N2 Reduction Reaction Research Articles

Cerium-promoted conversion of dinitrogen into high-energy-density material CeN6 under moderate pressure

Synthesis pressure and structural stability are two crucial factors for highly energetic materials, and recent investigations have indicated that cerium is an efficient catalyst for N2 reduction reactions. Here, we systematically explore Ce–N compounds through first-principles calculations, demonstrating that the cerium atom can weaken the strength of the N≡N bond and that a rich variety of cerium polynitrides can be formed under moderate pressure. Significantly, P1̄-CeN6 possesses the lowest synthesis pressure of 32 GPa among layered metal polynitrides owing to the strong ligand effect of cerium. The layered structure of P1̄-CeN6 proposed here consists of novel N14 ring. To clarify the formation mechanism of P1̄-CeN6, the reaction path Ce + 3N2 → trans-CeN6 → P1̄-CeN6 is proposed. In addition, P1̄-CeN6 possesses high hardness (20.73 GPa) and can be quenched to ambient conditions. Charge transfer between cerium atoms and N14 rings plays a crucial role in structural stability. Furthermore, the volumetric energy density (11.20 kJ/cm3) of P1̄-CeN6 is much larger than that of TNT (7.05 kJ/cm3), and its detonation pressure (128.95 GPa) and detonation velocity (13.60 km/s) are respectively about seven times and twice those of TNT, and it is therefore a promising high-energy-density material.

Plasmonic Au nanoparticles anchored 2D WS2@RGO for high-performance photoelectrochemical nitrogen reduction to ammonia

The photoelectrochemical reduction of nitrogen to ammonia (NH3) is a sustainable and cost-effective process. The photoelectrocatalysts adsorb light, activate N2, and transport electrons efficiently to achieve high-yield NH3. In the present work, gold-tungsten sulfide-anchored reduced graphene oxides (Au-WS2@RGO) are developed as highly efficient photoelectrocatalysts for the N2 reduction reaction (NRR) to synthesize NH3. The effect of Au nanoparticles loaded on WS2@RGO is optimized to achieve hierarchical 2D Au-WS2@RGO with excellent electrical conductivity, large active surface area, and unique porous network. Photoelectrocatalytic NRR of Au-WS2@RGO achieves remarkable NH3 production rates with ultrahigh NH3 yield of 34 μgh-1mgcat-1 at −0.6 V, tremendous faradaic efficiency (FE) of 16.2 %, long durability for about 14 h, and prolonged lifetime of photo-carriers. DFT calculations support the experimental findings and demonstrate that Au-WS2@RGO as an effeient NRR catalyst with low overpotential. The Au-WS2@RGO shows the highest NRR performances even in atmospheric air (AirRR) and outperforms the state-of-the-art NRR catalysts. The high AirRR performance and durability of Au-WS2@RGO make it a promising alternative to Au-based NRR catalysts in photo electrolyzers. Further, an innovative methodology will be proposed for high-efficiency urea fertilizer production using Au-WS2@RGO-based NRR photocatalysts.

NiO Matrix Decorated by Ru Single Atoms: Electron-Rich Ru-Induced High Activity and Selectivity toward Electrochemical N2 Reduction.

Developing a single-atom catalyst with electron-rich active sites is a promising strategy for catalyzing the electrochemical N2 reduction reaction (NRR). Herein, we choose NiO(001) as a model template and deposit a series of single transition metal (TM) atoms with higher formal charges to create the electron-rich active centers. Our first-principles calculations show that low-valent Ru (+2) on NiO(001) can significantly activate N2, with its oxidation states varying from +2 to +4 throughout the catalytic cycle. The Ru/NiO(001) catalyst exhibits the best activity with a relatively low limiting potential of -0.49 V. Furthermore, under NRR operating conditions, the Ru site is primarily occupied by *N2 rather than *H, indicating that NRR overwhelms the hydrogen evolution reaction and thus exhibits excellent selectivity. Our work highlights the potential of designing catalysts with electron-rich active sites for NRR.

Electrocatalyst Microenvironment Engineering for Enhanced Product Selectivity in Carbon Dioxide and Nitrogen Reduction Reactions.

Carbon and nitrogen fixation strategies are regarded as alternative routes to produce valuable chemicals used as energy carriers and fertilizers that are traditionally obtained from unsustainable and energy-intensive coal gasification (CO and CH4), Fischer-Tropsch (C2H4), and Haber-Bosch (NH3) processes. Recently, the electrocatalytic CO2 reduction reaction (CO2RR) and N2 reduction reaction (NRR) have received tremendous attention, with the merits of being both efficient strategies to store renewable electricity while providing alternative preparation routes to fossil-fuel-driven reactions. To date, the development of the CO2RR and NRR processes is primarily hindered by the competitive hydrogen evolution reaction (HER); however, the corresponding strategies for inhibiting this undesired side reaction are still quite limited. Considering such complex reactions involve three gas-liquid-solid phases and successive proton-coupled electron transfers, it appears meaningful to review the current strategies for improving product selectivity in light of their respective reaction mechanisms, kinetics, and thermodynamics. By examining the developments and understanding in catalyst design, electrolyte engineering, and three-phase interface modulation, we discuss three key strategies for improving product selectivity for the CO2RR and NRR: (i) targeting molecularly defined active sites, (ii) increasing the local reactant concentration at the active sites, and (iii) stabilizing and confining product intermediates.

Highly Selective N2 Electroreduction to NH3 Using a Boron-Vacancy-Rich Diatomic NbB Catalyst.

The ambient electrochemical N2 reduction reaction (NRR) is a future approach for the artificial NH3 synthesis to overcome the problems of high-energy consumption and environmental pollution by Haber-Bosch technology. However, the challenge of N2 activation on a catalyst surface and the competitive hydrogen evolution reaction make the current NRR unsatisfied. Herein, this work demonstrates that NbB2 nanoflakes (NFs) exhibit excellent selectivity and durability in NRR, which produces NH3 with a production rate of 30.5µg h-1 mgcat -1 and a super-high Faraday efficiency (FE) of 40.2%. The high-selective NH3 production is attributed to the large amount of active B vacancies on the surface of NbB2 NFs. Density functional theory calculations suggest that the multiple atomic adsorption of N2 on both unsaturated Nb and B atoms results in a significantly stretched N2 molecule. The weakened NN triple bonds are easier to be broken for a biased NH3 production. The diatomic catalysis is a future approach for NRR as it shows a special N2 adsorption mode that can be well engineered.

Engineering Graphdiyne for Solar Photocatalysis

AbstractGraphdiyne (GDY) with a direct band gap, excellent carrier mobility and uniform pores, is regarded as a promising photocatalytic material for solar energy conversion, while the research on GDY in photocatalysis is a less developed field. Herein, the distinctive structure, adjustable band gap, and electronic properties of GDY for photocatalysis is firstly summarized. The construction and progress of GDY‐based photocatalysts for solar energy conversion, including H2 evolution reaction (HER), CO2 reduction reaction (CO2RR) and N2 reduction reaction (NRR) are then elaborated. At last, the challenges and perspectives in developing GDY‐based photocatalysts for solar fuel production are discussed. It is anticipated that a timely Minireview will be helpful for rapid progress of GDY in solar energy conversion.

Engineering Graphdiyne for Solar Photocatalysis.

Graphdiyne (GDY) with a direct band gap, excellent carrier mobility and uniform pores, is regarded as a promising photocatalytic material for solar energy conversion, while the research on GDY in photocatalysis is a less developed field. Herein, the distinctive structure, adjustable band gap, and electronic properties of GDY for photocatalysis is firstly summarized. The construction and progress of GDY-based photocatalysts for solar energy conversion, including H2 evolution reaction (HER), CO2 reduction reaction (CO2 RR) and N2 reduction reaction (NRR) are then elaborated. At last, the challenges and perspectives in developing GDY-based photocatalysts for solar fuel production are discussed. It is anticipated that a timely Minireview will be helpful for rapid progress of GDY in solar energy conversion.

Fluorine‐Stabilized Defective Black Phosphorene as a Lithium‐Like Catalyst for Boosting Nitrogen Electroreduction to Ammonia

AbstractElectrocatalytic N2 reduction reaction (NRR) is recognized as a zero‐carbon emission method for NH3 synthesis. However, to date, this technology still suffers from low yield and low selectivity associated with the catalyst. Herein, inspired by the activation of N2 by lithium metal, a highly reactive defective black phosphorene (D−BPene) is proposed as a lithium‐like catalyst for boosting electrochemical N2 activation. Correspondingly, we also report a strategy for producing environmentally stable D−BPene by simultaneously constructing defects and fluorination protection based on topochemical reactions. Reliable performance evaluations show that the fluorine‐stabilized D−BPene can induce a high NH3 yield rate of ≈70 μg h−1 mgcat.−1 and a high Faradaic efficiency of ≈26 % at −0.5 V vs. RHE in an aqueous electrolyte. This work not only exemplifies the first stable preparation and practical application of D−BPene, but also brings a new design idea for NRR catalysts.

Fluorine-Stabilized Defective Black Phosphorene as a Lithium-Like Catalyst for Boosting Nitrogen Electroreduction to Ammonia.

Electrocatalytic N2 reduction reaction (NRR) is recognized as a zero-carbon emission method for NH3 synthesis. However, to date, this technology still suffers from low yield and low selectivity associated with the catalyst. Herein, inspired by the activation of N2 by lithium metal, a highly reactive defective black phosphorene (D-BPene ) is proposed as a lithium-like catalyst for boosting electrochemical N2 activation. Correspondingly, we also report a strategy for producing environmentally stable D-BPene by simultaneously constructing defects and fluorination protection based on topochemical reactions. Reliable performance evaluations show that the fluorine-stabilized D-BPene can induce a high NH3 yield rate of ≈70 μg h-1 mgcat. -1 and a high Faradaic efficiency of ≈26 % at -0.5 V vs. RHE in an aqueous electrolyte. This work not only exemplifies the first stable preparation and practical application of D-BPene , but also brings a new design idea for NRR catalysts.

Importance of Adatom on Pure Iron Catalyst Towards Electrocatalytic N2 Reduction Reaction.

The Haber-Bosch process using Fe-based catalysts is still the predominant technique for ammonia production despite tough reaction conditions and high energy consumption. In the present work, we have investigated iron adatom on the (110) surface of pure iron catalyst towards the electrocatalytic N2 reduction reaction (NRR) activity using density function theory (DFT) calculations. We demonstrate that the presence of adatom over the iron catalyst favours the NRR via alternating associative mechanistic pathway through a barrierless rate determining step (*NNH formation). Besides, the adatom-based catalyst requires lower working potential than the previously reported Fe(110) surface and Fe-nanocluster based catalysts. These findings may open a scope in terms of scrutinizing the atomicity effects over catalyst surface for various catalytic reactions.

Cooperative electrocatalytic N2 reduction based on WS2-covered Co9S8 hexagonal heterostructures derived from ZIF-67@POMs

Electrochemical N2 reduction reaction (NRR) to produce NH3 at ambient conditions is a promising route to replace the energy-intensive Haber–Bosch process, but electrochemical NRR with satisfied efficiency remains challenging. Therefore, a number of efforts have been committed to develop high-performance NRR electrocatalysts for highly efficient NH3 synthesis. Herein, Co9S8 nanosheets with a WS2 outer layer (Co9S8@WS2) are designed and prepared from ZIF-67@polyoxometalates (polyoxometalates , H3PW12O40·xH2O) and used for NRR at ambient temperature and pressure. The successful introduction of S-vacancies can adjust the electronic structure of the material by forming a electron-deficient environment, can make N2 molecules easily adsorbed and activated on the W active site of the catalyst surface, and thus, can promote the electrocatalytic NRR activity of the catalyst. In 0.1 M KOH, the optimized Co9S8@WS2-900 exhibits enhanced Faradaic efficiency (46.81%) and good NH3 yield (50.25 μg h−1 mgcat.−1) at −0.4 V vs. a reversible hydrogen electrode, exceeding many recently reported cobalt- or tungsten-based materials. The superior electrocatalytic activity is attributed to the unique composite structures and synergistic effect of electronic couplings between Co9S8 and sulfur-rich vacancies WS2. A density functional theory calculation indicates that the inert N2 can be activated by bare W atoms on the rim of the S-vacancies in Co9S8@WS2. The protonation of N2 to form N–NH∗ species is the potential-limiting step (ΔG = 1.05 eV). Therefore, the unique bimetallic sulfide clad architecture and rich S vacancies of Co9S8@WS2 provide the reference and inspiration for better designing of high-efficiency nitrogen-fixing catalysts.

Effects of Molybdenum Doping on the Enhanced Electrocatalytic Nitrogen Reduction Reaction Performance of CeO2 Nanorods: Theoretical and Experimental Investigations.

As a green and sustainable strategy, the electrocatalytic N2 reduction reaction (NRR) has been considered the best potential approach to replace the traditional Haber-Bosch process under ambient conditions. The key is to exploit efficient and low-cost electrocatalysts according to the current situation. Herein, a series of Molybdenum (Mo) doped CeO2 nanorods (NR) catalysts were successfully fabricated via a hydrothermal reaction coupled with high temperature calcination. The nanorod structures were not altered after Mo atom doping. The obtained 5 %-Mo-CeO2 nanorods act as a superior electrocatalyst in neutral electrolytes of 0.1 M Na2 SO4 . Such electrocatalyst significantly enhances NRR performance with an NH3 yield of 10.9 μg h-1 mg-1 cat at -0.45 V vs reversible hydrogen electrode (RHE) and a Faradaic efficiency (FE) of 26.5 % at -0.25 V vs RHE. That outcome is 4 times higher than that of CeO2 nanorods (2.6 μg h-1 mg-1 cat ; 4.9 %). Meanwhile, density functional theory (DFT) calculation shows the characteristics after Mo doping: the band gap value lowers, the density of states increases, electrons are more easily excited, and N2 molecules are more easily adsorbed, thereby enhancing the activity of the electrocatalytic NRR.

Heterogeneous metal trimer catalysts on Mo2TiC2O2 MXene for highly active N2 conversion to NH3

Activating the inert basal plane of functional-group-terminated MXenes is highly desirable for non-noble metal MXenes applied for the N2 reduction reaction (NRR) to value-added ammonia (NH3), but remains a significant challenge. Herein, we report the coupled interactions and catalytic mechanism of the supported trimeric metal M3 single-cluster catalysts (SCCs) on oxygen-vacancy-rich Mo2TiC2O2 (VO−Mo2TiC2O2) MXene materials for catalyzing this difficult reaction via spin-polarized density functional theory (DFT) calculations. Energy and electronic property analysis showed that the robust structural stability of the M3/VO−Mo2TiC2O2 catalysts stemmed from the vacancy defects, electronegativity difference, and significant charge redistribution. Based on the unique bidirectional electron transfer activation mechanism, the N2 adsorption strength can be well represented by a simple descriptor of the valence electrons in the d orbitals of M3 trimers. Remarkably, these confined Rh3, Ru3, Ni3 and Co3 SCCs on VO−Mo2TiC2O2 were capable of providing superior electrocatalytic activity and selectivity toward the NRR with ultra-low limiting potentials of −0.23, −0.32, −0.42 and −0.44 V, respectively. Finally, a mechanistic investigation illustrated that the valence electrons, charge transfer, and d-band center of the M3 active sites could collectively act as good descriptors to correlate the structure and NRR activity.

Noble-Metal-Metalloid Alloy Architectures: Mesoporous Amorphous Iridium-Tellurium Alloy for Electrochemical N2 Reduction.

Amorphous noble metals with high surface areas have attracted significant interest as heterogeneous catalysts due to the numerous dangling bonds and abundant unsaturated surface atoms created by the amorphous phase. However, synthesizing amorphous noble metals with high surface areas remains a significant challenge due to strong isotropic metallic bonds. This paper describes the first example of a mesoporous amorphous noble metal alloy [iridium-tellurium (IrTe)] obtained using a micelle-directed synthesis method. The resulting mesoporous amorphous IrTe electrocatalyst exhibits excellent performance in the electrochemical N2 reduction reaction. The ammonia yield rate is 34.6 μg mg-1 h-1 with a Faradaic efficiency of 11.2% at -0.15 V versus reversible hydrogen electrode in 0.1 M HCl solution, outperforming comparable crystalline and Ir metal counterparts. The interconnected porous scaffold and amorphous nature of the alloy create a complementary effect that simultaneously enhances N2 absorption and suppresses the hydrogen evolution reaction. According to theoretical simulations, incorporating Te in the IrTe alloy effectively strengthens the adsorption of N2 and lowers the Gibbs free energy for the rate-limiting step of the electrocatalytic N2 reduction reaction. Mesoporous chemistry enables a new route to achieve high-performance amorphous metalloid alloys with properties that facilitate the selective electrocatalytic reduction of N2.

Electrocatalytic reduction of N2 on FeRu dual-atom catalyst anchored in N-doped phosphorene

The highly efficient electrochemical synthesis of ammonia is regarded as a promising alternative compared to the traditional Haber-Bosch (H-B) process. However, the high-activity, low-cost, and long-term stability of electrocatalysts are still barriers to their rapid development. Herein, utilizing density functional theory (DFT), FeRu dual-atom catalyst anchored in N-doped phosphorene (FeRu@N4-P) is developed as a potential candidate for reducing inert N2 through electrocatalysis. Our results reveal that the distal and alternating pathways occur on the FeRu@N4-P with the lowest overpotential (0.29 V and 0.36 V). Moreover, we notice that there is a transformation from the alternating pathway to the enzymatic pathway for the step *NH2NH2 + H+ + e−→*NH2+*NH3. Considering the influence of the electrolyte solution in the actual experiment, we compared the sensitivity of electrocatalytic N2 reduction reaction (e-NRR) catalyst to the adsorption of H, demonstrating the efficient selectivity of FeRu@N4-P. The catalysts still maintain good stability and performance at room temperature. Finally, combining the physical properties of the metal atom, Φ is chosen to as the descriptor linearly correlating to the ΔG*N2 on the catalyst. This study deepens our understanding on the e-NRR mechanism on the dual-atoms doped phosphorene and opens a new way for the design of catalyst of the N2 fixation.

Atomically Precise Dinuclear Ni2 Active Site-Modified MOF-Derived ZnO@NC Heterojunction toward High-Performance N2 Photofixation

The development of heterogeneous catalysts with atom-dispersed active sites is essential to facilitate nitrogen (N2) activation for the N2 reduction reaction (NRR). However, it remains a major challenge to tune the coordination configuration of the metal centers to further accelerate the activation kinetics. Herein, an atomically precise dinuclear Ni2 site-modified metal–organic framework (MOF)-derived ZnO@NC heterojunction (ZnO@NC-Ni2) was developed for effective N2 photofixation under mild conditions. Moreover, advanced structural characterization indicates that the most active N-coordinated bimetallic site configurations are Ni2–N6, where two Ni1–N4 moieties are shared with two N atoms. Theoretical calculations further demonstrate that the binuclear Ni2 active sites of ZnO@NC-Ni2 could adjust the N2 adsorption configuration as the side-on bridging adsorption mode (denoted as “*N≡N*”), while the single metal Ni1 sites of ZnO@NC-Ni1 tend to form a terminal adsorption configuration with N2 (“*N≡N” type). As a result, the unique electronic structure of binuclear Ni2 active sites in ZnO@NC-Ni2 tends to proceed as an associative alternating pathway, thereby decreasing the activation energy barrier of the reaction procedure and favoring the photocatalytic NRR. The present study provides a perspective to probe the relationship between the coordination architecture of earth-abundant metal active centers and NRR activities.

Boosting Electroreduction Kinetics of Nitrogen to Ammonia via Atomically Dispersed Sn Protuberance.

Atomically dispersed metal catalysts show potential advantages in N2 reduction reaction (NRR) due to their excellent activity and efficient metal utilization. Unfortunately, the reported catalysts usually exhibit unsatisfactory NRR activity due to their poor N2 adsorption and activation. Herein, we report a novel Sn atomically dispersed protuberance (ADP) by coordination with substrate C and O to induce positive charge accumulation on Sn site for improving its N2 adsorption, activation and NRR performance. The extended X-ray absorption fine structure (EXAFS) spectra confirmed the local coordination structure of the Sn ADPs. NRR activity was significantly promoted via Sn ADPs, exhibiting a remarkable NH3 yield (RNH3 ) of 28.3 μg h-1 mgcat -1 (7447 μg h-1 mgSn -1 ) at -0.3 V. Furthermore, the enhanced N2 Hx intermediates was verified by in situ experiments, yielding consistent results with DFT calculation. This work opens a new avenue to regulate the activity and selectivity of N2 fixation.

Boosting Electroreduction Kinetics of Nitrogen to Ammonia via Atomically Dispersed Sn Protuberance

AbstractAtomically dispersed metal catalysts show potential advantages in N2 reduction reaction (NRR) due to their excellent activity and efficient metal utilization. Unfortunately, the reported catalysts usually exhibit unsatisfactory NRR activity due to their poor N2 adsorption and activation. Herein, we report a novel Sn atomically dispersed protuberance (ADP) by coordination with substrate C and O to induce positive charge accumulation on Sn site for improving its N2 adsorption, activation and NRR performance. The extended X‐ray absorption fine structure (EXAFS) spectra confirmed the local coordination structure of the Sn ADPs. NRR activity was significantly promoted via Sn ADPs, exhibiting a remarkable NH3 yield (RNH3) of 28.3 μg h−1 mgcat−1 (7447 μg h−1 mgSn−1) at −0.3 V. Furthermore, the enhanced N2Hx intermediates was verified by in situ experiments, yielding consistent results with DFT calculation. This work opens a new avenue to regulate the activity and selectivity of N2 fixation.

Rational design of bimetallic MXene solid solution with High-Performance electrocatalytic N2 reduction

Electrocatalytic N2 reduction reaction (eNRR) was an effective alternative method for green synthesis of NH3. By combining the first-principal Density functional theory (DFT) calculations and Monte Carlo (MC) simulation, we systematacially investigated 24 types equal-ratio bimetallic MXene solid solution, involving 88 different catalysts. Our focus was on the catalytic performance of these materials in eNRR. The computational result indicate that MoW(3Mo) has high stability, selectivity (93.8 % against the hydrogen evolution reaction (HER)) and activity (UL = -0.26 V), which is significantly better than that of monometal Mo2CO2 and W2CO2. This improvement in catalytic properties is attributed to the unique electronic structure (e.g. d-band center, charge) of bimetallic MXene solid solution. In explicit solvent conditions, the microenvironment of hydrogen bond in aqueous liquid thermodynamically promotes the catalytic property for eNRR and reduce the catalytic property of HER side reaction, but the kinetic barrier is also increased due to the effect of the hydrogen-bond microenvironment on proton migration. Overall, the obtained bimetallic MXene solid solution MoW(3Mo) exhibits excellent catalytic performance in eNRR.

Electronic metal-support interaction via defective-induced platinum modified BiOBr for photocatalytic N2 fixation

Designing atomic-scale catalytic sites to facilitate N2 adsorption and transport of photogenerated electrons to the target active sites offers new opportunities to achieve highly-efficiently photocatalytic N2 reduction reactions. Herein, Pt was photodeposited on BiOBr along with formation of oxygen vacancies (OVs) under ultraviolet light. The modulation of chemical states of Pt and the formation of electron metal-support interactions (EMSI) between BOB and Pt facilitated the charge transfer between the modifiers (i.e. Pt and OVs) and the support (i.e. BiOBr). The production rate of ammonia on Pt and OVs co-modified BiOBr reached 23.8 μmol g−1 h−1, which was much higher than that either on OVs-BiOBr or pristine BiOBr. Density functional theory (DFT) calculations showed that EMSI effect led to a significant charge redistribution between Pt and BOBr carriers, whereby Pt doping could significantly reduce energy barrier of N2 hydrogenation process to facilitate photocatalytic N2 reduction.