Sp2 Carbon Research Articles

Si-C atomic line achieving efficient electrocatalytic nitrogen reduction reactions

In this study, the concept of a Si-C atomic line (SCAL) featuring fully exposed atomic sites is introduced for the first time, and the SCAL serves as a highly efficient electrocatalyst for nitrogen reduction reactions (NRR). Thanks to the strong binding strength of the Si-C bonds (polar covalent bonds), the SCAL exhibits exceptional structural stability at 298.15 K. With a band gap of 1.86 eV characterized by a semiconductor, SCAL exhibits relatively high conductivity which is advantageous for electrocatalytic processes. N2 is adsorbed on the C sites in an end-on mode due to the most negative adsorption energy (–0.39 eV), and the nature of adsorption is s-p orbital hybridization. Based on the end-on N2 adsorption, the entire NRR pathway is simulated and shows a relatively low energy barrier of 0.50 eV, which is relatively low compared to reported metal-free NRR electrocatalysts. The charge transfer mechanism reveals that the active sites (C atoms) are responsible for charge transfer, while other parts of SCAL act as storage warehouses for charge. Moreover, SCAL demonstrates a preference for NRR over hydrogen evolution reaction (HER), underscoring its excellent electrocatalytic selectivity. This study opens new avenues for designing high-performance catalysts.

Cation-induced interface electric field redistribution and molecular orbital coupling in Co-FeS/MoS2 for boosting electrocatalytic overall water splitting

A green hydrogen economy requires efficient bifunctional electrocatalysts for simultaneous hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In this study, a mild sulfuration strategy was used to create a Co-FeS/MoS2 catalyst from metal-organic frameworks (MOFs) on foam nickel. This catalyst exhibits exceptional activity in 1 M KOH, only requiring ultralow overpotentials of 63 mV and 230 mV to achieve current densities of 10 mA cm−2 and 100 mA cm−2 for the HER and OER processes. Additionally, it achieves a low cell voltage of 1.45 V at 10 mA cm−2, surpassing reported catalysts. DFT calculations and XPS tests show that Co introduction induces high-valence Fe active sites and facilitates interface electric field redistribution. Crystal orbital Hamilton population (COHP) calculations reveal d-p orbital hybridization, enhancing conductivity and charge transfer kinetics. This research sheds light on the catalytic impacts of metal cations on transition metal sulfides to design high efficient electrocatalysts.

C1‐4 Alkylation of Aryl Bromides with Light Alkanes enabled by Metallaphotocatalysis in Flow

The homologous series of gaseous C1‐4 alkanes represents one of the most abundant sources of short alkyl fragments. However, their application in synthetic organic chemistry is exceedingly rare due to the challenging C–H bond cleavage, which typically demands high temperatures and pressures, thereby limiting their utility in the construction of complex organic molecules. In particular, the formation of C(sp2)–C(sp3) bonds is crucial for constructing biologically active molecules, including pharmaceuticals and agrochemicals. In this study, we present the previously elusive coupling between gaseous alkanes and (hetero)aryl bromides, achieved through a combination of Hydrogen Atom Transfer (HAT) photocatalysis and nickel‐catalyzed cross coupling at room temperature. Utilizing flow technology allowed us to conduct this novel coupling reaction with reduced reaction times and in a scalable fashion, rendering it practical for widespread adoption in both academia and industry. Density Functional Theory (DFT) calculations unveiled that the oxidative addition constitutes the rate‐determining step, with the activation energy barrier increasing with smaller alkyl radicals. Furthermore, radical isomerization observed in propane and butane analogues could be attributed to the electronic properties of the bromoarene coupling partner, highlighting the crucial role of oxidative addition in the observed selectivity of this transformation.

C1-4 Alkylation of Aryl Bromides with Light Alkanes enabled by Metallaphotocatalysis in Flow.

The homologous series of gaseous C1-4 alkanes represents one of the most abundant sources of short alkyl fragments. However, their application in synthetic organic chemistry is exceedingly rare due to the challenging C-H bond cleavage, which typically demands high temperatures and pressures, thereby limiting their utility in the construction of complex organic molecules. In particular, the formation of C(sp2)-C(sp3) bonds is crucial for constructing biologically active molecules, including pharmaceuticals and agrochemicals. In this study, we present the previously elusive coupling between gaseous alkanes and (hetero)aryl bromides, achieved through a combination of Hydrogen Atom Transfer (HAT) photocatalysis and nickel-catalyzed cross coupling at room temperature. Utilizing flow technology allowed us to conduct this novel coupling reaction with reduced reaction times and in a scalable fashion, rendering it practical for widespread adoption in both academia and industry. Density Functional Theory (DFT) calculations unveiled that the oxidative addition constitutes the rate-determining step, with the activation energy barrier increasing with smaller alkyl radicals. Furthermore, radical isomerization observed in propane and butane analogues could be attributed to the electronic properties of the bromoarene coupling partner, highlighting the crucial role of oxidative addition in the observed selectivity of this transformation.

Photoreductive 1,4-Dicarbofunctionalization of 1,3-Enynes with Organoiodides and Cyanoarenes via Halogen-Atom Transfer.

A photoreductive halogen-atom transfer (XAT) strategy for 1,4-dicarbofunctionalization of 1,3-enynes with organoiodides and cyanoarenes is disclosed, enabling access to functionalized allenes in a highly regio-, chemo-, and stereoselective manner. Upon the photoredox catalysis and the activation of Et3N XAT agents, the mild conditions and high functional group tolerance of this protocol enable the formation of two C-C bonds, including a C(sp3)-C(sp3) bond and a C(sp2)-C(sp2) bond, in a single reaction step, and provides a general avenue to polysubstituted allenes and late-stage modification of bioactive compounds.

Unveiling the Nature of Chemical Bonds in Real Space.

Recent advent of diverse chemical entities necessitates a re-evaluation of chemical bond concepts, underscoring the importance of experimental evidence. Our prior study introduced a general methodology, termed Core Differential Fourier Synthesis (CDFS), for mapping the distribution of valence electron density (VED) in crystalline substances within real space. In this study, we directly compare the VED distributions obtained through CDFS with those derived from high-accuracy theoretical calculation using long-range corrected density functional theory, which quantitatively reproduces accurate orbital energies. This comparison serves to demonstrate the precision of the CDFS in replicating complex details. The VED patterns observed experimentally exhibited detailed structures and phases of wave functions indicative of sp3 hybrid orbitals, closely aligning with theoretical predictions. This alignment underscores the utility of our approach in gathering quantum chemical data experimentally, a crucial step for discussing the chemical properties, such as reaction mechanisms.

Structural modulation and frictional, antibacterial and biocompatible properties of Ag-incorporated DLC films: Dependence on Ag precipitation behavior

Ag-incorporated DLC (Ag-DLC) film attracted widespread attention in the bio-alloy implants field due to its excellent mechanical, biocompatible, and antibacterial properties. However, how to balance the short-term efficient antibacterial and biocompatibility of films, and the correlation between Ag precipitation and structural properties are still unclear. Hence, Ag-DLC films with different Ag contents were deposited by modulating Ag target current, focusing on the influence of Ag precipitation behavior. Results show that Ag dopants exist in the form of Ag crystals rather than bond with carbon matrix, which can easily precipitate and aggregate to film surface. The precipitated Ag amount with Ag target current enhances from 2.75% to 35.04% while promotes the formation of sp2 carbon structure catalyzed by Ag, corresponding to decreased mechanical property. Interestingly, a small number of Ag dopants could effectively improve the friction behavior due to the lubrication effect of soft metal Ag and the friction interface transformation. Importantly, the best antibacterial property of film is obtained at high Ag precipitation content, while the surfaces with low Ag precipitation content are more favorable for cell adhesion and cytotoxicity reduction. Therefore, the Ag target current for better comprehensive performance is suggested within the range of 0.4 to 0.6 A.

Customized Heteronuclear Dual Single-Atom and Cluster Assemblies via D-Band Orchestration for Oxygen Reduction Reaction.

Advanced oxygen reduction reaction (ORR) catalysts, integrating with well-dispersed single atom (SA) and atomic cluster (AC) sites, showcase potential in bolstering catalytic activity. However, the precise structural modulation and in-depth investigation of their catalytic mechanisms pose ongoing challenges. Herein, a proactive cluster lockdown strategy is introduced, relying on the confinement of trinuclear clusters with metal atom exchange in the covalent organic polymers, enabling the targeted synthesis of a series of multicomponent ensembles featuring FeCo (Fe or Co) dual-single-atom (DSA) and atomic cluster (AC) configurations (FeCo-DSA/AC) via thermal pyrolysis. The designed FeCo-DSA/AC surpasses Fe- and Co-derived counterparts by 18 mV and 49 mV in ORR half-wave potential, whilst exhibiting exemplary performance in Zn-air batteries. Comprehensive analysis and theoretical simulation elucidate the enhanced activity stems from adeptly orchestrating dz 2-dxz and O 2p orbital hybridization proximate to the Fermi level, fine-tuning the antibonding states to expedite OH* desorption and OOH* formation, thereby augmenting catalytic activity. This work elucidates the synergistic potentiation of active sites in hybrid electrocatalysts, pioneering innovative targeted design strategies for single-atom-cluster electrocatalysts.

Origins of Giant Anisotropic Phonon Heat Transfer in True‐1D van der Waals Material

AbstractThermal rectification devices, which facilitate preferential heat flow in a singular direction, stands as pivotal tools in the realization of solid‐state thermal circuits. 1D atomic chains, exhibit heightened thermal rectification efficiency owing to their exceptional directional heat conduction properties. These will find widespread utility in many applications, encompassing areas such as cooling, energy harvesting, and thermal isolation systems. However, unlike quasi‐1D materials, the intrinsic anisotropic heat transport in true‐1D atomic chains is yet to be systematically studied. Herein, the origins of the anisotropic heat transfer in three representative 1D structures (TaSe3 and BaTiS3 marked as quasi‐1D, MoI3 labeled as true‐1D) is first investigated by integrating a first‐principles density functional theory‐based framework of two‐channel heat conduction model. In contrast to quasi‐1D, MoI3 exhibits a giant anisotropy of lattice thermal conductivity (κL) in chain‐ and cross chain‐directions with a high ratio up to ≈20, which far exceeds the previous report for HfTe5 and ZrTe5. Such unique heat transfer reveals comprehensively by charge‐sharing and transferred charges, p‐‐d orbital hybridization and Young's modulus changes, induces an exceptionally large anisotropy. This study presents a high‐performance implementation of thermal rectification designed to regulate directional heat current, demonstrating its potential applicability in solid‐state thermal circuits.

Strongly Coupled NiMo@Alloy‐LDH Interfaces with Low‐Barrier Schottky Junctions for Oxygen Evolution Reaction

AbstractThe main challenge in developing Schottky‐contact OER catalytic devices based on layered double hydroxides (LDHs) is to achieve metal–semiconductor junctions with low contact resistance and high charge transfer capacity. However, due to the presence of high potential barriers and Fermi pinning, conventional Schottky contacts are usually unsatisfactory, resulting in poor‐working electrode performance and high energy consumption. In this study, a new concept of “hindrance factor” is introduced to quantify the difficulty of electron transfer, and a low‐hindrance factor Schottky contact formed by strong coupling of semiconductor LDH and NiMo alloy clusters is designed. This interface guides charge redistribution, optimizes the bonding and orbital states of adsorption sites, and enhances the targeted adsorption of OH intermediates. The results show that the configured NiMo@NiFeCe‐LDH working electrode only needs 1.445 V (vs RHE) to drive the reaction and shows excellent durability in 400 h of testing. At the same time, based on this study, a strategy for screening high‐performance Schottky junctions is developed. This strategy provides a bridge for studying interface properties, orbital hybridization, and charge transfer, reveals the potential mechanism for reducing contact resistance, and has important guiding significance for screening high‐performance metal–semiconductor electrocatalysts and stability.

Direct N[sbnd]H heteroarylation of NH-sulfoximines under electrochemical conditions

Given the pivotal importance of sulfoximines in the field of medicine, they have garnered considerable attention in synthetic chemistry, and the development of novel catalytic methods to achieve their functionalization is highly valuable. Herein, a direct and practical electrochemical strategy for the synthesis of heteroaromatic-substituted products was developed using NH-sulfoximines and quinoxalin-2(1H)-ones as starting materials. The direct construction of the NC(sp2) bonds of NH-sulfoximines is achieved through the cleavage of the C3H bonds of quinoxalin-2(1H)-ones. This protocol features good functional group tolerance, simplicity in operation, and easy to scalability. By utilizing this electrochemical strategy, the structural modification of biomolecular derivatives has been successfully carried out, which is unattainable with other traditional oxidants. The mechanistic investigation demonstrates that quinoxalin-2(1H)-ones serve dual roles as both substrates and redox mediators, thereby avoiding the addition of extra hydrogen atom transfer (HAT) reagents.

Monitoring the formation of infinite-layer transition metal oxides through in situ atomic-resolution electron microscopy.

Infinite-layer transition metal oxides with two-dimensional oxygen coordination exhibit intriguing electronic and magnetic properties due to strong in-plane orbital hybridization. The synthesis of this distinctive structure has primarily relied on kinetically controlled reduction of oxygen-rich phases featuring three-dimensional polyhedral oxygen coordination. Here, using in situ atomic-resolution electron microscopy, we scrutinize the intricate atomic-scale mechanisms of oxygen conduction leading to the transformation of SrFeO2.5 to infinite-layer SrFeO2. The oxygen release is highly anisotropic and governed by the lattice reorientation aligning the fast diffusion channels towards the outlet, which is facilitated by cooperative yet shuffle displacements of iron and oxygen ions. Accompanied with the oxygen release, the three-dimensional to two-dimensional reconfiguration of oxygen is facilitated by the lattice flexibility of FeOx polyhedral layers, adopting multiple discrete transient states following the sequence determined by the least energy-costing pathways. Similar transformation mechanism may operate in cuprate and nickelate superconductors, which are isostructural with SrFeO2.

Metal–Organic Frameworks with Axial Cobalt–Oxygen Coordination Modulate Polysulfide Redox for Lithium–Sulfur Batteries

AbstractAlthough the ultrahigh theoretical energy density and cost‐effectiveness, lithium–sulfur (Li‐S) batteries suffer from sluggish conversion kinetics and the shuttling effect of soluble lithium polysulfides (LiPSs). Herein, conductive hexagonal cobalt‐organic framework (Co‐HTP) nanosheets are anchored in situ on carboxyl graphene (CG) substrates and serve as host catalysts to modulate the polysulfide redox. Substantial characterizations identify that the local coordination environment of the quadrilateral Co–N4 units transforms into an asymmetric penta‐coordinated O–Co–N4 with axial Co─O coordination, which triggers spin polarization and remarkable electron delocalization of Co 3d orbital. The higher spin state and lower local electron density of the O–Co–N4 sites induce more active electronic states in Co‐HTP/CG and facilitate orbital hybridization with polysulfides to form more stable bond orders. Such optimized electronic structure significantly accelerates redox kinetics and enhances the adsorption strength of polysulfides. These merit the lithium–sulfur battery based on Co‐HTP/CG with a high reversible capacity, impressive rate capability, and prolonged cycling performance over 500 cycles. This work will enrich the design philosophy of modulating the spintronic structure of electrocatalysts for advanced Li–S batteries and beyond.

Nature of the Active Center for the Oxygen Reduction on Ag-Based Single-Atom Alloy Clusters.

The development of alternative alloy catalysts with high activity, surpassing platinum group metals, for the oxygen reduction reaction (ORR) is urgently needed in the field of electrocatalysis. The Ag-based single-atom alloy (AgSAA) cluster has been proposed as a promising catalyst for the ORR; however, enhancing its activity under operational conditions remains challenging due to limited insights into its actual active site. Here, we demonstrate that the operando formation of the MO x (OH) y complex serves as the key active site for catalyzing the ORR over AgSAA cluster catalysts, as revealed through comprehensive neural network potential molecular dynamics simulations combined with first-principles calculations. The volcano plot of the ORR over the MO x (OH) y complex addresses the gaps inherent in traditional metallic alloy models for pure AgSAA cluster catalysts in ORR catalysis. The appropriate orbital hybridization between OH and the dopant metal in the MO x (OH) y complexes indicated that the Ag54Co1, Ag54Pd1, and Ag54Au1 clusters are optimal AgSAA catalysts for the ORR. Our work underscores the significance of theoretical modeling considering the reaction atmosphere in uncovering the true active site for the ORR, which can be extended to other reaction systems for rational catalyst design.

The “d-p orbital hybridization”-guided design of novel two-dimensional MOFs with high anchoring and catalytic capacities in Lithium − Sulfur batteries

The energy system of lithium-sulfur batteries is quite promising, however, lithium-sulfur batteries still suffer from considerable problems, such as the abominable shuttle effect of polysulfides (LiPSs), the low conductivity of the solid-phase products, the slow redox kinetics during charging and discharging, and the volume expansion. Herein, the hybridization pattern between the d-orbitals of various transition metal atoms and the p-orbitals of sulfides is revealed grounded in the theory of density function, which explains the high adsorption strength of two-dimensional metal–organic frameworks (MOFs) with LiPSs and accelerates the screening of high-performance anchoring and catalytic materials. The results elucidate that the coordinated transition metal–organic frameworks (Mo-NH MOF) monolayers increase the capacity of LiPSs to anchor by forming more π-bonds from the hybridization of the S p orbitals and Mo d orbitals. Notably, Mo-NH MOF exhibits bifunctional catalytic activity for sulfur reduction as well as Li2S decomposition reactions during charging and discharging, which improves the conversion efficiency of redox reactions. As a result, new MOF materials featuring unique active centers and the potential mechanism by which the active centers modulate the performance of the substrate materials are revealed, and this finding may accelerate the development of high-performance Li-S batteries.

P-d Orbital Hybridization in Ag-based Electrocatalysts for Enhanced Nitrate-to-Ammonia Conversion.

Considering the substantial role of ammonia, developing highly efficient electrocatalysts for nitrate-to-ammonia conversion has attracted increasing interest. Herein, we proposed a feasible strategy of p-d orbital hybridization via doping p-block metals in an Ag host, which drastically promotes the performance of nitrate adsorption and disassociation. Typically, a Sn-doped Ag catalyst (SnAg) delivers a maximum Faradaic efficiency (FE) of 95.5±1.85 % for NH3 at -0.4 V vs. RHE and reaches the highest NH3 yield rate to 482.3±14.1 mg h-1 mgcat. -1. In a flow cell, the SnAg catalyst achieves a FE of 90.2 % at an ampere-level current density of 1.1 A cm-2 with an NH3 yield of 78.6 mg h-1 cm-2, during which NH3 can be further extracted to prepare struvite as high-quality fertilizer. A mechanistic study reveals that a strong p-d orbital hybridization effect in SnAg is beneficial for nitrite deoxygenation, a rate-determining step for NH3 synthesis, which as a general principle, can be further extended to Bi- and In-doped Ag catalysts. Moreover, when integrated into a Zn-nitrate battery, such a SnAg cathode contributes to a superior energy density of 639 Wh L-1, high power density of 18.1 mW cm-2, and continuous NH3 production.

Engineering p-d orbital hybridization in PdSb bimetallene for energy-saving H2 production parallel upgrade plastic waste

The electrochemical conversion of PET-derived ethylene glycol into high-quality chemicals parallel energy-saving H2 production is an optimal solution to the serious environmental pollution of plastics. In this paper, p-d orbital hybrid PdSb bimetallene with defect-rich crimped surface is synthesized by a one-step solvent approach. PdSb bimetallene exhibits excellent electrocatalytic performance in ethylene glycol and PET hydrolysate oxidation attributed to the unconventional p-d orbital hybridization feature and metallene structure. PdSb bimetallene shows better properties than Pd metallene and commercial Pd black catalysts under ethylene glycol conditions and PET hydrolysate. Besides PdSb bimetallene can oxidize ethylene glycol to produce the valuable product glycolic acid with high Faradaic efficiency and selectivity. Besides, PdSb bimetallene can oxidize PET-derived ethylene glycol into glycolic acid with high selectivity in EGOR||HER system. This study provides insights into the synthesis of metallene with p-d orbital hybridization properties, coupled with energy-saving H2 production parallel upgrade plastic waste.

First-principle and experimental investigation into the interfacial characters of Ti-doped ZTA and high chromium cast iron

Ti doping can improve the interfacial wettability and bonding condition between ZTA ceramic and high chromium cast iron (HCCI), but the underlying mechanism is still unclear. Therefore, the effects of Ti doping on the interfacial characters between ZTA and HCCI were investigated by experiment and first-principles calculations. Results of XRD, SEM, and high-temperature drop test indicate the presence of Ti at the interface and its effect on the formation of interfacial diffusion layer to improve the interface wettability and bonding obviously. The heat of segregation and work of adhesion obtained by first-principle calculations shows that the improvement in interface wettability and bonding is due to the promotion of dopped Ti atoms on the diffusion of Fe, Al, and Zr elements, but not the diffusion of Ti itself. Further investigation from the electronic level reveals that the doped Ti changes the charge distribution and orbital hybridization, and thus makes the formation or enhancement of strong ionic bonds and covalent bonds at the interface, improving the bonding strength and wettability of interfaces in ZTA/HCCI. The findings of this research can offer new insights into the modification of ceramics and enlarge the application of advanced ceramic materials.

Risk assessment of general FPSO supply system based on hybrid fuzzy fault tree and Bayesian network

One of the major risks to the operation of a FPSO (Floating, Production, Storage and Offloading) is collision of supply vessels. Experiences have shown that collisons of supply vessel take place frequently, although the consequences are limited. The offshore oil&gas industry has established relevant design standards and operational procedures, which are proven to be effective in reducing this risk. As the risk assessment becomes increasingly applied, there is a need to quantify the likelihood of supply vessel collisions especially duing the early design/project stage when historical incident data does not exist. This paper proposees a method for estimating the likelihood of supply vessel collision based on fault tree analysis (FTA), Bayesian network (BN), hybrid theory and fuzzy theory. In liew of using historicval data, this method combines the fuzzy logic with expert heuristics to determine the basic events(BEs). The triangular fuzzy membership functions and a hybrid theory were adopted to define factors that lack data or had no data in the events. To account for the imprecise information of human error, a scheme is devised to use the fuzzy fault probability(FFP) based on the hybrid theory, or a hybrid fuzzy fault tree analysis (HFFT). The algorithm transforms the FT into a BN with a conditional probability table (CPT). This new method was demonstrated in an example of a FPSO, and the results were has been validated through case studies and accident reports. A sensitivity analysis was also conducted to illustrate key parameters.

Main-Group Elements Enhance Electrochemical Nitrogen Reduction Reaction of Vanadium-Based Single Atom Catalysts Through d-p Orbital Hybridization.

Developing active sites with flexibility and diversity is crucial for single atom catalysts (SACs) towards sustainable nitrogen fixation at ambient conditions. Herein, the effects of doping main group metal elements (MGM) on the stability, catalytic activity, and selectivity of vanadium-based SACs is systematically investigated based on density functional theory calculations. It is found that the catalytic activity of V site can be significantly enhanced by the synergistic effect between MGM and vanadium atoms. More importantly, a volcano curve between the catalytic activity and the adsorption free energy of NNH* can be established, in which V-Pb dimer embedded on N-coordinated graphene (VPb-NG) exhibits optimal NRR activity due to its location at the top of volcano. Further analysis of electronic structures reveals that the unoccupancy ratio (eg/t2g) of V site is dramatically increased by the strong d-p orbital hybridization between V and Pb atoms, subsequently, N2 is activated to a larger extent. These interesting findings may provide a new path for designing active sites in SACs with excellent performance.