Surface-enhanced Raman Spectroscopic Study On Electrochemical Catalytic Reduction Of CO₂ Promoted By Pyridine Adsorption On Pt Electrodes

Photo/electrocatalytic reduction of CO₂ has been considered as a promising approach to solve the problem of energy conversion and storage,and to deal with the increasing carbon emissions,which put a huge burden on earth.Due to the limited understanding of the mechanism of CO₂ reduction reaction（CO₂RR）,further developments on the the catalytic efficiency,selectivity,and stability have been hindered.Thus,a deeper understanding on the mechanism of CO₂RR may greatly help us to optimize the catalysts and reaction conditions.Electrochemical surface-enhanced Raman spectroscopy（EC-SERS）,an in-situ surface/interface molecular-vibrational spectroscopic technique endowed with the ultra-high surface sensitivity and energy resolution,is capable to detect the adsorbed and reactive molecules in the region of the electrode-electrolyte interface,and to trace and analyze the active reaction intermediates,thus is essential to investigate the mechanism of CO₂RR process.In this thesis,Au@Pt nanoparticle-assembled working electrode with a high SERS activity was applied to study the mechanism of Pt/pyridine catalytic CO₂RR process.Borrowing the strong SERS enhancement from the plasmonic Au core,we acquired rich spectroscopic information for the pyridine and α-pyridyl species,which is a newly discovered adsorbate on the Pt surface in electrochemical environments.Through detailed analyzing of the potential-dependent intensity and the frequency of correlative peaks,we constructed a model which reveals the co-adsorption behavior of pyridine,α-pyridyl,hydrogen atoms and water molecules in the interface of the Pt electrode-pyridine containing solution.By comparing the Raman spectrum in the Ar deaearted with that in the CO₂ saturated solution,strongly adsorbed CO at the Pt surface was detected.The isotope experiment confirmed that the adsorbed CO,derived from CO₂RR,could not be further reduced and is a blocker of the reaction site for CO₂ reduction.In addition to this,we observed the mutual relationship between pyridine,a-pyridyl and CO,that is,CO hampered the adsorption of pyridine and α-pyridyl,meanwhile the adsorption of pyridine and α-pyridyl delayed the generation and adsorption potential of CO.Based on all of these results,the mechanisms of pyridine catalytic reduction of CO₂ electroreduction reported in literature were discussed and our conclusions were given.