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V.T.T. Phan et al. / C. R. Chimie xxx (xxxx) xxx
In reality, the support material plays a decisive role in
that nanostructured 20 wt. % Pt/Ti1-xIrxO2 catalysts could be
prospective candidates for anode electrocatalysis in DMFCs.
both the activity and durability of catalysts, which is
generally used for dispersing catalyst particles [6,7]. At
present, black carbon, which is commonly Vulcan XCe72, is
widely used as a support for platinum (Pt) catalysts in
DMFCs because of its large surface area and high electrical
conductivity [8,9]. However, the poor durability of these
catalysts under practical conditions is still problematic
considering the serious degradation of carbonaceous sup-
ports [10]. Recently, Pt supported on modified reducible
metal oxide materials, such as SnO2 [11], WO3 [12], SiO2
[13], and CeOx [14], has been considered to be a promising
candidate to replace the commercial Pt/C (E-TEK) catalyst
for fuel cell applications. Among numerous metal oxides,
titanium dioxide (TiO2) with prominent properties, such as
effective cost, harmlessness, availability, and especially
high corrosion resistance and good electrochemical stabil-
ity in a highly corrosive environment, attracted great in-
terest of researchers. However, the intrinsically low electric
conductivity was the primary barrier for developing TiO2 as
a support material for electrocatalysts in fuel cells [15].
In this study, the robust non-carbon Ti1-xIrxO2 (x ¼ 0.1,
0.2, 0.3) supports with the high corrosion resistance in
acidic and oxidative environment and high electrical con-
ductivity were prepared by using a facile hydrothermal
route without applying any surfactants and further heat
treatment for solving the major restriction of the carbon
support and the issue of the TiO2 material. Among several
transition metals, iridium (Ir) shows many excellent prop-
erties, such as high stability, high electrical conductivity of
2.12 ꢀ 105 S/cm [16], and the radius approximation of Ti4þ
(0.605 Å) and Ir4þ (0.625 Å) [17]. The incorporation of Ir
ions into the TiO2 lattice not only could enhance the
intrinsically low electric conductivity of TiO2 [18] but also
promoted the performance of Ir-doped TiO2-supported Pt
NPs by the bifunctional mechanism, the electronic effect,
and the strong metal-support interaction (SMSI) effect
[19e21]. After doping, the electrical conductivity and sur-
face area of Ti1-xIrxO2 materials are observed to be higher
than those of the undoped TiO2 thanks to the very high
electrical conductivity of Ir metal. Therefore, Ir-doped TiO2
materials have been considered as the promising materials
for replacing carbonaceous materials prone to corrosion.
In addition, the possible applicability of a series of
20 wt. % Pt/Ti1-xIrxO2 catalysts toward methanol electro-
oxidation in DMFCs was also investigated and they were
compared with the commercial 20 wt. % Pt/C (E-TEK)
catalyst. The same Pt loading of 20 wt. % was deposited
on Ti1-xIrxO2 materials by a modified sodium borohy-
dride reduction method. The cyclic voltammetry (CV)
curves in the methanol solution showed that all of the
20 wt. % Pt/Ti1-xIrxO2 catalysts possess higher forward
current density and smaller onset potential, a representa-
tive of catalyst activity, as compared with the commercial
20 wt. % Pt/C (E-TEK) catalyst. Moreover, the If/Ib ratios of
20 wt. % Pt/Ti1-xIrxO2 catalysts are significantly higher than
that of the commercial 20 wt. % Pt/C (E-TEK) catalyst in all
cases, suggesting their superior CO tolerance. The superior
stability of 20 wt. % Pt/Ti1-xIrxO2 catalysts to the commercial
20 wt. % Pt/C (E-TEK) catalyst was confirmed by the chro-
noamperometric (CA) test. Finally, these results suggest
2. Experimental section
2.1. Materials
Iridium trichloride hydrate (IrCl3$xH2O, 99.9%, 52 wt. %
Ir) was purchased from Sigma-Aldrich, USA, and titanium
tetrachloride (TiCl4, 99.5%) was purchased from Aladdin,
China. Hexachloroplatinic acid (H2PtCl6$xH2O, 99.9%,
38e40% Pt) was purchased from Sigma-Aldrich. Sodium
borohydride (NaBH4, ꢁ98%) and sodium hydroxide (NaOH,
ꢁ98%) were purchased from Sigma-Aldrich. Ethylene glycol
(EG, 99.5%) and hydrochloric acid (HCl, 37%) were pur-
chased from Merck, Belgium. All chemical reagents and
solvents were used without further purification. Purified
water was used during the experiments.
2.2. Synthesis
2.2.1. Synthesis of Ti1-xIrxO2 supports
Ti1-xIrxO2 supports with various iridium compositions
(labeled as Ti0.9Ir0.1O2, Ti0.8Ir0.2O2, and Ti0.7Ir0.3O2) were
carefully prepared from iridium trichloride hydrate and
titanium tetrachloride precursors by the same facile hy-
drothermal route without applying any surfactants and
further heat treatment. The appropriate amounts of tita-
nium tetrachloride were mixed with the specified amounts
of iridium trichloride hydrate for the synthesis of Ti1-xIrxO2
materials. Then, the solutions were adjusted to obtain the
pH value of 1 by using 37% HCl solution and vigorous stir-
ring at ambient temperature to obtain 50 mL of each ho-
mogeneous solution containing 28 mM TiCl4 and 12 mM
IrCl3, 32 mM TiCl4 and 8 mM IrCl3, and 36 mM TiCl4 and
4 mM IrCl3 corresponding to the desired molar ratios of
Ti:Ir (0.7:0.3, 0.8:0.2, and 0.9:0.1). Thereafter, the final so-
lutions were transferred into Teflon-lined autoclaves to
perform the hydrothermal process at 210 ꢂC in 8 h and then
the solutions were naturally cooled down to ambient
temperature. Subsequently, Ti1-xIrxO2 precipitants were
separated by centrifugation, filtered, and dried overnight
in an oven at 80 ꢂC for further analysis. Finally, undoped
TiO2 materials were prepared by the same procedure as
Ti1-xIrxO2 materials were used for comparison.
2.2.2. Synthesis of 20 wt. % Pt/Ti1-xIrxO2 catalysts
The same Pt loadings of 20 wt. % were anchored over the
Ti1-xIrxO2 supports by using a modified reduction method
with NaBH4 at ambient temperature. In a typical prepara-
tion method, the homogeneous suspensions were prepared
by dispersing 110 mg of the Ir-doped TiO2 materials into the
mixed solution of 3 mL of 0.05 M H2PtCl6, 0.5 mL of EG, and
25 mL of purified water associated with ultrasonic blending
for 15 min, followed by adjusting the pH value to 11 by
slowly adding the 1 M NaOH solution. Then, the reduction
process was carried out by adding 3 mL of NaBH4 dropwise
into the mixture under vigorous stirring for 2 h. Thereafter,
the resultant products were collected by centrifugation,
washed several times with purified water, and dried over-
night at 80 ꢂC in an oven. Finally, the obtained catalysts
Please cite this article as: V.T.T. Phan et al., Investigation of iridium composition in Ti1exIrxO2 (x ¼ 0.1, 0.2, 0.3) nanostructures as
j.crci.2019.09.001
Phan, Vi Thuy Thi
