1 3
Topics in Current Chemistry (2019) 377:11
be used as a measure of the poisoning of the catalyst. It is obvious that the band is
absent in the spectra of Pt–Rh–SnO 2 , signifying the ability of the ternary catalyst
to oxidize ethanol without surface poisoning. This is corroborated by DFT calculations, which reveal that the electron transfer from Rh to Pt weakens the interaction
between d-states of Pt with dissociated oxygenates (including CO) and hydrocarbons, making them active only for dissociated H [23].
3.1.2 Quantitative Optimization of the Pt–Rh Ratio
In situ IRRAS studies have demonstrated the effect of Rh component and the superior performance of the Pt–Rh–SnO 2 ternary catalyst. Optimizing the content of Rh
is of great importance because high EOR activity and high selectivity towards CO 2
formation are both essential goals in ethanol electrocatalysis. Moreover, Rh is a very
rare and quite expensive metal and minimizing its content is essential for production
of a viable catalyst. Four Pt–Rh–SnO 2 /C catalysts with atomic ratio of Pt:Rh:Sn of
1:x:1, where x = 1, 1/2, 1/3, and 1/4, were synthesized via a seeded growth approach,
and were employed to establish composition-selectivity correlation and to optimize
the catalysts’ composition [84]. Figure 6a–d displays in situ IRRAS spectra recorded
from these catalysts. It can be observed that the two Pt–Rh–SnO 2 /C with moderate Rh contents (i.e., Pt:Rh:Sn = 1:1/2:1 and 1:1/3:1) show considerably higher
CO 2 production compared to the ones with too high or too low Rh content (i.e.,
Pt:Rh:Sn = 1:1:1 and 1:1/4:1).
3.1.3 In Situ FTIR as a Quantitative Analysis Method
In situ FTIR results were used for quantitative estimation of the products formed in
studies of ethanol oxidation, EOR products distribution, and the dependence of the
selectivity of Pt–Ru catalysts on Ru contents [2, 90–92]. To compare the selectivity of the four Pt–Rh–SnO 2 /C electrocatalysts and to understand the effect of Rh
content on the catalysts’ capability in C–C bond cleavage, the quantity of different oxidation products is determined following the method described by Weaver’s
group [90]. The EOR total oxidation current efficiency, defined as the ratio between
charge contribution from total oxidation pathway ( C CO 2 ) and charge contribution
from both total oxidation and partial oxidation pathways ( C CO 2 +CH 3 COOH+CH 3 CHO ), is
directly correlated to the capability of the catalysts to split the C–C bond. The integrated band intensities of CO 2 , CH 3 CHO, and CH 3 COOH at 2343 cm
−1
, 933 cm
−1
,
and 1280 cm
−1
, respectively, obtained from the spectra in Fig. 6 were used to calculate the EOR total oxidation current efficiency for different Pt–Rh–SnO 2 /C
catalysts. CO 2 produces the strongest band in the spectra of Pt–Rh 1/2 –SnO 2 /C
and Pt–Rh 1/3 –SnO 2 /C catalysts, while CH 3 COOH bands are intensified for the
Pt–Rh 1 –SnO 2 /C and Pt–Rh 1/4 –SnO 2 /C catalysts. CH 3 CHO is only produced in small
amounts in EOR of all four Pt–Rh–SnO 2 /C catalysts. The variation of total oxidation efficiency versus applied potential is plotted in Fig. 7. For comparison purposes,
those of Pt/C and Pt–SnO 2 /C catalysts are also included.
Reprinted from the journal
13
Topics in Current Chemistry (2019) 377:11
be used as a measure of the poisoning of the catalyst. It is obvious that the band is
absent in the spectra of Pt–Rh–SnO 2 , signifying the ability of the ternary catalyst
to oxidize ethanol without surface poisoning. This is corroborated by DFT calculations, which reveal that the electron transfer from Rh to Pt weakens the interaction
between d-states of Pt with dissociated oxygenates (including CO) and hydrocarbons, making them active only for dissociated H [23].
3.1.2 Quantitative Optimization of the Pt–Rh Ratio
In situ IRRAS studies have demonstrated the effect of Rh component and the superior performance of the Pt–Rh–SnO 2 ternary catalyst. Optimizing the content of Rh
is of great importance because high EOR activity and high selectivity towards CO 2
formation are both essential goals in ethanol electrocatalysis. Moreover, Rh is a very
rare and quite expensive metal and minimizing its content is essential for production
of a viable catalyst. Four Pt–Rh–SnO 2 /C catalysts with atomic ratio of Pt:Rh:Sn of
1:x:1, where x = 1, 1/2, 1/3, and 1/4, were synthesized via a seeded growth approach,
and were employed to establish composition-selectivity correlation and to optimize
the catalysts’ composition [84]. Figure 6a–d displays in situ IRRAS spectra recorded
from these catalysts. It can be observed that the two Pt–Rh–SnO 2 /C with moderate Rh contents (i.e., Pt:Rh:Sn = 1:1/2:1 and 1:1/3:1) show considerably higher
CO 2 production compared to the ones with too high or too low Rh content (i.e.,
Pt:Rh:Sn = 1:1:1 and 1:1/4:1).
3.1.3 In Situ FTIR as a Quantitative Analysis Method
In situ FTIR results were used for quantitative estimation of the products formed in
studies of ethanol oxidation, EOR products distribution, and the dependence of the
selectivity of Pt–Ru catalysts on Ru contents [2, 90–92]. To compare the selectivity of the four Pt–Rh–SnO 2 /C electrocatalysts and to understand the effect of Rh
content on the catalysts’ capability in C–C bond cleavage, the quantity of different oxidation products is determined following the method described by Weaver’s
group [90]. The EOR total oxidation current efficiency, defined as the ratio between
charge contribution from total oxidation pathway ( C CO 2 ) and charge contribution
from both total oxidation and partial oxidation pathways ( C CO 2 +CH 3 COOH+CH 3 CHO ), is
directly correlated to the capability of the catalysts to split the C–C bond. The integrated band intensities of CO 2 , CH 3 CHO, and CH 3 COOH at 2343 cm
−1
, 933 cm
−1
,
and 1280 cm
−1
, respectively, obtained from the spectra in Fig. 6 were used to calculate the EOR total oxidation current efficiency for different Pt–Rh–SnO 2 /C
catalysts. CO 2 produces the strongest band in the spectra of Pt–Rh 1/2 –SnO 2 /C
and Pt–Rh 1/3 –SnO 2 /C catalysts, while CH 3 COOH bands are intensified for the
Pt–Rh 1 –SnO 2 /C and Pt–Rh 1/4 –SnO 2 /C catalysts. CH 3 CHO is only produced in small
amounts in EOR of all four Pt–Rh–SnO 2 /C catalysts. The variation of total oxidation efficiency versus applied potential is plotted in Fig. 7. For comparison purposes,
those of Pt/C and Pt–SnO 2 /C catalysts are also included.
Reprinted from the journal
13