Nitrogen Reduction Reaction Selectivity Research Articles

Surface electronic fine-perturbation driven by distal atom coupling at W-Se pair sites for enhanced ammonia synthesis

Engineering single-atom electrocatalysts (SACs) of geometries and electronic structures at atomic level to overcome the critical trade-off in catalytic performance remains a significant challenge. Here, we report a novel metal–nonmetal pair sites with non-bonding interaction to achieve dual enhancements of activity and selectivity for nitrogen reduction reaction (NRR). The stable non-bonding structure of W-Se atom pairs on C3N4 support (W-SeC3N4) was engineered by photo-assisted cryogenic reduction. Distal Se-atom coupling drives a fine-tuning of surface-localized electronic state on center W-atom through genuine chemical interaction and modulates the adsorption energies of intermediates like *NNH, *NH and *NH2. W-SeC3N4 thus demonstrates a NH3 yield rate of 74.6 ug h−1 mgcat−1 and >38.2 % selectivity, surpassing all current non-precious metal SACs. Our work supplies an advanced strategy for the rational design of SACs in complex chemical reactions involving multi-step intermediates.

Activity of CeO2(111) supported Mnx(x = 1–6) for electrochemical N2 reduction reaction: Insights from density functional theory

It is challenging to realize an efficient nitrogen reduction reaction (NRR) under mild conditions, which suffers from low ammonia yield and low Faraday efficiency due to the extremely stable NN triple bond of N2 as well as competitive hydrogen evolution reaction. In this work, the NRR reactivity of Mnx(x= 1–6) clusters supported on CeO2(111) (Mnx(x = 1–6)/CeO2(111)) was systematically investigated using density functional theory. A volcanic relationship between the limiting potential of NRR on Mnx(x = 1–6)/CeO2(111) and the atom number of Mnx was found. Mn3/CeO2(111) shows the highest activity for NRR with a limiting potential of -0.36, -0.55 and -0.53 V along distal, alternating and enzymatic reaction pathway, respectively. Its high activity is attributed to the triangular geometry and optimal average number of electrons every Mn transferred from Mn3 to CeO2(111), which leads to the strong N2 activation and the stabilization of nitrogen-containing intermediates. Also, Mn3/CeO2(111) exhibits a high NRR selectivity by hindering H adsorption and a high thermal stability at both 298 and 773 K, suggesting its promising potential as effective NRR catalyst. This work provides new insights into the rational design of single cluster catalysts.

Efficient nitrogen-doped graphene supported heteronuclear diatomic electrocatalyst for nitrogen reduction reaction: D-band center assisted rapid screening

In recent years, the electrocatalytic nitrogen reduction reaction (NRR) has attracted considerable attention as a promising method for ammonia synthesis. Currently, various diatomic catalysts (DACs) composed of metal and non-metal combinations have been studied and reported for the NRR. These catalysts have been proven the ability to lower the reaction overpotential and enhance its activity. Among them, DACs supported on two-dimensional nitride materials have been widely applied in the NRR. In this work, ten heteronuclear diatomic catalysts supported on nitrogen-doped graphene were constructed. The research results demonstrated that MoCrN6-G exhibited the best catalytic performance among these catalysts due to its lowest overpotential (0.45 V) and low desorption free energy (0.15 eV) of NH3, as well as a higher selectivity for NRR compared to the hydrogen evolution reaction. It is worth emphasizing that the d-band center (εd) is considered as a descriptor for rapidly screening efficient NRR electrocatalysts, further guiding the rational design of catalysts.

Density Functional Theory Study of Triple Transition Metal Cluster Anchored on the C2N Monolayer for Nitrogen Reduction Reactions.

The electrochemical nitrogen reduction reaction (NRR) is an attractive pathway for producing ammonia under ambient conditions. The development of efficient catalysts for nitrogen fixation in electrochemical NRRs has become increasingly important, but it remains challenging due to the need to address the issues of activity and selectivity. Herein, using density functional theory (DFT), we explore ten kinds of triple transition metal atoms (M3 = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) anchored on the C2N monolayer (M3-C2N) as NRR electrocatalysts. The negative binding energies of M3 clusters on C2N mean that the triple transition metal clusters can be stably anchored on the N6 cavity of the C2N structure. As the first step of the NRR, the adsorption configurations of N2 show that the N2 on M3-C2N catalysts can be stably adsorbed in a side-on mode, except for Zn3-C2N. Moreover, the extended N-N bond length and electronic structure indicate that the N2 molecule has been fully activated on the M3-C2N surface. The results of limiting potential screen out the four M3-C2N catalysts (Co3-C2N, Cr3-C2N, Fe3-C2N, and Ni3-C2N) that have a superior electrochemical NRR performance, and the corresponding values are -0.61 V, -0.67 V, -0.63 V, and -0.66 V, respectively, which are smaller than those on Ru(0001). In addition, the detailed NRR mechanism studied shows that the alternating and enzymatic mechanisms of association pathways on Co3-C2N, Cr3-C2N, Fe3-C2N, and Ni3-C2N are more energetically favorable. In the end, the catalytic selectivity for NRR on M3-C2N is investigated through the performance of a hydrogen evolution reaction (HER) on them. We find that Co3-C2N, Cr3-C2N, Fe3-C2N, and Ni3-C2N catalysts possess a high catalytic activity for NRR and exhibit a strong capability of suppressing the competitive HER. Our findings provide a new strategy for designing NRR catalysts with high catalytic activity and selectivity.

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.

Vacancy engineering of BiFeO3 perovskite for low-barrier electrochemical nitrogen fixation

Because of its environmental and intrinsic benefits, the nitrogen reduction reaction (NRR) using electrocatalysts has garnered significant attention. Engineering on the surface is commonly utilized to improve electrocatalytic activity by introducing atomic defects. In this study, we have developed a successful strategy to promote nitrogen activation by introducing oxygen vacancies into BiFeO3 perovskite. BiFeO3 with oxygen vacancies (denoted as VO-BiFeO3) possesses a high NH3 yield rate (89.3 μg h−1 mgcat−1) and Faradaic efficiency (FE) (13.5 %) at −0.40 V versus the reversible hydrogen electrode (RHE). According to density functional theory (DFT) calculations, the introduction of oxygen vacancies increases the binding capacity for nitrogen immobilization and reduces the energy barrier for the rate-determining step of NRR. Moreover, the analysis of the thermodynamic limiting potentials towards N2 reduction and H2 evolution demonstrates that VO-BiFeO3 has a higher selectivity for NRR than pristine BiFeO3.

Catalysts with Trimetallic Sites on Graphene-like C2N for Electrocatalytic Nitrogen Reduction Reaction: A Theoretical Investigation.

Electrocatalytic nitrogen reduction reaction (NRR) is a green and highly efficient way to replace the industrial Haber-Bosch process. Herein, clusters consisting of three transition metal atoms loaded on C2N as NRR electrocatalysts are investigated using density functional theory (DFT). Meanwhile, Ca was introduced as a promoter and the role of Ca in NRR was investigated. It was found that Ca anchored to the catalyst can act as an electron donor and effectively promote the activation of N2 on M3. In both M3@C2N and M3Ca@C2N (M=Fe, Co, Ni), the limiting potential (UL) is less negative than that of the Ru(0001) surface and has the ability to suppress the competitive hydrogen evolution reaction (HER). Among them, Fe3@C2N is suggested to be the most promising candidate for NRR with high thermal stability, strong N2 adsorption ability, low limiting potential, and good NRR selectivity. The concepts of trimetallic sites and alkaline earth metal promoters in this work provide theoretical guidance for the rational design of atomically active sites in electrocatalytic NRR.

Enhanced Activity and Selectivity for Nitrogen Reduction Reaction in Electrode-based Heterostructures: A DFT Computational Study.

Developing sustainable and efficient catalysts for ammonia synthesis from atmospheric molecular N2 under ambient conditions presents a significant 21st-century challenge. Two-dimensional heterostructures, particularly single-atom catalysts (SACs) supported on two-dimensional materials, have emerged as a promising avenue due to their remarkable catalytic activity and selectivity. Electrides, characterized by an abundance of free electrons and high surface activity, have attracted substantial attention in this context. Through density functional theory (DFT) calculations, this study proposes electride-graphene heterostructures (EGHS) as catalysts to effectively regulate charge distribution at the catalytic center, facilitating the optimization of catalytic performance. The EGHS model addresses challenges related to excessive adsorbate binding, mitigating electron transfer compared to electride monolayer adsorption. This novel approach utilizes heterogeneous heterostructures to finely tune the catalytic site, optimizing electron input for enhanced catalysis.Based on the optimized charge transfer for N2 activation, the Cr-doped EGHS (Cr@EGHS) exhibits a promising performance in the nitrogen reduction reaction, leading to, a relatively low limiting potential of -0.85 V and high selectivity. The hypothesis charge transfer depend on N2 activation is further supported by modulating the distance between component layers of heterostructure. These findings contribute to design principles for 2D heterostructure catalysts and offer a reference for experimental synthesis.

Electrochemical nitrogen reduction reaction catalyzed by a cucurbit[6]uril-phosphomolybdic-copper cation hybrid

The electrocatalytic nitrogen reduction reaction (NRR) provides an energy-saving and environmentally friendly method to synthesize ammonia. Herein, a molybdenum-containing hybrid material (Q[6]-PMA-Cu) was prepared form the assembly of Keggin-type phosphomolybdic acid (PMA) with cucurbit[6]uril (Q[6]) and Cu2+ cations. Q[6]-PMA-Cu with multiple active sites and stable properties not only enables a high selectivity for NRR, but also shows a distinct advantage to suppress HER process, affording a high ammonia yield of 135.04±4.25 µg h−1 mgcat−1 with a Faradaic efficiency (FE) of 85.48±3.33%. 15N2 isotope labeling and control experiments were conducted to verified the nitrogen resource of ammonia formation. The results of experiments and DFT calculations demonstrates the reaction mechanism along the alternate association pathway, of which the metal active sites (Mo & Cu) play crucial role in electron transfer and the presence of hydrophobic Q[6] is responsible to inhibit side reaction of HER.

Screening of borophene-supported highly active and selective single-atom catalysts for electrocatalytic nitrogen reduction reactions

Ammonia (NH3) is an ideal zero-carbon clean energy source because of its substantial hydrogen capacity, high-energy density and facile transportability. Compared to disadvantages of Haber–Bosch processes, such as demanding reaction conditions, high energy consumption and inefficiency, the electrocatalysis nitrogen reduction reaction (NRR) can achieve green synthesis of NH3 due to mild reactive conditions. Utilizing density functional theory (DFT), explored the potential of borophene-supported transition metals as single atom catalysts (SACs) for NRR. The NRR pathways and Gibbs free-energy (ΔG) of the selected V@Bβ12, Cr@Bβ12, Zr@Bβ12 and Mo@Bβ12 were studied in detail after rigorous screening processes. The limiting potentials of NRR in optimal path are -0.10, -0.27, -0.18 and -0.07 V, respectively, which are excellent catalysts for NRR. Under operating voltage conditions, TM@Bβ12 has excellent ability to resist surface oxidation and inhibit hydrogen evolution reaction (HER). In addition, V@Bβ12, Cr@Bβ12, Zr@Bβ12 and Mo@Bβ12 have good selectivity for NRR. Cr@Bβ12 and Mo@Bβ12 are also potential catalysts for HER. The source of TM@Bβ12 catalytic activity in NRR fully confirms the good conductive properties, and the transmission of the charge contribute to improve catalytical activity of NRR. This paper provides theoretical guidance on the synthesis of a new type of NRR catalyst.

Achieving 78.2 % Faraday Efficiency for Electrochemical Ammonia Production Via Covalent Modification of CNTs with B4C

AbstractElectrochemical reduction of N2 to NH3 provides an alternative to the Haber‐Bosch process for sustainable NH3 production driven by renewable electricity. Here, we reported carbon nanotubes (CNTs) covalently modified with boron carbide (B4C) as a nonmetallic catalyst for efficient electrochemical nitrogen reduction reaction (NRR) under ambient conditions. The structure of the catalyst was characterized by transmission electron microscopy (TEM), X‐ray diffraction (XRD), elemental mapping, X‐ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The catalyst held a superior selectivity for NRR with high Faraday efficiency of 78.2 % accompanying with NH3 yield rate of 14.0 μg mg−1cat. h−1 under the condition of 0.1 M Na2SO4 and −0.6 V vs. RHE. Electrochemical experiments including cyclic voltammetry, electrochemical impedance spectroscopy and Tafel polarization curves were performed to explain the best electrochemical properties of B4C/CNTs among the samples. This work demonstrates that the strategy of covalent modification plays an important role to improve the selectivity of electrochemical NRR catalyst, thus allowing the reactions to proceed more efficiently.

A Coherent Pd–Pd16B3 Core–Shell Electrocatalyst for Controlled Hydrogenation in Nitrogen Reduction Reaction

AbstractThe manipulation of surface catalytic sites has rarely been explored for metal borides, and the subsurface effects on the electrocatalytic activity of the nitrogen reduction reaction (NRR) remain unknown. Herein, this work develops a core–shell nanoparticle catalyst with a Pd core that ensures high electron transfer rates and an Pd16B3 atomical shell that possess tunable active sites for regulating the NRR. The atomic structural evolution from Pd to Pd16B3 is investigated by precisely controlling the B atom diffusion, molecular rearrangement, and d–sp orbital hybridization. Pd/Pd16B3 core–shell nanocrystals exhibit an exceptional NRR performance with a high NH3 Faradaic efficiency of 30.8%, which is superior to those of pristine Pd (1.2%) and B‐doped Pd (4.8%) under identical conditions, and a yield rate of 0.81 µmol h−1 cm−2. This work discovers that the Pd16B3 shell could promote the NRR selectivity by separating the separating the hydrogen evolution reaction proceeded on hole sites and NRR proceeded on bridge sites, and the Pd core could provide the excellent conductivity to Pd16B3 shell through regulated electron interactions. Consequently, the controlled chemical ordering of palladium boride on palladium surfaces provides insight into the synthesis of advanced NRR electrocatalysts.

Screening Efficient C-N Coupling Catalysts for Electrosynthesis of Acetamide and Output Ammonia through a Cascade Strategy of Electrochemical CO2 and N2 Reduction Using Cu-Based Nitrogen-Carbon Nanosheets.

Due to the limitation of the high-value-added products obtained from electrocatalytic CO2 reduction within an acid environment, introducing additional elements can expand the diversity of the products obtained during the CO2 reduction reaction (CO2RR) and nitrogen reduction reaction (NRR). Thus, coelectroreduction of CO2 and N2 is a new strategy for producing acetamide (CH3CONH2) via both C-C and C-N bond coupling using Cu-based nitrogen-carbon nanosheets. CO2 can reduce to CO, and a key ketene (*C═C═O) can be generated from *CO*CO dimerization; this ketene is postulated as an intermediate in the formation of acetamide. However, most studies focus on promoting the C-C bond formation. Here, we propose that C-N bond coupling can form acetamide through the interaction of *C═C═O with NH3. The acetamide is formed via a nucleophilic attack between *NH3 and the *C═C═O intermediate. The C-N coupling mechanism was successfully applied to expand the variety of nitrogen-containing products obtained from CO2 and N2 coreduction. Thus, we successfully screened Cu2-based graphite and Cu-based C3N4 as catalysts that can produce C2+ compounds by integrating CO dimerization with acetamide synthesis. In addition, we observed that Cu2-based C2N and Cu-based C3N4 catalysts are suitable for the NRR. Cu-based C3N4 showed high CO2RR and NRR activities with small negative limiting potential (UL) values of -0.83 and -0.58 V compared to those of other candidates, respectively. The formation of *COHCOH from *COHCO was considered the rate-determining step (RDS) during acetamide electrosynthesis. The limiting potential value of Cu2-based C2N was only -0.46 V for NH3 synthesis, and the formation of *NNH was via the RDS via an alternating path. The adsorption energy difference analysis both CO2 and N2 compare with the hydrogen evolution reaction (HER), suggesting that Cu2-based C2N exhibited the highest CO2RR and NRR selectivity among the 13 analyzed catalysts. The results of this study provide innovative insights into the design principle of Cu-based nitrogen-carbon electrocatalysts for generating highly efficient C-N coupling products.

Surface Electronic Properties-Driven Electrocatalytic Nitrogen Reduction on Metal-Conjugated Porphyrin 2D-MOFs.

Two-dimensional (2D) metal organic framework (MOF) or metalloporphyrin nanosheets with a stable metal-N4 complex unit present the metal as a single-atom catalyst dispersed in the 2D porphyrin framework. First-principles calculations on the 3d-transition metals in M-TCPP are investigated in this study for their surface-dependent electronic properties including work function and d-band center. Crystal orbital Hamiltonian population (-pCOHP) analysis highlights a higher contribution of the bonding state in the M-N bond and antibonding state in the N-N bond to be essential for N-N bond activation. A linear relationship between ΔGmax and surface electronic properties, N-N bond strength, and Bader charge has been found to influence the rate-determining potential for nitrogen reduction reaction (NRR) in M-TCPP MOFs. 2D Ti-TCPP MOF, with a kinetic energy barrier of 1.43 eV in the final protonation step of enzymatic NRR, shows exclusive NRR selectivity over competing hydrogen reduction (HER) and nitrogenous compounds (NO and NO2). Thus, Ti-TCPP MOF with an NRR limiting potential of -0.35 V in water solvent is proposed as an attractive candidate for electrocatalytic NRR.

Design of high performance nitrogen reduction electrocatalysts by doping defective polyoxometalate with a single atom promoter.

Single-atom catalysts (SACs) are emerging as promising candidates for electrochemical nitrogen reduction reaction (NRR). Previous studies have shown that the single-atom centers of SACs can not only serve as active sites, but also act as promoters to affect the catalytic properties. However, the use of single metal atoms as promoters in electrocatalysis has rarely been studied. In this work, the defective Keggin-type phosphomolybdic acid (PMA) is used as a substrate to support the single metal atoms. We aim to tune the electronic structures of the exposed molybdenum active sites on defective PMA by using these supported single atoms as promoters for efficient NRR. Firstly, the stability and N2 adsorption capacity were studied to screen for an effective catalyst capable of activating N2. Most of the SACs were found to have good stability and N2 adsorption capacity. Then, we compared the selectivity and NRR activity of the catalysts and found that catalysts with metal atom promoters have improved NRR selectivity and activity. Finally, electronic structure analysis was carried out to understand the promoting effect of the promoter on N2 activation and the activity of the NRR process. This work provides a new strategy for designing efficient catalysts for electrocatalytic reactions by introducing promoters.

Unveiling the synergistic effect between the metallic phase and bridging S species over MoS2 for highly efficient nitrogen fixation

Electrocatalytic nitrogen reduction reaction (NRR) is considered an appealing approach towards sustainable NH3 production but still undergoes serious challenges with unsatisfactory catalytic performance, which hinders its large-scale application. In this work, the S-rich 1T‐MoS2 with an ultrahigh 1T phase content and S-enrichment has been successfully synthesized and firstly verified as an exceptional NRR catalyst with high activity and selectivity. The optimized MoS2.30 catalyst exhibits a high NH3 yield rate (98.30±1.63 μg h–1 mg–1cat.) and FE (23.10±0.38%), surpassing nearly all the reported MoS2-based NRR catalysts and the overwhelming majority of advanced NRR catalysts, demonstrating the encouraging role-playing of the synergistic effect between 1T phase and bridging S22– species on NRR performances. DFT calculations reveal that the high properties empowered by MoS2.30 are on account of the synergistic effect that induces the enhanced NRR activity via the strengthened N2 adsorption and reduced energy barrier (Eb) as well as the improved NRR selectivity through the optimized competitive adsorption and reduced energy barrier against the hydrogen evolution reaction (HER). This work fabricates a MoS2-based electrocatalyst for highly efficient NRR and proves an effective strategy to improve the catalytic performance, which is worth being extended to other catalytic reactions.

Modulating the coordination environment of active site structure for enhanced electrochemical nitrogen reduction: The mechanistic insight and an effective descriptor

The effect of coordination environment of active site structure can never be underestimated in the rational design of a high-performance catalyst especially in electrochemical application. We designed a B-modified C2N-based double-atom catalyst (M2@B2-C2N) with the hybrid coordination of B2N4, on which electrochemical nitrogen reduction reaction (NRR) was computationally studied. Our DFT calculations revealed that the NRR could proceed highly efficiently for M2 = Mo2 and W2 with the onset potential of UL = -0.25 V and UL = -0.27 V, respectively. Remarkably, the NRR complied with a special quasi-dissociative mechanism instead of the conventional associative mechanism on M2@B2-C2N (M2 = Mo2 and W2). Using the optimal metal-based catalyst as a reference, these two model catalysts could yield superior NRR selectivity with respect to HER. The AIMD simulation demonstrated that the NRR could proceed with the applied potential of cathode as URHE = -0.20 V (Mo2) and −0.39 V (W2). The underlying chemical and structural origin of coordination environment was formulated as an effective descriptor Ω, which enables to bridge the NRR activity and active site structure. Our study could further the understanding of metal active site structure that catalyzes an electrochemical reaction involving small molecules.

High efficiency carbon nanotubes-based single-atom catalysts for nitrogen reduction

Carbon-based single-atom catalysts (SACs) for electrochemical nitrogen reduction reaction (NRR) have received increasing attention due to their sustainable, efficient, and green advantages. However, at present, the research on carbon nanotubes (CNTs)-based NRR catalysts is very limited. In this paper, using FeN3@(n, 0) CNTs (n = 3 ~ 10) as the representative catalysts, we demonstrate that the CNT curvatures will affect the spin polarization of the catalytic active centers, the activation of the adsorbed N2 molecules and the Gibbs free energy barriers for the formation of the critical intermediates in the NRR processes, thus changing the catalytic performance of CNT-based catalysts. Zigzag (8, 0) CNT was taken as the optimal substrate, and twenty transition metal atoms (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Nb, Mo, Tc, Ru, Rh, Pd, W, Re, Ir, and Pt) were embedded into (8, 0) CNT via N3 group to construct the NRR catalysts. Their electrocatalytic performance for NRR were examined using DFT calculations, and TcN3@(8, 0) CNT was screened out as the best candidate with a low onset potential of − 0.53 V via the distal mechanism, which is superior to the molecules- or graphene-support Tc catalysts. Further electronic properties analysis shows that the high NRR performance of TcN3@(8, 0) CNT originates from the strong d-2π* interaction between the N2 molecule and Tc atom. TcN3@(8, 0) CNT also exhibits higher selectivity for NRR than the competing hydrogen evolution reaction (HER) process. The present work not only provides a promising catalyst for NRR, but also open up opportunities for further exploring of low-dimensional carbon-based high efficiency electrochemical NRR 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 (UL) 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.

The transition metal doped B cluster (TM4B18) as catalysis for nitrogen fixation

Renewable electrically/light-driven nitrogen reduction from earth's abundant nitrogen is considered one of the most attractive strategies for clean energy transport and storage through nitrogen cycle. To this end, developing inexpensive, rich and excellent performance catalysts for nitrogen reduction reaction (NRR) is essential but challenging. Here, we systematically studied 18 kind of transition metal boron clusters TM4B18 (TM = 3d, 4d and 5d) as promising photocatalytic catalysis for NRR. Our first-principles calculations demonstrate that these TM4B18 clusters possess outstanding water environment stability and high selectivity for NRR under hydrogen evolution reaction (HER) side reaction. In particular, three candidate catalysts (Zr4B18, V4B18 and Mn4B18) for ammonia synthesis with excellent performance are selected by high-throughput screening of TM4B18 materials using a "Four-Step" method. Most notably, Zr4B18 cluster performs best with onset potential lower -0.50 eV through the enzymatic mechanism, such result is owing to the part of occupied d orbitals of the active metal atoms. Furthermore, these TM4B18 clusters with appropriate energy gap that is able to absorb light from the visible to ultraviolet to driven NRR. These theoretical researches offer vital physical views for using the superior transition metal doped B cluster materials for driving by solar energy and ammonia production.