In addition to SEM and XPS, characterization was also conducted
using the cyclic voltammetry method. Fig. 4a–c shows comparisons of
cyclic voltammograms (CVs) of 0.1 M PBS in the absence and in the
presence of 1 mM H2O2 at the BDD, Pt, and Pt-BDD electrodes. At the
BDD electrode, no significant difference was observed between the CVs with and without the presence of H2O2 (Fig. 4a), whereas a small increase
of oxidation currents around +0.35 V as well as reduction current
around +0.1 V was found at the CVs at the Pt electrode (Fig. 4b).
The results suggested that H2O2 is not electrochemically active at the
BDD surface, while it is oxidized and reduced at the Pt surface. In the
case of the CVs at the Pt-BDD electrode (Fig. 4c), the increase of oxidation
and reduction peak currents at around +0.4 V and −0.1 V, respectively,
was obviously observed when H2O2 is present in the system. It is
well known that the Pt electrode has catalytic activity for oxidation–reduction
of H2O2 as shown in the following equation
Reduction : H2O2 þ 2e− → 2OH− ð1Þ
Oxidation : 2H2O2 → O2 þ 2Hþ þ 2e−: ð2Þ