Electronic properties and oxygen reduction reaction catalytic activity of h-BeN2 and MgN2 by first-principles calculations

Piezoelectric, Thermoelectric, and Photocatalytic Water Splitting Properties of Janus Arsenic Chalcohalide Monolayers

In this study, we systematically investigate the piezoelectric, thermoelectric, and photocatalytic properties of novel two-dimensional Janus arsenic chalcohalide monolayers, AsXX' (X = S and Se and X' = Cl, Br, and I) using density functional theory. The positive phonon spectra and ab initio molecular dynamics simulation plots indicate these monolayers to be dynamically and thermally stable. The mechanical stability of these monolayers is confirmed by a nonzero elastic constant (C ij ), Young's modulus (Y 2D), and Poisson ratio (ν). These monolayers exhibit strong out-of-plane piezoelectric coefficients, making them candidate materials for piezoelectric devices. Our calculated results indicate that these monolayers have a low lattice thermal conductivity (κl) and high thermoelectric figure of merit (zT) up to 1.51 at 800 K. These monolayers have an indirect bandgap, high carrier mobility, and strong visible light absorption spectra. Furthermore, the AsSCl, AsSBr, and AsSeI monolayers exhibit appropriate band alignment for water splitting. The calculated value of the corrected solar-to-hydrogen conversion efficiency can reach up to 19%. The nonadiabatic molecular dynamics simulations reveal the prolonged electron-hole recombination rates of 1.52 0.98, and 0.67 ns for AsSCl, AsSBr, and AsSeI monolayers, respectively. Our findings demonstrate these monolayers to be potential candidates in energy-harvesting fields.

Engineering 2D Materials for Photocatalytic Water-Splitting from a Theoretical Perspective

Splitting of water with the help of photocatalysts has gained a strong interest in the scientific community for producing clean energy, thus requiring novel semiconductor materials to achieve high-yield hydrogen production. The emergence of 2D nanoscale materials with remarkable electronic and optical properties has received much attention in this field. Owing to the recent developments in high-end computation and advanced electronic structure theories, first principles studies offer powerful tools to screen photocatalytic systems reliably and efficiently. This review is organized to highlight the essential properties of 2D photocatalysts and the recent advances in the theoretical engineering of 2D materials for the improvement in photocatalytic overall water-splitting. The advancement in the strategies including (i) single-atom catalysts, (ii) defect engineering, (iii) strain engineering, (iv) Janus structures, (v) type-II heterostructures (vi) Z-scheme heterostructures (vii) multilayer configurations (viii) edge-modification in nanoribbons and (ix) the effect of pH in overall water-splitting are summarized to improve the existing problems for a photocatalytic catalytic reaction such as overcoming large overpotential to trigger the water-splitting reactions without using cocatalysts. This review could serve as a bridge between theoretical and experimental research on next-generation 2D photocatalysts.

Realizing Efficient Catalytic Performance and High Selectivity for Oxygen Reduction Reaction on a 2D Ni2SbTe2 Monolayer

One of the immediate challenges for the large-scale commercialization of hydrogen-based fuel cells is to develop cost-effective electrocatalysts to enable cathodic oxygen reduction reaction (ORR). Herein, we focus on the potential of the two-dimensional (2D) ternary chalcogenide Ni₂SbTe₂ monolayer as a high-performance electrocatalyst for the ORR using density function theory. Our computed results reveal that there are an obvious hybridization and electron transfer between the O 2p and Te 5p orbitals, which can activate the adsorbed oxygen and trigger the whole ORR process, with an overpotential as low as 0.33 V. In addition, the adsorption capacity of the monolayer surface for oxygen molecules can be effectively enhanced by doping with Fe or Co atoms. The Ni₂SbTe₂ monolayers doped with Fe or Co atoms not only maintain their original excellent ORR catalytic activity but also improve selectivity toward the four-electron (4e) reduction pathway. We highly anticipate that this work can provide excellent candidates and new ideas for designing low-cost and high-performance ORR catalysts to replace noble metal Pt-based catalysts in fuel cells.

High-Pressure Synthesis of Dirac Materials: Layered van der Waals Bonded BeN_{4} Polymorph

High-pressure chemistry is known to inspire the creation of unexpected new classes of compounds with exceptional properties. Here, we employ the laser-heated diamond anvil cell technique for synthesis of a Dirac material BeN_{4}. A triclinic phase of beryllium tetranitride tr-BeN_{4} was synthesized from elements at ∼85  GPa. Upon decompression to ambient conditions, it transforms into a compound with atomic-thick BeN_{4} layers interconnected via weak van der Waals bonds and consisting of polyacetylene-like nitrogen chains with conjugated π systems and Be atoms in square-planar coordination. Theoretical calculations for a single BeN_{4} layer show that its electronic lattice is described by a slightly distorted honeycomb structure reminiscent of the graphene lattice and the presence of Dirac points in the electronic band structure at the Fermi level. The BeN_{4} layer, i.e., beryllonitrene, represents a qualitatively new class of 2D materials that can be built of a metal atom and polymeric nitrogen chains and host anisotropic Dirac fermions.

Theoretical investigation on [Formula: see text] monolayer for an efficient bifunctional water splitting catalyst

The search for an active, stable, and abundant semiconductor-based bifunctional catalysts for solar hydrogen production will make a substantial impact on the sustainable development of the society that does not rely on fossil reserves. The photocatalytic water splitting mechanism on a [Formula: see text] monolayer has here been investigated by using state-of-the-art density functional theory calculations. For all possible reaction intermediates, the calculated changes in Gibbs free energy showed that the oxygen evolution reaction will occur at, and above, the potential of 2.06 V (against the NHE) as all elementary steps are exergonic. In the case of the hydrogen evolution reaction, a potential of 0.52 V, or above, was required to make the reaction take place spontaneously. Interestingly, the calculated valence band edge and conduction band edge positions for a [Formula: see text] monolayer are located at the potential of 2.60 V and 0.56 V, respectively. This indicates that the photo-generated holes in the valence band can oxidize water to oxygen, and the photo-generated electrons in the conduction band can spontaneously reduce water to hydrogen. Hence, the results from the present theoretical investigation show that the [Formula: see text] monolayer is an efficient bifunctional water-splitting catalyst, without the need for any co-catalyst.

Strategies for computational design and discovery of two-dimensional transition-metal-free materials for electro-catalysis applications

In this perspective, we review two new strategies for computational design and discovery of two-dimensional (2D) transition-metal (TM) free electro-catalysts for the oxygen reduction reaction (ORR) and the nitrogen reduction reaction (NRR). The "2D binary compound" strategy for designing ORR electro-catalysts shows promising applications, which benefits from abundant intrinsic catalytic sites for the adsorption of reaction intermediates. And with the "activated B site" strategy for designing NRR electro-catalysts, several novel NRR electro-catalysts with extremely low limiting potential are developed. Computational-simulation-driven material design from a bottom-up method could not only provide rational strategies, but also accelerate the discovery of novel materials.