Nanostructured Carbons As Supports For Direct-methanol Fuel Cell Catalysts

Developing novel catalyst support is an efficient approach to improve the performance of direct methanol fuel cell (DMFC) catalyst and to promote the commercialization of DMFCs. In the present study, one-dimensional nanostructured carbons such as carbon nanotubes (CNTs) and carbon nanofibers (CNFs) were used as catalyst supports, and their nanostructure was tailored to improve the performance of DMFC catalysts.The synthesis of cathode Pt/C and anode PtRu/C catalysts by polyol reduction was studied firstly. Using Vulcan carbon black as the support, Pt nanoparticles with different size distributions were prepared. An abnormal particle size effect of Pt on the electroactive surface area was observed. The influences of reaction temperature on the composition distribution, structure and activities of ployl-synthesized PtRu/C catalysts were further studied.Bamboo-shaped CNTs (BCNTs), with a large amount of pentagon defects introduced in the walls, were explored as the support of DMFC catalysts for the first time. It was found that the pentagon defects could produce more oxygen-containing functional groups and show stronger interaction with metal particles. Highly dispersed Pt nanoparticles were facilely supported on BCNTs and showed improved performance at 30℃using as the DMFC cathode catalyst. PtRu/BCNT anode catalyst with a high metal loading (60 wt%) was further synthesized and significantly enhanced the DMFC performance. The different influences of the surface oxygen-containing functional groups on the performance of DMFC anode and cathode catalyst were discussed.Nitrogen-doped CNTs (N_xCNTs) with different nitrogen content were synthesized by chemical vapor deposition. The influence of nitrogen-doping on the structure of N_xCNTs was studied. PtRu/ N_xCNTs catalysts were synthesized by polyol reduction. It was found that, a low content of nitrogen (ca. 1 at.%) could promote a well dispersion of PtRu nanoparticles and thus improved the DMFC anode performance; while a higher content of nitrogen (ca. 8 at.%) decreased the electron conductivity and therefore lowered the DMFC anode performance. The cathode Pt catalysts supported on N_xCNTs did not show enhanced catalytic activity, and a high content of nitrogen significantly lowered the DMFC cathode performance.The CNFs after thermal treatment were explored as the support for Pt catalysts, and the influence of surface reconstruction of CNFs on the performance was investigated. After being thermal treated at 900℃, the graphite edges on CNFs were reconstructured into single-walled nano-loops, which induced a enhanced surface diffusion of oxygen and thus improved the catalytic performance on oxygen reduction in cyclic voltammetry tests. For graphitized CNFs (GCNFs), the electron conductivity could be improved greatly, and the surface graphite edges were reconstructured into multi-walled nano-loops that could maintain the well dispersion of Pt catalysts. Therefore, the Pt/GCNF catalyst showed much improved DMFC cathode performance.