Topics in Current Chemistry (2019) 377:11
1 3
of studied electrodes (prepared by casting nanoparticle catalysts ink on an Au disk),
the consequently thicker and uneven electrolyte layer, and the strong IR absorption
by the amorphous carbon support.
On-line differential electrochemical mass spectroscopy (DEMS) has been
accepted as a quantitative tool for determining ethanol electro-oxidation products.
In the above studies, the Pt–SnO 2 catalyst shows lower CO 2 production than that on
pure Pt catalyst, which is consistent with literature reports from both on-line DEMS
and in situ FTIR studies [10, 11, 24]. The CO 2 production current efficiency on pure
Pt appears to be 5–10% and it is consistent with the FTIR results reported by Camara
and Iwasita [2]. However, this value is considerably higher than the values determined from DEMS measurements, which are mostly in the range of 2–3% [10, 11,
24]. Moreover, the IRRAS studies show a very low production of CH 3 CHO, while
DEMS determines considerably higher CH 3 CHO generation (average current efficiency around 37% for CH 3 CHO) in a similar electrolyte. We attribute the different
results from the two techniques, IRRAS and DEMS, to their different reaction environments: thin-layer cell versus flow cell. In the thin-layer configuration, CH 3 CHO
is more likely to be re-adsorbed on the catalyst surface and further oxidized to CO 2
or CH 3 COOH, while in the flow-cell setup in DEMS studies, CH 3 CHO could easily desorb from catalyst surface once it formed. Nevertheless, IRRAS could be an
important quantitative complement to the DEMS technique.
3.2 In Situ ATR‑SEIRAS Study of Ethanol Oxidation on a Pt Electrode
The Kretschmann configuration for in situ FTIR studies on a thin metal film has
mainly been used to study CO oxidation, because of the strong enhancement in IR
bands of adsorbed CO molecules. It is also used to characterize the electrooxidation
of small organic molecules such as formic acid, methanol, ethanol, dimethyl ether,
etc., although the results are more difficult to interpret due the complexity of these
reactions on metal surfaces [94–97].
Shao et al. carried out the study of ethanol oxidation on a polycrystalline Pt film
electrode using the ATR-SEIRAS technique [97]. The Pt film was deposited on the
flat side of a Si hemisphere by chemical deposition. The polished Si surface was
treated with 4% HF for 1 min first to remove the surface oxide, and then 2 ml of plating solution (0.01 M K 2 PtCl 6 + 10% HF) was repeatedly dropped on the Si surface
for 30 min at room temperature.
The cyclic voltammetry curve of ethanol oxidation is shown in Fig. 8a, and the
in situ ATR-SEIRA spectra recorded during EOR in the first potential sweep are
shown in Fig. 8c. The bands for the linear and bridge-bonded CO at 2030–2065
and 1800–1840 cm
−1
, respectively, are clearly observed at all potentials. In addition,
another prominent band located at 1396–1410 cm
−1
is attributed to the symmetric
OCO stretching mode (ν s OCO) of the adsorbed acetate, as its position matches that
of the spectrum in the solution of 0.1 M HClO 4 + 0.1 M CH 3 COOH at 0.6 V (dotted
line in the bottom of Fig. 8c).
Reprinted from the journal
16
1 3
of studied electrodes (prepared by casting nanoparticle catalysts ink on an Au disk),
the consequently thicker and uneven electrolyte layer, and the strong IR absorption
by the amorphous carbon support.
On-line differential electrochemical mass spectroscopy (DEMS) has been
accepted as a quantitative tool for determining ethanol electro-oxidation products.
In the above studies, the Pt–SnO 2 catalyst shows lower CO 2 production than that on
pure Pt catalyst, which is consistent with literature reports from both on-line DEMS
and in situ FTIR studies [10, 11, 24]. The CO 2 production current efficiency on pure
Pt appears to be 5–10% and it is consistent with the FTIR results reported by Camara
and Iwasita [2]. However, this value is considerably higher than the values determined from DEMS measurements, which are mostly in the range of 2–3% [10, 11,
24]. Moreover, the IRRAS studies show a very low production of CH 3 CHO, while
DEMS determines considerably higher CH 3 CHO generation (average current efficiency around 37% for CH 3 CHO) in a similar electrolyte. We attribute the different
results from the two techniques, IRRAS and DEMS, to their different reaction environments: thin-layer cell versus flow cell. In the thin-layer configuration, CH 3 CHO
is more likely to be re-adsorbed on the catalyst surface and further oxidized to CO 2
or CH 3 COOH, while in the flow-cell setup in DEMS studies, CH 3 CHO could easily desorb from catalyst surface once it formed. Nevertheless, IRRAS could be an
important quantitative complement to the DEMS technique.
3.2 In Situ ATR‑SEIRAS Study of Ethanol Oxidation on a Pt Electrode
The Kretschmann configuration for in situ FTIR studies on a thin metal film has
mainly been used to study CO oxidation, because of the strong enhancement in IR
bands of adsorbed CO molecules. It is also used to characterize the electrooxidation
of small organic molecules such as formic acid, methanol, ethanol, dimethyl ether,
etc., although the results are more difficult to interpret due the complexity of these
reactions on metal surfaces [94–97].
Shao et al. carried out the study of ethanol oxidation on a polycrystalline Pt film
electrode using the ATR-SEIRAS technique [97]. The Pt film was deposited on the
flat side of a Si hemisphere by chemical deposition. The polished Si surface was
treated with 4% HF for 1 min first to remove the surface oxide, and then 2 ml of plating solution (0.01 M K 2 PtCl 6 + 10% HF) was repeatedly dropped on the Si surface
for 30 min at room temperature.
The cyclic voltammetry curve of ethanol oxidation is shown in Fig. 8a, and the
in situ ATR-SEIRA spectra recorded during EOR in the first potential sweep are
shown in Fig. 8c. The bands for the linear and bridge-bonded CO at 2030–2065
and 1800–1840 cm
−1
, respectively, are clearly observed at all potentials. In addition,
another prominent band located at 1396–1410 cm
−1
is attributed to the symmetric
OCO stretching mode (ν s OCO) of the adsorbed acetate, as its position matches that
of the spectrum in the solution of 0.1 M HClO 4 + 0.1 M CH 3 COOH at 0.6 V (dotted
line in the bottom of Fig. 8c).
Reprinted from the journal
16