Preparation of Rh/C and its high electro-catalytic activity for ethanol oxidation in alkaline media

Article abstract of DOI:10.1039/c5ra16859g

The ethanol electrooxidation behaviors on Rh/C in alkaline media were studied compared with that on Pd/C. The Rh/C and Pd/C catalysts were synthesized by a microwave heating-glycol reduction method and characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The electrocatalytic activities of the catalysts were investigated by cyclic voltammetry (CV), chronoamperometry (CA), electrochemical impedance spectroscopy (EIS) and single cell discharge testing methods. The results showed that Rh/C presented higher activity and better stability toward ethanol oxidation than Pd/C. On the CV plots, it was observed that the onset potential of oxidation on Rh/C shifted negatively and the backward peak current on Rh/C decreased as compared to that of Pd/C. Intermediate species are produced during the oxidation process, as revealed by the complex impedance spectra. Rh/C presented higher tolerance for surface poisoning than Pd/C, which can be reflected by the negative impedance on the Pd/C electrode. The selectivity for ethanol oxidation to CO₂ (existing as CO₃^2- in alkaline media) on Rh/C and Pd/C electrodes were determined to be as low as 10.07% and 2.18%, respectively. Nevertheless, the ability of Rh for breaking the C-C bond in ethanol is still slightly higher than that of Pd under the same conditions.

Full text of DOI:10.1039/c5ra16859g

RSC Advances
View Article Online
View Journal | View Issue
PAPER
Preparation of Rh/C and its high electro-catalytic
activity for ethanol oxidation in alkaline media
Cite this: RSC Adv., 2015, 5, 91829
Fangfang Zhang, Debi Zhou,* Zejie Zhang, Mingda Zhou* and Qian Wang
The ethanol electrooxidation behaviors on Rh/C in alkaline media were studied compared with that on
Pd/C. The Rh/C and Pd/C catalysts were synthesized by a microwave heating-glycol reduction
method and characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The
electrocatalytic activities of the catalysts were investigated by cyclic voltammetry (CV),
chronoamperometry (CA), electrochemical impedance spectroscopy (EIS) and single cell discharge
testing methods. The results showed that Rh/C presented higher activity and better stability toward
ethanol oxidation than Pd/C. On the CV plots, it was observed that the onset potential of oxidation on
Rh/C shifted negatively and the backward peak current on Rh/C decreased as compared to that of Pd/
C. Intermediate species are produced during the oxidation process, as revealed by the complex
impedance spectra. Rh/C presented higher tolerance for surface poisoning than Pd/C, which can be
reflected by the negative impedance on the Pd/C electrode. The selectivity for ethanol oxidation to
Received 20th August 2015
Accepted 18th October 2015
2
ꢀ
CO
2
(existing as CO
3
in alkaline media) on Rh/C and Pd/C electrodes were determined to be as low
DOI: 10.1039/c5ra16859g
as 10.07% and 2.18%, respectively. Nevertheless, the ability of Rh for breaking the C–C bond in ethanol
www.rsc.org/advances
is still slightly higher than that of Pd under the same conditions.
is the need for highly active catalysts for the EOR that involve
1
. Introduction
2
complete oxidation per ethanol molecule to CO releasing 12
2
4
The Direct Alcohol Fuel Cells (DAFCs) are considered as electrons and the cleavage of the C–C bond. In recent years,
a promising technology for transportation and portable elec- Rh based catalysts have been investigated by several research
1
21
tronic devices. Ethanol is environmental friendly and may groups. For example, de Souza et al. found that PtRh
serve as a potential alternative due to its higher energy density combined in bimetallic surfaces for ethanol oxidation
2
than methanol. Pt and Pt-based catalysts have been exten- decreases the acetaldehyde yield, compared to pure platinum
1
9,20
sively investigated as electro-catalysts for oxidation of meth- on Pt73Rh27 and Pt55Rh45. Kowal et al.,
synthesized
3
–10
anol and ethanol,
and signicant progress has been made PtRhSnO
2
/C electrocatalysts by depositing Pt and Rh atoms on
in their development. For example, Xin et al. developed Sn oxides nanoparticles. The authors argue that these catalysts
a highly active PtSn catalyst for the ethanol oxidation reaction are efficient to cleave the C–C bond of ethanol at room
4
,5
(
EOR). However, the high price and limited supply of Pt temperature and cause its predominant oxidation to CO
2
at
constitute a major barrier to the development of DAFCs. very low overpotentials compared to platinum. In another
2
5
Therefore, there is a desire to develop low cost non-platinum study, Q. He et al. reported that RhCeO
electro-catalysts with comparable or improved kinetics for ethanol oxidation and Stephen K. Murphy et al. reported
towards the EOR.
/C has better activity
2
2
6
1
1,12
Among the non-platinum catalysts, Pd that a Rhodium (Xantphos) (benzoate) catalyst activates alde-
and Rh are suitable low-cost transition metals and shown hyde carbon–hydrogen (C–H) bonds with high chemo-
marked superiority over Pt in terms of oxidation rate and selectivity to trigger carbon–carbon (C–C) bond cleavage.
1
3–21
13–15
electrode stability.
Shen et al.
prepared a series of Pd- However, the information and the understanding of the
based catalysts and found that Pd catalysts exhibited higher activity of Rh-based electrocatalysts for ethanol electro-
activity and stability than did Pt catalysts in the EOR in alka- oxidation are still very scarce. Also, little is known about the
line solutions. However, Pd is easily poisoning by intermediate mechanism of the ethanol oxidation reaction on Rh catalysts
2
2,23
products and difficult to break C–C bond.
Therefore, in alkaline media. The present work investigates the electro-
a signicant challenge in the development of DAFC technology oxidation behaviors of Rh/C by compared to Pd/C. The differ-
ences of EIS patterns of the ethanol oxidation on Rh/C and Pd/
C and the selectivity for ethanol oxidation to CO will be
2
College of Chemistry and Chemical Engineering, Central South University, Lushan discussed.
South Road, Changsha, 410083, China. E-mail: chemcsu@126.com;
zhoumingda2015@163.com; Tel: +86 13875977107; +86 13874870330
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 91829–91835 | 91829

View Article Online
RSC Advances
Paper
2 2
CO ion selective electrode was only responsive to CO and
2
. Experimental
different concentration of CO corresponds to different poten-
2
2.1 Catalyst preparation and characterization
tial values (E). In this work, NaHCO was used as a standard
3
ꢀ2
ꢀ
5
ꢀ4
ꢀ3
ꢀ1
All chemicals used were of analytical grade, and all solutions solution. First, 10 , 10 , 10 , 10 , 10 M NaHCO
were freshly prepared in deionized water. Rh/C catalyst was tions were prepared. Secondly, adding hydrochloric acid to the
solu-
3
2
ꢀ
synthesized by the intermittent microwave heating-glycol solutions and adjusting pH < 3.8 respectively, CO
3
was
reduction method. Firstly, 2.5 mL of 0.05 M RhCl
3
aqueous transformed to CO completely and detected by CO ion selec-
2
2
solution was added to the 100 mL reactor containing 50 mL tive electrode, thus E can be obtained. Then obtained E and
glycol, 2 mL of 1.0 M KOH solution, and 0.24 g Vulcan XC-72 ꢀlg C(CO2) can be used to draw a standard curve. Finally, under
carbon powder (Cabot Corp. USA). Aer that, the mixed solu- the same condition, E of the sample solutions, i.e., Pd/C elec-
tion was changed into carbon paste by ultrasonic concussion trolyte solution, Rh/C electrolyte solution and blank group, was
and moderately heated in a microwave oven (900 W, 2.45 GHz, measured to obtain the CO
Galanz, WD900ASL23-2, China). The reaction product was curve. To be specic, Pd/C electrolyte solution was obtained by
concentrations from the standard
2

ltered and washed extensively with water and ethanol. The the mixed solution of 3.0 M C
2
H
5
OH and 6.0 M KOH aer the
ꢁ
residue was dried at 90 C for 24 h. Pd/C was prepared by using single cell discharge of AEM DEFC using Pd/C electrolyte for 3 h,
the same method for comparing the performance of different while Rh/C electrolyte solution was gotten in the same way.
catalysts. The electrodes containing different catalysts were Blank group was achieved by laying the mixed solution of 3.0 M
prepared using 60% PTFE emulsion as bonder and foamed
nickel as the electric collector. The loading of each electrode was carried out at room temperature.
C H OH and 6.0 M KOH in electrolytic cell for 3 h. All the text
2 5
ꢀ
2
was 0.1 mg cm
.
Structure and morphology of the catalyst was investigated
using XRD and TEM. The XRD patterns were generated by the 2q 3. Results and discussion
ꢁ
ꢀ1
scan with the scanning rate of 8 min and the angular reso-
3
.1 XRD and TEM
ꢁ
lution of 10–80 . TEM was taken through a JEOL-1230 micro-
scope, operating at the applied voltage of 200 kV.
XRD pattern of the Rh/C is shown in Fig. 1. The broad diffrac-
tion peak at about 25 is ascribed to Vulcan XC-72 carbon. The
ꢁ
XRD reections showed face-centered cubic lattice structures
2
.2 Electrochemical measurements
ꢁ
with diffraction peaks at Bragg angles of 2q ¼ 42, 46.5, 72.121 ,
Electrochemical measurements were carried out using CHI corresponding to the (111), (200), (220) planes of the Rh metallic
760D (Chen Hua, Shanghai, China) electrochemistry station in phase, respectively. The average crystal size of Rh is about 3.8
a conventional three-electrode cell with a Pt coil (counter elec- nm, which is calculated by using the Scherrer equation from
trode), a saturated Hg/HgO electrode (reference electrode) and XRD patter, indicating that Rh nanoparticles dispersed on
a prepared electrode (working electrode). The CV, CA and EIS Vulcan XC-72 could be very small. TEM image was obtained to
2 5
were collected in 1.0 M KOH and 1.0 M C H OH solution. The provide more information on particle size and distribution.
ꢀ
1
CV tests were conducted at a 10 mV s with potential ranging Fig. 2 shows the TEM image of Rh/C particle. As seen clearly in
from ꢀ0.8 to 0.4 V. The EIS were recorded in the constant Fig. 2, the Rh/C particles are uniform and well distributed on
potential mode with the amplitude of 50 mV by scanning the carbon support, while the average particle size of Rh/C from
5
frequency from 10 to 0.1 Hz.
TEM image is 3–5 nm, which is consistent with the XRD results.
2.3 Single cell discharge testing
The discharge testing of single cell was carried out to further
elucidate the performance of Pd/C and Rh/C (Pd and Rh loading
ꢀ
2
of 0.1 mg cm ) on the ethanol oxidation in an anion-exchange
membrane DEFC, using a Neware charge–discharge device
(Shenzhen Neware Corporation, China) at room temperature.
The anode was Pd/C and Rh/C electrodes, while the cathode was
the gas diffusion electrode which involves diffusion layer (acety-
lene black) and activation layer (MnO /C). The redox reaction
2
2
area on both electrodes was 2 ꢂ 2 cm , the current density of
ꢀ
2
discharge was 15, 20, and 30 mA cm . The anodic electrolyte was
2 5
the mixed solution of 3.0 M C H OH and 6.0 M KOH, accord-
ingly, the cathodic electrolyte was 6.0 M KOH solution.
2
.4 Estimation of reaction product
The CO ion selective electrode was used to detect CO
concentration in the solution aer single cell discharge testing. Fig. 1 XRD pattern of Rh/C.
2
2
91830 | RSC Adv., 2015, 5, 91829–91835
This journal is © The Royal Society of Chemistry 2015

View Article Online
Paper
RSC Advances
observed in the forward scan, which correspond to different
electrochemical processes occurring over the electrode surface.
The peak on Rh/C that appears at potentials range between ꢀ0.8
and ꢀ0.6 V is associated with the oxidation of absorbed and
desorbed hydrogen. The second peak on Rh/C, which emerges
ꢀ
in ꢀ0.45 V, can be attributed to the adsorption of OH . The
third peak occurs at potentials above 0.3 V on Rh/C catalyst. It
can be attributed to the formation of the rhodium oxide layer on
the surface of the catalyst. The negative current observed during
the backward scan suggests a reduction process, probably
reduction of oxygen. When add ethanol to the solution, the
hydrogen absorbed/desorbed region is signicantly suppressed
in the presence of ethanol in the solution. The ethanol oxida-
tion reaction starts at ꢀ0.78 V and a current peak centered at
Fig. 2 TEM image of Rh/C.
ꢀ
0.20 V is observed during the forward scan. In the reverse
scan, another current peak is found centered at ꢀ0.59 V.
Fig. 3(b) shows the CV curves of ethanol oxidation on Pd/C and
Rh/C catalysts. In the forward scan, peaks current are related to
the oxidation of freshly chemisorbed species derived from
ethanol adsorption. In the reverse scan, peaks are associated
with the removal of carbonaceous species that are not
completely oxidized in the positive scan, rather than the
3
.2 Cyclic voltammetry
Fig. 3(a) shows CV curves of Rh/C catalyst in 1.0 M KOH and 1.0
M KOH + 1.0 M C OH solutions at room temperature,
2
H
5
respectively. In absence of ethanol, three potential peaks can be
27–29
oxidation of freshly chemisorbed species.
It is worth noting
that, in the reverse scan, on the Pd/C at ꢀ0.18 V, a sharp
increasing current (about 90 mA) is seen, while the current of
Rh/C (about 22 mA) increases slowly and its current density is
much smaller than Pd/C, indicating that the adsorption degree
is less serious than Pd/C. The onset potential on Rh/C (about
ꢀ
0.78 V) is shied negatively as much as 0.28 V as compared to
that on Pd/C (about ꢀ0.5 V), indicating better activity of the Rh/
C catalyst for ethanol oxidation. The anodic onset potential is
important parameter for evaluating the activity of catalysts
during the electro-oxidation process. In addition, one oxidation
peak along with a shoulder for Rh/C can be seen (around ꢀ0.08
V), indicating that the products may not be the same in the case
of Pd/C. According to the published articles that Rh presents
excellent selectivity for complete conversion of ethanol to
25,26
CO
2
.
Therefore, the shoulder oxidation peak may be due to
the oxidation of intermediates from decomposition of ethanol.
3.3 Chronoamperometry
Chronoamperometric experiment was carried out to observe the
stability and possible poisoning of the catalyst under short-time
continuous operation. Fig. 4 provides the CA curves under
various potentials for Rh/C and Pd/C catalysts in a 1.0 M KOH +
2 5
1.0 M C H OH solution aer 1000 s. It can be clearly seen that,
at low potentials from ꢀ0.6 to ꢀ0.4 V, the current densities on
Rh/C electrode are higher than that on Pd/C electrode, indi-
cating a higher catalytic activity of Rh/C for ethanol oxidation
compared with Pd/C, which is consists with our CV results
(Fig. 3(b)).
3
.4 Mechanism investigation of ethanol oxidation by EIS
Fig. 3 Cyclic voltammograms for (a) Rh/C electrode in 1.0 M KOH and
To provide more insight into the ethanol oxidation behavior on
the Rh/C electrodes, EIS is used in this study to investigate the
kinetics of ethanol oxidation. EIS has been shown to be
1
.0 M KOH + 1.0 M C
KOH + 1.0 M C OH. The catalysts loading are all 20 mg cm , and
the potential sweep rate is 10 mV s
2 5
H OH; (b) Pd/C and Rh/C electrodes in 1.0 M
ꢀ2
2 5
H
ꢀ1
.
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 91829–91835 | 91831

View Article Online
RSC Advances
Paper
Fig. 4 Chronoamperograms for Rh/C and Pd/C electrodes in 1.0 M
KOH + 1.0 M C
2
H
5
OH at the potentials from ꢀ0.6 to ꢀ0.4 V.
a sensitive electrochemical technique for the studies on the
30
electro-oxidation kinetics of formic acid oxidation on Pd/C
31
and methanol oxidation on Pt/C. Complex impedance plots of
the formic acid oxidation on Pd/C catalysts at different applied
potentials are shown in Fig. 4. At potentials below ꢀ0.1 V, as
shown in Fig. 5(a), impedance plots occur in the rst quadrant
and the diameters of the arcs decrease with the increase of
potentials, indicating a decreasing polarization resistance with
the increase of potential. At ꢀ0.40 V, the arc become very small,
indicating faster electron-transfer kinetics at higher potentials.
However, with the increase of potentials above ꢀ0.30 V, the
impedance plot starts becoming larger than ꢀ0.4 V in Fig. 5(b),
suggesting the surface with little activity for ethanol oxidation.
Here in the ethanol oxidation system, the phenomenon could
be caused by the inhibiting effect of carbonaceous species that
are not completely oxidized. At potential between 0 and 0.3 V
(Fig. 5(c)), the spectra become small again and the diameter of
the arc decreases with the increases of potential, indicating
a new electrochemical reaction kicks in at this higher potential
30
regime.
In order to discuss the ethanol oxidation mechanism on
different catalytic surfaces, the impedance plots of ethanol
oxidation on Pd/C were compared with that on Rh/C. Fig. 6
shows the complex impedance plots of ethanol oxidation on
Pd/C. As shown in Fig. 6(a), the impedance patterns on Pd/C
are similar to those on Rh/C at potentials below ꢀ0.1 V.
2 5
Fig. 5 Complex impedance plots for 1.0 M KOH + 1.0 M C H OH
oxidation on Rh/C catalyst at room temperature as a function of
potential (a) between ꢀ0.6 and ꢀ0.4 V; (b) between ꢀ0.3 and ꢀ0.1 V;
However, at ꢀ0.1 V, the impedance plot starts transiting from (c) between 0 and 0.3 V.
the rst quadrant to the second quadrant in Fig. 6(b).
Impedance plot in the second quadrant indicates the polari-
zation resistance is negative and that is to say the steady state Pd surface and inhibits the reaction of ethanol oxidation by
oxidation current decreases with the increase of polarization blocking the active surface of Pd/C electrode with the associ-
potential. This phenomenon observed previously in the ated loss of surface active sites. It should be noted that all the
3
2
electro-oxidation of methanol on Pt and formic acid on Pd/ impedance spectra obtained on Rh/C electrode are located
3
0
C. In their study, the negative impedance behaviors are within the rst quadrant, suggesting the ability of resist
usually attributed to the adsorption of reaction intermediates poisoning of Rh/C is stronger than Pd/C. In addition, the
on the catalyst surface. In this work, the negative resistance reaction mechanism on both catalysts may different and it will
could be caused by the heavy intermediates adsorption on the be discussed in detail later.
91832 | RSC Adv., 2015, 5, 91829–91835
This journal is © The Royal Society of Chemistry 2015

View Article Online
Paper
RSC Advances
Fig. 7 Equivalent circuits for electrooxidayion of ethanol: (a) for
normal impedance, and (b) for special impedance.
shown in Fig. 7(b). C
resistance of the electrooxidation of adsorbed intermediates.
CT, an indicative of the rate of electrochemical reaction, is
1 1
and R represent the capacitance and
R
always a positive number and its value can be determined from
an impedance arc at a low frequency domain. From the tting,
the variation of the RCT with electrode potentials was evaluated,
which was depicted in Fig. 8. First, negative RCT was only ob-
tained on the Pd/C electrode at potentials between from ꢀ0.1 to
0.05 V, due to the strong surface-adsorbed carbonaceous
species. It can be noted that RCT on Rh/C electrode increases
with increasing potential between from ꢀ0.3 to ꢀ0.1 V, and not
obtained negative R , indicating that Rh/C has excellent
CT
carbonaceous species tolerance. Second, RCT for ethanol
oxidation on Pd/C electrode is much larger than that on the Rh/
C electrode, suggesting that Rh/C display better catalytic activity
because of its fast reaction kinetics.
3.5 Single cell performance
Fig. 9 shows the constant-current discharging curve of the
oxidation of ethanol in an anion-exchange membrane direct
2 5
Fig. 6 Complex impedance plots for 1.0 M KOH + 1.0 M C H OH
oxidation on Pd/C catalyst at room temperature as a function of
potential (a) between ꢀ0.6 and ꢀ0.2 V; (b) between ꢀ0.1 and 0.05 V;
(
c) between 0.1 and 0.4 V.
Based on the voltammetric and impedance results, the
equivalent circuit shown in Fig. 7 was used to t the EIS data.
Fig. 7(a) depicts the equivalent circuit for the electrodes that
exhibit normal impedance behaviors on Rh/C and Pd/C elec-
trodes. Constant-phase element (CPE) is the double-layer
capacitance. RS and RCT are the solution resistance and
charge-transfer resistance, respectively. For the special imped-
ance behaviors observed on Rh/C electrode at ꢀ0.3 to ꢀ0.1 V
and ꢀ0.1 to ꢀ0.05 V on Pd/C electrode, the equivalent circuit is
Fig. 8
R
CT of ethanol electrooxidation at Rh/C and Pd/C electrodes.
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 91829–91835 | 91833

View Article Online
RSC Advances
Paper
3
Fig. 10 Standard curve of NaHCO solution.
Fig. 9 Comparison of the single AEM DEFC constant-current dis-
charging curves respectively using Pd/C and Rh/C electrodes as the
anode at room temperature.
E ¼ ꢀ199.8 + 48.2 lg C
(1)
ethanol fuel cell (AEM DEFC) that consists of Rh/C (or Pd/C)
In this investigation, CO
2
ion selective electrode is used to
anode, an AEM, and a MnO /C cathode at room temperature.
2
detect CO concentration in the three sample solutions and the
2
The constant-current discharging tests are carried out by
data are tabulated in Table 2. As shown in Table 2, the E of Pd/C,
Rh/C and blank group is ꢀ308, ꢀ278 and ꢀ402, respectively.
Substituting E into eqn (1), the C(CO ) can be obtained. And n(CO )
can be calculated by the volume of the three sample solutions. As
shown in Table 2 and Fig. 11, the CO concentration in black
group is very low, while that in the group Pd/C and Rh/C are
higher than black group. The reason is that ethanol is converted
2 2
to CO by catalytic oxidation. It also be noted that the CO
ꢀ2
varying the current density at 15, 20 and 30 mA cm . It can be
observed that the cell voltage of the fuel cell decreases with the
current density; for instance, in Rh/C electrode, when the
2
2
ꢀ
2
current density increases from 15, 20, to 30 mA cm , the cell
voltage decreases from 0.57, 0.55 to 0.45 V, respectively.
However, the cell voltages for Pd/C are 0.41, 0.37 and 0.32 V
respectively, which are much lower than Rh/C under the same
current density. In addition, it is clear from Fig. 6 that the cell
voltage for Rh/C is more stable than that of Pd/C under the same
current density, which further shows that Rh/C electrode
exhibits much better catalytic activity and stability than Pd/C.
2
ꢀ2
concentration in Rh/C group (1.628 ꢂ 10 M) is higher than that
ꢀ
3
of Pd/C (3.529 ꢂ 10 M), indicating that Rh/C has better catalytic
ability. By further calculation, the selectivity for ethanol oxidation
to CO on the Pd/C and Rh/C are 2.18% and 10.07%, respectively.
2
A dual-path mechanism for ethanol oxidation in alkaline
3
.6 Oxidation product analysis through CO ion selective
23,33
2
media was proposed.
ethanol remains intact upon oxidation. Ethanol is converted to
acetaldehyde and eventually to acetic acid/acetate. In the C
2
In the C -pathway, the C–C bond of
electrode
-
The CO ion selective electrode is merely responsive and very
1
2
pathway, the C–C bond can be broken in ethanol or acetalde-
sensitive to CO and it displays different potential values in the
2
hyde, leading eventually to carbon dioxide (or (bi)carbonate).
solution with different CO concentrations. As shown in Table
2
For the Pd/C, the selectivity for ethanol oxidation to CO
Pd/C is only 2.18% and much less than that on the Rh/C
10.07%). This suggests that the ability of Pd for breaking C–C
bond in ethanol to produce CO is very limited. Therefore, the
-pathway will be considered on the Pd/C. This assumption is
reasonable considering that the selectivity for ethanol oxidation
to CO on the Pd/C was determined to be as low as 2.5% by the
2
on the
1
, different concentrations of NaHCO
3
solution ranging from
to 10 M correspond to different E. Then tting E and
lg C(CO2) of different concentrations, a standard curve can be
obtained as shown in Fig. 10. It can be observed that E and
lg C(CO2) are in linear relationship, thus a standard eqn (1) can
ꢀ5
ꢀ1
10
(
ꢀ
2
C
2
ꢀ
be achieved:
2
Table 1 The E value of NaHCO
3
standard solution
Table 2 The data of sample solutions
ꢀ1
C
(NaHCO3) (mol L
)
ꢀlg C(CO2)
E (mV)
Sample
ꢀ5
ꢀ4
ꢀ3
ꢀ2
ꢀ1
ꢀ1
1
1
1
1
1
0
5
4
3
2
1
ꢀ443
ꢀ390
ꢀ344
ꢀ296
ꢀ249
solution
Volume (mL) E (mV) C(CO2) (mol L
)
n(CO2) (mol)
0
0
0
0
ꢀ3
ꢀ2
ꢀ5
ꢀ6
Pd/C
Rh/C
Blank group 2.5
2.5
2.5
ꢀ318
ꢀ286
ꢀ402
3.529 ꢂ 10
1.628 ꢂ 10
6.382 ꢂ 10
8.824 ꢂ 10
4.069 ꢂ 10
1.596 ꢂ 10
ꢀ5
ꢀ7
91834 | RSC Adv., 2015, 5, 91829–91835
This journal is © The Royal Society of Chemistry 2015

View Article Online
Paper
RSC Advances
7
8
9
L. Jiang, A. Hsu, D. Chu and R. Chen, Int. J. Hydrogen Energy,
2010, 35, 365–372.
J. Anderson, A. Karakoti, D. J. D ´ı az and S. Seal, J. Phys. Chem.
C, 2010, 114, 4595–4602.
J. Melke, A. Schoekel, D. Gerteisen, D. Dixon,
F. Ettingshausen, C. Cremers, C. Roth and D. E. Ramaker,
J. Phys. Chem. C, 2012, 116, 2838–2849.
1
1
1
1
1
1
0 M. Subhramannia, K. Ramaiyan and V. K. Pillai, Langmuir,
2008, 24, 3576–3583.
1 T. Maiyalagan, B. Viswanathan and U. Varadaraju, J. Nanosci.
Nanotechnol., 2006, 6, 2067–2071.
2 K. Chen, P. Shen and A. Tseung, J. Electrochem. Soc., 1995,
1
42, L185–L187.
3 P. K. Shen and C. Xu, Electrochem. Commun., 2006, 8, 184–
88.
4 C. Xu, P. K. Shen and Y. Liu, J. Power Sources, 2007, 164, 527–
31.
1
2
Fig. 11 CO concentration in sample solutions.
5
5 F. Hu, C. Chen, Z. Wang, K. S. Pei and G. Wei, Electrochim.
Acta, 2006, 52, 1087–1091.
22
FTIR experiments. The selectivity for ethanol oxidation to CO2
on the on the Rh/C is ve times as much as Pd/C, indicating Rh/ 16 Z. Liang, T. Zhao, J. Xu and L. Zhu, Electrochim. Acta, 2009,
C catalyst has a better capability for breaking the C–C bond
54, 2203–2208.
cleavage. The oxidation ethanol on the Rh/C can be contributed 17 R. Singh and A. Singh, Carbon, 2009, 47, 271–278.
via both the C
1
-pathway and the C
2
-pathway.
18 Q. He, W. Chen, S. Mukerjee, S. Chen and F. Laufek, J. Power
Sources, 2009, 187, 298–304.
1
2
2
2
2
2
2
9 M. Li, N. S. Marinkovic and K. Sasaki, Electrocatalysis, 2012,
4
. Conclusions
3
, 376–385.
In this work, Rh/C and Pd/C were synthesized by microwave
heating-glycol reduction method. Electrochemical evaluation
shows that Rh/C catalyst has a higher activity and stability towards
ethanol oxidation in alkaline media at room temperature. As
compared to Pd/C electrode, the onset potential on Rh/C is shied
negatively as much as 0.28 V and the backward peak current on
Rh/C was smaller 78 mA. Moreover, in a direct fuel cell, Rh/C has
higher activity and stability than Pd/C. The Rh/C catalyst is more
resistant to the poise caused by adsorbed oxygen intermediates
than the Pd/C catalyst. Finally, the selectivity for ethanol oxidation
´
0 A. Kowal, S. L. Gojkovic, K. S. Lee, P. Olszewski and
Y. E. Sung, Electrochem. Commun., 2009, 11, 724–727.
1 J. P. I. d. Souza, S. L. Queiroz, K. Bergamaski, E. R. Gonzalez
and F. C. Nart, J. Phys. Chem. B, 2002, 106, 9825–9830.
2 Z. Y. Zhou, Q. Wang, J. L. Lin, N. Tian and S. G. Sun,
Electrochim. Acta, 2010, 55, 7995–7999.
3 L. Ma, D. Chu and R. Chen, Int. J. Hydrogen Energy, 2012, 37,
1
1185–11194.
4 A. Dutta and J. Datta, J. Phys. Chem. C, 2012, 116, 25677–
5688.
5 Q. He, S. Mukerjee, B. Shyam, D. Ramaker, S. Parres-
2
2
to CO on the Rh/C is ve times as much as Pd/C. This is mainly
due to the relatively inert nature of Rh/C on C–C bond cleavage
and the different reaction pathways on Pd/C and Rh/C.
Esclapez, M. J. Illan-Gomez and A. Bueno-Lopez, J. Power
´
´
´
Sources, 2009, 193, 408–415.
2
2
2
2
3
3
3
3
6 S. K. Murphy, J. W. Park, F. A. Cruz and V. M. Dong, Science,
2015, 347, 56–60.
7 Y. Wang, X. Wang and C. M. Li, Appl. Catal., B, 2010, 99, 229–
References
1
2
3
A. L. West, M. H. Griep, D. P. Cole and S. P. Karna, Anal.
Chem., 2014, 86, 7377–7382.
Y. H. Qin, H. C. Li, H. H. Yang, X. S. Zhang, X. G. Zhou, L. Niu
and W. K. Yuan, J. Power Sources, 2011, 196, 159–163.
S. Song, W. Zhou, Z. Liang, R. Cai, G. Sun, Q. Xin,
V. Stergiopoulos and P. Tsiakaras, Appl. Catal., B, 2005, 50,
234.
8 J. Liu, J. Ye, C. Xu, S. P. Jiang and Y. Tong, Electrochem.
Commun., 2007, 9, 2334–2339.
9 M. W. Xu, G. Y. Gao, W. J. Zhou, K. F. Zhang and H. L. Li,
J. Power Sources, 2008, 175, 217–220.
0 Y. Suo and I. M. Hsing, Electrochim. Acta, 2009, 55, 210–
65–72.
2
17.
1 I. M. Hsing, X. Wang and Y. J. Leng, J. Electrochem. Soc., 2002,
49, A615–A621.
2 G. X. Cai, J. W. Guo, J. Wang and S. Li, J. Power Sources, 2015,
76, 279–290.
4
5
C. Coutanceau, L. Demarconnay, C. Lamy and J.-M. L ´e ger, J.
Power Sources, 2006, 156, 14–19.
W. J. Zhou, S. Q. Song, W. Z. Li, Z. H. Zhou, G. Q. Sun, Q. Xin,
S. Douvartzides and P. Tsiakaras, J. Power Sources, 2005, 140,
1
2
50–58.
¨
3 S. C. Lai, S. E. Kleijn, F. T. Ozt u¨ rk, V. C. van Rees Vellinga,
6
Q. He, S. Mukerjee, B. Shyam, D. Ramaker, S. Parres-
Esclapez, M. J. Ill ´a n-G ´o mez and A. Bueno-L ´o pez, J. Power
Sources, 2009, 193, 408–415.
J. Koning, P. Rodriguez and M. T. Koper, Catal. Today,
2010, 154, 92–104.
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 91829–91835 | 91835