电化学原位表面增强拉曼光谱研究Au@Pd纳米粒子薄膜电极上吸附+CO的斯塔克效应.pdf

Chinese Journal of Catalysis 37 (2016) 1156–1165 催化学报 2016年 第37卷 第7期 | www.cjcatal.org available at journal homepage: Article (Special Issue on Electrocatalysis Transformation) Nonlinear Stark effect observed for carbon monoxide chemisorbed on gold core/palladium shell nanoparticle film electrodes, using in situ surface‐enhanced Raman spectroscopy Pu Zhang a, Yi Wei a, Jun Cai a, Yan‐Xia Chen a,*, Zhong‐Qun Tian b a Hefei National Laboratory for Physical Sciences at Microscale Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, Anhui, China b State Key Laboratory of Physical Chemistry of Solid Surfaces, Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, 361005, Fujian, China A R T I C L E I N F O A B S T R A C T Article history: Received 14 March 2016 Accepted 14 April 2016 Published 5 July 2016 The potential (E)‐dependent vibrational behavior of a saturated CO adlayer on Au‐core Pd‐shell nanoparticle film electrodes was investigated over a wide potential range, in acidic, neutral, and basic solutions, using in situ surface‐enhanced Raman spectroscopy (SERS). Over the whole of the examined potential region (–1.5 to 0.55 V vs. NHE), the peak frequencies of both the C–OM and the Pd–COM band (here, M denotes the multiply‐bonded configuration) displayed three distinct linear regions: dνC–OM/dE decreased from ~185–207 (from –1.5 to –1.2 V) to ~83–84 cm–1/V (–1.2 to –0.15 V), and then to 43 cm–1/V (–0.2 to 0.55 V); on the other hand, dνPd–COM/dE changed from ~–10 to –8 cm–1/V (from –1.5 to –1.2 V) to ~–31 to –30 cm–1/V (–1.2 to –0.15 V), and then to –15 cm–1/V (–0.2 to 0.55 V). The simultaneously recorded cyclic voltammograms revealed that at E 800 cm–1), and the strong absorption in the far‐infrared region by water, which is typically used as the solvent in such studies. In contrast, surface‐enhanced Raman spectroscopy (SERS) can be used to obtain vibrational infor‐ mation in a wide spectral window (5–4000 cm–1), and does not require the use of the spectral‐difference method to remove solution‐phase interferences. However, few electrochemical in‐situ SERS studies have been carried out on CO adsorption on Pd substrates, because SERS studies on pure roughened Pd electrodes are typically limited by the poor surface sensitivity. Zou et al. [2] studied the Stark effects of CO adsorption on Pd film‐coated Au electrodes by borrowing the strong SERS en‐ hancement from the Au substrate, and found that the slope for the Pd–CO stretching vibration (dνPd–COM/dE) was roughly line‐ ar (–10 cm–1/V). However, because of the limited range of potentials applied in the above studies, it is difficult to infer how the external electric field effect influenced the adsorption behavior for COad at the Pd electrodes. Here, we report potential‐dependent vibrational Stark be‐ havior, based on surface‐enhanced Raman measurements of a CO adlayer at an Au‐core/Pd‐shell nanoparticle film electrode in acidic, neutral, and basic aqueous media, in a broad potential region from –1.5 to 0.55 V. The potential range accessible for SERS measurements is determined by the onset of COad oxida‐ tion and a strong hydrogen evolution reaction (HER); the po‐ tential range can be expanded by using different electrolytes. Our results revealed distinct Stark slopes in three different potential regions, with a pronounced increase in dνC–O/dE, and a decrease in |dνPd–CO/dE| (the absolute value of dνPd–CO/dE) at potentials where the HER reaction occurred. Such spectral be‐ havior was preliminarily attributed to the COad site transition induced by the co‐adsorbed hydrogen atoms involved in the HER, as confirmed using periodic density functional theory (DFT) calculations. 2. Experimental and computational 2.1. Experimental set‐up The design of the electrochemical flow cell used in the pre‐ sent SERS study has been described in detail elsewhere [17]. The electrolyte flowing through the cell could be switched be‐ tween different electrolytic reservoirs, where the flow rate was controlled by changing the hydraulic pressure. In this experi‐ ment, the flow rate was 50 μL/s. All measurements were per‐ formed at ambient temperature (25 ± 3 C). A thin Au foil (thickness 50 m) and a saturated calomel electrode (SCE) were used as the counter electrode (CE) and the reference electrode (RE), respectively. Here, all potentials are reported with respect to normal hydrogen electrode (NHE). Electrochemical measurements were conducted using a CHI631B electrochemical workstation (CH Instruments, Shanghai, China). SERS measurements were carried out using a confocal microprobe Raman system (LabRam I from Dilor, France), using an air‐cooled CCD and a He‐Ne laser operating at 632.8 nm. The laser power 。