In Situ Observation of O-Metal Vibrations at Pt and Au Electrodes By Plasmonic Crystalline-Based SERS

Abstract

For practical applications of polymer electrolyte fuel cell (PEFC), designing a high performance and low cost membrane electrode assembly (MEA) is necessary, and performance and cost of a MEA is closely related to the properties of catalysts. Improvement of cathode catalyst becomes a key, and fundamental understandings of cathode reaction mechanism has been essential.For the reaction mechanism investigation, in situ, dynamic measurement tools should be required. We have been developing a combination of surface enhanced vibrational spectroscopic techniques, such as surface enhanced Raman scattering (SERS), surface enhanced infrared absorption spectroscopy (SEIRAS) and sum frequency generation (SFG) spectroscopy. Generator-collector regime in the electrochemical microchannel device has been also investigated to realize time-resolved measurement by detecting adsorbed intermediates during electrocatalytic reaction.The recent development in nanofabrication technology affects in the field of plasmonics and various types of novel SERS-active substrates have been reported. We have already prepared the micrometer-scale inverse pyramid-type plasmonic crystalline SERS-active substrates [1-2] with flat (111)-oriented Au surfaces and strong SERS signals from self-assembled monolayers (SAMs) of thiophenol were detected[3]. Although SERS activity of the plasmonic crystalline substrate covered by Pt was not high, strong SERS signal has been reported at sphere segment void (SSV)-type plasmonic crystalline substrates covered with Pt or Pd.[4-5] By tuning the size and depth of SSVs, SERS signal from atomically thickness-controlled Pt thin film covering only the top most surfaces of Au-SSV has proved to give information about adorbates on Pt surfaces selectively. Furthermore, by remaining PS templates, only the Pt surface becomes electrochemically active and SERS intensity from Pt-rim is enhanced much higher. Electrochemical SERS measurement are also carried out in situ at Au- and Pt/Au-SSV substrates. Acknowledgement This work was supported by New Energy, Industrial Technology Development Organization (NEDO), Fuel Cell Promotion Office of the Agency of Natural Resources and Energy, Ministry of Economy, Trade and Industry (METI).