In-situ SERS Study Of C₁ Organic Molecules Electro-catalytic Oxidation On Au_core@Pt_shell Nanoparticles

The electrocatalytic oxidation of small organic molecules has attracted great interest due to their prospect being used as fules for the anodic reaction of fule cells. Because of its great significance to both the practical application and fundamental researches, the extensive investigation of the electrocatalytic oxidation of small organic molecules on transitional metal is very necessary.The investigation of the electrocatalytic oxidation of small organic molecules on transitional metal has in this field have been carried out and great progress has been made in the past four dacads. However, due to the complexity of the system during the reaction process, especially, the limitation of the detection techniques, at least at present, the detailed mechanism on the reaction process is still in controversy. Among the various techniques in investigating the adsorption and reaction behavior of small organic molecules, infrared (IR) spectroscopy is the most widely used in-situ spectroscopic method, and has made tremendous contributions to provide a better understanding of this field. But the most widely used systems in IR, are easy to interfere by the solvent such as water, and are too severe to extract the signal of the solid/aqueous interface. On the other hand, SERS can provide a wider spectral window, which is quite convenient to obtain the vibrational information reflecting the interaction of the adsorbates and the substrates located under 600 cm-1. However, in the past two decades, the application of SERS was mainly restricted to Ag, Au and Cu surfaces which provide giant surface enhancement because the SERS activity of the transitional metal with high catalitic such as Pt and Pd are low. Athough in recent years has its application been extended to transition metals by using electrochemical roughing methode in our research group, it is still not effective in investigating electrocatalytic reaction. On the purpose of extending SERS to the study of the adsorption and reaction of C₁ molecules on Pt surface effectively, and improving the electrocatalytic activity of anodic catalyst through fabricating nanoparticles with unique structure .Three parts of work have been performed, and the main results a of which are listed as follows:(1) Au_core@Pt_shell nanoparticles with controllable Platinum shell thickness were synthesized by chemical reduction method. The samples were characterized by scanning electron microscopy(SEM),Cyclic voltammetry (CV) and surface enhanced Raman spectroscope(SERS). Results showed that the Au_core@Pt_shell nanoparticles with compact surface are uniform, exhibit good SERS activity and the electrochemial behavor is similar to traditional bulk Pt electrode with polymorphic crystal Structure.(2) In-situ SERS combined with CV was utilized to investigate the electrocatalytic oxidation behaviors of Methanol,Formaldehyde and formic acid adsorbed on Au_core@Pt_shell nanoparticles. Surface-enhanced Raman scattering spectra with high quality was acquired. Results showed that the Methanol and Formaldehyde could dissociate spontaneously to produce strongly adsorbed intermediate, CO, in acidic, neutral, and alkaline media on Au_core@Pt_shell nanoparticles. Au_core@Pt_shell nanoparticles exhibited better electro-catalytic properties for the oxidation of formaldehyde in alkaline media than in acidic or neutral media. A peak of HCOO, the weakly adsorbed intermediate of the dissociative adsorption of formic acid were successfully obtained for the first time. At the same time, the peak of the finally oxidized product CO₂ of formic acid was also detected. The dual path reaction mechanism for the oxidation of formic acid was confirmed at molecular level.(3) Transitional metal hollow nanospheres were synthesized using selenium nanoparticles as template. The samples were characterized by SEM,TEM,SAED,etc. The SERS activity of Au hollow nanospheres was measured by using Pyridine and SCN- as the probe molecule, the surface enhancement factor of Pyridine from gold hollow nanospheres reaches as high as 7.6×10⁴ . The electrocatalytic activity of Platinum hollow nanospheres was measured by using methanol as the probe molecule. The results showed that the onset potential of methanol electrocatalytic oxidation on Platinum hollow nanospheres is negatively shifted about 200 mV than Platinum nanospheres and Platinumblack, the peak current density of methanol electrocatalytic oxidation on Platinum hollow nanospheres is 2³ times as large as Platinum nanospheres and Platinumblack. It also reveals good stability of electrocatalytic oxidation after CV scanning for a long time.