Highly efficient electrode catalysts prepared with ordered nanoporous carbons with tunable pore sizes as catalyst suppor
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Highly efficient electrode catalysts prepared with ordered nanoporous carbons with tunable pore sizes as catalyst supports Geun Seok Chai and Jong-Sung Yu* Department of Chemistry, Hannam University, Daejeon, 306-791, Republic of Korea (+82) 42-629-7446, Fax: (+82) 42-629-7469, E-mail:[email protected] ABSTRACT Ordered uniform nanoporous carbons with pore sizes in the range of 10 – 600 nm were synthesized against removable colloidal crystalline templates by carbonization of phenol and formaldehyde as a carbon precursor. The porous carbons have high surface areas, large pore volumes, and three-dimensionally interconnected uniform pore structures, and thus were used as a support of a Pt(50)-Ru(50) alloy catalyst to study their effect on the anodic performance of the catalyst in direct methanol fuel cell. The use of the ordered uniform porous carbon allowed higher degree of dispersion of the catalysts and efficient diffusion of reagents, resulting in much improved catalytic activity for methanol oxidation in the fuel cell. In general, the smaller pore sizes the porous carbons have, the higher surface areas and the better catalytic activity for methanol oxidation they showed. INTRODUCTION Direct methanol fuel cell (DMFC) has recently attracted great attention for its future potential as a clean and ideal power source. To increase the catalytic activity of methanol electro-oxidation, intense studies have been devoted mainly towards the development of new metal catalysts [1]. These catalysts are generally dispersed as small particles on conductive carbon supports with high surface area in order to give the high dispersion of the catalysts [2]. Recently, in addition to the development of catalysts themselves, there also arises a great attention for new carbon materials as supports as well in order to help achieve optimum catalytic performance. High surface area and well-developed porosity are essential for a catalyst support to result in high catalytic activities. Carbon black, called Vulcan XC-72, has been commonly used as a carbon support for electrode catalysts in DMFCs [3]. Vulcan XC-72 carbon consists of aggregation of amorphous carbon nanoparticles with size in the range of 30 ~ 60 nm. In fact, commercially available E-TEK catalysts are Pt-Ru alloys supported on the Vulcan XC-72. Several different carbon materials such as mesostructured carbon materials [4],
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graphitic carbon nanofiber [5] and mesocarbon micro-bead (MCMB) [6] were also reported as supports of Pt or Pt alloy catalysts mainly for higher dispersion of the catalysts and for improved synergic effects. Recently, a remarkable progress has been made in the synthesis of carbons with periodic porous structures using templates, such as ordered mesoporous silica [7] and silica colloidal crystals [8] for the synthesis of ordered mesoporous (2-50 nm) and macroporous (>50 nm) carbons, respectively. Recently, the fabrication of new uniform porous carbons with spherical cavities of 50-70 nm through colloidal crystalline templates in diameter interc
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