The Research And Application Of Anode Single-Walled Carbon Nanotubes Loaded Pt-Ru Catalyst For Direct Methanol Fuel Cell

Fuel cells are considered as a 21st century power system due to their low pollution and high efficiency. Recently, the direct methanol fuel cell (DMFC) becomes the research project of general interest because methanol is a kind of rich, cheap liquid fuel and is easy to be stored and transported. At present, one of the main problems that restrict DMFC's use is "methanol crossover" and the other is the low electrocatalytic activity of the anode catalyst at normal temperature. Higher electrocatalytic activity of the anode catalyst can make methanol react qiuckly and reduce the concentration at the interface between anode and PEM to lessen the methanol crossover. In this thesis, the liquid phase reduction method were used to prepare the nano particles of PtRu loaded on single-walled carbon tubes(SWCNTs). Using the XRD and TEM techniqiues, the size and the specific surface were studied. The electrocatalytic activities for methanol oxidation were evaluated with the electrochemical techniques. The main work and results abtained are as follows:(1) SWCNTs were purified and opened by oxidation method with HNO3, the influences of temperature ,concentration of nitric acid and time on the reaction were studied. The optimized condition were obtained: concentration of nitric acid was 4mol/L, temperature was 103℃, time of reaction was 16h.(2) Using liqued phase reduction method with formaldehyde as reductant and SWCNTs as support, prepare the PtRu/SWCNTs catalyst with 20wt% Pt and 10% Ru. The influences of reaction condition were studied and abtained the relatively feasible preparation technics: purified and activated SWCNTS, appropriate concentration of H₂PtCl₆- RUCl₃, lower temperature of reaction. They are better than the PtRu particles supported by activated carbon. For the PtRu/SWCNTs catalyst, the diameter of PtRu particles is 3.8nm.(3) The cyclic voltammetry was carried out to examine the electrochemical performance and stability of PtRu/SWCNTs. With increasing of the operating temperature, the oxidation peak current of methanol increased as well as the oxidation peak potential for the complete oxidation. The lower oxidation peak potential indicates that the PtRu/SWCNTS catalyst makes the methanol oxidated more easily than theJohnson-Matthey PtRu/C catalyst dose. At lower operation temperature, the PtRu/SWCNTs catalyst has the lower oxidation peak current than Johnson-Matthey PtRu/C catalyst. As the operation temperature raised higher than 70°C, the oxidation peak current of PtRu/SWCNTs catalyst is higher than tne industrializd PtRu/C catalyst. The electrocatalytic activity of PtRu/SWCNTs catalyst is slightly better than that of Johnson-Matthey PtRu/C catalyst.(4) Membrane Electrode Assembly(MEA) was prepared with PtRu/SWCNTs catalyst and was made use of set up a single liquid feed DMFC. The performance of the cell was studied by changing the Pt, Nafion and PTFE loadings in methanol anode catalyzed layer. The optimum Pt loading was 0.6mgPt/cm2, the optimum Nafion loading was 7%, the optimum PTFE loading was 5 %. The open cricuit voltage of the single cell was about 0.6V and it sustain a load current density of 24mA/cm2 with an output voltage of 0.4V and 72mA/cm2 with an output voltage of 0.2V at 80 °C with 2.5mol/L liquid methanol and air-fed cathode at near-ambient pressure with a low anode and cathode catatyst loading of 0.6mgPt/cm2 of Pt.