1D Pd-Based Nanomaterials as Efficient Electrocatalysts for Fuel Cells - Low-cost Nanomaterials: Toward Greener and More Efficient Energy Applications - page 344

Fig. 25 Cyclic
voltammograms of the Pd-Cd
electrodes in 0.1 M HClO 4
performed with a scan rate of
20 mV s -1 . The overall
hydrogen desorption charge
Q H versus the normalized
atomic composition of Cd is
shown in the inset. Reprinted
from Ref. [ 94 ] with
permission by the American
Chemical Society
of Pd-Cd nanomaterials with different compositions was evaluated by using
electrochemical cyclic voltammetry technique. Under the acid condition, it is easy
to clearly separate the region of hydrogen sorption/desorption from the potential of
the palladium oxide formation. However, it is not so easy to decouple adsorption
from absorption of hydrogen. Thus, they used the total charge, Q H , obtained by
integrating the area under the anodic peaks in the CVs to determine the hydrogen
storage ability. As shown in Fig. 25 , the charges for hydrogen desorption on the
Pd-Cd nanostructures displays a volcano shape with 10-15 % Cd possessing the
highest capacity. The authors found that with the amount of Cd increasing from 0
to 15 %, the crystallite size decreased from 25.81 to 9.16 nm and the surface area
was increased from 11.58 to 46.64 m 2 g -1 . However, when the amount of Cd was
further increased to 20 %, larger PdCd nanopartilces were formed and decreased
surface area was obtained, thus resulting in the lower hydrogen storage capacity.
Therefore, the hydrogen storage ability of the PdCd nanostructures depends on the
surface structure and crystallite size. The enhanced hydrogen storage capacity
upon the addition of Cd can be ascribed to the formation of small dendritic
structures, dilation of the lattice constant, and decrease of the crystalline size.
By using electrochemical cyclic voltammetry, our group studied the hydrogen
storage properties of the PdAg nanotubes obtained by galvanic displacement
between Ag nanorods and Pd(NO 3 ) 2 at different reaction times [ 125 ]. From the
SEM images (Fig. 26 a-d) of the PdAg-(10), PdAg-(90), PdAg-(150) and PdAg-
(180) nanotubes, which were collected at reaction times of 10, 90, 150, and
180 min, respectively, the hollow structure could be seen gradually with the
reaction time increasing. Based on the inductive coupling high frequency plasma-
mass spectrophotometry (ICP-MS) measurements, the ratios of Pd to Ag with 5:95,
10:90, 15:85, and 18:82 were determined for the samples. That is, the Pd content in
the PdAg nanotubes increases with the increase ingalvanic reaction time. In the