自组装纳米金膜上铂微/纳结构电催化剂的制备及性能

基于纳米金(AuNP)表面基团的静电自组装作用制备了多层有序的纳米金超薄膜. 研究了自组装纳米金超薄膜上铂微/纳结构催化剂(Pt/AuNP)的制备过程. 考察了沉积电位和沉积时间对甲酸电氧化活性的影响, 确定了最佳沉积电位为0 V, 最佳沉积时间为600 s. 同时对比考察了Pt/AuNP/PE/GCE, AuNP/PE/GCE和纯Pt电极在0.1 mol/L H2SO4介质中对甲酸电氧化活性以及载体对沉积物形态和甲酸氧化活性的影响. 研究结果表明, 纳米金组装体对铂的电沉积有明显的促进作用; Pt/AuNP/PE/GCE对甲酸的电氧化有很好的电催化性能.     

甲酸在纳米金承载铂(Pt^Au)电催化剂上的电化学氧化

采用循环伏安扫描测试对不同浓度的甲酸在纳米Au颗粒((10.0±1.2)nm)承载Pt电催化剂(记为Ptm^Au,其中m为Pt/Au原子比)上的电化学氧化过程进行了研究.结果表明,Pt在纳米Au颗粒表面的形态对甲酸的电化学氧化行为影响显著.当Pt对Au颗粒形成壳层覆盖(m>0.2)时,甲酸电氧化反应主要发生在高电势(相对SCE电极为0.6~1.0 V)范围,与常规Pt/C电催化剂上甲酸的电氧化行为类似;当Au表面Pt的形态由单原子壳层(m=0.2)递变为不大于1.0 nm的Pt原子簇或原子筏(m<0.2)时,在低电势(-0.2~0.6 V)范围也能明显检测到甲酸的电氧化反应,而且随着m的减小,Pt的质量比活性显著提高.Pt呈现100%暴露(电化学活性面积EAS=236 m2/g-Pt)的Pt0.05^Au/C电催化剂在甲酸电氧化峰(0.38 V)处的质量比活性是通常Pt/C电催化剂(Pt分散度为30%或EAS为74 m2/g-Pt)的40倍,表明随着Au颗粒上Pt尺寸的减小或分散度的提高,Ptm^Au/C电催化剂对甲酸电氧化反应的催化活性也显著提高.在甲酸浓度由0.2 mol/L渐提高至3.2 mol/L时,Ptm^Au/C和Pt/C催化剂上甲酸电氧化反应的比电流均呈先增大后减小的火山形变化,表明适宜的甲酸工作浓度也是在Pt基催化剂上实现高功率直接甲酸燃料电池的关键因素之一.     

不同Pt壳厚度Au_(core)@Pt_(shell)纳米粒子SERS效应

以Au粒子(55nm)为核,抗坏血酸为还原剂,将不同量的Pt沉积在Au核上,制得可控壳层厚度(0.3～6nm)的Pt包Au纳米粒子(Aucore@Ptshell).用紫外-可见吸收光谱、扫描电镜(SEM)、透射电镜(TEM)和电化学循环伏安法等观测Aucore@Ptshell纳米粒子的表面形貌、结构和性能.另以SCN-为探针,考察了Pt壳厚度对Aucore@Ptshell纳米粒子SERS信号的影响.结果表明,SCN-离子的SERS信号强度随Pt壳厚度的增加呈指数衰减,当Pt壳厚度为1.4nm时,Aucore@Ptshel纳米粒子表现出铂良好的电化学性能,又具有较强的SERS活性.     

(PtAuPt)HN/GC的制备及对甲酸氧化的电催化性能

以Se溶胶为模板,合成了多层核壳结构的Se@Pt@Au@Pt实心纳米粒子;采用化学与电化学相结合的除硒方法制得了(PtAuPt)HN/GC,并表征了(PtAuPt-Se)HN的表面形貌、结构与组成;以甲酸为探针分子,比较了(PtAuPt)HN/GC和Pt/C/GC对甲酸氧化的电催化行为,发现(PtAuPt)HN/GC催化甲酸氧化只有1个氧化峰,峰电位和峰电流分别约为0.35V和1.22mA/cm2,而Pt/C/GC则有2个氧化峰,在0.35V时所对应的电流密度仅约为0.30mA/cm2,前者在该电位时的电流密度是后者的4倍;在0.30mA/cm2的电流密度下,(PtAuPt)HN/GC对应的电极电位为0.01V,比Pt/C/GC负移了340mV;在600s时的计时电流分别为0.06和0.02mA/cm2.(PtAuPt)HN对甲酸氧化的电催化活性不但比Pt/C高,而且具有一定的抗CO中毒性能.     

组装在贵金属基底上的金纳米粒子对CO的电化学催化氧化

研究了组装在Au, Pt电极表面的金纳米粒子对CO的电化学催化氧化行为, 首次在实验上观察到较大粒径金纳米粒子(粒径＞10 nm)对CO的电催化氧化活性. 考察了金粒子表面金氧化物对粒子电催化活性的影响, 发现表面金氧化物的形成是金纳米粒子对CO具有电催化氧化活性的前提. 对于相同粒径的金纳米粒子, 随着粒子表面金氧化物量的增加,催化活性增大.     

碳纳米粒子支撑的钯纳米催化剂在甲酸氧化中的电催化活性

采用化学还原法制备了碳纳米粒子支撑的钯纳米结构(Pd-CNP). 透射电镜表征显示在Pd-CNP纳米复合物中,金属Pd呈菜花状结构,粒径约20~30 nm。它们由许多更小的Pd纳米粒子（3~8 nm）组成. 电化学研究表明,虽然Pd-CNP的电化学活性面积比商业Pd黑低40%（可能原因是部分Pd表面被一层碳纳米粒子覆盖）,但其对甲酸氧化却表现出更好的电催化活性：质量比活性和面积比活性都比Pd黑高几倍. 催化活性增强的原因可能是碳纳米粒子支撑的Pd纳米结构具有特殊的层次化结构,可以形成更多的活性位,以及表面位更利于反应进行.     

钯纳米晶体在电催化甲酸氧化反应中的形貌效应

本文基于课题组前期工作,选用适当的金属前驱物、还原剂、稳定剂和保护剂,通过调控氧化刻蚀和反应动力学等,成功合成了形貌和尺寸均不相同的Pd纳米晶.经过认真的纳米粒子清洗和电极修饰组装,考察了它们在电催化甲酸氧化反应中的形貌与性能的关系.研究结果表明,Pd纳米晶样品的最大电流密度以纳米八面体（nanooctahedra）、纳米线（nanowires）、纳米立方体（nanocubes）、纳米瓜子（nanotapers）、凹面纳米立方体（concave nanocubes）的顺序递增,催化甲酸氧化反应的起始氧化电位均小于0.2V.研究结果印证了Pd纳米晶催化甲酸氧化反应的催化性能在尺寸效应上主要受活性表面积的影响,扣除表面积效应后的催化性能与其尺寸没有明确关系.该系列Pd纳米晶的催化性能主要取决于其表面结构,得出Pd纳米晶催化甲酸氧化反应遵循{111}晶面〈{100}晶面〈高指数晶面的性能活性顺序.综合最大电流密度和最小操作电位因素发现,Pd凹面纳米立方体和Pd纳米瓜子具有相对较好的商用价值.     

壳层厚度可调控的Ag@Pd@Pt纳米粒子的合成和甲酸电催化研究

在本课题组研究55 nm Au@Pd@Pt对甲酸电催化效果基础上,我们采用Ag取代Au制备55 nm Ag@Pd@Pt纳米粒子以降低催化剂的成本,并对甲酸的电催化行为进行研究. 研究表明：少量Pt的存在可大幅度提高催化剂的活性,当Pt的覆盖度为0.5 单原子层（ML）时,起始氧化电位最为靠前,氧化峰电流最大,这与Au@Pd@Pt纳米粒子对甲酸电催化行为类似. 与Au@Pd@Pt纳米粒子相比,其最佳起始氧化电位偏正0.05 V,但电催化活性并没有明显的降低. 通过改变催化剂比表面积研究甲酸的电催化行为,发现将9 nm Ag纳米粒子作为内核的9 nm Ag@Pd@Pt负载在活性炭中,在保持催化活性不变的情况下,碳载的催化剂价格可比55 nm Au@Pd@Pt纳米粒子降低220倍左右.     

中空介孔三氧化钨微球载钯催化剂的甲酸氧化电催化性能(英文)

采用喷雾干燥法和焙烧处理制备中空介孔三氧化钨微球(HMTTS),在其表面进一步负载活性成分Pd,得到纳米Pd/HMTTS复合催化剂.采用X射线粉末衍射(XRD)、扫描电镜(SEM)和透射电镜(TEM)等对催化剂的形貌和晶型结构进行了表征.结果表明,Pd纳米粒子为面心立方晶体结构,均匀地分布在HMTTS表面.采用循环伏安和计时电流法研究了在酸性溶液中Pd/HMTTS催化剂对甲酸的电催化氧化性能,结果表明Pd/HMTTS催化剂比普通的三氧化钨载钯催化剂(Pd/WO3)对甲酸呈现出更高的电催化氧化活性和稳定性.HMTTS独特的中空介孔结构和表面特性以及氢溢流效应有利于甲酸在钯表面的直接脱氢氧化过程的发生.     

利用壳层厚度调节核壳Au@Pd纳米粒子的SERS活性

设计合成了一种尺寸可控, 且外壳上无“针孔”的核壳钯包金(Au@Pd)纳米粒子, 通过改变核的尺寸和外壳的厚度来调控其光学性质, 并用TEM、HRTEM、UV-Vis和SERS等手段对其进行了表征. 通过研究Au@Pd纳米粒子的SERS活性随Pd壳层厚度变化的规律, 发现薄壳Au@Pd纳米粒子远远优于Pd金属本身的SERS活性, 其原因主要是内层金核电磁场增强的长程效应.     

Localized Pd overgrowth on cubic Pt nanocrystals for enhanced electrocatalytic oxidation of formic acid

Binary Pt/Pd nanoparticles were synthesized by localized overgrowth of Pd on cubic Pt seeds for the investigation of electrocatalytic formic acid oxidation. The binary particles exhibited much less self-poisoning and a lower activation energy relative to Pt nanocubes, consistent with the single crystal study.     

Highly efficient and stable electrooxidation of methanol and ethanol on 3D Pt catalyst by thermal decomposition of In_2O_3 nanoshells

In this paper In_2O_3 nanoshells have been synthesized via a facile hydrothermal approach.The nanoshells can be completely cracked into pony-size nanocubes by annealing,which are then used as a support of Pt catalyst for methanol and ethanol electrocatalytic oxidation.The prepared In_2O_3 and supported Pt catalysts(Pt/In_2O_3) were characterized by X-ray diffraction(XRD),energy dispersive X-ray spectroscopy(EDS),X-ray photoelectron spectroscopy(XPS),field effect scanning electron microscopy(FESEM),and transmission electron microscopy(TEM).Cyclic voltammetry(CV),linear sweep voltammetry(LSV),chronoamperometry and electrochemical impedance spectroscopy(EIS) were carried out,indicating the excellent catalytic performance for alcohol electrooxidation can be achieved on Pt/In_2O_3 nanocatalysts due to the multiple active sites,high conductivity and a mass of microchannels and micropores for reactant diffusions arising from 3D frame structures compared with that on the Pt/C catalysts.     

电化学置换法制备高Pt利用率的类核壳型Ni-Pt电催化剂(英文)

采用电化学置换法,在VulcanXC-72表面制备得到了活性高和分散性好的纳米Ptshell-Nicore电催化剂.该方法先以NaH2PO2为还原剂,化学沉积得到Ni核,Pt在Ni核表面通过原位置换形成Ni-Pt类核壳型结构.通过透射电镜(TEM)、X射线衍射(XRD)、紫外-可见光光谱(UV-Vis)和循环伏安(CV)测试证明了Pt壳层完全包覆在Ni核的表面.电化学氢吸/脱附测试结果显示,Ptshell-Nicore/XC-72的电化学活性面积为Pt/C(JM)的1.2倍,而其理论Pt担载量只为Pt/C(JM)的40%.这表明,核壳型Ni-Pt纳米粒子可以显著提高Pt的催化活性和利用率.     

An effective hydrothermal route for the synthesis of multiple PDDA-protected noble-metal nanostructures

In this article, we demonstrate an effective hydrothermal route for the synthesis of multiple PDDA-protected (PDDA = poly(diallyl dimethylammonium) chloride) noble-metal (including silver, platinum, palladium, and gold) nanostructures in the absence of any seeds and surfactants, in which PDDA, an ordinary and water-soluble polyelectrolyte, acts as both a reducing and a stabilizing agent. Under optimal experimental conditions, Ag nanocubes, Pt and Pd nanopolyhedrons, and Au nanoplates can be obtained, which were characterized by transmission electron microscopy , scanning electron microscopy, energy-dispersive spectroscopy, and X-ray diffraction. More importantly, the nanostructures synthesized show potential applications in surface-enhanced Raman scattering and electrocatalysis, in which Ag nanocubes and Pt nanopolyhedrons were chosen as the examples, respectively.     

Designed Synthesis of Well‐Defined Pd@Pt Core–Shell Nanoparticles with Controlled Shell Thickness as Efficient Oxygen Reduction Electrocatalysts

Improving the electrocatalytic activity and durability of Pt‐based catalysts with low Pt content toward the oxygen reduction reaction (ORR) is one of the main challenges in advancing the performance of polymer electrolyte membrane fuel cells (PEMFCs). Herein, a designed synthesis of well‐defined Pd@Pt core–shell nanoparticles (NPs) with a controlled Pt shell thickness of 0.4–1.2 nm by a facile wet chemical method and their electrocatalytic performances for ORR as a function of shell thickness are reported. Pd@Pt NPs with predetermined structural parameters were prepared by in situ heteroepitaxial growth of Pt on as‐synthesized 6 nm Pd NPs without any sacrificial layers and intermediate workup processes, and thus the synthetic procedure for the production of Pd@Pt NPs with well‐defined sizes and shell thicknesses is greatly simplified. The Pt shell thickness could be precisely controlled by adjusting the molar ratio of Pt to Pd. The ORR performance of the Pd@Pt NPs strongly depended on the thickness of their Pt shells. The Pd@Pt NPs with 0.94 nm Pt shells exhibited enhanced specific activity and higher durability compared to other Pd@Pt NPs and commercial Pt/C catalysts. Testing Pd@Pt NPs with 0.94 nm Pt shells in a membrane electrode assembly revealed a single‐cell performance comparable with that of the Pt/C catalyst despite their lower Pt content, that is the present NP catalysts can facilitate low‐cost and high‐efficient applications of PEMFCs.     

Synthesis and characterization of platinum monolayer oxygen-reduction electrocatalysts with Co–Pd core–shell nanoparticle supports

We synthesized Pt monolayer electrocatalysts for oxygen-reduction using a new method to obtain the supporting core–shell nanoparticles. They consist of a Pt monolayer deposited on carbon-supported Co–Pd core–shell nanoparticles with the diameter of 3–4 nm. The nanoparticles were made using a redox-transmetalation (electroless deposition) method involving the oxidation of Co by Pd cations, yielding a Pd shell around the Co core. The quality of the thus-formed core–shell structure was verified using transmission electron microscopy and X-ray absorption spectroscopy, while cyclic voltammetry was employed to confirm the lack of Co oxidation (dissolution). A Pt monolayer was deposited on the Co–Pd core–shell nanoparticles by the galvanic displacement of a Cu monolayer obtained by underpotential deposition. The total noble metal mass-specific activity of this Pt monolayer electrocatalyst was ca. 3-fold higher than that of commercial Pt/C electrocatalysts.     

Effects of the Pt Shell Thickness on the Oxygen Reduction Reaction on a Well-Defined Pd@Pt Core-Shell Model Surface

The effect of the Pt shell thickness on the oxygen reduction reaction (ORR) of a Pd@Pt core-shell catalyst was studied using surface science technics and computational approaches. We found Pt shells on Pd rods to be negatively charged because of charge transfer from the Pd substrate when the shell thicknesses were 0.5 or 1 monolayer (ML). The activities of the ORR of the model surface with a Pt shell of 0.5 or 1 ML were similar and more than twice the activities of a Pt/C or Pt rod. The relationship between the ORR activity and the thickness of the Pt shell was the exact opposite of the relationship between the Pt binding energy and the Pt shell thickness. The indication was that more negatively charged Pt had higher ORR activity. Density functional theory calculations confirmed that a single layer of Pt atoms located on Pd was negatively charged compared to pure Pt and resulted in a lower barrier to the rate-limiting step of the ORR.     

Highly selective synthesis of catalytically active monodisperse rhodium nanocubes

Monodisperse sub-10 nm Rh nanocubes were synthesized with high selectivity (>85%) by a seedless polyol method. The {100} faces of the Rh NCs were effectively stabilized by chemically adsorbed Br- ions from trimethyl(tetradecyl)ammonium bromide (TTAB). This simple one-step polyol route can be readily applied to the preparation of Pt and Pd nanocubes. Moreover, the organic molecules of PVP and TTAB that encapsulated the Rh nanocubes did not prevent catalytic activity for pyrrole hydrogenation and CO oxidation.     

Hydrogen dissociative chemisorption and desorption on saturated subnano palladium clusters (Pdn, n = 2-9)

H(2) sequential dissociative chemisorption on small palladium clusters was studied using density functional theory. The chosen clusters Pd(n) (n = 2-9) are of the lowest energy structures for each n. H(2) dissociative chemisorption and subsequent H atom migration on the bare Pd clusters were found to be nearly barrierless. The dissociative chemisorption energy of H(2) and the desorption energy of H atom in general decrease with the coverage of H atoms and thus the catalytic efficiency decreases as the H loading increases. These energies at full cluster saturation were identified and found to vary in small energy ranges regardless of cluster size. As H loading increases, the clusters gradually change their bonding from metallic character to covalent character. For the selected Pd clusters, the capacity to adsorb H atoms increases almost proportionally with cluster size; however, it was found that the capacity of Pd clusters to adsorb H atoms is, on average, substantially smaller than that of small Pt clusters, suggesting that the catalytic efficiency of Pt nanoparticles is superior to Pd nanoparticles in catalyzing dissociative chemisorption of H(2) molecules.