δ-SnS: An Emerging Bidirectional Auxetic Direct Semiconductor with Desirable Carrier Mobility and High-Performance Catalytic Behavior toward the Water-Splitting Reaction

Janus monolayer PXC (X = As/Sb) for photocatalytic water splitting with a negative Poisson's ratio

Two-dimensional (2D) Janus materials have attracted considerable attention in photocatalysis owing to their robust redox capability and efficient segregation. In this study, we propose a novel Janus monolayer structure, denoted as PXC (X = As/Sb), exhibiting favorable stability in terms of dynamics, thermal properties, and mechanical characteristics. The PXC monolayers demonstrate a relatively smaller Young's modulus (132.5/119.5 N m-1 for PAsC/PSbC) and large negative Poisson's ratios (-0.15/-0.101 for PAsC/PSbC). Moreover, the HSE06 + SOC functional results show that PAsC/PSbC are indirect semiconductors with a 2.33/1.43 eV band gap, exhibiting a suitable band alignment for photocatalytic water splitting. The calculated high carrier mobility (104 cm2 V-1 s-1), along with a significant discrepancy, determined by the deformation potential theory and the built-up field induced by the large intrinsic dipole, effectively suppresses the recombination of photogenerated carriers. Furthermore, PXC monolayers possess a strong absorption capacity in the visible and ultraviolet light region (105 cm-1). Therefore, our results indicate that PXC monolayers hold great potential for application in the field of photocatalytic water splitting.

Transition Metal Functionalized C30N12S6 as High-Performance Trifunctional Catalysts with Integrated Descriptors toward Hydrogen Evolution, Oxygen Evolution, and Oxygen Reduction Reactions: A Case of High-Throughput First-Principles Screening within the Framework of TM-N2@C30N10S6

In energy conversion and storage technologies, the design of highly efficient trifunctional electrocatalysts integrating with the high hydrogen evolution reaction (HER) and oxygen evolution/reduction reaction (OER/ORR) activities is highly desirable. Herein, utilizing first-principles computations, a novel periodically ordered macropore C30N12S6 monolayer was proposed, and the stability analysis attests to its good stability. Single transition metal (TM) atom anchored onto this newly proposed C30N12S6 monolayer to form single-atom catalysts, as achieved by TM-N2@C30N10S6, among which the Co-N2@C30N10S6 is the most promising multifunctional catalyst toward HER/OER/ORR with low overpotential of 0.01/0.59/0.3 V; meanwhile, the Rh-N2@C30N10S6 can be used as a bifunctional OER/ORR catalyst with low overpotential of 0.37/0.44 V, overmatching the landmark Pt (111) and IrO2/RuO2 catalysts. Particularly, the TM-d orbital in TM@CNS is remarkably hybridized with the O-p orbital of oxygenated intermediates, so that the lone electrons initially located at the antibonding orbital pair up and fill the downward bonding orbital, allowing OH* to be suitably adsorbed on TM@CNS, enhancing the catalytic performance. The relevant attributes, such as good stabilities and metallic features, ensured their applications in ambient conditions. Moreover, multilevel descriptors were constructed to clarify the origin of activity on TM@CNS, such as ΔGOH* (Gibbs free energy of OH*), εd (d-band center), COHP (crystal orbital Hamilton population), Nd/Nd + s (number of d/d + s electrons) and φ (descriptor), among which the filling of outer d-electrons of TM atom significantly affects the value of ΔGOH* that can determine the overpotential and, thus, become a key descriptor.

Kagome-like BiP3 Monolayer: An Emerging Quasi-Direct Auxetic Semiconductor Coupled with High Anisotropic Mobility toward Visible-Light-Driven Photoelectrocatalytic pH-Robust Overall Water-Splitting

Two-dimensional (2D) Janus materials exhibit an outstanding potential that can meet the rigorous requirements of photocatalytic water splitting resulting from their unique atomic arrangement. However, these materials are quite scarce. Through ab initio density functional theory calculations, we introduce a kagome topology into the honeycomb lattice of blue phosphorene using phosphorus and bismuth atoms to build a hybrid honeycomb-like kagome lattice, realized by a hitherto unknown kagome-like Janus-like BiP3 monolayer with robust stability. Excitingly, the out-of-plane asymmetry benefiting from kagome and honeycomb topologies gives rise to a significantly negative out-of-plane Poisson's ratio and an obvious built-in electric field pointing from the sublayer of the P atom to the sublayer of the Bi atom. In conjunction with the investigations that encompass semiconducting properties, such as a quasi-direct gap, suitable band-edge positions, effective visible-light absorption, and high carrier mobility, the BiP3 monolayer achieves overall water splitting at pH 0-14 regardless of strain. Moreover, this intrinsic electric field provides a sufficient photogenerated carrier driving force for water splitting. The bare BiP3 comprises P and Bi atoms that function as catalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) active sites, respectively. Upon exposure to light, the reaction of water into H2 and O2 can be observed across a pH range of 0-14. Meanwhile, by designing a transition-metal single-atom catalyst (TM@BiP3), our investigations have shown that embedding a single TM on BiP3 is a feasible route to improving the HER/OER activity by reducing the overpotentials to -0.039 and 0.58 eV for Mo and Os atoms, respectively. In this case, the positive value of the external potential acts as a sufficient OER driving force, i.e., in the light environment, the Os@BiP3 system can promote water molecules spontaneously oxidized into O2 at pH 0-14.

Density Functional Theory Approximations and Experimental Investigations on Co1-xMoxTe2 Alloy Electrocatalysts Tuning the Overall Water Splitting Reactions

Understanding the relationship between electronic structure, surface characteristic, and reaction process of a catalyst helps to architect proficient electrodes for sustainable energy development. The highly active and stable catalysts made of earth-abundant materials provide a great endeavor toward green hydrogen production. Herein, we assembled the Co_1-xMo_xTe (x = 0-1) nanoarray structures into a bifunctional electrocatalyst to achieve high-performance hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) kinetics under alkaline conditions. The designed Co_0.75Mo_0.25Te and Co_0.50Mo_0.50 electrocatalysts require minimum overpotential and Tafel slope for high-efficacy HER and OER, respectively. Furthermore, we constructed a Co_0.50Mo_0.50Te₂∥Co_0.50Mo_0.50Te₂ device for overall water splitting with an overpotential of 1.39 V to achieve a current density of 10 mA cm^-2, which is superior to noble electrocatalyst performance, with stable reaction throughout the 50 h continuous process. Density functional theory approximations and Gibbs free energy calculations validate the enhanced water splitting reaction catalyzed by the Co_0.50Mo_0.50Te₂ nanoarrays. The partial replacement of Co atoms with Mo atoms in the Co_0.50Mo_0.50Te₂ structure substantially enhances the water electrolysis kinetics through the synergistic effects between the combined metal atoms and the bonded chalcogen.

Fabrication of ultra-stable and high-efficient CoP-based electrode toward seawater splitting at industrial-grade current density

The mild and rapid construction of economical, efficient and ultrastable electrodes for hydrogen production via water splitting at industrial-grade current density remains extremely challenging. Herein, a one-step mild electroless plating method is proposed to deposit cobalt phosphorus (CoP)-based species on robust nickel net (NN, denoted as Co-P@NN). The tight interfacial contact, corrosion-proof self-supporting substrate and synergistic effect of Co-P@Co-O contribute greatly to the rapid electron transport, high intrinsic activity and long-term durability in the alkaline simulated seawater (1.0 M KOH + 0.5 M NaCl). Attractively, Co-P@Co-O also achieves ultrastable catalysis for over 2880 h with negligible activity attenuation under various alkaline extreme conditions (simulated seawater, high-salt environment, domestic sewage and so on). Furthermore, this work successfully constructs a series of ternary elemental doped (Ni, S, B, Fe and so on) CoP-based catalytic electrodes for highly efficient overall seawater splitting (OSWS). This work demonstrates not only an ideal platform for the versatile strategy of mildly obtaining CoP-based electrocatalysts but also the pioneering philosophy of large-scale hydrogen production.

A High-Throughput Screening toward Efficient Nitrogen Fixation: Transition Metal Single-Atom Catalysts Anchored on an Emerging π-π Conjugated Graphitic Carbon Nitride (g-C10N3) Substrate with Dirac Dispersion

TM-N_x is becoming a comforting catalytic center for sustainable and green ammonia synthesis under ambient conditions, resulting in increasing interest in single-atom catalysts (SACs) for the electrochemical nitrogen reduction reaction (NRR). However, given the poor activity and unsatisfactory selectivity of existing catalysts, it remains a long-standing challenge to design efficient catalysts for nitrogen fixation. Currently, the two-dimensional (2D) graphitic carbon-nitride substrate provides abundant and evenly distributed holes for stably supporting transition-metal atoms, which presents a fascinating prospect for overcoming this challenge and promoting single-atom NRR. An emerging holey graphitic carbon-nitride skeleton with a C₁₀N₃ stoichiometric ratio (g-C₁₀N₃) from a supercell of graphene is constructed, which provides outstanding electric conductivity for achieving high-efficiency NRR due to the Dirac band dispersion. Herein, a high-throughput first-principles calculation is carried out to evaluate the feasibility of π-d conjugated SACs resulting from a single TM atom anchored on g-C₁₀N₃ (TM = Sc-Au) for NRR. We find that W metal embedded in g-C₁₀N₃ (W@g-C₁₀N₃) can compromise the ability to adsorb the key target reaction species (N₂H and NH₂), hence acquiring an optimal NRR behavior among 27 TM-candidates. Our calculations demonstrate that W@g-C₁₀N₃ shows a well-suppressed HER ability and, impressively, a low energy cost of -0.46 V. Additionally, all-around descriptors are proposed to uncover the fundamental mechanism of NRR activity, among which a 3D volcano plot (limiting potential, screening strategy, and electron origin) uncovers the NRR activity trend, achieving a quick and high-efficiency prescreening for numerous candidates. Overall, the strategy of the structure- and activity-based TM-N_x-containing unit design will offer useful insight for further theoretical and experimental attempts.

Fabrication of Ultra-Durable and Flexible NiPx -Based Electrode toward High-Efficient Alkaline Seawater Splitting at Industrial Grade Current Density

Designing nonprecious metal-based electrocatalysts to yield sustainable hydrogen energy by large-scale seawater electrolysis is challenging to global emissions of carbon neutrality and carbon peaking. Herein, a series of highly efficient, economical, and robust Ni-P-based nanoballs grown on the flexible and anti-corrosive hydrophobic asbestos (NiP_x @HA) is synthesized by electroless plating at 25 °C toward alkaline simulated seawater splitting. On the basis of the strong chemical attachment between 2D layered substrate and nickel-rich components, robust hexagonal Ni₅ P₄ crystalline modification, and fast electron transfer capability, the overpotentials during hydrogen/oxygen evolution reaction (HER/OER) are 208 and 392 mV at 200 mA cm^-2 , and the chronopotentiometric measurement at 500 mA cm^-2 lasts for over 40 days. Additionally, the versatile strategy is broadly profitable for industrial applications and enables multi-elemental doping (iron/cobalt/molybdenum/boron/tungsten), flexible substrate employment (nickel foam/filter paper/hydrophilic cloth), and scalable synthesis (22 cm × 22 cm). Density functional theory (DFT) also reveals that the optimized performance is due to the fundamental effect of incorporating O-source into Ni₅ P₄ . Therefore, this work exhibits a complementary strategy in the construction of NiP_x -based electrodes and offers bright opportunities to produce scalable hydrogen effectively and stably in alkaline corrosive electrolytes.

Multifunctional PbS2 Monolayer with an In-Plane Negative Poisson Ratio and Photocatalytic Water Splitting Properties

Designing novel multifunctional materials at the nanoscale is vitally important for flexible electronics. Here, we have uncovered a two-dimensional metal dichalcogenide PbS₂ with intriguing negative Poisson ratio behavior and favorable optical and photocatalytic water splitting properties. The calculations indicate that the Poisson ratio of the PbS₂ monolayer is -0.061 along both x and y lattice directions, which is attributed to its unique tetrahedral motif and the ligand field of the local PbS₄ units in the PbS₂ monolayer. The electronic band structures show that the narrow band gap (1.59 eV) of the PbS₂ monolayer could be effectively modulated by strain engineering. Most importantly, the strain-induced tunability of optical absorbance and suitable band edge alignment make the PbS₂ monolayer a promising catalyst for photocatalytic water splitting, which is further confirmed by the reaction free energies. These findings offer an effective avenue for the design and synthesis of a novel optoelectronic functional material.

A novel two-dimensional transition metal dichalcogenide as water splitting photocatalyst with excellent performances

With the rising demand for renewable energy, photocatalysts are considered the most promising solution to harness solar energy, and the search for photocatalysts with excellent performances remains an urgent task. Here, based on density functional theory (DFT), the photocatalytic properties of MoWS₄ are systematically investigated. The MoWS₄ monolayer and bilayer are demonstrated as semiconductors with indirect band gaps of 2.01 and 1.48 eV. Moreover, they exhibit high and anisotropic light absorption coefficients of up to ∼10⁵ cm⁻¹ in the visible-ultraviolet region. The intrinsic band edge positions could fully satisfy the redox potentials of water without any external adjustment. The electron mobility of MoWS₄ monolayer is 557 cm² V⁻¹s⁻¹, which is seven times higher than MoS₂ monolayer. Hence, MoWS₄ can be regarded as a promising 2D photocatalyst candidate for water splitting.

Computational screening of highly selective and active electrocatalytic nitrogen reduction on single-atom-embedded artificial holey SnN3 monolayers

Billowy interest during nitrogen reduction reaction (NRR) for single-atom catalysts (SACs) has been evoked by the discovery of single transition metal (TM) atom structures featured by TM-N_x coordinate sites as an excellent catalytic center. However, a great challenge of currently available SACs, far away from industrial requirement, is the low activity and poor selectivity. Therefore, in NRR, the first-principles high-throughput screening calculations were performed to evaluate the feasibility of a single TM atom (from Sc to Au) embedded an artificial holey defective SnN₃ (d-SnN₃) monolayer. Here, all TM atoms can be stably anchored on d-SnN₃ (TM/d-SnN₃), meanwhile, most of adsorbed N₂ molecules can be favorably activated via the "σ donation - π* back-donation" interaction. Eventually, among 27 TM centers, V, Mo, Hf and Ta/d-SnN₃ stand out because of extremely low limiting potential (-0.21, -0.40, -0.56 and -0.54 V, respectively), lower than majority of TM-based NRR catalysts and far below that of the Ru (0001) surface (0.98 V), indicative of fast kinetics and low energy cost of NRR. Moreover, their intrinsic characteristic, such as centralized spin-polarization on these TM atoms, high-efficient prohibition of the competitive hydrogen evolution reaction is responsible for high selectivity with theoretical faradic efficiency of 100%. Also, multiple-level descriptors including ΔG_∗N, ICOHP, and Φ were used to make the source of NRR activity clear, realizing an efficient and quick prescreening among different candidates. Particularly, their excellent durability, kinetic stability and synthetic accessibility guarantee the feasibility in real experimental conditions.