Tan Fatang, Du Bingchen, Danberry Aaron L, Park In-Su, Sung Yung-Eun, Tong YuYe
Department of Chemistry, Georgetown University, 37th & O Streets, NW, Washington DC 20057, USA.
Faraday Discuss. 2008;140:139-53; discussion 185-207. doi: 10.1039/b803073a.
This paper reports a detailed in situ 195Pt electrochemical-nuclear magnetic resonance (EC-NMR) study of PtRu nanoparticles (NPs) that had a nominal atomic ratio of Pt : Ru = 1 : 1 and were supported on carbon nanocoils and carbon black (Vulcan XC-72) respectively. The particle sizes of the two samples were determined by X-ray diffraction using the Sherrer equation: 3.6 nm for the former and 3.2 nm for the latter, which were further corroborated by transmission electron microscope measurements. By taking advantage of a unique correlation between the spectral frequency of the 195Pt NMR resonance and the radial atomic position in a particle, qualitatively- and spatially-resolved local Pt atomic fractions in the particles were deduced by using a Ruderman-Kittel-Kasuya-Yosida (RKKY) J-coupling-based method as a function of different electrode potentials. The results indicated that both samples had Pt-enriched cores and Pt-deprived surfaces and, most importantly, the local Pt concentration varied as the electrochemical environment changed. The spatially-resolved Fermi level local densities of states (E(f)-LDOS), which are a measure of the electronic frontier orbitals in metals, were deduced across the NMR spectrum and correlated with the EC activity in methanol electro-oxidation. The results were also compared to those obtained previously from Pt/Ru NPs supported respectively on carbon and graphite nanofibers.
本文报道了一项详细的原位¹⁹⁵Pt电化学 - 核磁共振（EC - NMR）研究，该研究针对标称原子比为Pt : Ru = 1 : 1、分别负载在碳纳米线圈和炭黑（Vulcan XC - 72）上的PtRu纳米颗粒（NPs）。使用谢乐方程通过X射线衍射确定了两个样品的粒径：前者为3.6 nm，后者为3.2 nm，这一结果通过透射电子显微镜测量得到了进一步证实。利用¹⁹⁵Pt NMR共振的光谱频率与颗粒中径向原子位置之间的独特关联，采用基于Ruderman - Kittel - Kasuya - Yosida（RKKY）J耦合的方法，根据不同的电极电位推导出颗粒中定性和空间分辨的局部Pt原子分数。结果表明，两个样品均具有富含Pt的核心和贫Pt的表面，最重要的是，局部Pt浓度随电化学环境的变化而变化。通过NMR光谱推导了空间分辨的费米能级局部态密度（E(f) - LDOS），它是衡量金属中电子前沿轨道的指标，并将其与甲醇电氧化中的EC活性相关联。还将结果与先前分别负载在碳和石墨纳米纤维上的Pt/Ru NPs所获得的结果进行了比较。
