (Pt(147)) is correlated to density functional theory (DFT) calculations. Specifically, the voltammetric peak positions are in good agreement with the calculated energies for Cu deposition and stripping on the Pt(100) and Pt(111) facets of the DENs. Partial Cu shells on Pt(147) are more stable on the Pt(100) facets, compared to the Pt(111) facets, and therefore, Cu UPD occurs on the 4-fold hollow sites of Pt(100) first. Finally, the structures of Pt DENs having full and partial monolayers of Cu were characterized in situ by X-ray absorption spectroscopy (XAS). The results of XAS studies are also in good agreement with the DFT-optimized models.     

Atomically Dispersed Copper–Platinum Dual Sites Alloyed with Palladium Nanorings Catalyze the Hydrogen Evolution Reaction

Designing highly active catalysts at an atomic scale is required to drive the hydrogen evolution reaction (HER). Copper–platinum (Cu‐Pt) dual sites were alloyed with palladium nanorings (Pd NRs) containing 1.5 atom % Pt, using atomically dispersed Cu on ultrathin Pd NRs as seeds. The ultrafine structure of atomically dispersed Cu‐Pt dual sites was confirmed with X‐ray absorption fine structure (XAFS) measurements. The Pd/Cu‐Pt NRs exhibit excellent HER properties in acidic solution with an overpotential of only 22.8 mV at a current density of 10 mA cm⁻² and a high mass current density of 3002 A g⁻¹_(Pd+Pt) at a −0.05 V potential.     

电化学去合金化Pt(Pd)-Cu对氧的电催化还原活性的研究

应用电化学去合金法制备了表面覆盖有Pt(Pd)原子层的Pt(Pd)-Cu合金催化剂.研究该催化剂在0.1mol.L-1HClO4酸性溶液中对氧气电化学还原的催化活性,并采用同步辐射反常X-射线衍射法(Anomalous X-ray Diffraction,AXRD)和表面X-射线散射法(Surface X-ray Scattering,SXS)从原子尺度研究了去合金化后催化剂的结构.分析对比纳米颗粒、薄膜和单晶3种不同形式的去合金化Pt-Cu的结构和催化活性以及Pt-Cu和Pd-Cu两种不同合金薄膜的结构和催化活性.结果表明,表面应力是影响催化剂催化活性的关键因素,而应力大小则与去合金化后所形成的表面Pt(Pd)层的厚度相关,材料尺寸和组成元素等都影响表面Pt(Pd)层的厚度.提出可利用调控材料表面的应力来设计高催化活性的催化剂.     

Voltammetric surface dealloying of Pt bimetallic nanoparticles: an experimental and DFT computational analysis

Voltammetric dealloying of bimetallic platinum-copper (Pt-Cu) alloys has been shown to be an effective strategy to modify the surface electrocatalytic reactivity of Pt bimetallic nanoparticles (S. Koh and P. Strasser, J. Am. Chem. Soc., 2007, 129, 12624). Using cyclic voltammetry and structural XRD studies, we systematically characterize the Pt-Cu precursor compounds as well as the early stages of the selective Cu surface dissolution (dealloying) process for Pt(25)Cu(75), Pt(50)Cu(50), and Pt(75)Cu(25) alloy nanoparticles annealed at both low and high temperature. We also assess the impact of the synthesis conditions on the electrocatalytic reactivity for the oxygen reduction reaction (ORR). To gain atomistic insight into the observed voltammetric profiles, we compare our experimental results with periodic DFT calculations of trends in the thermodynamics of surface Cu dissolution potentials from highly stepped and kinked Pt(854) single crystal surfaces. The modeling suggests a dependence of the electrochemical Cu dissolution potentials on the detailed atomic environment (coordination number, nature of coordinating atoms) of the bimetallic Pt-Cu surfaces. The DFT-predicted shifts in electrochemical Cu dissolution potentials are shown to qualitatively account for the observed voltammetric profiles during Cu dealloying. Our study suggests that metal-specific energetics have to be taken into account to explain the detailed dealloying behavior of bimetallic surfaces.     

Size‐Controlled Synthesis of Platinum–Copper Hierarchical Trigonal Bipyramid Nanoframes

Mastery over the structure of materials at nanoscale can effectively tailor and control their catalytic properties, enabling enhancement in both activity and durability. We report a size‐controlled synthesis of novel Pt–Cu hierarchical trigonal bipyramid nanoframes (HTBNFs). The obtained nanocrystals looked like a trigonal bipyramid on the whole, composed of similar ordered frame structural units. By varying the amount of KI involved in the reaction, HTBNFs with variable sizes from 110 to 250 nm could be obtained. In addition, the structure of HTBNFs could be preserved only in a limited range of the Pt/Cu feeding ratio. Relative to the commercial Pt/C, these Pt–Cu HTBNFs with different Pt/Cu ratio exhibited enhanced electrocatalytic activity toward formic acid oxidation reaction as much as 5.5 times in specific activity and 2.1 times in mass activity. The excellent electrocatalytic activity and better durability are due to the unique structure of HTBNFs and probably synergetic effects between Pt and Cu.     

The use of galvanic displacement in synthesizing Pt(Cu) catalysts with the core-shell structure

The formation of a Pt(Cu) bimetallic catalyst on the carbon support by galvanic displacement of copper electrodeposits with platinum (PtCl ₆ ^2? as the displacing agent) is systematically studied. Composition, structure, and electrocatalytic properties of samples corresponding to different stages of copper displacement are analyzed. For substantially long displacement times, the formation of stable Pt(Cu)_st particles with the atomic ratio Pt: Cu ≈ 7: 3 is observed. The Pt(Cu)_st/C electrodes are shown to be close to the Pt/C electrode as regards the adsorption of hydrogen and copper atoms and the specific activity in methanol oxidation (with 0.5 M H₂SO₄ as the supporting electrolyte). Such electrocatalytic behavior of Pt(Cu)_st particles makes it possible to infer the formation of the “core(Pt, Cu)-shell(Pt)” structure, as confirmed by the XPS data.     

A Cu/Pt near-surface alloy for water-gas shift catalysis

The primary route to hydrogen production from fossil fuels involves the water-gas shift (WGS) reaction, and an improvement in the efficiency of WGS catalysts could therefore lead to a major leap forward in the realization of hydrogen economy. On the basis of a combination of high-resolution scanning tunneling microscopy, X-ray photoelectron spectroscopy, and density functional theory (DFT) calculations, we suggest the existence of a new thermodynamically stable Cu/Pt near-surface alloy (NSA). Temperature-programmed desorption and DFT reveal that this Cu/Pt NSA binds CO significantly more weakly than does Pt alone, thereby implying a considerable reduction in the potential for CO poisoning of the Cu/Pt NSA surface as compared to that of pure Pt. In addition, DFT calculations show that this Cu/Pt NSA is able to activate H2O easily, which is the rate-determining step for the WGS on several metal surfaces, and, at the same time, to bind the products of that reaction and formate intermediates rather weakly, thus avoiding possible poisoning of the catalyst surface. The Cu/Pt NSA is thus a promising candidate for an improved WGS catalyst.     

Underpotential Deposition‐Induced Synthesis of Composition‐Tunable Pt?Cu Nanocrystals and Their Catalytic Properties

Pt? Cu alloy octahedral nanocrystals (NCs) have been synthesized successfully by using N,N‐dimethylformamide as both the solvent and the reducing agent in the presence of cetyltrimethylammonium chloride. Cu underpotential deposition (UPD) is found to play a key role in the formation of the Pt? Cu alloy NCs. The composition in the Pt? Cu alloy can be tuned by adjusting the ratio of metal precursors in solution. However, the Cu content in the Pt? Cu alloy NCs cannot exceed 50 %. Due to the fact that Cu precursor cannot be reduced to metallic copper and the Cu content cannot exceed 50 %, we achieved the formation of the Pt? Cu alloy by using Cu UPD on the Pt surface. In addition, the catalytic activities of Pt? Cu alloy NCs with different composition were investigated in electrocatalytic oxidation of formic acid. The results reveal that the catalytic performance is strongly dependent on Pt? Cu alloy composition. The sample of Pt₅₀Cu₅₀ exhibits excellent activity in electrocatalytic oxidation of formic acid.     

发光PtⅡ-CuⅠ异核配合物[Pt4Cu2(edt)4(PPh3)6](ClO4)2(4H2O)的合成及其表征

Self-assembly between Pt(phen)(edt) (phen=phenanthroline, edt=1,2-ethanedithiolate) and [Cu(PPh₃)₂(MeCN)₂](ClO₄) (PPh₃=triphenylphosphine) gave rise to formation of heterohexanuclear complex [Pt₄Cu₂(edt)₄(PPh₃)₆](ClO₄)₂(4H₂O) (1). The complex was characterized by elemental analyses, ES-MS, UV-Vis, IR, ³¹P NMR spectroscopy and X-ray crystallography. The molecule consists of two [Pt₂Cu(edt)₂(PPh₃)₃] units which has a centrosymmmetric inversion to give a cyclic heterohexanuclear skeleton. The Pt^Ⅱ and Cu^Ⅰ center adopt square-planar and trigonal coordination modes, respectively. The compound shows intense emission at 632 nm in the solid state and at 678 nm in frozen dichloromethane glass at 77 K.     

Heterobimetallic dioxygen activation: synthesis and reactivity of mixed Cu-Pd and Cu-Pt bis(mu-oxo) complexes

Heterobimetallic CuPd and CuPt bis(mu-oxo) complexes have been prepared by the reaction of (PPh3)2MO2 (M=Pd, Pt) with LCu(I) precursors (L=beta-diketiminate and di- and triamine ligands) and characterized by low-temperature UV-vis, resonance Raman, and 1H and 31P[1H] NMR spectroscopy in conjunction with DFT calculations. The complexes decompose upon warming to yield OPPh3, and in one case this was shown to occur by an intramolecular process through crossover experiments using double-labeling (oxo and phosphine). The reactivity of one of the complexes, LMe2Cu(mu-O)2Pt(PPh3)2 (LMe2 = beta-diketiminate), with a variety of reagents including CO2, 2,4-di-tert-butylphenol, 2,4-di-tert-butylphenolate, [NH4][PF6], and dihydroanthracene, was compared to that of homometallic Pt2 and Cu2 counterparts. Unlike typical [Cu2(mu-O)2]2+ cores which have electrophilic oxo groups, the oxo groups in the [Cu(mu-O)2Pt]+ core behave as bases and nucleophiles, similar to previously described Pt2 compounds. In addition, however, the [Cu(mu-O)2Pt]+ core is capable of oxidatively coupling 2,4-di-tert-butylphenol and 2,4-di-tert-butylphenolate. Theoretical evaluation of the electron affinities, basicities, and H-atom transfer kinetics and thermodynamics of the Cu2 and CuM (M=Pd, Pt) cores showed that the latter are more basic and form stronger O-H bonds.     

基于银/铂纳米模拟酶表面修饰的铜离子比色检测方法研究

通过对银/铂纳米簇(Ag/Pt NCs)的表面修饰调控其催化活性,建立了一种高灵敏的比色法检测Cu2+.巯基丙酸能够抑制Ag/Pt NCs的催化活性,而巯基丙酸与Cu2+作用后,将导致上述抑制作用减弱.基于上述原理,通过测量Ag/Pt NCs 催化TMB-H2O2反应产生的显色信号,可以实现Cu2+的比色检测.本方法检测Cu2+的线性范围为10～100 nmol/L,检出限(3σ)为5.0 nmol/L.将本方法应用于实际水样中Cu2+的检测,结果表明,本方法具有操作简单、成本低、灵敏度高、特异性好等优点.     

Pt(Cu)/C Electrocatalysts with Low Platinum Content

The structure characteristics and the electrochemical behavior of Pt(Cu)/C electrocatalysts synthesized by consecutive deposition of copper and platinum on carbon-support microparticles is studied. The stability and catalytic activity of Pt(Cu)/C materials in reactions of oxygen electroreduction and methanol electrooxidation are assessed and compared with analogous characteristics of a commercial Pt/C material. It is shown that combining the method of galvanic displacement of Cu by Pt with the additional chemical deposition of Pt favors optimization of the structure and functional characteristics of Pt(Cu)/C electrocatalysts. The effect of thermal treatment on the characteristics and properties of electrocatalysts is studied and the optimal conditions of such pretreatment are revealed.     

Cationic tetrakis(nucleobase)complexes of PtII as metalloligands and potential building blocks for molecular architectures

Three cationic tetrakis(nucleobase) complexes of Pt(II) have been synthesized: [Pt(Hmhyp-N7)4](NO3)2.H2O 1, [Pt(Hegua-N7)4](NO3)2.2KNO(3).5H2O and trans-[Pt(Hmcyt-N3)2(Hegua-N7)2](NO3)2 3 (Hmhyp = 9-methylhypoxanthine, Hegua = 9-ethylguanine, Hmcyt = 1-methylcytosine). The X-ray crystal structure of has been determined. All three cationic compounds rapidly react with Hg(II), but gel formation prevented an adequate characterization of the products formed. However, a Cu(II) adduct of was isolated in crystalline form and characterized crystallographically. [{(H2O)Cu(Hmhyp)4Pt}2Cu(ClO4)4)](ClO4)2(NO3)4.6H2O crystallizes in a centrosymmetric Cu-Pt-Cu-Pt-Cu chain structure with Cu-Pt separations of 2.791(1)A(outside) and 3.8980(9)A(inside). Two of the three Cu(II) ions are bound via exocyclic O(6) sites of the Hmhyp nucleobases. At neutral and moderate alkaline pH both and form virtually insoluble precipitates, which redissolve at strongly alkaline pH to give eventually anionic [Pt(L)4]2- species (L = mhyp, egua). Finally, interacts with complementary Hmcyt to give Watson-Crick associates, as demonstrated by 1H NMR spectroscopy in DMSO-d(6).     

Kinetics and mechanism of nitrate and nitrite electroreduction on Pt(100) electrodes modified by copper adatoms

Kinetics and mechanism of nitrate and nitrite reduction on Pt(100) electrode modified by Cu adatoms have been studied in solutions of sulfuric and perchloric acids by means of cyclic voltammetry and in situ IR-spectroscopy. It has been shown that the surface redox process with participation of ammonia or hydroxylamine at 0.5–0.9 V occurs only on the Cu-free platinum. The causes of this effect could be low adsorption energy of nitrate reduction products on copper or changes in the composition of the products (ammonia for Pt(100) and N₂O for Pt(100)+Cu). Nitrate reduction on Pt(100)+Cu electrode is much faster in the perchloric acid solution (by several orders of magnitude) as compared with unmodified platinum as a result of induced adsorption of nitrate anions in the presence of partly charged Cu atoms. In the solutions of sulfuric acid the rate of nitrate reduction is considerably lower as copper adatoms facilitate adsorption of sulfate anions, which block the adsorption sites for the nitrate.     

Pd/Pt二元合金电极的制备及氧还原性能

本文利用欠电位沉积亚单层的Cu及Pt置换取代Cu的方法, 制备了具有不同表面元素组成的Pd/Pt二元合金电极(用Pd/Ptx表示, x指欠电位沉积Cu-Pt置换取代Cu过程的次数),并对其表面元素组成、氧还原性能进行了表征. 在控制欠电位沉积Cu的下限电位恒定(0.34 V)的前提下, 表面Pt/Pd的元素组成比通过重复欠电位沉积Cu及Pt置换取代Cu的次数(1~5次)来可控地调变. 光电子能谱(XPS) 以及红外光谱实验表明,Pd/Ptx电极表层区的Pt：Pd元素组成比随着Pt沉积次数增加而增加, 对Pd/Pt4电极, 在电极表层区约2~3 nm内的Pt/Pd的原子比大约是1:4,而最表层裸露Pd原子的比例仍在20%以上。循环伏安结果显示, 随着Pt沉积次数的增加(1-5次), Pd/Ptx电极表面越不易被氧化。氧还原测试结果显示随着Pt沉积次数的增加(1~4次), Pd/Ptx二元金属电极的氧还原活性依次增加, 经过第3次沉积后其氧还原活性已优于纯Pt,而经4次以上沉积,其氧还原活性基本不变。在其它反应条件相同条件的前提下, Pd/Pt4电极上氧还原的半波电位与纯Pt相比右移约25 mV。结合本文与文献的实验结果,我们初步认为Pd/Ptx二元金属体系氧还原性能改善主要源自表层Pd原子导致其邻近的Pt原子上含氧物种吸附能的降低.     

Bimetallic Cu–Pt/nanoporous carbon composite as an efficient catalyst for methanol oxidation

A novel bimetallic Cu–Pt nanoparticle supported onto Cu/indirectly carbonized nanoporous carbon composite (Cu–Pt/ICNPCC) was prepared through a two-step process: first, carbonization of furfuryl alcohol-infiltrated MOF-199 [metal–organic framework Cu₃(BTC)₂ (BTC?=?1,3,5-benzene tricarboxylate)], without removing the Cu metal with HF aqueous solution; second, the partial galvanic replacement reaction (GRR) of Cu nanoparticles by Pt^IV upon immersion in a platinum(IV) chloride solution. The synthesized materials characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy (EDS), and electrochemical methods. The EDS result revealed that part of Cu nanoparticles have been substituted by Pt nanoparticles after GRR. The methanol oxidation at the surface of Cu–Pt/ICNPCC was investigated by cyclic voltammetry method in 0.5 M H₂SO₄ and indicated good electro-catalytic activity towards methanol oxidation (E_p?=?0.85 V vs. NHE and j_f?=?1.00 mA cm^?2). It is suggested that this improvement is attributed to the effect of proper Cu/ICNPCC for fine dispersion, efficient adhesion, and prevention of Pt coalescing.     

Mesoscopic self-structuring on metal surfaces: Geometry and electronic structure

The relation between surface stress and surface reconstruction and the electronic origin of surface stress are briefly discussed. Three examples of stress induced mesoscopic self-structuring on metal surfaces are presented, namely O/Cu(110), Au(111) and Pt(110). While the principles underlying the domain formation on the first two systems seem to be understood quite well, the origin of the periodic hill-and-valley structure of Pt(110) is not yet clear. The confinement of electronic surface states in stress induced quasi-one-dimensional domains was studied recently by photoemission on O/Cu(110) and by scanning tunneling spectroscopy on Au(111). The results are briefly reviewed. The same basic effects were found in the two different studies.     

甲硫醇、甲醇在金属表面上的分解反应性能比较研究

用键级守恒-Morse势法比较了XH₃SH、CH₃OH在Ni(111)、Pt(111)和Cu(111)面上的热分解反应性能.结果表明,由Ni至Pt再至Cu,CH₃SH中C-S键断裂几率降低,而S-H键裂相对几率增加,而在Cu上仅发生S-H键裂.CH₃OH在Ni上易解离为CH₃和CH₃O-,在Pt、Cu上则较难解离.按Ni、Pt、Cu的顺序,CH₃S-选择性断裂C-S键的几率增加,而CH₃O-则选择性断裂C-H键的几率增加.CH₃XH、CH₃X-(X=O,S)解离活化能垒依Ni、Pt、Cu的顺序增加,CH₃OH在Ni上最终解离为CO,而在Cu上则解离为H₂CO.     

Tuning supported catalyst reactivity with dendrimer-templated Pt-Cu nanoparticles

The effects of particle composition on heterogeneous catalysis were studied using dendrimer-encapsulated nanoparticles (DENs) as precursors to supported Pt-Cu catalysts. Bimetallic Pt-Cu DENs with varying Pt/Cu ratios were prepared in an anaerobic aqueous solution and deposited onto a high-purity commercial alumina support. The dendrimer template was then thermally removed to yield supported nanoparticle catalysts, which were studied with toluene hydrogenation and CO oxidation catalysis as well as infrared spectroscopy of adsorbed CO. Incorporating Cu into Pt nanoparticles had opposite effects on the two test reactions. Cu acted as a mild promoter for CO oxidation catalysis, and the promoting effect was independent of the amount of Cu present. Conversely, Cu acted as a strong poison for toluene hydrogenation catalysis, and the normalized rate tracked inversely with Cu content. Infrared spectroscopy of the supported nanoparticles indicated that electronic effects (electron donation from Cu to Pt) were minimal for these materials. Consequently, the catalysis results are interpreted in terms of potential structural differences as a function of Cu incorporation and reaction conditions.     

Electrodeposition of copper on a Pt(111) electrode in sulfuric acid containing poly(ethylene glycol) and chloride ions as probed by in situ STM

This study employed real-time in situ STM imaging to examine the adsorption of PEG molecules on Pt(111) modified by a monolayer of copper adatoms and the subsequent bulk Cu deposition in 1 M H(2)SO(4) + 1 mM CuSO(4)+ 1 mM KCl + 88 μM PEG. At the end of Cu underpotential deposition (~0.35 V vs Ag/AgCl), a highly ordered Pt(111)-(√3 × √7)-Cu + HSO(4)(-) structure was observed in 1 M H(2)SO(4) + 1 mM CuSO(4). This adlattice restructured upon the introduction of poly(ethylene glycol) (PEG, molecular weight 200) and chloride anions. At the onset potential for bulk Cu deposition (~0 V), a Pt(111)-(√3 × √3)R30°-Cu + Cl(-) structure was imaged with a tunneling current of 0.5 nA and a bias voltage of 100 mV. Lowering the tunneling current to 0.2 nA yielded a (4 × 4) structure, presumably because of adsorbed PEG200 molecules. The subsequent nucleation and deposition processes of Cu in solution containing PEG and Cl(-) were examined, revealing the nucleation of 2- to 3-nm-wide CuCl clusters on an atomically smooth Pt(111) surface at overpotentials of less than 50 mV. With larger overpotential (η > 150 mV), Cu deposition seemed to bypass the production of CuCl species, leading to layered Cu deposition, starting preferentially at step defects, followed by lateral growth to cover the entire Pt electrode surface. These processes were observed with both PEG200 and 4000, although the former tended to produce more CuCl nanoclusters. Raising [H(2)SO(4)] to 1 M substantiates the suppressing effect of PEG on Cu deposition. This STM study provided atomic- or molecular-level insight into the effect of PEG additives on the deposition of Cu.