Nitrogen Reduction Reaction Performance Research Articles

Regulating Interfacial Microenvironment in Aqueous Electrolyte via a N2 Filtering Membrane for Efficient Electrochemical Ammonia Synthesis.

Electrochemical synthesis of ammonia (NH3) in aqueous electrolyte has long been suffered from poor nitrogen (N2) supply owing to its low solubility and sluggish diffusion kinetics. Therefore, creating a N2 rich microenvironment around catalyst surface may potentially improve the efficiency of nitrogen reduction reaction (NRR). Herein, a delicately designed N2 filtering membrane consisted of polydimethylsiloxane is covered on catalyst surface via superspreading. Because this membrane let the dissolved N2 molecules be accessible to the catalyst but block excess water, the designed N2 rich microenvironment over catalyst leads to an optimized Faradaic efficiency of 39.4% and an NH3 yield rate of 109.2µgh-1mg-1, which is superior to those of the most report metal-based catalysts for electrochemical NRR. This study offers alternative strategy for enhancing NRR performance.

Synergistic Al−Al Dual‐Atomic Site for Efficient Artificial Nitrogen Fixation

AbstractSynthesis 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.

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.

The intermediate valence state Mo5+ in Fe doping La2(MoO4)3 boosting electrochemical nitrogen reduction

NH3 is considered as an ideal fuel for fuel cells to achieve zero carbon emissions due to its high energy density (at liquefaction) and carbon-free properties. The zero-carbon clean electrocatalytic nitrogen reduction reaction (NRR) is one of the alternative routes for NH3 synthesis. The efficiency of NRR is restricted by the high stability of N N and the slow reaction rate. In this study, La2(MoO4)3 (LaMo), and x%Fe doping-LaMo (x = 3, 5, 7, and 10) are synthesized via a hydrothermal method. The strong electron-donating ability of Fe converts a part of Mo6+ to Mo5+ and Mo4+ improving the electronic environment. The presence of Mo5+, an intermediate valence state, facilitates the oxidation and reduction reactions and establishes rapid electron transport channels. The electron transport of Mo6+↔e−Mo5+ is easier than Mo6+↔2e−Mo4+. Furthermore, the Mo5+ activates N2 and enhances N2 adsorption, boosting the NRR performance. Importantly, the content of Mo5+ exhibits a positive correlation with NH3 yield rate (R2 = 0.89), and Faradaic efficiency (FE, R2 = 0.95). Consequently, the 5%Fe–LaMo exhibits the highest Mo5+ percentage (75.9 %) and NRR performance (NH3 yield rate:30.4 μg h−1 mgcat−1, FE: 3.6 %). Thus, this study proposes a method to enhance the NRR performance by element doping with strong electron-donating ability to regulate the Mo5+ percentage.

Enhancing Nitrogen Reduction Reaction through Formation of 2D/2D Hybrid Heterostructures of MoS2@rGO.

Given the challenging task of constructing an efficient nitrogen reduction reaction (NRR) electrocatalyst with enhanced ambient condition performance, properties such as high specific surface area, fast electron transfer, and design of the catalyst surface constitute a group of key factors to be taken into consideration to guarantee outstanding catalytic performance and durability. Thereof, this work investigates the contribution of the 2D/2D heterojunction interface between MoS2 and reduced graphene oxide (rGO) on the electrocatalytic synthesis of NH3 in an alkaline media. The results revealed remarkable NRR performance on the MoS2@rGO 2D/2D hybrid electrocatalyst, characterized by a high NRR sensitivity (faradaic efficiency) of 34.7% with an NH3 yield rate of 3.98 ± 0.19 mg h-1 cm-2 at an overpotential of -0.3 V vs RHE in 0.1 M KOH solution. The hybrid electrocatalysts also exhibited selectivity for NH3 synthesis against the production of the hydrazine (N2H4) byproduct, hindrance of the competitive hydrogen evolution reaction (HER), and good durability over an operation period of 8 h. In hindsight, the study presented a low-cost and highly efficient catalyst design for achieving enhanced ammonia synthesis in alkaline media via the formation of defect-rich ultrathin MoS2@rGO nanostructures, consisting predominantly of an HER-hindering hexagonal 2H-MoS2 phase.

Tuning electronic environment of B sites in boron carbonitride nanoribbon boosts catalytic activity of reducing N2 to NH3

The electrocatalytic nitrogen reduction reaction (NRR) to synthesize ammonia is an important and challenging task in chemistry, where low-cost, highly active non-metallic catalysts such as boron carbonitride (BCN) are still highly desired. Tuning the electronic environment of the active site B is an effective approach to improve the NRR performance of BCNs. However, the study on the mechanism of this effect has been seriously neglected. The diversity and controllability in atomic arrangements of BCN make it suitable for studying the relationship between the local chemical environment of boron and the catalytic properties. To this end, we design four kinds of BCN materials named as homogeneous BCN nanoribbon and BCN nanosheet enriched with B − C active sites and localized phase-separated BCN nanoribbon and BCN nanosheet rich in B − N active sites, and theoretically screen the homogeneous type BCN nanoribbons that have better NRR performances. Meanwhile, we experimentally demonstrate that the optimized charge redistribution of B atoms in BCN skeleton by tuning the electronic environment makes the B − C sites being the effective centers in NRR, and arising the excellent NH3 productivity of 63.02 μg h−1 mg − 1 cat with a highest Faraday efficiency of 32.28 %.

Highly efficient N2 electroreduction to NH3 on Cu7·2S4/C with sulfur vacancies synthesized using a continuous microchannel reactor

The electrochemical nitrogen reduction reaction (NRR) has emerged as a sustainable and environmental–friendly alternative for ammonia synthesis compared with conventional Haber–Bosch process. However, considerable challenges persist in developing cost-effective catalysts for NRR. Herein, Cu7·2S4/C was synthesized using a continuous microchannel reactor followed by carbonization sulfurization at 600 °C. The as-prepared Cu7·2S4/C catalyst, featuring abundant sulfur vacancies, exhibited outstanding electrochemical performance for NRR, achieving an ammonia yield of 52 μg h−1mgcat.−1 and Faraday efficiency of 32.2%. In addition, density functional theory calculations suggest that sulfur vacancies contribute to a decrease in Gibbs free energy during N2-activated hydrogenation, thereby facilitating adsorption of N2 and formation of Cu–N bonds at catalytic active centers. This study introduces a novel strategy for synthesizing economical and efficient NRR electrocatalysts based on transition metal-based metal–organic frameworks.

Recent Progress on Computation‐Guided Catalyst Design for Highly Efficient Nitrogen Reduction Reaction

AbstractElectrochemical nitrogen reduction reaction (NRR) for ammonia synthesis has attracted great interest in recent years, which presents a carbon‐free alternative to the energy‐intensive Haber–Bosch process. Besides, NRR also provides a promising coverage route of renewable energy since NH3 is considered the second generation of hydrogen energy while possessing established technologies of liquefaction, storage, and transport. However, there are long‐term challenges in catalyst design for NRR due to its low intrinsic activity and unsatisfied selectivity. Fortunately, by conducting extensive explorations in this field, much progress is achieved in boosting the NRR performance. Herein, from a view of the atomic/electronic level, three promotion effects are summarized for NRR (i.e., electron effect, geometry effect, and ligand effect), which tackle the challenges of activity and selectivity. Representative studies with taking fully advantages of the promotion effects are reviewed, which realized remarkable NRR performance. Finally, the future research directions and prospects are discussed. It is highly expected that this review will enable the advancement of NRR catalysts and promote the further development of electrochemical NRR.

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.

Asymmetric empty orbitals in ZrO2-BCN for enhancing electrocatalytic hydrogenation of nitrogen to ammonia

Electrocatalytic nitrogen reduction reaction (NRR) provides an environment-friendly and sustainable approach for nitrogen fixation at ambient conditions. However, simultaneously activating N≡N triple bond and suppressing the competitive hydrogen evolution reaction (HER) in aqueous electrolytes remain challenges. Herein, we construct ZrO2-BCN hetero-catalyst with tunable Zr-B-N interfacial structure for efficiently improving selectivity of the NRR. The asymmetric electron acceptance and back-donation capacity of the empty orbitals of Zr and B favors the activation of the N≡N triple bond during the NRR. The optimal ZrO2-BCN catalyst exhibits excellent NRR performance with a high ammonia yield of 17.8 μg mg-1cat. h−1 at −0.65 V vs. reversible hydrogen electrode (RHE) and a faradaic efficiency of 23.1 % at −0.45 V vs. RHE in 0.1 M HCl electrolyte, surpassing most previous reports. In-situ electrochemical attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy demonstrates the effect of the Zr-B-N interface on activating N2. This study paves a new way for hetero-interface catalyst design that would accelerate the implementation of NRR technology.

Strategies to achieve effective nitrogen activation

AbstractAmmonia serves as a crucial chemical raw material and hydrogen energy carrier. Aqueous electrocatalytic nitrogen reduction reaction (NRR), powered by renewable energy, has attracted tremendous interest during the past few years. Although some achievements have been revealed in aqueous NRR, significant challenges have also been identified. The activity and selectivity are fundamentally limited by nitrogen activation and competitive hydrogen evolution. This review focuses on the hurdles of nitrogen activation and delves into complementary strategies, including materials design and system optimization (reactor, electrolyte, and mediator). Then, it introduces advanced interdisciplinary technologies that have recently emerged for nitrogen activation using high‐energy physics such as plasma and triboelectrification. With a better understanding of the corresponding reaction mechanisms in the coming years, these technologies have the potential to be extended in further applications. This review provides further insight into the reaction mechanisms of selectivity and stability of different reaction systems. We then recommend a rigorous and detailed protocol for investigating NRR performance and also highlight several potential research directions in this exciting field, coupling with advanced interdisciplinary applications, in situ/operando characterizations, and theoretical calculations.

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.

Boosting Electrochemical Nitrogen Fixation via Regulating Surface Electronic Structure by CeO2 Hybridization.

Electrocatalytic nitrogen reduction reaction (NRR) paves a sustainable way to produce NH3 but suffering from the relatively low NH3 yield and poor selectivity. High-performance NRR catalysts and a deep insight into the structure-performance relationship are higher desired. Herein, a molten-salt approach is developed to synthesize tiny CeO2 nanoparticles anchored by ultra-thin MoN nanosheets as advanced catalysts for NRR. Specifically, a considerably high NH3 yield rate of 27.5µgh-1 mg-1 with 17.2% Faradaic efficiency (FE) can be achieved at -0.3V vs (RHE) under ambient conditions. Experimental and density functional theory (DFT) calculations further point out that the incorporation of MoN with CeO2 can promotes the enlargement of the electron deficient area of nitrogen vacancy site. The enlarged electron deficient area contributes to the accommodation of lone pair electrons of N2 , which dramatically improves the N2 adsorption/activation and the key intermediates (*NNH and *NH3 ) generation, thus boosting the NRR performance.

Rational design single-atom modified Zr2CO2 MXene as a promising catalyst for nitrogen reduction reaction

Renewable production of ammonia via the electrocatalytic nitrogen reduction reaction (NRR) is highly desirable. However, rational design of electrocatalysts with high promising activity under ambient conditions is a challenging subject. In this work, the stability, NRR activity and selectivity of single transition metal (TM, TM = Ti, V, Fe, Ni, Nb, Mo, Ru, and W), nonmetal B and N, and TM and N3 co-modification Zr2CO2 (named TM/Zr2CO2, B(N)/Zr2CO2, and TMN3/Zr2CO2, respectively) are investigated by density functional theory (DFT) calculations. The results revealed that single atom (both transition metal and nonmetal atoms) modification can greatly enhance the NRR catalytic activity and selectivity of original Zr2CO2, and different nonmetal doping concentration can deliver different NRR activity by adjust the interaction strength between doping atom and Zr atom. Among the studied materials, W/Zr2CO2 possesses the highest NRR performance via the distal pathway with the NRR overpotential (ηNRR) of 0.14 V, B/Zr2CO2 possesses the highest NRR performance (ηNRR = 0.26 V) and selectivity via the enzymatic pathway, and for the co-doped systems, RuN3/Zr2CO2 delivers the highest NRR activity with the corresponding ηNRR of 0.54 V. The crystal orbital Hamilton population (COHP), density of states, charge transfers, and work function (Φ) results indicated that the TM and nonmetal atoms can adjust the electronic properties of the Zr2CO2 surface to break the inertness of N2 and form the key intermediate *NNH or *N-*NH, and therefore enhance their NRR activity. The ab initio molecular dynamics (AIMD) simulation results suggested that the structures of the modified Zr2CO2 are dynamically stable at reaction temperature. These results indicated that the proposed surface modifications by W and nonmetal B are the effective approaches for achieving promising NRR electrocatalysts for N2 fixation.

Fabrication of High Surface Area Fe/Fe3 O4 with Enhanced Performance for Electrocatalytic Nitrogen Reduction Reaction.

The development of high-efficient and large-scale non-precious electrocatalysts to improve sluggish reaction kinetics plays a key role in enhancing electrocatalytic nitrogen reduction reaction (NRR) for ammonia production under mild condition. Herein, Fe3 O4 and Fe supported by porous carbon (denoted as Fe/Fe3 O4 /PC-800) composite with a high specific surface area of 1004.1 m2 g-1 was prepared via a simple template method. On one hand, the high surface area of Fe/Fe3 O4 /PC-800 provides a large area to enhance N2 adsorption and promote more protons and electrons to accelerate the reaction, thereby greatly improving the dynamics. On the other hand, mesoporous Fe/Fe3 O4 /PC-800 provides high electrochemically active surface area for promoting the occurrence of catalytic kinetics. As a result, Fe/Fe3 O4 /PC-800 exhibited significantly enhanced NRR performance with an ammonia yield of 31.15 μg h-1 mg-1 cat. and faraday efficiency of 22.26 % at -0.1 V vs. reversible hydrogen electrode (RHE). This study is expected to provide a new strategy for the synthesis of catalysts with large specific area and pave the way for the foundational research in NRR.

Heterogeneous N-heterocyclic carbenes supported single-atom catalysts for nitrogen fixation: A combined density functional theory and machine learning study

Electrocatalytic nitrogen reduction reaction (NRR) has emerged as a sustainable and eco-friendly alternative for ammonia production at ambient conditions. Exploring highly efficient and selective electrocatalysts for NRR continues to gain significant attention, but remains a challenge. In this work, we conducted a series of single-atom catalysts (SACs) by embedding 29 kinds of transition metal (TM) atoms on the two-dimensional heterogeneous N-heterocyclic carbene, and systematically investigated their catalytic performance for NRR using density functional theory, high-throughput screening, and machine learning. Two promising candidates (TM = Mn and Ta) with high catalytic activity and selectivity were identified, with limiting potentials of - 0.51 and - 0.53 V, respectively. Moreover, considering solvation effects, the limiting potential for Mn was further reduced to -0.43 V. Machinelearning(ML)analysis revealedthat the adsorption energy of N2 emerged as an efficient descriptor for NRR activity, and transition metal atomic Mendeleev number (Nm), the molar volume of TM atoms (Vm) and the 1st ionization energy of TM atoms (Im) were intrinsic to the difference in NRR performance of these SACs. Our findings demonstrate a novel class of efficient SACs based on heterogeneous N-heterocyclic carbene, offering valuable insights for further design of NRR electrocatalysts with exceptional catalytic performance.

Theoretical screening of single-atom electrocatalysts of MXene-supported 3d-metals for efficient nitrogen reduction

Single-atom catalysts (SACs) with metal atoms embedded in MXenes are potentially low-cost, highly efficient, and environment-friendly electrocatalysts for ammonia production due to their high stability, unique electronic structure, and the highest atom utilization. Here, density functional theory calculations are carried out to systematically investigate the geometries, stability, electronic properties of SACs with the 3d-transition metal M (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn) atoms embedded in the Ti defect sites of Ti2CO2 (denoted as M1@Ti2CO2). A highly stable V1@Ti2CO2 catalyst has been found to show excellent catalytic performance for N2 reduction reaction to produce NH3 after screening the 3d transition metals. The results show that V1@Ti2CO2 can not only strongly adsorb N2, but also exhibits an excellent Nitrogen reduction reaction (NRR) catalytic activity with a limiting potential of only −0.20 V and a high ability to suppress the competing hydrogen evolution reaction. The excellent NRR catalytic activity of V1@Ti2CO2 is attributed to the strong covalent metal-support interaction that leads to superb N2 adsorption ability of V atom. Furthermore, the embedded V single atoms facilitate electron transfer, thus improving the catalytic performance for NRR. These results demonstrate that V1@Ti2CO2 is a potentially promising 2D material for building robust electrocatalyst for NRR.

Tuning electrocatalytic nitrogen reduction on supported nickel cluster via substrate phase engineering

Metal clusters supported on the substrate is promising nitrogen reduction reaction (NRR) electrocatalysts due to their diversity and tunable sizes. However, how to rationally select clusters depending on substrates to promote NRR performance is not elucidated yet. To address this problem, we systematically investigate the NRR activity of Nin (n = 4, 13) clusters anchored on H and T′-phases WTe2 substrates, which offer ‘uniform’ and ‘nonuniform’ surfaces, respectively. Based on density functional theory calculations, we find that Ni4@H-WTe2 exhibits the highest NRR activity with an ultralow overpotential of 0.24 V, which is superior to that of Ni13@H-WTe2. While for the T′ phase WTe2, a larger cluster Ni13@T′-WTe2 is preferred. These differences arise from the distorted interaction between clusters and H and T′-WTe2 surfaces. The ‘uniform surface’ possessing one type of Te atom tends to deform small clusters severely, while the ‘nonuniform surface’ offers a buckling surface that deforms large Ni13 sufficiently. With the phases engineered deformation of Nin, the NRR performance is modulated. Our work highlights a strategy to design efficient NRR electrocatalysts via matching substrate phase and cluster size.

Machine Learning Design of Single-Atom Catalysts for Nitrogen Fixation.

First-principles calculations have been combined with machine learning in the design of transition-metal single-atom catalysts. Readily available descriptors are selected to describe the nitrogen activation capability of metals and coordinating atoms. Thus, a series of V/Nb/Ta-Nx single-atom catalysts are screened out as promising structures upon considering the stability, activity, and selectivity investigated computationally. Furthermore, by using the gradient boosting regression algorithm, an accurate prediction of the hydrogenation barriers for the nitrogen reduction reaction (NRR) is achievable, with a root-mean-squared error of 0.07 eV. The integration of high-throughput computation and machine learning constitutes a powerful strategy for the acceleration of catalyst design. This approach facilitates the rapid and accurate prediction of the NRR performance of more than 1000 single-atom catalyst structures. Moreover, the current work provides further insights by elaborately correlating the structure and performance, which may be instructive for both the design and application of vanadium-group catalysts.

Multi-site intermetallic Ni3Mo effectively boosts selective ammonia synthesis

Carbon-free electrocatalytic nitrogen reduction reaction (NRR) offers an environmentally sustainable alternative to the current Haber-Bosch process in the industry. However, this process is still limited by the scaling relations and the competitive hydrogen evolution reaction (HER). Using the density functional theory, we theoretically present a strategy for separating the active sites of the N2 activation and the hydrogenation of NHz (z = 1, 2) intermediates on the Ni3Mo surface, which subtly optimized the adsorption of intermediates and bypasses the scaling relations, achieving efficient NRR with an ultralow limiting potential of − 0.19 V. Besides, the Ni3Mo greatly protects the active centers of NRR from competitive H adsorption and retard the undesired HER, enabling highly selective NH3 synthesis. The above theoretical designs are supported by proof-of-concept experimental results, where Ni3Mo exhibits excellent NRR performance with the NH3 yield rate of 17.35 ± 0.3 μg h−1 cm−2 at − 0.35 V.