Catalytic activity of Pd-Ag nanoparticles supported on carbon nanotubes for the electro-oxidation of ethanol and propanol
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摘要: 在乙二醇和水混合溶剂中，采用硼氢化钠还原的方法制备了多壁碳纳米管（MWCNT）负载的Pd和Pd-Ag纳米颗粒催化剂；在碱性介质中，用循环伏安法测试了这些催化剂对乙醇、正丙醇和异丙醇的电氧化性能。结果表明，Pd和Pd-Ag纳米颗粒均匀地分散在MWCNT表面；Pd/MWCNT、Pd4Ag1/MWCNT、Pd2Ag1/MWCNT和Pd1Ag1/MWCNT催化剂上金属颗粒的平均粒径分别为7、4、7和11 nm。相比乙醇和异丙醇，所制备的催化剂对正丙醇的氧化表现出较大的电流密度。与Pd/MWCNT催化剂相比，双金属PdnAg1/MWCNT（n=4、2、1）催化剂，尤其是Pd4Ag1/MWCNT上的电流密度更大，表明Ag的加入提高了Pd催化剂对醇氧化的电化学活性，其原因是因为醇氧化过程所产生的中间体物种在双金属Pd-Ag/MWCNT催化剂上的吸附力有所减弱。Abstract: Pd and Pd-Ag nanoparticles supported on multi-walled carbon nanotubes (MWCNT) were prepared by using the NaBH4 reduction method in a mixed solvent of ethylene glycol and water; their catalytic activity for the electro-oxidation of ethanol, n-propanol and iso-propanol was investigated in alkaline media by the voltammetric method. The results indicate that Pd and Pd-Ag nanoparticles are well-dispersed on the surface of MWCNTs and the average sizes of metal particles on the Pd/MWCNT, Pd4Ag1/MWCNT, Pd2Ag1/MWCNT and Pd1Ag1/MWCNT catalysts are 7, 4, 7 and 11 nm, respectively. Over these catalysts, the electro-oxidation of n-propanol exhibits larger current density than the oxidation of ethanol and iso-propanol. Moreover, the binary PdnAg1/MWCNT catalysts (n=4, 2, 1), especially Pd4Ag1/MWCNT, gives higher current density for the oxidation of ethanol and propanols than the Pd/MWCNT catalyst, suggesting that the addition of Ag can enhance the activity of Pd-based catalyst for the electro-oxidation of alcohols. The excellent activity of binary Pd-Ag/MWCNT catalysts is probably attributed to the weak absorption of intermediate species on Pd due to the interaction between Pd and Ag, which may promote the oxidation of alcohols.
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Key words:
- palladium /
- multi-walled carbon nanotube /
- fuel cell /
- alcohol oxidation /
- electrocatalysis
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Figure 1 SEM images of (a) Pd/MWCNT, (b) Pd4Ag1/MWCNT, (c) Pd2Ag1/MWCNT, and (d) Pd1Ag1/MWCNT
Figure 2 TEM images of (a) Pd/MWCNT, (b) Pd4Ag1/MWCNT, (c) Pd2Ag1/MWCNT, and (d) Pd1Ag1/MWCNT
Figure 3 XRD patterns of (a) Pd/MWCNT, (b) Pd4Ag1/MWCNT, (c) Pd2Ag1/MWCNT, and (d) Pd1Ag1/MWCNT
Figure 5 Cyclic voltammograms of various catalysts in 1 mol/L NaOH solution at 50 mV/s
Figure 6 Cyclic voltammograms of various catalysts in 1 mol/L NaOH solution in the presence of 0.5 mol/L ethanol at 50 mV/s
Figure 7 Cyclic voltammograms of the Pd4Ag1/MWCNT catalyst in 1 mol/L NaOH solution with various ethanol concentrations (c1 to c5: 0.1, 0.3, 0.5, 0.7 and 1.0 mol/L) at 50 mV/s
inset (a) is a plot of anodic peak current density (jp) vs. the ethanol concentration c(EtOH) and inset (b) is a plot of anodic peak potential (Ep) vs. the ethanol concentration c(EtOH)
Figure 8 Cyclic voltammograms of various catalysts in 1 mol/L NaOH solution in the presence of 0.5 mol/L n-propanol (a) and 0.5 mol/L iso-propanol (b) at 50 mV/s
Figure 9 Cyclic voltammograms of the Pd4Ag1/MWCNT catalyst in 1 mol/L NaOH solution with various concentrations of n-propanol (a) and iso-propanol (b) (c1 to c5: 0.1, 0.3, 0.5, 0.7 and 1.0 mol/L) at 50 mV/s
inset (a1) is a plot of anodic peak current density jp vs. n-propanol concentration c(n-C3H7OH), whereas inset (a2) is a plot of anodic peak potential (Ep) vs. c(n-C3H7OH). inset (b1) is a plot of jp vs. the iso-propanol concentration c(iso-C3H7OH), whereas inset (b2) is a plot of Ep vs. c(iso-C3H7OH)
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