| dc.description.abstract | Direct methanol fuel cell (DMFC) has the advantages of higher energy conversion rate less air pollution. However, its high cost becomes a major challenge for large-scale commercialization. The development of highly effective catalyst support to reduce the amount of platinum while increasing the activity of the catalyst has become the major goal in fuel cell technology. In recent years, the attempt of treating metal oxide material as catalyst support has drawn increasing attentions. This is primary due to high inherent dimensional and electrochemical stability enhance the interaction between the metal and the support, which help stabilize metal particles with improved fuel reaction and raised proton conductivity. However, limited by the low surface area and low electronic conductivity, metal oxide material inhibits catalytic activity. Purpose of this study is to modify the metal oxide with thin layer of conducting carbon in order to circumvent this deficiency.
The first part of this research examines the activity of such surface functionalized metal oxides (titanium dioxide, silicon dioxide and zirconium dioxide). The nitrogen-graphitized metal oxide (NG-MO) were prepared by first coating a thin layer of conducting polymer (e.g. polyaniline) on ceramic metal oxides (TiO2, SiO2, and ZrO2) followed by graphitization at 900℃under N2 atmosphere. The thin layer of N-containing graphite coated on the ceramics served as electron conductor. Furthermore, it served as stable anchorage for metal nano-catalysts. Surface topography mapping showed that Pt nanoparticle with stable size of 3~4 nm was homogeneously dispersed on NG-MO compared to that on XC-72 or on the other graphite-based carbons. The current density derived from cyclo voltametry suggested that Pt/NG-MO exhibits distinctively higher methanol catalytic performance compared to those at XC-72 supports. The topology of the Pt nanoparticle on NG-MO and its methanol oxidation activity depends heavily on the type of the ceramic metal oxide with SiO2 appeared to give the best results. However, all the Pt/NG-MO system displayed lower life-time durability compared to that of commercial catalyst (E-TEK).
The second part of the research studied the polyaniline content on catalytic behavior. Three supports with polyaniline to metal oxide ratio of 1:1、1:5、1:10 are prepared. In TiO2 system, higher content of metal oxide lead to higher methanol oxidation activity; however, in SiO2 and ZrO2 system, lower content of metal oxide lead to higher methanol oxidation activity .The results showed that metal oxide may be involved in the oxidation reaction of methanol. TiO2 performed better adsorption of OH group, enhancing the methanol oxidation reaction. Better methanol oxidation reaction activity is observed with higher TiO2 . In contrast, SiO2 and ZrO2 served as dormant substrate that the MOR only increases with increasing polyaniline coating.
Finally, the third part of the study explored the effect of NG-MO support on alloy system. We compared the activity and stability of alloy metal catalyst with that on carbon support. Since the platinum-rhodium alloy system displayed the best MOR in the research, we supported the platinum-rhodium alloy on graphite metal oxides containing nitrogen in the proportions of 1:1. The results showed that platinum-rhodium alloy catalyst displayed higher catalytic activity and stability than single-platinum metal. SiO2 and TiO2 system performed better stability than the commercial catalyst (E-TEK), but ZrO2 is much worse. Further work is required to verify such difference. | en_US |