Tackling the Activity and Selectivity Challenges of Electrocatalysts toward the Nitrogen Reduction Reaction via Atomically Dispersed Biatom Catalysts

Enhanced conversion of CO2 into C2H4 on single atom Cu-anchored graphitic carbon nitride: Synergistic diatomic active sites interaction

Single atom metal-nitrogen-carbon materials have emerged as remarkably potent catalysts, demonstrating unprecedented potential for the photo-driven reduction of CO2. Herein, a unique Cu@g-C3N5 catalyst obtained by cooperation of single atom Cu and nitrogen-rich g-C3N5 is proposed. The particular CuN diatomic active sites (DAS) in Cu@g-C3N5 contribute to the formation of highly stable CuOCN adsorption, a key configuration for CO2 activation and CC coupling. The synergistic diatomic active sites interaction is found responsible for the efficient photoreduction of CO2 to C2H4 which has been demonstrated in our Gibbs free energy calculation and COHP analysis. The CO2 activation mechanism was studied, the charge density difference and DOS analysis show that the low oxidation state Cu atom significantly affects the electronic structure of g-C3N5 and then enhance the catalytic activity of CO2 hydrogenation.

Constructing a interfacial electric field for efficient reduction of nitrogen to ammonia

Electrochemical nitrogen reduction (eNRR) is a cost-effective and environmentally sustainable approach for ammonia production. MoS2, as a typical layered transition metal compound, holds significant potential as an electrocatalyst for the eNRR. Nevertheless, it suffers from a limited number of active sites and low electron transfer efficiency. In this study, we constructed a heterostructure by depositing SnO2 (an n-type semiconductor) nanoparticles on MoS2 (a p-type semiconductor). This unique interfacial structure not only generates abundant interfacial contacts but also facilitates the transfer of electrons from SnO2 to MoS2, leading to the formation of an interfacial electric field. Theoretical calculations demonstrate that this electric field increases the number of active electrons, facilitating N2 adsorption and NN bond activation. Moreover, it increases the degree of orbital overlap between N2 and SnO2/MoS2, effectively reducing the energy barrier of the rate-determining step. Benefiting from the interfacial electric field effect, the SnO2/MoS2 catalyst exhibits significant catalytic activity and selectivity towards eNRR, with an ammonia yield of 47.1 µg h-1 mg-1 and a Faraday efficiency of 19.3 %, surpassing those reported for the majority of MoS2- and SnO2-based catalysts.

Uniting Synergistic Effect of Single-Ni Site and Electric Field of B- Bridged-N for Boosted Electrocatalytic Nitrate Reduction to Ammonia

Electrochemical conversion of nitrate, a prevalent water pollutant, to ammonia (NH3) is a delocalized and green path for NH3 production. Despite the existence of different nitrate reduction pathways, selectively directing the reaction pathway on the road to NH3 is now hindered by the absence of efficient catalysts. Single-atom catalysts (SACs) are extensively investigated in a wide range of catalytic processes. However, their application in electrocatalytic nitrate reduction reaction (NO3 -RR) to NH3 is infrequent, mostly due to their pronounced inclination toward hydrogen evolution reaction (HER). Here, Ni single atoms on the electrochemically active carrier boron, nitrogen doped-graphene (BNG) matrix to modulate the atomic coordination structure through a boron-spanning strategy to enhance the performance of NO3 -RR is designed. Density functional theory (DFT) study proposes that BNG supports with ionic characteristics, offer a surplus electric field effect as compared to N-doped graphene, which can ease the nitrate adsorption. Consistent with the theoretical studies, the as-obtained NiSA@BNG shows higher catalytic activity with a maximal NH3 yield rate of 168 µg h-1 cm-2 along with Faradaic efficiency of 95% and promising electrochemical stability. This study reveals novel ways to rationally fabricate SACs' atomic coordination structure with tunable electronic properties to enhance electrocatalytic performance.

Direct Eight-Electron N2O Electroreduction to NH3 Enabled by an Fe Double-Atom Catalyst

N2O is a dominant atmosphere pollutant, causing ozone depletion and global warming. Currently, electrochemical reduction of N2O has gained increasing attention to remove N2O, but its product is worthless N2. Here, we propose a direct eight-electron (8e) pathway to electrochemically convert N2O into NH3. As a proof of concept, using density functional theory calculation, an Fe2 double-atom catalyst (DAC) anchored by N-doped porous graphene (Fe2@NG) was screened out to be the most active and selective catalyst for N2O electroreduction toward NH3 via the novel 8e pathway, which benefits from the unique bent N2O adsorption configuration. Guided by theoretical prediction, Fe2@NG DAC was fabricated experimentally, and it can achieve a high N2O-to-NH3 Faradaic efficiency of 77.8% with a large NH3 yield rate of 2.9 mg h-1 cm-2 at -0.6 V vs RHE in a neutral electrolyte. Our study offers a feasible strategy to synthesize NH3 from pollutant N2O with simultaneous N2O removal.

Advanced dual-atom catalysts on graphitic carbon nitride for enhanced hydrogen evolution via water splitting

In this comprehensive investigation, we explore the effectiveness of 55 dual-atom catalysts (DACs) supported on graphitic carbon nitride (gCN) for both alkaline and acidic hydrogen evolution reactions (HER). Employing density functional theory (DFT), we scrutinize the thermodynamic and kinetic profiles of these DACs, revealing their considerable potential across a diverse pH spectrum. For acidic HER, our results identify catalysts such as FePd-gCN, CrCr-gCN, and NiPd-gCN, displaying promising ΔGH* values of 0.0, 0.0, and -0.15 eV, respectively. This highlights their potential effectiveness in acidic environments, thereby expanding the scope of their applicability. Within the domain of alkaline HER, this study delves into the thermodynamic and kinetic profiles of DACs supported on gCN, utilizing DFT to illuminate their efficacy in alkaline HER. Through systematic evaluation, we identify that DACs such as CrCo-gCN, FeRu-gCN, and FeIr-gCN not only demonstrate favorable Gibbs free energy change (ΔGmax) for the overall water splitting reaction of 0.02, 0.27, and 0.38 eV, respectively, but also feature low activation energies (Ea) for water dissociation, with CrCo-gCN, FeRu-gCN, and FeIr-gCN notably exhibiting the Ea of just 0.42, 0.33, and 0.42 eV, respectively. The introduction of an electronic descriptor (φ), derived from d electron count (Nd) and electronegativity (ETM), provides a quantifiable relationship with catalytic activity, where a lower φ corresponds to enhanced reaction kinetics. Specifically, φ values between 4.0-4.6 correlate with the lowest kinetic barriers, signifying a streamlined HER process. Our findings suggest that DACs with optimized φ values present a robust approach for the development of high-performance alkaline HER electrocatalysts, offering a pathway towards the rational design of energy-efficient catalytic systems.

Single Atom Catalysts Based on Earth-Abundant Metals for Energy-Related Applications

Anthropogenic activities related to population growth, economic development, technological advances, and changes in lifestyle and climate patterns result in a continuous increase in energy consumption. At the same time, the rare metal elements frequently deployed as catalysts in energy related processes are not only costly in view of their low natural abundance, but their availability is often further limited due to geopolitical reasons. Thus, electrochemical energy storage and conversion with earth-abundant metals, mainly in the form of single-atom catalysts (SACs), are highly relevant and timely technologies. In this review the application of earth-abundant SACs in electrochemical energy storage and electrocatalytic conversion of chemicals to fuels or products with high energy content is discussed. The oxygen reduction reaction is also appraised, which is primarily harnessed in fuel cell technologies and metal-air batteries. The coordination, active sites, and mechanistic aspects of transition metal SACs are analyzed for two-electron and four-electron reaction pathways. Further, the electrochemical water splitting with SACs toward green hydrogen fuel is discussed in terms of not only hydrogen evolution reaction but also oxygen evolution reaction. Similarly, the production of ammonia as a clean fuel via electrocatalytic nitrogen reduction reaction is portrayed, highlighting the potential of earth-abundant single metal species.

Size-Dependent Catalysis in Fenton-like Chemistry: From Nanoparticles to Single Atoms

State-of-the-art Fenton-like reactions are crucial in advanced oxidation processes (AOPs) for water purification. This review explores the latest advancements in heterogeneous metal-based catalysts within AOPs, covering nanoparticles (NPs), single-atom catalysts (SACs), and ultra-small atom clusters. A distinct connection between the physical properties of these catalysts, such as size, degree of unsaturation, electronic structure, and oxidation state, and their impacts on catalytic behavior and efficacy in Fenton-like reactions. In-depth comparative analysis of metal NPs and SACs is conducted focusing on how particle size variations and metal-support interactions affect oxidation species and pathways. The review highlights the cutting-edge characterization techniques and theoretical calculations, indispensable for deciphering the complex electronic and structural characteristics of active sites in downsized metal particles. Additionally, the review underscores innovative strategies for immobilizing these catalysts onto membrane surfaces, offering a solution to the inherent challenges of powdered catalysts. Recent advances in pilot-scale or engineering applications of Fenton-like-based devices are also summarized for the first time. The paper concludes by charting new research directions, emphasizing advanced catalyst design, precise identification of reactive oxygen species, and in-depth mechanistic studies. These efforts aim to enhance the application potential of nanotechnology-based AOPs in real-world wastewater treatment.

High catalytic activity and abundant active sites in M2C12 monolayer for nitrogen reduction reaction

Developing highly efficient single-atom catalysts (SACs) for the nitrogen reduction reaction (NRR) to ammonia production has garnered significant attention in the scientific community. However, achieving high activity and selectivity remains challenging due to the lack of innate activity in most existing catalysts or insufficient active site density. This study delves into the potential of M2C12 materials (M = Cr, Ir, Mn, Mo, Os, Re, Rh, Ru, W, Fe, Cu, and Ti) with high transition metal coverage as SACs for NRR using first-principles calculations. Among these materials, Os2C12 exhibited superior catalytic activity for NRR, with a low overpotential of 0.39 V and an Os coverage of up to 72.53 wt%. To further boost its catalytic activity, a nonmetal (NM) atom doping (NM = B, N, O, and S) and C vacancy modification were explored in Os2C12. It is found that the introduction of O enables exceptional catalytic activity, selectivity, and stability, with an even lower overpotential of 0.07 V. Incorporating the O atom disrupted the charge balance of its coordinating C atoms, effectively increasing the positive charge density of the Os-d-orbit-related electronic structure. This promoted strong d-π* coupling between Os and N2H, enhancing N2H adsorption and facilitating NRR processes. This comprehensive study provides valuable insights into NRR catalyst design for sustainable ammonia production and offers a reference for exploring alternative materials in other catalytic reactions.

Coordination Structure Modulation in Group-VIB Metal Doped Ag3PO4 Augments Active Site Density for Electrocatalytic Conversion of N2 to NH3

Doping is considered a promising material engineering strategy in electrochemical nitrogen reduction reaction (NRR), provided the role of the active site is rightly identified. This work concerns the doping of group VIB metal in Ag3PO4 to enhance the active site density, accompanied by d-p orbital mixing at the active site/N2 interface. Doping induces compressive strain in the Ag3PO4 lattice and inherently accompanies vacancy generation, the latter is quantified with positron annihilation lifetime studies (PALS). This eventually alters the metal d-electronic states relative to Fermi level and manipulate the active sites for NRR resulting into side-on N2 adsorption at the interface. The charge density deployment reveals Mo as the most efficient dopant, attaining a minimum NRR overpotential, as confirmed by the detailed kinetic study with the rotating ring disk electrode (RRDE) technique. In fact, the Pt ring of RRDE fails to detect N2H4, which is formed as a stable intermediate on the electrode surface, as identified from in-situ attenuated total reflectance-infrared (ATR-IR) spectroscopy. This advocates the complete conversion of N2 to NH3 on Mo/Ag3PO4-10 and the so-formed oxygen vacancies formed during doping act as proton scavengers suppressing hydrogen evolution reaction resulting into a Faradaic efficiency of 54.8% for NRR.

Metal-support spin orders: Crucial effect on electrocatalytic oxygen reduction

Magnetic property (e.g. spin order) of support is of great importance in the rational design of heterogeneous catalysts. Herein, we have taken the Ni-supported ferromagnetic (FM) CrBr3 support (Nix/CrBr3) to thoroughly investigate the effect of spin-order on electrocatalytic oxygen reduction reaction (ORR) via spin-polarized density functional theory calculations. Specifically, Ni loading induces anti-FM coupling in Ni-Cr, leading to a transition from FM-to-ferrimagnetic (FIM) properties, while Ni-Ni metallic bonds create a robust FM direct exchange, benefiting the improvement of the phase transition temperature. Interestingly, with the increase in Ni loading, the easy magnetic axis changes from out-of-plane (2D-Heisenberg) to in-plane (2D-XY). The adsorption properties of Nix/CrBr3, involving O2 adsorption energy and configuration, are not governed by the d-band center but strongly correlate with magnetic anisotropy. It is noteworthy that the applied potential and electrolyte acidity triggers spin-order transition phenomena during the ORR and induces the catalytic pathway change from 4e- ORR to 2e- ORR with the excellent onset potential of 0.93 V/reversible hydrogen electrode, comparable to the existing most excellent noble-metal catalysts. Generally, these findings offer new avenues to understand and design heterogeneous catalysts with magnetic support.

Synergistic Al-Al Dual-Atomic Site for Efficient Artificial Nitrogen Fixation

Synthesis of ammonia by electrochemical nitrogen reduction reaction (NRR) is a promising alternative to the Haber-Bosch process. However, it is commonly obstructed by the high activation energy. Here, we report the design and synthesis of an Al-Al bonded dual atomic catalyst stabilized within an amorphous nitrogen-doped porous carbon matrix (Al2NC) with high NRR performance. The dual atomic Al2-sites act synergistically to catalyze the complex multiple steps of NRR through adsorption and activation, enhancing the proton-coupled electron transfer. This Al2NC catalyst exhibits a high Faradaic efficiency of 16.56±0.3 % with a yield rate of 29.22±1.2 μg h-1 mgcat -1. The dual atomic Al2NC catalyst shows long-term repeatable, and stable NRR performance. This work presents an insight into the identification of synergistic dual atomic catalytic site and mechanistic pathway for the electrochemical conversion of N2 to NH3.

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 C5 ${_5 }$ N2 ${_2 }$ . With high selectivity and outstanding activity, Zr, Nb, Mo, Ta, W and Re-doped C5 ${_5 }$ N2 ${_2 }$ are identified as potential nominees for NRR. Particularly, Mo@C5 ${_5 }$ N2 ${_2 }$ 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@C5 ${_5 }$ N2 ${_2 }$ can be well characterized by the adsorption strength of intermediate *N2 ${_2 }$ H. Moreover, there exists a volcanic relationship between the catalytic property UL ${_{\rm{L}} }$ and the structure descriptor Ψ ${{{\Psi }}}$ , which validates the robustness and universality of Ψ ${{{\Psi }}}$ , combined with our previous study. This work sheds light on the design of SACs with eminent NRR performance.

Structural Design of Single-Atom Catalysts for Enhancing Petrochemical Catalytic Reaction Process

Petroleum, as the "lifeblood" of industrial development, is the important energy source and raw material. The selective transformation of petroleum into high-end chemicals is of great significance, but still exists enormous challenges. Single-atom catalysts (SACs) with 100% atom utilization and homogeneous active sites, promise a broad application in petrochemical processes. Herein, the research systematically summarizes the recent research progress of SACs in petrochemical catalytic reaction, proposes the role of structural design of SACs in enhancing catalytic performance, elucidates the catalytic reaction mechanisms of SACs in the conversion of petrochemical processes, and reveals the high activity origins of SACs at the atomic scale. Finally, the key challenges are summarized and an outlook on the design, identification of active sites, and the appropriate application of artificial intelligence technology is provided for achieving scale-up application of SACs in petrochemical process.

A two-dimensional covalent organic framework with single-atom manganese for electrochemical NO reduction: a computational study

Covalent organic frameworks (COFs) exhibit great potential for electrocatalysis. Here, using DFT calculations and constant-potential modelling, we report the feasibility of a series of COFs toward NO reduction via regulating their central metal atoms and linking ligands. A COF with single-atom Mn is identified to possess superior activity while maintaining high NH3 selectivity.

Design of Multifunctional Electrocatalysts for ORR/OER/HER/HOR: Janus Makes Difference

Multifunctional electrocatalysts for hydrogen evolution reaction (HER), hydrogen oxidation reaction (HOR), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR) have broad application prospects; However, realization of such kinds of materials remain difficulties because it requires the materials to have not only unique electronic properties, but multiple active centers to deal with different reactions. Here, employing density functional theory (DFT) computations, it is demonstrated that by decorating the Janus-type 2D transition metal dichalcogenide (TMD) of TaSSe with the single atoms, the materials can achieve multifunctionality to catalyze the ORR/OER/HER/HOR. Out of sixteen catalytic systems, Pt-VS (i.e., Pt atom embedded in the sulfur vacancy), Pd-VSe, and Pt-VSe@TaSSe are promising multifunctional catalysts with superior stability. Among them, the Pt-VS@TaSSe catalyst exhibits the highest activity with theoretical overpotentials ηORR = 0.40 V, ηOER = 0.39 V, and ηHER/HOR = 0.07 V, respectively, better than the traditional Pt (111), IrO2 (110). The interplays between the catalyst and the reaction intermediate over the course of the reaction are then systematically investigated. Generally, this study presents a viable approach for the design and development of advanced multifunctional electrocatalysts. It enriches the application of Janus, a new 2D material, in electrochemical energy storage and conversion technology.

Regulated Dual Defects of Bridging Organic and Terminal Inorganic Ligands in Iron-based Metal-Organic Framework Nodes for Efficient Photocatalytic Ammonia Synthesis

Engineering advantageous defects to construct well-defined active sites in catalysts is promising but challenging to achieve efficient photocatalytic NH3 synthesis from N2 and H2O due to the chemical inertness of N2 molecule. Here, we report defective Fe-based metal-organic framework (MOF) photocatalysts via a non-thermal plasma-assisted synthesis strategy, where their NH3 production capability is synergistically regulated by two types of defects, namely, bridging organic ligands and terminal inorganic ligands (OH- and H2O). Specially, the optimized MIL-100(Fe) catalysts, where there are only terminal inorganic ligand defects and coexistence of dual defects, exhibit the respective 1.7- and 7.7-fold activity enhancement comparable to the pristine catalyst under visible light irradiation. As revealed by experimental and theoretical calculation results, the dual defects in the catalyst induce the formation of abundant and highly accessible coordinatively unsaturated Fe active sites and synergistically optimize their geometric and electronic structures, which favors the injection of more d-orbital electrons in Fe sites into the N2 π* antibonding orbital to achieve N2 activation and the formation of a key intermediate *NNH in the reaction. This work provides a guidance on the rational design and accurate construction of porous catalysts with precise defective structures for high-performance activation of catalytic molecules.

Impact of Vacancy Defects on Electrochemical Nitrogen Reduction Reaction Performance of MXenes

We investigated electrochemical nitrogen reduction reaction (eNRR) on MXenes consisting of the vacancy defects in the functional layer using density functional theory calculations. We considered Mo2C, W2C, Mo2N, and W2N MXenes with F, N, and O functionalization and investigated distal and alternative associative pathways. We analyzed these MXenes for eNRR based on N2 adsorption energy, NH3 desorption energy, NRR selectivity, and electrochemical limiting potential. While we find that most of the considered MXenes surfaces are more favorable for eNRR compared to hydrogen evolution, these surfaces also have strong NH3 binding (>-1.0 eV) and thus will be covered with NH3 during operating conditions. Amongst all considered MXenes, only W2NF2 is found to have a low NH3 desorption energy along with low eNRR overpotential and selectivity towards eNRR. The obtained eNRR overpotential and NH3 desorption energy on W2NF2 are superior to those reported for pristine W2N3 as well as functionalized MXenes.

Advances in Naked Metal Clusters for Catalysis

The properties of sub-nano metal clusters are governed by quantum confinement and their large surface-to-bulk ratios, atomically precise compositions and geometric/electronic structures. Advances in metal clusters lead to new opportunities in diverse aspects of sciences including chemo-sensing, bio-imaging, photochemistry, and catalysis. Naked metal clusters having synergic multiple active sites and coordinative unsaturation and tunable stability/activity enable researchers to design atomically precise metal catalysts with tailored catalysis for different reactions. Here we summarize the progress of ligand-free naked metal clusters for catalytic applications. It is anticipated that this review helps to better understand the chemistry of small metal clusters and facilitates the design and development of new catalysts for potential applications.

Theoretical exploration of the nitrogen fixation mechanism of two-dimensional dual-metal FeTM@GY (TM = Fe, Mo, Co, and V) electrocatalysts

In contrast to the energy-consuming Haber-Bosch process, ammonia synthesis by electrocatalysis under ambient conditions is an efficient and environmentally friendly method. In this work, through first principles calculations, the potential of four dual-atom FeTM (TM = Fe, Mo, Co, and V) anchored graphyne (FeTM@GY) as efficient nitrogen reduction reaction (NRR) catalysts is systematically investigated. Among them, FeMo@GY is the most promising, with excellent NRR catalytic activity, high ability to suppress the competing hydrogen evolution reaction (HER), and good stability. Moreover, NRR prefers the maximum pathway with the calculated onset potentials of -0.27 V for FeMo@GY. This work not only suggests that FeMo@GY holds great promise as an efficient, low-cost, and stable dual-atom catalyst for NRR but also further provides a guiding idea for the design of efficient NRR catalysts.

Strategies Toward High Selectivity, Activity, and Stability of Single-Atom Catalysts

Single-atom catalysts (SACs) hold immense promise in facilitating the rational use of metal resources and achieving atomic economy due to their exceptional atom-utilization efficiency and distinct characteristics. Despite the growing interest in SACs, only limited reviews have holistically summarized their advancements centering on performance metrics. In this review, first, a thorough overview on the research progress in SACs is presented from a performance perspective and the strategies, advancements, and intriguing approaches employed to enhance the critical attributes in SACs are discussed. Subsequently, a comprehensive summary and critical analysis of the electrochemical applications of SACs are provided, with a particular focus on their efficacy in the oxygen reduction reaction , oxygen evolution reaction, hydrogen evolution reaction , CO2 reduction reaction, and N2 reduction reaction . Finally, the outline future research directions on SACs by concentrating on performance-driven investigation, where potential areas for improvement are identified and promising avenues for further study are highlighted, addressing challenges to unlock the full potential of SACs as high-performance catalysts.

Proposals for gas-detection improvement of the FeMPc monolayer towards ethylene and formaldehyde by using bimetallic synergy

Development and fabrication of a novel gas sensor with superb performance are crucial for enabling real-time monitoring of ethylene (C2H4) and formaldehyde (H2CO) emissions from industrial manufacture. Herein, first-principles calculations and AIMD simulations were carried out to investigate the effect of the Fe-M dimer on the adsorption of C2H4 and H2CO on metal dimer phthalocyanine (FeMPc, M = Ti-Zn) monolayers, and the electronic structures and sensing properties of the above adsorption systems were systematically discussed. The results show that the FeMPc (M = Ti, V, Cr, Mn) monolayers interact with C2H4 and H2CO by chemisorption except for the FeMnPc/H2CO system, while the other adsorption systems are all characterized by physisorption. Interestingly, the adsorption strength of C2H4 and H2CO can be effectively regulated by the bimetallic synergy of the Fe-M dimer. Moreover, the FeCrPc and FeMnPc monolayers exhibit excellent sensitivity towards C2H4 and H2CO, and have short recovery time (4.69 ms-2.31 s) for these gases at room temperature due to the effective surface diffusion at 300 K. Consequently, the FeCrPc and FeMnPc materials can be utilized as high-performance, reusable gas sensors for detecting C2H4 and H2CO, and have promising applications in monitoring the release of ethylene and formaldehyde from industrial processes.

Electrochemical nitrogen reduction reaction on anchored SnS2 nanosheets with TM2 dimers

The design of efficient, high-stability nitrogen fixation catalysts remains a great challenge to achieve electrochemical nitrogen reduction reaction (NRR) under ambient conditions. Herein, the high-throughput first-principles calculations are performed to obtain potential electrochemical NRR catalysts from transition metal (TM) dimers anchored on SnS2 nanosheets. The selected W2/SnS2 behaves as a promising NRR candidate possessing -0.27 V limiting potential and 0.81 eV maximum kinetic potential, and it exhibits the adsorption advantages of *N2 over other small molecules (*H2O, *O, *OH, *H). More importantly, the moderate d orbital valence electron number and electronegativity of TM atom could obtain better NRR activity, and a new descriptor φ considering the effects of coordination environments and adsorbates is proposed to achieve the fast pre-screening among various candidates. This work presents practical insights into the fast screening of TM2/SnS2 candidates for efficient nitrogen fixation and further streamlining the design of electrochemical NRR catalysts.

Graphene-based iron single-atom catalysts for electrocatalytic nitric oxide reduction: a first-principles study

The electrocatalytic NO reduction reaction (NORR) emerges as an intriguing strategy to convert harmful NO into valuable NH3. Due to their unique intrinsic properties, graphene-based Fe single-atom catalysts (SACs) have gained considerable attention in electrocatalysis, while their potential for NORR and the underlying mechanism remain to be explored. Herein, using constant-potential density functional theory calculations, we systematically investigated the electrocatalytic NORR on the graphene-based Fe SACs. By changing the local coordination environment of Fe single atoms, 26 systems were constructed. Theoretical results show that, among these systems, the Fe SAC coordinated with four pyrrole N atoms and that co-coordinated with three pyridine N atoms and one O atom exhibit excellent NORR activity with low limiting potentials of -0.26 and -0.33 V, respectively, as well as have high selectivity toward NH3 by inhibiting the formation of byproducts, especially under applied potential. Furthermore, electronic structure analyses indicate that NO molecules can be effectively adsorbed and activated via the electron "donation-backdonation" mechanism. In particular, the d-band center of the Fe SACs was identified as an efficient catalytic activity descriptor for NORR. Our work could stimulate and guide the experimental exploration of graphene-based Fe SACs for efficient NORR toward NH3 under ambient conditions.

Novel magneto-electrocatalyst Cr2CO2-MXene for boosting nitrogen reduction to ammonia

Ammonia (NH3) plays important roles in chemistry, the environment, and energy; however, the synthesis of NH3 relies heavily on the Haber-Bosch process, causing serious environmental pollution and energy consumption. A clean and effective strategy for the synthesis of NH3 involves nitrogen (N2) being transformed to ammonia (NH3) using electrocatalysis. Adjusting the magnetism of electrocatalysts may improve their performance, and therefore, four magnetic states, nonmagnetic (NM), ferromagnetic (FM), interlayer antiferromagnetic (Inter-AFM), and intra-layer antiferromagnetic (Intra-AFM) Cr2CO2-MXene were designed to explore magnetoelectrocatalysis performance using well-defined density functional theory (DFT) calculations in this study. Upon comparing the nitrogen reduction limiting potentials of N2 molecules on the surface of the four different magnetic states in Cr2CO2-MXene, and the selectivity calculations of the hydrogen evolution reaction (HER) and nitrogen reduction reaction (NRR), the Inter-AFM Cr2CO2-MXene is shown to be a better NRR electrocatalyst than the other three cases. This study paves way to unravel the mystery of the spin-catalytic mechanism and will lay a solid foundation for eNRR electrocatalysts with magnetic materials for environmental and energy applications.

Mechanism of electrocatalytic CO2 reduction reaction by borophene supported bimetallic catalysts

Bimetal atom catalysts (BACs) hold significant potential for various applications as a result of the synergistic interaction between adjacent metal atoms. This interaction leads to improved catalytic performance, while simultaneously maintaining high atomic efficiency and exceptional selectivity, similar to single atom catalysts (SACs). Bimetallic site catalysts (M2β12) supported by β12-borophene were developed as catalysts for electrocatalytic carbon dioxide reduction reaction (CO2RR). The research on density functional theory (DFT) demonstrates that M2β12 exhibits exceptional stability, conductivity, and catalytic activity. Investigating the most efficient reaction pathway for CO2RR by analyzing the Gibbs free energy (ΔG) during potential determining steps (PDS) and choosing a catalyst with outstanding catalytic performance for CO2RR. The overpotential required for Fe2β12 and Ag2β12 to generate CO is merely 0.05 V. This implies that the conversion of CO2 to CO can be accomplished with minimal additional voltage. The overpotential values for Cu2β12 and Ag2β12 during the formation of HCOOH were merely 0.001 and 0.07 V, respectively. Furthermore, the Rh2β12 catalyst exhibits a relatively low overpotential of 0.51 V for CH3OH and 0.65 V for CH4. The Fe2β12 produces C2H4 through the *CO-*CO pathway, while Ag2β12 generates CH3CH2OH via the *CO-*CHO coupling pathway, with remarkably low overpotentials of 0.84 and 0.60 V, respectively. The study provides valuable insights for the systematic design and screening of electrocatalysts for CO2RR that exhibit exceptional catalytic performance and selectivity.

Ambient Electrochemical Ammonia Synthesis: From Theoretical Guidance to Catalyst Design

Ammonia, a vital component in the synthesis of fertilizers, plastics, and explosives, is traditionally produced via the energy-intensive and environmentally detrimental Haber-Bosch process. Given its considerable energy consumption and significant greenhouse gas emissions, there is a growing shift toward electrocatalytic ammonia synthesis as an eco-friendly alternative. However, developing efficient electrocatalysts capable of achieving high selectivity, Faraday efficiency, and yield under ambient conditions remains a significant challenge. This review delves into the decades-long research into electrocatalytic ammonia synthesis, highlighting the evolution of fundamental principles, theoretical descriptors, and reaction mechanisms. An in-depth analysis of the nitrogen reduction reaction (NRR) and nitrate reduction reaction (NitRR) is provided, with a focus on their electrocatalysts. Additionally, the theories behind electrocatalyst design for ammonia synthesis are examined, including the Gibbs free energy approach, Sabatier principle, d-band center theory, and orbital spin states. The review culminates in a comprehensive overview of the current challenges and prospective future directions in electrocatalyst development for NRR and NitRR, paving the way for more sustainable methods of ammonia production.

Breaking linear scaling relations by strain engineering on MXene for boosting N2 electroreduction

The development of N2 reduction reaction (NRR) electrocatalysts with excellent activity and selectivity is of great significance, but adsorption-energy linear scaling relations between reaction intermediates severely hamper the realization of this aspiration. Here, we propose an elegant strain engineering strategy to break the linear relations in NRR to promote catalytic activity and selectivity. Our results show that the N-N bond lengths of adsorbed N2 with side-on and end-on configurations exhibit opposite variations under strains, which is illuminated by establishing two different N2 activation mechanisms of "P-P" (Pull-Pull) and "E-E" (Electron-Electron). Then, we highlight that strain engineering can break the linear scaling relations in NRR, selectively optimizing the adsorption of key NH2NH2** and NH2* intermediates to realize a lower limiting potential (UL). Particularly, the catalytic activity-selectivity trade-off of NRR on MXene can be circumvented, resulting in a low UL of -0.25 V and high Faraday efficiency (FE), which is further elucidated to originate from the strain-modulated electronic structures. Last but not least, the catalytic sustainability of MXene under strain has been guaranteed. This work not only provides fundamental insights into the strain effect on catalysis but also pioneers a new avenue toward the rational design of superior NRR catalysts.

Nanocatalytic theranostics with intracellular mutual promotion for ferroptosis and chemo-photothermal therapy

The reactive oxygen species (ROS) produced through the Fenton reaction, induces lipid peroxide (LPO), causing cellular structural damage and ultimately triggering ferroptosis. However, the generation of ROS in the tumor microenvironment (TME) is limited by the catalytic efficiency of the Fenton reaction. Herein, a novel hollow mesoporous silica nanoparticle (HMSN) combined with multi-metal sulfide-doped mesoporous silica nanocatalyzers (NCs) was developed, namely MxSy-HMSN NCs (M represents Cu Mn and Fe, S denotes sulfur). The MxSy-HMSN can dramatically enhanced the ferroptosis by: (1) facilitating the conversion of H2O2 to ·OH through Fenton or Fenton-like reactions through co-catalysis; (2) weakening ROS scavenging systems by depleting the over expressed glutathione (GSH) in TME; (3) providing exceptional photothermal therapy to augment ferroptosis. The MxSy-HMSN can also act as smart cargos for anticancer drug-doxorubicin (DOX). The release of DOX is responsive to GSH/pH/Near-infrared Light (NIR) irradiation at the tumor lesion, significantly improving therapeutic outcomes while minimizing side effects. Additionally, the MxSy-HMSN has demonstrated excellent magnetic resonance imaging (MRI) potential. This smart MxSy-HMSN offer a synergetic approach combining ferroptosis with chemo-photothermal therapy and magnetic resonance imaging (MRI) diagnose, which could be an informative guideline for the design of future NCs.

Unraveling the Performance Descriptors for Designing Single-Atom Catalysts on Defective MXenes for Exclusive Nitrate-To-Ammonia Electrocatalytic Upcycling

Electrocatalytic nitrate reduction reaction (NO3 RR) is a promising approach for converting nitrate into environmentally benign or even value-added products such as ammonia (NH3 ) using renewable electricity. However, the poor understanding of the catalytic mechanism on metal-based surface catalysts hinders the development of high-performance NO3 RR catalysts. In this study, the NO3 RR mechanism of single-atom catalysts (SACs) is systematically explored by constructing single transition metal atoms supported on MXene with oxygen vacancies (Ov -MXene) using density functional theory (DFT) calculations. The results indicate that Ag/Ov -MXene (for precious metal) and Cu/Ov -MXene (for non-precious metal) are highly efficient SACs for NO3 RR toward NH3 , with low limiting potentials of -0.24 and -0.34 V, respectively. Furthermore, these catalysts show excellent selectivity toward ammonia due to the high energy barriers associated to the formation of byproducts such as NO2 , NO, N2 O, and N2 on Ag/Ov -MXene and Cu/Ov -MXene, effectively suppressing the competitive hydrogen evolution reaction (HER). The findings not only offer new strategies for promoting NH3 production by MXene-based SACs electrocatalysts under ambient conditions but also provide insights for the development of next-generation NO3 RR electrocatalysts.

Current Status and Perspectives of Dual-Atom Catalysts Towards Sustainable Energy Utilization

The exploration of sustainable energy utilization requires the implementation of advanced electrochemical devices for efficient energy conversion and storage, which are enabled by the usage of cost-effective, high-performance electrocatalysts. Currently, heterogeneous atomically dispersed catalysts are considered as potential candidates for a wide range of applications. Compared to conventional catalysts, atomically dispersed metal atoms in carbon-based catalysts have more unsaturated coordination sites, quantum size effect, and strong metal-support interactions, resulting in exceptional catalytic activity. Of these, dual-atomic catalysts (DACs) have attracted extensive attention due to the additional synergistic effect between two adjacent metal atoms. DACs have the advantages of full active site exposure, high selectivity, theoretical 100% atom utilization, and the ability to break the scaling relationship of adsorption free energy on active sites. In this review, we summarize recent research advancement of DACs, which includes (1) the comprehensive understanding of the synergy between atomic pairs; (2) the synthesis of DACs; (3) characterization methods, especially aberration-corrected scanning transmission electron microscopy and synchrotron spectroscopy; and (4) electrochemical energy-related applications. The last part focuses on great potential for the electrochemical catalysis of energy-related small molecules, such as oxygen reduction reaction, CO2 reduction reaction, hydrogen evolution reaction, and N2 reduction reaction. The future research challenges and opportunities are also raised in prospective section.

Computational investigation of single and multiple boron atom doped WS2 monolayers for superior electrocatalytic reduction of nitrogen

The efficient conversion of nitrogen into ammonia plays a significant role in our modern society. Therefore, the design and development of associated catalysts have become an area of major research interest. Nowadays, an increasing number of studies have been exploring single-atom or double-atom metal-free electrocatalysts for the N2 reduction reaction, where regulating the precise number of catalyst atoms anchored on the substrate posed a real challenge. Herein, with density functional theory (DFT) simulations, this study investigated the activity of single and multiple B atom doped monolayer WS2 catalysts and observed superior efficiencies for nitrogen fixation and reduction. Computational results reveal that these novel catalysts have excellent thermodynamic stability, suitable adsorption of N2, superior catalytic activity and high selectivity for the nitrogen reduction reaction. Notably, this study clearly illustrates that the steric hindrance arising from the adjacent atoms of catalytic sites can be an effective route for manipulating the catalytic performance, offering new insights for the synthesis of high efficiency catalysts. In summary, this series of novel boron doped monolayer WS2 catalysts does not require precise control of the number of catalytic atoms on the substrate, making their preparation easier.

From Synthesis to Mechanisms: In-Depth Exploration of the Dual-Atom Catalytic Mechanisms Toward Oxygen Electrocatalysis

Dual-atom catalysts (DACs) hold a higher metal atom loading and provide greater flexibility in terms of the structural characteristics of their active sites in comparison to single-atom catalysts. Consequently, DACs hold great promise for achieving improved catalytic performance. This article aims to provide a focused overview of the latest advancements in DACs, covering their synthesis and mechanisms in reversible oxygen electrocatalysis, which plays a key role in sustainable energy conversion and storage technologies. The discussion starts by highlighting the structures of DACs and the differences in diatomic coordination induced by various substrates. Subsequently, the state-of-the-art fabrication strategies of DACs for oxygen electrocatalysis are discussed from several different perspectives. It particularly highlights the challenges of increasing the diatomic loading capacity. More importantly, the main focus of this overview is to investigate the correlation between the configuration and activity in DACs in order to gain a deeper understanding of their active roles in oxygen electrocatalysis. This will be achieved through density functional theory calculations and sophisticated in situ characterization technologies. The aim is to provide guidelines for optimizing and upgrading DACs in oxygen electrocatalysis. Additionally, the overview discusses the current challenges and future prospects in this rapidly evolving area of research.

Mo-X4 (X = O, NH and S)-mediated triphenylene-based two-dimensional carbon-rich conjugate frameworks for an efficient nitrogen reduction reaction

The electrocatalytic nitrogen reduction reaction (NRR) is a highly competitive approach for the ammonia synthesis to overcome the problems of high energy consumption and air pollution by the traditional Haber-Bosch process. However, the challenges of inert N2 molecule activation and the competitive hydrogen evolution reaction (HER) restrict the real utilization of the NRR. Herein, by means of density functional theory (DFT) calculations, we proposed three two-dimensional carbon-rich conjugate frameworks (2D-CCFs) with hexa-substituted triphenylene organic linkers with a metal atom Mo and functional groups X (X = O, NH, and S), namely Mo3(HOTP)2, Mo3(HITP)2 and Mo3(THT)2, to investigate their NRR performance. Our theoretical calculations reveal that Mo atoms in 2D-CCFs can efficiently capture and activate N2 molecules. Among the three structures, Mo3(HOTP)2 exhibited the most superior performance toward the NRR with a favorable limiting potential of -0.41 V and good selectivity for the HER. Furthermore, the catalytic efficiency of 2D-CCFs can be regulated by changing the atoms X in Mo-X4 motifs, providing a new scenario for the development of highly efficient NRR catalysts.

First-Principles Study of Bimetallic Pairs Embedded on Graphene Co-Doped with N and O for N2 Electroreduction

The electrocatalytic nitrogen reduction reaction (NRR) is considered a viable alternative to the Haber-Bosch process for ammonia synthesis, and the design of highly active and selective catalysts is crucial for the industrialization of the NRR. Dual-atom catalysts (DACs) with dual active sites offer flexible active sites and synergistic effects between atoms, providing more possibilities for the tuning of catalytic performance. In this study, we designed 48 graphene-based DACs with N4O2 coordination (MM'@N4O2-G) using density functional theory. Through a series of screening strategies, we explored the reaction mechanisms of the NRR for eight catalysts in depth and revealed the "acceptance-donation" mechanism between the active sites and the N2 molecules through electronic structure analysis. The study found that the limiting potential of the catalysts exhibited a volcano-shaped relationship with the d-band center of the active sites, indicating that the synergistic effect between the bimetallic components can regulate the d-band center position of the active metal M, thereby controlling the reaction activity. Furthermore, we investigated the selectivity of the eight DACs and identified five potential NRR catalysts. Among them, MoCo@N4O2-G showed the best NRR performance, with a limiting potential of -0.20 V. This study provides theoretical insights for the design and development of efficient NRR electrocatalysts.

Fe nanoparticles confined by multiple-heteroatom-doped carbon frameworks for aqueous Zn-air battery driving CO2 electrolysis

Metal-organic frameworks (MOF) derived carbon materials are considered to be excellent conductive mass transfer substrates, and the large specific surface area provides a favorable platform for loading metal nanoparticles. Tuning the coordination of metals through polyacid doping to change the MOF structure and specific surface area is an advanced strategy for designing catalysts. Modification of Fe-doped ZIF-8 pre-curing by pyrolysis of phosphomolybdic acid hydrate (PMo), Fe nanoparticles confined by Mo and N co-doped carbon frameworks (Fe-NP/MNCF) were fabricated, and the impact of PMo doping on the shape and functionality of the catalysts was investigated. The Zn-air battery (ZAB) driven CO2 electrolysis was realized by using Fe-NP/MNCF, which was used as bifunctional oxygen reduction reaction (ORR) and carbon dioxide reduction reaction (CO2RR) catalysts. The results show that the half-wave potential (E1/2) of Fe-NP/MNCF is 0.89 V, and the limiting diffused current density (jL) is 6.4 mA cm-2. The ZAB constructed by Fe-NP/MNCF shows a high specific capacity of 794.8 mAh gZn-1, a high open-circuit voltage (OCV) of 1.475 V, and a high power density of 111.6 mW cm-2. Fe-NP/MNCF exhibited efficient CO2RR performance with high CO Faraday efficiency (FECO) of 87.5 % and current density for the generation of carbon dioxide (jCO) of 10 mA cm-2 at -0.9 V vs RHE. ZAB-driven CO2RR had strong catalytic stability. These findings provide new methods and techniques for the preparation of advanced carbon-based catalysts from MOFs.

Coordination Engineering of Heteronuclear Fe-Mo Dual-Atom Catalyst for Promoted Electrocatalytic Nitrogen Fixation: A DFT Study

Developing efficient nanostructured electrocatalysts for N2 reduction to NH3 under mild conditions remains a major challenge. The Fe-Mo cofactor serves as the archetypal active site in nitrogenase. Inspired by nitrogenase, we designed a series of heteronuclear dual-atom catalysts (DACs) labeled as FeMoN6-a Xa (a=1, 2, 3; X=B, C, O, S) anchored on the pore of g-C3 N4 to probe the impact of coordination on FeMo-catalyzed nitrogen fixation. The stability, reaction paths, activity, and selectivity of 12 different FeMoN6-a Xa DACs have been systematically studied using density functional theory. Of these, four DACs (FeMoN5 B1 , FeMoN5 O1 , FeMoN4 O2 , and FeMoN3 C3 ) displayed promising nitrogen reduction reaction (NRR) performance. Notably, FeMoN5 O1 stands out with an ultralow limiting potential of -0.11 V and high selectivity. Analysis of the density of states and charge/spin changes shows FeMoN5 O1 's high activity arises from optimal N2 binding on Fe initially and synergy of the FeMo dimer enabling protonation in NRR. This work contributes to the advancement of rational design for efficient NRR catalysts by regulating atomic coordination environments.

Mechanistic study of Eu single atoms occupying four vacancy centers as potential electrocatalysts for the oxygen reduction reaction

The oxygen reduction reaction (ORR) on the oxygen electrode plays a critical role in rechargeable metal-air batteries, and the development of electrochemical energy storage and conversion technologies for the ORR is of great significance. In this study, the catalytic performance of rare earth-doped graphene (EuNxC6-x-Gra) as an electrocatalyst for the ORR was investigated. The results showed that a majority of the catalysts exhibited good ORR catalytic activity under acidic conditions, with some approaching or even surpassing commercial Pt-based catalysts (ηORR = 0.45 V). Particularly, EuN2C4-2-Gra demonstrated an ηORR of 0.38 V. It has been observed that the f-band center of Eu atoms increases with an increasing number of N atoms, and the charge distribution exhibits a "U" shape. There is a decreasing trend from N0 to N3 and an increasing trend from N4 to N6. By incorporating the proportional relationship of the adsorption free energies of reaction intermediates (ΔG*ads), a volcano diagram was constructed to rapidly assess catalytic activity. Finally, an intrinsic characteristic descriptor φ was formulated to quantitatively describe the relationship between φ and ηORR, providing a new tool for predicting and designing catalysts. This will provide guidance for the development and design of high-performance rare earth single atom catalysts.

Carbon doped hexagonal boron nitride as an efficient metal-free catalyst for NO capture and reduction

The electrochemical NO reduction reaction (NORR) towards NH3 is considered a promising strategy to cope with both NO removal and NH3 production. Currently, the research on NORR electrocatalysts mainly focuses on metal-based catalysts, while metal-free catalysts are quite scarce. In this work, we have systematically investigated the properties of pristine and C/O doped h-BN for efficient NO capture and reduction. Our results reveal that the basal plane of pristine h-BN is inert to the adsorption of NO, while doping C or O can significantly enhance the NO capture abilities of h-BN. Then, we highlight that C-doped h-BN exhibits excellent NORR catalytic performance with a relatively low limiting potential of -0.28 V. Further analysis shows that the suitable adsorption strength of NO on the C-doped h-BN surface is the prime reason for its excellent NO reduction activity, which is shown to be due to appropriate electronic interactions between the active site and NO. Last but not least, the catalytic selectivity of h-BN towards the NORR is confirmed by inhibiting the competing hydrogen evolution reaction. Our findings not only provide deeper insight into the essential effect of element doping on the catalytic activities of h-BN, but also propose general design principles for high-performance metal-free NORR electrocatalysts.

Electronic Perturbation of Isolated Fe Coordination Structure for Enhanced Nitrogen Fixation

Modulation of the local electronic structure of isolated coordination structures plays a critical role in electrocatalysis yet remains a grand challenge. Herein, we have achieved electron perturbation for the isolated iron coordination structure via tuning the iron spin state from a high spin state (FeN4) to a medium state (FeN2B2). The transition of spin polarization facilitates electron penetration into the antibonding π orbitals of nitrogen and effectively activates nitrogen molecules, thereby achieving an ammonia yield of 115 μg h-1 mg-1cat. and a Faradaic efficiency of 24.8%. In situ spectroscopic studies and theoretical calculations indicate that boron coordinate sites, as electron acceptors, can regulate the adsorption energy of NxHy intermediates on the Fe center. FeN2B2 sites favor the NNH* intermediate formation and reduce the energy barrier of rate-determining steps, thus accounting for excellent nitrogen fixation performance. Our strategy provides an effective approach for designing efficient electrocatalysts via precise electronic perturbation.

Single-atom catalysts supported on a hybrid structure of boron nitride/graphene for efficient nitrogen fixation via synergistic interfacial interactions

Hexagonal boron nitride (BN) shows significant chemical stability and promising thermal nitrogen reduction reaction (NRR) activity but suffers from low conductivity in electrolysis with a wide band gap. To overcome this problem, two-dimensional (2D) BN and graphene (G) are designed as a heterostructure, namely BN/G. According to density functional theory (DFT), the higher conductivity of G narrows the band gap of BN by inducing some electronic states near the Fermi energy level (Ef). Once transition metals (TMs) are anchored in the BN/G structure as single atom catalysts (SACs), the NRR activity improves as the inert BN basal layer activates with moderate *NH2 binding energy and further the band gap is reduced to zero. V (vanadium) and W (tungsten) SACs exhibit the best performance with limiting potentials of -0.22 and -0.41 V, respectively. This study helps in understanding the improvement of the NRR activity of BN, providing physical insights into the adsorbate-TM interaction.

Well-defined N3 C1 -anchored Single-Metal-Sites for Oxygen Reduction Reaction

N-, C-, O-, S-coordinated single-metal-sites (SMSs) have garnered significant attention due to the potential for significantly enhanced catalytic capabilities resulting from charge redistribution. However, significant challenges persist in the precise design of well-defined such SMSs, and the fundamental comprehension has long been impeded in case-by-case reports using carbon materials as investigation targets. In this work, the well-defined molecular catalysts with N3 C1 -anchored SMSs, i.e., N-confused metalloporphyrins (NCPor-Ms), are calculated for their catalytic oxygen reduction activity. Then, NCPor-Ms with corresponding N4 -anchored SMSs (metalloporphyrins, Por-Ms), are synthesized for catalytic activity evaluation. Among all, NCPor-Co reaches the top in established volcano plots. NCPor-Co also shows the highest half-wave potential of 0.83 V vs. RHE, which is much better than that of Por-Co (0.77 V vs. RHE). Electron-rich, low band gap and regulated d-band center contribute to the high activity of NCPor-Co. This study delves into the examination of well-defined asymmetric SMS molecular catalysts, encompassing both theoretical and experimental facets. It serves as a pioneering step towards enhancing the fundamental comprehension and facilitating the development of high-performance asymmetric SMS catalysts.

Functionalization strategies of metal-organic frameworks for biomedical applications and treatment of emerging pollutants: A review

One of the representative coordination polymers, metal-organic frameworks (MOFs) material, is of hotspot interest in the multi field thanks to their unique structural characteristics and properties. As a novel hierarchical structural class, MOFs show diverse topologies, intrinsic behaviors, flexibility, etc. However, bare MOFs have less desirable biofunction, high humid sensitivity and instability in water, restraining their efficiencies in biomedical and environmental applications. Thus, a structural modification is required to address such drawbacks. Herein, we pinpoint new strategies in the synthesis and functionalization of MOFs to meet demanding requirements in in vitro tests, i.e., antibacterial face masks against corona virus infection and in wound healing and nanocarriers for drug delivery in anticancer. Regarding the treatment of wastewater containing emerging pollutants such as POPs, PFAS, and PPCPs, functionalized MOFs showed excellent performance with high efficiency and selectivity. Challenges in toxicity, vast database of clinical trials for biomedical tests and production cost can be still presented. MOFs-based composites can be, however, a bright candidate for reasonable replacement of traditional nanomaterials in biomedical and wastewater treatment applications.

Electrocatalytic Urea Synthesis via N2 Dimerization and Universal Descriptor

Electrocatalytic urea synthesis through N2 + CO2 coreduction and C-N coupling is a promising and sustainable alternative to harsh industrial processes. Despite considerable efforts, limited progress has been made due to the challenges of breaking inert N≡N bonds for C-N coupling, competing side reactions, and the absence of theoretical principles guiding catalyst design. In this study, we propose a mechanism for highly electrocatalytic urea synthesis using two adsorbed N2 molecules and CO as nitrogen and carbon sources, respectively. This mechanism circumvents the challenging step of N≡N bond breaking and selective CO2 to CO reduction, as the free CO molecule inserts into dimerized *N2 and binds concurrently with two N atoms, forming a specific urea precursor *NNCONN* with both thermodynamic and kinetic feasibility. Through the proposed mechanism, Ti2@C4N3 and V2@C4N3 are identified as highly active catalysts for electrocatalytic urea formation, exhibiting low onset potentials of -0.741 and -0.738 V, respectively. Importantly, taking transition metal atoms anchored on porous graphite-like carbonitride (TM2@C4N3) as prototypes, we introduce a simple descriptor, namely, effective d electron number (Φ), to quantitatively describe the structure-activity relationships for urea formation. This descriptor incorporates inherent atomic properties of the catalyst, such as the number of d electrons, the electronegativity of the metal atoms, and the generalized electronegativity of the substrate atoms, making it potentially applicable to other urea catalysts. Our work advances the comprehension of mechanisms and provides a universal guiding principle for catalyst design in urea electrochemical synthesis.

The regulatory function of the d-orbital structure in TM@g-t-C4N3 for bifunctional catalysis of the oxygen evolution/reduction reaction

Highly efficient catalysts for the oxygen evolution/reduction reaction (OER/ORR) have attracted great attention in research for energy devices with high conversion efficiency. Herein, systematic first-principles investigations are performed to explore the catalytic performance of graphitic C4N3 loaded with single transition metal atoms (TM@g-t-C4N3) for the OER/ORR. The results show that Fe, Co, Ni and Rh@g-t-C4N3 exhibit fascinating bifunctional catalytic activities for both the OER and ORR. Moreover, it is observed that better activities are easily achieved when the valence d orbitals of doped TM atoms are nearly fully occupied. Further analysis reveals the volcano relationship between the OER/ORR performance and the adsorption Gibbs free energy. The adsorption free energy of intermediates in the OER/ORR process is also found to highly correlate with the electronic structures of TM@g-t-C4N3, which are mainly characterized by two quantities, one is the descriptor φ related to the electronegativity and the number of valence electrons in d orbitals, and the other is the projected d band center. The results indicate that it is possible to predict the catalytic performance of TM@g-t-C4N3 by a detailed examination of the electronic properties of the doped TM atoms to some extent. This research not only provides several highly active g-t-C4N3-based single-atom catalysts (SACs) for the OER/ORR, but also reveals some potential regularities of SAC systems.

Theoretical Insight into the Special Synergy of Bimetallic Site in Co/MoC Catalyst to Promote N2 -to-NH3 Conversion

The catalytic mechanisms of nitrogen reduction reaction (NRR) on the pristine and Co/α-MoC(001) surfaces were explored by density functional theory calculations. The results show that the preferred pathway is that a direct N≡N cleavage occurs first, followed by continuous hydrogenations. The production of second NH3 molecule is identified as the rate-limiting step on both systems with kinetic barriers of 1.5 and 2.0 eV, respectively, indicating that N2 -to-NH3 transformation on bimetallic surface is more likely to occur. The two components of the bimetallic center play different roles during NRR process, in which Co atom does not directly participate in the binding of intermediates, but primarily serves as a reservoir of H atoms. This special synergy makes Co/α-MoC(001) have superior activity for ammonia synthesis. The introduction of Co not only facilitates N2 dissociation, but also accelerates the migration of H atom due to the antibonding characteristic of Co-H bond. This study offers a facile strategy for the rational design and development of efficient catalysts for ammonia synthesis and other reactions involving the hydrogenation processes.

Controllable Electrocatalytic to Photocatalytic Conversion in Ferroelectric Heterostructures

Photocatalytic and electrocatalytic reactions to produce value-added chemicals offer promising solutions for addressing the energy crisis and environmental pollution. Photocatalysis is driven by light excitation and charge separation and relies on semiconducting catalysts, while electrocatalysis is driven by external electric current and is mostly based on metallic catalysts with high electrical conductivity. Due to the distinct reaction mechanism, the conversion between the two catalytic types has remained largely unexplored. Herein, by means of density functional theory (DFT) simulations, we demonstrated that the ferroelectric heterostructures Mo-BN@In2Se3 and WSe2@In2Se3 can exhibit semiconducting or metallic features depending on the polarization direction as a result of the built-in field and electron transfer. Using the nitrogen reduction reaction (NRR) and hydrogen evolution reaction (HER) as examples, the metallic heterostructures act as excellent electrocatalysts for these reactions, while the semiconducting heterostructures serve as the corresponding photocatalysts with improved optical absorption, enhanced charge separation, and low Gibbs free energy change. The findings not only bridge physical phenomena of the electronic phase transition with chemical reactions but also offer a new and feasible approach to significantly improve the catalytic efficiency.

Vacancy-Mediated Control of Local Electronic Structure for High-Efficiency Electrocatalytic Conversion of N2 to NH3

Ambient electrocatalytic nitrogen (N2 ) reduction has gained significant recognition as a potential substitute for producing ammonia (NH3 ). However, N2 adsorption and *NN protonation for N2 activation reaction with the competing hydrogen evolution reaction remain a daunting challenge. Herein, a defect-rich TiO2 nanosheet electrocatalyst with PdCu alloy nanoparticles (PdCu/TiO2-x ) is designed to elucidate the reactivity and selectivity trends of N2 cleavage path for N2 -to-NH3 catalytic conversion. The introduction of oxygen vacancy (OV) not only acts as active sites but also effectively promotes the electron transfer from Pd-Cu sites to high-concentration Ti3+ sites, and thus lends to the N2 activation via electron donation of PdCu. OVs-mediated control effectively lowers the reaction barrier of *N2 H and *H adsorption and facilitates the first hydrogenation process of N2 activation. Consequently, PdCu/TiO2-x catalyst attains a high rate of NH3 evolution, reaching 5.0 mmol gcat. -1  h-1 . This work paves a pathway of defect-engineering metal-supported electrocatalysts for high-efficient ammonia electrosynthesis.

Direct Electrochemical Synthesis of Acetamide from CO2 and N2 on a Single-Atom Alloy Catalyst

The electrochemical conversion of carbon dioxide into value-added compounds not only paves the way toward a sustainable society but also unlocks the potential for electrocatalytic synthesis of amides through the introduction of N atoms. However, it also poses one of the greatest challenges in catalysis: achieving simultaneous completion of C-C coupling and C-N coupling. Here, we have meticulously investigated the catalytic prowess of Cu-based single-atom alloys in facilitating the electrochemical synthesis of acetamide from CO2 and N2. Through a comprehensive screening process encompassing catalyst stability, adsorption capability, and selectivity against the HER, W/Cu(111) SAA has emerged as an auspicious contender. The reaction entails CO2 reduction to CO, C-C coupling leading to the formation of a ketene intermediate *CCO, N2 reduction, and C-N coupling between NH3 and *CCO culminating in the production of acetamide. The W/Cu(111) surface not only exhibits exceptional activity in the formation of acetamide, with a barrier energy of 0.85 eV for the rate-determining CO hydrogenation step, but also effectively suppresses undesired side reactions leading to various C1 and C2 byproducts during CO2 reduction. This work presents a highly effective approach for forming C-C and C-N bonds via coelectroreduction of CO2 and N2, illuminating the reaction mechanism underlying acetamide synthesis from these two gases on single-atom alloy catalysts. The catalyst design strategy employed in this study has the potential to be extended to a range of amide chemicals, thereby broadening the scope of products that can be obtained through CO2/N2 reduction.

A simple hydrothermal synthesis of an oxygen vacancy-rich MnMoO4 rod-like material and its highly efficient electrocatalytic nitrogen reduction

Electrocatalytic nitrogen reduction (NRR) for artificial ammonia synthesis under ambient conditions is considered a promising alternative to the traditional Haber-Bosch process. However, it still faces multiple challenges such as the difficulty of N2 adsorption and activation and limited Faraday efficiency. In this work, a bimetallic oxide MnMoO4 was prepared by a hydrothermal method and low temperature calcination. The influence of the sintering temperature on the microstructure (crystallinity and oxygen vacancies) of the oxide and its NRR properties were systematically explored. The results showed that MnMoO4 sintered at 500 °C had the highest concentration of OVs and showed excellent NRR performance, with the highest NH3 yield (up to 12.28 μg h-1 mgcat-1), high Faraday efficiency (23.04% at -0.30 V vs. RHE), and good stability at -0.40 V vs. RHE, and the catalytic performance was about two times higher than that of Mn2O3 and MoO3. It is also superior to other bimetallic oxide NRR electrocatalysts reported in some cases. In addition, we also explored the ratio between Mn and Mo metals, and the catalytic effect was the best when Mn : Mo = 1 : 1. Due to the synergistic effect between Mn and Mo metals and the large number of OVs present internally, the catalytic activity for the NRR was largely improved. This study suggests that the bimetallic oxide MnMoO4 may be a promising NRR electrocatalyst.

Emerging Liquid Metal Catalysts

Catalysts serve pivotal roles in facilitating the development of sustainable energy systems on a global scale. Liquid metal usually refers to metal that is liquid below 330 °C, also known as low melting point metal. Liquid metal has emerged as an intriguing catalyst due to its commendable electrical conductivity, favorable fluidity, solubility in metals, phase transition capabilities, and modifiable oxide surface, thereby presenting a plethora of prospects for diverse catalytic reactions. In this Perspective, we elucidate the four primary merits of liquid metal catalysts: resistance to coking, the ability to tune elemental composition, the potential for structural transformation, and the capacity to inhibit coalescence. In light of this, a comprehensive summary is presented on the research advancements pertaining to liquid metal in methane pyrolysis, alkane dehydrogenation, carbon dioxide reduction, alcohol oxidation, and various other catalytic reactions. Finally, the challenges and prospects of liquid metal catalysts are elucidated.