Titania nanotubes coated with graphene as a promising catalyst for the oxygen reduction reaction

Article abstract of DOI:10.1039/d0nj00547a

The research on non-noble metal oxide catalysts is significant for solving the problems of high cost, low abundance and poor stability of platinum-based catalysts used in the oxygen reduction reaction of fuel cells. In this study, a novel non-noble metal electrocatalyst consisting of a titanium dioxide nanotube (TiO₂NTs) array and reduced graphene oxide (rGO) was prepared using a facile chronoamperometry route. High-resolution transmission electron microscopy (HRTEM) and mapping images clearly show that rGO is tangled on the TiO₂ nanotube wall. The comparative study on the electrocatalytic performance of rGO, TiO₂NTs, rGO/TiO₂NTs and commercial Pt/C for the oxygen reduction reaction (ORR) reveals that rGO/TiO₂NTs shows a more positive onset potential, higher current density, and higher electron transfer number (～4) in alkaline media compared with bulk TiO₂NTs and rGO for the ORR, and a better durability and methanol tolerance than the commercial Pt/C catalyst, which may be attributed to the synergetic effects between TiO₂NTs and rGO. The rGO is coated on a well-organized TiO₂ nanotube wall improving the stability and conductivity, thus further improving the catalytic performance. It will open up a new strategy for developing effective non-noble metal oxide catalysts for the oxygen reduction reaction.

Full text of DOI:10.1039/d0nj00547a

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Chechia Hu, Tzu-Jen Lin et al.
Yellowish and blue luminescent graphene oxide quantum dots
prepared via a microwave-assisted hydrothermal route using
H2O2 and KMnO4 as oxidizing agents
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Titania nanotubes coated with graphene as a promising catalyst
for oxygen reduction reaction
Jiannan Cai1, Xiaofeng Zhang1, Yi Zhang1, Mingxing Yang1, Baohua Huang1, Shen Lin1,*
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
The research of non-noble metal oxide catalysts is significant for solving problems of high cost,
low abundance and poor stability of platinum-based catalysts used in oxygen reduction reaction of fuel cells.
In this study, a novel non-noble metal electrocatalyst consisting of titanium dioxide nanotubes (TiO2NTs)
array and reduced graphene oxide (rGO) was prepared by a facile chronoamperometry route. High-
resolution transmission electron microscopy (HRTEM) and mapping image clearly show that rGO is tangled
on TiO2 nanotubes wall. The comparative study on electrocatalytic performance of rGO, TiO2NTs,
rGO/TiO2NTs and commercial Pt/C for oxygen reduction reaction (ORR) reveals that rGO/TiO2NTs shows a
more positive onset potential, higher current density, and higher electron transfer number (~4) in alkaline
media than bulk TiO2NTs and rGO for ORR, and better durability and methanol tolerance than the
commercial Pt/C catalyst, which may attribute to synergetic effects between TiO2NTs and rGO. The rGO is
coated on well-organized TiO2 nanotubes wall improving stability and conductivity, thus further improve
catalytic performance. It will open up a new strategy for developing effective non-noble metal oxide
catalysts for oxygen reduction reaction.
on. Well-organized titanium oxide nanotubes will provide many
catalytic active sites and enhance electrochemical stability18,19. So
TiO2NTs is considered to be a suitable catalyst for electrocatalysis.
1.Introduction
Fuel cells is considered as the most promising energy conversion
devices for sustainable energy applications in the future due to their
high conversion efficiency and power density1,2. Electrocatalyst is
one of the most important materials for fuel cells application, among
which platinum catalyst is considered to be the most effective
commercial electrocatalyst, but its high cost, low stability and low
For example, M Manikandan et al20 combined TiO2 nanotubes with
Pt to enhance the electrocatalytic performance and stability of
catalyst for ORR, but its poor conductivity restricts its practical
application in fuel cells. In order to enhance the conductivity of
catalyst, carbon-based materials with excellent electrochemical
properties have been taken into account. Among them, rGO is a
promising material for catalyst carrier with high electron
anti-methanol properties seriously affect its utilization efficiency3-6
.
Developing Pt-free catalysts with superior catalytic performance for
ORR remains a great challenge. In recent years, many researchers
have been devoted to the development of metalloid or non-precious
metal catalysts which include carbonaceous material doped with B,
N and S , transition metal chalcogenide and transition metal carbon
families7-11. Due to the harsh acid environment of proton exchange
membrane fuel cell (PEMFC), the stability of non-precious metal
catalysts have serious problems----lower activity and durability than
Pt-based catalysts. It can be solved in alkaline anion exchange
membrane fuel cell (AEMFC). And AEMFC also has the advantages
of fast kinetic performance, higher current and lower overpotential
under alkaline condition relative to acidic medium, so the reasonable
design of non-precious metal catalyst can achieve excellent catalytic
conductivity, high surface area, excellent chemical stability21,22
.
Zhao et al.23 reported a flower-like composite consisting of titanium-
dioxide and rGO supported heme (TiO2/Gr/Hem) by low
temperature solvothermal reaction. The TiO2/Gr/Hem composite
shows the increased electrocatalytic activity, stability and anti-
methanol performance in alkaline medium.
The methods for preparing titania nanotubes include template
synthesis, hydrothermal method and electrochemical anodic
treatment. Among these methods, the anodic treatment is a relatively
facile method to obtain well-organized TiO2 nanotubes with high
specific surface. In our work, TiO2 nanotube arrays was prepared by
a facile anodized method and the rGO/TiO2NTs composite was
synthesized by electrodeposition. Electrochemical synthesis of rGO
nanocomposites in situ on the suface of TiO2NTs has intrinsic
advantages characterized by mild conditions and good controllability
for reduction of graphite oxide. Higher specific surface area of
titanium dioxide nanotubes obtained by anodic treatment can expose
more active sites. After the encapsulation of the conductive rGO, the
specific surface area, active sites and conductivity of the
rGO/TiO2NTs composite are all increased, enhancing the contact
adsorption of oxygen and improving electrocatalytic performance for
ORR.24,25 The electrochemical studies have shown that the as-
prepared rGO/TiO2NTs composite exhibits superior electrocatalytic
performance in AEMFC12,13
.
Among all kinds of non-noble metal oxide catalysts, TiO2 has
the advantages of low cost, high activity14 and varieties of
morphology such as nanorods15, nanoplates16 and nanotubes17 and so
1
College of Chemistry and Materials Science, Fujian Normal University, Fuzhou,
Fujian, China, 350007
Address correspondence to E-mail: shenlin@fjnu.edu.cn
† Footnotes relating to the title and/or authors should appear here.
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
activity for ORR, which propose
a new approach for the
development of cheap alternative Pt/C catalysts.
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parameters is analyzed in the electro-catalytic processVbieywtAhrteicldeaOtanlionef
LSV30
2.Experimental
.
DOI: 10.1039/D0NJ00547A
To further comprehend the kinetic behaviour and adsorption
mechanism of oxygen on rGO/TiO2NTs composite. Tafel curve was
obtained by potential as Y-axis and the logarithm of current density
as X-axis (correspond to the data of LSV), tafel slope was obtained
by extrapolation.
The rotating ring-disk electrode technique was used to take
linear sweep voltammetry in order to determine the electrons transfer
number n value and yield of H2O2 in ORR process using
rGO/TiO2NTs composite as an electrocatalyst. The number of
electron transfer number n and the yield of H2O2 in the ORR process
can be calculated by the following formulas：
2.1Reagents
Graphite powder (-325 mesh,99.9995%), commercial Pt/C (20%)
were purchased from Alfa Aesar Inc. 5% Nafion 117 solution was
purchased from Sigma-Aldrich Inc. Potassium thiosulfate (K2S2O8),
phosphorus pentoxide (P2O5), potassium hydroxide (KOH),
ammonium fluoride (NH4F), concentrated sulfuric acid (H2SO4),
hydrochloric acid (HCl), hydrogen peroxide (H2O2), methanol
(CH3OH), anhydrous ethanol (C2H5OH), ethylene glycol were all
analytical pure and were purchased from Sinopharm Chemical
Reagent Co., Ltd. Titanium sheet (300 mm×100 mm×0.1 mm,
99.99%) was purchased from Shenzhen Hongwang Mould Co., Ltd.
High purity oxygen (O2, 99.999%), nitrogen (N2, 99.999%) were
purchased from Huaxinda Industrial Gas Co., Ltd. The laboratory
water was redistilled water.
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n = 4ID / (ID + IR/N)
H2O2% = 200IR / (NID + IR)
(2)
(3)
Where ID and IR represent the test current of the disk and the ring,
the collection efficiency N is 0.3731,32
.
The front working electrode is prepared by coating method on
the basis of clean glassy carbon electrode. The specific steps are as
follows. 5.5 mg rGO/TiO2NTs composite was transferred to 3 mL
centrifuge tube, and added 100 μL Nafion solution, 300 μL
isopropanol, 600 μL distilled water into it. Then the mixture was
treated by ultrasound for 60 min to obtain an uniform dispersing
solution. The solution of 3.6 μL or 10 μL was coated on the glassy
carbon electrode with diameter of 3 mm or 5 mm and dried at room
temperature. rGO, TiO2NTs and commercial Pt/C was coated by
above method.
2.2Synthesis and characterization
Titanium sheet was pretreated as follow procedure. The titanium
sheet was firstly cut into 50 mm × 10 mm × 0.1 mm specification,
then cleaned by ultrasonic for 10 min with acetone, ethanol and
distilled water successively, afterwards dried naturally.
In a typical preparation of rGO/TiO2NTs composite , the
pretreated titanium sheet (50 mm×10 mm×0.1 mm) was first placed
in mixed solution of 0.5 g NH4F, 10 mL distilled water and 89.6 mL
ethylene glycol, then anodized with constant voltage of 40 V for 24
hours in a bipolar system (titanium sheet as anode, platinum wire as
cathode) and dried naturally26. After that, the anodized titanium sheet
3.Results and Discussion
was placed in the mixed solution of GO (Synthesized by improved
Hummer method, 2 mg mL-1)
and Na2SO4 (0.1 mol L-1). Then The crystal phase of rGO/TiO2NTs composite prepared by facile
27,28
the rGO/TiO2NTs composite was prepared by electrodeposition at -
1.5 V potential for 3 h and gently peeled off with a knife29. As a
control, TiO2NTs and rGO using ITO as a substrate were synthesized
by the same procedure mentioned above.
The crystal phase analysis of the composite were performed by
X-ray powder diffractometer (XRD, X’pert Pro). Raman
spectrometer (Raman, inVia-Reflex) was used to analyze reduction
degree of GO. Element valence was analyzed by X-ray
photoelectron Spectrometer (XPS, ESCALAB 250). Field emission
scanning electron microscopy (FESEM, JSM-7500F) and high-
resolution transmission electron microscopy (HRTEM, TECNAI G2)
were used to observe the surface morphology and crystal structure of
composite.
electrochemical synthesis was firstly determined by XRD. Fig.1A
exhibits the XRD spectra of (a) rGO, (b) TiO2NTs and (c)
rGO/TiO2NTs composite, respectively. As shown in Fig.1A(a), the
characteristic diffraction peaks ascribed to (002) crystal plane of
rGO are observed33,34. In Fig.1A(b), the characteristic diffraction
peaks at 25.4o, 38.8o and 53.3o are assigned to (101), (004), (105)
plane of the anatase crystal TiO2, respectively (JCPDS21-1272)35.
Two characteristic diffraction peaks assigned to Ti metal are also
observed at 40.2oand 70.7o in Fig.1A curve b and c, which may be
2.3Electrochemical test and Calculation
Electrochemical test were carried out in three-electrode system
(glassy carbon electrode as working electrode, saturated silver
chloride electrode (3.4M KCl, Ag/AgCl）as reference electrode, the
platinum wire electrode as the auxiliary electrode). All the potentials
in this work were converted into reference potential of reversible
hydrogen electrode (RHE) by the conversion formula as follows.
RHE=EAg/AgCl+0.059pH+0.2224V-0.059 lg a(Cl-)
(1)
Where EAg/AgCl represent potential which is measured by silver
chloride electrode as reference electrode. 0.2224V is the standard
electrode potential of silver chloride electrode at 25℃.The a(Cl-) is
the concentration of Cl- in saturated silver chloride electrode (3.4M).
Cyclic voltammetry (CV) was measured in potassium hydroxide
(0.1 M KOH) solution saturated with oxygen or nitrogen at a
scanning rate of 20 mv s-1. In order to ensure gas saturation before
testing, it was necessary to inflate KOH solution with oxygen or
nitrogen over 40 min. Linear sweep voltammetry (LSV, polarization
curves) is measured on a rotating disk electrode at a scanning rate of
5 mv s-1, and the electrolyte was O2 saturated KOH solution.
According to the Koutecky-Levich (K-L) equation, accurate kinetic
Fig. 1 A: XRD patterns of rGO(a), TiO2NTs(b), rGO/TiO2NTs(c). B:
Raman spectra of GO(d), rGO(e) and rGO/TiO2NTs(f). C: BET spectra
of rGO/TiO2NTs(g), rGO(h), TiO2NTs(i), Commercial TiO2(j)
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Fig. 2 XPS spectra: Full scan of rGO/TiO2NTs composite (A); Ti 2p
spectrum of rGO/TiO2NTs composite(B); C1s spectrum of GO(C) and
rGO/TiO2NTs composite (D)
attributed to the fact that TiO2NTs is formed on titanium
metal36.Compare curve a with curve c, the characteristic diffraction
peaks assigned to rGO are formed on titanium metal36. Compare
curve a with curve c, the characteristic diffraction peaks assigned to
rGO are not found, which may be due to low content of rGO
obtained by electrodeposition and failure to meet detection limit37.
In Fig.1B, it shows the Raman spectra of (d) GO, (e) rGO and (f)
rGO/TiO2NTs composite. The D band at 1325 cm-1 and G band at
1586 cm-1 correspond to structural defects on graphite carbon plane
and E2g mode of vibration of sp2 hybrid carbon atom, respectively38-
40. It can be seen that the ID/IG values (the intensity ratio of D band to
G band) of GO, rGO and rGO/TiO2NTs composite are 0.98, 1.37
and1.59, respectively. From Fig.1B, it confirms that GO was reduced
to rGO by the G band redshift and the increase of ID/IG41 , which
causes the G band of rGO to close that of non-doped reduced
Fig. 3 SEM (A, B), TEM (C,E), HRTEM (D) and TEM-EDS mapping
images of rGO/TiO2NTs composite(F,G,H).
graphene oxide (1582 cm-1). In Fig.1B (e) and (f), the intensity of G 2.2 ~ 2. 4 μm (Fig.3B). Reduced graphene oxide layer can be
band was change by the combination of TiO2NTs and rGO which observed on the surface of nanotubes. As shown in Fig.3C, it is
aggrandize ID/IG42,43. According to Fig.1C and Table S1, the specific clearly seen that rGO is tangled on the TiO2 tube wall, which
surface area of rGO/TiO2NTs , TiO2NTs, rGO and commercial TiO2 promotes the interface charge transfer to improve catalytic
was 240.7 m2 g-1, 141.4 m2 g-1, 184.1 m2 g-1 and 78.59 m2 g-1, performance for ORR. High resolution transmission electron
respectively. High ID/IG and large specific surface area not merely microscopy (HRTEM, Fig.3 D) shows two distinct lattice stripes, the
have more active site, but also is benifit for the adsorption of the O2 spacing d of which is 0.234 and 0.329 nm, belonging to the (004) of
and the diffusion of ions, thus promoting the ORR process44,45
.
anatase and the (002) of rGO, Respectively48. The selected electron
The elemental composition and chemical state of rGO/TiO2NTs diffraction patterns (SEAD) of rGO/TiO2NTs composite illustrate
composite can been obtained by XPS. XPS spectra of rGO/TiO2NTs that the rGO/TiO2NTs composite are polycrystalline, and two
(Fig.2A) shows the presence of C and Ti elements in the characteristic rings correspond to (004) and (101) crystal plane of
rGO/TiO2NTs composite. According to the high resolution Ti 2p anatase. The results show that the TiO2NTs has been successfully
grown after anodizing Ti sheet49. The distribution of Ti, O and C
spectrogram（Fig.2B）, the signal peaks of Ti 2p 3/2 and Ti 2p
1/2
assigned to Ti4+ are observed at 459.1 eV and 464.9 eV46,
respectively. It can be seen from XPS (Fig.2C and D) that the peaks
assigned to C-O bond (286.4 eV）and C=O bond (287.5 eV) are
weaken, the peaks assigned to O-C-O( 288.9 eV) and the dominant
graphitic C=C/C-C (284.6 eV) are disappeared in rGO47, which
confirms that GO was mostly reduced to rGO during
electrodeposition. In addition, when it is compared with TiO2NTs of
XPS full spectrum (Fig.S1), we can find that C content in
rGO/TiO2NTs is increased to 53.24% (15.22% in TiO2NTs),
indicating successful preparation of rGO.
elements is illustrated in Fig.3E-H. In addition, C component
was distributed uniformly in TiO2NTs as shown in Fig.S2B, but
more concentrated on TiO2 tube wall of rGO/TiO2NTs (Fig.3H). The
results show that the distribution of C is not onlyaffected by ethylene
glycol and carbon dioxide, but also the presence of rGO in TiO2 tube
wall of rGO/TiO2NTs. Therefore, it can be deduced that rGO is
successfully coated on the tube wall of TiO2 by electrodepositon.
Fig.4A and Fig.S3 shows cyclic voltammetry curves of rGO,
TiO2NTs and rGO/TiO2NTs composite in 0.1 M KOH solution
saturated with N2 and O2. Compared with the CV curve in N2
saturated KOH solution, oxygen reduction peaks can be detected in
O2 saturated KOH solution when rGO, TiO2NTs and rGO/TiO2NTs
was respectively used as an electrocatalyst in oxygen reduction
reaction50. As shown in Fig.4B, in O2 saturated KOH solution, the
The SEM images of rGO/TiO2NTs (Fig.3A) reveal that the
hollow oriented TiO2NTs is perpendicular to the surface of Ti wafer.
The thickness of the nanotubes wall is about 15 nm, the mean
diameter of TiO2NTs is about 80 ~ 100 nm, and the length is about
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Fig. 4 Cyclic voltammograms of rGO/TiO2NTs (A and B): (a) O2 ,
(b)N2-saturated , (c) rGO/TiO2NTs, (d) TiO2NTs and (e) rGO in O2-
saturated 0.1 M KOH solution at scanning rate of 10 mV s-1. LSV
curves of rGO/TiO2NTs (C and D) in O2-saturated 0.1 M KOH solution
with various rotation rates at scanning rate of 10 mV s-1 and
Koutecky-Levich plots for different catalysts at different electrode
potentials
Fig.6 RRDE curves of rGO/TiO2NTs (A) and Pt/C (B) electrode in O2-
saturated 0.1 M KOH solution at different rotation rates; (C)Electron
transfer numbers and (D) H2O2 yield in O2-saturated 0.1 M KOH
solution (1600rpm) at different electrode potential.
electrocatalytic performance and have great potential for ORR (as
oxygen reduction peak potential of rGO/TiO2NTs composite Table S2). It is also observed that the current density of
rGO/TiO2NTs composite (3.75 mA cm-2) at 0 V (vs. RHE) is much
(0.650V) is more positive than that of rGO (0.605V) and TiO2NTs
(0.615V). Hence, it indicates that either TiO2 nanotubes or rGO has
higher than that of TiO2NTs (1.30 mA cm-2) and rGO (1.49 mA cm-2)
electrocatalytic activity for ORR, so it may be concluded that there and is much closer to that of Pt/C (5.19 mA cm-2). The better
are active sites for ORR both in TiO2 nanotubes and rGO. But it is catalytic activity of the rGO/TiO2NTs composite is attributed to
worth mentioning that the synergistic effect of TiO2NTs with high
specific surface and highly conductive rGO makes electrocatalytic
activity of rGO/TiO2NTs for ORR to be notably improved.
synergistic effect of TiO2NTs and the high conductivity of rGO. As
shown in Fig.5B, Tafel slope of rGO/TiO2NTs composite is 34 mv
dec-1 at low current density, which is much smaller than that of
Linear sweep voltammetry (LSV) test was performed with a TiO2NTs ( 67 mv dec-1 ) and rGO ( 66 mv dec-1 ) but more closer to
rotating disk electrode (RDE) device for rGO/TiO2NTs, TiO2NTs that of Pt/C ( 33 mv dec-1)51. The interaction between TiO2NTs and
and rGO as shown in Fig.4C and Fig.S2-AB. According to the data
of Fig.4C and Fig S4-AB, the K-L diagram can be obtained by linear
fitting at 0.2 V, 0.3 V and 0.4 V potential with ω-1/2 as abscissa and -
J-1 as ordinate. The average electron transfer number of
rGO/TiO2NTs, TiO2NTs and rGO is 3.70, 2.94 and 1.75, respectively,
which indicatesthat the oxygen reduction reaction on rGO/TiO2NTs
mainly proceed through 4 e- transfer mechanism.
From Fig.5A，it is found that the initial potentials (the starting
point of current change) of rGO/TiO2NTs, TiO2NTs, rGO and Pt/C
are 0.80 V, 0.69 V, 0.68 V and 0.95 V (vs.RHE), respectively，which
indicates that the initial potentials of rGO/TiO2NTs composite is
closest to that of Pt/C. Moreover, as comparing with other Ti doped
carbon-based ORR catalysts reported previously, It can clearly been
seen that the as-prepared rGO/TiO2NTs composite shows batter
rGO is responsible for improving conductivity of rGO/TiO2NTs
Fig.7 A: Nyquist plots of rGO/TiO2NTs (a), rGO (b) and TiO2NTs (c) in
0.1
M KOH solution. B: Chronoamperometric responses for
rGO/TiO2NTs (d), Pt/C (e), TiO2NTs (f) and rGO (g) in 0.1 M KOH
solution for 20000 s at a potential of 0.78V. The CV curves of
rGO/TiO2NTs (C) and Pt/C (D) in O2-saturated 0.1 M KOH solution
(scanning rate: 10 mV s-1) after 1000 cycles.
Fig.5 Linear sweep voltammetry curves of different compounds in
O2-saturated 0.1 M KOH solution at rotation rate of 1600 rpm and
scan rate of 10 mV s-1 (A); Tafel plot of rGO/TiO2NTs, TiO2NTs, rGO,
and Pt/C (B)
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The rGO/TiO2NTs composite were syntVhieewsiAzreticdle Onlbinye
DOI: 10.1039/D0NJ00547A
electrochemical method at room temperature. TEM and
mapping images show that rGO is coated on the TiO2 tube wall.
Under alkaline conditions, the ORR on the rGO/TiO2NTs
composite modified electrode proceed mainly by 4 electrons
transfer meachanism with onset potential of 0.80 V and Tafel
slope of 46.9 mV dec-1. Moreover, it is worth mentioning that
the rGO/TiO2NTs composite as a electrocatalyst for ORR has
better stability and methanol resistance than the commercial
Pt/C catalyst. Its excellent electrocatalytic performance for
ORR is mainly attributed to the synergistic effect of TiO2NTs
with high specific surface and highly conductive rGO.
Although the activity of rGO/TiO2NTs is a little lower than that
of Pt/C catalyst, we believe that the research results in this
paper are of scientific significance and application prospect for
exploring non-precious metal catalysts for fuel cells and their
synthesis methods.
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Fig.8 The CV curves of rGO/TiO2NTs (A) and Pt/C (B) in N2-saturated,
O2-saturated and in an O2-saturated 0.1 M KOH solution upon the
addition of CH3OH (10 vol%).
composites and enhancing catalytic efficienc for oxygen reduction52.
As shown in Fig.6 A and B, the current value of disk (ID) is
much larger than that of the ring (IR) in the rotating disk-ring
electrode. According to the formula (2) and (3), n and yield of H2O2
were calculated in the range of 0.2 V to 0.7 V (vs.RHE). As shown in
Fig.6 C and D, n values of rGO/TiO2NTs composite is 3.69 to 3.79,
which is in agreement with that obtained by K-L equation (Fig.4D).
The H2O2yield of rGO/TiO2NTs composite is lower than 14.48%,
which further shows that the oxygen reduction reaction on Conflicts of interest
rGO/TiO2NTs follows mainly four-electron (4e-) process with the
No conflict of interest exits in the submission of this manuscript,
high selectivity of OH- as the main product.
and manuscript is approved by all authors for publication. I
would like to declare that the work described was original
research that has not been published previously, and not under
consideration for publication elsewhere.
Fig.7A is the AC impedance (EIS) diagram of rGO/TiO2NTs,
rGO and TiO2NTs. The radius of capacitive reactance arc is related
to the charge transfer efficiency of solid-liquid interface. It can be
seen that the arc radius of rGO/TiO2NTs composite is obviously
smaller than that of TiO2NTs, which means rGO/TiO2NTs composite
provides better conductivity by the combination of TiO2NTs and
rGO in the electrocatalysis process of ORR resulting in enhanced
catalytic activity53
In addition, rGO/TiO2NTs composite, using as a promising
cathode catalyst, has superior stability and anti-methanol
performance. As shown in Fig.7B, the stability of rGO/TiO2NTs
composite and commercial Pt/C were measured by
chronoamperometry ( I-T ) in 0.1 M KOH solution saturated with
oxygen. The relative current density of rGO/TiO2NTs composite
Acknowledgements
This work was supported by the National Natural Science
Foundation of China (No. 21571034).
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The enhanced electrocatalytic of rGO/TiO2NTs for ORR result from increasing specific
surface, active site and accelerating the electron conductivity.
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