DOI: 10.1039/C5CC01240F
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Fig. 2c shows the i-t chronoamperometric response for the Mo2C-
G at the overpotential of 160 mV. The as-measured i-t curve is in
typical serrate shape, which results from the alternating processes of
bubble accumulation and bubble release. The current density differs
by less than 0.2 mA cm-2 before and after release, indicating that the
bubbles can be easily released on the surface of the Mo2C-G. This
efficient bubble release is likely originated from the porous structure
of the Mo2C-G. The HER activity of the Mo2C-G was further
evaluated by depositing catalyst on the glassy carbon electrode at
different loadings. Fig. 2d shows the optimal loading is 0.8 mg cm-2.
† Electronic Supplementary Information (ESI) available: Experimental
section and Additional experimental data. See DOI: 10.1039/b000000x/
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Time / h
,
Fig. 3 Stability test of the MoC-G and Mo2C-G catalysts.
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High durability in acid media is also a challenge to the Mo-based
compounds in their practical application. The long-term stability of
the MoC-G and Mo2C-G catalysts were examined by extended
electrolysis at fixed overpotentials and shown in Fig. 3. After a long
period of 20 h, the current density on the MoC-G and Mo2C-G
electrodes only show negligible degradation, which could be due to
the consumption of proton in the system and the hindrance of the
reaction by hydrogen bubbles remaining on the electrodes. The
cyclic voltammograms of MoC-G and Mo2C-G electrodes obtained
before and after 2,000 cycles are shown in Fig. S5. No obvious
degradation on both MoC-G and Mo2C-G electrodes. The high
durability of the MoC-G and Mo2C-G mianly originates from: 1) the
coupling effect between molybdenum carbides and graphene; 2) the
tight anchoring result fom the in situ synthesis method.
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We report the synthesis of nanostructured molybdenum
carbides with clean surface on graphene via a simple in situ
method. The sizes of the MoC and Mo2C are 2.5 nm and 5.0 nm,
respectively, which are much smaller than those of
molybdenum carbides previously reported. The MoC-G and
Mo2C-G show extraordinary high acitivity for HER with
negligible onset overpotentials (15 mV for the MoC-G and
nearly zero onset overpotential for the Mo2C-G), also the
smallest onset overpotentials in existing literature. In addition,
both the MoC-G and Mo2C-G exhibit superior durability. The
outstanding performance of MoC-G and Mo2C-G for HER is
attributed to the large number of active sites due to the small
sizes, fast available electron transfer capabilities offered by
graphene, clean surfaces of the MoC and Mo2C nanoparticles
and the porous microstructure. The MoC-G and Mo2C-G are
promising non-precious metal catalysts for HER with their
good activity, high stability, and low price.
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This work was supported by the 100 Talents Project of
Chinese Academy of Sciences, China (H9291440S3).
21 E. J. Popczun, J. R. McKone, C. G. Read, A. J. Biacchi, A. M.
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Notes and references
Dongguan Neutron Science Center, Institute of High Energy Physics,
,
a
Chinese Academy of Sciences, Dongguan 523808, China. Fax: +86 769
89156463; Tel: +86 769 89156463; E-mail: taoj@ihep.ac.cn
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