Preparation and anode property of Pt-CeO_2 electrodes supportec on carbon black for direct methanol fuel cell applications

摘要

A platinum (Pt) on pure ceria (CeO_2) supported by carbon black (CB) anode was synthesized using a combined process of precipitation and coimpregnation methods. The electrochemical activity of methanol oxidation reaction on synthesized Pt-CeO_2/CB anodes was investigated by cyclic voltammetry and chronoamperometry experimentation. To improve the anode property on Pt-CeO_2/CB, the influence of particle morphology and particle size on anode properties was examined. The morphology and particle size of the pure CeO_2 particles could be controlled by changing the preparation conditions. The anode properties (i.e., peak current density and onset potential for methanol oxidation) were improved by using nanosize CeO_2 particles. This indicates that a larger surface area and higher activity on the surface of CeO_2 improve the anode properties. The influence of particle morphology of CeO_2 on anode properties was not very large. The onset potential for methanol oxidation reaction on Pt-CeO_2/CB, which consisted of CeO_2 with a high surface area, was shifted to a lower potential compared with that on the anodes, which consisted of CeO_2 with a low surface area. The onset potential on Pt-CeO_2/CB at 60 deg C became similar to that on the commercially available Pt-Ru/carbon anode. We suggest that the rate-determining steps of the methanol oxidation reaction on Pt-CeO_2/CB and commercially available Pt-Ru/carbon anodes are different, which accounts for the difference in performance. In the reaction mechanism on Pt-CeO_2/CB, we conclude that the released oxygen species from the surface of CeO_2 particles contribute to oxidation of adsorbed CO species on the Pt surface. This suggests that the anode performance of the Pt-CeO_2/CB anode would lead to improvements in the operation of direct methanol fuel cells at 80 deg C by the enhancement of diffusion of oxygen species created from the surface of nanosized CeO_2 particles. Therefore, we conclude that fabrication of nanosized CeO_2 with a high surface area is a key factor for development of a high-quality Pt-CeO_2/CB anode in direct methanol fuel cells.