Multi-wall carbon nanotube supported Pt-Sn nanoparticles as an anode catalyst for the direct ethanol fuel cell

摘要

Direct alcohol fuel cells (DAFCs) have attracted much attention recently as potential mobile power sources [1]. Fuel cells based on direct ethanol conversion (DEFCs) offer advantages over those based on methanol (DMFCs), because they are safer, more convenient to use, easier to produce, and yield a higher energy density (8.01 vs. 6.09kW/kg) [1]. However, the low reaction kinetics of ethanol oxidation reaction is still challenging research. The complete ethanol electro-oxidation involves the release of 12 electrons per molecule and the cleavage of the C-C bond. The latter is believed to play a key role in the ethanol electro-oxidation and determine the fuel efficiency and electrical energy yield efficiency. Besides, the CO-like intermediates formed during ethanol dissociative adsorption also need an oxidative removal. Therefore, the ethanol electro-oxidation was considered more complicated than that of methanol, and consequently needs more active and selective catalysts. Our previous work showed an 86 percent enhancement in power density of DEFC when employing PtSn/XC-72 as anode catalyst instead of PtRu/XC-72 via a modified polyol method [2-4]. Many novel carbon supports are known to promote high electrocatalyst activities [5-7]. For instance, a 12 wt. percent Pt/carbon nanotube electrode gave 10 percent higher voltages than a 29 wt. percent Pt/carbon black electrode, implying 60 percent lower Pt usage in a PEMFC [8]. Multi-wall carbon nanotubes (MWNTs) performed better in DMFC cathodes than a carbon black (XC-72) both during catalyst preparation and cell performance tests [3,4]. In this study we report the preparation of highly dispersed PtSn/MWNTs catalyst and its use as anode catalysts for DEFCs. The MWNTs used in this work were produced from high purity graphite by the classical arc-discharge method. The MWNTs with hollow tubular structure and highly graphitic multi-layer walls were mostly from 4 to 60 nm in diameter and were purified and surface oxidized following a procedure described in Ref. [4]. The PtSn/MWNTs catalyst with a metal loading of 20wt percent was prepared according to Ref. [3]. For comparison, commercial XC-72 carbon (Vulcan XC-72, Johnson Matthey, S_(BET) = 267 m~2/g) was also used as the support to prepare PtSn/XC-72 catalyst with the same metal loading by the same procedure.