Environmental Engineering Reference
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Figure 13.5 Potential-step electro-oxidation of formic acid on a Pt/Vulcan thin-film electrode
(7 mg
Pt
cm
22
, geometric area 0.28 cm
2
) in 0.5 M H
2
SO
4
solution containing 0.1 M HCOOH
upon stepping the potential from 0.16 to 0.6 V (electrolyte flow rate 5 mLs
21
, at room tempera-
ture). (a) Solid line, faradaic current transients; dashed line, partial current for HCOOH
oxidation to CO
2
. (b) Solid line, m/z ¼ 44 ion current transients; gray line, potential-step
oxidation of pre-adsorbed CO derived upon HCOOH adsorption at 0.16 V, in HCOOH-free
H
2
SO
4
solution.
13.3.3.1 Formic Acid Oxidation
After passing through the initial spike, the
faradaic current continues to increase, and finally reaches saturation after 7 - 8 minutes.
Similar types of current transients were also obtained in potential-step rotating disk
electrode (RDE) experiments for formic acid oxidation on bare Pt(111) electrodes
and on Pt(111) electrodes irreversibly modified by adsorbed Bi [Schmidt et al.,
2000; Yang and Sun, 2002], as well as on Pt film electrodes [Chen et al.,
2006a, b, c]. The m/z ¼ 44 mass signal closely follows the faradaic current transients,
except for the initial current spike, which is absent in this case, confirming that this
feature is caused by pseudocapacitive effects (see also Fig. 13.2 and the discussion
in Section 13.3.1.2). For comparison, we also include the CO
2
signal (multiplied by
10) obtained for formic acid adsorbate oxidation (gray solid line in Fig. 13.5b, data
from Fig. 13.2b). Conversion of the m/z ¼ 44 ion current into a faradaic current for
formic acid oxidation to CO
2
(dashed line in Fig. 13.5a) shows excellent agreement
with the measured faradaic current (solid line in Fig. 13.5a) between the two signals,
similar to our findings for potentiodynamic formic acid oxidation. A 100% current
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