“Capture-Backdonation-Recapture” Mechanism for Promoting N₂ Reduction by Heteronuclear Metal-Free Double-Atom Catalysts

Facing the increasingly serious energy and environmental crisis, the development of heteronuclear metal-free double-atom catalysts is a potential strategy to realize efficient catalytic nitrogen reduction with low energy consumption and no pollution because it could combine the advantages of flexible active sites in double-atom catalysts while also being pollution-free and have high Faraday efficiency in metal-free catalysts simultaneously. However, according to the existing mechanism, the finite orbits of other nonmetallic atoms, except the boron atom, reduce the possibility of metal-free catalysis and hinder the development of heteronuclear metal-free double-atom catalysts. Herein, we propose a new “capture-backdonation-recapture” mechanism, which skillfully uses the electron capture-backdonation-recapture between boron, the substrate, and other nonmetallic elements to solve the above problems. Based on this mechanism, by means of the first-principle calculations, the material structure, adsorption energy, catalytic activity, and selectivity of 36 catalysts are systematically investigated to evaluate their catalytic performance. B–Si@BP1 and B–Si@BP3 are selected for their good catalytic performance and low limiting potentials of −0.14 and −0.10 V, respectively. Meanwhile, the “capture-backdonation-recapture” mechanism is also verified by analyzing the results of adsorption energy and electron transfer. Our work broadens the ideas and lays the theoretical foundation for the development of heteronuclear metal-free double-atom catalysts in the future

Primitive and O‑Functionalized R‑Graphyne-like BN Sheet: Candidates for SO₂ Sensor with High Sensitivity and Selectivity at Room Temperature

In recent years, the successful production of various boron nitride allotropes has raised exciting prospects for 2D materials in the nano device area. Herein, two novel two-dimensional boron nitride allotropes, a rectangular graphyne-like sheet (R-BNyne) and an O-functionalized R-BNyne nanosheet (R-BNOyne), are proposed and investigated by first-principle calculations. The structural stabilities of metallic R-BNyne and indirect gap semiconducting R-BNOyne are proved through the phonon dispersion and Molecular Dynamic calculations. Furthermore, the adsorptions of CH4, CO, CO2, SO2, and H2 on R-BNyne and R-BNOyne have been calculated to explore the possibilities of being as gas sensors. The significant change in the current–voltage curve with and without SO2 adsorption on R-BNyne and R-BNOyne implies that both of them could be used as candidates for SO2 superior sensor with high sensitivity and selectivity at room temperature. Our studies not only reveal a new solution to modulate the electronic properties of 2D nanosheets but are also helpful for designing novel boron nitride allotropes for expanding the possibilities of being as gas sensors as well as superior capturer of SO2 with high sensitivity

Design of Novel Transition-Metal-Doped C₆N₂ with High-Efficiency Polysulfide Anchoring and Catalytic Performances toward Application in Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries are highly expected because of their high theoretical specific capacity and energy density. However, its application still faces challenges, including the shuttle effect affecting the sulfur reduction reaction, the high decomposition energy barrier of Li2S during charging, the volume change of sulfur, and the poor conductivity during charging and discharging. Here, combined with density functional theory and particle swarm optimization algorithm for the nitrogen carbide monolayer structural search (CmN8–m, m = 1–8), the surprising discovery is that a single metal-atom-doped C6N2 monolayer could effectively accelerate the conversion of lithium polysulfide and anchor lithium polysulfide during discharging and decrease the decomposition energy barrier of Li2S during charging. This “anchoring and catalyzing” mechanism effectively reduces the shuttle effect and greatly improves the reaction kinetics. Among a series of metal atoms, Cr is the best doping element, and it exhibits suitable adsorption energy for polysulfides and the lowest decomposition energy barrier for Li2S. This work opens up a new way for the development of transition-metal-doped carbon–nitrogen materials with an excellent catalytic activity for lithium polysulfide as cathode materials for Li–S batteries

Instructive Synergistic Effect of Coordinating Phosphorus in Transition-Metal-Doped β‑Phosphorus Carbide Guiding the Design of High-Performance CO₂RR Electrocatalysts

Developing efficient electrocatalysts for the CO2 reduction reaction (CO2RR) is the key and difficult point to alleviate energy and climate issues. The synergistic catalytic effects between metal and nonmetal elements have gained attention for the design of the CO2RR electrocatalysts. The realization of this effect requires a suitable combination of metal and nonmetal elements, as well as the support of suitable substrates. Based on this, the transition-metal-doped β-phosphorus carbide (TM-PC) (TM = 4d and 5d transition metals except Tc) catalysts are designed, and their structures, electronic properties, and CO2RR catalytic performances are studied in depth via first-principle calculations. The strong bonding ability and high reactivity brought by the moderate electronegativity and abundant electrons and orbitals of phosphorus are the key to the excellent catalytic performance of TM-PCs. Coordinating phosphorus atoms improve the catalyst activity in two ways: (1) regulating the electron transfer of the TM active site, and (2) acting as the active site and changing the reaction mechanism. With the participation of coordinating P atoms, the “relay” of active sites reduces the limiting potential values for the reduction from CO2 to CH4 catalyzed by Cr-PC and Mo-PC by 0.27 and 0.23 V, respectively, compared with pathways where only the TM atom is the active site, reaching −0.55 and −0.63 V, respectively. Regarding the coordinating P atom as the second active site, Cr-PC and Mo-PC can catalyze the production of CH3CH2OH at limiting potential values of −0.54 and −0.67 V, respectively. This study demonstrates the dramatic enhancement of catalytic activity caused by suitable nonmetal coordinating atoms such as P and provides a reference for the design of high-performance CO2RR electrocatalysts based on metal–nonmetal coordinating active centers

Novel Design Strategy of High Activity Electrocatalysts toward Nitrogen Reduction Reaction via Boron–Transition-Metal Hybrid Double-Atom Catalysts

Electrocatalytic nitrogen reduction reaction (NRR) is a promising method for sustainable production of NH3, which provides an alternative to the traditional Haber–Bosch process. However, the poor Faraday efficiency caused by NN triple bond activation and competitive hydrogen evolution reaction (HER) have seriously hindered the application of NRR. In this work, a novel strategy to promote NRR through boron–transition-metal (TM) hybrid double-atom catalysts (HDACs) has been proposed. The excellent catalytic activity of HDACs is attributed to a significant difference of valence electron distribution between boron and TMs, which could better activate NN bonds and promote the conversion of NH2 to NH3 compared with boron or metal single-atom catalysts and traditional double-atom catalysts (DACs). Hence, by means of DFT computations, the stability, activity, and selectivity of 29 HDACs are systematically investigated to evaluate their catalytic performance. B–Ti@g-CN and B–Ta@g-CN are screened as excellent nitrogen-fixing catalysts with particularly low limiting potentials of 0.13 and 0.11 V for NRR and rather high potentials of 0.54 and 0.82 V for HER, respectively. This work provides a new idea for the rational design of efficient nitrogen-fixing catalysts and could also be widely used in other catalytic reactions

Checking table of model precision.

<p>Checking table of model precision.</p

Metal–Organic Framework-Encapsulated Anthraquinone for Efficient Photocatalytic Hydrogen Atom Transfer

Anthraquinone (AQ) as an effective hydrogen atom transfer catalyst was limited in photocatalysis application due to the dimerization of reduced AQ. Sr–NDI@AQ, encapsulating AQ into the channel of Sr–NDI, paved a new way for solving the problem of dimerization of reduced AQ and improving the catalytic efficiency owing to the fast electron transfer from reduced AQ to the ligand through host–guest interaction. The structure of Sr–NDI@AQ was determined by single-crystal X-ray diffraction, and the value for distance and torsion angle between the ligand and AQ was calculated. The photochemical and electrochemical properties for Sr–NDI@AQ were characterized through a series of experiments. The coupling reaction between aldehyde and phenyl vinyl sulfone and photoacetalization reaction were carried out, displaying the improving catalytic efficiency of Sr–NDI@AQ compared to Sr–NDI and AQ. The reaction mechanisms were proposed through radical capture and electron paramagnetic resonance experiments

Schematic diagram of scanning point coordinate calculation.

<p>——P abscissa values; ——P ordinate values; ——P Elevation Value; ——included angle of P was perpendicular to the YZ plane with X axis; ——included angle of P with XY plane.</p

Metal–Organic Framework-Encapsulated Anthraquinone for Efficient Photocatalytic Hydrogen Atom Transfer

Anthraquinone (AQ) as an effective hydrogen atom transfer catalyst was limited in photocatalysis application due to the dimerization of reduced AQ. Sr–NDI@AQ, encapsulating AQ into the channel of Sr–NDI, paved a new way for solving the problem of dimerization of reduced AQ and improving the catalytic efficiency owing to the fast electron transfer from reduced AQ to the ligand through host–guest interaction. The structure of Sr–NDI@AQ was determined by single-crystal X-ray diffraction, and the value for distance and torsion angle between the ligand and AQ was calculated. The photochemical and electrochemical properties for Sr–NDI@AQ were characterized through a series of experiments. The coupling reaction between aldehyde and phenyl vinyl sulfone and photoacetalization reaction were carried out, displaying the improving catalytic efficiency of Sr–NDI@AQ compared to Sr–NDI and AQ. The reaction mechanisms were proposed through radical capture and electron paramagnetic resonance experiments

Table1_New 2D roughness parameters with geometric and physical meanings for rock joints and their correlation with joint roughness coefficient.DOCX

Determining the joint roughness accurately will better serve the peak shear strength estimation models of rock joints used for stability assessment of rock masses. Considering the defects of the existing quantitative characterization parameters for two-dimensional (2D) joint roughness, especially the lack of explicit geometric and physical meaning, we proposed two new 2D roughness parameters, θ2D and h2D. The former, θ2D, represents the average inclination angle of all potential contact asperities over the entire joint profile, while the latter, h2D, characterizes their average undulation height. Both parameters are closely related to the shear strength of rock joints. Then, the roughness parameters θ2D and h2D of 102 rock joint profiles digitized at 0.5 mm sampling interval were calculated, and a new nonlinear regression equation for the determination of the 2D joint roughness coefficient (JRC) was established by combining the calculated results of the two roughness parameters. It was verified that the proposed equation could give accurate JRC estimation values of the 10 standard profiles of rock joints. Through the comparative analysis of the experimental data collected from earlier studies for the peak shear strength of 73 rock joint samples and corresponding estimated values, the equation was further verified to be applicable and accurate for estimating the JRC values of rock joints. Furthermore, we discussed the effects of shear direction and sampling interval on roughness and further provided another equation that could be applied to estimate the JRC values of joint profiles at the sampling interval of 1.0 mm.</p