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ment, USA. Deionized water with an electrical resistivity of
18.4 MWcm was used to prepare suspensions and electrolytes.
sion was drop-casted on the GC surface, and GC could be renewed
by polishing with 0.05 mm alumina particles on a polishing pad
after each measurement. Deionized water was evaporated at room
temperature to give randomly distributed materials. CV and linear
sweep voltammetry (LSV) measurements were conducted by using
a three-electrode system: modified GC, Pt, and Ag/AgCl as work-
ing, counter, and reference electrodes. PBS (50 mm, pH 7.2) was
used as a background electrolyte for CV measurements at a scan
rate of 100 mVSꢀ1, whereas 0.5m sulfuric acid was utilized as an
Apparatus
SEM was performed by using a JEOL 7600F field-emission scanning
electron microscope (JEOL, Japan), at a voltage of 2 KV. EDS data
were recorded at an accelerating voltage of 15 KV. XPS measure-
ments were carried out by utilizing a MgKa source (SPECS, Germa-
ny) at 1253 eV, as well as a Phibos 100 spectrometer. Wide-scan
and high-resolution spectra of Ga 3d, In 3d, S 2p, Se 3d, C 1s, and
O 1s were obtained to analyze the surface composition and metal-
to-chalcogen ratio of the materials. The 284.5 eV peak of C 1s was
used for calibration. Powder XRD data were collected at room tem-
perature with a Bruker D8 Discoverer powder diffractometer with
parafocusing Bragg–Brentano geometry by using CuKa radiation
(l=0.15418 nm, U=40 kV, I=40 mA). Data were scanned with an
ultrafast detector (Lynxeye XE) over the angular range 2q=10–808
with a step size of 0.028 (2q). Data evaluation was performed in
the software package Eva. An inVia Raman microscope (Renishaw,
England) with a charge-coupled device (CCD) detector was used
for Raman spectroscopy in back-scattering geometry. A Nd-YAG
laser (l=532 nm, 50 mW) with a 50ꢁ magnification objective was
used for measurements. Instrument calibration was performed
with a silicon reference that gave a peak center at 520 cmꢀ1 and
a resolution of less than 1 cmꢀ1. To avoid radiation damage, the
laser power output used for these measurements was kept at
5 mW. The micro-photoluminescence measurements were per-
formed by using a Nd-YAG laser (l=532 nm, 50 mW) with a 50ꢁ
magnification objective and l=325 nm HeꢀCd laser (22 mW) with
a 40ꢁ magnification UV objective. For measurements with Nd-YAG
and HeꢀCd lasers, laser powers of 0.5 and 2.2 mW, respectively,
were used. Characterization by AFM was performed on a NT-MDT
Ntegra spectrometer from NT-MDT in tapping mode. The measure-
ments were performed on freshly cleaved basal planes. Edge
planes were prepared for measurements by cutting and polishing
crystals perpendicularly to the basal plane. The electrochemical
measurements were conducted by using a mAutolab III electro-
chemical analyzer (Eco Chemie, The Netherlands) with the NOVA
version 1.8 software.
electrolyte for LSV experiments at a scan rate of 2 mVSꢀ1
.
Acknowledgements
M.P. acknowledges a Tier 2 grant (MOE2013-T2-1-056; ARC 35/
13) from the Ministry of Education, Singapore. Z.S. and J.L.
were supported by the Czech Science Foundation (GACR no.
15-07912S) and Specific University Research Fund (MSMT no.
20-SVV/2016).
Keywords: chalcogens
· electrochemistry · heterogeneous
catalysis · hydrogen evolution reaction · layered compounds
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&
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Chem. Eur. J. 2016, 22, 1 – 8
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