Chemistry Reference
In-Depth Information
measurements all indicated that using CO blocking after the first deposition step
resulted in the coverage of remaining exposed Au sites with Pt deposited in the
subsequent step rather than continued growth at the ends of the NRs. The effect of
smoothing Pt deposition and increasing its coverage of Au also resulted in greater
stability of the NRs. STEM-HAADF carried out on the same samples after more
than 18 months showed that the NRs prepared with CO blocking retained their
structure [
82
].
Our study also showed that the different surface compositions of the Au-Pt NRs
prepared with CO blocking and without CO blocking had an influence on catalytic
activity and selectivity towards the electrochemical reduction of oxygen. This
reaction was more selective towards water as a product and had higher rate constant
and specific activity (per area Pt) when carried out with NRs prepared with CO
blocking, as a result of the higher Pt:Au surface ratio [
82
].
7 Conclusions
In this brief review, we have shown the potential to gain a fundamental understand-
ing of, and control over, the atomic detail of metal-metal bonding at the interfaces
of core-shell nanorods and nanoparticles. Using a combination of experimental and
computer simulation techniques and by making comparisons between related
bimetallic systems has proved to be very effective.
Using examples from our recent work, we have shown that experimental struc-
tural characterisation can be conducted to great effect by exploiting the atomically
resolved capabilities of ac-STEM imaging. For bimetallic nanosystems comprising
elements from different rows in the period table (such as AuRh and AuPd), STEM-
HAADF imaging can provide elemental information about the interface at the
atomic scale. For systems such as AuPt with similar atomic numbers, ac-STEM
in combination with EDX elemental mapping provides a very effective method for
investigating interfacial structures. The direct visualisation of the interface at the
atomic scale highlights the complex range of factors that drive the metal-metal
interactions in bimetallic systems and the need for targeted computer simulation of
metal-on-metal growth to provide insight into the mechanisms of the observed
interfacial structures.
Using molecular dynamic simulations, we have shown the key role played by
kinetics in forming the interfacial structures in these AuM systems. Although the
complexity of real systems cannot be fully reproduced in computer simulation, this
work shows how improved understanding can be achieved through the effective use
of computer simulation. [It should be noted that an alternative kinetic Monte Carlo
approach could be used to study growth over longer timescales, though this
approach is better for fixed-lattice systems and where there is good epitaxy.] Our
simulation results have also revealed the potential for kinetic control of synthesis
structure during chemical synthesis. Our study using CO blocking during the
chemical synthesis of AuPt nanorods has demonstrated experimentally how particle
