Nano-composite based on platinum particles and modified polyaniline for methanol, formic acid, and ethanol oxidation

Article abstract of DOI:10.1002/jccs.201300634

Polyaniline (PANI) is doped with poly(styrenesulfonic acid) (PSS) via a doping-dedoping-redoping process. Fourier transform infrared (FT-IR) spectroscopy results confirm that PANI is doped with PSS. X-ray photoelectron spectroscopy (XPS) results indicate that the strong interaction between Pt particles and sulfonic acid groups of PANI-PSS. Scanning electron microscopy (SEM) images reveal that PANI-PSS is composed of highly porous nanowires. Platinum (Pt) can be deposited onto PANI-PSS film using the potentiostatic mode to obtain PANI-PSS-Pt composite electrode. Transmission electron microscopy (TEM) image result indicates that Pt particles are dispersed uniformly into the electrode. The effects of concentration on electrocatalytic oxidation of ethanol, formic acid, and methanol are investigated. Cyclic voltammetry results and chronoamperometric response measurements show that the activity and stability toward methanol oxidation of the PANI-PSS-Pt electrode are better than those of the PANI-PSS-Pt electrodes toward ethanol and formic acid oxidation. Pt particles are successfully embedded into the PANI-PSS nanowire network structure to form a PANI-PSS-Pt composite electrode. The anodic currents of methanol and formic acid oxidation have optimum H2SO4 concentration at 0.5 M. Cyclic voltammetry results and chronoamperometric response measurements show that the activity and stability toward methanol oxidation of the PANI-PSS-Pt electrode are better than those toward ethanol and formic acid oxidation.

Full text of DOI:10.1002/jccs.201300634

JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Article
Nano-composite Based on Platinum Particles and Modified Polyaniline for Methanol,
Formic Acid, and Ethanol Oxidation
Chung-Wen Kuo,a Cheng-Jang Tsai,b Wan-Ping Chen,a Pin-Rong Chen,c Tzi-Yi Wuc,* and
Ching-Guey Tsenga
aDepartment of Chemical and Materials Engineering, National Kaohsiung University of Applied Sciences, Kaohsiung
80778, Taiwan
bDepartment of Energy Application Engineering, Far East University, 74448 Tainan, Taiwan, ROC
cDepartment of Chemical Engineering and Materials Engineering, National Yunlin University of Science and
Technology, Yunlin 64002, Taiwan
(Received: Dec. 5, 2013; Accepted: Mar. 4, 2014; Published Online: Mar. 26, 2014; DOI: 10.1002/jccs.201300634)
Polyaniline (PANI) is doped with poly(styrenesulfonic acid) (PSS) via a doping-dedoping-redoping pro-
cess. Fourier transform infrared (FT-IR) spectroscopy results confirm that PANI is doped with PSS. X-ray
photoelectron spectroscopy (XPS) results indicate that the strong interaction between Pt particles and
sulfonic acid groups of PANI-PSS. Scanning electron microscopy (SEM) images reveal that PANI-PSS is
composed of highly porous nanowires. Platinum (Pt) can be deposited onto PANI-PSS film using the
potentiostatic mode to obtain PANI-PSS-Pt composite electrode. Transmission electron microscopy
(TEM) image result indicates that Pt particles are dispersed uniformly into the electrode. The effects of
concentration on electrocatalytic oxidation of ethanol, formic acid, and methanol are investigated. Cyclic
voltammetry results and chronoamperometric response measurements show that the activity and stability
toward methanol oxidation of the PANI-PSS-Pt electrode are better than those of the PANI-PSS-Pt elec-
trodes toward ethanol and formic acid oxidation.
Keywords: Polyaniline; Nanowires; Electrocatalytic oxidation; Cyclic voltammetry.
INTRODUCTION
Direct alcohol fuel cells (DAFCs) are considered
porting materials for the dispersion of Pt particles play an
important role in methanol/formic acid/ethanol oxida-
tion.17
promising power sources for electric vehicles and elec-
tronic portable devices when compared to conventional re-
chargeable power sources, such as Li ion batteries.1-11
There are many variable types of fuel cells,12-14 such as pro-
ton exchange membrane, phosphoric acid, alkaline, solid
oxide, and molten carbonate fuel cells. Among these, pro-
ton exchange membrane fuel cells (PEMFC) based on
methanol, formic acid, and ethanol have aroused particular
interests because of their high power density, high vehicle
efficiency, low pollutant emission, rapid response to varia-
tions in loading, long life, simple system design, and low
operating temperature. However, important problems must
be still solved to make PEMFC commercially viable, such
as the relatively poor kinetics of the methanol, formic acid,
and ethanol oxidation on the anode, generally a Pt-based
catalyst, and the self-poisoning of the Pt catalyst by (CO)ad,
an intermediate product of the methanol/formic acid/etha-
nol oxidation.15 To overcome these problems, researchers
have utilized catalysts with a high surface area.16 The sup-
The development of a supporting material is essential
to minimize noble metal loadings and achieve optimum
catalytic performance. A promising strategy for the devel-
opment of a supporting material is the introduction of con-
ducting polymers (CPs). CPs, showing interesting optical,
electrochemical, and electrical properties are attractive
candidates for composite components.18-24 CPs are widely
employed as porous supports on which electrocatalysts are
dispersed and make low-loading catalysts feasible for fuel
cell operation, lowering the cost of the system. It has been
shown that electrodes modified with a polymer exhibit
better catalytic performance for methanol/formic acid/eth-
anol oxidation than those without a polymer.25
CPs used as host matrices for the development of
such systems are mainly polyaniline (PANI),26-28 polypyr-
role (PPy),29 and polythiophene (PT)30 by virtue of their ex-
cellent conducting properties and very good adhesion to
the substrate electrode. Among these conducting polymers,
Special Issue for Green & Sustainable Chemistry
* Corresponding author. E-mail: wuty@yuntech.edu.tw
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PANI is the most widely studied due to its inherent charac-
teristics of unique electronic properties, simple synthesis
process, environmental stability, and low cost. Recently,
one-dimensional micro/nanostructured PANI has attracted
interest as a potential building block for miniaturized nano-
electronic devices31 and highly sensitive (or biological)
sensors.32 Moreover, the introduction of PANI into the
electrode catalyst layer increases Pt utilization, and thus
less Pt is required. Furthermore, functionalized polymeric
acids have been doped for PANI to increase its applicabil-
ity. For instance, poly(styrenesulfonic acid) (PSS) has been
shown to be easily incorporated in a CP matrix as a dopant
of support for Pt particles. Huang et al.33 reported that
PANI-PSS acts as a matrix that leads to the uniform distri-
bution of Pt particles. As a result, the electrocatalytic activ-
ity for methanol oxidation of PANI-PSS-Pt is much higher
than that of PANI-Pt.
constant potential of -0.2 V (vs. Ag/AgCl). After Pt particle incor-
poration, the electrode was rinsed with double distilled water for
5 min and then dried at 120 °C for 3 min. The weight of Pt loaded
into PANI-PSS is calculated using XPS, and it is 79 mg cm-2.
Physical and electrochemical characterizations: The
Fourier transform infrared (FT-IR) spectra of PANI-H2SO4 (emer-
aldine salt), emeraldine base (EB), and PANI redoped with PSS
(PANI-PSS, emeraldine salt) in KBr pellets were obtained using a
Perkin Elmer FT-IR instrument with a resolution of 4 cm-1. The
average of 16 scans was used to obtain each spectrum. All sam-
ples were vacuum-dried overnight prior to measurement. An
X-ray photoelectron spectroscopy (XPS) study was performed
using an ESCA 210 spectrometer with Mg Ka (hn = 1253.6 eV)
irradiation as the photon source. The primary tension was 12 kV
and the pressure during the scans was approximately 10-10 mbar.
The surface morphologies of PANI-PSS and PANI-PSS-Pt films
were compared using a scanning electron microscope (SEM)
(JEOL JSM-6700F) equipped with an energy-dispersive X-ray
spectroscopy (EDS) detector. The morphology was characterized
by Transmission electron microscopy (TEM, JEOL 1200 EX) at a
100 kV accelerating voltage. Specimens for TEM were prepared
by spreading a small drop of one of the sample solutions onto a
400-mesh copper grid. The drop was dried in air at room tempera-
ture for nearly 4 days.
In the work, PANI doped with PSS forms a spatial
network structure, which behaves as a 3D-random matrix
for the deposition Pt particles. The electrocatalytic activi-
ties of these composite catalysts were evaluated by cyclic
voltammetry and chronoamperometry methods in 0.1 M
C2H5OH + 0.5 M H2SO4 solution, 0.1 M HCOOH + 0.5 M
H2SO4 solution, and 0.1 M CH3OH + 0.5 M H2SO4 solu-
tion. The comparison of PANI-PSS films as platinum cata-
lyst support for methanol, formic acid, and ethanol elec-
tro-oxidation has been studied.
Electrochemical characterizations of PANI-PSS-Pt com-
posite electrodes toward the ethanol, formic acid, and methanol
oxidation were carried out using a CHI627D electrochemical ana-
lyzer (U.S.A.). All experiments were performed in a three-com-
ponent cell. An Ag/AgCl electrode (in 3 M KCl), a Pt wire, and SS
(1-cm2 area) were used as the reference, counter, and working
electrodes, respectively. ALuggin capillary, whose tip was set at a
distance of 1-2 mm from the surface of the working electrode, was
used to minimize errors due to the iR drop in the electrolytes.
Electro-oxidation and stability for PANI-PSS-Pt elec-
trodes toward ethanol, formic acid, and methanol: The cata-
lytic activities of PANI-PSS-Pt composite electrodes were exam-
ined by cyclic voltammetry (CV) at 0.1 M C2H5OH + 0.5 M
H2SO4 solution, 0.1 M HCOOH + 0.5 M H2SO4 solution, and 0.1
M CH3OH + 0.5 M H2SO4 solution. Chronoamperometric re-
sponse curves were obtained at 0.6 V. All the electrochemical ex-
periments were carried out at room temperature.
EXPERIMENTAL
Preparation of PANI-PSS: A mixture solution of 50 mM
aniline (Merck) and 0.5 M H2SO4 (Merck) aqueous solution was
prepared. The electrochemical polymerization of the solution was
carried out using the galvanostatic method with stainless steel 316
(SS) as the working electrode for a charge of 0.1 C cm-2; details of
the procedure are described elsewhere.34 Before each experiment,
the SS was cleaned in an ultrasonic bath using detergent, deion-
ized water, and isopropanol, and then dried in a nitrogen flow. The
electrochemically deposited PANI film was rinsed with double
distilled water for 5 min and then dried at 120 °C for 3 min. The
emeraldine base (EB) form of PANI was obtained by treating the
PANI film in 0.1 M ammonium hydroxide (Aldrich) for 3 min.
The EB film was then redoped with PSS (Mw = 70,000, Aldrich).
EB film redoped with PSS is denoted as PANI-PSS.
RESULTS AND DISCUSSION
Deposition of Pt into PANI-PSS matrixes: Pt particles
were incorporated into PANI-PSS film via electrochemical depo-
sition from 0.01 M HCl + 0.1 M KCl solution containing 5 mM
H2PtCl6×6H2O with a constant deposition charge of 0.15 C at a
FT-IR analysis of PANI-PSS
The FT-IR spectra of doped PANI (electrochemical
polymerization of PANI in H2SO4 medium), dedoped PANI
(EB), and PANI redoped with PSS are shown in Fig. 1a-c,
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respectively. The doped PANI (doped with H2SO4, curve a)
exhibits some peaks. The absorption peak at 801 cm-1 is at-
tributed to the para-substituted aromatic out-of-plane bend-
ing. The absorption peaks of the -S=O group in PANI-
H2SO4 are located at 1000 and 1020 cm-1. The -C-N stretch-
ing vibration of PANI is observed clearly at 1300 cm-1. The
main characteristic peaks at 1560 and 1480 cm-1 are as-
cribed to the stretching vibrations of the -C=N quinonoid
and the -C=C benzenoid rings of PANI doped with H2SO4,
respectively.23 Dipping the emeraldine salt of PANI with
ammonium hydroxide yields the dedoped form of PANI,
whose two main characteristic peaks (1560 and 1480 cm-1)
shift to 1590 and 1500 cm-1 (curve b), respectively. After
the dedoped form of PANI is redoped by PSS, the two main
characteristic peaks shift to 1564 and 1470 cm-1 (curve c),
respectively. This indicates that PANI can be doped with
PSS via a simple doping-dedoping-redoping technique.
XPS analysis
is shown in Fig. 2c(I). The curve shows binding energy de-
pending on the S location of PSS. The peak at 168.5 eV is
from the sulfur atom of PSS dopants. After the addition of
Pt particles on PANI-PSS film, significant changes oc-
curred in S2p core value of PANI-PSS. The curve (II) shows
the formation of a weak peak (C-S-Pt binding energy) at
Figure 2a shows the survey scan of the PANI-PSS and
PANI-PSS-Pt nanocomposite materials. It is evident from
the spectra that the survey scan of the PANI-PSS-Pt nano-
composite is similar to that of the spectra obtained for the
PANI-PSS. The PANI-PSS-Pt with the signals due to C1s,
N1s, O1s, S2p, Pt4f, and Pt4d can be also seen. To understand
the incorporation of Pt particles, a survey scan in the Pt4f re-
gion was made (Fig. 2b). Pt4f7/2 and Pt4f5/2 peaks are cen-
tered at 71.3 and 74.7 eV, respectively. Also, XPS study
was employed to analyze the binding energy related to S2p
core-level spectra of PANI-PSS and PANI-PSS-Pt. The
sulfur core level spectrum of PANI-PSS film coated on SS
Fig. 2. XPS spectra of (a) the survey scan for PANI-
PSS (I) and PANI-PSS-Pt (II). (b) XPS spectra
of Pt 4f for PANI-PSS-Pt. (c) XPS spectra of S2p
for PANI-PSS (I) and PANI-PSS-Pt (II).
Fig. 1. FT-IR spectra of (a) PANI-H2SO4 (emeraldine
salt), (b) emeraldine base (EB) PANI, and (c)
PANI redoped with PSS (PANI-PSS, emeral-
dine salt).
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163 eV. This evaluation is a good agreement for typical
C-S-metal bonds appearing in the range between 164 eV
and 162 eV.35 Jönsson et al.36 reported that aluminum/
PEDOT-PSS contains an interfacial layer formed by chem-
ical interactions between aluminum and mainly sulfonic
groups of poly(styrenesulfonic acid) (PSS). The sulfur at-
oms of PSS might be bonded with Pt atoms. From the anal-
ysis of S elements, we concluded that the strong interaction
between Pt particles and sulfonic acid groups of PANI-
PSS.
PANI-PSS electrode. The bright spots indicate the exis-
tence of Pt in PANI-PSS.
Fig. 3c, 3d, and 3e are the TEM images of Pt particles
incorporated into PANI-PSS with electrochemical deposi-
tion charge of 0.10 C, 0.15 C, and 0.20 C at a constant po-
tential of -0.2 V (vs. Ag/AgCl), respectively, the black
spots indicate the Pt in the electrodes. PANI doped with
PSS nanowires shows typical diameters in the range of 50-
80 nm. The particle size of Pt on the electrodes is ca. 20-90
nm in Fig 3c and 3d. However, the aggregation of Pt parti-
cles can be clearly seen in Fig 3e. The particle size of Pt in
Fig 3d is smaller than that in Fig 3e. PANI doped with PSS
to form a spatial network structure (3D-random matrix),
Surface morphology of PANI-PSS and PANI-PSS-Pt
electrodes
Pt particles were incorporated into PANI-PSS film by
electrochemical deposition at a constant potential of -0.2 V
(vs. Ag/AgCl) with a charge of 0.15 C. Fig. 3a-b show the
scanning electron microscopy (SEM) analysis results of
surface morphology of PANI-PSS and PANI-PSS-Pt elec-
trodes; Pt particle mapping analysis result for PANI-PSS-
Pt is shown in the inset. The nanowire morphology of
PANI-PSS film can be clearly seen in Fig. 3a. The PANI-
PSS nanowires were found to have an average diameter of
40-80 nm. It is noted that the incorporation of Pt prrticles
into PANI-PSS does not significantly change the nanowire
morphology. We believe that Pt particles were incorporated
into the PANI-PSS nanowire network structures. Pt parti-
cles cannot be clearly seen on PANI-PSS-Pt composite
electrodes from SEM image (Fig. 3b). Hence, particle map-
ping analysis was conducted to examine the surface mor-
phology. The inset in Fig. 3b shows EDS result of Pt in
SO3 groups of PANI-PSS help the uptake of Pt4+ ions, and a
-
protective layer prevents the aggregation of Pt particles af-
ter Pt formation. The homogenous distribution of Pt in the
PANI-PSS spatial network structure may increase the use
of Pt for ethanol, formic acid, and methanol oxidation.
Electrocatalytic activity of PANI-PSS-Pt for ethanol,
formic acid, and methanol oxidation
Cyclic voltammograms (CVs) are convenient and
useful tools for investigating the electrocatalytic activity of
test electrodes for ethanol, formic acid, and methanol oxi-
dation. Fig. 4a-c show the CVs of PANI-PSS-Pt composite
electrodes in 0.5 M H2SO4 solution containing 0.1 M etha-
nol, 0.1 M formic acid, and 0.1 M methanol, obtained at a
scan rate of 10 mV s-1, respectively. The onset potential val-
ues of the electrodes toward ethanol, formic acid, and
methanol oxidation occur at about 0.41, 0.40, and 0.39 V
Fig. 3. SEM images of (a) PANI-PSS and (b) PANI-
PSS-Pt (Pt particles deposition charge of 0.15
C). Inset in (b) shows X-ray map (bright spots
indicate Pt). TEM images of Pt particles incor-
porated into PANI-PSS with electrochemical
deposition charge of (c) 0.10 C (d) 0.15 C (e)
0.20 C at a constant potential of -0.2 V (vs.
Ag/AgCl), respectively.
Fig. 4. Cyclic voltammograms of PANI-PSS-Pt in (a)
0.1 M C2H5OH + 0.5 M H2SO4 solution, (b) 0.1
M HCOOH + 0.5 M H2SO4 solution, and (c) 0.1
M CH3OH + 0.5 M H2SO4 solution with a scan-
ning rate of 10 mV s-1.
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Table 1. Cyclic voltammetric data for PANI-PSS-Pt electrodes in
solutions of 0.1 M CH3OH + 0.5 M H2SO4, 0.1 M
HCOOH + 0.5 M H2SO4, and 0.1 M C2H5OH + 0.5 M
H2SO4, respectively
for PANI-PSS-Pt, respectively, indicating that PANI-PSS-
Pt has superior electrocatalytic performance in methanol
solution. The CV of the PANI-PSS-Pt electrode (curve a)
toward ethanol oxidation shows that there is weak charac-
teristic peak at 0.60 V, indicating that PANI-PSS-Pt is
electrocatalytically low active toward ethanol oxidation.
Comparing the CV results of PANI-PSS-Pt electrodes for
ethanol, formic acid, and methanol oxidation, the highest
oxidation current toward methanol oxidation can be ob-
served for the PANI-PSS-Pt electrode. For instance, maxi-
mum anodic peak mass specific current densities (Jpa in Ta-
ble 1) of 25.1, 14.0, and 3.5 mAcm-2 mg-1 toward methanol,
formic acid, and ethanol oxidation can be observed at about
0.60 V, respectively.
Methanol
Formic acid
Ethanol
Jpa (mA cm-2 mg-1)
Onset (V)
25.1
0.39
14.0
0.40
3.50
0.41
To remove the poisonous (CO)ad intermediate is to
oxidize it by reacting with OHads formed by the dissociation
of water molecules on Pt surface (step 6 and 7).
The electrocatalytic oxidation of ethanol at Pt begins
with its oxidative adsorption (step 8 and 9) followed by its
oxidative dissociation to a mixture of -CHx and oxygen
containing species (step 10 and 11)40,41
The mechanism is proposed for the oxidation of meth-
anol in 0.5 M H2SO4 at the PANI-PSS-Pt electrode by the
dissociative adsorption process. The current for the metha-
nol oxidation increases slowly below 0.4 V in the forward
sweep. This is due to the formation of reaction intermedi-
ates.37,38.
CH3CH2OH + Pt ® Pt-O-CH2CH3 + H+ + e-
CH3CH2OH + Pt ® Pt-CH(OH)CH3 + H+ + e-
Pt-O-CH2CH3 or Pt-CH(OH)CH3 ®
Pt-CHOCH3 + H+ + e-
(8)
(9)
(10)
Pt-O-CH2CH3 or Pt-CH(OH)CH3 ®
Pt-CHx + Pt-CHyO + (5-x-y)H+ + (5-x-y) e- (11)
CH3OH + Pt ® Pt-(CHZO)ad + (4-Z)H+ + (4-Z) e-
(0 £ Z £ 4)
(1)
Both the adsorbed Pt-CHx and Pt-CHyO type species
can be further oxidized to adsorbed CO (step 12) and then
to CO2 (step 13).
The current increases quickly and reaches a peak at
around +0.6 V. This is ascribed to the partial oxidation of
surface Pt, which helps the transformation of intermediates
to carbon dioxide:
Pt-CH2O ® Pt-(CO)ad + 2H+ + 2e-
(12)
(13)
Pt-(CO)ad + Pt-OH ® 2Pt + CO2 + H+ + e-
Pt + H2O ® Pt-OH + H+ + e-
(2)
(3)
Pt-(CHZO)ad + (2+Z)Pt-OH ®
(2+Z)Pt + CO2 + (1+Z)H2O (0 £ Z £ 4)
Effect of ethanol/formic acid/methanol and H2SO4
concentration
The effect of ethanol, formic acid, and methanol con-
centration at PANI-PSS-Pt electrodes on the anodic current
of electrocatalytic oxidation is shown in Fig. 5. It is clearly
observed that the anodic peak mass specific current density
(Jpa) of methanol oxidation increases with increasing meth-
anol concentration and levels off at concentrations higher
than 0.7 M (Fig. 5c). This effect can be attributed to the sat-
uration of active sites at the surface of the electrode, the op-
timum concentration of methanol for a higher current den-
sity may be considered as about 0.7 M.17 The Jpa of formic
acid oxidation increases with increasing formic acid con-
centration (Fig. 5b). Under similar conditions, the Jpa of
ethanol oxidation increases with increasing ethanol con-
centration slowly (Fig. 5a).
On the backward sweep, the peak corresponds to
methanol adsorption occurs at a less negative potential (0.5
V) than noticed on the forward sweep (0.6 V). This can be
ascribed to the presence of fresh naked Pt available from
the reduction of Pt oxide during the negative sweep.
Similarly, the mechanism is proposed for the oxida-
tion of formic acid in 0.5 M H2SO4 at the PANI-PSS-Pt
electrode as explained below (step 4 to 7).39
HCOOH + Pt ® Pt-(HCOOH)ad + H+ + e-
Pt-(HCOOH)ad ® Pt-(CO)ad + H2O
Pt + H2O ® Pt-OH + H+ + e-
(4)
(5)
(6)
(7)
Pt-(CO)ad + Pt-OH ® 2Pt + CO2 + H+ + e-
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The effect of H2SO4 concentration on the Jpa related to
crease in H2SO4 concentration depressed the Jpa. Under
similar conditions, a similar behavior was observed for
electrooxidation of formic acid at the electrode (Fig. 6b). In
high concentrations of H2SO4, the dissociation of acid de-
creases that causes the reduction of the solution conductiv-
ity.42
the electrooxidation of ethanol, formic acid, and methanol
at the electrode has been investigated by cyclic voltam-
metry. The variation of Jpa obtained for ethanol, formic
acid, and methanol oxidation were plotted against H2SO4
concentration in Fig. 6. The Jpa of ethanol oxidation (Fig.
6a) decreases slowly with the increase of H2SO4 concentra-
tion, and then levels off at concentrations higher than 0.7
M. The Jpa of methanol oxidation (Fig. 6c) decreases with
the increase of H2SO4 concentration to 0.3 M, and then it
has optimum H2SO4 concentration at 0.5 M, further in-
Fig. 7a-c show dependence of the peak current on the
scan rate by cyclic voltammograms for PANI-PSS-Pt elec-
trodes in 0.5 M H2SO4 solution containing 0.1 M ethanol,
0.1 M formic acid, and 0.1 M methanol, respectively. It is
known that the linearity of a plot of peak current density
(jpa) versus scan rates (v) corresponds to the surface-bound
transport process and a different type of linear for the plot
of peak current density versus v1/2 signifies a diffusion con-
trolled process.43 The slope values of the double logarith-
mic plots are 0.86, 0.52, and 0.35 for PANI-PSS-Pt elec-
trodes towards the ethanol, formic acid, and methanol oxi-
dation, respectively. Thus, PANI-PSS-Pt electrodes to-
wards the ethanol, formic acid, and methanol oxidation
have surface-bound transport processes.
Long-time operation stability of PANI-PSS-Pt for
ethanol, formic acid, and methanol oxidation
The performance of PANI-PSS-Pt electrodes toward
the ethanol, formic acid, and methanol oxidation reaction
after long-time operation was tested using chronoampero-
metry. Fig. 8 shows the chronoamperograms of PANI-
PSS-Pt electrodes recorded at 0.6 V in solutions of 0.1 M
C2H5OH + 0.5 M H2SO4, 0.1 M HCOOH + 0.5 M H2SO4,
and 0.1 M CH3OH + 0.5 M H2SO4 for 120 min. After long-
Fig. 5. Plot of anodic peak mass specific current den-
sity as a variable (a) C2H5OH, (b) HCOOH, and
(c) CH3OH concentration for PANI-PSS-Pt
electrodes. Supporting electrolyte: 0.5 M
H2SO4. Scan rate: 10 mV s-1.
Fig. 7. Dependence of the peak current density on the
scan rate by cyclic voltammograms for PANI-
PSS-Pt electrodes in (a) 0.1 M C2H5OH + 0.5 M
H2SO4 solution, (b) 0.1 M HCOOH + 0.5 M
H2SO4 solution, and (c) 0.1 M CH3OH + 0.5 M
H2SO4 solution.
Fig. 6. The variation of anodic peak mass specific cur-
rent density for (a) 0.1 M C2H5OH, (b) 0.1 M
HCOOH, and (c) 0.1 M CH3OH electrooxida-
tion vs. H2SO4 concentration on PANI-PSS-Pt
electrodes with a scanning rate of 10 mV s-1.
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Science Council of Taiwan under NSC 101-2221-E-151-
058, NSC 102-2221-E-224-055, and NSC 102-2221-E-
269-016 is gratefully acknowledged.
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Fig. 8. Chronoamperometric responses of PANI-PSS-
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time operation, a steady state current density was achieved.
Comparing the chronoamperograms results of the elec-
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nol oxidation maintained the highest current density. For
example, the J at 100 min was 0.1 mA cm-2 mg-1 in 0.1 M
C2H5OH + 0.5 M H2SO4 solution (curve a), 0.51 mA cm-2
mg-1 in 0.1 M HCOOH + 0.5 M H2SO4 solution (curve b),
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PANI-PSS nanowires can be synthesized via a dop-
ing-dedoping-redoping method. Pt particles were success-
fully embedded into the PANI-PSS nanowire network struc-
ture to form a PANI-PSS-Pt composite electrode. The com-
parison of PANI-PSS-Pt electrodes towards the ethanol,
formic acid, and methanol electro-oxidation has been stud-
ied. The anodic currents of methanol and formic acid oxi-
dation have optimum H2SO4 concentration at 0.5 M. In ad-
dition, the electro-oxidation of ethanol, formic acid, and
methanol on the electrodes are surface-bound transport
processes. Among the ethanol, formic acid, and methanol
oxidation, the PANI-PSS-Pt electrode toward methanol ox-
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ACKNOWLEDGEMENTS
The financial support of this work by the National
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J. Chin. Chem. Soc. 2014, 61, 819-826
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