3 research outputs found
Effect of Chloride Anions on the Synthesis and Enhanced Catalytic Activity of Silver Nanocoral Electrodes for CO<sub>2</sub> Electroreduction
Metallic silver (Ag) is known as
an efficient electrocatalyst for
the conversion of carbon dioxide (CO<sub>2</sub>) to carbon monoxide
(CO) in aqueous or nonaqueous electrolytes. However, polycrystalline
silver electrocatalysts require significant overpotentials in order
to achieve high selectivity toward CO<sub>2</sub> reduction, as compared
to the side reaction of hydrogen evolution. Here we report a high-surface-area
Ag nanocoral catalyst, fabricated by an oxidation–reduction
method in the presence of chloride anions in an aqueous medium, for
the electro-reduction of CO<sub>2</sub> to CO with a current efficiency
of 95% at the low overpotential of 0.37 V and the current density
of 2 mA cm<sup>–2</sup>. A lower limit of TOF of 0.4 s<sup>–1</sup> and TON > 8.8 × 10<sup>4</sup> (over 72 h)
was
estimated for the Ag nanocoral catalyst at an overpotential of 0.49
V. The Ag nanocoral catalyst demonstrated a 32-fold enhancement in
surface-area-normalized activity, at an overpotential of 0.49 V, as
compared to Ag foil. We found that, in addition to the effect on nanomorphology,
the adsorbed chloride anions play a critical role in the observed
enhanced activity and selectivity of the Ag nanocoral electrocatalyst
toward CO<sub>2</sub> reduction. Synchrotron X-ray photoelectron spectroscopy
(XPS) studies along with a series of control experiments suggest that
the chloride anions, remaining adsorbed on the catalyst surface under
electrocatalytic conditions, can effectively inhibit the side reaction
of hydrogen evolution and enhance the catalytic performance for CO<sub>2</sub> reduction
High Performance Pt Monolayer Catalysts Produced via Core-Catalyzed Coating in Ethanol
Platinum monolayer core–shell
nanocatalysts were shown to
have excellent catalytic activities and stabilities. Usually, they
are fabricated via electrochemical routes. Here, we report a surfactant-free,
ethanol-based, wet chemical approach to coating Pd nanoparticles with
uniform Pt atomic layers, inspired by aerobic alcohol oxidation catalyzed
by the Pd cores. The as-prepared Pt monolayer electrocatalysts also
exhibited high electrocatalytic performance toward the oxygen reduction
reaction
DFT Study of Oxygen Reduction Reaction on Os/Pt Core–Shell Catalysts Validated by Electrochemical Experiment
Proton
exchange membrane fuel cells (PEMFCs) have attracted much
attention as an alternative source of energy with a number of advantages,
including high efficiency, sustainability, and environmentally friendly
operation. However, the low kinetics of the oxygen reduction reaction
(ORR) restricts the performance of PEMFCs. Various types of catalysts
have been developed to improve the ORR efficiency, but this problem
still needs further investigations and improvements. In this paper,
we propose advanced Os/Pt core–shell catalysts based on our
previous study on segregation of both bare surfaces and surfaces exposed
to ORR adsorbates, and we evaluate the catalytic activity of the proposed
materials by density functional theory (DFT). Quantum mechanics was
applied to calculate binding energies of ORR species and reaction
energy barriers on Os/Pt core–shell catalysts. Our calculations
predict a much better catalytic activity of the Os/Pt system than
that of pure Pt. We find that the ligand effect of the Os substrate
is more important than the lattice compression strain effect. To validate
our DFT prediction, we demonstrate the fabrication of Os/Pt core–shell
nanoparticles using the underpotential deposition (UPD) technique
and succeeding galvanic displacement reaction between the Pt ions
and Cu-coated Os nanoparticles. The Os/Pt/C samples were evaluated
for electrocatalytic activities toward the ORR in acidic electrolytes.
The samples with two consecutive UPD-displacement reaction cycles
show 3.5 to 5 times better ORR activities as compared to those of
commercially available Pt/C. Our results show good agreement between
the computational predictions and electrochemical experimental data
for the Os/Pt core–shell ORR catalysts