Regulating the catalytic behaviour of iron oxyhydroxide by introducing Ni sites for facilitating polysulfide anchoring and conversion.

The sluggish conversion kinetics and notorious shuttle effect of polysulfides are critical hindrances to practical implementation of lithium-sulfur batteries. Herein, bimetallic oxyhydroxide (FeNiOOH) as a functional sulfur host is proposed to overcome these obstacles. The introduction of Ni sites can modulate the electronic structure of the active sites to implement strong soluble polysulfide species immobilization and accelerate the conversion reaction kinetics of polysulfides, resulting in improved sulfur utilization and reduced polarization during the electrochemical reaction process. Benefiting from these advantages, FeNiOOH enables the sulfur cathode to deliver superior rate capability and cycling stability.

Nitrogen-vacancy-modulated efficient ammonia desorption over 3d TM-anchored BC3N2 monolayer.

Nitrogen fixation using electrochemical methods on the surface of single-atom catalysts (SACs) provides a highly feasible strategy for green and low-energy-consumption ammonia (NH3) production. Herein, using density functional theory (DFT) calculations, we explored in detail the potential of monolayer BC3N2 SACs supported with 3d transition metal (TM) atoms (TM@BC3N2) to facilitate nitrogen reduction. The results revealed that the TM@BC3N2 systems exhibited remarkable catalytic activity in the nitrogen-reduction reaction (NRR). The fine NRR activity was related to the just-right bonding/antibonding orbital interactions between the 2π* of N2 and the d orbitals of the TM ions. The nitrogen-adsorption configurations were found to have different activation mechanisms. In addition, the effects of convectively formed convex nitrogen defects (VN) on the interaction between N2 and VN-TM@BC3N2 and the NRR process of VN-TM@BC3N2 were studied, and it was found that VN could fine-tune the reaction efficiency of the eNRR because after N atom dissociation to form VN, the interaction of TM-C3 was enhanced, and the activation of nitrogen and adsorption of NH3 by the TM-active centers were weakened. The present study can be used as a motivation for further experimental and theoretical research of 2D monolayers as NRR electrocatalysts.

Robust photogalvanic effect, full spin polarization and pure spin current in the BiC photodetector by vacancy- and substitution-doping.

The photogalvanic effects (PGEs) in low-dimensional devices have attracted great interests recently. Herein, based on non-equilibrium Green's function combined with density functional theory, we investigated spin-dependent PGE phenomena in the BiC photodetector for the case of linearly polarized light and zero bias. Due to the presence of strong spin-orbital interaction (SOI) and C3v symmetry for the BiC monolayer, the armchair and zigzag BiC photodetectors produce robust spin-dependent PGEs which possess the cos(2θ) and sin(2θ) relations on the photon energies. Especially, the armchair and Bi-vacancy armchair BiC photodetector can produce fully spin polarization, and pure spin current was found in the armchair and zigzag BiC photodetector. Furthermore, after introducing the Bi-vacancy, C-vacancy, Bi-doping and C-doping respectively, corresponding armchair and zigzag BiC photodetector can produce higher spin-dependent PGEs for their Cs symmetry. Moreover, the behaviors of spin-dependent photoresponse are highly anisotropic and can be tuned by the photon energy. This work suggested great potential applications of the BiC monolayer on PGE-driven photodetectors in low energy-consumption optoelectronics and spintronic devices. .

Reversible active bridging sulfur sites grafted on Ni3S2 nanobelt arrays for efficient hydrogen evolution reaction.

Elaborate and rational design of cost-effective and high-efficiency non-noble metal electrocatalysts for pushing forward the sustainable hydrogen fuel production is of great significance. Herein, a novel VS4 nanoparticle decorated Ni3S2 nanobelt array in-situ grown on nickel foam (VS4/Ni3S2/NF NBs) was prepared by a self-templated synthesis strategy. Benefitting from the unique nanobelt array structure, abundant highly active bridge S22- sites and strong electronic interaction between VS4 and Ni3S2 on the heterointerface, the integrated VS4/Ni3S2/NF NBs exhibited excellent electrocatalytic hydrogen evolution activity and robust stability. The density functional theory (DFT) further revealed the reversible conversion catalysis mechanism of bridging S22- sites in VS4/Ni3S2/NF NBs during HER process. Notably, bidentate bridging SS bonds as the predominant catalytically active centers can spontaneously open once H adsorbed its surface, leading to the aggregation of negative charges on S atoms and thus facilitating the generation of H* intermediates, and spontaneously close when H* desorption is going to form H2. Our work provides fresh insights for developing potential polysulfides as high-performance hydrogen-evolving electrocatalysts for prospective clean energy production from water splitting.

Tunable electronic and magnetic properties of planar and corrugated phases of two-dimensional metal-organic frameworks.

The stability of two-dimensional (2D) metal-organic frameworks (MOFs) and their physical and chemical properties for potential applications are contentious. We herein investigated geometric, electronic and magnetic properties of the planar (p-) and corrugated (c-) phases of nickel ions with hexathiolbenzene (HTB)-based coordination nanosheets (Ni3HTB). The c-Ni3HTB is an antiferromagnetic semiconductor with a direct band gap of 0.33 eV, while the p-Ni3HTB is a ferromagnetic metal. This indicates that the electronic and magnetic properties of c-Ni3HTB and p-Ni3HTB depend on their geometric pattern. Furthermore, we applied biaxial strain and molecular adsorption to control their electronic and magnetic properties. In addition, we have proved that the corrugated phase in some kinds of 2D MOFs is common. Our work not only demonstrates that the potential applications of 2D MOFs should be scrupulously explored but also offers a new platform to investigate the physical and chemical properties of 2D MOFs.

Ultramicroporous Metal-Organic Framework with Inert Pore Surfaces for Inversed Separation of Ethylene from C2 Hydrocarbons Mixtures.

The achievement of direct C2H4 separation from C2 hydrocarbons is very challenging in the petrochemical industry due to their similar molecular sizes, boiling points, and physicochemical properties. In this work, a nonpolar/inert ultramicroporous metal-organic framework (MOF), [Co3(µ3-OH)(tipa)(bpy)1.5]·3DMF·6H2O (1), with stand-alone one-dimensional square tubular channels was successfully constructed, its pore enriched with plenty of aromatic rings causing nonpolar/inert pore surfaces. The MOF shows preferential adsorption of C2H6 compared to C2H4 and C2H2 in the low-pressure region, which is further verified by adsorption heats and selectivities. The C2H4 separation potential in one step for binary C2H6/C2H4 (50/50 and 10/90) and ternary C2H4/C2H6/C2H2 (89/10/1) is also examined by transient breakthrough simulations. Moreover, grand canonical Monte Carlo simulations demonstrate that the unique reversed adsorption mechanism is due to the shortest and most number of C-H···π interactions between C2H6 and the framework.

A graphene-like semiconducting BC2P monolayer as a promising material for a Li-ion battery and CO2 adsorbent.

Searching for high-performance anode materials and CO2 adsorption materials are key factors for next-generation renewable energy technologies and mitigation of the greenhouse effect. Herein, we report a novel two-dimensional (2D) BC2P monolayer with great potential as an anode material for lithium-ion batteries (LIBs) and as a material for CO2 adsorption. The adsorption energies of Li atoms and CO2 molecules on the BC2P supercell are negative enough to assure stability and safety under operating conditions. More intriguingly, the BC2P monolayer possesses a very high theoretical capacity of 1018.8 mA g h-1 for LIBs. In addition, the diffusion energy barriers of Li on the BC2P supercell are 0.26 and 0.87 eV, showing good charge/discharge capability, and the electrode potential of Li is beneficial to their performance as an anode material. Moreover, four chemical and three physical adsorption sites were verified, indicating that the CO2 molecule was effectively adsorbed on the BC2P supercell. These desirable properties make the BC2P monolayer a promising 2D material for application in LIBs and for CO2 adsorbents aimed at highly efficient CO2 capture.

Engineering a Series of Isoreticular Pillared Layer Ultramicroporous MOFs for Gas and Vapor Uptake.

The accurate design and systematic engineering of MOFs is a large challenge due to the randomness of the synthesis process. Isoreticular chemistry provides a powerful approach for the regulation of pore environment in a more predictable and precise way to systematically control gas/vapor adsorption performances. Herein, utilizing an effective strategy of altering the "pillared" motifs of pillared layer structures, three isoreticular ultramicroporous MOFs were successfully constructed. Combined with the reported parent MOFs and two other recorded isoreticular MOFs modified with -NH2 and -CH3, gas and vapor uptake performances of this family of isoreticular pillared layer MOFs were systematically explored.

Efficient electrocatalytic reduction of NO to ammonia on BC3 nanosheets.

Searching for an economical and highly efficient electrocatalytic reduction catalyst for ammonia synthesis under controllable conditions is a very attractive and challenging subject in chemistry. In this study, we systematically studied the electrocatalytic performance of BC3 nanosheets as potential NO reduction reaction (NORR) electrocatalysts using density functional theory (DFT) calculations. It was found that BC3 two-dimensional (2D) materials exhibit excellent catalytic activity with a very low limiting potential of -0.29/-0.11 V along three reaction paths. The total reaction is NO (g)+5H++5e-→NH3(g)+ H2O. The density of states of adsorbed NO, NH3, and the corresponding crystal orbital hamiltonian population (COHP) analysis revealed the mechanism of NO being activated and the reasons for NH3 adsorption/desorption on the surface of BC3. The reaction path, limiting potential, and Gibbs free energy calculations of BC3 catalyzed NO to ammonia synthesis revealed that for path 1, the potential-determining step is *NO+H++e-→*NOH, and for path 2/3 the potential-determining step is *NO+(H++e-)→*HNO. Calculation of the thermodynamic energy barriers for NO dissociation at the BC3 surface and NO hydrogenation reveals that NO is more likely to be hydrogenated rather than dissociated. The influences of the proton-electron hydrogenation site on the process of ammonia synthesis in the key reduction step were analyzed by Bader charge analysis and charge density, it is pointed out that the electronic structure and affects the reaction process can be controlled by hydrogenation at different sites of intermediates. These results pave the way for using nitrogen oxides not just nitrogen as raw materials for ammonia synthesis with 2D materials.

Adsorption Characteristics of Gas Molecules Adsorbed on Graphene Doped with Mn: A First Principle Study.

Herein, the adsorption characteristics of graphene substrates modified through a combined single manganese atom with a vacancy or four nitrogen to CH2O, H2S and HCN, are thoroughly investigated via the density functional theory (DFT) method. The adsorption structural, electronic structures, magnetic properties and adsorption energies of the adsorption system have been completely analyzed. It is found that the adsorption activity of a single vacancy graphene-embedded Mn atom (MnSV-GN) is the largest in the three graphene supports. The adsorption energies have a good correlation with the integrated projected crystal overlap Hamilton population (-IpCOHP) and Fermi softness. The rising height of the Mn atom and Fermi softness could well describe the adsorption activity of the Mn-modified graphene catalyst. Moreover, the projected crystal overlap Hamilton population (-pCOHP) curves were studied and they can be used as the descriptors of the magnetic field. These results can provide guidance for the development and design of graphene-based single-atom catalysts, especially for the support effect.

Metastable FeCN2@nitrogen-doped carbon with high pseudocapacitance as an anode material for sodium ion batteries.

Pseudocapacitive materials are good candidates for fast charging anodes of sodium ion batteries (SIB). However, pseudocapacitive materials with a high surface area face the severe problem of low initial coulombic efficiency. In this work, micro-sized nitrogen-doped carbon (NC) coated and supported polyhedron FeCN2 networks are designed and synthesized by a facile in situ gel-swelling technique. Impressively, FeCN2@NC as an SIB anode exhibits excellent rate performance with highly reversible rate capacities of 466 and 303 mA h g-1 at 0.2 and 10.0 A g-1, respectively. Furthermore, the FeCN2@NC anode shows a high initial coulombic efficiency (ICE) of 86% due to a low surface area. Electrochemical tests and density functional theory (DFT) calculation indicate that the metastable character enables the low intercalation/conversion reaction energy for FeCN2 and further greatly promotes the fast pseudocapacitive storage mechanism for FeCN2@NC. This work provides evidence that FeCN2 is a new type of metastability induced pseudocapacitive material with high initial coulombic efficiency.

Boosting polysulfides immobilization and conversion through CoS2 catalytic sites loaded carbon fiber for robust lithium sulfur batteries.

The practical applications of lithium sulfur battery is impeded by the lithium polysulfide shuttling and sluggish redox kinetics. To address the issues, herein, a multifunctional host is developed by the combination of nitrogen, phosphorus co-doped carbon fiber (NPCF) and CoS2 towards boost the soluble polysulfides adsorption and transformation. Benefiting from the NPCF originated from biomass cattail fibers, a high conductive network is provided, and shuttle effect is reduced due to the strong chemical interaction between abundant heteroatom polar sites and lithium polysulfides. Moreover, the electrocatalytic CoS2 on the carbon skeleton facilitate lithium polysulfides conversion and lithium sulfide deposition based on the density functional theory calculations and experiments. The efficient lithium polysulfides entrapment and subsequent electrocatalytic conversion improve dynamic stability during cycling, especially for rate capability. With these advantageous features, the electrode with NPCF/CoS2 host can deliver a good rate capability (903 and 782 mAh g-1 at 1C and 2C, respectively) and stable cycling performance with an ultra-low capacity decay of 0.014% per cycle at 1C. Notably, the cell can achieve a high areal capacity of 4.96 mA h cm-2 under an elevated sulfur loading of 5.0 mg cm-2. Overall, the improvement on the electrochemical performance ascertains the validity of the design strategy based on synergy engineering, which is a highly suitable approach for energy storage and conversion application.

Design strategies of two-dimensional metal-organic frameworks toward efficient electrocatalysts for N2 reduction: cooperativity of transition metals and organic linkers.

Two-dimensional (2D) metal-organic frameworks (MOFs) serve as emerging electrocatalysts due to their high conductivity, chemical tunability, and accessibility of active sites. We herein proposed a series of 2D MOFs with different metal atoms and organic linkers with the formula M3C12X12 (M = Cr, Mo, and W; X = NH, O, S, and Se) to design efficient nitrogen reduction reaction (NRR) electrocatalysts. Our theoretical calculations showed that metal atoms in M3C12X12 can efficiently capture and activate N2 molecules. Among these candidates, W3C12X12 (X = O, S, and Se) show the best NRR performance due to their high activity and selectivity as well as low limiting potential (-0.59 V, -0.14 V, and -0.01 V, respectively). Moreover, we proposed a d-band center descriptor strategy to screen out the high activity and selectivity of M3C12X12 for the NRR. Therefore, our work not only demonstrates a class of promising electrocatalysts for the NRR but also provides a strategy for further predicting the catalytic activity of 2D MOFs.

Enhanced Electrocatalytic Activity of Nickel Cobalt Phosphide Nanoparticles Anchored on Porous N-Doped Fullerene Nanorod for Efficient Overall Water Splitting.

Design and fabrication of bifunctional efficient and durable noble-metal-free electrocatalyst for hydrogen and oxygen evolution is highly desirable and challenging for overall water splitting. Herein, a novel hybrid nanostructure with Ni2P/CoP nanoparticles decorated on a porous N-doped fullerene nanorod (p-NFNR@Ni-Co-P) was developed as a bifunctional electrocatalyst. Benefiting from the electric current collector (ECC) effect of FNR for the active Ni2P/CoP nanoparticles, the p-NFNR@Ni-Co-P exhibited outstanding electrocatalytic performance for overall water splitting in alkaline medium. To deliver a current density of 10 mA cm-2, the electrolytic cell assembled by p-NFNR@Ni-Co-P merely required a potential as low as 1.62 V, superior to the benchmark noble-metal-based electrocatalyst. Experimental and theoretical results demonstrated that the surface engineered FNR serving as an ECC played a critical role in accelerating the charge transfer during the electrocatalytic reaction. The present work paves the way for fullerene nanostructures in the realm of energy conversion and storage.

B-Doped 2D-InSe as a bifunctional catalyst for CO2/CH4 separation under the regulation of an external electric field.

The separation of CO2 or CH4 from a CO2/CH4 mixture has drawn great attention in relation to solving air pollution and energy shortage issues. However, research into using bifunctional catalysts to separate CO2 and CH4 under different conditions is absent. We have herein designed a novel B-doped two-dimensional InSe (B@2DInSe) catalyst, which can chemically adsorb CO2 with covalent bonds. B@2DInSe can separate CO2 and CH4 in different electric fields, which originates from different regulation mechanisms by an electric field (EF) on the electric properties. The hybridization states between CO2 and B@2DInSe near the Fermi level have experienced gradual localization and eventually merged into a single narrow peak under an increased EF. As the EF further increased, the merged peak shifted towards higher energy states around the Fermi level. In contrast, the EF mainly alters the degree of hybridization between CH4 and B@2DInSe at states far below the Fermi level, which is different from the CO2 situation. These characteristics can also lead to perfect linear relationships between the adsorption energies of CO2/CH4 and the electric field, which may be beneficial for the prediction of the required EF without large volumes of calculations. Our results have not only provided novel clues for catalyst design, but they have also provided deep understanding into the mechanisms of bifunctional catalysts.

NiWO4 Microflowers on Multi-Walled Carbon Nanotubes for High-Performance NH3 Detection.

NiWO4 microflowers with a large surface area up to 79.77 m2·g-1 are synthesized in situ via a facile coprecipitation method. The NiWO4 microflowers are further decorated with multi-walled carbon nanotubes (MWCNTs) and assembled to form composites for NH3 detection. The as-fabricated composite exhibits an excellent NH3 sensing response/recovery time (53 s/177 s) at a temperature of 460 °C, which is a 10-fold enhancement compared to that of pristine NiWO4. It also demonstrates a low detection limit of 50 ppm; the improved sensing performance is attributed to the porous structure of the material, the large specific surface area, and the p-n heterojunction formed between the MWNTs and NiWO4. The gas sensitivity of the sensor based on daisy-like NiWO4/MWCNTs shows that the sensor based on 10 mol % (MWN10) has the best gas sensitivity, with a sensitivity of 13.07 to 50 ppm NH3 at room temperature and a detection lower limit of 20 ppm. NH3, CO2, NO2, SO2, CO, and CH4 are used as typical target gases to construct the NiWO4/MWCNTs gas-sensitive material and study the research method combining density functional theory calculations and experiments. By calculating the morphology and structure of the gas-sensitive material NiWO4(110), the MWCNT load samples, the vacancy defects, and the influence law and internal mechanism of gas sensitivity were described.

Computational Screening of 3 d Transition Metal Atoms Anchored on Defective Graphene for Efficient Electrocatalytic N2 Fixation.

The synthesis of ammonia (NH3 ) through the electrochemical reduction of molecular nitrogen (N2 ) is a promising strategy for significantly reducing energy consumption compared to traditional industrial processes. Herein, we report the design of a series of monovacancy and divacancy defective graphenes decorated with single 3d transition metal atoms (TM@MVG and TM@DVG; TM=Sc-Zn) as electrocatalysts for the nitrogen-reduction reaction (NRR) aided by density functional theory (DFT) calculations. By comparing energies for N2 adsorption as well as the free energies associated with *N2 activation and *N2 H formation, we successfully identified V@MVG, with the lowest potential of -0.63 V, to be an effective catalytic substrate for the NRR in an enzymatic mechanism. Electronic properties, including Bader charges, charge density differences, partial densities of states, and crystal orbital Hamilton populations, are further analyzed in detail. We believe that these results help to explain recent observations in this field and provide guidance for the exploration of efficient electrocatalysts for the NRR.

Density functional theory study of transition metal single-atoms anchored on graphyne as efficient electrocatalysts for the nitrogen reduction reaction.

Ammonia (NH3) is the main raw material for the organic chemical industry and a critical feedstock for the fertilizer industry with great significance for the global economy. The NH3 demand has gradually increased with modern society development. Moreover, the electrocatalytic nitrogen reduction reaction (NRR) is a promising NH3 synthesis technology. However, the design of efficient electrocatalysts for the NRR is still challenging. In this study, we systematically analyzed transition metal (TM) single-atoms (Ti, V, Cr, Mn, Zr, Nb, and Mo) anchored on graphyne (GY) as NRR catalysts using density functional theory calculations. The calculation results for the first and last hydrogenation steps (*NNH formation and *NH3 desorption, respectively) revealed that Mn@GY (with an end-on configuration) and V@GY (with a side-on configuration) were the most suitable catalytic substrates for the NRR. The free-energy profiles of the TM@GY catalysts indicated that Mn@GY was the best NRR electrocatalyst owing to its distal pathway with a minimum free-energy barrier of 0.36 eV. In addition, the electronic properties, namely the Bader charge, charge density difference, partial density of states, and crystal orbital Hamilton population, of the TM@GY catalysts were analyzed in detail, and the results further confirmed that Mn@GY was an efficient electrocatalyst. The insights obtained from this comprehensive study can provide useful guidelines for designing new and efficient electrocatalysts.

Ag (111) surface for ambient electrolysis of nitrogen to ammonia.

In this paper, the reaction process of N2 convert to NH3 catalyzed by Ag (111) surface was obtained through the construction of Ag (111) surface and computational simulation. The charge transfer in the reaction process and the change of N≡N bond length are described. Since the N2 reduction reaction (NRR) usually occurs under alkaline solution conditions, we calculated and described the coexistence of OH* and N2. At the same time, the co-adsorption structure of OH* and N2 at different adsorption sites was studied.

Formaldehyde Molecules Adsorption on Zn Doped Monolayer MoS2: A First-Principles Calculation.

Based on the first principles of density functional theory, the adsorption behavior of H2CO on original monolayer MoS2 and Zn doped monolayer MoS2 was studied. The results show that the adsorption of H2CO on the original monolayer MoS2 is very weak, and the electronic structure of the substrate changes little after adsorption. A new kind of surface single cluster catalyst was formed after Zn doped monolayer MoS2, where the ZnMo3 small clusters made the surface have high selectivity. The adsorption behavior of H2CO on Zn doped monolayer MoS2 can be divided into two situations. When the H-end of H2CO molecule in the adsorption structure is downward, the adsorption energy is only 0.11 and 0.15 eV and the electronic structure of adsorbed substrate changes smaller. When the O-end of H2CO molecule is downward, the interaction between H2CO and the doped MoS2 is strong leading to the chemical adsorption with the adsorption energy of 0.80 and 0.98 eV. For the O-end-down structure, the adsorption obviously introduces new impurity states into the band gap or results in the redistribution of the original impurity states. All of these may lead to the change of the chemical properties of the doped MoS2 monolayer, which can be used to detect the adsorbed H2CO molecules. The results show that the introduction of appropriate dopant may be a feasible method to improve the performance of MoS2 gas sensor.