关键词: 质子交换膜燃料电池, 核壳型, 二氧化锰, 电催化剂, 电化学活性面积

The core-shell structure catalysts with reduced Pt loading and improved catalytic activity which are inter-metallic Pt electrocatalyst with a cheap transition metal core have become a critical issue in fuel cells. In this study, Cu@Pt/MWCNTs core-shell electrocatalyst was prepared through the impregnation chemical reduction method, by using ethylene glycol as the reducing agent, H₂PtCl₆ as a precursor of Pt and CuSO₄ as a precursor of Cu. At the appropriate temperature and pH (adjusted by KOH/EG solution), Cu nanoparticles were reduced on the surface of MWCNTs (140 ℃, pH＝10), and then Pt atoms were deposited on the surface of Cu nanoparticles (90 ℃, pH＝7～8). α-MnO₂ and β-MnO₂ were prepared by hydrothermal method with KMnO₄ and Mn(NO₃)₂ as the manganese source, the reaction time of α-MnO₂ and β-MnO₂ is 8 h and 72 h, respectively. The obtained manganese dioxide was doped onto Cu@Pt/MWCNT under ultrasound to make Cu@Pt/MWCNTs-MnO₂ composite catalysts. The structure and morphology of Cu@Pt/MWCNTs and MnO₂ were characterized by XRD, SEM and TEM, electrochemical performances were investigated by cyclic voltammetry, cathodic polarization and other electrochemical methods. In order to discuss the oxygen reduction method of Cu@Pt/MWCNTs-MnO₂, RRDE (rotating ring-disk electrode) was further used to examine the catalytic oxygen reduction reactions of Cu@Pt/MWCNTs-MnO₂. Our results demonstrated that the Cu@Pt nanoparticles have the core-shell structure. The diameter of the nanoparticles is about 6～8 nm. The crystal morphology of MnO₂ is α-MnO₂ and β-MnO₂. It was also found that the Cu@Pt/MWCNTs-β-MnO₂ composite catalysts have better catalytic performance and higher electrochemical activity surface (up to 71.1 m²·g^-1). The RRDE results for the ORR indicate that, the main reaction of Cu@Pt/MWCNTs-β-MnO₂ catalyst is the direct reduction of O₂ to H₂O which is same as the mechanism of Cu@Pt/MWCNTs catalyst, both with a four-electron charge transfer. Moreover, the mechanism of MnO₂-promoting effects for the oxygen reduction was also discussed in this paper.

Key words: PEMFC core-shell, manganese dioxide, electrocatalyst, oxygen reduction, electrochemical active surface