Study On Microstructure Characterization And Electrocatalytic Activities Of Pt-Sn/MWCNTs

Carbon nanotubes become an expected candidate of the catalyst carrier in Direct Methanol Fuel Cell(DMFC) in recent years owe to their excellent conductivity, high specific surface area and good thermal stability and so on. The common catalyst for DMFC is platinum, Pt, which is easily poisoned with carbon monoxide generated in the oxidation process of Methanol. In order to solve this problem, other metals are added to improve the catalytic activity and further reduce the usage amount of Pt. Sn has been widely concerned because its cost is low and Pt-Sn binary catalyst can improve the catalytic activity. At present, the best atomic ratio of binary catalyst is the focus of inner depth research.In this paper we chose Sn as the second metal and used Multi-walled carbon nanotubes(MWCNTs) as the vector, to study the catalytic activities of Pt-Sn/MWCNTs catalysts with different atomic ratios and confirm the optimum atom ratio of Pt-Sn/MWCNTs with the best catalytic activity. Also we explore the internal relationship of the catalytic activity and microstructure. Eight kinds of PtSn with different atomic ratios were on the MWNTs by the impregnation reduction method to form Pt-Sn/MWCNTs catalysts. Field Emission Scanning Electron Microscope(FESEM), X-ray Diffraction(XRD), Energy Dispersive Spectrometer(EDS) spectrum were used to reveal the structures and morphology of the catalysts of different atom ratios, Cyclic voltammetry and AC impedance electrochemical were used to test the electrocatalytic properties of the eight samples. The relation between the catalytic activity and the atomic ratio of PtSn was confirmed by studying the effect of atomic ratios of catalysts on the electrocatalytic performance of methanol.The following results were obtained:(1)The complex catalyst Pt-Sn/MWCNTs was prepared by impregnation reduction method, in which the metal particle size was about 3.5-6.5nm and it was in the range of the best particle size.(2)XRD and EDS results showed that A highly dispersed fabric with PtSn alloy and SnO2 on MWCNTs could be seen. Pt-Sn alloy could reduce the adsorption capacity of CO, and SnO2 could provide OHads in low electric potential, both could effectively inhibit CO poisoning of the catalyst, and improve its activity for methanol oxidation.(3)Cyclic voltammetry and AC impedance reflected that when the atomic ratio of Pt&Sn was 3:1, the Pt-Sn/MWCNTs catalyst performed the best electrochemical activity.That is to say, when the atomic ratio of Pt/Sn was in the 2.5:1 (Pt:Sn)～3.5:1 (Pt:Sn) range, the particle size was optimal size, charge resistance of the catalyst was minimum, and the spread speed of the active substance was maximum, which led to the best catalytic activity relative to the state.