Direct Methanol Fuel Cell Gold Platinum Nano-composite Catalyst Preparation And Research

As it has many advantages, such as high energy density, cheap and rich energy resource, simple structure, easy storage and transportation of methanol, the direct methanol fuel cell(DMFC), which is one of the hottest research centers in fuel cell, can be used as mobile energy sources for electric vehicles, micro-electronic products and spacecraft.Now the main anode catalytic materials of DMFC are platinum-based materials, but during the electro-catalytic oxidation of methanol Pt easily suffers from CO poison, and the price of Pt is very high and fluctuates great, both are major obstacles of wide application of Pt as the active component of DMFC catalysts. Hen, searching for new active component materials of catalysts is becoming a key problem for the further development of DMFC. Gold has always been considered as an inert metal and its catalytic activity is far lower than Pt.Since the research team of professor Haruta found that nano-scale gold has high catalytic activity toward CO oxidation at low temperature,the investigation of Au catalysts has become more and more. As the preparation of Au catalyst has great effect on the catalytic activity, we studied the preparation of Au-based catalysts and their catalytic activity in this paper.In order to optimize the preparation technics of Au and AuPt nano-particles, we have adopted different chemical reduction method to prepare Au and AuPt colloids, the Uv-vis spectra was used to analysis the size of Au and Au-Pt nanoparticles, the results showed that nano-particles with KBH4 as reducing agent are relatively small, only about 2-3nm. We also found that the protection agent and reducing agent had a significant impact on the preparation of nano-particles. To obtain uniform and highly dispersed catalysts, protective agent and reducing agent both had appropriate proportion.Pre-processing of supports not only affects their own structures and properties, but also affects the catalytic activity of catalysts. Multi-walled carbon nanotubes and VulcanXC-72, which were functionally treated by concentrated nitric acid and thiophenol were used as supports. The carbon black treated by concentrated nitric acid had a poor load, while the carbon black chemically modified by thiophenol had a high load of Au-Pt alloy nanoparticles. TEM images showed that Au-Pt nanoparticles highly dispersed on the surface of the carbon black and had no agglomeration. The surface of carbon nanotubes is smooth, so they are difficult to load gold nano-particles, even when treated by concentrated nitric acid, but carbon nanotubes functionalized by thiophenol was able to bond gold nanoparticles strongly, which make gold nanoparticles to self-assembly onto the surface of multi-walled carbon nanotubes easily.Through TEM and XRD analysis of Au/MWCNTs, we found that gold nanoparticles had high dispersity and uniformity on the surface of carbon nanotubes, and the distance between nanoparticles is uniform, the electronic layer structure of multi-walled carbon nanotubes has been keeped and still maintained its high conductivity during the chemical treatment, which constructed a foundation for the study of the multi-walled carbon nanotubes as the support of Au and AuPt nanoparticles.During the preparation of Au-Pt binary nano-colloid, the one-step reduction method and two-step reduction method were used to prepare alloying nanoparticles and core-shell structure nanoparticles respectively. The obtained nanoparticles were loaded onto carbon supports to prepare catalysts. The cyclic voltammetry (CV) measurement shows that catalytic activity of alloying gold-platinum nanoparticles is higher. In order to improve the catalytic activity, we prepared nano-Au-Pt binary colloid through microwave liquid-phase alloying approach under high-temperature and high-pressure. The TEM and XRD analysis showed that microwave treatment of Au-Pt nano-particles didn't increase the size of nanoparticles, and improved their dispersity and uniformity on carbon supports. The CV, LSV, IT and other electrochemical tests showed that catalysts prepared through microwave treatment had higher catalytic activity and stability for methanol oxidation, and the 3AuPt/C catalyst had the highest activity.