Chemistry Division, U.S. Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, DC 20375, USA.
Langmuir. 2010 May 4;26(9):6809-17. doi: 10.1021/la904107j.
Raman spectroscopy and electrochemical methods were used to study the behavior of the model adsorbate benzenethiol (BT) on nanostructured Pt, Pd, and PtPd electrodes as a function of applied potential. Benzenethiol adsorbs out of ethanolic solutions as the corresponding thiolate, and voltammetric stripping data reveal that BT is oxidatively removed from all of the nanostructured metals upon repeated oxidative and reductive cycling. Oxidative stripping potentials for BT increase in the order Pt < PtPd < Pd, indicating that BT adsorbs most strongly to nanoscale Pd. Yet, BT Raman scattering intensities, measured in situ over time scales of minutes to hours, are most persistent on the film of nanostructured Pt. Raman spectra indicate that adsorbed BT desorbs from nanoscale Pt at oxidizing potentials via cleavage of the Pt-S bond. In contrast, on nanoscale Pd and PtPd, BT is irreversibly lost due to cleavage of BT C-S bonds at oxidizing potentials, which leaves adsorbed sulfur oxides on Pd and PtPd films and effects the desulfurization of BT. While Pd and PtPd films are less sulfur-resistant than Pt films, palladium oxides, which form at higher potentials than Pt oxides, oxidatively desulfurize BT. In situ spectroelectrochemical Raman spectroscopy provides real-time, chemically specific information that complements the cyclic voltammetric data. The combination of these techniques affords a powerful and convenient method for guiding the development of sulfur-tolerant PEMFC catalysts.
拉曼光谱和电化学方法被用来研究模型吸附物苯硫醇（BT）在纳米结构 Pt、Pd 和 PtPd 电极上的行为，作为施加电位的函数。苯硫醇从乙醇溶液中吸附出来作为相应的硫醇，伏安 stripping 数据表明，BT 在反复氧化和还原循环过程中从所有纳米结构金属上被氧化去除。BT 的氧化剥离电位按 Pt < PtPd < Pd 的顺序增加，表明 BT 对纳米级 Pd 的吸附最强。然而，BT 的拉曼散射强度在纳米结构 Pt 膜上随时间尺度从分钟到小时实时测量，最为持久。拉曼光谱表明，吸附的 BT 通过 Pt-S 键的断裂，在氧化电位下从纳米级 Pt 上解吸。相比之下，在纳米级 Pd 和 PtPd 上，BT 由于在氧化电位下 BT C-S 键的断裂而不可逆地损失，这在 Pd 和 PtPd 薄膜上留下吸附的硫氧化物，并影响 BT 的脱硫。虽然 Pd 和 PtPd 薄膜比 Pt 薄膜的硫耐受性差，但在比 Pt 氧化物更高的电位下形成的钯氧化物会氧化脱硫 BT。原位光谱电化学拉曼光谱提供了实时、化学特异性的信息，补充了循环伏安数据。这些技术的结合为指导开发耐硫质子交换膜燃料电池催化剂提供了一种强大而方便的方法。
