Design of Single-atom Catalysts on C5N2 for Nitrogen Fixation at Ambient Conditions : A First-principles Study.

Single atom catalysts (SACs) exhibit the flexible coordination structure of the active site and high utilization of active atoms, making them promising candidates for nitrogen reduction reaction (NRR) under ambient conditions. By the aid of first-principles calculations based on DFT, we have systematically explored the NRR catalytic behavior of thirteen 4d- and 5d-transition metal atoms anchored on 2D porous graphite carbon nitride C5N2. With high selectivity and outstanding activity, Zr, Nb, Mo, Ta, W and Re-doped C5N2 are identified as potential nominees for NRR. Particularly, Mo@C5N2 possesses an impressive low limiting potential of -0.39 V (corresponding to a very low temperature and atmospheric pressure), featuring the potential determining step involving *N-N transitions to *N-NH via the distal path. The catalytic performance of TM@C5N2 can be well characterized by the adsorption strength of intermediate *N2H. Moreover, there exists a volcanic relationship between the catalytic property UL and the structure descriptor Ψ, which validates the robustness and universality of Ψ, combined with our previous study. This work sheds light on the design of SACs with eminent NRR performance.

Toward Heisenberg scaling in non-Hermitian metrology at the quantum regime.

Non-Hermitian quantum metrology, an emerging field at the intersection of quantum estimation and non-Hermitian physics, holds promise for revolutionizing precision measurement. Here, we present a comprehensive investigation of non-Hermitian quantum parameter estimation in the quantum regime, with a special focus on achieving Heisenberg scaling. We introduce a concise expression for the quantum Fisher information (QFI) that applies to general non-Hermitian Hamiltonians, enabling the analysis of estimation precision in these systems. Our findings unveil the remarkable potential of non-Hermitian systems to attain the Heisenberg scaling of 1/t, where t represents time. Moreover, we derive optimal measurement conditions based on the proposed QFI expression, demonstrating the attainment of the quantum Cramér-Rao bound. By constructing non-unitary evolutions governed by two non-Hermitian Hamiltonians, one with parity-time symmetry and the other without specific symmetries, we experimentally validate our theoretical analysis. The experimental results affirm the realization of Heisenberg scaling in estimation precision, marking a substantial milestone in non-Hermitian quantum metrology.

Topological wetting states of microdroplets on closed-loop structured surfaces: Breakdown of the Gibbs equation at the microscale.

Microdroplets are a class of soft matter that has been extensively employed for chemical, biochemical, and industrial applications. However, fabricating microdroplets with largely controllable contact-area shape and apparent contact angle, a key prerequisite for their applications, is still a challenge. Here, by engineering a type of surface with homocentric closed-loop microwalls/microchannels, we can achieve facile size, shape, and contact-angle tunability of microdroplets on the textured surfaces by design. More importantly, this class of surface topologies (with universal genus value = 1) allows us to reveal that the conventional Gibbs equation (widely used for assessing the edge effect on the apparent contact angle of macrodroplets) seems no longer applicable for water microdroplets or nanodroplets (evidenced by independent molecular dynamics simulations). Notably, for the flat surface with the intrinsic contact angle ~0°, we find that the critical contact angle on the microtextured counterparts (at edge angle 90°) can be as large as >130°, rather than 90° according to the Gibbs equation. Experiments show that the breakdown of the Gibbs equation occurs for microdroplets of different types of liquids including alcohol and hydrocarbon oils. Overall, the microtextured surface design and topological wetting states not only offer opportunities for diverse applications of microdroplets such as controllable chemical reactions and low-cost circuit fabrications but also provide testbeds for advancing the fundamental surface science of wetting beyond the Gibbs equation.

The confined surface C2N/Pt(111) as a highly efficient catalyst for CO oxidation.

The problem of poisoning on the surface of catalysts used in CO oxidation reactions, such as Pt, needs to be solved. In this work, we constructed lattice-matched C2N/Pt(111) catalysts with different configurations (top/fcc/hcp) and found that, within the confined space between the cover and the substrate, the adsorption energy of CO is reduced by 0.35 eV to 0.43 eV, while the adsorption of other reactants O/O2 is strengthened and the adsorption energy of the product CO2 is positive, indicating that the constraint effect produced by C2N and Pt(111) is beneficial to CO oxidation, when compared to the pure Pt(111). Our work suggests that the C2N cover not only protects the Pt surface under harsh conditions but also allows gaseous molecules CO and O2 to approach the Pt surface through a facile intercalation process, with enhanced surface reactivity for CO oxidation and reduced catalyst poisoning.

HER catalytic activity and regulation of a transition metal atom-anchored BC3 monolayer: a first-principles study.

An atomic-level understanding of the hydrogen evolution reaction (HER) on a transition metal (TM) atom-anchored 2D monolayer is vital to explore highly efficient catalysts for hydrogen production. Here, the catalytic activities and modulation of TM atom (Ti, Fe, Cu, Zn, Mo, Ag, Au)-doped BC3 monolayers are investigated by first-principles calculations. Au@BC3 and Fe@BC3 are proven to be potentially excellent HER catalysts. Partial oxidation engineering on Zn@BC3 could improve its performance. Au@BC3 and Ti, Cu and Mo-anchored BC3 with the support of a NbB2 (0001) surface are expected to replace Pt due to the Gibbs free energy changes extremely close to zero. It is revealed that the catalytic activity of the adsorption site is highly related to the degree of charge transfer between the adsorption site and substrate.

Two-dimensional ternary pentagonal BCX (X = P, As, and Sb): promising photocatalyst semiconductors for water splitting with strong piezoelectricity.

Seeking high-performance energy conversion materials is one of the most important issues in designing 2D materials. In the framework of density functional theory, we propose a series of ternary monolayers, penta-BCX (X = P, As, and Sb), and systematically investigate their structural stability, mechanical, piezoelectric, and photocatalytic properties. All three materials are semiconductors with a bandgap ranging from 2.56 eV to 3.24 eV, so they could be promising catalysts for the photolysis of water. Penta-BCX exhibits significant piezoelectric properties attributed to their non-centrosymmetric structure and low in-plane Young's modulus, which are expected to efficiently drive photocatalytic water decomposition. Moreover, the bandgap, band edge position, and light absorption of penta-BCX can be modulated by tensile or compressive strain to enhance their photocatalytic performance in the visible light and ultraviolet regions.

Construction of a BC3-based TM single-atom catalyst for efficient reduction of CO2 to CH4: a computational study.

The electrocatalytic conversion of CO2 into fuels or chemicals presents an effective approach to mitigate greenhouse gas emissions and address the traditional fuel crisis. Based on density functional theory, we systematically investigate a series of transition metal atoms bound to a BC3 monolayer as novel single-atom catalysts (SACs) for the CO2 reduction reaction (CO2RR). Our results demonstrate that most of the constructed SACs exhibit superior selectivity for the CO2RR over the hydrogen evolution reaction, with CH4 as the dominant product. Notably, the Pt@BC3 monolayer emerges as the best CO2RR catalyst with a low limiting potential of -0.36 V, surpassing many previously reported catalysts. Additionally, we explore the correlations between the SAC's catalytic activity and both ΔG*OCHO and the structural descriptor φ, revealing volcano relationships. A catalyst with better performance is constructed with the aid of the volcano diagram. These findings are beneficial for understanding the CO2RR mechanism and designing efficient catalysts.

Catalytic Ozonation of Polluter Benzene from -20 to >50 °C with High Conversion Efficiency and Selectivity on Mullite YMn2O5.

Catalytic decomposition of aromatic polluters at room temperature represents a green route for air purification but is currently challenged by the difficulty of generating reactive oxygen species (ROS) on catalysts. Herein, we develop a mullite catalyst YMn2O5 (YMO) with dual active sites of Mn3+ and Mn4+ and use ozone to produce a highly reactive O* upon YMO. Such a strong oxidant species on YMO shows complete removal of benzene from -20 to >50 °C with a high COx selectivity (>90%) through the generated reactive species O* on the catalyst surface (60 000 mL g-1 h-1). Although the accumulation of water and intermediates gradually lowers the reaction rate after 8 h at 25 °C, a simple treatment by ozone purging or drying in the ambient environment regenerates the catalyst. Importantly, when the temperature increases to 50 °C, the catalytic performance remains 100% conversion without any degradation for 30 h. Experiments and theoretical calculations show that such a superior performance stems from the unique coordination environment, which ensures high generation of ROS and adsorption of aromatics. Mullite's catalytic ozonation degradation of total volatile organic compounds (TVOC) is applied in a home-developed air cleaner, resulting in high efficiency of benzene removal. This work provides insights into the design of catalysts to decompose highly stable organic polluters.

Prediction of 2D IV-V semiconductors: flexible monolayers with tunable band gaps and strong optical absorption as water-splitting photocatalysts.

Seeking novel photocatalysts for water splitting is one of the tasks in developing 2D materials. In the framework of density functional theory, we predict a family of 2D pentagonal sheets called penta-XY2 (X = Si, Ge, and Sn; Y = P, As, and Sb), and modulate their properties via strain engineering. Penta-XY2 monolayers exhibit flexible and anisotropic mechanical properties, due to their low in-plane Young's modulus in the range of 19-42 N m-1. All six XY2 sheets are semiconductors with a band gap ranging from 2.07 eV to 2.51 eV, and the positions of their conduction and valence band edges match well with the reaction potentials of H+/H2 and O2/H2O, so they are suitable for photocatalytic water splitting. Under tensile/compression strains, the band gaps, band edge positions and light absorption of GeAs, SnP2 and SnAs2 could be tuned to improve their photocatalytic performance.

Charge-controlled switchable CO2 capture and gas separation using BC3 nanosheets.

The technique of CO2 capture and separation using charge-modulated sorbent materials holds promise for reducing CO2 emissions. Density functional theory with long-range dispersion correction has been used to study the adsorption of CO2, H2, CH4, and N2 on BC3 nanosheets with/without charge injections. We find that CO2 is weakly adsorbed on pristine BC3, but injection of 3 negative charges (3 e) can change the adsorption to chemical adsorption. Removing the charge results in the release of CO2 without any energy barrier. A high capacity of 4.30 × 1014 cm-2 can be achieved with 5 e charge injection, and CO2 molecules could automatically desorb after charge removal. Additionally, negatively charged BC3 exhibits high selectivity for separating CO2 from other industrial gases such as CH4, H2, and N2. Our findings provide useful guidance for the development of switchable CO2 capture and storage materials.

Evidence of Formation of Monolayer Hydrated Salts in Nanopores.

Despite much effort being devoted to the study of ionic aqueous solutions at the nanoscale, our fundamental understanding of the microscopic kinetic and thermodynamic behaviors in these systems remains largely incomplete. Herein, we reported the first 10 µs molecular dynamics simulation, providing evidence of the spontaneous formation of monolayer hexagonal honeycomb hydrated salts of XCl2·6H2O (X = Ba, Sr, Ca, and Mg) from electrolyte aqueous solutions confined in an angstrom-scale slit under ambient conditions. By using both the classical molecular dynamics simulations and the first-principles Born-Oppenheimer molecular dynamics simulations, we further demonstrated that the hydrated salts were stable not only at ambient temperature but also at elevated temperatures. This phenomenon of formation of hydrated salt in water is contrary to the conventional view. The free energy calculations and dehydration analyses indicated that the spontaneous formation of hydrated salts can be attributed to the interplay between ion hydration and Coulombic attractions in the highly confined water. In addition to providing molecular-level insights into the novel behavior of ionic aqueous solutions at the nanoscale, our findings may have implications for the future exploration of potential existence of water molecules in the saline deposits on hot planets.

In silico design of single transition metal atom anchored defective boron carbide monolayers as high-performance electrocatalysts for the nitrogen reduction reaction.

Development of low-cost and high-efficiency single atom catalysts (SACs) is essential for catalyzing nitrogen reduction reactions (NRR) under ambient conditions. Current SACs suffer from low selectivity and poor activity, making it hard for them to meet the requirements of industrial applications. Here, we present a graphene-like BC3 monolayer as a substrate for single metal atoms. The catalytic performance of 4d and 5d metal atoms anchored in a vacancy containing BC3 monolayer for NRR is systematically investigated by first-principles calculations. We find that Re@VB is outstanding among all candidates, exhibiting high catalytic activity and selectivity, with a low limiting potential of -0.28 V. A new descriptor involving the active site and its environment is proposed, which has a volcano relationship with several factors in the catalytic process, establishing a link between the intrinsic properties of the active site and the catalytic performance. This study opens a new route to designing efficient catalysts with BC3 as a substrate.

Computational screening of single transition-metal atoms anchored to g-C9N4 as catalysts for N2 reduction to NH3.

The electrocatalytic nitrogen reduction reaction (NRR) is considered to be the most desirable strategy for ammonia production but still faces many challenges in terms of high activity and high selectivity. Based on density functional theory (DFT) calculations, the catalytic performance of a series of (3d, 4d and 5d series) transition metals atoms (TMs) anchored on a novel graphitic carbon-nitrogen (g-C9N4) monolayer has been systematically investigated. We find that TMs can bind tightly to g-C9N4 and form single-atom catalysts (SACs) with high thermodynamic stability. The four candidates, Nb, Ta, W and Re@g-C9N4, not only exhibit high NRR catalytic activity but also effectively inhibit the competitive HER. Among them, Nb@g-C9N4 is the most promising NRR catalyst with a lowest limiting potential of -0.21 V. The optimal reaction path for Nb, W and Re@g-C9N4 is via the enzymatic mechanism, while Ta@g-C9N4 tends to be through the distal mechanism. In addition, the decomposition potential of the g-C9N4 monolayer is higher than the limiting potential of all four SACs, ensuring the feasibility of the experimental implementation. This work identifies efficient NRR catalysts and provides a feasible screening scheme.

Phthalo-carbonitride nanosheets as excellent N2 reduction reaction electrocatalysts: a first-principles study.

Based on density functional theory computation, a series of transition metal atoms anchored on phthalo-carbonitride (pc-C3N2) nanosheets have been investigated for the nitrogen reduction reaction (NRR). The results show that Mo and W atoms anchored on the large holes of pc-C3N2 exhibit excellent performance in the NRR with low limiting potentials of -0.24 V and -0.23 V, respectively. Moreover, W@pc-C3N2 can effectively suppress the hydrogen evolution reaction. We predict that the porous carbon-nitrogen catalyst W@pc-C3N2 has a promising future to explore more favorable applications for the NRR.

Theoretical study of SnS2encapsulated in graphene as a promising anode material for K-ion batteries.

Rechargeable batteries with superior electronic conductivity, large capacity, low diffusion barriers and moderate open circuit voltage have attracted amount attention. Due to abundant resources and safety, as well as the high voltage and energy density, potassium ion batteries (KIBs) could be an ideal alternative to next-generation of rechargeable batteries. Based on the density functional theory calculations, we find that the SnS2monolayer expands greatly during the potassiumization, which limits its practical application. The construction of graphene/SnS2/graphene (G/SnS2/G) heterojunction effectively prevents SnS2sheet from deformation, and enhances the electronic conductivity. Moreover, the G/SnS2/G has not only a high theoretical special capacity of 680 mAh g-1, but an ultra-low K diffusion barrier (0.08 eV) and an average open circuit voltage (0.22 V). Our results predict that the G/SnS2/G heterostructure could be used as a promising anode material for KIBs.

Two-dimensional monolayer salt nanostructures can spontaneously aggregate rather than dissolve in dilute aqueous solutions.

It is well known that NaCl salt crystals can easily dissolve in dilute aqueous solutions at room temperature. Herein, we reported the first computational evidence of a novel salt nucleation behavior at room temperature, i.e., the spontaneous formation of two-dimensional (2D) alkali chloride crystalline/non-crystalline nanostructures in dilute aqueous solution under nanoscale confinement. Microsecond-scale classical molecular dynamics (MD) simulations showed that NaCl or LiCl, initially fully dissolved in confined water, can spontaneously nucleate into 2D monolayer nanostructures with either ordered or disordered morphologies. Notably, the NaCl nanostructures exhibited a 2D crystalline square-unit pattern, whereas the LiCl nanostructures adopted non-crystalline 2D hexagonal ring and/or zigzag chain patterns. These structural patterns appeared to be quite generic, regardless of the water and ion models used in the MD simulations. The generic patterns formed by 2D monolayer NaCl and LiCl nanostructures were also confirmed by ab initio MD simulations. The formation of 2D salt structures in dilute aqueous solution at room temperature is counterintuitive. Free energy calculations indicated that the unexpected spontaneous salt nucleation behavior can be attributed to the nanoscale confinement and strongly compressed hydration shells of ions.

Photoinduced Dynamic Defects Responsible for the Giant, Reversible, and Bidirectional Light-Soaking Effect in Perovskite Solar Cells.

Perovskite solar cells (PSCs) exhibit large, reversible, and bidirectional light-soaking effects (LSEs); however, these anomalous LSEs are poorly understood, limiting the stability engineering and commercialization. We present a unified defect theory for the LSEs in lead halide perovskites by reconciling their defect photochemistry, ionic migration, and carrier dynamics. We considered typical detrimental defects (IPb, Ii, VI) and observed that two atomic configurations were favored, where the carrier lifetime of one configuration was nearly 1 order of magnitude longer than that in the other. First-principles calculations showed that light illumination promotes ion-diffusion-assisted transitions from energetically stable configurations to metastable configurations, which are converted back to stable configurations in the dark. Fermi-level-dependent formation energies of stable/metastable configurations were used to rationalize contradictory experimental results of anomalous LSEs in PSCs observed in various studies, thus providing insights for minimizing the LSE to achieve high-performance stable PSCs.

Single metal atom anchored on a CN monolayer as an excellent electrocatalyst for the nitrogen reduction reaction.

Based on first-principles calculations, we have studied the behavior of single-atom catalysts formed by a series of single metal atoms (from Ti to Cu) and a CN monolayer in nitrogen reduction reactions (NRRs). It was demonstrated that TM atoms could be anchored on CN and Ti@CN has good electrical conductivity, high stability and good catalytic performance. The onset potential of Ti@CN is as low as -0.38 V through the enzymatic mechanism, which well suppresses the competitive hydrogen evolution reaction. In addition, the determinate step of Ti@CN for the N2 reduction reaction is lower than that of the Ru(0001) stepped surface (-0.98 V). We further examine the effect of coordination on activity and propose a single Ti atom anchored on CN as a promising catalyst with high catalytic capability for N2 reduction to NH3. Our work offers a new opportunity and useful guidance for the NRR in an ambient environment.

Direct Observation of ß-Barrel Intermediates in the Self-Assembly of Toxic SOD128-38 and Absence in Nontoxic Glycine Mutants.

Soluble low-molecular-weight oligomers formed during the early stage of amyloid aggregation are considered the major toxic species in amyloidosis. The structure-function relationship between oligomeric assemblies and the cytotoxicity in amyloid diseases are still elusive due to the heterogeneous and transient nature of these aggregation intermediates. To uncover the structural characteristics of toxic oligomeric intermediates, we compared the self-assembly dynamics and structures of SOD128-38, a cytotoxic fragment of the superoxide dismutase 1 (SOD1) associated with the amyotrophic lateral sclerosis, with its two nontoxic mutants G33V and G33W using molecular dynamics simulations. Single-point glycine substitutions in SOD128-38 have been reported to abolish the amyloid toxicity. Our simulation results showed that the toxic SOD128-38 and its nontoxic mutants followed different aggregation pathways featuring distinct aggregation intermediates. Specifically, wild-type SOD128-38 initially self-assembled into random-coil-rich oligomers, among which fibrillar aggregates composed of well-defined curved single-layer ß-sheets were nucleated via coil-to-sheet conversions and the formation of ß-barrels as intermediates. In contrast, the nontoxic G33V/G33W mutants readily assembled into small ß-sheet-rich oligomers and then coagulated with each other into cross-ß fibrils formed by two-layer ß-sheets without forming ß-barrels as the intermediates. The direct observation of ß-barrel oligomers during the assembly of toxic SOD128-38 fragments but not the nontoxic glycine-substitution mutants strongly supports ß-barrels as the toxic oligomers in amyloidosis, probably via interactions with the cell membrane and forming amyloid pores. With well-defined structures, the ß-barrel might serve as a novel therapeutic target against amyloid-related diseases.

Single transition metal anchored C9N4 sheets as an efficient catalyst for CO oxidation: a first-principles study.

Single-atom catalysts (SACs) often exhibit superb catalytic activity due to their high atom utilization. By comparing the adsorption energies of O2 and CO adsorbed on TM@C9N4, we expect that Co and Ni anchored at the cavity of C9N4 exhibit a higher catalytic activity for CO oxidation. For the entire reaction, the Eley-Rideal, New Eley-Rideal, Ter-molecular Eley-Rideal and Langmuir-Hinshelwood mechanisms are all taken into account. Depending on the reaction mechanisms, the catalysts Co@C9N4 and Ni@C9N4 show excellent activity, with a kinetic energy barrier ranging from 0.19 eV to 0.54 eV for the former, while the corresponding energy barrier is 0.26 eV to 0.44 eV for the latter. The superior stability and activity of Co/Ni@C9N4 can efficiently oxidize the large amounts of CO caused by inadequate combustion of coal and natural gas resources.