Promotion effects of CeO2 with different morphologies to Pt catalyst toward methanol electrooxidation reaction

In the present work, CeO2 nanocrystals with three well-defined morphologies including nanooctahedra, nanosphere and nanocube are synthesized and used as the promoter to Pt catalyst toward methanol electrooxidation reaction (MOR). The promotion effects of the CeO2 nanocrystals are investigated through electrochemical techniques including cyclic voltammetry (CV), linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA). Results indicate that the promotion effects are closely related to the nanostructure of CeO2 nanocrystals. Among the Pt-CeO2/C catalysts, Pt-CeO2/C-S catalyst with CeO2 nanosphere as the promoter shows the highest catalytic performance for MOR, which arises from both physical interaction and electronic effects between CeO2 and Pt. The loosened nanosphere structure with rough surface allows the Pt nanoparticles (NPs) to highly disperse onto the surface and thereby produce a strong physical interaction between Pt and CeO2. In addition, the change in the valence state from Ce4+ to Ce3+ generates abundant oxygen vacancies (VO) into the crystal lattice, and the increased vacancies lead to surplus electrons which would transfer from CeO2 to Pt. The increased electron density lowers the d-band center and thus improves the intrinsic activities (IA) of Pt. These data are used to discuss the role of physical interaction and electronic effects between the promoter and Pt and would be promising in designing the nanostructure of the Pt-based catalysts for DMFCs and other applications.