One step NaBH4 reduction of Pt-Ru-Ni catalysts on different types of carbon supports for direct ethanol fuel cells: Synthesis and characterization
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Abstract: The ternary catalyst Pt75Ru5Ni20 was conducted on various types of carbon supports including functionalized Vulcan XC-72R (f-CB), functionalized multi-walled carbon nanotubes (f-MWCNT), and mesoporous carbon (PC-Zn-succinic) by sodium borohydride chemical reduction method to improve the ethanol electrooxidation reaction (EOR) for direct ethanol fuel cell (DEFC). It was found that the particle size of the metals on f-MWCNT was 5.20 nm with good particle dispersion. The alloy formation of ternary catalyst was confirmed by XRD and more clearly described by SEM element mapping, which was relevant to the efficiency of the catalysts. Moreover, the mechanism of ethanol electrooxidation reaction based on the surface reaction was more understanding. The activity and stability for ethanol electrooxidation reaction (EOR) were investigated using cyclic voltammetry and chronoamperometry, respectively. The highest activity and stability for EOR were observed from Pt75Ru5Ni20/f-MWCNT due to a good metal-carbon interaction. Ru and Ni presented in Pt-Ru-Ni alloy improved the activity and stability of ternary catalysts for EOR. Moreover, the reduction of Pt content in ternary catalyst led to the catalyst cost deduction in DEFC.
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Key words:
- ternary catalyst /
- ethanol electrooxidation reaction /
- multiwall carbon nanotubes /
- mesoporous carbon
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Figure 1 SEM images of MWCNT (a), f-MWCNT (b), CB (c), f-CB (d), PC-Zn-succinic (e) and f-PC-Zn-succinic (f)
Figure 5 XRD patterns of Pt75Ru5Ni20/PC-Zn-succinic (a), Pt75Ru5Ni20/f-MWCNT (b), Pt75Ru5Ni20/f-CB (c), Pt75Ru25/f-CB (d) and Pt/f-CB (e) (inset: close-up of Pt (220) planes)
Figure 6 SEM element mapping images of Pt75Ru5Ni20/PC-Zn-succinic (a), Pt75Ru5Ni20/f-MWCNT (b), Pt75Ru5Ni20/f-CB (c), Pt75Ru25/f-CB (d) and Pt/f-CB (e)
Figure 9 TEM images and particle size histograms of Pt75Ru5Ni20/PC-Zn-succinic (a), Pt75Ru5Ni20/f-MWCNT (b), Pt75Ru5Ni20/f-CB (c), Pt75Ru25/f-CB (d) and Pt/f-CB (e)
Figure 10 Cyclic voltammograms of all catalysts operated in 0.5 mol/L CH3CH2OH containing 0.5 mol/L H2SO4 solution at scan rate of 20 mV/s
Figure 11 Chronoamperometry curves of all catalysts operated in 0.5 mol/L CH3CH2OH containing 0.5 mol/L H2SO4 solution at a fixed potential of 0.70 V and scan rate of 20 mV/s
Table 1 Surface area and pore volume of carbon supports
Sample ABET
/(m2·g-1)Amicro
/(m2·g-1)Aext
/(m2·g-1)vtot
/(cm3·g-1)vmicro
/(cm3·g-1)vmeso+macro
/(cm3·g-1)MWCNT 138 3 135 1.19 0 1.19 f-MWCNT 148 8 140 1.04 0 1.04 CB 206 54 151 1.4 0.03 1.37 f-CB 116 26 89 0.75 0.01 0.73 PC-Zn-succinic 2 176 435 1 740 5.23 0.19 5.04 f-PC-Zn-succinic 0.06 0.12 0 0 0 0 
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Table 2 Component of C and O reported from XPS results
Material Relative intensity /% C O MWCNT 98.22 1.78 f-MWCNT 92.75 7.25 CB 95.67 4.33 f-CB 88.05 11.95 PC-Zn-succinic 98.02 1.98
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Table 3 XRD parameters of all catalysts determined from Pt (220) planes
Catalyst 2θ/(°) d-spacing /nm Crystallite size d/nm Lattice parameter d/nm Pt75Ru5Ni20/PC-Zn-succinic 67.66 0.138 471 4.37 0.339 18 Pt75Ru5Ni20/f-MWCNT 68.03 0.137 815 4.22 0.337 58 Pt75Ru5Ni20/f-CB 67.91 0.138 013 5.11 0.338 06 Pt75Ru25/f-CB 67.98 0.137 893 4.41 0.337 77 Pt/f-CB 67.70 0.138 395 5.16 0.339 00
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Table 4 Composition of catalysts evaluated from SEM-EDX
Catalyst Atomic ratio Pt Ru Ni Pt75Ru5Ni20/PC-Zn-succinic 89.23 ± 1.5 6.92 ± 1.14 3.85 ± 0.46 Pt75Ru5Ni20/f-MWCNT 77.80 ± 0.93 6.73 ± 0.41 15.47 ± 1.18 Pt75Ru5Ni20/f-CB 77.15 ± 1.23 3.11 ± 1.01 19.74 ± 0.57 Pt75Ru25/f-CB 73.66 ± 1.13 26.34 ± 1.13 - Pt/f-CB 100.00 ± 0.00 - -
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Table 5 Metal loading evaluated from TGA
Sample Metal loading /% Pt75Ru5Ni20/PC-Zn-succinic 17.24 Pt75Ru5Ni20/f-MWCNT 24.47 Pt75Ru5Ni20/f-CB 22.46 Pt75Ru25/f-CB 24.34 Pt/f-CB 23.84
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Table 6 Metal components obtained from XPS results
Form of metal Relative intensity /% Pt75Ru5Ni20/PC-Zn-succinic Pt75Ru5Ni20/f-MWCNT Pt75Ru5Ni20/f-CB Pt (0) 55.9 61.5 57.8 Pt (2+) 23.5 22.6 26.0 Pt (3+) 11.4 10.4 9.1 Pt (4+) 9.3 5.4 7.0
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