Electrochemical Nitrogen Reduction Reaction 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.

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.

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 3604µgh-1cm-2 and a significant Faradaic efficiency of 31.4% at -0.75V vs. RHE in a 0.5M Na2SO4 solution, while only 446µgh-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.

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±4.25µgh-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.

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.

Interface Engineering-Modulated Nanoscale Bimetallic CoFe-MIL-88A In-Situ-Grown on 2D V2CTx MXene for Electrocatalytic Nitrogen Reduction.

The electrochemical nitrogen reduction reaction (eNRR) provides a sustainable green development route for the nitrogen-neutral cycle. In this work, bimetallic CoFe-MIL-88A with two active sites (Fe, Co) were immobilized on a 2D V2CTx MXene surface by in situ growth method to achieve the purpose of the control interface. A large number of heterostructures are formed between small CoFe-MIL-88A and V2CTx, which regulate the electron transfer between the catalyst interfaces. The adsorption and activation of nitrogen on the active sites were enhanced, and the NRR reaction kinetics was accelerated. CoFe-MIL-88A is tightly arranged on V2CTx, which makes CoFe-MIL-88A/V2CTx have better hydrophobicity and can significantly inhibit the hydrogen evolution reaction. The synergistic effect of multicatalytic active sites and multi-interface structure of CoFe-MIL-88A/V2CTx MXene is propitious to nitrogen efficiently and stably to convert into ammonia under environmental conditions with superior selectivity and good catalytic activity. The NH3 yield rate is 29.47 μg h-1 mgcat-1 at -0.3 V vs RHE, and the Faradaic efficiency (FE) is 28.86% at -0.1 V vs RHE. The catalytic mechanism was verified to conform to the distal pathway. This work will provide a new way to develop an MXene-based electrocatalyst for eNRR.

Synergistic multisite CuPdP nanodendrites for efficient ambient neutral electrosynthesis of ammonia from nitrate

Electrochemical nitrogen reduction reaction (NO3RR) is considered a promising alternate of the Haber–Bosch process for ammonia (NH3) synthesis, in which optimization of the catalyst composition and morphology is essential. Herein, Pd and P was simultaneously doped into Cu nanodendrites supported on Cu foam (CuPdP NDs/CF) by a one-step solvothermal reaction. The introduction of Pd atoms could improve the inert hydrogen adsorption capacity of Cu, while the presence of P atoms could effectively inhibit the competitive hydrogen evolution process. Additionally, the electron interaction between Cu, Pd and P could optimize the electronic structure of Cu and regulate the adsorption of reaction intermediates, and thus boosting the nitrate-to-ammonia capability. With the synergistic effect of multisites, the CuPdP NDs/CF showed excellent performance for NO3RR with an optimal ammonia Faradaic efficiency reaching 96.7%. This study provides an avenue for metal/nonmetal co-doping to synergistically enhance the performance of nitrate reduction to ammonia.

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.

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 Faradic 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.

Effect of Facet on Local Electron Density of Oxygen Vacancy in Catalysts for Nitrogen Electro-Reduction.

Oxygen-vacancy (Ov) engineering is an effective strategy to manipulate the electronic configuration of catalysts for electrochemical nitrogen reduction reaction (eNRR). The influence of the stable facet on the electronic configuration of Ov is widely studied, however, the effect of the reactive facet on the local electron density of Ov is unveiled. In this work, an eNRR electrode R(111)-TiO2/HGO is provided with a high proportion exposed reactive facet (111) of rutile-TiO2 (denoted as R(111)-TiO2) nanocrystals with Ov anchored in hierarchically porous graphite oxide (HGO) nanofilms. The R(111)-TiO2/HGO exhibits excellent eNRR performance with an NH3 yield rate of 20.68 µg h-1 cm-2, which is ≈20 times the control electrode with the most stable facet (110) exposed (R(110)-TiO2/HGO). The experimental data and theoretical simulations reveal that the crystal facet (111) has a positive effect on regulating the local electron density around the oxygen vacancy and the two adjacent Ti-sites, promoting the π-back-donation, minimizing the eNRR barrier, and transforming the rate determination step to *NNH→*NNHH. This work illuminates the effect of crystal facet on the performance of eNRR, and offers a novel strategy to design efficient eNRR catalysts.

Mechanistic insights into the stepwise lithium-mediated electrochemical nitrogen reduction for enhanced ammonia synthesis

The lithium-mediated electrochemical nitrogen reduction reaction (Li-NRR) is a sustainable route for green NH3 synthesis. It accelerates the N2 reduction by reacting the inert N ≡ N with active Li metal. However, the study on the mechanism of the Li-NRR process remains limited. Herein, a novel stepwise Li-NRR system is established to separately optimize the major steps of Li-NRR: lithium-ion reduction, lithium nitridation, and Li3N protonation. It is revealed that during the Solid Electrolyte Interface (SEI) decomposition, the carbon chains in organic species become shorter, and LixBFy is converted to LiF, which is similar to the continuous Li-NRR. Contrary to the continuous Li-NRR, the O/C ratio decreases as the SEI decomposes due to the absence of ethanol. Commercial Cu, Ni, and Zn are employed as cathodes in the experiments at various currents. The highest Faraday efficiency of 33.2 % and ammonia yield rate of 1404.5 μg h−1 cm−2 are achieved on Zn electrode owing to its superior electron transfer and enhanced Li+ diffusion than those of Cu and Ni. The current has also been found to affect Faraday efficiency through the portion of active lithium in coulomb efficiency experiments. Moreover, the LiCl generated in protonation process is found to facilitate lithium cycling.

Evaluation of Pt–Rh Nanoparticle–Based Electrodes for the Electrochemical Reduction of Nitrogen to Ammonia

Ammonia (NH3) is one of the most used chemicals. Industrially, ammonia is produced by hydrogenation of N2 through the Haber–Bosch process, a process in which enormous amounts of CO2 are released and requires a huge energy consumption (~ 2% of the total global energy). Therefore, it is of paramount importance to explore more sustainable and environmentally friendly routes to produce NH3. The electrochemical nitrogen reduction reaction (NRR) to ammonia represents a promising alternative that is receiving great attention but still needs to be significantly improved to be economically competitive. In this work, the NRR is studied on Pt–Rh nanoparticle–based electrodes. Carbon-supported Pt–Rh nanoparticles (2–4 nm) with different Pt:Rh atomic compositions were synthesized and subsequently airbrushed onto carbon Toray paper to fabricate electrodes. The electrochemical NRR experiments were performed in a H-cell in 0.1 M Na2SO4 solution. The results obtained show interesting faradaic efficiencies (FE) towards NH3 which range between 5 and 23% and reasonable and reliable NH3 yield values of about 4.5 µg h−1 mgcat−1, depending on the atomic composition of the electrocatalysts and the metal loading. The electrodes also showed good stability and recyclability (constant FE and NH3 yield in five consecutive experiments).Graphical Pt–Rh nanoparticle–based electrodes were employed for the NRR to NH3 in 0.1 M Na2SO4. Interesting FE towards NH3 and reasonable and reliable NH3 yield values were observed depending on atomic composition and metal loading. Good stability and recyclability (constant FE and NH3 yield in five consecutive experiments) were also observed.

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.

Recent Advance of Single‐Atom Metal@Support Catalysts and Their Applications in Artificial Electrocatalytic N2 Reduction Reaction

AbstractThe electrochemical nitrogen reduction reaction (ENRR) is the fundamental solution to the high pollution and emissions associated with the industrial synthesis of ammonia (NH3). However, nowadays ENRR still faces some great challenges, such as low NH3 yield rates and low Faradaic efficiency (FE), etc. In this context, single‐atom catalysts (SACs) with high catalytic activity and selectivity have emerged as shining stars in ENRR. Adjusting the support of SAC to leverage strong metal‐support interactions can address the activity limitations of the SAC itself and significantly enhance the activity of ENRR. Therefore, the review covers a range of topics including characterization techniques of single atoms, the mechanism of ENRR, in situ techniques in ENRR, synthesis methods of SACs, design principles of SACs in ENRR, and the application of SACs loaded with different supports in ENRR. Finally, the review offers a prospective outlook on the application of SACs in ENRR.

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.

Phosphomolybdic acid regulated the defective metal-organic framework UiO-66 for electrochemical nitrogen reduction reaction

In recent years, electrochemical ammonia synthesis has been considered a green process with excellent application prospects. The nitrogen reduction process (NRR) needs more activation energy when NN bonds are broken, which decreases the ammonia yield rate and Faraday efficiency (FE) for ammonia synthesis. Herein, UiO-66-xHPMo electrocatalysts are effectively synthesized by regulating the defects of the metal-organic framework (UiO-66) using phosphomolybdic acid (HPMo) as a defect regulator. XRD, FT-IR, TEM, XPS, TPD, etc., characterized the catalysts. As a result, the reasons for the increase in NH3 yield rate (RNH3) are catalysts losing the ligand of terephthalic acid, exposing more Zr6 nodes as active sites, and providing numerous active sites for NN cleavage. However, introducing HPMo makes catalysts more alkaline and have lower charge transfer resistance, which are more inclined to adsorb H+ and enhance hydrogen evolution reaction (HER), reducing FEs. Thus, with a voltage of −0.3 V (vs. RHE) and a neutral electrolyte (0.1 mol L−1 Na2SO4), UiO-66–2HPMo has excellent NRR performance (RNH3: 36.61 μg h−1 mg−1, FE: 31.09%).

Breaking linear scaling relationships in NRR with hydrogen bonding in confined space: A case study of g-C3N4 covered Ru(001) system

The electrochemical nitrogen reduction reaction (NRR) is a very efficient method for sustainable NH3 production under mild conditions, but it requires effective catalysts to expedite the NRR kinetics. However, the linear scaling relationships between the energies of elementary steps in NRR severely limit the rates of thermally catalysis reactions. Using density functional theory calculations, we demonstrate that these scaling relations can be circumvented by introducing hydrogen bonding and confinement field in g-C3N4/Ru(Rh) catalysis. Specially, the adsorption strength of key intermediate *N2H can be enhanced on the g-C3N4/Ru(Rh) own to the formation of H···N hydrogen bonding, while the adsorption of N2 is weakened due to the steric confinement field of the covered g-C3N4, resulting a significantly decrease of the energy barrier for the potential-limiting step in g-C3N4/Ru(Rh) system compared that in pure Ru(Rh) surface. Moreover, the hydrogen bonding strength between g-C3N4 and *NxHy increases with increasing of H atoms, which lower the energy barrier for the following protonation steps. Our results provide guidance for optimizing catalysts for application with hydrogen bonding and steric confinement.

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.

Reshaping hydrogen bond network in aqueous-aprotic hybrid electrolyte to achieve highly selective ambient ammonia synthesis

Aqueous electrolytes are extensively applied in electrochemical nitrogen reduction reaction, while the overwhelming H2O always produce much protons, favoring the electron-stealing hydrogen evolution reaction (HER) and thus leaving the current ammonia synthesis much to be desired. Here, we propose an aqueous-aprotic hybrid electrolyte system by introducing trimethyl phosphate (TMP) as a cosolvent to achieve highly selective ammonia synthesis. TMP features higher Gutmann donors than that of H2O, preferring to serve as hydrogen bond (HB) acceptor and reshaping the HB network in the electrolyte. Molecular dynamics simulations suggest that, compared with H2O-H2O HB, the H2O-TMP HB exhibits longer lifetime and better stability. The intensified interaction between H2O and TMP weakens the interaction between H2O and H2O, which strengthens the O-H bond of H2O and makes it more difficult to be broken, thus greatly inhibiting the dissociation of H2O and leading to a suppressed HER activity. Correspondingly, a significantly improved NRR performance with a superior NH3 yield rate of 82.1 ± 2.7 μg h–1 mg–1 and an optimum Faradaic efficiency of 73.3 ± 2.7% is achieved in the H2O-TMP hybrid electrolyte, indicative of order of magnitude enhancement compared with that delivered in the conventional aqueous electrolyte.