Improving effects of poly (vinyl pyrrolidone) addition on Pt/copper phosphate hydroxide/carbon black bifunctional catalysts for fuel cells

• Main Authors: Jian-Hong Lin, 林建宏
• Other Authors: 顏秀崗
• Format: Others
• Language: en_US
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/05928457179863004804

碩士 === 國立中興大學 === 材料科學與工程學系所 === 105 === Direct methanol fuel cells (DMFCs) are widely used in small-scale portable applications, and Pt is the superior and major catalyst in them, due to its excellent catalytic activity and chemical stability. However, Pt catalysts have two major problems should be overcome in DMFCs. One is that CO poisoning effects on the Pt catalysts should be deleted, and the other is that the amount of Pt should be reduced by increasing its activity, in order to reduce the cost of devices. Based on the previous study in our laboratory the copper phosphate hydroxide (Cu2PO4(OH)), named libethenite and assigned to CuPH, with the excellent performance in oxidation of olefins and alcohols, reveals hydroxyl radicals which could be used as a catalyst to alleviate CO poisoning effects. Phosphate salts have shown poor electronic conductivity. In order to enhance its conductivity, the precipitation of CuPH was directly deposited on the surface modified carbon black (CB) to form CuPH/CB. Then, nano-sized Pt was reduced on CuPH/CB to form Pt/CuPH/CB catalyst and finally annealed at 100℃ for 3 hours. However, the agglomeration of catalyst was seriously found. Therefore, in this study, we try to add poly(vinyl pyrrolidone)(PVP) for dispersing catalysts and hence enhancing the detoxifying function as well as electrochemical performance. The features of these catalysts were characterized by the electric resistance measurement, X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), field emission transmission electron microscopy – live fast Fourier transform (FETEM-Live FFT), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma-mass spectrometry (ICP-MS), Fourier transform infrared (FTIR) spectroscopy and cyclic voltammetry (CV). It is found that the resistance is reduced from 95.2 to 79 Ω, the ECSA is enhanced from 752 to 805.0 cm2/mg, the mass activity is improved from 262.12 to328 (A/gPt), and the on-set potential is lowered from 0.315 to 0.256V (vs. Ag/AgCl), in the methanol oxidation reaction. Besides, no forward or reverse current peaks are observed, indicating no CO poison effects. For 1000 cyclic life tests, the retained capacity of Pt/CuPH-PVP-C is reaching up to 80.1%. In membrane electrode assembly (MEA) tests, all prepared Pt/CPH-PVP-C catalysts reveal the greater power density and open circuit voltage than Pt/CuPH/CB and Pt/C (Alfa), since Cu2+ in these catalysts activates the water at low potential to yield Cu-OHads and detoxify the nearby nano-sized Pt poisoned by CO to create the opportunity for forming CO2 and H+, beside the enhanced conductivity. This argument also reasons results of MOR tests out. Obviously, both electric resistance and CO poisoning effect play the major role on the performance of catalysts in DMFC, and the Pt/CuPH-PVP-C improved from Pt/CuPH/CB has revealed the acceptable performance due to its well-dispersed catalysts with enhanced conductivity and detoxifying function.