PREPARATION OF COBALT/SULFUR/GRAPHITE ELECTROCATALYST
1673
Monowave 200) at atmospheric pressure. The initial Microscopy (TEM) using an FESEM- MIRA III
materials cobalt(II) chloride (1.625 g, 12.5 mmol), (TESCAN) and an EM10C-100 KV (Zeiss) devices,
high purity urea (3 g, 50 mmol), and phthalic anhy- respectively. Pores size and specific surface area of
dride (7.4 g, 50 mmol) were dissolved in 50 mL of sat- Co–S–GC were determined on a BELSORP-MINI
urated solution of sodium chloride. Then 0.1 mmol of the (Japan. Inc) instrument.
ammonium heptamolybdate catalyst and 0.5 mmol of
the lauric acid capping agent were added to the mix-
Electrochemical Evaluation
ture. The resulting mixture was exposed to microwave
irradiation for 30 min at a controlled temperature
(120°C). The CoPc powders were filtered, washed,
and dried in air oven at 80°C for overnight. Elemental
Microanalysis (flash EA112 automatic elemental ana-
lyzer) was used for synthesized CoPc (%): Co, 10.41;
C, 67.39; N, 19.48; H, 2.72. Experimental results are
in good agreement with theoretical data.
The catalyst performance of the obtained samples
for ORR were evaluated by liner sweep voltammetry
(LSV) and cyclic voltammetry (CV) using an Autolab
PGSTAT302N potentiostat/galvanostat. The mea-
surements were completed with employing a conven-
tional three electrode cell. Next, the glassy carbon rod
(2 mm diameter) was used as counter electrode and
the Ag/AgCl electrode was employed as a reference
electrode. Afterward, a catalyst film coated glassy car-
bon rotating-disk electrode (RDE) with a surface area
of 0.19625 cm2 was used as a working electrode. Then,
the catalyst ink was produced by adding 2 mg of cata-
lyst to in a solution containing 50 μL of Nafion (5 wt %)
and 450 μL of deionized water, moreover, the suspen-
sion was sonicated for 30 min. At the next step, 20 μL
of the catalyst ink was placed onto RDE surface and
was dried slowly to form dry catalyst film (catalyst
loading ≈ 0.4 mg/cm2). Additionally, CVs and LSVs
were performed in O2-saturated KOH (0.1 mol/L)
solution by varying the potential from –1.00 to 0.20 V vs.
Ag/AgCl electrode at scan rate of 50 mV/s and
10 mV/s, respectively. The electrolyte temperature was
25 1°C and the background CV and LSV measure-
ments were performed in the N2-saturated KOH
(0.1 mol/L) solution.
Found (%): Co, 10.41; C, 67.39; N, 19.48; H, 2.72.
For CoPc anal. calcd. (%): Co, 10.32; C, 67.27; N,
19.61; H, 2.80.
Preparation of Co–S–GC Catalyst: Partial Oxidation
of Graphite and Linking of CoPc on the Surface of S-GC
Co–S–GC preparation was included the following
steps. Briefly, ca. 100 mmol of graphite powder was
immersed in 200 mL of concentrated hydrochloric
acid (37%) for partially oxidation of graphite surface
and stirred for 24 h. After acid treatment, the black
powder was washed, filtered, and dried in air oven at
80°C for overnight. Then, about 50 mmol of Na2S
powder was added to 50 mL of dimethylformamide
(DMF) to obtain a solution and after that temperature
decreased by ice bath. About 50 mmol of dried graph-
ite oxide powder was broadcasted in the solution and
the mixture was stirred and reacted for 12 h. The
obtained sample was filtered, washed, and dried in air
oven at 80°C for overnight. To prepare the Co–S–GC,
250 mg of dried powder and 250 mg obtained CoPc
powder were dispersed in DMF (50 mL) and then
cooled by ice bath. The mixture was stirred (60 rpm)
and reacted for 24 h. The Co–S–GC was filtered,
washed, and dried in air oven at 80°C for overnight.
RESULTS AND DISCUSSION
The CoPc and Co–S–GC catalysts were synthe-
sized via a low temperature method. The CoPc was
obtained using a microwave reactor with cheap raw
materials at low temperature. Graphite oxide was pre-
pared in a mild oxidizing medium. The graphite oxide
surface was then modified by sulfur atoms and CoPc
via a low temperature process (Co–S–GC). The
enzyme-like structure of Co–S–GC contains 5.54 wt %
of cobalt atoms and 2.91 wt % of sulfur atoms (ICP-
OES results).
Physical Characterization
The FT-IR spectra for the CoPc, Graphite (GC),
and Co–S–GC catalyst were recorded using a Ther-
moNicolet model NEXUS FT-IR 670 spectrometer
between 4000–400 cm–1. X-ray diffraction (XRD) of
the samples were specified using an X’ Pert Pro-Pan-
alytical device with CuKα radiation with a wavelength
of 1.54 A at room temperature. The 2θ angular data
were collected between 2° and 80° at the scan rate of
1° per step. Amounts of laded cobalt (55 412 ppm) and
sulfur (29 071 ppm) in Co–S–GC were determined by
an inductively coupled plasma-optical emission spec-
trometer (ICP-MS 7900). The catalyst particles size
and morphology were directed by Scanning Electron
Microscopy (SEM) and Transmission Electron
SEM and TEM Images of Co–S–GC
Figures 1a and 1b show morphological images of
Co–S–GC catalyst that was characterized by field
emission SEM.
A network structure of Co–S–GC consist of ran-
domly crumpled sheets observe in the form of multi-
layer solid, which might be attributed to the presence
of foreign sulfur atoms. The TEM images indicate the
homogeneously amorphous texture of graphitic car-
bon that the Co (N4) centers with diameter less than
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 64 No. 13 2019