Nitrogen Reduction Reaction Electrocatalysts Research Articles

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.

Mapping the Binary Covalent Alloy Space to Pursue Superior Nitrogen Reduction Reaction Catalysts

AbstractThe electrochemical nitrogen reduction reaction (NRR) has the potential to decarbonize industrial ammonia production. However, NRR has poor activity and selectivity versus the competing hydrogen evolution reaction for catalysts that adhere to scaling relations. Overcoming the limitations imposed by scaling relations requires more complex catalyst materials, however, evaluating materials beyond simple metal systems is a large combinatorial problem that requires an improved understanding of the electrocatalyst surface to rationally guide the discovery of superior catalysts. The study uses grand canonical density functional theory to uncover NRR trends on a large and disparate set of binary covalent alloys (BCA) with variable compositions and active‐site geometries. The studied BCAs generally follow scaling relations, albeit with larger variance and several systems that significantly break scaling. BCAs with early‐ to mid‐transition metals tend to lie near the volcano peak and activate the N2 triple bond via a side‐on binding configuration. Trends in the BCA space cannot be readily predicted using simple electronic descriptors, which is ascribed to the large geometric variability of the BCA surfaces. It is anticipated that these findings will provide a foundation for the rational design of superior NRR electrocatalysts with increasing material complexity.

Cooperation between single atom catalyst and support to promote nitrogen electroreduction to ammonia: A theoretical insight

The co-catalysis between single atom catalyst (SAC) and its support has recently emerged as a promising strategy to synergistically boost the catalytic activity of some complex electrochemical reactions, encompassing multiple intermediates and pathways. Herein, we utilized defective BC3 monolayer-supported SACs as a prototype to investigate the cooperative effects of SACs and their support on the catalytic performance of the nitrogen reduction reaction (NRR) for ammonia (NH3) production. The results showed that these SACs can be firmly stabilized on these defective BC3 supports with high stability against aggregation. Furthermore, co-activation of the inert N2 reactant was observed in certain embedded SACs and their neighboring B atoms on the certain BC3 sheets due to the noticeable charge transfer and significant N–N bond elongation. Our high-throughput screening revealed that the Mo/DVCC and W/DVCC exhibit superior NRR catalytic performance, characterized by a low limiting potential of −0.33 and −0.43V, respectively, which can be further increased under acid conditions based on the constant potential method. Moreover, varying NRR catalytic activities can be attributed to the differences in the valence state of active sites. Remarkably, further microkinetic modeling analysis displayed that the turnover frequency of N2–to–NH3 conversion on Mo/DVCC is as large as 1.20 × 10−3 s−1 site−1 at 700 K and 100 bar, thus guaranteeing its ultra-fast reaction rate. Our results not only suggest promising advanced electrocatalysts for NRR, but also offered an effective avenue to regulate the electrocatalytic performance via the co-catalytic metal–support interactions.

Recent progress in single atomic catalysts for electrochemical N2 fixation

Ammonia (NH3), as an important chemical product, is industrially produced using the traditional energy-intensive Haber-Bosch method at high temperature and pressure. Electrochemical nitrogen reduction reaction (NRR) to synthesize NH3 at ambient conditions has been considered as a promising candidate for replacing Haber-Bosch process. However, major obstacles, such as poor catalytic activity and selectivity and extensive competitive hydrogen evolution reaction, remain in NRR, which urgently need to be addressed. Single atom electrocatalysts (SACs) have attracted wide attention in view of their nearly 100% atomic utilization and outstanding catalytic performance. In this review, recent theoretical and experimental advances on novel atomically dispersed electrocatalysts for NRR are summarized and highlighted. We start with the fundamental reaction mechanism of NRR. Then, different preparation methods and the strategies of boosting catalytic performance of SACs from the aspects of coordination environment, coordination number, metal-support interaction and spatial microenvironment regulation are presented and analyzed in detail. Following this, the extensive applications of SACs in terms of noble metal based-SACs and transition metal-based SACs in NRR are discussed. Finally, we provide a perspective of the challenges of SACs for NRR, aiming to guide the rational design of advanced NRR catalysts.

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.

Metal organic framework derived vanadium nitride anchored on nitrogen-doped carbon sheet as an efficient electrocatalyst for nitrogen reduction reaction

A metal organic framework-assisted annealing and nitriding method is employed to prepare a heterostructured nanocomposite incorporating VN nanoparticles with nitrogen-doped carbonaceous sheets as an earth-abundant catalyst of electrochemical nitrogen reduction reaction (ENRR). In this as-synthesized nanocomposite (VN@NC), nanosized VN particles with diameter of ∼50 nm are in situ fabricated and are anchored on the metal organic frameworks-derived nitrogen-doped carbon sheets. Benefitting from its structural merits such as increased surface areas, abundant active sites, improved electroconductivity as well as the synergism between the components, the composite electrocatalyst exhibits a greatly enhanced catalytic activity for ENRR in comparison with the commercial bulk VN. The as-prepared VN@NC can catalyze nitrogen to yield ammonia with a rate up to 17.31 μg mg−1cat h−1 at a low potential (-0.2 V vs RHE) in 0.1 M hydrochloric acid solution under mild conditions, delivering a Faradaic efficiency of 10.99 % simultaneously. Furthermore, VN@NC also demonstrates a favourable selectivity without generation of hydrazine byproduct and a stable electrocatalytic performance.

Computational screening of transition metal anchored C9N10 as the highly active and selective electrocatalysts for NH3 synthesis

Electrochemical nitrogen reduction reaction (NRR) is a very prospective approach for generating green and sustainable NH3 under mild conditions. However, the development of NRR electrocatalysts with high performance remains a huge hurdle in the field of energy conversion today. Herein, by means of first-principles calculations, we employed a hierarchical screening strategy of structural stability, catalytic activity, and selectivity to systematically investigate the potentials of a series of transition metal atoms anchored on g-C9N10 (TM@C9N10) as the electrocatalysts for NRR. Particularly, we proposed the multiple-level descriptors (φ and ICOHP), realizing the preliminary prescreening of numerous candidates. The results reveal that V@C9N10 and W@C9N10 stand out from all candidates with the significantly low limiting potentials of −0.17 V and −0.26 V, respectively. Meanwhile, they can efficiently suppress the competing hydrogen evolution reaction. Such the outstanding activity can be attributed to the donation-feedback process between the d-electrons of V and W atoms and the anti-orbitals of *N2, as well as the efficient charge transfer in hydrogenation steps. Our work not only broadens the theoretical foundation for the rational design of highly efficient SACs, but also provides an attempt to develop the NRR electrocatalysts with high activity and selectivity.

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.

High throughput screening for electrocatalysts for nitrogen reduction reaction using metal-doped bilayer borophene: A combined approach of DFT and machine learning

NH3 plays an important role in industrial production, while it is still a challenge to develop a promising catalyst for NH3 synthesis. In particular, the metal borides have attracted much attention because of their excellent catalyst performances towards N2. In this paper, we have theoretically studied the N2 reduction reaction (NRR) by employing the transition metal (TM = Co, Cr, Cu, Fe, Mn, Mo, Ni, Sc, Ti, V, Zn, Nb, Pd, Rh, Ru or Zr) doped bilayer borophene (BB). After the screening, it is found that Sc-doped BB (Sc@BB) exhibits excellent NRR performance with the limiting potential of -0.43 V, and the hydrogen evolution reaction (HER) could be well suppressed. The limiting potential could be further improved into -0.40 V by applying 0.30 % uniaxial strains to the system. In addition, the machine learning method was employed to understand the catalytic mechanism, the results revealed that the NRR performance of TM@BB is strongly related to the inherent properties of TM atoms, such as the d-electron number, electronegativity, first ionization energy, atomic radius, and atomic number. Therefore, our paper not only proposed a promising electrocatalyst for NRR, but also further extend the application of transition metal-boron based two dimensional materials in NRR.

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.

Nitrogen-vacancy-rich molybdenum nitride nanosheets as highly efficient electrocatalysts for nitrogen reduction reaction.

The development of low-cost earth-abundant electrocatalysts to produce ammonia (NH3) with high efficiency for the nitrogen (N2) reduction reaction (NRR) remains challenging. Herein, we propose the development of highly efficient ultrathin nitrogen-vacancy-rich molybdenum nitride nanosheets (MoN-NV) for NRR using basic electrolytes under ambient conditions. In 0.1 M KOH, this catalyst attained a high faradaic efficiency (FE) of ∼14% with an NH3 yield of 22.5 μg h-1 mg-1cat at -0.3 V vs. a reversible hydrogen electrode under ambient conditions. The characterization results and electrochemical studies disclosed that nitrogen vacancies in the MoN-NV nanosheets played a critical role in the enhanced electrocatalytic activity for NRR. Furthermore, the recycling tests confirmed the stability of the catalyst during NRR electrolysis.

Novel Mn–Bi–S hybrid mesoporous nanosheets as an efficient electrocatalyst for nitrogen reduction reaction

A non-precious and efficient catalyst was developed to enhance N2 adsorption by electronic interaction and ideal synergistic effect to improve the NRR activity.

Nitrogen-vacancy-modulated efficient ammonia desorption over 3d TM-anchored BC3N2 monolayer.

Nitrogen fixation using electrochemical methods on the surface of single-atom catalysts (SACs) provides a highly feasible strategy for green and low-energy-consumption ammonia (NH3) production. Herein, using density functional theory (DFT) calculations, we explored in detail the potential of monolayer BC3N2 SACs supported with 3d transition metal (TM) atoms (TM@BC3N2) to facilitate nitrogen reduction. The results revealed that the TM@BC3N2 systems exhibited remarkable catalytic activity in the nitrogen-reduction reaction (NRR). The fine NRR activity was related to the just-right bonding/antibonding orbital interactions between the 2π* of N2 and the d orbitals of the TM ions. The nitrogen-adsorption configurations were found to have different activation mechanisms. In addition, the effects of convectively formed convex nitrogen defects (VN) on the interaction between N2 and VN-TM@BC3N2 and the NRR process of VN-TM@BC3N2 were studied, and it was found that VN could fine-tune the reaction efficiency of the eNRR because after N atom dissociation to form VN, the interaction of TM-C3 was enhanced, and the activation of nitrogen and adsorption of NH3 by the TM-active centers were weakened. The present study can be used as a motivation for further experimental and theoretical research of 2D monolayers as NRR electrocatalysts.

Vanadium doped B5N3 and B7N5 monolayer as single atom catalyst for nitrogen reduction reaction – a first-principles study

The Haber-Bosch process, commonly used for ammonia synthesis, can be replaced by the electrochemical nitrogen reduction reaction (NRR), which offers a more environmentally conscious and sustainable approach. However, developing electrocatalysts with low potential, high selectivity, and fast reaction kinetics remains challenging. In the current work, we have theoretically calculated the potential of V@B5N3 and V@B7N5 (V = Vanadium) material which serves as an electrocatalyst for NRR using density functional theory (DFT) simulations. Our results reveal that the monolayer of V@B7N5 exhibits remarkable catalytic activity and effectively suppresses the hydrogen evolution reaction at an overpotential of 0.13 V. Furthermore, the potential-determining step involving the conversion of *N2-*N2H demonstrates a favourable energy barrier, indicating facile kinetics. The V@B7N5 monolayer shows promising selectivity, with an anticipated ammonia production efficiency of 99%. These findings open avenues for employing single-atom catalysts under ambient conditions to synthesise ammonia, offering a potential solution for sustainable ammonia production.

Metal dimers anchored on boron nitride monolayers with boron divacancy as an effective nitrogen fixation electrocatalyst: A computational study

As a fascinating approach for sustainable NH3 production, the electrocatalytic nitrogen reduction reaction (NRR) is still hampered by low Faraday efficiency due to high energy required for inert N N triple bond activation and competitive hydrogen evolution reaction (HER). In this paper, we propose a method to increase the NRR catalytic activity by constructing bimetallic sites on boron nitride (BN) monolayer. In order to approach the efficient NRR region, the metal-based linear-scaling relationship between adsorbed intermediates is broken by synergistic effects between the bimetallic active sites. TiRu-BN was identified as an effective NRR electrocatalyst with low limiting potential (−0.28 V) and superior selectivity after systematic evaluation of the thermal stability, electrochemical stability, activity, and selectivity of 36 homo- and heteronuclear diatomic catalyst candidates. Analysis on the origin of high performance shows the screened high-performance diatomic catalyst is located in the region of moderate linear-scaling relationship breaking of intermediates. Breaking the linear scale relationship to the most significant extend does not imply the most improved catalytic activity. This work not only provides experimentally synthesizable exceptional NRR electrocatalyst candidates, but also provides theoretical guidance for practical application of efficient NRR electrocatalyst.

DFT Simulations on the Nitrogen Reduction Reaction Activity of Transition Metal Nitride and Oxynitride

Transition metal nitride (TMN) is a promising material towards the energy related applications including catalysis and energy storage.1 The sluggish nitrogen reduction reaction (NRR) due to the high energy input to activate N2 remains a significant challenge for NRR electrocatalysts. The surface N of TMN can be a solution to this with initial N vacancy formation via hydrogenation steps and ammonia formation. In addition, with a small amount of surface oxygen present in the catalyst surface, the resulting oxynitride seems very interesting and active towards NRR.2 But the mechanism behind this is not yet understood.In this study, we first focused on the modelling of the structure of metal nitride (ZrN) and oxynitride (ZrOxNy/ZrN) surfaces. The structure of oxynitride is obtained by running molecular dynamics (MD) calculations at both room temperature and experimental deposition temperature (90°C and 750°C). NRR reaction is then studied via the Mars-Van Krevelen (MvK) mechanism with introducing surface N vacancy and subsequent N2 adsorption and N filling. With computing the reaction energy and activation barriers of key reaction steps on both ZrN and ZrOxNy/ZrN, we can find a clue on how surface N of TMN helps to activate N2 and the role of small amount of surface oxygen on activating N2. To study the origin of small amount of oxygen, reaction energies and full reaction pathway along the deposition process are computed and plotted. Finally, dopant effect will be modeled with transition metal dopants (e.g. Cu and Hf) at surface region to study any localized electronic effect on NRR.These results can be useful to design and deposit ZrN acting as effective NRR electrocatalysts.

An In situ Proton Filter Covalent Organic Framework Catalyst for Highly Efficient Aqueous Electrochemical Ammonia Production

AbstractThe electrocatalytic nitrogen reduction reaction (NRR) driven by renewable electricity provides a green synthesis route for ammonia (NH3) production under ambient conditions but suffers from a low conversion yield and poor Faradaic efficiency (F.E.) because of strong competition from hydrogen evolution reaction (HER) and the poor solubility of N2 in aqueous systems. Herein, an in situ proton filter covalent organic framework catalyst (Ru‐Tta‐Dfp) is reported with inherent Ruthenium (Ru) sites where the framework controls reactant diffusion by suppressing proton supply and enhancing N2 flux, causing highly selective and efficient catalysis. The smart catalyst design results in a remarkable ammonia production yield rate of 2.03 mg h−1 mgcat−1 with an excellent F.E. of ≈52.9%. The findings are further endorsed with the help of molecular dynamics simulations and control COF systems without in situ proton filter feasibility. The results point to a paradigm shift in engineering high‐performance NRR electrocatalysts for more feasible green NH3 production.

Enhancing electrocatalytic ammonia synthesis through theoretical design of cluster catalysts supported on TiO2 surface

The electrocatalytic nitrogen reduction reaction (NRR), conducted under ambient conditions, holds promise as a viable alternative to the traditional Haber-Bosch process. However, the progress in developing effective electrocatalysts for NRR is stymied by the intense competition with the hydrogen evolution reaction (HER), which leads to low rates of ammonia yield and Faradaic efficiencies. This challenge can be tackled by utilizing well-defined loaded two-dimensional TiO2 structured model catalysts. In this study, we introduce an efficient Cobalt–Nickel electrocatalyst (Co1Ni2@TiO2) based on theoretical predictions. Through a rational screening of 16 TiO2-based catalysts, we identified Co3, Co1Ni2, and Ni1Mn2@TiO2 as effective suppressors of the HER reaction. Among these, Co1Ni2@TiO2 demonstrated the lowest energy barrier for the potential-determining step, at 0.39 eV. We then experimentally synthesized Co1Ni2@TiO2. This catalyst exhibited a superior yield of 20.396 μgNH3/mgcat/h and a Faradaic efficiency of 13.327 %. This signifies a minimum of 2.9-time enhancement when compared to Co3@TiO2 and Ni3@TiO2.

A DFT Investigation of B-Doped C3 N as Single Atom Electrocatalysts for N2 -to-NH3 Conversion.

The NH3 synthesis from N2 plays an important role in the ecological cycle and industrial production. Different from industrial NH3 synthesis with high pollution and energy consumption, electrocatalytic NH3 synthesis is favored because of its environmental protection, energy saving, ambient reaction conditions and other characteristics. However, due to the low efficiency and poor reaction selectivity of the existing electrocatalysts, which can not be used actually, the development of new electrocatalysts for nitrogen reduction reaction (NRR) is particularly urgent. Herein, we designed a series of transition metal atoms anchored B-doped defective C3 N surface (TM@B2 C3 N) as single-atom catalysts. Through the screening process of N2 adsorption activation, N2 H formation and NH3 desorption, finally the excellent electrocatalysts with strong stability and high activity (Cr@B2 C3 N and Mn@B2 C3 N) were obtained. After simulating the entire pathway, it was found that the NRR process on Cr@B2 C3 N and Mn@B2 C3 N via consecutive and distal pathways with the lowest limiting potential of -0.42 and -0.52 V, which have the good ability to inhibit hydrogen evolution reaction. Finally, the electronic properties were analyzed, and the reason for their high catalytic activity was summarized. This work provides a new idea for the rational design of NRR electrocatalysts and promotes the practical application of electrocatalysts.

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.