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Room-Temperature Wet Chemical Synthesis of Au NPs/TiH2/Nanocarved Ti Self-Supported Electrocatalysts for Highly Efficient H2 Generation
journal contribution
posted on 2017-08-03, 00:00 authored by Mohammed A. Amin, Sahar A. Fadlallah, Ghaida S. Alosaimi, Emad M. Ahmed, Nasser Y. Mostafa, Pascal Roussel, Sabine Szunerits, Rabah BoukherroubSelf-supported
electrocatalysts are a new class of materials exhibiting
high catalytic performance for various electrochemical processes and
can be directly equipped in energy conversion devices. We present
here, for the first time, sparse Au NPs self-supported on etched Ti
(nanocarved Ti substrate self-supported with TiH2) as promising
catalysts for the electrochemical generation of hydrogen (H2) in KOH solutions. Cleaned, as-polished Ti substrates were etched
in highly concentrated sulfuric acid solutions without and with 0.1
M NH4F at room temperature for 15 min. These two etching
processes yielded a thin layer of TiH2 (the corrosion product
of the etching process) self-supported on nanocarved Ti substrates
with different morphologies. While F–-free etching
process led to formation of parallel channels (average width: 200
nm), where each channel consists of an array of rounded cavities (average
width: 150 nm), etching in the presence of F– yielded
Ti surface carved with nanogrooves (average width: 100 nm) in parallel
orientation. Au NPs were then grown in situ (self-supported)
on such etched surfaces via immersion in a standard gold solution
at room temperature without using stabilizers or reducing agents,
producing Au NPs/TiH2/nanostructured Ti catalysts. These
materials were characterized by scanning electron microscopy/energy-dispersive
spectroscopy (SEM/EDS), grazing incidence X-ray diffraction (GIXRD),
and X-ray photoelectron spectroscopy (XPS). GIXRD confirmed the formation
of Au2Ti phase, thus referring to strong chemical interaction
between the supported Au NPs and the substrate surface (also evidenced
from XPS) as well as a titanium hydride phase of chemical composition
TiH2. Electrochemical measurements in 0.1 M KOH solution
revealed outstanding hydrogen evolution reaction (HER) electrocatalytic
activity for our synthesized catalysts, with Au NPs/TiH2/nanogrooved Ti catalyst being the best one among them. It exhibited
fast kinetics for the HER with onset potentials as low as −22
mV vs. RHE, high exchange current density of 0.7 mA cm–2, and a Tafel slope of 113 mV dec–1. These HER
electrochemical kinetic parameters are very close to those measured
here for a commercial Pt/C catalyst (onset potential: −20 mV,
Tafel slope: 110 mV dec–1, and exchange current
density: 0.75 mA cm–2). The high catalytic activity
of these materials was attributed to the catalytic impacts of both
TiH2 phase and self-supported Au NPs (active sites for
the catalytic reduction of water to H2), in addition to
their nanostructured features which provide a large-surface area for
the HER.
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Keywords
titanium hydride phaseXPSTafel slopeTiH 2 phaseRHEnanocarved Ti substrate self-supported2 Ti phasehydrogen evolution reactionmVenergy conversion devices0.1 M NH 4 FEfficient H 2 Generation Self-supported electrocatalystsNPSEMHERchemical composition TiH 2GIXRDas-polished Ti substratesincidence X-ray diffractionetching processTiH 2nanocarved Ti substratesX-ray photoelectron spectroscopy0.1 M KOH solutionroom temperature
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