高性能Pt-PbOx復合電催化劑的制備及應用基礎研究.pdf

1、Aimed at searching for highly active and stable Pt-based catalysts that can improve significantly the energy conversion efficiency of direct ethanol fuel cells (DEFCs), a novel Pt-PbOx (～87％ of Pb3O4 in PbOx) nanocomposi

2、te (Pt-PbOx NC) catalyst with a mean size of 3.23 nm was firstly synthesized through a simple wet chemistry method without using surfactant, organometallic precursors and high temperature. Electrocatalytic tests demonstr

3、ated that the as-prepared Pt-PbOx NC catalyst possesses a much higher catalytic activity and a longer durability than Pt nanoparticles (nm-Pt) and commercial Pt black catalysts for ethanol electrooxidation.For instance,

4、Pt-PbOx NC showed an onset potential that was 30 mV and 44 mV less positive, together with a peak current density 1.7 and 2.6 times higher than those observed for nm-Pt and Pt black catalysts in the cyclic voltammogram t

5、ests.The ratio of current densities per unit Pt mass on Pt-PbOx NC, nm-Pt and Pt black catalysts is 27.3 ∶ 3.4 ∶ 1 for the long-term (2 hours) chronoamperometric experiments measured at-0.4 V (vs.SCE).In situ FTIR spectr

6、oscopic studies revealed that the activity of breaking C-C bond of ethanol of the Pt-PbOx NC is as high as 5.17 times that of the nm-Pt, which illustrates a high efficiency of ethanol oxidation into CO2 on the as-prepare

7、d Pt-PbOx NC catalyst.
　　In order to further promote the simplification, industrialization of Pt-based catalysts doping with lead oxides, PbO2 nanoparticles were used directly to modify commercial Pt black catalyst.El

8、ectrocatalytic tests demonstrated that the prepared Pt black-PbO2 catalysts possess much higher catalytic activity and longer durability than commercial Pt black for ethanol electrooxidation, and Pt black-PbO2(4∶1) catal

9、yst, the mass ratio of Pt black and PbO2 is 4∶1, is in especial, which showed an onset potential of about 98 mV less positive, together with a peak current density 4 times higher than that observed for Pt black catalyst

10、in the cyclic voltammogram tests.The current density on Pt black-PbO2(4∶1) is 35.5 times that on Pt black catalyst for the long-term (2 hours) chronoamperometric experiments measured at-0.4 V (vs.SCE).The in situ FTIR sp

11、ectroscopic studies reveal that Pt black-PbO2(4∶1) catalyst holds an excellent activity for breaking the C-C bond of ethanol, which is 3.21 times that of Pt black catalyst at (0)V(vs.SCE).Therefore, these simple preparat

12、ion methods is suitable for production on an enlarged scale in industry and can promote the commercialization of DEFCs due to its easy operation, facility, significant electrocatalytic performance and excellent C-C bond

13、cleavage activity.However, the catalytic performance of Pt black-PbO2 catalysts is related with the mass ratio of Pt and PbO2.Excess PbO2 can lower the catalytic performance of Pt black-PbO2 catalysts, which may be attri

14、buted to the increase in the apparent resistivity and the blocking of Pt active sites with PbO2.The relatively lower durability of Pt black-PbO2 catalysts compared with that of Pt-PbOx NC catalyst may be related with the

15、 doping pattern of lead oxides.The Pt-PbOx NC is a kind of nanocomposite catalyst, while as for Pt black-PbO2 catalysts, PbO2 is directly modified on the Pt black surface and is easy loss in the oxidation process.So we b

16、elieve that if the doping pattern is improved, the durability of Pt black-PbO2 catalysts may be significantly enhanced.
　　It is known that ethylene glycol has superior energy density and higher boiling point than some

17、 typical alcohol fuels such as methanol and ethanol.And, surprisingly, ethylene glycol provides larger oxidation currents than other fuels.Besides, with respect to the difficulties in breaking the C-C bond, ethylene glyc

18、ol possesses higher electron transfer ability and therefore it is an interesting alternative fuel for direct alcohol fuel cells.So, in chapter 6, the electrocatalytic performance of ethylene glycol oxidized on Pt black-P

19、bO2(4∶1) and Pt-PbOx NC catalysts were investigated.The results show that the as-prepared Pt black-PbO2(4∶1) and Pt-PbOx NC catalysts manifest rather high activity and durability for ethylene glycol electrooxidation.For

20、example, Pt black-PbO2(4∶1) showed the most lowest onset potential (measured at j =25 mA (mg Pt)-1),-0.588 V, then is Pt-PbOx NC catalyst, which are negatively shifted by about 160 mV and 130 mV in comparison with that o

21、f Pt black, respectively.And the forward peak current densities for ethylene glycol oxidation on Pt black-PbO2(4∶1) and Pt-PbOx NC catalysts are 2.56 and 2.06 times that of commercial Pt black severally.However, nm-Pt po

22、ssesses higher onset potential, the highest forward peak current density, 1215.3 mA(mg Pt)-1, together with relative lower durability.The in situ FTIR spectroscopic studies reveal that the oxidization passway, products a

23、nd content are different on the four catalysts, oxalate cannot be produced on nm-Pt and Pt black catalysts.As a result, the cleavage ability of C-C bond of ethylene glycol on the prepared Pt black-PbO2(4∶1) and Pt-PbOx N

24、C catalysts may be slightly superior than that of nm-Pt and Pt black catalysts. But the two catalysts hold excellent electron transfer ability, namely Faradic efficiency, especially at low oxidation potentials.
　　In c

25、onclusion, the results in this work indicate that both Pt-PbOx NC and Pt black-PbO2 catalysts display enhanced electrocatalytic activity and excellent durability towards ethanol and ethylene glycol oxidation.It reveals t

26、hat Pb3O4 and PbO2 may be co-catalysts and can improve the electrocatalytic performance of Pt significantly.The significant enhancement in catalytic performance may be explained by electronic effects and bi-functional me

27、chanism.Pt black-PbO2 catalysts possess relatively higher catalytic activity, which may be attributed to the stronger ability of PbO2 for activating water at lower potentials than that of Pb3O4.In a word, this research w