رزگار احمدی

The development of catalysts to promote methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR) is a key to the development and commercialization of direct methanol fuel cells (DMFCs), which have attracted much attention as green power sources for automobiles and portable electronics. Pure Pt is not suitable as a catalyst in DMFCs due to rapid poisoning and its high cost. Therefore, much effort has been devoted to decrease the amount of Pt catalyst used in fuel cells by synthesizing supported Pt nanoparticles on new carbon supports and developing Pt alloys to increase utilization efficiency of the noble metal catalyst and to enhance its tolerance against adsorbed CO-like intermediates. In this regard, particular interest has been devoted to alloying Pt with the non precious metals with the aim of increasing Pt resistance to poisoning as well as facilitating the commercialization of DMFCs. The stability of Pt alloys in the acidic and electrochemical environment of DMFCs highly depends on the degree of alloying. Generally, high degree of alloying can be achieved by annealing at high temperatures. However, high temperature treatment results in undesired particle size increase and broad particle size distribution, which in turn, results in a significant reduction in the electrochemical active surface area, and, consequently, in the catalytic activity of the catalysts. We have developed a simple route for preparation of sulfur-modified CNTs as a precursor for the successful synthesis of catalysts based on Pt (Pt/CNT) and Pt-Co alloys (Pt-Co/CNT) with highly dispersed nanoparticles having narrow size distribution. The modification is based on sulfur impregnation of CNTs followed by a melt-coat step. We have shown that when these catalysts are synthesized on sulfur-modified carbon nanotube support, no sintering of the nanoparticles occurs upon high temperature annealing at 800 ˚C, and the particle sizes remain around 3 nm and the particles are highly disperse