Dispersing Effects of Poly (Vinyl Pyrrolidone) Addition on Platinum/Tin Hydrogen Phosphate-Carbon Black Bifunctional Catalysts for Direct Methanol Fuel Cells

• Main Authors: Chun-Yuan Huang, 黃俊淵
• Other Authors: Shiow-Kang Yen
• Format: Others
• Language: en_US
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/yhv2b4

碩士 === 國立中興大學 === 材料科學與工程學系所 === 106 === Direct methanol fuel cells (DMFC) are electrochemical conversion devices which can produce electricity at high fuel efficiencies, where platinum is the excellent and major catalyst. However, it is too expensive to be applied widely. Before large-scale applications, three technological problems should be solved. 1. The activity of electrodes should be improved to increase efficiency, in order to reduce the amount (i.e. cost) of platinum catalyst in electrodes. 2. Poisoning effects of CO on Pt catalyst should be deleted. 3. The conductivity of catalyst should be enhanced to reduce the energy waste in system. Previously in our laboratory, the tin (II) hydrogen phosphate (SnHPO4) assigned to SnHP, has precipitated on surface modified carbon black (CB) by H2O2 to form SnHP-CB composite supports, subsequently H2PtCl6, cetyltrimethylammonium bromide (CTABr), and alcohol added in respectively to reduce Pt to form Pt/SnHP-CB catalysts. In methanol oxidation reaction (MOR), though theses catalysts have revealed the more electrochemical mass activity and less obvious CO poisoning effects than Pt/C and could become potential for bi-functional catalysts, the serious agglomeration of Pt is observed by high resolution transmission electron microscope (HR-TEM). In this study, poly vinyl pyrrolidone (PVP) is firstly added to disperse carbon black, which is assigned to padCB, before the surface modification by H2O2, to avoid the further agglomeration after SnHP precipitating on them for increasing the specific surface area of SnHP-padCB composite on which platinum is reduced to form Pt/SnHP-padCB catalyst for enhancing the electrochemical performance as well as deleting CO toxic effects. The material characterization of catalyst is carried out by Fourier transform infrared spectroscopy, X-ray diffraction (XRD), field emission scanning electron microscopy, HR-TEM, and inductively coupled plasma-mass spectrometry (ICP-MS), while the characterization of electrochemical performance by cyclic voltammetry including hydrogen oxidation reaction (HOR), MOR, CO stripping, and membrane electrode assembly (MEA) tests. For Pt/SnHP-padCB, compared with Pt/SnHP-CB, the electric resistance is reduced from 120.1 to 113.7 Ω, the particle size lightly increases from 4.26 to 4.43 nm (XRD) and from 3.90 to 3.97 nm (HR-TEM), and the yield of Pt increase from 0.91 to 0.97 through ICP-MS analysis. The electrochemical surface area is enhanced form 765 to 970 cm2/mg in HOR, the mass activity from 37.57 to 61.6 A/gPt at 0.4 V (Ag/AgCl) and the on-set potential reduced from 0.223 to 0.158 V in MOR. No forward and backward current peaks are observed, indicating the complete deletion of CO poisoning effect on Pt. For 1000 cyclic life tests, the retained capacity of Pt/SnHP-padCB is reaching up from 60% to 67%. MEA tests also reveal the greater power density from 5.28 to 6.32 mWcm-2mgPt-1 and open circuit voltage from 0.44 to 0.47 V. HR-TEM observations conclude that Pt of Pt/SnHP-padCB is more dispersed than Pt/SnHP-CB, leading to the better electrochemical performances.