Characterization was also performed using XPS. Generally, asdeposited
BDD electrodes are terminated by hydrogen since they are
prepared under hydrogen plasma condition [14]. Previously, it was
also reported by Uchikado et al. that oxygen termination is required to
deposit metal particles electrochemically at the surface of BDD [32] as
Pt particles have better affinity to oxygen than hydrogen. Therefore,
prior to the deposition of Pt particles, electrochemical oxidation in
0.1 M H2SO4 solution was performed at the BDD surface to change the
surface termination to oxygen termination. Electrochemical oxidation
can change the surface to oxygen termination as shown by the XPS results
(Fig. 3a and b), which show the increase of O 1s peak intensity at
532 eV after the electrochemical oxidation process. Comparison of the
intensity of the O 1s peak related to C 1s at 284 eV before and after oxidation
showed that O/C ratio increased from 0.21 to 0.38, indicating that
some hydrogen terminations have already changed to oxygen terminations.
The peak at 284 eV is presumed as deconvolution of the peaks at
283.3 eV and 284.8 eV attributed to diamond and carbon [33–35]. The
result was also confirmed to the previous result of oxygen-terminated
BDD characterization [36]. Fig. 3c shows typical XPS of Pt modification
at the BDD surface. After Pt modification, XPS spectra show that peak
intensities of Pt 4f7/2 and Pt 4f5/2 at the binding energies of 71 eV and
74 eV, respectively, increase with the number of cyclic voltammetry
(Fig. 3d). Pt/C ratios of 0.033, 0.050 and 0.062 were obtained with cyclic
numbers of 20, 40 and 80, respectively. On the contrary to the increasing
peak of Pt 4f7/2 and Pt 4f5/2, decrease of O 1s peak was observed, indicating
that the Pt particles deposited at the O site rather than at the H site at
the BDD surface. XPS spectra of the BDD electrodes before and after
modification were summarized in Table 1.