Two nickel/nitrogenated
graphene hybrid electrodes (
Ni-NrGO
NH3
and
Ni-NrGO
APTES
) were
synthesized, and their catalytic activity with respect
to the hydrogen evolution reaction (HER) in alkaline media was analyzed.
Incorporation of nitrogen to the carbon structure in graphene oxide
(GO) or reduced GO (rGO) flakes in aqueous solutions was carried out
based on two different configurations.
NrGO
NH
3
particles were obtained
by a hydrothermal method using ammonium hydroxide as the precursor,
and
NGO
APTES
particles were obtained
by silanization (APTES functionalization) of GO sheets. Aqueous dispersions
containing
NrGO
NH
3
and
NGO
APTES
particles
were added to the traditional nickel Watts plating bath in order to
prepare the
Ni-NrGO
NH
3
and
Ni-NrGO
APTES
catalysts, respectively. Nickel substrates were coated with the
hybrid nickel electrodeposits and used as electrodes for hydrogen
production. The
Ni-NrGO
catalysts show a higher activity
than the conventional nickel electrodeposited electrodes, particularly
the ones containing APTES molecules because they allow obtaining a
hydrogen current density 130% higher than conventional Ni-plated electrodes
with a Watts bath in the absence of additives. In addition, both catalysts
show a low deactivation rate during the ageing treatment, which is
a sign of a longer midlife for the catalyst. Cyclic voltammetry and
electrochemical impedance spectroscopy measurements were used for
examination of the catalytic efficiency of hybrid
Ni-NrGO
electrodes for HER in KOH solution. High values of exchange current
densities, 8.53 × 10
–4
and 2.53 × 10
–5
mA cm
–2
for HER in alkaline solutions
on
Ni-NrGO
NH
3
and
Ni-NrGO
APTES
electrodes,
respectively, were obtained.
Hybrid Ni–MoS2 electrocatalysts
are one of the
most promising materials for the generation of hydrogen in an alkaline
medium. This paper presents a simple and economical method for the
rational synthesis of Ni–MoS2 nanocomposites, maximizing
the contact area and reducing the contact resistance between MoS2 and the nickel surface. In this way, it is possible to maximize
the synergistic effect between both materials, obtaining a hybrid
nanomaterial with high electroactivity toward the generation of hydrogen.
A conventional nickel catalyst (NWts) was compared with the one obtained
by dispersing a small amount of MoS2 (0.1425 μg cm–2) over the surface denoted as NMS, and with the same
type of catalyst after a 10 s electrodeposition of Ni (NMSN), to have
a Ni–MoS2–Ni laminar structure. Thus, the
NMSN catalyst shows a current density value of 59% higher than the
observed value on the NMS catalyst and 113% higher than that found
in the conventional NWts catalyst. Finally, these results were analyzed
using DFT theoretical studies. DFT calculations predict a charge transfer
between MoS2 and nearby Ni atoms, which becomes more important
when a second Ni layer is placed on MoS2 explaining the
increase in catalytic activity in the NMSN catalyst. Furthermore,
the high hydrophobicity of the MoS2 plays an important
role in the electrochemically active surface when comparing NMS and
NMSN catalysts.
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