Article pubs.acs.org/JPCC
Insights into the Electrooxidation of Formic Acid on Pt and Pd Shells on Au Core Surfaces via SERS at Dendritic Au Rod Electrodes Miri Ahn and Jongwon Kim* Department of Chemistry, Chungbuk National University, Cheongju, Chungbuk 361-763, Korea S Supporting Information *
ABSTRACT: Highly surface-enhanced Raman scattering (SERS)-active Pt and Pd layers were fabricated using dendritic Au rod (DAR) structures, prepared by simple electrodeposition, as core substrates. Electrochemical and SERS measurements using CO as a probe revealed that the SERS activity on DAR@Pt/Pd core−shell substrates originated exclusively from the Pt/Pd shell layers. The SERS enhancement factors obtained with DAR@Pt and DAR@Pd were 4.5 × 104 and 3.5 × 104, respectively. The unique structures of DAR with sharp edge sites and long-range enhancement caused by the underlying DAR cores contributed to the high activity of SERS. The well-defined and homogeneous surface morphology of DAR@Pt/Pd substrates resulted in good SERS reproducibility and stable electrochemical SERS behavior under potential excursions. The DAR@Pt and DAR@Pd substrates were used for the in-situ electrochemical SERS examination during the oxidation of formic acid (FA) at wavenumbers below 1000 cm−1, where the SERS provided unique spectral information regarding the oxidation/reduction of electrode surfaces. Based on the results of the electrochemical SERS examinations, the electrocatalytic activity of the DAR@Pt and DAR@Pd surfaces for FA oxidation was evaluated in a comparative way. The highly active and robust Pt/Pd SERS substrates could be used for the spectroelectrochemical investigation of other important electrode reactions.
1. INTRODUCTION
Considerable efforts have been made to develop SERS-active substrates on the surfaces of Pt-group metals.7 Tian and coworkers have conducted extensive research for creating SERSactive Pt and Pd substrates with roughened surface structures.6,8,9 Although this strategy was successful in introducing the SERS activity on the Pt and Pd surfaces, a wide variation in the surface features resulted in a variation of the SERS intensities. SERS-active Pt and Pd substrates can also be fabricated by the “borrowed SERS” technique, wherein the SERS-active Au or Ag surface is covered with an ultrathin layer of Pt or Pd to induce the SERS activity. Weaver and co-workers implemented the borrowed SERS techniques with Pt layers on roughened Au surfaces.10,11 Tian et al. expanded this technique to apply Pt or Pd shell on Au nanoparticles, wherein a high enhancement of SERS was observed from the SERS-active Au cores.12 Bartlett et al. have shown that the hexagonal arrays of Pt or Pd sphere segment voids, prepared by template electrodeposition, exhibited the SERS activity.7 In this work, we utilized dendritic Au rod (DAR) structures as the underlying SERS-active cores in the borrowed SERS systems for in-situ electrochemical SERS examinations. We have shown that the DAR nanostructures, prepared by a simple,
Surface-enhanced Raman scattering (SERS) has attracted increasing attention because of its applications in biological sensing, trace analysis, and electrochemistry.1,2 In particular, the combination of in-situ SERS techniques with electrochemistry is a powerful tool for spectroscopic investigation of electrochemically active species at electrode surfaces.3,4 In comparison to other in-situ spectroscopic techniques such as infrared (IR) and sum frequency generation (SFG), SERS can readily obtain the spectral information on redox species at the electrode surface in the low-frequency region (
