N2 Reduction Reaction Research Articles

N2 dissociation on AuCoFeMoRu high-entropy alloys: Circumventing scaling relations and step dependencies

Finding a better catalyst for the reduction of nitrogen to ammonia would be of considerable use to the chemical industry, allowing for cheaper and possibly decentralized ammonia production. One approach to find a better catalyst is to explore the element component space continuously via the use of high-entropy alloys, uncovering as of yet untested multi-element catalysts and reaction sites to optimize reaction activity. Utilizing DFT calculations and microkinetic modeling, we use the AuCoFeMoRu high-entropy alloy as a discovery platform for N2 reduction catalysts. Testing both terrace and step sites, we find that high-entropy alloy terraces can reach as high activities as steps for the N2 reduction reaction, due to their heterogeneous surface structure. We also find that high-entropy alloys are able to circumvent the scaling relations to an extent, due to the decoupling of the transition state and final state structure of the reaction. We discover several promising high-entropy alloy reaction sites, with a roughly twofold improvement in activity over the best monometallic surface. However, significantly larger gains in activity seem to still be fundamentally limited by the scaling relations.

Photocatalytic Nitrogen Fixation Coupled with the Generation of Value-Added Chemicals from N2 and Cellulose over MoO3 Nanosheets.

Photocatalytic nitrogen fixation from N2 provides an alternative strategy for ammonia (NH3) production, but it was limited by the consumption of a sacrificial electron donor for the currently reported half-reaction system. Here, we use naturally abundant and renewable cellulose as the sacrificial reagent for photocatalytic nitrogen fixation over oxygen-vacancy-modified MoO3 nanosheets as the photocatalyst. In this smartly designed photocatalytic system, the photooxidation of cellulose not only generates value-added chemicals but also provides electrons for the N2 reduction reaction and results in the production of NH3 with a maximum rate of 68 μmol·h-1·g-1. Also, the oxygen vacancies provide efficient active sites for both cellulose oxygenolysis and nitrogen fixation reactions. This work represents useful inspiration for realizing nitrogen fixation coupled with the generation of value-added chemicals from N2 and cellulose through a photocatalysis strategy.

Boosting Electrochemical Nitrogen Reduction via Axial Coordination Engineering on Single‐Iron‐Atom Catalysts

AbstractElectrocatalytic nitrogen (N2) reduction reaction (NRR) presents a sustainable alternative to the Haber–Bosch process for ammonia (NH3) synthesis. Iron phthalocyanine (FePc) is demonstrated as a promising catalyst for the electrocatalytic NRR. However, FePc with planar symmetric Fe‐N4 sites exhibits poor N2 adsorption and activation capabilities, resulting in an unsatisfactory NRR performance. Herein, an axial oxygen coordination strategy is developed to optimize the local electron distribution on FePc for improving N2 adsorption and activation. The as‐obtained FePc‐O‐CP shows a superior NH3 yield rate (59.72 µg h−1 mg−1cat.) and a considerable Faradaic efficiency (13.76%) in 0.1 m HCl. Density functional theory (DFT) calculations verify that the axial oxygen ligand on FePc inhibits the adsorption of H+ and enhances the N2 adsorption and activation, thereby greatly promoting NH3 generation. This work reveals the significance of regulating the local coordination environment of single‐atom catalysts for improving electrocatalytic NRR performance and provides a feasible strategy for the rational design of atomic‐scale active sites.

Lithium‐Mediated Nitrogen Reduction for Ammonia Synthesis: Reviewing the Gap between Continuous Electrolytic Cells and Stepwise Processes through Galvanic Li─N2 Cells

AbstractElectrochemical N2 reduction reaction (E‐NRR) has recently gained increasing interest within the scientific community, due to the ongoing energy crisis and pursuit of process sustainability. In this scenario, emerging lithium‐mediated (Li‐m) strategies are obtaining promising Faradaic efficiency (FE) and NH3 production rate values. In this work, the Li‐m scenarios are classified and explained toward a more sustainable process. Continuous processes, with a lithium salt and a proton donor in an electrolytic cell, are analyzed and compared with stepwise pathways. Different parameters are summarized in relation to the system stability, for which the importance of a tailored solid electrolyte interphase (SEI) layer emerged. Among stepwise processes, the thermochemical direct nitridation of lithium is discussed together with the recently developed Galvanic Li─N2 cell strategy.

Oxygen vacancy optimization of the titanium carbide MXene surface for enhanced electrochemical nitrogen reduction

Electrochemical N2 reduction reaction (NRR) provides a hopeful way for sustainable NH3 production. It is the key to realize efficient NRR reaction to optimize the structure and electronic configuration of catalyst materials. Increasing the number of active centers in Ti3C2Tx MXene allows for the development of effective NRR electrocatalysts. Herein, we rationally integrated defect engineering to create oxygen vacancy-rich Ti3C2-MXene (K-Ti3C2-400) as an efficient NRR catalyst with an NH3 yield of 32.25 ± 0.8 μg·h−1·mg−1cat. at − 0.55 V and a Faradaic efficiency of 12.85 % ± 0.26 % at −0.45 V versus reversible hydrogen electrode. According to the density functional theory, oxygen vacancies can prevent the hydrogen evolution reaction by delaying H adsorption, thereby activating absorbed N2 and encouraging *N2H synthesis. This research opens up new possibilities for creating MXene-based catalysts with surface reactivity and selectivity for electrochemical N2 fixation.

Tuning oxygen vacancies on Bi2MoO6 surface for efficient electrocatalytic N2 reduction reaction

Electrocatalytic nitrogen reduction reaction (NRR) is a green and environmentally friendly ammonia production method, which is expected to replace the conventional Haber-Bosch process. In this paper, a Bi2MoO6 electrocatalyst with abundant oxygen vacancies was obtained by solvothermal method and sodium hydroxide etching treatment. The introduction of oxygen vacancies increased the active site of the catalyst and promoted the charge transfer and N2 adsorption, which finally significantly increased the activity of the catalyst. In 0.1 M Na2SO4 solution at a potential of -0.2 V (vs. RHE), the Bi2MoO6 with oxygen vacancies obtained an excellent Faradaic efficiency of 16.51% and an NH3 yield of 13.18 μg h−1 mg−1, which is about 4 times that of bare Bi2MoO6. This study provides a new idea to improve the activity of the catalyst for NRR.

Enhanced Visible Light Photocatalytic Activity of Exfoliated Boron‐TiO2 Composite for Degradation of Rhodamine B and Nitrogen Fixation

AbstractThe design of an efficient, recyclable, visible light photocatalytic system was examined as a viable new green way to address environmental challenges such as removal of pollutants from wastewater and N2 fixation. The exfoliated boron (Bexf)‐Titanium oxide (TiO2) composite visible light active photocatalysts were successfully constructed via a simple wet chemical method by utilizing acetone as a solvent. The composite was evaluated for the photodegradation of Rhodamine B (RhB) dye and reduction of N2, which exhibits improved photocatalytic activity for degradation of RhB as well as for reduction of N2. Experiments with different quenchers indicate that the photogenerated superoxide radical anion (O2⋅−) plays a significant role in the degradation of RhB as well as for N2 reduction reactions. The composite catalyst shows good photostability and there is no significant reduction of the catalyst activity for dye degradation up to 4 cycles of reaction. This work affords a significant view into the design of reusable TiO2 composite materials for photocatalytic RhB degradation and nitrogen fixation.

Tuning Surface Potential Polarization to Enhance N2 Affinity for Ammonia Electrosynthesis.

Electrocatalytic N2 reduction reaction (NRR) to synthesize ammonia is a sustainable reaction that is expected to replace Haber Bosch process. Laminated Bi2WO6 has great potential as an NRR electrocatalyst, however, the effective activity requires that the inert substrate is fully activated. Here, for the first time, success is achieved in activating the Bi2WO6 basal planes with NRR activity through Ti doping. The introduction of Ti successfully tunes the surface potential distribution and enhances the N2 adsorption. The subsequently strong hybrid coupling of d(Ti)-p(N) orbitals fills the electronic state of N2 antibonding molecular orbital, which greatly weakens the bonding strength of N≡N bonds. Further, in situ synchrotron radiation-based Fourier transform infrared(SR-FTIR) spectrum and theoretical calculations show that surface potential polarization enhances the adsorption of HNN* by Bi-Ti dual-metal sites, which is beneficial for the subsequent activation hydrogenation process. The Ti-Bi2WO6 nanosheets achieve 11.44% Faradaic efficiency (-0.2V vs. RHE), a NH3 yield rate of 23.14µgmg-1h-1 (15N calibration), and satisfactory stability in 0.1M HCl environment. The mutual assistance of theory and experiment can help understand and develop of excellent two-dimensional (2D) materials for the NRR.

Engineering of local electron properties optimization in single-atom catalysts enabling sustainable photocatalytic conversion of N2 into NH3

Photocatalytic synthesis of ammonia (NH3) from nitrogen (N2) offers a promising strategy for carbon neutrality, as it avoids the energy-intensive and carbon-emitting industrial processes. The exploration of high-efficiency N2 photofixation systems for photocatalytic N2 reduction reaction (pNRR) is critical but it remains a challenge since the lack of rational structural design and atomic-level insights into molecular N2 activation mechanism. Herein, an atomically dispersed single-atom palladium (Pd) active sites decorated oxygen-deficient molybdenum oxide (Pd/MoO3-x) was creatively designed for assessing pNRR performance. Interestingly, the integration of single-atom Pd active sites in MoO3-x can significantly weaken the N≡N bond of adsorbed N2 and effectively lower the activation energy barrier during the pNRR process. This is attributed to the fact that the modified Pd single-atom sites of Pd/MoO3-x play a dominant role in the N2 spontaneous adsorption process as well as possess a remarkable photogenerated electron trapping ability, which could be assisted to inject electrons into N2 antibonding orbital, thus significantly accelerates the reaction kinetics. Consequently, the Pd/MoO3-x photocatalyst reaches an impressive NH3 yield rate of 103.2 μggcat.−1h−1, which is superior to that of pristine MoO3-x (21.2 μggcat.−1h−1) and commercial MoO3 (6.5 μggcat.−1h−1), respectively. The present study not only creates a reliable approach to expand efficient N2 photofixation system under mild conditions through the fabrication of atomically dispersed monometallic active sites, but also offers atomic-level insights into the underlying mechanism of pNRR catalytic process.

Atom-Pd catalysts supported by hollow N-doped carbon nanospheres for ultra-efficient nitrogen reduction reaction

Electrochemical N2 reduction reaction (eNRR) presents a promising alternative to the Haber-Bosch process, owing to its mild preparation conditions, absence of costly reagents, and high energy conversion efficiency. However, the process poses significant challenges due to its poor selectivity and low yield. Here, single atom Pd is successfully anchored on N-doped hollow carbon nanospheres via a simple wet impregnation method under relatively mild loading temperature, anhydrous and anaerobic environments. Our experiment demonstrates that SA-Pd/N@C exhibits outstanding catalytic performance in comparison to Pd nanoparticles which is consistent with the results of the DFT calculations, achieving an NH3 yield rate of 132.8 μg·h − 1·mgcat−1 and a corresponding FE of 6 % at -0.2 V versus RHE in HCl electrolyte (pH=1), as well as superior stability with only 5 % decrease after 10 consecutive cycles of electrochemical testing at room temperature, positioning it as one of the most effective catalyst materials reported for eNRR. The exceptional eNRR activity and stability can be attributed to the abundant active sites resulting from the relatively mild loading temperature, as well as electronic effects and structural engineering, which further diminish *H adsorption and efficiently suppress hydrogen evolution reaction. This work will provide a novel approach to enhance the eNRR performance through the effective design of Pd single-atom catalyst

Multivalent Sulfur Vacancy-Rich NiCo2S4@MnO2 Urchin-Like Heterostructures for Ambient Electrochemical N2 Reduction to NH3.

Innovative advances in the exploitation of effective electrocatalytic materials for the reduction of nitrogen (N2) to ammonia (NH3) are highly required for the sustainable production of fertilizers and zero-carbon emission fuel. In order to achieve zero-carbon footprints and renewable NH3 production, electrochemical N2 reduction reaction (NRR) provides a favorable energy-saving alternative but it requires more active, efficient, and selective catalysts. In current work, sulfur vacancy (Sv)-rich NiCo2S4@MnO2 heterostructures are efficaciously fabricated via a facile hydrothermal approach followed by heat treatment. The urchin-like Sv-NiCo2S4@MnO2 heterostructures serve as cathodes, which demonstrate an optimal NH3 yield of 57.31µgh-1mgcat -1 and Faradaic efficiency of 20.55% at -0.2V versus reversible hydrogen electrode (RHE) in basic electrolyte owing to the synergistic interactionsbetween Sv-NiCo2S4 and MnO2. Density functional theory (DFT) simulation further verifies that Co-sites of urchin-like Sv-NiCo2S4@MnO2 heterostructures are beneficial to lowering the energy threshold for N2 adsorption and successive protonation. Distinctive micro/nano-architectures exhibit high NRR electrocatalytic activities that might motivate researchers to explore and concentrate on the development of heterostructures for ambient electrocatalytic NH3 generation.

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.

NH3 Electrosynthesis from N2 Molecules: Progresses, Challenges, and Future Perspectives.

Green ammonia (NH3), made by using renewable electricity to split nearly limitless nitrogen (N2) molecules, is a vital platform molecule and an ideal fuel to drive the sustainable development of human society without carbon dioxide emission. The NH3 electrosynthesis field currently faces the dilemma of low yield rate and efficiency; however, decoupling the overlapping issues of this area and providing guidelines for its development directions are not trivial because it involves complex reaction process and multidisciplinary entries (for example, electrochemistry, catalysis, interfaces, processes, etc.). In this Perspective, we introduce a classification scheme for NH3 electrosynthesis based on the reaction process, namely, direct (N2 reduction reaction) and indirect electrosynthesis (Li-mediated/plasma-enabled NH3 electrosynthesis). This categorization allows us to finely decouple the complicated reaction pathways and identify the specific rate-determining steps/bottleneck issues for each synthesis approach such as N2 activation, H2 evolution side reaction, solid-electrolyte interphase engineering, plasma process, etc. We then present a detailed overview of the latest progresses on solving these core issues in terms of the whole electrochemical system covering the electrocatalysts, electrodes, electrolytes, electrolyzers, etc. Finally, we discuss the research focuses and the promising strategies for the development of NH3 electrosynthesis in the future with a multiscale perspective of atomistic mechanisms, nanoscale electrocatalysts, microscale electrodes/interfaces, and macroscale electrolyzers/processes. It is expected that this Perspective will provide the readers with an in-depth understanding of the bottleneck issues and insightful guidance on designing the efficient NH3 electrosynthesis systems.

Leveraging Dual‐Atom Catalysts for Electrocatalysis Revitalization: Exploring the Structure‐Performance Correlation

AbstractIn light of the profound shift toward renewable fuels, dual‐atom catalysts (DACs) are impressively prospected as auspicious catalysts for electrocatalysis revitalization, toward accomplishing environmental remediation and sustainable global energy security. Leveraging appealing attributes such as inspiring synergistic effect, additional adjacent adsorption sites, and ultrahigh atom utilization, DACs are endowed with unprecedented stability, activity, and selectivity in multifarious energy‐related applications. By virtue of addressing time and technological prominence to review this ground‐breaking atomic electrocatalyst, this review first encompasses a correlation elucidation between the substrate, dual‐atoms, and facile synthetic approaches with intriguing modification strategies. Furthermore, the state‐of‐the‐art characterization techniques specially employed for DACs are spotlighted, alongside rigorously unveiling the novel mechanistic insights’ milestone gained from both theoretical modeling and experimental research in multitudes of environmentally benign electrocatalytic applications, including O2 reduction, CO2 reduction, H2 evolution, O2 evolution, N2 reduction, and other fundamental reactions. As a final note, this review presents a brief conclusion highlighting current challenges and outlining prospects for this frontier. Importantly, this review deciphers the structure‐performance correlation while excavating the advancement gained in DACs, thus is anticipated to shed light for the catalysis community on bolstering an intense evolution of DACs while triggering sapient inspiration for more robust next‐generation catalysts.

Engineering Pt‐Cu diatomics electrocatalysts enables highly efficient urea synthesis

AbstractThe rational design of novel heterogeneous urea‐synthesis electrocatalysts (HUECs) poses an immense challenge due to their inherent complexity. Moreover, the ideal HUECs must also possess the ability to suppress two major competitive reactions: hydrogen evolution reaction (HER) and N2 reduction reaction (NRR). However, this daunting task can be made feasible with the use of heterogeneous diatomic catalysts that have been supported by unambiguous theoretical models. Herein, we report a design for an efficient platinum‐copper diatomic electrocatalyst (Pt1Cu1‐TiO2) for urea production based on theoretical predictions. Through rational screening of 8 Pt‐diatomics HUECs, we discovered that Pt1Cu1‐TiO2 can effectively suppress HER and NRR while promoting the adsorption of CO2 and N2. Subsequently, we experimentally fabricated Pt1Cu1‐TiO2 which exhibited optimal urea electrosynthesis activity of 51.71 molurea molPt+Cu−1 h−1. Pt1‐Cu1 diatomics in Pt1Cu1‐TiO2 could synergistically encourage the activation of *CO2/*N2 and crucial C‐N coupling with an optimal energy barrier (0.25 eV).

Bi2WO6 Incorporation of g‐C3N4 to Enhance the Photocatalytic N2 Reduction Reaction and Antibiotic Pollutants Removal

Synthesis of ammonia from photocatalytic N2 reduction is challenging due to the fast recombination of electron–hole pairs and the low selectivity of N2 on catalysts. This can be addressed by creating heterojunctions to separate the photogenerated carriers adequately. In this regard, BW/g‐C3N4 is synthesized and the weight percentage of g‐C3N4 is varied. The best photocatalytic activity for N2 reduction reaction (N2RR) is achieved with a ratio of BW/gC3N4 in 3.5:2 ratio, deemed to be the optimized heterojunction. N2‐temperature programmed desorption analysis shows outstanding chemisorption of N2 adsorbed on the BW/g‐C3N4 surface compared to pristine g‐C3N4 and BW. Additionally, forming a heterojunction enhances the charge transfer process and well‐separated electron–hole pairs, significantly boosting the water oxidation process on the catalytic surface. Photoelectrochemical analysis reveals that BW/g‐C3N4 exhibits the shortest hole relaxation lifetime and higher current density than its pristine counterparts. The robust contact between g‐C3N4 and BW reduces the work function of BW/g‐C3N4 based on ultraviolet photoelectron spectroscopy data. Ammonia production with the optimized BW/gC3N4‐3.5:2 is 5.3 and 2.1 times higher than pure g‐C3N4 and Bi2WO6, respectively. Meanwhile, BW/g‐C3N4 demonstrates excellent photocatalytic activity toward antibiotic pollutant degradation as well. After 150 min of visible light irradiation, the removal of 94% ciprofloxacin (CIP) is observed. Finally, a possible mechanism is proposed for photocatalytic N2RR and CIP degradation.

Hole-scavenging in photo-driven N2 reduction catalyzed by a CdS-nitrogenase MoFe protein biohybrid system

The light-driven reduction of dinitrogen (N2) to ammonia (NH3) catalyzed by a cadmium sulfide (CdS) nanocrystal‑nitrogenase MoFe protein biohybrid is dependent on a range of different factors, including an appropriate hole-scavenging sacrificial electron donor (SED). Here, the impact of different SEDs on the overall rate of N2 reduction catalyzed by a CdS quantum dot (QD)-MoFe protein system was determined. The selection of SED was guided by several goals: (i) molecules with standard reduction potentials sufficient to reduce the oxidized CdS QD, (ii) molecules that do not absorb the excitation wavelength of the CdS QD, and (iii) molecules that could be readily reduced by sustainable processes. Earlier studies utilized buffer molecules or ascorbic acid as the SED. The effectiveness of ascorbic acid as SED was compared to dithionite (DT), triethanolamine (TEOA), and hydroquinone (HQ) across a range of concentrations in supporting N2 reduction to NH3 in a CdS QD-MoFe protein photocatalytic system. It was found that TEOA supported N2 reduction rates comparable to those observed for dithionite and ascorbic acid. HQ was found to support significantly higher rates of N2 reduction compared to the other SEDs at a concentration of 50 mM. A comparison of the rates of N2 reduction by the biohybrid complex to the standard reduction potential (Eo) of the SEDs reveals that Eo is not the only factor impacting the efficiency of hole-scavenging. These findings reveal the importance of the SED properties for improving the efficiency of hole-scavenging in the light-driven N2 reduction reaction catalyzed by a CdS QD–MoFe protein hybrid.

Strategies Toward High Selectivity, Activity, and Stability of Single-Atom Catalysts.

Single-atom catalysts (SACs) hold immense promise in facilitating the rational use of metal resources and achieving atomic economy due to their exceptional atom-utilization efficiency and distinct characteristics. Despite the growing interest in SACs, only limited reviews have holistically summarized their advancements centering on performance metrics. In this review, first, a thorough overview on the research progress in SACs is presented from a performance perspective and the strategies, advancements, and intriguing approaches employed to enhance the critical attributes in SACs are discussed. Subsequently, a comprehensive summary and critical analysis of the electrochemical applications of SACs are provided, with a particular focus on their efficacy in the oxygen reduction reaction , oxygen evolution reaction, hydrogen evolution reaction , CO2 reduction reaction, and N2 reduction reaction . Finally, the outline future research directions on SACs by concentrating on performance-driven investigation, where potential areas for improvement are identified and promising avenues for further study are highlighted, addressing challenges to unlock the full potential of SACs as high-performance catalysts.

Enhanced N2 Adsorption and Activation by Combining Re Clusters and In Vacancies as Dual Sites for Efficient and Selective Electrochemical NH3 Synthesis.

The electrochemical N2 reduction reaction (NRR) is a green and energy-saving sustainable technology for NH3 production. However, high activity and high selectivity can hardly be achieved in the same catalyst, which severely restricts the development of the electrochemical NRR. In2Se3 with partially occupied p-orbitals can suppress the H2 evolution reaction (HER), which shows excellent selectivity in the electrochemical NRR. The presence of VIn can simultaneously provide active sites and confine Re clusters through strong charge transfer. Additionally, well-isolated Re clusters stabilized on In2Se3 by the confinement effect of VIn result in Re-VIn active sites with maximum availability. By combining Re clusters and VIn as dual sites for spontaneous N2 adsorption and activation, the electrochemical NRR performance is enhanced significantly. As a result, the Re-In2Se3-VIn/CC catalyst delivers a high NH3 yield rate (26.63 μg h-1 cm-2) and high FEs (30.8%) at -0.5 V vs RHE.

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.