Preparation Of Platinum Catalysts Supported On Modified Nanocarbon Materials And Their Performances For Methanol Electrocatalytic Oxidation

Direct methanol fuel cells(DMFC) have attracted more and more attention due to the characteristics of high power density, low working temperature, fast start and so on. In recent years,nano-carbon materials including carbon nanotubes(CNTs) and graphene(G) have been widely used as supports of Pt-based catalysts to boost the catalytic performance for methanol electrocatalytic oxidation. In this thesis, in order to improve the activity of Pt-based catalyst and promote the oxidation of CO, the nonmetal-doped CNTs and G were prepared and used as Pt-based catalyst support; FeP and FeB were also introduced to further modify nitrogen-doped CNTs supported Pt catalyst. Their catalytic performances for methanol electrocatalytic oxidation were studied comparatively. The aim of this thesis is to promote the utilization of Pt catalyst and improve the activity of methanol electrocatalytic oxidation through the modification of Pt/CNT and Pt/G catalysts. This study has provided the experimental basis and reference for the development of DMFC anode Pt-based catalyst. The main contents and conclusions of this thesis are follows:(1) N-doped carbon nanotubes(NCNTs), P and N co-doped carbon nanotubes(PNCNTs) and N-doped graphene(NG) were prepared and used support to prepare a series of Pt-based catalysts. The results showed that the doping of N significantly enhanced the interaction between Pt and support, promoted the dispersion of Pt particles and decreased the size of Pt particles. For Pt/NCNTs catalyst with 13.64% Pt, the average size of Pt nanoparticles was calculated to be 2.56, while it was 3.11 nm for Pt/CNTs. The electrochemical measurement showed that Pt/NCNTs exhibited excellent electrocatalytic activity to methanol with mass-specific current density of 935 A/gPt, which was 1.58 times that of Pt/CNTs. As to graphene, Pt/NG-NH3 prepared by NH3 as nitrogen source showed better performance for methanol oxidation. Compared Pt/NG-NH3 with Pt/G, the average size of Pt nanoparticles decreased to 2.04 nm from 3.11 nm and the mass-specific activity increased to 889 A/gPt, from 638 A/gPt. The appropriate amount of phosphorus doping into NCNTs could further reduce average size of Pt particles, enhanced the electro-conductivity and methanol oxidation activity of Pt catalyst. However, the doping with excessive phosphorus atoms changed morphology of carbon nanotube and lowered the electrical conductivity of catalyst, which led to the lower catalytic activity. Among Pt/PNCNTs-x, Pt/PNCNTs-5% catalyst has small Pt nanoparticles size of 2.32 nm and the best activity to methanol oxidation of 1300 A/gPt.(2) FeP and Fe B were introduced to further modify NCNTs, a series of Pt/FeP/CNTs and Pt/FeB/NCNTs catalysts were prepared. The loadings of FeP and Fe B have been optimized and the structure and electrochemical activity of modified catalysts have been investigated. According to results of TEM, XRD and XPS, the modification of FeP and FeB onto NCNTs facilitated the dispersion of Pt nanoparticles, decreased the average size of Pt nanoparticles and enhanced the interaction between Pt and support significantly. Among all these catalysts, Pt/15%FeP/CNTs and Pt/15%Fe B/NCNTs catalyst with smaller Pt particles sizes of 1.56 and 1.58 nm exhibited excellent catalytic activity towards the methanol oxidation of 1737 and 1640 A/gPt, while for Pt/NCNTs, the average size and activity were 2.56 nm and 935 A/gPt, respectively. Moreover, electrochemical impedance spectroscopy(EIS) showed a reduced charge transfer resistance, thereby promoting the catalytic activity of Pt/Fe B/NCNTs during methanol electro-oxidation.