Preparation and Characterization of Tungsten Hexachloride Derived Pt-WO3/C Electrocatalysts for Methanol Oxidation Reaction

• Main Authors: Chih-Chung Wang, 王志仲
• Other Authors: Cheng-Lan Lin
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/33273502104910146517

碩士 === 淡江大學 === 化學工程與材料工程學系碩士班 === 100 === The major goals of this research are the preparation and characterization of Pt-WO3/C electrocatalysts for the methanol oxidation reaction (MOR) at the anode of a direct methanol fuel cell (DMFC). Pt-based electrocatalysts were generally employed as the anode electrocatalysts for DMFCs. However, the surface of Pt could be easily occupied by intermediates generated during MOR (especially CO), which are difficult to be removed and leading to a rapid decrease in the DMFC performance. Such phenomenon is known as “CO-poisoning” phenomenon. In this study, WO3 nanoparticles were synthesized and added to conventional Pt/C to give Pt-WO3/C electrocatalysts in order to enhance the MOR efficiencies as well as the CO-tolerance abilities. The Pt-WO3/C electrocatalysts were prepared by two-step procedure. N,N-Dimethyl-formamide (DMF) solution of tungsten hexachloride (WCl6) was used as the precursor, and the WO3/C nanocomposites were firstly synthesized. Then, Pt nanoparticles were decorated onto the WO3/C nanocomposites by polyol method using ethylene glycol (EG) as both the reducing agent and solvent to obtain the Pt-WO3/C electrocatalysts. X-ray diffractometer (XRD)、transmission electron microscope (TEM)、scanning electron microscope (SEM)、fourier transform infrared spectroscopy (FT-IR) and energy dispersive X-ray spectrometer (EDS) were used to investigate the surface morphologies and compositions of the electrocatalysts. The MOR efficiency, electrochemical active surface area (EASA), CO stripping and MOR stability of the electrocatalysts were evaluated by cyclic voltammetry (CV) and chronoamperometry (CA) experiments. For the PtW(0.06 ~ 0.14)/C450 series electrocatalysts using pristine Vulcan XC-72 carbon black as the support and calcined at 450 oC, the WO3 nanoparticle aggregates with sizes of 50 ~ 200 nm were obtained, and their MOR efficiencies were all lower then the commercial E-TEK Pt/C electrocatalyst. The MOR efficiencies were sighificantly improved for the PtW(0.06 ~ 0.14)/Cs450 series electrocatalysts using NaOH-pretreated Vulcan XC-72 carbon black as the support, however the aggregates of WO3 nanoparticles were still observed. In order to avoid the aggregation of WO3 nanoparticles, the PtW(0.06 ~ 0.14)/Cs200 series electrocatalyst were synthesized using NaOH-pretreated Vulcan XC-72 carbon black and calcined at 200 oC. Evenly distributed amorphous WO3 nanoparticles on carbon support were obtained and confirmed by XRD and TEM investigates. The MOR efficiencies as well as the CO-tolerance abilities of these electrocatalysts were all higher than the commercial E-TEK Pt/C electrocatalyst. The PtW(0.08)/Cs200 electrocatalyst achieved the highest MOR efficiency of 873 ± 96 A/g-Pt among all the electrocatalysts prepared in this study, and which was about 2.2 times higher than that of the commercial E-TEK Pt/C electrocatalyst (389 ± 56 A/g-Pt).