Prediction of stable BC3N2 monolayer from first-principles calculations: Stoichiometry, crystal structure, electronic and adsorption properties

A first-principles study of the BC3N2 monolayer and a BC3N2/graphene heterostructure as promising anode materials for sodium-ion batteries

High-performance sodium-ion batteries (SIBs) require anode materials with high capacity and fast kinetics. Based on first-principles calculations, we propose BC3N2 and BC3N2/graphene (B/G) heterostructure as potential SIB anode materials. The BC3N2 monolayer exhibits intrinsic metallic behavior. In addition, BC3N2 possesses a low Na+ diffusion barrier (0.15 eV), a high storage capacity (777 mA h g-1), a low open-circuit voltage (0.72 V), and a tiny axial expansion (0.36%). Compared with the BC3N2 monolayer, the B/G heterostructure exhibits a lower diffusion barrier of 0.027 eV, suggesting a much faster diffusion. More importantly, although the B/G heterostructure possesses heavier molar weight, its theoretical capacity (689 mA h g-1) is comparable to that of the BC3N2 monolayer. Based on the above-mentioned properties, we hope both the BC3N2 monolayer and the B/G heterostructure would be promising anodes for SIBs.

Theoretical Investigation of the BCN Monolayer and Their Derivatives for Metal-free CO2 Photocatalysis, Capture, and Utilization

In recent years, carbon capture and utilization (CCU) has been explored as an attractive solution to global warming, which is mainly caused by increasing CO2 emission levels. Many functional materials have been developed for removing atmospheric CO2 and converting it to more useful forms of carbon. Traditional metallic photocatalytic species have drawbacks-photocorrosion, low visible-light absorbance, and environmental damage; therefore, metal-free materials have attracted considerable research attention. In particular, boron nitride (BN) possesses unique B-N bonds, characterized by a large difference in the electronegativity of atoms that facilitates CO2 reduction, and catalytic CO2 reduction by boron carbon nitride (BCN) has been demonstrated under visible light; hence, these two materials can be considered potential CO2 reduction photocatalysts. However, further modification of the materials and their applicability to other CCU applications have not been extensively explored. Therefore, we decided to investigate the modification of BCN monolayers, with the aim of ensuring that the properties of the materials are better suited, first, to the requirements of CO2 photocatalysis, and second, to those of carbon capture or other optoelectronic applications. In this study, we considered various novel BCN monolayers, based on modification via metal-free substitutional doping and nitrogen vacancy creation, and performed first-principles density functional theory calculations. The effects of the modifications on band gap tuning, charge transfer, and the CO2 adsorption ability were all studied. Specifically, ON-B13C8N11 and SiC-2 × 2-BC6N were shown to possess excellent properties for photocatalytic CO2 reduction, and OC-2 × 2-BC6N and Nv-4 × 4-BN can be considered for future CO2 capture materials. These results contribute to existing CCU approaches, suggesting that BCN monolayer modification merits further investigation, and offering insights relevant to other photocatalytic applications.

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.

High gas sensing performance of inorganic and organic molecule sensing devices based on the BC3N2 monolayer

Recently, a novel two-dimensional (2D) BC₃N₂ monolayer has gained a lot of attention due to its graphene-like structure, and it was first reported by using the particle swarm optimization algorithm and ab initio calculations. Combining density functional theory with the non-equilibrium Green's function method, a 2D BC₃N₂-based nanodevice has been theoretically constructed and the gas sensing performance of the BC₃N₂ monolayer for inorganic and organic molecules has been extensively investigated. The results revealed that the BC₃N₂ monolayer remains metallic with thermodynamic stability. Meanwhile, the results of sensing performance analysis show that the inorganic molecules CO, NO, and NO₂ and organic molecules C₂H₂ and HCHO have strong chemical interactions with BC₃N₂ and were chemically adsorbed onto BC₃N₂. In contrast, the interactions between NH₃, SO₂, CH₄, C₂H₄ and CH₃OH and BC₃N₂ are very weak and these molecules adopt physical adsorption. In the case of chemisorption, the electronic transport behaviors of the 2D BC₃N₂ devices are sensitive to molecules, and the gas sensitivity of BC₃N₂ is strongly anisotropic, especially for organic C₂H₂ with the gas sensing ratios from 7.30 to 10.43 (from 2.51 to 2.79) under different bias voltages along the zigzag (armchair) direction. For inorganic molecules, the gas sensing device is not particularly sensitive, and the maximum gas sensing ratio is only 1.36 for CO. Meanwhile, the large anisotropic gas sensitivity can reach up to 2.66/6.22 for electron transport along the armchair and zigzag directions for CO/C₂H₂ in the BC₃N₂-based sensing devices. Accordingly, the high gas sensitivity can be disclosed by displaying the scattering state around the Fermi level at different bias voltages during the transport process. As a result, BC₃N₂ could be used in 2D gas sensing devices, especially for sensing organic molecule C₂H₂.

Cu Nanoparticle-Decorated Boron-Carbon-Nitrogen Nanosheets for Electrochemical Determination of Chloramphenicol

In the present work, irregular Cu nanoparticle-decorated boron-carbon-nitrogen (Cu-BCN) nanosheets were successfully synthesized. A Cu-BCN dispersion was deposited on a bare glassy carbon electrode (GCE) to prepare an electrochemical sensor (Cu-BCN/GCE) for the detection of chloramphenicol (CAP) in the environment. Cu-BCN was characterized using high-resolution scanning transmission electron microscopy (HRSTEM), scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis, and X-ray photoelectron spectroscopy (XPS). The performance of the Cu-BCN/GCE was studied using electrochemical impedance spectroscopy (EIS), and its advantages were proven by electrode comparison. Differential pulse voltammetry (DPV) was used to optimize the experimental conditions, including the amount of Cu-BCN deposited, enrichment potential, deposition time, and pH of the electrolyte. A linear relationship between the CAP concentration and current response was obtained under the optimized experimental conditions, with a wide linear range and a limit of detection (LOD) of 2.41 nmol/L. Cu-BCN/GCE exhibited high stability, reproducibility, and repeatability. In the presence of various organic and inorganic species, the influence of the Cu-BCN-based sensor on the current response of CAP was less than 5%. Notably, the prepared sensor exhibited excellent performance in real-water samples, with satisfactory recovery.

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.

Activation of Carbon Dioxide by CoCDn- (n = 0-4) Anions

Laser ablation generated CoCD_n^- (n = 0-4) anions were mass selected and then reacted with CO₂ in an ion trap reactor. The reactions were characterized by mass spectrometry and quantum chemical calculations. The experimental results demonstrated that the CoC^- anion can convert CO₂ into CO. In contrast, the bare Co^- anion is inert toward CO₂. Coordinated D ligands can modify the reactivity of CoCD_1-4^- in which CoCD_1-3^- can reduce CO₂ into CO selectively and CoCD₄^- can only adsorb CO₂. The crucial roles of the coordinated C and D ligands to tune the reactivity of CoCD_n^- (n = 0-4) toward CO₂ were rationalized by theoretical calculations. Note that the hydrogenation process that is usually observed in the reactions of gas-phase metal hydrides with CO₂ is completely suppressed for the reactions CoCD_n^- + CO₂. This study provides insights into the molecular-level origin for the observations that CO can be selectively generated from CO₂ catalyzed by cobalt-containing carbides in heterogeneous catalysis.