Two-Dimensional Single-Atom Catalyst TM3(HAB)2 Monolayers for Electrocatalytic Dinitrogen Reduction Using Hierarchical High-Throughput Screening

Spin: an essential factor in advancing the oxygen evolution reaction on 2D Fe-MOF

The oxygen evolution reaction (OER) is a crucial component in oxygen-involving reactions and plays a vital role in developing sustainable energy conversion technologies. However, it still requires developing efficient catalysts that can overcome the sluggish reaction kinetics. Recent studies on oxygen electrocatalysis predominantly focussed on the thermodynamic viewpoint of oxygen adsorption, while the catalytic role of spin remains greatly elusive. In this work, we investigated the impact of spin on the OER performance of a two-dimensional iron-based metal-organic framework (2D Fe-MOF) using spin-polarized first-principles calculations. Our results reveal that the pristine Fe-MOF in the high spin state exhibits electronic properties suitable for an OER electrocatalyst. Even after adsorption, the Fe-MOF preserves its high spin state; such magnetic stability ensures the consistent application of the OER. Moreover, adsorption on a 2D Fe-MOF is spin-dependent. It validates that the spin states can regulate the adsorption strength for the OER. Remarkably, the spin-sensitive 2D Fe-MOF yields a significantly low overpotential of 0.49 V, comparable to precious catalysts. Furthermore, the spin-related charge transfer and orbital interaction originate from the overlapping between the O pz of the oxygen intermediates and the Fe dz2 of the Fe active site. This reveals that the OER on the Fe-MOF is dependent on the selective spin-orbital. Overall, the spin is inevitable in enhancing the OER process, making our work valuable in the development of MOF catalysts. Our finding enriches the atomistic understanding of the OER in the development of noble-metal-free MOF catalysts.

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.

Modulation of d-Orbital Interactions in Dual-Atom Catalysts for Enhanced Polysulfide Anchoring and Kinetics in Lithium-Sulfur Batteries

Modulating the electronic structure is essential for improving the anchoring and catalytic capabilities of catalysts in lithium-sulfur batteries (LSBs). This study delves into the modulation of d-orbitals in transition metal dual-atom catalysts (DACs) supported by boron nitride and graphene (BNC) hybrid sheets for LSBs. This study reveals that the d-band center of the DACs, a key determinant of material chemical properties, is primarily determined by the electronic configuration of the dyz and dx2-y2 orbitals. Furthermore, the interaction between dz2 of transition metals and S_3 p orbitals is critical for the binding strength of LiPSs. By understanding these interactions, the functionality of DACs can be customized for optimal performance in LSBs. For example, the MnCrBNC catalyst with 10 d-electrons exhibits the optimal d-band center and demonstrates exceptional LiPSs binding capability, the lowest Li2S decomposition energy barrier, and the lowest Gibbs free energy of reaction for the rate-determining step of sulfur reduction. This study elucidates the fundamental mechanisms for designing high-performance LSB catalysts through electronic structure modulation.

Diatomic Active Sites Embedded Graphyne as Electrocatalysts for Ammonia Synthesis

Ammonia (NH3) is a vital chemical compound in industry and agriculture, and the electrochemical nitrogen reduction reaction (eNRR) is considered a promising approach for NH3 synthesis. However, the development of eNRR faces the challenge of high overpotential and low Faradaic efficiency. In this work, graphyne (GY) is anchored by 3d, 4d, and 5d dual transition metal atoms to form diatomic catalysts (DACs) and is roundly investigated as an electrocatalyst for eNRR via density functional theory calculations. Due to the protrusion of anchored metal atoms, the active sites of GY are better exposed compared to other substrates, exhibiting higher activity. Through four-step hierarchical high-throughput screening (ΔG*N2 < 0 eV, ΔG*N2 → *N2H < 0.4 eV, ΔG*NH2 → *NH3 < 0.4 eV, and ΔG*N2 < ΔG*H), the number of selected catalysts in each step is 325, 240, 145, and 20, respectively. Considering a series of factors, including stability, initial potential, and selectivity, 13 kinds of eligible catalysts are identified. Optimal eNRR paths studies show that the best catalyst Mn2@GY features no onset potential. For the three catalysts (Mn2@GY, Ir2@GY, and RhOs@GY), the onset potentials of the most favorable eNRR pathways are -0.07, -0.12, and -0.17 V, respectively. The excellent catalytic activity can be credited to the effective charge transfer and orbital interaction between the active site and adsorbed N2. Our work demonstrates the significance of DACs for ammonia synthesis and provides a paradigm for the study of DACs even for other important reactions.

Density Functional Theory Investigation on the Nitrogen Reduction Mechanism in Two-Dimensional Transition-Metal Boride with Ordered Metal Vacancies

The creation of ordered collective vacancies in experiment proves challenging within a two-dimensional lattice, resulting in a limited understanding of their impact on catalyst performance. Motivated by the successful experimental synthesis of monolayer molybdenum borides with precisely ordered metal vacancies [Zhou et al. Science 2021, 373, 801-805] through dealloying, the nitrogen reduction reaction (NRR) in monolayer borides was systematically investigated to elucidate the influence of such ordered metal vacancies on catalytic reactions and the underlying mechanisms. The results reveal that the N-containing intermediates tend to dissociate, facilitating the NRR process with reduced UL. The emergence of ordered metal vacancies modulates the electronic properties of the catalyst and partially facilitates the decomposition of N-containing intermediates. However, the UL for NRR in Mo4/3B2 and W4/3B2 exhibits a significant increase. The compromised electrochemical performance is explained through the development of a simple electronic descriptor of the d-p band center (ΔdM-pB). Among these materials, Mo4/3Sc2/3B2 exhibits the most superior catalytic activity with a UL of -0.5 V and favorable NRR selectivity over the HER. Our results provide mechanistic insights into the role of ordered metal vacancies in transition-metal boride for the NRR and highlight a novel avenue toward the rational design of superior NRR catalysts.

Electrochemical CO2 Reduction on Cu-Based Monatomic Alloys: A DFT Study

In recent years, single-atom alloy catalysts (SAAs) have received much attention due to the combination of structural features of both single-atom and alloy catalysts, as well as their efficient catalytic activity, high selectivity, and high stability in various chemical reactions. In this work, we designed a series of Cu-based SAAs by doping isolated 3d transition metal (TM1) atoms on the surface of Cu(111) (TM1 = Fe, Co, Ru, Rh, Os and Ir), in which Ir1/Cu(111) SAAs are considered to be the most stable among 3d-series SAAs due to their optimal binding energy (Eb). The density of states of SAAs have been systematically investigated to further discuss structural properties. Based on density functional theory calculations, the activity and selectivity of Ir1/Cu(111) SAAs are investigated for electrocatalytic CO2 reduction reaction (CO2RR). The initial hydrogenation of CO2 on Ir1/Cu(111) SAAs can form *CO intermediates, which will be further to CH4 production by the pathway of *CO → *CHO → *CHOH → *CH2OH → *CH2 → *CH3 → CH4. This study provides theoretical insights for the rational design of selective Cu-based monatomic alloy catalysts.

A feasible strategy for designing cytochrome P450-mimic sandwich-like single-atom nanozymes toward electrochemical CO2 conversion

Carbon dioxide electroreduction (CO2ER) presents a promising strategy for environmentally friendly CO2 utilization due to its low energy consumption. Single-atom nanozymes (SANs), amalgamating the benefits of single-atom catalysts and nanozymes, have become a hot topic in catalysis. Inspired by the intricate structure of cytochrome P450, we designed 81 sandwich-like SANs using Group-VIII transition metals (TMN4-S-TM'N4) and evaluated their performance in CO2ER using density functional theory (DFT). Our investigation revealed that most SANs display superior catalytic activity and improved specific product selectivity in comparison to the Cu (211) surface. Notably, IrN4-S-TMN4 (TM = Co, Rh, Pd) exhibited selective CO2 reduction to CO with remarkable limiting potentials (UL) of -0.11, -0.07, and -0.09 V, respectively, demonstrating potential as artificial CO dehydrogenases. Furthermore, RuN4-S-RuN4 exhibited formate dehydrogenase-like activity, resulting in selective production of HCOOH at a UL of -0.10 V. Machine learning analysis elucidated that the exceptional activity and selectivity of these SANs stemmed from precise modulation of electron density on sulfur atoms, achieved by varying transition metals in the subsurface. Our research not only identifies exceptional SANs for CO2ER but also provides insights into innovative methods for regulating non-bonding interactions and achieving sustainable CO2 conversion.

Structural Design of π-d Conjugated TMx B3 N3 S6 (x=2, 3) Monolayer Toward Electrocatalytic Ammonia Synthesis

Single-atom catalysts (SACs) have attracted wide attention to be acted as potential electrocatalysts for nitrogen reduction reaction (NRR). However, the coordination environment of the single transition metal (TM) atoms is essential to the catalytic activity for NRR. Herein, we proposed four types of 3-, 4-coordinated and π-d conjugated TMx B3 N3 S6 (x=2, 3, TM=Ti, V, Cr, Mn, Fe, Zr, Nb, Mo, Tc, Ru, Hf, Ta, W, Re and Os) monolayers for SACs. Based on density functional theory (DFT) calculations, I-TM2 B3 N3 S6 and III-TM3 B3 N3 S6 are the reasonable 3-coordinated and 4-coordinated structures screening by structure stable optimizations, respectively. Next, the structural configurations, electronic properties and catalytic performances of 30 kinds of the 3-coordinated I-TM2 B3 N3 S6 and 4-coordinated III-TM3 B3 N3 S6 monolayers with different single transition metal atoms were systematically investigated. The results reveal that B3 N3 S6 ligand is an ideal support for TM atoms due to existence of strong TM-S bonds. The 3-coordinated I-V2 B3 N3 S6 is the best SAC with the low limiting potential (UL ) of -0.01 V, excellent stability (Ef =-0.32 eV, Udiss =0.02 V) and remarkable selectivity characteristics. This work not only provides novel π-d conjugated SACs, but also gives theoretical insights into their catalytic activities and offers reference for experimental synthesis.

High-Throughput Computational Design of 2D Ternary Chalcogenides for Sustainable Energy

Two-dimensional materials are considered to be promising for next-generation electronic and energy devices. However, the limited availability of 2D materials hinders their applications. Herein, we employed high-throughput computation to discover new 2D materials by cleaving the bulk and to investigate their electronic, thermoelectric, and optoelectronic properties. Using our database containing 810 structures of chalcogenides ABX3 (A or B = Al, Ga, In, Si, Ge, Sn, P, As, Sb, and Bi; X = S, Se, and Te), we identified 204 new 2D compounds promising for experimental preparation according to the exfoliation energy. Notably, 96 of them are more easily exfoliated than graphene, 52 compounds show higher Seebeck coefficients than Bi2Te3 at 300 K, and 20 compounds have power factors beyond 2 × 10-3 Wm-1 K-2 at 900 K. Also, 6 new compounds exhibit high theoretical photovoltaic efficiency exceeding 30%. Our findings expand the 2D materials family and provide new 2D compounds for sustainable thermoelectric and optoelectronic energy applications.

Electrochemical ammonia synthesis under ambient conditions using TM-embedded porphine-fused sheets as single-atom catalysts

In this research, we systematically investigated the reaction mechanism and electrocatalytic properties of transition metal anchored two-dimensional (2D) porphine-fused sheets (TM-Por) as novel single-atom catalysts (SACs) for the electrochemical nitrogen reduction reaction (eNRR) under ambient conditions. Using high-throughput screening and first-principles calculations based on the density functional theory (DFT) method, three eNRR catalyst candidates, i.e. Mo-Por, Tc-Por, and Nb-Por, were screened out, with the eNRR onset potentials on them being -0.36, -0.53, and -0.74 V, respectively. Furthermore, these catalyst candidates all have good stability and selectivity. Analyzing the band structures found that these catalyst candidates all are metallic, which is needed for good electrocatalysts. Ab initio molecular dynamics (AIMD) simulations show that these catalyst candidates have good stability at 500 K. It is hoped that our work will open up new possibilities for the experimental synthesis of electrochemical ammonia catalysts.

Role of Peripheral Coordination Boron in Electrocatalytic Nitrogen Reduction over N-Doped Graphene-Supported Single-Atom Catalysts

In this work, we investigate the effect of peripheral B doping on the electrocatalytic nitrogen reduction reaction (NRR) performance of N-doped graphene-supported single-metal atoms using density functional theory (DFT) calculations. Our results showed that the peripheral coordination of B atoms could improve the stability of the single-atom catalysts (SACs) and weaken the binding of nitrogen to the central atom. Interestingly, it was found that there was a linear correlation between the change in the magnetic moment (μ) of single-metal atoms and the change in the limiting potential (U_L) of the optimum NRR pathway before and after B doping. It was also found that the introduction of the B atom suppressed the hydrogen evolution reaction, thereby enhancing the NRR selectivity of the SACs. This work provides useful insights into the design of efficient SACs for electrocatalytic NRR.

Magnetic Moment Is an Effective Descriptor for Electrocatalytic Nitrogen Reduction Reaction on Two-Dimensional Organometallic Nanosheets

Electrocatalytic reduction of nitrogen to ammonia (eNRR) under ambient condition is a potential sustainable and promising alternative to the traditional Haber-Bosch process. However, this electrochemical transformation is limited by the high overpotential, poor selectivity, low efficiency, and low yield. Herein, a new class of two-dimensional (2D) organometallic nanosheets c-TM-TCNE (c = cross motif, TM = 3d/4d/5d transition metals, TCNE = tetracyanoethylene) were comprehensively investigated as potential electrocatalysts for eNRR through high-throughput screening combined with spin-polarized density functional theory computations. After a multistep screening and follow-up systematic evaluation, c-Mo-TCNE and c-Nb-TCNE were selected as eligible catalysts, and c-Mo-TCNE showed the lowest limiting potential of -0.35 V via a distal pathway, displaying high catalytic performance. In addition, the desorption of NH₃ from the surface of c-Mo-TCNE catalyst is also easy, with the free energy being 0.34 eV. Furthermore, the stability, metallicity, and eNRR selectivity are preeminent, making c-Mo-TCNE a promising catalyst. Unexpectedly, the magnetic moment of the transition metal shows a strong correlation with the catalytic activity (limiting potential), i.e., the larger the magnetic moment of the transition metal, the smaller the limiting potential of the electrocatalyst. The Mo atom has the largest magnetic moment and the c-Mo-TCNE catalyst features the smallest magnitude of limiting potential. Thus, the magnetic moment can be used as an effective descriptor for eNRR on c-TM-TCNE catalysts. The present study opens a way toward the rational design of highly efficient electrocatalysts for eNRR with novel two-dimensional functional materials. This work will promote further experimental efforts in this field.

Computational screening of effective g-C3N4 based single atom electrocatalysts for the selective conversion of CO2

Two-dimensional (2D) material-based single-atom catalysts (SACs) have demonstrated their potential in electrochemical reduction reactions but exploring suitable 2D material-based SACs for the CO₂ reduction reaction (CO₂RR) by experiments is still a formidable task. In this study, theoretical screening of transition metal (TM)-doped graphitic carbon nitride (g-C₃N₄) materials as catalysts for the CO₂RR was systematically performed based on density functional theory (DFT) calculations. An indicator for the selective formation of one carbon (C1) products was developed to screen catalysts that are active and selective in the CO₂RR. The results indicated that Ti- and Ag-g-C₃N₄ demonstrate excellent catalytic activity and selectivity for the formation of CO and HCOOH, with limiting potentials of -0.330 and -0.096 V, respectively, while Cr-g-C₃N₄ exhibits the highest catalytic activity for yielding CH₃OH and CH₄ (-0.355 and -0.420 V, respectively), but none of the screened catalysts have been identified as ideal candidates for the selective production of CH₃OH and CH₄. Furthermore, Bader charge analysis suggested that excessive electron transfer from TM leads to stronger adsorption of intermediates and high limiting potentials, which subsequently result in lower catalytic activity. This work provides theoretical insights into the effective screening of active and selective 2D material-based SACs which has the potential to significantly reduce the time and resources required for the discovery of novel electrocatalysts for the controlled formation of various products.

Breaking the Volcano-Shaped Relationship for Highly Efficient Electrocatalytic Nitrogen Reduction: A Computational Guideline

The volcano-shaped relationship is very common in electrocatalytic nitrogen reduction reaction (e-NRR) and is usually caused by the competition between the first and last hydrogenation steps. How to break such a relationship to further improve the catalytic performance remains a great challenge. Herein, using first-principles calculations, we investigate a range of transition-metal (TM)-doped Cu-based single-atom alloys (TM₁-Cu(111)) as catalysts for e-NRR. When the adsorption of N₂ on the catalysts is strong enough, the inert N₂ molecules can be effectively activated for the first hydrogenation step. Meanwhile, the last hydrogenation step is not affected by the scaling relationship and remains easy on all of the catalysts due to the unstable top-site adsorption of NH₂, resulting in the break of the volcano-shaped relationship in e-NRR. Thus, only the first hydrogenation step is identified as the potential determining step. Four TM₁-Cu(111) catalysts (TM = Re, W, Tc, and Mo) are selected as promising catalysts with limiting potential ranging from -0.38 to -0.56 V, showing outstanding e-NRR activity. Besides, the four catalysts also inhibit the competing hydrogen evolution reaction and long-term stability. Our work provides a guideline for breaking the volcano-shaped relationship in e-NRR and significant in the rational design of highly efficient electrocatalysts.

Regulating the spin state of single-atom doped covalent triazine frameworks for efficient nitrogen fixation

Covalent triazine frameworks (CTFs), served as a versatile platform, can form expedient metal-N single-atom coordination sites as promising catalytic centers. To seek out excellent candidate catalysts of M/CTFs (M = Transition metal) for nitrogen reduction reaction (NRR), a "five-step" strategy involving spin states has been established for hierarchical high-throughput screening and reveals strong coordination ability of the CTFs, outstanding conductivity of the M/CTFs, effective adsorption and activation of N₂* attributed to the electron transfer and orbital hybridization between the M/CTFs and N₂*. Among the potential candidates, the Cr/CTF is screened out to be an excellent one for nitrogen fixation, which can not only inhibit hydrogen evolution reaction (HER) greatly but also has good thermodynamic stability (E_b =  -4.40 eV), narrow band gap (E_g = 0.03 eV), moderate adsorption energy (E_a =  -0.84 eV), large activation energy (ΔG_N2* = -0.71 eV) and a theoretical Faradaic efficiency of 100%. The spin state has been confirmed to be an important descriptor of catalytic activity and the two-state reactivity (TSR) is validated to exist in the NRR. Reaction mechanism with different spin states of Cr/CTF has been demonstrated to give a great impact on the nitrogen fixation, providing solid theoretical support for the design of more efficient NRR catalysts.

Computational Insight into Metallated Graphynes as Single Atom Electrocatalysts for Nitrogen Fixation

The electrochemical nitrogen reduction reaction (NRR) is expected to achieve sustainable ammonia synthesis via direct nitrogen fixation; however, the high-quality catalysts that play a crucial role in the NRR are still lacking. The emerging transition metal-1,3,5-triethynylbenzene (TM-TEB) frameworks offer attractive possibilities in the electrochemical catalysis due to the featured atomic and electronic structures. This work presents a comprehensive first-principles study of the TM-TEB systems for TMs from the first three d-block series and systematically explores their potential applications as NRR electrocatalysts. By designing a hierarchical screening strategy, the TM-TEB systems are evaluated based on the NRR catalytic activity as well as the competition from the hydrogen evolution reaction. In addition, in order to have a deeper understanding of the catalytic activities of the TM-TEB systems, diverse possible NRR paths on the TM-TEB surfaces are completely analyzed as well. Our analysis reveals that the TM-TEB systems with TM = V, Mo, Tc, W, and Os are electrocatalysts with a high NRR catalytic activity, while among them, only Mo- and V-TEB show promising NRR selectively. This work demonstrates the great potential of the TM-TEB systems as electrocatalysts in the NRR process, which improves the understanding of the TM-TEB systems and can motivate further exploration of their application in catalysis.

Simultaneously Enhancing Catalytic Performance and Increasing Density of Bifunctional CuN3 Active Sites in Dopant-Free 2D C3N3Cu for Oxygen Reduction/Evolution Reactions

Atomically dispersed M-N-C has been considered an effective catalyst for various electrochemical reactions such as oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), which faces the challenge of increasing metal load while simultaneously maintaining catalytic performance. Herein, we put forward a strategy for boosting catalytic performances of a single Cu atom coordinated with three N atoms (CuN₃) for both ORR and OER by increasing the density of connected CuN₃ moieties. Our calculations first show that a single CuN₃ moiety exhibiting no catalytic performance for ORR and OER can be activated by increasing the density of metal centers, which weakens the binding affinity to *OH due to the lowered d-band center of the metal atoms. These findings stimulate the further theoretical design of a two-dimensional compound of C₃N₃Cu with a high concentration of homogeneously distributed CuN₃ moieties serving as bifunctional active sites, which demonstrates efficient catalytic performance for both ORR and OER as reflected by the overpotentials of 0.71 and 0.43 V, respectively. This work opens a new avenue for designing effective single-atom catalysts with potential applications as energy storage and conversion devices possessing high density of metal centers independent of the doping strategy and defect engineering, which deserves experimental investigation in the future.

Transition Metals Embedded Two-Dimensional Square Tetrafluorotetracyanoquinodimethane Monolayers as a Class of Novel Electrocatalysts for Nitrogen Reduction Reaction

The combination of transition metal (TM) atoms and high electron affinity organic framework tetrafluorotetracyanoquinodimethanes (F₄TCNQs) makes the TM-embedded two-dimensional (2D) square F₄TCNQ monolayers (TM-sF₄TCNQ) possible to have excellent characteristics of single-atom catalysts and 2D materials. For the first time, the TM-sF₄TCNQ monolayers have been considered for application in the electrocatalytic nitrogen reduction reaction (eNRR) field. Through high-throughput screening, the catalytic performance of 30 TM-sF₄TCNQ (TM = 3d∼5d TMs) monolayers for eNRR was comprehensively evaluated. The Mo-, Nb-, and Tc-sF₄TCNQ catalysts stand out with the onset potentials of -0.18, -0.44, and -0.54 V, respectively, through the optimal reaction paths. Our work will provide guidance for the green and sustainable development of electrocatalytic nitrogen fixation.

Defective UiO-66-NH2 Functionalized with Stable Superoxide Radicals toward Electrocatalytic Nitrogen Reduction with High Faradaic Efficiency

The electrocatalytic nitrogen reduction reaction (NRR) to NH3 is limited by low Faradaic efficiency (FE). Herein, defective UiO-66-NH2 functionalized with quite stable superoxide radicals (O2•) is developed as a highly active NRR catalyst. The experimental and computational results show that one linker per Zr6 node is missed and two Zr atoms are exposed in the defective UiO-66-NH2. One of the two exposed Zr atoms can stably adsorb O2•, and thus, a Zr-OO• site forms during the preparations without light excitation or postoxidation, while the other Zr atom is activated as an active site. The synergistic effects of the two Zr sites in the defective UiO-66-NH2 suppress hydrogen and hydrazine evolutions considerably. They are as follows: (i) due to repulsion of the proton on the active Zr site and stabilization of the proton on the Zr-OO• site, the active Zr site is unfavorable for the adsorption of the proton with a high energy barrier, which is the HER rate-determining step (RDS); (ii) under the assistance of the OO• of the Zr-OO• site, the first hydrogenation step of *N2 (i.e., NRR RDS) on the active Zr site is promoted; and (iii) relying on the assistance of the OO• of the Zr-OO• site, the continuous hydrogenation of *NH2NH2 to produce NH3 on the active Zr site is spontaneously exothermic, whereas its desorption to hydrazine is blocked. Accordingly, an extremely high FE of ∼85.21% has been realized along with a high yield rate of NH3 (∼52.81 μg h-1 mgcat-1). To the best of our knowledge, it is the highest FE that has been achieved in recent years. Radical scavenging treatment of the defective UiO-66-NH2 and detailed investigations of two categories of control samples further verify the favorable effects of the O2• that closely correlates with the missed linkers on the performance of the NRR to NH3. This work opens a new way toward highly efficient NRR catalysts, i.e., stable radical-activating defective metal-organic frameworks.

Direct conversion of methane to methanol on boron nitride-supported copper single atoms

Direct conversion of methane to methanol (DMTM) under mild conditions is one of the most attractive and challenging processes in catalysis. By using density functional theory calculations, we systematically investigate the catalytic performance of Cu single atoms supported on O-doped BN in different coordination environments as a DMTM catalyst. Computations demonstrate that Cu coordinated with one O atom and two N atoms on O-doped BN (Cu₁/O₁N₂-BN) exhibited the highest catalytic activity for DMTM at room temperature with quite a low rate-determining step energy barrier of 0.46 eV. The moderate adsorption of *O atoms, selective stabilization of CH₃ species, and easy desorption of CH₃OH are responsible for the unique activity of Cu₁/O₁N₂-BN for DMTM. In addition, the adsorption free energy of *O atoms produced by the dissociation of O-donor molecules is a suitable descriptor for predicting the catalytic performance of materials and accelerating the discovery of catalysts for DMTM. This work opens new avenues to develop highly efficient catalysts for DMTM.

Screening of Transition-Metal Single-Atom Catalysts Anchored on Covalent-Organic Frameworks for Efficient Nitrogen Fixation

Two-dimensional (2D) covalent-organic frameworks (COFs) offer abundant hollow sites for stably anchoring transition-metal (TM) atoms to promote single-atom catalysis (SACs), which is expected to overcome the poor stability of SACs on conventional substrate materials. Using first-principles calculations within density-functional theory, a number of TM atoms embedded on a 2D COF Pc-TFPN (TMPc-TFPN) as SACs for ammonia synthesis under ambient conditions are investigated. Through a "five-step" screening strategy, WPc-TFPN is highlighted from 26 TMPc-TFPNs as the best SACs for nitrogen reduction reaction (NRR) with a low limiting potential of -0.19 V. Meanwhile, multiple-level descriptors are developed to uncover the origins of NRR activity, among which a simple descriptor φ that involves the electronegativity and number of d electrons of TM atoms shows volcano plot trends of limiting potential of NRR. This work provides a rational strategy for fast screening SACs for the electrochemical N₂ fixation using 2D COFs containing TM-N₄ units as host materials, which could also be applied to other electrochemical reactions.

Praseodymia–titania mixed oxide supported gold as efficient water gas shift catalyst: modulated by the mixing ratio of oxides

Modulating the active sites for controllable tuning of the catalytic activity has been the goal of much research, however, this remains challenging. The O vacancy is well known as an active site in reducible oxides. To modify the activity of O vacancies in praseodymia, we synthesized a series of praseodymia–titania mixed oxides. Varying the Pr : Ti mole ratio (2 : 1, 1 : 2, 1 : 1, 1 : 4) allows us to control the electronic interactions between Au, Pr and Ti cations and the local chemical environment of the O vacancies. These effects have been studied study by X-ray photoelectron spectroscopy (XPS), CO diffuse reflectance Fourier transform infrared spectroscopy (CO-DRIFTS) and temperature-programmed reduction (CO-TPR, H₂-TPR). The water gas shift reaction (WGSR) was used as a benchmark reaction to test the catalytic performance of different praseodymia–titania supported Au. Among them, Au/Pr₁Ti₂O_x was identified to exhibit the highest activity, with a CO conversion of 75% at 300 °C, which is about 3.7 times that of Au/TiO₂ and Au/PrO_x. The Au/Pr₁Ti₂O_x also exhibited excellent stability, with the conversion after 40 h time-on-stream at 300 °C still being 67%. An optimal ratio of Pr content (Pr : Ti 1 : 2) is necessary for improving the surface oxygen mobility and oxygen exchange capability, a higher Pr content leads to more O vacancies, however with lower activity. This study presents a new route for modulating the active defect sites in mixed oxides which could also be extended to other heterogeneous catalysis systems.

Schematic illustration of H₂O activation on the Pr-TiO_x support and the following reaction with CO in the Au–oxide interface.

A composite approach to synthesize a high-performance Pt/WO3–carbon catalyst for optical and electrocatalytic applications

Optical and electrocatalytic activity of the synthesized Pt/WO3–C nanocomposite in acidic and alkaline media.