Electrochemically roughened palladium electrodes for surface-enhanced Raman spectroscopy: Methodology, mechanism, and application

Abstract

Palladium is one of the important materials in surface sciences due to its unique catalytic activities toward various reactions. To study the process occurring on the palladium surface by Raman spectroscopy, it is necessary to obtain a surface with surface-enhanced Raman scattering (SERS) activity. We reported here the preparation method for obtaining SERS-active pure massive palladium electrodes via an electrochemical roughening method by strictly controlling the roughening potential and frequency. The roughened surface consists mostly of spherical nanoparticles with a diameter of 50 similar to 60 nm. The SERS activity of the electrode was demonstrated by using pyridine as a model molecule, and it was found that the surface enhancement could be as high as 3 orders of magnitude. With such high enhancement, we were able to study processes related to molecules with small Raman cross sections, such as CO. Distinctly different from other transition metals in the VIIIB group, palladium electrode shows SERS activity clearly dependent on the wavelength of the excitation laser, with highest enhancement appearing at 632.8 nm. To understand the enhancement mechanism, a finite difference time domain method was used to simulate the optical properties of the roughened palladium surface, and it was found that electromagnetic enhancement plays an important role in the SERS of the palladium, which is in good agreement with the experimental result.