We
present a systematic analysis of CO adsorption on Pt nanoclusters
in the 0.2–1.5 nm size range with the aim of unraveling size-dependent
trends and developing predictive models for site-specific adsorption
behavior. Using an empirical-potential-based genetic algorithm and
density functional theory (DFT) modeling, we show that there exists
a size window (40–70 atoms) over which Pt nanoclusters bind
CO weakly, the binding energies being comparable to those on (111)
or (100) facets. The size-dependent adsorption energy trends are,
however, distinctly nonmonotonic and are not readily captured using
traditional descriptors such as d-band energies or
(generalized) coordination numbers of the Pt binding sites. Instead,
by applying machine-learning algorithms, we show that multiple descriptors,
broadly categorized as structural and electronic descriptors, are
essential for qualitatively capturing the CO adsorption trends. Nevertheless,
attaining quantitative accuracy requires further refinement, and we
propose the use of an additional descriptorsthe fully frozen
adsorption energythat is a computationally inexpensive probe
of CO–Pt bond formation. With these three categories of descriptors,
we achieve an absolute mean error in CO adsorption energy prediction
of 0.12 eV, which is similar to the underlying error of DFT adsorption
calculations. Our approach allows for building quantitatively predictive
models of site-specific adsorbate binding on realistic, low-symmetry
nanostructures, which is an important step in modeling reaction networks
as well as for rational catalyst design in general.
Black phosphorus is a fascinating layered material, with extraordinary anisotropic mechanical, optical and electronic properties. However, the sensitivity of black phosphorus to oxygen and moisture poses significant challenges for technological applications of this unique material. Here, we report a viable solution that overcomes degradation of few-layer black phosphorus by passivating the surface with self-assembled monolayers of octadecyltrichlorosilane that provide long-term stability in ambient conditions. Importantly, we show that this treatment does not cause any undesired carrier doping of the bulk channel material, thanks to the emergent hierarchical interface structure. Our approach is compatible with conventional electronic materials processing technologies thus providing an immediate route toward practical applications in black phosphorus devices.
Two-dimensional (2D) materials are believed to hold significant promise in nanoscale optoelectronics. While significant progress has been made in this field over the past decade, the ability to control charge carrier density with high spatial precision remains an outstanding challenge in 2D devices. We present an approach that simultaneously addresses the dual issues of charge-carrier doping and spatial precision based on a functional lithographic resist that employs methacrylate polymers containing zwitterionic sulfobetaine pendent groups for noncovalent surface doping of 2D materials. We demonstrate scalable approaches for patterning these polymer films via electron-beam lithography, achieving precise spatial control over carrier doping for fabrication of high-quality, all-2D, lateral p-n junctions in graphene. Our approach preserves all of the desirable structural and electronic properties of graphene while exclusively modifying its surface potential. The functional polymer resist platform and concept offers a facile route toward lithographic doping of graphene- and other 2D material-based optoelectronic devices.
Defective
graphene has been shown experimentally to be an excellent
support for transition-metal electrocatalysts in direct methanol fuel
cells. Prior computational modeling has revealed that the improved
catalytic activity of graphene-supported metal clusters is in part
due to increased resistance to catalyst sintering and to CO poisoning,
but the increased reaction rate for the methanol decomposition reaction
(MDR) is not yet fully explained. Using density functional theory,
we investigate the adsorption and reaction thermodynamics of MDR intermediates
on defective graphene-supported Pt13 nanoclusters with
realistic, low-symmetry morphologies. We find that the support-induced
shifts in catalyst electronic structure correlate well with an overall
change in adsorption behavior of MDR intermediates and that the reaction
thermodynamics are modified in a way that suggests the potential of
greater catalytic activity. We also show that adsorption energy predictors
established for traditional heterogeneous catalysis studies of MDR
on macroscopic crystalline facets are equally valid on catalyst nanoclusters
(supported or otherwise) with irregular, low-symmetry surface morphologies.
Our studies provide theoretical insights into experimental observations
of enhanced catalytic activity of graphene-supported Pt nanoclusters
for MDR and suggest promising avenues for further tuning of catalytic
activity through engineering of catalyst–support interactions.
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