1D Pd-Based Nanomaterials as Efficient Electrocatalysts for Fuel Cells - Low-cost Nanomaterials: Toward Greener and More Efficient Energy Applications - page 341

Fig. 22 TEM and SEM images of the Pd nanotube arrays fabricated at different current densities
for 12 h: -1mAcm -2 (Pd-NT-1) (a, b, c); -3mAcm -2 (Pd-NT-3) (d, e, f) and -5mAcm -2
(Pd-NT-5) (g, h, i). Reprinted from Ref. [ 78 ] with permission by Elsevier
densities and the Pd-NT-5 tube arrays electrodeposited under the highest applied
current density display the roughest surface. This suggests that the fast tube array
growth under higher current density may result in rougher surface structure. In the
electrocatalytic studies for formic acid oxidation, it was found that the Pd-NT-5
exhibited the largest electrochemical active surface area and the highest electro-
catalytic activity among the three samples, but the catalytic activities of all the Pd
nanotubes are lower than that of the commercial Pd catalyst (20 wt%). The authors
compared the electrochemical stability of the Pd-NT-5 and commercial Pd/C
catalyst. As shown in Fig. 23 a, the Pd-NT-5 exhibits nearly maintained electro-
catalytic activity after the stability test. Simultaneously, the size and morphology
of the Pd-NT-5 also remained after the stability test. In contrast, the electrocata-
lytic activity of the Pd/C deteriorated significantly after the stability test
(Fig. 23 b). Furthermore, the Pd/C showed increased particle size and nonuniform
size distribution. The results strongly suggest that the Pd nanotubes have enhanced
electrocatalytic stability, which may be ascribed to the less aggregation of 1D Pd
nanotubes during the catalytic reaction in comparison with the Pd/C.