4 research outputs found
Data-Driven Discovery of Intrinsic Direct-Gap 2D Materials as Potential Photocatalysts for Efficient Water Splitting
Intrinsic direct-gap two-dimensional
(2D) materials hold great
promise as photocatalysts, advancing the application of photocatalytic
water splitting for hydrogen production. However, the time- and resource-efficient
exploration and identification of such 2D materials from a vast compositional
and structural chemical space present significant challenges within
the realm of materials science research. To this end, we perform a
data-driven study to find 2D materials with intrinsic direct-gap and
desirable photocatalytic properties for overall water splitting. By
implementing a three-staged large-scale screening, which incorporates
machine-learned data from the V2DB, high-throughput density functional
theory (DFT), and hybrid-DFT calculations, we identify 16 direct-gap
2D materials as promising photocatalysts. Subsequently, we conduct
a comprehensive assessment of materials properties that are related
to the solar water splitting performance, which include electronic
and optical properties, solar-to-hydrogen conversion efficiencies,
and carrier mobilities. Therefore, this study not only presents 16
2D photocatalysts but also introduces a rigorous data-driven approach
for the future discovery of functional 2D materials from currently
unexplored chemical spaces
First-Principles Study of LiBH<sub>4</sub> Nanoclusters and Their Hydrogen Storage Properties
Recent experimental studies suggest faster desorption
kinetics,
improved reversibility, and more favorable thermodynamics for confined
LiBH<sub>4</sub> nanoparticles as compared to bulk. We study the structures,
total energies, and decomposition reactions of LiBH<sub>4</sub> nanoparticles
using density functional theory calculations. We find that the reaction
energies of nanoclusters with a diameter ≳2 nm are very close
to that of bulk LiBH<sub>4</sub>. Only very small clusters with a
diameter <1 nm are significantly destabilized relative to the bulk.
The thermodynamics of such small clusters is unfavorable, however,
and leads to dehydrogenation temperatures that are higher than that
of the bulk. Although small (LiBH<sub>4</sub>)<sub><i>n</i></sub> nanoclusters exhibit a number of different geometries, they
show only little variation in the total energy per formula unit. Of
all possible decomposition reactions of (LiBH<sub>4</sub>)<sub><i>n</i></sub>, the reaction where diborane is released, is unfavorable
for most cluster sizes, whereas the hydrogen desorption reaction to
Li<sub>2</sub>H<sub>12</sub>B<sub>12</sub> is most favorable. This
suggests that the experimentally observed improvement of the (de)Âhydrogenation
properties of LiBH<sub>4</sub> can be attributed to an improvement
of the kinetics of the latter reaction
Probing the Reactivity of ZnO with Perovskite Precursors
To achieve more stable
and efficient metal halide perovskite devices,
optimization of charge transport materials and their interfaces with
perovskites is crucial. ZnO on paper would make an ideal electron
transport layer in perovskite devices. This metal oxide has a large
bandgap, making it transparent to visible light; it can be easily
n-type doped, has a decent electron mobility, and is thought to be
chemically relatively inert. However, in combination with perovskites,
ZnO has turned out to be a source of instability, rapidly degrading
the performance of devices. In this work, we provide a comprehensive
experimental and computational study of the interaction between the
most common organic perovskite precursors and the surface of ZnO,
with the aim of understanding the observed instability. Using X-ray
photoelectron spectroscopy, we find a complete degradation of the
precursors in contact with ZnO and the formation of volatile species
as well as new surface bonds. Our computational work reveals that
different pristine and defected surface terminations of ZnO facilitate
the decomposition of the perovskite precursor molecules, mainly through
deprotonation, making the deposition of the latter on those surfaces
impossible without the use of passivation
Defects in Halide Perovskites: Does It Help to Switch from 3D to 2D?
Two-dimensional (2D) organic–inorganic hybrid
iodide perovskites
have been put forward in recent years as stable alternatives to their
three-dimensional (3D) counterparts. Using first-principles calculations,
we demonstrate that equilibrium concentrations of point defects in
the 2D perovskites PEA2PbI4, BA2PbI4, and PEA2SnI4 (PEA, phenethylammonium;
BA, butylammonium) are much lower than in comparable 3D perovskites.
Bonding disruptions by defects are more destructive in 2D than in
3D networks, making defect formation energetically more costly. The
stability of 2D Sn iodide perovskites can be further enhanced by alloying
with Pb. Should, however, point defects emerge in sizable concentrations
as a result of nonequilibrium growth conditions, for instance, then
those defects likely hamper the optoelectronic performance of the
2D perovskites, as they introduce deep traps. We suggest that trap
levels are responsible for the broad sub-bandgap emission in 2D perovskites
observed in experiments