Observing CO Electrooxidation And ORR Reaction Process At Pt(hkl) Surfaces By In Situ Raman Spectroscopy

As the most promising new energy source,fuel cells have received widespread attention.In the research of fuel cells,the oxygen reduction reaction(ORR)at the cathode and the electro-oxidation process of the small organic molecules on the anode are the most important reactions.The slow kinetics is one of the main bottlenecks for the development of fuel cells.At the same time,CO as a toxic intermediate of the anode Pt catalyst severely hinders the development of fuel cells.After years of research,people have a deeper understanding of these two basic reactions.However,However,the complexity of the substrate catalyst structure and the complexity of the electrocatalytic reaction process together lead to the unknown structure-activity relationship.Single crystal system with atomic level flat and clear structure as a bridge between theory and experiment is of great significance in the study of structure-activity relationship.However,direct spectral evidence of intermediate species has not been available on the electrode surfaces of defined structures for many years,and the exact reaction process of these two basic reactions has not been determined.In this paper,shell-isolated nanoparticle enhanced Raman spectroscopy(SHINERS)technology will be used to further explore the ORR and CO electrooxidation process on Pt(hkl)surface and high index Pt(hkl)surface.The detailed analysis of the adsorption configuration of the surface adsorbent and even the active intermediate and its interaction with the surface of the single crystal were given.Finally,we further combined theoretical calculations and experimental results to explain the reaction mechanism at the molecular level which are important for the research and design of actual electrocatalysts significance.1.According to the analysis of electrochemical studies,the Pt(21 1)single crystal surface of the[011]crystal band has the highest ORR catalytic activity while not the Pt(311)crystal plane with the highest step density.Thus,we used in situ SHINERS method to monitor the ORR process on the surface of Pt(111),Pt(211)and Pt(311)single crystals,and obtained direct spectral evidence of the OOH*species on the three crystal planes.Based on the relative intensity of the Raman peak,the difference in the binding energy of OOH*on the crystal plane was obtained.The DFT theoretical calculations confirmed that the binding energy of OOH*on the surface of Pt(311)was higher than that of Pt(211),which resulting in the OOH*adsorbed on the surface of Pt(211)is easier to migrate and this is also the reason that the ORR activity of Pt(211)is higher than Pt(311).2.Using Cu underpotential deposition method,Pd/Au(111)and Pt/Au(111)hetero single crystal interfaces were constructed,and the ORR on these heterogeneous single crystals was explored using SHINERS spectroscopy.The gold substrate can change the electronic structure of surface atoms which resulted in the ORR reaction process on the surface of e heterogeneous single crystals is different from that of pure Pt and Pd surfaces.On the surface of heterogeneous single crystals,OOH*species were observed on Pt/Au(111)while OOH*and OH*species were observed on Pd/Au(111).It shows that OOH*is unstable on the surface of 1 ML Pd/Au(111)and is more easily decomposed into OH*.The adsorption of OH*hinders the ORR reaction and affects its reactivity.3.In situ studies of CO electro-oxidation of basic Pt(hkl)and high-index crystal planes using SHINERS spectroscopy under acidic conditions were conducted,and direct spectral evidence of OH*and COOH*species co-adsorbed with CO was found on the basic Pt(hkl)crystal plane.Based these experimental results and DFT calculations,we proposed a reasonable reaction process.Then,a variety of CO adsorption configurations were found on the terrace and step positions of the high-index crystal plane.Under alkaline conditions,as the oxidation progressed,the CO molecules were observed to migrate and rearranged,which proved that the "reaction pair"mechanism and the Eley-Rideal mechanism co-existed in the process of CO electrooxidation.