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YAO LI et al.
surface areas of the reported NiS samples were less Emmett-Teller (BET) surface area were measured at
2
2
–1
77 K on a Micromeritics ASAP 2020M system.
than 300 m g .
Herein, a novel oxidative ethanol catalyst has been
successfully developed using high surface area meso-
2
.3. Electrochemical Measurements
2
–1
porous NiS (368.5 m g ) as catalytic materials. NiS
2
2
Cyclic voltammetry (CV) and chronoamperomet-
is rationally and readily prepared via a hydrothermal
route. The method achieves a controllable BET sur-
face area of the as-synthesized sample by adjusting pH
ric studies were performed using a CHI660D electro-
chemical workstation (Shanghai Chenhua, China),
which were carried out in a conventional three-elec-
trode electrochemical cell. A Pt wire, a saturated calo-
mel electrode (SCE, 3 M KCl) and a glassy carbon
electrode (GCE, a diameter of 3 mm) were used as the
counter, reference and working electrodes, respec-
tively. All potential values were referred to the SCE.
Cyclic voltammetry (CV) and Chronoamperometry
value. The electrochemical performances of the NiS
2
catalysts were evaluated. The optimized sample of
NiS -4 contains small NiS pore width of 32.6 nm in
2
2
2
–1
size, large surface area of 368.5 m g . The high sur-
face areas and abundant mesopores render NiS -4 an
2
excellent electrocatalytic performance for ethanol oxi-
dation and a good long-term cycling stability.
(
CA) were used to study the activity and stability of the
catalysts for ethanol oxidation reaction. The current
densities were calculated using the geometrical area of
the electrode. The glassy carbon electrode was
mechanically polished with 50 nm gamma alumina
powders, rinsed thoroughly with distilled water, and
dried at room temperature. Electrochemical imped-
ance spectroscopy (EIS) tests started from 100 kHz to
2
. EXPERIMENT
2
.1. Preparation of Catalysts
All reagents were of analytical grade without fur-
ther purification and post-treatment. Distilled water
was used in all experiments. In a typical synthesis of
1
Hz with 5 mV potential amplitude. To prepare work-
NiS samples, 1.6 g sodium sulfide, 0.7 g nickel chlo-
2
ing electrode, a slurry was prepared by mixing 0.78 mg
ride was successively dissolved in 50 mL distilled
water. The pH values were adjusted to 4–7. Subse-
quently, the mixtures solution was introduced into a
NiS samples, 30 μL Nafion solution, 270 μL water,
2
and 90 μL isopropyl alcohol. After sonicated for
3
0 min at room temperature, 10 μL of the slurry was
1
00 mL Teflon-lined autoclave. The reaction was kept
dropped on the active area of the glassy carbon elec-
trode and then dried.
at 120°C for 10 h, respectively. After cooling to room
temperature, centrifugation treatment produced a
series of products. The products were washed with
1
.0 M HCl solution and deionized water for several
3. RESULTS AND DISCUSSION
times, and all of the samples were finally dried in a
vacuum oven at 60°C overnight. The obtained samples
with the different pH value were sequentially denoted
as NiS -4, NiS -5, NiS -6, and NiS -7, respectively.
3.1. Physical Characterization of As-Prepared Catalysts
The morphologies of the as-synthesized NiS cata-
2
2
2
2
2
lysts were characterized by SEM. NiS catalysts are
2
composed of dispersive particles of nanometer in sizes.
All NiS samples are aggregates of irregular particles
2.2. Characterization
2
with coarse surfaces. Figure 1a shows that the NiS -4
2
The morphologies of the samples were studied by
field-emission scanning electron microscope
is dominated by small and uniform nanoparticles. The
fundamental unit of these nanoparticles is an agglom-
erate rather than ultimate nanoparticle. Compared to
the Fig. 1a, the Figs. 1b–1d shows the uniformity of
NiS -5, NiS -6, and NiS -7 are slightly reduced
(
FESEM, Hitachi S-4800). Hitachi H-7650 transmis-
sion electron microscope (TEM, operating voltage
00 kV), and JEOL JEM 2010 field emission transmis-
sion electron microscope (HRTEM, operating voltage
00 kV) were used to characterize the microstructures
1
2
2
2
because of the emergence of irregular shaped particles.
And the aggregation with irregular structure is still the
major product, demonstrating that it is a promising
route for facile and scalable synthesis of high-purity
2
of the samples. The samples for TEM and HRTEM
observations were prepared by dipping sonicated etha-
nol suspensions of powdery samples onto the copper
grids. The phase identifications were carried out with
powder X-ray diffraction (XRD) on a Bruker D8 Dis-
NiS without any additional procedure.
2
TEM test was carried out to further explore the
cover with CuK radiation (λ = 1.5418 Å). The diffrac- microstructure of NiS -4 catalyst. The TEM image of
2
α
tions were collected in a two theta range of 10°‒80° the as-prepared NiS -4 catalyst in Fig. 2a clearly dis-
2
–1
with a step of 0.02° and a rate of 8° min . X-ray pho- plays an irregular sphere structure with a diameter of
toelectron spectroscopy (XPS, ESCALAB 250 X-ray about 150 nm. In inset of Fig. 2b, The distances of two
photoelectron spectrometer) was applied to investigate adjacent lattice fringes are 0.283 and 0.327 nm,
the compositions and chemical states. The nitrogen respectively, corresponding to the d-spacing of the
adsorption-desorption isotherms and the Brunauer- (200) plane and the (111) plane of the NiS [16].
2
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
Vol. 93
No. 8
2019