In situ construction of a poly-3,4-ethylenedioxythiophene skeleton on carbon nanotubes to improve long-term stability for oxygen reduction reaction

Article abstract of DOI:10.1039/d0nj00289e

Although carbon nanomaterials show good potential as efficient electrocatalysts for oxygen reduction reaction (ORR), their inferior long-term stability due to their high surface energy resulting in compact restacking limits their practical performance. To overcome this issue, here, we design and construct an anti-agglomerating single-walled carbon nanotube (SWNT) catalyst by using poly-3,4-ethylenedioxythiophene (PEDOT) as an upholder. Physical characteristic results indicate that PEDOT effectively fills in the interweaved zone or adheres to the SWNT surface. Furthermore, S atoms can be doped into the lattice and produce more defects. Electrochemical tests show that SWNTs?PEDOT exhibits similar catalytic activities towards ORR to SWNTs, and both of them can realize a quasi-4e ORR pathway. Within a 32 000 s long-term test, the cathodic current of the SWNTs toward ORR gradually decays to 58% of the initial value; in contrast, SWNTs?PEDOT shows excellent stability with several stages of rise, fall, rise to 105% of the initial current. The excellent stability is due to the stable skeleton caused by PEDOT preventing agglomeration of SWNTs. The equilibrium of swelling and shrinkage of PEDOT even lead to an increase and favorable stability of the current. This suggests a practical method to overcome the weakness of agglomeration, thus enhancing the long-term stability for nano-carbon catalysts.

Full text of DOI:10.1039/d0nj00289e

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In situ construction of a poly-3,4-ethylenedioxy-
thiophene skeleton on carbon nanotubes to improve
long-term stability for oxygen reduction reaction†
Cite this: New J. Chem., 2020,
44, 6435
Jing Li, Jinfu Ma, * Hui Lu, Zhilin Sheng, Shaolin Yang and Jiandong Wu
Although carbon nanomaterials show good potential as efficient electrocatalysts for oxygen reduction
reaction (ORR), their inferior long-term stability due to their high surface energy resulting in compact
restacking limits their practical performance. To overcome this issue, here, we design and construct an anti-
agglomerating single-walled carbon nanotube (SWNT) catalyst by using poly-3,4-ethylenedioxythiophene
(PEDOT) as an upholder. Physical characteristic results indicate that PEDOT effectively fills in the interweaved
zone or adheres to the SWNT surface. Furthermore, S atoms can be doped into the lattice and produce
more defects. Electrochemical tests show that SWNTs@PEDOT exhibits similar catalytic activities towards
ORR to SWNTs, and both of them can realize a quasi-4e ORR pathway. Within a 32 000 s long-term test, the
cathodic current of the SWNTs toward ORR gradually decays to 58% of the initial value; in contrast,
SWNTs@PEDOT shows excellent stability with several stages of rise, fall, rise to 105% of the initial current. The
excellent stability is due to the stable skeleton caused by PEDOT preventing agglomeration of SWNTs.
The equilibrium of swelling and shrinkage of PEDOT even lead to an increase and favorable stability of
the current. This suggests a practical method to overcome the weakness of agglomeration, thus
enhancing the long-term stability for nano-carbon catalysts.
Received 20th January 2020,
Accepted 24th March 2020
DOI: 10.1039/d0nj00289e
rsc.li/njc
from the degradation mechanism of PGMs and non-PGMs,
such as (a) demetallization of metal active sites and (b) Fenton
Fuel cells or metal–air batteries have attracted extensive interest reaction. Qu et al. reported a nitrogen-doped graphene catalyst
1
. Introduction
10
11
in the field of electrochemical energy conversion. As a key part synthesized by chemical vapor deposition of methane in the
of these devices, developing the performances of the oxygen presence of NH , and there was no decay observed in the ORR
3
1
2
reduction reaction (ORR) is crucial due to the sluggish reaction current after 2 000 000 cycles in alkaline medium. Yu et al.
kinetics on the cathode. Various metal catalysts, especially developed nitrogen-doped SWNTs, which displayed exceptional
platinum-group metals (PGMs) have been used for ORR due to long-term stability for two days in acidic medium. At the same
their excellent catalytic activities. However, scarcity of resource time, nanoporous graphitic-C
3
N
4
, boron and nitrogen co-doped
-saturated
and inferior durability limit their application. Consequently, graphene (BCN) catalysts exhibited high stabilities in O
2
13
reducing the noble metal contents and exploring non-PGM or 0.1 M KOH solution. Recently, metal–organic frameworks
metal-free catalysts have been attempted in recent years. Among (MOFs) have attracted great interest as ORR catalysts owing to
1
–3
4–8
them, metal oxide, carbon materials and their composites
seem to be the most attractive ones.
their various combinations of metal ions and organic ligands,
large specific surface areas, and facile synthesis. Zhao et al.
1
4
Metal-free non-PGM catalysts, especially nano-carbon materials, reported a Co-ZnO@NC/CNT-700 catalyst and explored a slight
such as graphene, carbon nanotubes and other nano-structural degradation after 25 000 s toward ORR.
carbon materials, have excellent catalytic activities towards
As another kind of metal-free non-PGM catalyst, PEDOT
ORR. However, inferior long-term stability, that is, their practical towards ORR has been initially reported by Winther-Jensen,
1
5
performance at high energy density and power density is difficult et al. in science, 2008; a porous material coated was with
to maintain on account of the compact restacking that is PEDOT by a vapor phase-polymerized method, and it acted as
9
seriously caused by the large surface energy. This is different an ORR catalyst without material degradation or deterioration
in performance for 1500 hours continuous operation. Since
then, the theoretical research on the mechanism of oxygen
School of Materials Science and Engineering, North Minzu University,
reduction reaction (ORR) catalyzed by PEDOT demonstrated
Yinchuan 750021, China. E-mail: ma_jinfu@nun.edu.cn
Electronic supplementary information (ESI) available. See DOI: 10.1039/d0nj00289e that the remarkable catalytic activity of PEDOT was related to
†
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the formation of polaronic states and provided theoretical proof
1
6
17
of the energetically preferable 4e-ORR route. Chen et al. also
reported a PEDOT:PSS-MWCNT modified carbon black-based
gas diffusion electrode and concluded that the p–p interaction
between MWCNTs and PEDOT: PSS facilitated 2e-ORR. Zhang
1
8
et al. prepared PEDOT:PSS and rGO composites, then removed
a part of the insulating PSS from the surface of PEDOT:PSS/rGO
by H SO post-treatment, and the ORR performance was
2 4
equivalent to Pt/C and has excellent stability.
Here, we design a novel method to overcome the weakness
of inferior stability of nano-carbon catalysts. Utilizing the stable
structural characteristics and favorable ORR catalytic activity
of PEDOT to build a stable skeleton structure of SWNTs and
Fig. 1 Schematic diagram of the synthesis process for SWNTs@PEDOT.
prevent agglomeration, we thus enhance the long-term stability 2.3. Physical characterization
of SWNTs.
The micro morphologies of the samples were studied using
field emission scanning electron microscopy (FE-SEM, Zeiss
Supra-55) and transmission electron microscopy (Titan G260-300).
The exact characterization of the material surface was analyzed
using X-ray photoelectron spectroscopy (XPS, Thermo Fisher) with
Al K-Alpha (1486.7 eV) operating at 15 kV in high vacuum mode
2
. Experimental
2
.1. Chemicals
Single-walled carbon nano-tubes (SWNTs, Z95 wt%, f o 2 nm,
.3–5 mm length), 3,4-ethylenedioxythiophene (purity Z99%),
LiClO (AR, 99.0%), Nafion solution (5%, Dupont), 20 wt% Pt/C,
and NaOH (AR and KBH ) (AR) were purchased from Aladdin
and used directly without other modifications.
ꢀ
8
with a pressure of 10 Pa. The Raman spectrum was recorded
using an Invia Raman microscope (Renishaw, England).
0
4
4
2.2. Synthesis of electrocatalysts
In order to functionalize SWNTs, 100 mg of SWNT powder was
dispersed in 8 mL mixtures of concentrated sulfuric acid and
nitric acid with a volume ratio of 3 : 1, after ultrasonic dispersing
for 2 h and stirring for 24 h, and then washed by distilled water
and ethanol several times to pH = 7. Finally, the sample was
dried at 80 1C in a vacuum oven for 6 h and the functionalized
SWNTs (F-SWNTs) were obtained.
Before preparing the working electrodes, the glassy carbon
rotating disk electrode (RDE) was polished by an aqueous alumina
suspension and washed with deionized water and ethanol. 100 mg
of F-SWNTs was mixed with 0.95 mL of ethanol and 0.05 mL of
5
% Nafion and then ultrasonically dispersed for 1 h. 5 mL of the
2
suspension was then dropped onto the surface of disk (0.126 cm )
electrodes. The coated ink was dried using an infrared lamp for
5
min. The SWNT-catalyzed cathode was obtained. In order to
prepare PEDOT, 0.1 M LiClO and 1 mM EDOT monomers were
4
dissolved into 50 mL of deionized water. Then, the mixture was
ultrasonically dispersed for 0.5 h. PEDOT was prepared by electro-
polymerization on the surface of the disk electrode directly
through a constant potential of 1 V (vs. SCE) for 100 s. Finally,
2 2
the prepared electrode was rinsed in dichloromethane (CH Cl )
and absolute ethanol to remove the residual EDOT monomer and
other unreacted chemicals. Thus, the PEDOT-catalyzed cathode
for ORR was obtained. The SWNTs@PEDOT catalyzed cathode
was fabricated according to the process described above in
turn (Fig. 1).
For comparison, a 20 wt% Pt/C cathode was prepared with a
mass loading of 4 mg cm by the same method as that of the
SWNT-catalyzed cathode fabrication.
Fig. 2 The SEM images of PEDOT (a) and SWNTs-PEDOT (b), TEM images
of SWNTs (c) and SWNTs-PEDOT (d), and HAADF of SWNTs (e) and
SWNTs-PEDOT (f).
ꢀ2
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2
.4. Electrochemical characterization
measured at different rotating rates (600–3200 rpm) with a sweep
ꢀ1
rate of 50 mV s . The number of electron transfer toward ORR
Cyclic voltammetry (CV), linear scan voltammetry (LSV) and
chronoamperometry (CA) tests were conducted by a three-electrode
system controlled by a CHI 760E electrochemical workstation. A Pt
plate, Hg/HgO (1 M KOH), and the bare or functionalized rotating
ꢀ
1
1/2
was calculated from the slope of jd B w according to the
1
9
Koutecky–Levich (K–L) equation as follows,
1
1
1
1
1
2
¼ þ ¼ þ
jk jd jk Bw1=2
(2)
disk electrode (RDE) carbon disk with a surface area of 0.1256 cm
j
were used as auxiliary, reference and working electrodes, respectively.
The reference electrode was replaced by the SCE electrode
when electro-polymerization was carried out for PEDOT. The
potential of the HgO/Hg reference electrode was corrected with the
reversible hydrogen electrode (RHE), in 0.1 M KOH, E vs. RHE =
2=3 ꢀ1=6
v
O2
B ¼ 0:2nFACO D
(3)
2
where j is the measured current density; j
k
and j
d
are the kinetic-
and diffusion-limiting current densities; n is the electron transfer
ꢀ1
0.059pH + 0.098. Electrochemical surface area (ECSA) of the catalysts
number; F is the Faraday constant (F = 96 485 C mol ); A is the
2
was estimated by using the double-layer capacitance in the non-
geometric area of the electrode (0.1256 cm ); k is the electron
ꢀ1
Faraday area at scan rates of 10, 20, 30, 40, 50 mV s , and the ECSA
transfer rate constant, CO2 is the bulk concentration of O
2
2
14
ꢀ6
ꢀ3
(
cm ) was calculated according eqn (1),
(
0
1.2 ꢁ 10 mol cm ); DO2 is the diffusion coefficient of O
2
in
ꢀ5
2
ꢀ1
.1 M KOH solution (1.9 ꢁ 10 cm s ); n is the kinematic
CDL
ic
2
ꢀ1
ECSA ¼ Cs
¼
(1)
viscosity of the electrolyte (0.01 cm s ), and w is the electrode
rotating rate (rpm).
vCs
The double layer capacitance (Cdl) was estimated by plotting
Dj( j ꢀ j ) at 0.95 V vs. RHE against the scan rate.
The stability tests were carried out at 0.7 V vs. RHE in
O -saturated 0.1 M KOH (o = 1225 rpm) by CA. During the
a
c
2
CV and LSV were performed in O -saturated 0.1 M aqueous stability evaluation, 2 M methanol or 2 mM KBH was injected
2
4
ꢀ1
KOH solution at a scan rate of 50 mV s . And LSV curves were into O
2
-saturated 0.1 M KOH. Meanwhile, a commercial 20 wt%
Fig. 3 (a) XPS spectrum of PEDOT and SWNTs@PEDOT. The corresponding high resolution XPS spectra and fitting lines of (b) C1s, (c) O1s and (d) S2p
regions in PEDOT and SWNTs@PEDOT.
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Pt/C catalyst was measured as a contrast. All the tests were 532.1 ꢂ 0.1 eV for C–O–C/OQC bonds and 533.4 ꢂ 0.1 eV for
2
4
carried in 0.1 M KOH at ambient temperature.
O–C, demonstrating that the SWNTs were functionalized
successfully. The higher binding energy of 535.4 eV for SWNTs@
24,25
PEDOT can be attributed to adsorbed oxygen contaminants.
3
. Results and discussion
In the high-resolution S2p spectrum (Fig. 3d) of PEDOT and
SWNTs@PEDOT, the peaks at 163.9 eV and 165.1 eV are in
Fig. 2 shows the SEM and TEM images of the as-synthesized
catalysts. Fig. 2a exhibits an irregular flake structure. PEDOT
has been synthesized successfully by electro-polymerization in
agreement with the S2p3/2 and S2p1/2 positions associated with
21,26
C–S–C bonds.
One shakeup satellite peak at 168.5 eV of S2p
in PEDOT was also found that is assigned to a higher oxidation
LiClO
4
aqueous solution and many acicular crystals distributed
27
state of S. Again, SWNT@PEDOT exhibits two prominent
on the surface, which is unlike the microstructure of PEDOT
synthesized by the same method on fluorinated tin oxide (FTO)
satellite peaks at 168.5 eV and 169.7 eV that are assigned to
the surface sulfur species of higher oxidation states in C–SO –C
x
2
0
glass in our previous work, indicating that the polymerization
and growth of PEDOT are dramatically affected by the substrate.
On the SWNT-modified glassy carbon surface, PEDOT displayed a
regular linear polymer coating (Fig. 2b), which would be beneficial
to enhance the electro-catalytic activity for ORR. Fig. 2c and d
display the TEM images of SWNTs and SWNTs@PEDOT, with
Nafion gel only distributed in the lapping zone of the SWNTs
bonds from PEDOT and Nafion solution, respectively; the peak
of 168.5 eV of S2p for SWNTs@PEDOT remarkably grew relative
to PEDOT, indicating that S (from the integral area) of PEDOT
was doped into the carbon skeletons of the SWNTs, and this is very
useful as S doped in carbon materials is known as one of the most
26
probable active sites in ORR. Consequently, the electrochemical
ability is potentially enhanced due to the S doping. All the fitting
data of binding energies and their corresponding bonds are listed
in Table 1.
(Fig. 2c), and the distribution characteristics of S element from
Nafion shown in the HAADF image (Fig. 2e) also provide proof.
By comparison, for SWNTs@PEDOT, PEDOT attached to the
interweaved network of SWNTs (Fig. 2d), and the HAADF image
(Fig. 2f) shows that more S element distributes not only on the
surface of the SWNTs (S from Nafion and PEDOT) but also in
other zones (S from PEDOT), and Fig. S1 (ESI†) also shows the
structural characters described above.
In order to investigate the surface elemental composition
and electronic configuration of the catalyst, XPS was utilized.
The survey scan (Fig. 3a) shows the presence of C1s, O1s, and
S2p. Among the detected elements, F and some S element in the
SWNTs resulted from the Nafion solution. The high-resolution
C1s XPS spectra (Fig. 3b) of PEDOT can be deconvoluted into
three peaks with binding energies located at 284.5 eV, 285.1 eV
2
0,21
and 286.4 eV, associated with CQC, C–S and C–O.
The CQC
(
284.7 eV), C–S (285.0 eV) and C–O (286.2) peaks can be
22
deconvoluted for SWNTs/PEDOT in the same way. Furthermore,
23
CQO–C (289.2 eV) and C–F (291.8 eV) peaks can also be observed
with the F element resulting from the Nafion solution. The O1s
spectra (Fig. 3c) have asymmetric peaks for PEDOT and SWNTs-
PEDOT, which were deconvoluted with two peaks assigned to
Fig. 4 Raman spectra of SWNTs and SWNTs@PEDOT.
Table 1 Results obtained from fitting of XPS C1s, O1s and S2p spectra of
PEDOT and SWNTs-PEDOT
PEDOT
SWNTs-PEDOT
Assignment
BE/eV
284.5
BE/eV
284.6
285.0
286.2
C1s
CQC
C–S
C–O
2
2
85.1
86.4
2
2
89.1
91.8
OQC–O
C–F
O1s
S2p
532.2
33.3
532.0
533.5
C–O–C/OQC
O–C
O
ads
5
535.4
163.8
164.0
165.3
168.5
C–S–C
C–S–C
1
1
65.0
68.5
ꢀ1
C–SO
C–SO
x
–C
–C
Fig. 5 The CV curves of various catalysts toward ORR (scan rate: 0.05 V s ,
169.7
x
O - or N -saturated 0.1 M KOH solution).
2
2
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ꢀ1
Fig. 4 shows the Raman spectra of SWNTs and SWNTs@ 50 mV s . As shown in Fig. 5, no cathode reduction peak
PEDOT. For the SWNTs, there are typically three characteristic appears with the N -saturated solution, indicating that this
peaks containing a defect-related D band at 1356 cm and G band catalyst is inactive in N . An obvious cathode peak appears,
2
ꢀ1
2
ꢀ
1
2
at 1591 cm attributed to the vibration of the sp -hybridized and the onset potential and peak potential of PEDOT in
carbon atoms, and the second order of the D band (2D band) O -saturated 0.1 M KOH aqueous solution are B0.65 V and
2
ꢀ
1 28
ꢀ2
at 2672 cm
often used to indicate the defect level in carbon materials. polarization current or peaks appear under the condition of
The I /I values of 0.14 for the pure SWNTs and 0.28 for -saturation, indicating that PEDOT has catalytic ability
SWNTs@PEDOT suggest more sonication induced basal plane towards ORR. In contrast, the SWNT and SWNTs@PEDOT
defects and/or edge defects. catalyzed electrodes display excellent properties for ORR; the
.
D G
The intensity ratio of D band to G band (I /I ) is 0.51 V (0.55 mA cm ), respectively. However, no cathodic
D
G
N
2
The CV tests of the as-prepared samples were performed in corresponding onset potential is 0.75 and 0.8 V, and the peak
N - and O -saturated 0.1 M KOH solutions at a scan rate of potentials are 0.67 and 0.71 V with a similar peak current
2
2
Fig. 6 The LSV curves of PEDOT (a), SWNT (c), and SWNTs@PEDOT (e) catalysts toward ORR with various RDE rotating rates and a corresponding slope
1/2
ꢀ1
of j
d
B w of PEDOT (b), SWNT (d), and SWNTs@PEDOT (f) catalysts (scan rate: 0.05 V s , O
2
-saturated 0.1 M KOH solution).
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ꢀ2
density (Bꢀ0.85 mA cm ), respectively. The more positive that of the ORR catalytic activities. This is perhaps due to the p–p
1
7
onset potential of SWNTs@PEDOT indicates a higher catalytic conjugative effects of SWNTs and PEDOT that enhance the
activity for ORR. electron conductivity and provide the synergetic promotional
The LSV curves of various catalysts in the rotating rate of effect for ORR.
ꢀ
1
RDE range of 600–3200 rpm at 50 mV s are presented in
Fig. 6(a, c and e); the current densities gradually increase with and Pt/C were determined from chronoamperometric measure-
increasing disk rotating rate. The number of electron transfer ments performed in O -saturated 0.1 M KOH solution. As shown
B w according to in Fig. 8a, within 1000 s short-term tests, all catalysts exhibited a
The methanol tolerances of PEDOT, SWNTs, SWNTs@PEDOT
2
ꢀ
d
1
1/2
toward ORR is calculated from the slope of j
eqn (2) and (3), and the K–L plots are displayed in Fig. 6(b, d and f). sudden fluctuation when injecting 2 M methanol at B300 s.
For PEDOT, n is determined to be B2.2 ranging from ꢀ0.10 B With the increase of time, the current of PEDOT, SWNTs and
ꢀ
0.30 V of the limit current density ( j ) region. Within the j region SWNTs@PEDOT quickly returned to the initial state, but Pt/C
d d
of 0.50–0.40 V, SWNTs and SWNTs@PEDOT toward ORR have very exhibits a drop of ꢀ1000% of initial current with a gradual
similar n values greater than 3. Moreover, the potentials of the jd recovery, indicating that PEDOT, SWNTs and SWNTs@PEDOT
region are more positive, which would be beneficial to enhance have favorable anti-methanol tolerance. As shown in Fig. S3
4
the work voltage and power density for electrochemical devices. (ESI†), when 2 mM KBH was added into 0.1 M KOH during the
This indicates that the two catalysts have superior catalytic tests at 500 s, PEDOT and SWNTs@PEDOT retained good boro-
activities toward ORR in contrast to the PEDOT and SWNT hydride tolerance, while SWNTs and Pt/C did not. The anodic
catalysts that display a slightly larger n value of 3.41 than that of current on the SWNTs confirmed that they can also catalyze
SWNTs@PEDOT (3.13) at 0.30 V.
BOR. As a comparison, a sudden and large anodic current on
The catalytic activities were also explored by using Tafel plots Pt/C indicated that Pt/C has a good catalytic activity for boro-
within the mixed kinetic-diffusion ( j ) region of LSV curves at hydride oxidation reaction (BOR) with very poor selectivity, which
k
1600 rpm, as shown in Fig. 7a; the slopes of the Tafel plots of agreed with ref. 29. In contrast, the Pt/C electrode exhibits a
PEDOT, SWNTs and SWNTs@PEDOT toward ORR are 195.6, gradual decrease with more current loss and a lower relative
ꢀ
1
1
42.4 and 126.9 mV dec , respectively, which display that current (B43.9%). Thus, the tests show that the SWNTs@PEDOT
PEDOT has an inferior catalytic activity due to great polarization catalyst has great anti-poisoning effects in KBH and methanol
4
while SWNTs@PEDOT exhibits an ideal catalytic activity with tolerance, that is, PEDOT was beneficial for the enhancement of
a lower slope value, which is close to a general Tafel slope of the electro-catalytic activity and selectivity of SWNTs in ORR, and
ꢀ
1
1
20 mV dec , indicating the fast electron transfer rate- SWNTs@PEDOT has great potential for application in alkaline
1
9,22
determining step
of SWNTs@PEDOT toward ORR. Thus, direct borohydride fuel cells (DBFCs) and direct methanol fuel
this result demonstrated that the fast electron exchange is the cells (DMFCs).
rate-determining step on SWNTs@PEDOT. To further evaluate
For nano-structured carbon materials, a high surface energy
the different activities of the catalysts, ECSA was studied to can result in aggregation, which limits ion transport thus causing
characterize the amount of active sites exposed to the electrolyte. inferior long-term stability. Long-term tests for 32 000 s of SWNT
According to the CVs within the non-faradaic area (Fig. S2, ESI†), and SWNTs@PEDOT catalysts were carried in O -saturated 0.1 M
2
the Dj B v relation curves are shown in Fig. 7b and the Cdl values KOH solution at a constant potential of 0.7 V (vs. RHE). As displayed
calculated in terms of the slopes of Dj B v for PEDOT, SWNTs in Fig. 8b, the current of the SWNTs toward ORR gradually decays to
and SWNTs@PEDOT are 0.64, 0.93 and 1.16 mF with a trend of only 58% of the initial value at 32 000 s, mainly because the
PEDOT o SWNTs o SWNTs@PEDOT, which is consistent with agglomeration conductance of carbon nanotubes limited the
Fig. 7 (a) The Tafel plots within the mixed kinetic-diffusion ( j
in the non-faradaic region with scan rates of 10, 20, 30, 40, and 50 mV s of PEDOT, SWNT and SWNTs@PEDOT catalysts.
k
) region of LSV curves at 1600 rpm; (b) the anode and cathode current variance (Dj = j
a
ꢀ j
c
)
ꢀ1
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Fig. 8 (a) The anti-methanol tolerance tests of various catalysts (inset: enlarged view of j/j
0
B time of various catalysts except Pt/C); (b) the long-term
2
stability of SWNTs and SWNTs@PEDOT (constant potential: 0.7 V vs. RHE, O -saturated 0.1 M KOH solution, rotating rate: 1225 rpm).
migration of electrons, resulting in poor long-term stability. References
However, that of SWNTs@PEDOT shows excellent stability with
1
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several stages of rise, fall, rise to 105% of the initial current and
then stability. The excellent stability of SWNTs@PEDOT is due
to the stable skeleton of PEDOT that can effectively prevent the
aggregation of SWNTs; in addition, the swelling and shrinkage
of PEDOT result in the fluctuation of current and its equili-
brium leads to increased and favorable stability of current.
2
3
4
4
. Conclusion
A highly selective and long-term stable ORR catalyst of SWNTs@
PEDOT was prepared by electro-polymerization on surface SWNTs
directly. Several physical characterization and electrochemical tech-
niques were carried to determine the catalytic effects of PEDOT,
SWNTs and SWNTs@PEDOT toward ORR in alkaline medium. The
results indicated that PEDOT attached to the interweaved network
of SWNTs and trace amounts of S from PEDOT were doped into the
SWNTs to increase the ECSA and create structural defects; coupled
with the p–p conjugative effects of SWNTs and PEDOT, the
SWNTs@PEDOT exhibited similar catalytic activities to those
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