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 LiBH₄ Nanoclusters and Their Hydrogen Storage Properties

Recent experimental studies suggest faster desorption kinetics, improved reversibility, and more favorable thermodynamics for confined LiBH₄ nanoparticles as compared to bulk. We study the structures, total energies, and decomposition reactions of LiBH₄ 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 LiBH₄. 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 (LiBH₄)_<i>n</i> 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 (LiBH₄)_<i>n</i>, the reaction where diborane is released, is unfavorable for most cluster sizes, whereas the hydrogen desorption reaction to Li₂H₁₂B₁₂ is most favorable. This suggests that the experimentally observed improvement of the (de)­hydrogenation properties of LiBH₄ 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