Electrochemical Nitrogen Reduction Research Articles

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.

Insight into Fluoride Additives to Enhance Ammonia Production from Lithium-Mediated Electrochemical Nitrogen Reduction Reaction.

Demands for green ammonia production increase due to its application as a proton carrier, and recent achievements in electrochemical Li-mediated nitrogen reduction reactions (Li-NRRs) show promising reliability. Here, it is demonstrated that F-containing additives in the electrolyte improve ammonia production by modulating the solid electrolyte interphase (SEI). It is suggested that the anionic additives with low lowest unoccupied molecular orbital levels enhance efficiency by contributing to the formation of a conductive SEI incorporated with LiF. Specifically, as little as 0.3wt.% of BF4 - additive to the electrolyte, the Faradaic efficiency (FE) for ammonia production is enhanced by over 15% compared to an additive-free electrolyte, achieving a high yield of 161 ± 3nmol s-1 cm-2. The BF4 - additive exhibits advantages, with decreased overpotential and improved FE, compared to its use as the bulk electrolyte. The observation of the Li3N upper layer implies that active Li-NRR catalytic cycles are occurring on the outermost SEI, and density functional theory simulations propose that an SEI incorporated with LiF facilitates energy profiles for the protonation by adjusting the binding energies of the intermediates compared to bare copper. This study unlocks the potential of additives and offers insights into the SEIs for efficient Li-NRRs.

Effective Electrochemical Nitrogen Reduction through π Back-donation Process in Mn3+ of Mn-doped g-C3N4

Effective Electrochemical Nitrogen Reduction through π Back-donation Process in Mn3+ of Mn-doped g-C3N4

Effective Electrochemical Nitrogen Reduction through π Back-donation Process in Mn3+ of Mn-doped g-C3N4

Effective Electrochemical Nitrogen Reduction through π Back-donation Process in Mn3+ of Mn-doped g-C3N4

Exploring Dynamics in Single Atom Catalyst Research: A Comprehensive DFT-kMC Study of Nitrogen Reduction Reaction with Focus on TM Aggregation

Transition metal (TM)-based single atom catalysts (SACs) have emerged as a promising solution for the electrochemical nitrogen reduction reaction (NRR) due to their unique d-orbitals and low coordination, which facilitate efficient N2 bond weakening and increased reactivity. However, conventional theoretical approaches fail to incorporate the kinetics of TM aggregation, a crucial factor in SAC systems that affects catalyst stability and activity over time. Addressing this, we combined kinetic evaluations with thermodynamic and electronic analyses on 216 SAC candidates, using boron carbon nitride (BCN) as a substrate. Our findings revealed that Cr anchored to BCN exhibits a high turnover frequency (3.1 × 10−6 s-1) under mild conditions (300K, 1bar), attributed to its minimal TM aggregation over time. This research not only fills the gap in kinetic research within the SAC field but also proposes a SAC candidate distinguished by its superior kinetics, thermodynamic, and electronic properties.

Transition metal single-atom supported on W2N3 as efficient electrocatalysts for the nitrogen reduction reaction: A DFT study

The problems of poor Faraday efficiency and high overpotential usually limit electrochemical nitrogen reduction (NRR) catalysts. In this paper, 28 different transition metal single-atoms (TM-SAs) supported on W2N3 (TM@W2N3) were designed by density functional theory (DFT) for catalytic N2 reduction. The stability, N2 activation capacity, selectivity and NRR mechanism of TM@W2N3 were analyzed. Following the screening process, only 9 TM@W2N3 (TM=Sc, Ti, V, Co, Cu, Y, Mo, Ag, W) structures were identified as exhibiting high stability, strong activation capacity and high NRR selectivity. And then N2 activation mechanism of V@W2N3, Mo@W2N3 and W@W2N3, as well as the Gibbs free energies of its four NRR reaction pathways were further discussed. The overpotentials (η) of Mo@W2N3 and V@W2N3 to NRR are 0.129 V and 0.470 V, respectively. The overpotential (η) of W@W2N3 is the lowest at 0.059 V, while its catalytic activity is the highest. V@W2N3 and W@W2N3 are more likely to follow the distal pathway for NRR, while Mo@W2N3 is more likely to follow the enzymatic pathway. This study offers some theoretical foundation and reference for the design of new and efficient electrocatalytic NRR catalysts.

Heterostructure design on honeycomb borophene/Mo2C: A novel strategy for nitrogen fixation

In terms of its ecological and sustainable nature, electrochemical nitrogen reduction reaction (e-NRR) is widely recognized as the ideal solution to replace conventional ammonia production techniques. Unfortunately, poor Faraday efficiency (FE) with lower e-NRR selectivity limits its large-scale application. Previous studies have identified Mo2C as an optimistic electrocatalyst for e-NRR, exhibiting great ammonia yield. However, Mo2C suffers from Mo leaching during the electrochemical reaction process, thus reducing the stability of the catalyst. Herein, we propose a new electrocatalyst based on first-principles calculations: HB/α-Mo2C. This heterostructure is composed of Mo2C covered with a layer of Honeycomb Borophene (HB). The HB layer serves two purposes: to ensure the stability of the catalyst and improve the FE of the reaction. Our findings demonstrate the HB/α-Mo2C performs the highest catalytic activity via a mixed mechanism with a limiting potential as low as -0.16 V, which was determined to be caused by the transfer of electrons from the active sites of the boron atoms to the adsorbate. Furthermore, the limiting potential of HER, a competing reaction, was found to be as high as −0.56 V, confirming the high efficiency of HB/α-Mo2C towards e-NRR. This present work contributes to the development of new strategies for e-NRR catalyst design.

Tailored Metal-Porphyrin Based Molecular Electrocatalysts for Enhanced Artificial Nitrogen Fixation to Green Ammonia.

Electrochemical nitrogen reduction (E-NRR) is one of the most promising approaches to generate green NH3. However, scarce ammonia yields and Faradaic efficiencies (FE) still limit their use on a large scale. Thus, efforts are focusing on different E-NRR catalyst structures and formulations. Among present strategies, molecular electrocatalysts such as metal-porphyrins emerge as an encouraging option due to their planar structures which favor the interaction involving the metal center, responsible for adsorption and activation of nitrogen. Nevertheless, the high hydrophobicity of porphyrins limits the aqueous electrolyte-catalyst interaction lowering yields. This work introduces a new class of metal-porphyrin based catalysts, bearing hydrophilic tris(ethyleneglycol) monomethyl ether chains (metal = Cu(II) and CoII)). Experimental results show that the presence of hydrophilic chains significantly increases ammonia yields and FE, supporting the relevance of fruitful catalyst-electrolyte interactions. This study also investigates the use of hydrophobic branched alkyl chains for comparison, resulting in similar performances with respect to the unsubstituted metal-porphyrin, taken as a reference, further confirming that the appropriate design of electrocatalysts carrying peripheral hydrophilic substituents is able to improve device performances in the generation of green ammonia.

Enhancement of Electrochemical Nitrogen Reduction Activity and Suppression of Hydrogen Evolution Reaction for Transition Metal Oxide Catalysts: The Role of Proton Intercalation and Heteroatom Doping

Enhancement of Electrochemical Nitrogen Reduction Activity and Suppression of Hydrogen Evolution Reaction for Transition Metal Oxide Catalysts: The Role of Proton Intercalation and Heteroatom Doping

High-Throughput screening of metal nitrides for electrochemical nitrogen reduction

Metal nitrides have garnered considerable attention in the context of nitrogen reduction reactions (NRR) due to their rich lattice nitrogen and abundant nitrogen vacancies to activate N2. However, the identification of suitable metal nitrides with superior stability, activity, and selectivity (vs. hydrogen evolution reaction, HER) for electrochemical NRR under rigorous isotope labeling experiments remains a perplexing challenge in experiments. In this study, we implemented a systematic screening protocol to assess the electrochemical stability and efficiency of various metal nitrides for NRR by high-throughput density functional theory calculations, aiming to search out promising metal nitride catalysts. Through a set of predetermined criteria, a subset of 6 candidates emerges as the most promising metal nitrides for NRR from a pool of 668 metal nitrides sourced from the Materials Project Database, all of which catalyze NRR following the Mars-van Krevelen pathway. Importantly, based on the analysis of these candidates, the unique structural property (i.e., four(or three)-coordinate lattice nitrogen) and energy descriptor (i.e., the formation energy of the lattice nitrogen vacancy is around 2.1 eV) of potential metal nitrides for electrochemical NRR were extracted, which could be used as the direction to rationally design metal nitride catalyst. This research not only serves as a valuable guide for experimental investigations into potential metal nitrides for NRR, but also provides an efficient method for high-throughput screening of potential catalysts for other electrochemical reactions.

Electrochemical Nitrogen Reduction to Ammonia at Ambient Condition on the (111) Facets of Transition Metal Carbonitrides.

We conducted Density Functional Theory calculations to investigate a class of materials with the goal of enabling nitrogen activation and electrochemical ammonia production under ambient conditions. The source of protons at the anode could originate from either water splitting or H2, but our specific focus was on the cathode reaction, where nitrogen is reduced into ammonia. We examined the conventional associative mechanism, dissociative mechanism, and Mars-van Krevelen mechanism on the (111) facets of the NaCl-type structure found in early transition metal carbonitrides, including Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, Sc, Y, and W. We explored the catalytic activity by calculating the free energy of all intermediates along the reaction pathway and constructing free energy diagrams to identify the steps that determine the reaction's feasibility. Additionally, we closely examined the potential for catalyst poisoning within the electrochemical environment, considering the bias required to drive the reaction. Furthermore, we assessed the likelihood of catalyst decomposition and the potential for catalyst regeneration among the most intriguing carbonitrides. Our findings revealed that the only carbonitride catalyst considered here exhibiting both activity and stability, capable of self-regeneration and nitrogen-to-ammonia activation, is NbCN with a low potential-determining step energy of 0.58 eV. This material can facilitate ammonia formation via a mixed associative-MvK mechanism. In contrast, other carbonitrides of this crystallographic orientation are likely to undergo decomposition, reverting to their parent metals under operational conditions.

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.

Ambient N[tbnd]N bond weakening hydrogenation by utilizing the highly defective Cu3BiS3/MnO2 electrocatalyst for ammonia yield above 3 mg/h.cm2: The N2-nano dipole interaction micromechanism

This study introduces a novel Cu3BiS3/MnO2 composite catalyst for the electrochemical nitrogen reduction reaction (eNRR) to address challenges in sustainable ammonia production, aiming to replace the energy-intensive Haber-Bosch process. The ternary Cu3BiS3/MnO2 catalyst exhibited impressive results, achieving a high ammonia yield rate of 3604 µg h−1cm−2 and a significant Faradaic efficiency of 31.4 % at −0.75 V vs. RHE in a 0.5 M Na2SO4 solution, while only 446 µg h−1cm−2 from binary metal CuMn(2:3). This success was attributed to abundant cation and anion defects with multiple valence charges in the Cu3-xBiS3/MnO2-y catalyst, created by introducing the third metal, Bi, into the binary CuMn system. These defects served as trapping centers for dynamic nitrogen molecule activation and facilitated charge transport, enhancing the eNRR process. This study underscores the potential of highly defective Cu3-xBiS3/MnO2-y as an efficient and sustainable catalyst for electrochemical nitrogen fixation, offering a greener approach to ammonia production.

Membrane/electrolyte interplay on ammonia motion inside a flow-cell for electrochemical nitrogen and nitrate reduction

Electrochemical ammonia production from molecular nitrogen and nitrate reduction reactions at ambient conditions has gained a lot of attention in recent years, making this topic more and more appealing. The race towards good and quick results in terms of Faradaic efficiency and productivity is not always focused on the possible source of ammonia contamination. In particular, Nafion membrane is the most commonly used in this field as cell separator, discarding the possible known disadvantages coming from ammonium ions absorption and release. The wettable microporous Celgard membrane has been proposed as a substitute for Nafion membranes, despite the separation mechanism, in this case, is only dimension-driven, so it does not assure ammonium ions retention. This paper reveals that the mechanism of ammonium ions absorption and release by Nafion 117 is strongly related to the cations present in the electrolyte and to a lesser extent by its pH value. On the other hand, Celgard membrane does not show any relevant ammonium ions absorption. Moreover, the different trend of ammonium ions motion from catholyte to anolyte solution inside a flow-cell reactor shows that none of the membranes is able to avoid ammonium ions crossover and that there is a correlation between the applied potential and the motion trend. Electrochemical nitrogen and nitrate reduction tests confirm how Nafion membrane can have a big impact on the final result of ammonium ions production, especially when dealing with low production quantities, leading to mistakes in the real quantity of ammonium ions coming from the reduction reaction.

Synthesis of Rhenium-Doped Copper Twin Boundary for High-Turnover-Frequency Electrochemical Nitrogen Reduction.

The precise design and synthesis of active sites to improve catalyst's performance has emerged as a promising tactic for electrochemistry. However, it is challenging to combine different types of active sites and manipulate them simultaneously at atomic resolution. Here, we present a strategy to synthesize Re atom-doped Cu twin boundaries (TBs), through pulsed electrodeposition and boundary segregation. The Re-doped Cu TBs demonstrate a highly efficient nitrogen reduction reaction (NRR) performance. Re-doped Cu TBs showed a turnover frequency of ∼5889 s-1, ∼800 times higher than the pure Cu TB active centers (∼7 s-1). In addition to the "acceptance-donation" activation of N2 molecules, theoretical calculations also reveal that the Re-Re dimer on TB can boost the NRR and impede the hydrogen evolution reaction synchronously, rendering Re-doped Cu TB catalysts with high NRR activity and selectivity.

Mechanistic Studies of Stimulus-Response Integrated Catalysis of Single-Atom Alloys under Electric Fields for Electrochemical Nitrogen Reduction.

The present work introduces a novel catalytic strategy to promote the nitrogen reduction reaction (NRR) by employing a cooperative Cu-based single-atom alloy (SAA) and oriented external electric fields (OEEFs) as catalysts. The field strength (F)-dependent reaction pathways are investigated by means of first-principles calculations. Different dipole-induced responses of intermediates to electric fields break the original scaling relationships and effectively tune not only the activity but also the product selectivity of the NRR. When the most active Os1Cu SAA is taken as an example, in the absence of an OEEF, the overpotential (η) of the NRR is 0.62 V, which is even larger than that of the competitive hydrogen evolution reaction (HER). A negative field not only reduces η but switches the preference to the NRR over the HER. In particular, η at F = -1.14 V/Å reaches the bottom of 0.18 V, which is 70% lower than that in the field-free state.

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.

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.

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.