Synthesis and Electrocatalytic Performance of Cu@Pt/MWCNTs-MnO2 Electrocatalyst

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@PUMWCNTs 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 degrees C, pH = 10), and then Pt atoms were deposited on the surface of Cu nanoparticles (90 degrees C, pH = 7 similar to 8). alpha-MnO2 and beta-MnO2 were prepared by hydrothermal method with KMnO4 and Mn(NO3)(2) as the manganese source, the reaction time of alpha-MnO2 and beta-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 similar to 8 nm. The crystal morphology of MnO2 is alpha-MnO2 and beta-MnO2. It was also found that the Cu@Pt/MWCNTs-beta-MnO2 composite catalysts have better catalytic performance and higher electrochemical activity surface (up to 71.1 m(2).g(-1)). The RRDE results for the ORR indicate that, the main reaction of Cu@Pt/MWCNTs-beta-MnO2 catalyst is the direct reduction of O-2 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.