Baker Laboratory, Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853-1301, USA.
Chemistry. 2010 Dec 10;16(46):13689-97. doi: 10.1002/chem.201001211.
The composition of ordered intermetallic nanoparticles (PtBi and PtPb) has been quantitatively studied by in situ X-ray fluorescence (XRF) during active electrochemical control in solutions of supporting electrolyte and small organic molecules (SOMs). Because the Pt L(β1,2) lines and the Bi L(α1,2) lines are only separated by 200 eV, an energy-dispersive detector and a multiple-channel analyzer (MCA) were used to record the major fluorescent emission lines from these two elements. The molar ratios of platinum to the less-noble elements (Bi, Pb) in the nanoparticles dramatically changed as a function of the applied upper limit potentials (E(ulp)) in cyclic voltammetric (CV) characterization. Similar to previous investigations for bulk intermetallic surfaces, the less-noble elements leached out from the surfaces of the intermetallic nanoparticles. For PtBi nanoparticles, the ratios of fluorescence intensities of Pt/Bi in the samples were 0.42, 0.96, and 1.36 for E(ulp)=+0.40, +0.80, and 1.20 V, respectively, while cycling the potential from -0.20 V to the E(ulp) value for 10 cycles. The leaching-out process of the less-noble elements occurred at more negative E(ulp) values than expected. After cycling to relatively positive E(ulp) values, nonuniform PtM (M=Bi of Pb) nanoparticles formed with a Pt-rich shell and intermetallic PtM core. When the supporting solutions contained active fuel molecules in addition to the intermetallic nanoparticles (formic acid for PtBi, formic acid and methanol for PtPb), kinetic stabilization effects were observed for E(ulp)=+0.80 V, in a way similar to the response of the bulk materials. It was of great importance to quantitatively explore the change in composition and structure of the intermetallic nanoparticles under active electrochemical control. More importantly, this approach represents a simple, universal, and multifunctional method for the study of multi-element nanoparticles as electrocatalysts. This is, to our knowledge, the first report of nondestructive, quantitative characterization of bimetallic or multi-elemental nanoparticles electrocatalysts under active electrochemical control.
有序金属间化合物纳米粒子（PtBi 和 PtPb）的组成通过在含有支持电解质和小分子（SOM）的溶液中进行原位 X 射线荧光（XRF），在电化学主动控制过程中进行定量研究。由于 Pt L(β1,2)线和 Bi L(α1,2)线仅相差 200 eV，因此使用能量色散探测器和多通道分析仪（MCA）记录这两个元素的主要荧光发射线。在循环伏安（CV）特性中，纳米粒子中铂与较不活泼元素（Bi、Pb）的摩尔比随施加的上限电势（E(ulp)）的变化而剧烈变化。与以前对大块金属间化合物表面的研究类似，较不活泼的元素从金属间化合物纳米粒子的表面浸出。对于 PtBi 纳米粒子，当电势从-0.20 V 循环到 E(ulp)值时，E(ulp)分别为+0.40、+0.80 和+1.20 V，PtBi 纳米粒子的荧光强度比 Pt/Bi 比值分别为 0.42、0.96 和 1.36。在 10 个循环中，浸出过程发生在比预期更负的 E(ulp)值。在循环到相对正的 E(ulp)值后，形成具有富 Pt 壳和金属间化合物 PtM 核的非均匀 PtM（M=Bi 或 Pb）纳米粒子。当支撑溶液除了含有金属间化合物纳米粒子（对于 PtBi 为甲酸，对于 PtPb 为甲酸和甲醇）外还含有活性燃料分子时，在+0.80 V 的 E(ulp)下观察到动力学稳定化效应，这与块状材料的响应类似。在主动电化学控制下定量研究金属间化合物纳米粒子的组成和结构变化非常重要。更重要的是，这种方法代表了一种简单、通用和多功能的方法，用于研究作为电催化剂的多元素纳米粒子。据我们所知，这是首次在主动电化学控制下对双金属或多元素纳米粒子电催化剂进行无损、定量表征的报道。
