Exploring dual-iron atomic catalysts for efficient nitrogen reduction: a comprehensive study on structural and electronic optimization

The nitrogen reduction reaction (NRR), as an efficient and green pathway for ammonia synthesis, plays a crucial role in achieving on-demand ammonia production. This study proposes a novel design concept based on dual-iron atomic sites and nitrogen-boron co-doped graphene (Fe2NxBy@G) catalysts, exploring their high efficiency in the NRR. By modulating the NxBy co-doped ratios, we found that the Fe2N3B@G catalyst exhibited significant activity in the adsorption and hydrogenation of N2 molecules, especially with the lowest free energy (0.32 eV) in the NRR distal pathway, showing its excellent nitrogen activation capability and NRR performance. The computed electron localization function, crystal orbital Hamiltonian population, and the electrostatic potential map revealed that the improved NRR kinetics of the Fe2N3B@G catalyst derived by N3B co-doping induced optimization of the Fe-Fe electronic environment, regulation of Fe-N bond strength, and continuous electronic support during N2 breakage and hydrogenation. In particular, machine learning molecular dynamics (MLMD) simulations were employed to verify the high activity of the Fe2N3B@G catalyst in the NRR, which revealed that Fe2N3B@G effectively regulates the electron density of the Fe-N bond, ensuring the smooth generation and desorption of NH3 molecules and avoiding the competition with the hydrogen evolution reaction (HER). Furthermore, the determined higher HER overpotential of the Fe2N3B@G catalyst can effectively inhibit the HER and enhance the selectivity toward the NRR. In addition, the Fe2N3B@G catalyst also showed good thermal stability by MD simulations up to 500 K, offering its feasibility in practical applications. This study demonstrates the superior performance of Fe2N3B@G in nitrogen reduction catalysis and provides theoretical guidance for atomic catalyst design by a co-doping strategy and in-depth electronic environment modulation.

Size Effect of Surface Defects Dictates Reactivity for Nitrogen Electrofixation

Electrocatalytic nitrogen reduction reaction (eNRR) offers a sustainable pathway for ammonia (NH3) production. Defect engineering enhances eNRR activity but can concurrently amplify the competing hydrogen evolution reaction (HER), posing challenges for achieving high selectivity. Herein, VOx with systematically tuned defect sizes is engineered to establish a structure-activity relationship between defect size and eNRR performance. In situ spectroscopy and theoretical calculations reveal that medium-sized defects (VOx-MD, 1-2 nm) provide an optimal electronic environment for enhanced N2 adsorption and activation while maintaining spatial flexibility to facilitate efficient hydrogenation. Consequently, VOx-MD exhibits outstanding eNRR performance, achieving an NH3 yield rate of 81.94 ± 1.45 µg h-1 mg-1 and a Faradaic efficiency of 31.97 ± 0.75 % at -0.5 V (vs RHE). These findings highlight the critical role of defect size in governing eNRR activity, offering a scalable strategy for designing advanced catalysts for competitve electrocatalytic reactions.

Harnessing Lithium-Mediated Green Ammonia Synthesis with Water Electrolysis Boosted by Membrane Electrolyzer with Polyoxometalate Proton Shuttles

Integrating water electrolysis (WE) with lithium-mediated nitrogen reduction (Li-NRR) offers a sustainable route for green ammonia production by directly utilizing protons from water oxidation, eliminating reliance on grey or blue hydrogen. Here, polyoxometalates (POMs) function as electron-coupled proton buffers (ECPBs) to seamlessly link WE with Li-NRR in a three-compartment flow reactor comprising an aqueous anode, an organic cathode, and a gas feed chamber. POMs serve as proton shuttles while suppressing the competing hydrogen evolution reaction (HER), facilitating efficient ammonia synthesis. The addition of polymethyl methacrylate (PMMA) enhances catholyte hydrophobicity, mitigating water contamination. By optimizing ECPB concentration, a dynamic balance is achieved between lithium nitride intermediates (LiNxHy) formation and consumption, yielding ammonia at 573.7 ± 5.2 µg h⁻¹ cm⁻2 with a Faradaic efficiency of 54.2%. This design advances flow reactor technology by uniquely utilizing water oxidation as a direct proton source, bypassing conventional hydrogen oxidation methods. The use of POMs as proton shuttles establishes a new benchmark for green ammonia production, reinforcing its potential in sustainable chemistry.

MXene Jacketed Amorphous Ga2O3 Nanofibers Modulate the Fiber Surface-Rich Electron for Boosted Electrocatalytic Ammonia Synthesis

Nitrogen (N2) activation and the hydrogen evolution reaction pose significant limitations on the electrocatalytic nitrogen reduction reaction (NRR) performance. The exclusive electronic structure of the main group elements has the advantage of inhibiting hydrogen generation in electrochemical NRR. However, the poor conductivity and activity remain the obstacles to its application. Herein, we report a combination strategy of cation-induced amorphous Ga2O3 nanofibers and heterostructure engineering, thereby effectively enhancing electrocatalytic performance. The amorphization of Ga2O3 nanofibers generates more oxygen vacancies that enhance the N2 activation and electron transfer ability. Additionally, by constructing heterogeneous structures to drive the charge transfer, we enrich electronics on the surface of a-Ga2O3 nanofibers and increase their catalytic activity. Thus, the a-Ga2O3/MXene nanofibers deliver the NH3 yield of 50.00 μg h-1 mg-1 and FE of 19.13% at -0.35 V. We anticipate that these findings will offer a new reference value for further ammonia synthesis research on Ga2O3 materials.

Advanced Development of High-Entropy Alloys in Catalytic Applications

Conventional alloys have long been limited by their simple compositions, which make it difficult to meet the requirements of modern catalysis applications. In contrast, high-entropy alloys (HEAs), characterized by multi-principal elements in near-equimolar ratios, have become a transformative paradigm in materials science since their inception in 2004. The unique core effects of HEAs, including the high-entropy effect, severe-lattice distortion effect, sluggish-diffusion effect, and cocktail effect, endow them with superior catalytic properties of activity, selectivity, and durability. However, with the rapid advanced development of HEAs, a comprehensive review of their applications in catalysis is imperative to foster a deeper understanding. In this review, the catalytic capability of HEAs, commencing from the entropy-driven mechanism and core effects of HEAs is systematically explored. Then, their applications are comprehensively analyzed in diverse fields, including energy conversion, chemical industries, and environmental remediation, emphasizing their remarkable capabilities in catalytic applications. Finally, pivotal challenges are outlined in synthesis methods, mechanistic elucidation, and green manufacturing, and propose future directions such as database establishment and machine-learning-assisted design. By addressing knowledge gaps and inspiring innovative strategies, this review aims to accelerate the translation of HEAs into practical solutions for a sustainable energy and environmental future.

Urea Complete Conversion to Compound Fertilizer in Industrial-Scale Tandem Reactors

A compound fertilizer with NH4H2PO4 and KH2PO4 offer significant advantages in enhancing both crop yield and quality. Ammonia (NH3) is essential for the synthesis of the compound fertilizer, which was produced by an energy intensive chemical process. Developing efficient and environmental friendly methods to produce ammonia-containing compound fertilizers is crucial and extremely challenging. Here, we present a tandem catalysis system capable of achieving complete conversion of abundant urea into compound fertilizer in industrial-scale reactors by combining electrochemical and subsequent chemical processes. In a typical cycle, with the use of 200 g urea, 1580 g of solid compound fertilizer (KH2PO4 and NH4H2PO4) and 232 L of pure H2 are produced without any further separation process. The key to the realization of this system is to precisely control the rate of urea consumption and NO2 - formation in electrochemical process. By maintaining a precise molar concentration ratio of urea to NO2 - at 1/2 in electrolyte, urea can completely react with NO2 - to form N2, while CNO- can be converted into NH4 + to form compound fertilizer in the second step of H3PO4 treatment, achieving complete conversion of urea without by-products formation. This method remarkably reduces H2 production potential while allowing for extraction of ammonia from urea-containing wastewater or urine to create pure compound fertilizer at an anticipated lower price than that of current market.

Significant enhancement of nitrogen photofixation to ammonia and hydrogen storage by a MIL-53 (Fe) based novel plasmonic nanocatalysis at ambient condition

Since hydrogen (H2) plays a vital role in industry, its storage is crucial. Typically, H2 is produced through water-splitting and then stored as ammonia. This process is very time-consuming and costly. Plasmonic metal nanocatalysts, including copper (Cu), silver (Ag), and gold (Au), are promising new ways to stimulate photocatalytic reactions. In this study, Ag/AgCl and Pd plasmonic NPs on the MIL-53 (Fe) by solvothermal method for Nitrogen (N2) photofixation to ammonia (NH3) with high efficiency under ambient conditions. Famous techniques such as FT-IR, XRD, BET, SEM, EDX/Map TEM, and TGA/DSC have been used to determine and confirm physicochemical surface variation while preparing and modifying the MIL-53 (Fe)@Ag/AgCl and MIL-53 (Fe)@Pd0 nanocatalysts. The synthesized plasmonic nanocatalysts display better photocatalytic activities during N2 photofixation, with a maximum NH3 production rate of 183.547 µmol·h- 1·g- 1 (MIL-53 (Fe)@Ag/AgCl(20%)) and 106.746 µmol·h- 1·g- 1 (MIL-53 (Fe)@Pd0(2%)) under visible light irradiation. This issue was attributed to the ability of Ag and Pd plasmonic NPs to harvest light to produce abundant hot electrons and Fe NPs to create active sites for N2 adsorption and activation. The MIL-53 (Fe)@Ag/AgCl(20%) and MIL-53 (Fe)@Pd0(2%) plasmonic compared to MIL-53 (Fe), have increased by 20-fold and 12-fold, respectively. This work of MOF-based plasmonic nanocatalysts for the N2 to NH3 photofixation will provide insight into the rational design of catalysts with high efficiency at ambient conditions.

Revealing Mechanisms of Lithium-Mediated Nitrogen Reduction Reaction from First-Principles Simulations

Recently, lithium-mediated nitrogen reduction reaction (Li-NRR) in nonaqueous electrolytes has proven to be an environmentally friendly and feasible route for ammonia electrosynthesis, revealing tremendous economic and social advantages over the industrial Haber-Bosch process which consumes enormous fossil fuels and generates massive carbon dioxide emissions, and direct electrocatalytic nitrogen reduction reaction (NRR) which suffers from sluggish kinetics and poor faradaic efficiencies. However, reaction mechanisms of Li-NRR and the role of solid electrolyte interface (SEI) layer in activating N2 remain unclear, impeding its further development. Here, using electronic structure theory, we discover a nitridation-coupled reduction mechanism and a nitrogen cycling reduction mechanism on lithium and lithium nitride surfaces, respectively, which are major components of SEI in experimental characterization. Our work reveals divergent pathways in Li-NRR from conventional direct electrocatalytic NRR, highlights the role of surface reconstruction in improving reactivity, and sheds light on further enhancing efficiency of ammonia electrosynthesis.

The synergistic effect induced by "Z-bond" between cations and anions achieving a highly reversible zinc anode

Due to their high energy density, low cost, and environmental friendliness, aqueous zinc-ion batteries are considered a potential alternative to Li-ion batteries. However, dendrite growth and parasitic reactions of water molecules limit their practical applications. Herein, an ionic liquid additive, 1-butyl-3-methylimidazolium Bis(fluorosulfonyl)imide (BMImFSI), is introduced to regulate the electrical double layer (EDL). Both BMIm+ and FSI- can preferentially adsorb on the Zn anode, constructing a water-poor EDL and thus effectively suppressing side reactions. Additionally, under the synergistic effect of the mineralized solid-electrolyte interphase (SEI) formed by the decomposition of FSI- and the ion dispersion layer constructed by BMIm+ on the mineralized SEI, the deposition of zinc ions is effectively dispersed, preventing excessive aggregation of zinc ions and thus dendrite formation. The Zn‖Zn symmetric cells using the BMImFSI/ZnSO4 electrolyte operate stably for 1060 h and 560 h at 10 mA cm-2-10 mAh cm-2 and 20 mA cm-2-20 mAh cm-2, respectively. The Zn‖Cu asymmetric cell maintains an average Coulombic efficiency of 99.4 % after 1000 cycles. The capacity retention of a full cell using α-MnO2 as the cathode is significantly improved at 1 A g-1.

Microfluidics for Electrochemical Energy Conversion and Storage: Prospects Toward Sustainable Ammonia Production

Ammonia is a key chemical in the production of fertilizers, refrigeration and an emerging hydrogen-carrying fuel. However, the Haber-Bosch process, the industrial standard for centralized ammonia production, is energy-intensive and indirectly generates significant carbon dioxide emissions. Electrochemical nitrogen reduction offers a promising alternative for green ammonia production. Yet, current reaction rates remain well below economically feasible targets. This work examines the application of electrochemical microfluidics for the enhancement of the rates of electrochemical ammonia synthesis. The review is built on the introduction to electrochemical microfluidics, corresponding cell designs, and the main applications of microfluidics in electrochemical energy conversion/storage. Based on recent advances in electrochemical ammonia synthesis, with an emphasis on the critical role of robust experimental controls, electrochemical microfluidics represents a promising route to environmentally friendly, on-site and on-demand ammonia production. This review aims to bridge the knowledge gap between the disciplines of electrochemistry and microfluidics and promote interdisciplinary understanding and innovation in this transformative field.

Molecular Conjugated-Polymer Electrode Enables Rapid Proton Conduction for Electrosynthesis of Ammonia from Nitrate

Electrosynthesis of ammonia (NH3) from nitrate (NO3 -) using renewable energy holds promise as a supplementary alternative to the Haber-Bosch process for NH3 production. Most research focuses on tuning the catalytic activity of metal catalysts by modification of the catalyst structures. However, the electrode supports which could influence the catalytic activity have not been well-explored. The state-of-the-art electrocatalysts for NO3 - reduction to NH3 still exhibit limited energy efficiency at ampere-level current density. Herein, we report a polyaniline-based molecular electrode with Cu catalyst for selective and energy-efficient NO3 - reduction to NH3. In the electrode, the polyaniline promotes protonation of the key intermediate formed during NO3 - reduction at Cu, which circumvents the limitation of the Cu catalyst in the efficiency-limiting proton transfer step. The molecular electrode produces NH3 at a partial current density of 2.7 A cm-2 with an energy efficiency of 62 %, demonstrating much better electrochemical performance than common Cu-based electrocatalysts and indicating the great potential in molecular engineering of electrode supports for selective NO3 - reduction.

Boosting Electrocatalytic Nitrate Reduction through Enhanced Mass Transfer in Cu-Bipyridine 2D Covalent Organic Framework Films

Electrocatalytic nitrate reduction (NO3RR) is a promising method for pollutant removal and ammonia synthesis and involves the transfer of eight electrons and nine protons. As such, the rational design of catalytic interfaces with enhanced mass transfer is crucial for achieving high ammonia yield rates and Faradaic efficiency (FE). In this work, we incorporated a Cu-bipyridine catalytic interface and fabricated crystalline 2D covalent organic framework films with significantly exposed catalytic sites, leading to improved FE and ammonia yield (FE=92.7 %, NH3 yield rate=14.9 mg ⋅ h-1cm-2 in 0.5 M nitrate) compared to bulk catalysts and outperforming most reported NO3RR electrocatalysts. The film-like morphology enhances mass transfer across the Cu-bipyridine interface, resulting in superior catalytic performance. We confirmed the reaction pathway and mechanism through in situ characterizations and theoretical calculations. The Cu sites act as primary centers for adsorption and activation, while the bipyridine sites facilitate water adsorption and dissociation, supplying sufficient H* and accelerating proton-coupled electron transfer kinetics. This study provides a viable strategy to enhance mass transfer at the catalytic interface through rational morphology control, boosting the intrinsic activity of catalysts in the NO3RR process.

Exploration of Multidimensional Structural Optimization and Regulation Mechanisms: Catalysts and Reaction Environments in Electrochemical Ammonia Synthesis

Ammonia (NH3) is esteemed for its attributes as a carbon-neutral fuel and hydrogen storage material, due to its high energy density, abundant hydrogen content, and notably higher liquefaction temperature in comparison to hydrogen gas. The primary method for the synthetic generation of NH3 is the Haber-Bosch process, involving rigorous conditions and resulting in significant global energy consumption and carbon dioxide emissions. To tackle energy and environmental challenges, the exploration of innovative green and sustainable technologies for NH3 synthesis is imperative. Rapid advances in electrochemical technology have created fresh prospects for researchers in the realm of environmentally friendly NH3 synthesis. Nevertheless, the intricate intermediate products and sluggish kinetics in the reactions impede the progress of green electrochemical NH3 synthesis (EAS) technologies. To improve the activity and selectivity of the EAS, which encompasses the electrocatalytic reduction of nitrogen gas, nitrate, and nitric oxide, numerous electrocatalysts and design strategies have been meticulously investigated. Here, this review primarily delves into recent progress and obstacles in EAS pathways, examining methods to boost the yield rate and current efficiency of NH3 synthesis via multidimensional structural optimization, while also exploring the challenges and outlook for EAS.

Favoring the Originally Unfavored Oxygen for Enhancing Nitrogen-to-Nitrate Electroconversion

Current nitrate production involves a two-step thermochemical process that is energy-intensive and generates substantial CO2 emissions. Sustainable NO3- production via the nitrogen electrooxidation reaction powered by renewable electricity is highly desirable, but the Faradaic efficiency (FE) at high production rates is unsatisfactory due to competition from the oxygen evolution reaction (OER). In this study, we propose reengineering the catalyst's microstructure-to-macroenvironment interface by particularly utilizing the previously considered unfavored oxygen from the OER. We demonstrate that the re-engineered interface facilitates a record-breaking FE of 35.52% under 8 atm air, with an impressive increase in FE (41.56%) observed during a continuous electrochemical process lasting for 60 h due to the in situ formation of the O2-rich macro-interface environment. The revelation is anticipated to furnish groundbreaking perspectives for the reaction systems design in electrochemical nitrate production and other electrocatalytic fields.

Photo-Driven Ammonia Synthesis via a Proton-Mediated Photoelectrochemical Device

N2 reduction reaction (NRR) by light is an energy-saving and sustainable ammonia (NH3) synthesis technology. However, it faces significant challenges, including high energy barriers of N2 activation and unclear catalytic active sites. Herein, we propose a strategy of photo-driven ammonia synthesis via a proton-mediated photoelectrochemical device. We used redox-catalysis covalent organic framework (COF), with a redox site (-C=O) for H+ reversible storage and a catalytic site (porphyrin Au) for NRR. In the proton-mediated photoelectrochemical device, the COF can successfully store e- and H+ generated by hydrogen oxidation reaction, forming COF-H. Then, these stored e- and H+ can be used for photo-driven NRR (108.97 umol g-1) under low proton concentration promoted by the H-bond network formed between -OH in COF-H and N2 on Au, which enabled N2 hydrogenation and NH3 production, establishing basis for advancing artificial photosynthesis and enhancing ammonia synthesis technology.

Reshape Iron Nanoparticles Using a Zinc Oxide Nanowire Array for High Efficiency and Stable Electrocatalytic Nitrogen Fixation

As a type of century-old catalyst, the use of iron-based materials runs through the Haber-Bosch process and electrochemical synthesis of ammonia because of its excellent capability, low cost, and abundant reserves. How to continuously improve its catalytic activity and stability for electrochemical nitrogen fixation has always been a goal pursued by scientific researchers. Herein, we develop a free-standing iron-based catalyst, i.e., the iron nanoparticles with zinc oxide nanowire array support (Fe/ZnO NA), which exhibits a high ammonia yield of ∼54.81 μg h-1 mgcat.-1 and a Faradaic efficiency (FE) of ∼9.56% in a 0.5 M potassium hydroxide solution, along with good reusability and durability. Its electrocatalytic ability is superior to that of commercial Fe materials and most reported Fe-based catalysts, thus showing great competitiveness. This is because the ZnO NA not only supplies stable support for the homogeneous dispersion of Fe nanoparticles but also provides a very beneficial synergy to their catalytic activity. The work renews traditional iron-based catalysts and is thus of great significance for promoting the industrialization of electrochemical ammonia synthesis.

Cooperative Active Sites on Ag2Pt3TiS6 for Enhanced Low-Temperature Ammonia Fuel Cell Electrocatalysis

Ammonia has attracted considerable interest as a hydrogen carrier that can help decarbonize global energy networks. Key to realizing this is the development of low temperature ammonia fuel cells for the on-demand generation of electricity. However, the efficiency of such systems is significantly impaired by the sluggish ammonia oxidation reaction (AOR) and oxygen reduction reaction (ORR). Here, we report the design of a bifunctional Ag2Pt3TiS6 electrocatalyst that facilitates both reactions at mass activities exceeding that of commercial Pt/C. Through comprehensive density functional theory calculations, we identify that active site motifs composed of Pt and Ti atoms work cooperatively to catalyze ORR and AOR. Notably, in situ shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) experiments indicate a decreased propensity for *NOx formation and hence an increased resistance toward catalyst poisoning for AOR. Employing Ag2Pt3TiS6 as both the cathode and anode, we constructed a low temperature ammonia fuel cell with a high peak power density of 8.71 mW cm-2 and low Pt loading of 0.45 mg cm-2. Our findings demonstrate a pathway towards the rational design of effective electrocatalysts with multi-element active sites that work cooperatively.

Biomimetic Elastic Single-Atom Protrusions Enhance Ammonia Electrosynthesis

Electrocatalytic nitrogen (N2) reduction reaction (eNRR) is a promising route for sustainable ammonia (NH3) generation, but the eNRR efficiency is dramatically impeded by sluggish reaction kinetics. Herein, inspired by the dynamic extension-contraction of sea anemone tentacles in response to environmental changes, we propose a biomimetic elastic Mo single-atom protrusion on vanadium oxide support (pSA Mo/VOH) electrocatalyst featuring a symmetry-breaking Mo site and an elastic Mo-O4 pyramid for efficient eNRR. In situ spectroscopy and theoretical calculations reveal that the protruding Mo-induced symmetry-breaking structure optimizes the d-electron filling of Mo, enhancing the back-donation to the π* antibonding orbital, effectively polarizing the N≡N bond and reducing the barrier from *N2 to *N2H. Notably, the elastic Mo-O4 pyramidal structure of pSA Mo provides a dynamic Mo-O microenvironment during continuous eNRR processes. This optimizes the electronic structure of the Mo sites based on different reaction intermediates, enhancing the adsorption of various N intermediates and maintaining low barriers throughout the six-step hydrogenation process. Consequently, the elastic pSA Mo/VOH exhibits an excellent NH3 yield rate of 50.71±1.12 μg h-1 mg-1 and a Faradaic efficiency of 35.38±1.03 %, outperforming most electrocatalysts.

High-Entropy Metal-Organic Frameworks and Their Derivatives: Advances in Design, Synthesis, and Applications for Catalysis and Energy Storage

As a nascent class of high-entropy materials (HEMs), high-entropy metal-organic frameworks (HE-MOFs) have garnered significant attention in the fields of catalysis and renewable energy technology owing to their intriguing features, including abundant active sites, stable framework structure, and adjustable chemical properties. This review offers a comprehensive summary of the latest developments in HE-MOFs, focusing on functional design, synthesis strategies, and practical applications. This work begins by presenting the design principles for the synthesis strategies of HE-MOFs, along with a detailed description of commonly employed methods based on existing reports. Subsequently, an elaborate discussion of recent advancements achieved by HE-MOFs in diverse catalytic systems and energy storage technologies is provided. Benefiting from the application of the high-entropy strategy, HE-MOFs, and their derivatives demonstrate exceptional catalytic activity and impressive electrochemical energy storage performance. Finally, this review identifies the prevailing challenges in current HE-MOFs research and proposes corresponding solutions to provide valuable guidance for the future design of advanced HE-MOFs with desired properties.

Electrosynthesis of NH3 from NO with ampere-level current density in a pressurized electrolyzer

Electrocatalytic NO reduction reaction (NORR) offers a promising route for sustainable NH3 synthesis along with removal of NO pollutant. However, it remains a great challenge to accomplish both high NH3 production rate and long duration to satisfy industrial application demands. Here, we report an in situ-formed hierarchical porous Cu nanowire array monolithic electrode ensembled in a pressurized electrolyzer to regulate NORR reaction kinetics and thermodynamics, which delivers an industrial-level NH3 partial current density of 1007 mA cm-2 with Faradaic efficiency of 96.1% and remains stable at 1000 mA cm-2 for 100 hours. Integrating the Cu nanowire array monolithic electrode with pressurized electrolyzer boosts the NH3 production rate to 10.5 mmol h-1 cm-2, which is over tenfold that using commercial Cu foam at 1 atm. The NORR performance can be attributed to the promoted NO mass transfer to the enriched Cu surface, which could increase the NO coverage on Cu and then destabilize adsorbed NO and weaken hydrogen adsorption, thereby facilitating NO hydrogenation to NH3 while suppressing the competing hydrogen evolution.

Catalyst-Free Nitrogen Fixation by Microdroplets through a Radical-Mediated Disproportionation Mechanism under Ambient Conditions

Nitrogen fixation is essential for the sustainable development of both human society and the environment. Due to the chemical inertness of the N≡N bond, the traditional Haber-Bosch process operates under extreme conditions, making nitrogen fixation under ambient conditions highly desirable but challenging. In this study, we present an ultrasonic atomizing microdroplet method that achieves nitrogen fixation using water and air under ambient conditions in a rationally designed sealed device, without the need for any catalyst. The total nitrogen fixation rate achieved is 6.99 μmol/h, yielding ammonium as the reduction product and nitrite and nitrate as the oxidation products, with hydrogen peroxide produced as a byproduct at a rate of 4.29 μmol/h. Using electron paramagnetic resonance (EPR) spectroscopy, we captured reactive species, including hydrogen, hydroxyl, singlet oxygen, superoxide anion, and NO radicals. In conjunction with in situ mass spectrometry (MS) and isotope labeling, we confirmed the presence of nitrogen-containing intermediates, such as HN═NOH+•, H2N-N(OH)2+•, HNO+, and NH2OH+•. Supported by these findings and theoretical calculations, we propose a radical-mediated nitrogen disproportionation mechanism. Simulations of naturally occurring condensed microdroplets also demonstrated nitrogen redox fixation. This microdroplet-based method not only offers a potential pathway for nitrogen fixation in practical applications and sustainable development but also deepens our understanding of the natural nitrogen cycle.

Electrochemical Ammonia Synthesis: The Energy Efficiency Challenge

We discuss the challenges associated with achieving high energy efficiency in electrochemical ammonia synthesis at near-ambient conditions. The current Li-mediated process has a theoretical maximum energy efficiency of ∼28%, since Li deposition gives rise to a very large effective overpotential. As a starting point toward finding electrocatalysts with lower effective overpotentials, we show that one reason why Li and alkaline earth metals work as N2 reduction electrocatalysts at ambient conditions is that the thermal elemental processes, N2 dissociation and NH3 desorption, are both facile at room temperature for these metals. Many transition metals, which have less negative reduction potentials and thus lower effective overpotentials, can dissociate N2 at these conditions but they all bind NH3 too strongly. Strategies to circumvent this problem are discussed, as are the other requirements for a good N2 reduction electrocatalyst.

Modulating the Leverage Relationship in Nitrogen Fixation Through Hydrogen-Bond-Regulated Proton Transfer

In the electrochemical nitrogen reduction reaction (NRR), a leverage relationship exists between NH3-producing activity and selectivity because of the competing hydrogen evolution reaction (HER), which means that high activity with strong protons adsorption causes low product selectivity. Herein, we design a novel metal-organic hydrogen bonding framework (MOHBF) material to modulate this leverage relationship by a hydrogen-bond-regulated proton transfer pathway. The MOHBF material was composited with reduced graphene oxide (rGO) to form a Ni-N2O2 molecular catalyst (Ni-N2O2/rGO). The unique structure of O atoms in Ni-O-C and N-O-H could form hydrogen bonds with H2O molecules to interfere with protons being directly adsorbed onto Ni active sites, thus regulating the proton transfer mechanism and slowing the HER kinetics, thereby modulating the leverage relationship. Moreover, this catalyst has abundant Ni-single-atom sites enriched with Ni-N/O coordination, conducive to the adsorption and activation of N2. The Ni-N2O2/rGO exhibits simultaneously enhanced activity and selectivity of NH3 production with a maximum NH3 yield rate of 209.7 μg h-1 mgcat. -1 and a Faradaic efficiency of 45.7 %, outperforming other reported single-atom NRR catalysts.

Polymer-confined synthesis of gram-scale high-entropy perovskite fluoride nanocubes for improved electrocatalytic reduction of nitrate to ammonia

High-entropy perovskite fluoride (HEPF) has gradually attracted attention in the field of electrocatalysis due to its unique properties. Although traditional co-precipitation methods can efficiently produce HEPF, the resulting catalysts often lack regular morphology and tend to aggregate extensively. Here, nanocubic K(CuMgCoZnNi)F3 HEPF (HEPF-2) was successfully prepared on a gram-scale by a polyvinylpyrrolidone (PVP)-confined nucleation strategy. Benefiting from its large electrochemically active surface area and well-exposed active sites, the HEPF-2 demonstrates dramatically enhanced electrocatalytic activity in electrocatalytic nitrate reduction to ammonia, leading to an improved ammonia yield rate (7.031 mg h-1 mgcat.-1), a high faradaic efficiency (92.8%), and excellent long-term stability, outperforming the irregular HEPF nanoparticles (HEPF-0) prepared without the assistance of PVP. Our work presents an efficient and facile method to synthesize perovskite fluorides with a well-defined structure, showing great promise in the field of high-performance electrocatalysis.

Nanoporous Heterojunction Photocatalysts with Engineered Interfacial Sites for Efficient Photocatalytic Nitrogen Fixation

Photocatalytic N2 reduction reaction (PNRR) offers a promising strategy for sustainable production of ammonia (NH3). However, the reported photocatalysts suffer from low efficiency with great room to improve regarding the charge carrier utilization and active site engineering. Herein, a porous and chemically bonded heterojunction photocatalyst is developed for efficient PNRR to NH3 production via hybridization of two semiconducting metal-organic frameworks (MOFs), MIL-125-NH2 (MIL=Material Institute Lavoisier) and Co-HHTP (HHTP=2,3,6,7,10,11-hexahydroxytripehenylene). Experimental and theoretical results demonstrate the formation of Ti-O-Co chemical bonds at the interface, which not only serve as atomic pathway for S-scheme charge transfer, but also provide electron-deficient Co centers for improving N2 chemisorption/activation capability and restricting competitive hydrogen evolution. Moreover, the nanoporous structure allows the transportation of reactants to the interfacial active sites at heterojunction, enabling the efficient utilization of charge carriers. Consequently, the rationally designed MOF-based heterojunction exhibits remarkable PNRR performance with an NH3 production rate of 2.1 mmol g-1 h-1, an apparent quantum yield (AQY) value of 16.2 % at 365 nm and a solar-to-chemical conversion (SCC) efficiency of 0.28 %, superior to most reported PNRR photocatalysts. Our work provides new insights into the design principles of high-performance photocatalysts.

Sustainable ammonia and amines from chitin

Efforts are underway to explore alternative methods to the Haber-Bosch process for sustainable ammonia production, while the potential for ammonia extraction from natural nitrogenous biomass is under-exploited. Here, a synergistic catalytic strategy involving acid and modified Ru-based catalysts is communicated for the direct production of amines and ammonia from chitin. Phosphoric acid promotes the cleavage of ether bonds in biomass polymers and also serves to protect amino groups from being removed. Selective hydrogenation, deoxygenation, and amination can be achieved by controllably adjusting the ratio of Ru0/Run+. The utilization of nitrogen atoms in chitin can reach up to 95 % (21 % amines, 74 % ammonium), and the catalytic process is applicable to waste shrimp shells. This study demonstrates the possibility of efficient production of nitrogen-containing compounds from abundant biopolymers.

Localized High-Concentration Electrolyte in Li-Mediated Nitrogen Reduction for Ammonia Synthesis

The lithium-mediated nitrogen reduction reaction (Li-NRR) is a promising green alternative to the Haber-Bosch process for ammonia synthesis. The solid electrolyte interphase (SEI) is crucial for high efficiency and stability, as it regulates reactant diffusion and suppresses side reactions. The SEI properties are greatly influenced by the Li+ ion solvation structure, which is controllable through electrolyte engineering. Although anion-derived SEI enhances selectivity and stability, it has typically been engineered using high-concentration electrolytes (HCEs), which face mass transfer, viscosity, and cost issues. In this study, a localized high-concentration electrolyte (LHCE) in the Li-NRR is first introduced, enabling the formation of anion-derived SEI in a low-concentration electrolyte (LCE) by enhancing the Li-anion coordination using an antisolvent. Among various antisolvents, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) achieves the highest ammonia Faradaic efficiency (73.6 ± 2.5%), more than double that of the LCE (34.3 ± 2.8%) and exceeding the HCE (56.0 ± 2.8%). Systematic calculations and experimental analyses show that the LHCE exhibits anion-rich solvation structures and forms thin, inorganic SEI. Moreover, the LHCE has advantages of low viscosity and high N2 solubility, which facilitate mass transport. This study suggests the application of LHCE as an effective electrolyte engineering strategy to enhance the Li-NRR efficiency.

Enhanced electrochemical nitrate reduction to ammonia with nanostructured Mo2C on carbon nanotube-reduced graphene oxide hybrid support

The electrochemical nitrate reduction reaction (NO3-RR) is emerging as a promising method for ammonia production under ambient conditions while simultaneously addressing nitrate pollution. Due to the complexity of NO3-RR, which involves multi-electron/proton transfer and competes with the hydrogen evolution reaction (HER), the development of efficient electrocatalysts with high activity and stability is crucial. In this study, we report the use of Mo2C nanoparticles homogeneously dispersed on a carbon nanotube-reduced graphene oxide hybrid support (Mo2C/CNT-RGO) as an effective electrocatalyst for NO3-RR. The three-dimensional CNT-RGO hybrid provides a large surface area for electrolyte contact, enhanced electrical conductivity, and prevents the aggregation of Mo2C nanoparticles. Consequently, the Mo2C/CNT-RGO electrocatalyst demonstrated high NO3-RR performance, achieving a maximum NH3 production rate of 5.23 mg h-1 cm-2 with a faradaic efficiency of 95.9%. Mo2C/CNT-RGO also exhibited excellent long-term stability during consecutive cycling tests. This work presents a promising strategy for developing high-performance and durable NO3-RR electrocatalysts.

Main-Group Metal-Nonmetal Dynamic Proton Bridges Enhance Ammonia Electrosynthesis

The electrochemical nitrogen reduction reaction (eNRR) is a crucial process for the sustainable production of ammonia (NH3) for energy and agriculture applications. However, the reaction's efficiency is highly dependent on the activation of the inert N≡N bond, which is hindered by the electron back-donation to the π* orbitals of the N≡N bond, resulting in low eNRR capacity. Herein, we report a main-group metal-nonmetal (O-In-S) eNRR catalyst featuring a dynamic proton bridge, with In-S serving as the polarization pair and O functioning as the dynamic electron pool. In situ spectroscopic analysis and theoretical calculations reveal that the In-S polarization pair acts as asymmetric dual-sites, polarizing the N≡N bond by concurrently back-donating electrons to both the πx* and πy* orbitals of N2, thereby overcoming the significant band gap limitations, while inhibiting the competitive hydrogen evolution reaction. Meanwhile, the O dynamic electron pool acts as a "repository" for electron storage and donation to the In-S polarization pair. As a result, the O-In-S dynamic proton bridge exhibits exceptional NH3 yield rates and Faradaic efficiencies (FEs) across a wide potential window of 0.3 V, with an optimal NH3 yield rate of 80.07±4.25 μg h-1 mg-1 and an FE of 38.01±2.02 %, outperforming most previously reported catalysts.

Integrating Ozone Pollutant Elimination in N2 Electrolysis to Produce Nitrate with Reduced Reaction Steps

The synthesis of nitrate by the electrochemical N2 oxidation reaction (NOR) is currently one of the most promising routes. However, the traditional generation of nitrate depends on the oxidation reaction between N2 and H2O (or ·OH), which involves complex reaction steps and intermediates, showing strong competition from oxygen evolution reaction (OER). Here, an effective NOR method is proposed to directly oxidize N2 by using O3 as a reactive oxygen source to reduce the reaction step. Electrochemical tests demonstrate that the nitrate yield of Pd-Mn3O4/CNT electrocatalyst reaches the milligram level, which is the highest yield reported so far for electrocatalytic NOR. Quantitative characterization is employed to establish a comprehensive set of benchmarks to confirm the intrinsic nature of nitrogen activation and test the O3-mediated reaction mechanism. Density functional theory (DFT) calculations show that the heterostructure Pd-Mn3O4 leads to a strong adsorption preference for N2 and O3, which greatly reduces the activation energy barrier for N2. This accelerates the synthesis of nitrate based on the direct formation mechanism, which reduces energy barriers and the reaction steps, thus increasing the performance of electrocatalytic nitrate production. The techno-economic analysis underscores the promising feasibility and sustainable economic value of the presented method.

Radiocatalytic ammonia synthesis from nitrogen and water

The development of alternative methods to the Haber-Bosch process for ammonia (NH3) synthesis is a pressing and formidable challenge. Nuclear energy represents a low-carbon, efficient and stable source of power. The harnessing of nuclear energy to drive nitrogen (N2) reduction not only allows 'green' NH3 synthesis, but also offers the potential for the storage of nuclear energy as a readily transportable zero-carbon fuel. Herein, we explore radiocatalytic N2 fixation to NH3 induced by γ-ray radiation. Hydrated electrons (e- aq) that are generated from water radiolysis enable N2 reduction to produce NH3. Ru-based catalysts synthesized by using γ-ray radiation with excellent radiation stability substantially improve NH3 production in which the B5 sites of Ru particles may play an important role in the activation of N2. By benefitting from the remarkable penetrating power of γ-ray radiation, radiocatalytic NH3 synthesis can proceed in an autoclave under appropriate pressure conditions, resulting in an NH3 concentration of ≤5.1 mM. The energy conversion efficiency of the reaction is as high as 563.7 mgNH3·MJ-1. This radiocatalytic chemistry broadens the research scope of catalytic N2 fixation while offering promising opportunities for converting nuclear energy into chemical energy.

Ligand engineering towards electrocatalytic urea synthesis on a molecular catalyst

Electrocatalytic C-N coupling from carbon dioxide and nitrate provides a sustainable alternative to the conventional energy-intensive urea synthetic protocol, enabling wastes upgrading and value-added products synthesis. The design of efficient and stable electrocatalysts is vital to promote the development of electrocatalytic urea synthesis. In this work, copper phthalocyanine (CuPc) is adopted as a modeling catalyst toward urea synthesis owing to its accurate and adjustable active configurations. Combining experimental and theoretical studies, it can be observed that the intramolecular Cu-N coordination can be strengthened with optimization in electronic structure by amino substitution (CuPc-Amino) and the electrochemically induced demetallation is efficiently suppressed, serving as the origination of its excellent activity and stability. Compared to that of CuPc (the maximum urea yield rate of 39.9 ± 1.9 mmol h-1 g-1 with 67.4% of decay in 10 test cycles), a high rate of 103.1 ± 5.3 mmol h-1 g-1 and remarkable catalytic durability have been achieved on CuPc-Amino. Isotope-labelling operando electrochemical spectroscopy measurements are performed to disclose reaction mechanisms and validate the C-N coupling processes. This work proposes a unique scheme for the rational design of molecular electrocatalysts for urea synthesis.

Conversion of Nitrate to Ammonia by Amidinothiourea-Coordinated Metal Molecular Electrocatalysts with d-π Conjugation

The electrochemical reduction of nitrate to ammonia (NO3RR) provides a desired alternative of the traditional Haber-Bosch route for ammonia production, igniting a research boom in the development of electrocatalysts with high activity. Among them, molecular electrocatalysts hold considerable promise for the NO3RR, suppressing the competing hydrogen evolution reaction. However, the complicated synthesis procedure, usage of environmentally unfriendly organic solvents, and poor stability of Cu-based molecular electrocatalysts greatly limit their employment in NO3RR, and the development of desired Cu-based molecular catalysts remains challenging. Herein, a simple nonorganic solvent involving a one-step strategy was proposed to synthesize d-π-conjugated molecular electrocatalysts metal-amidinothiourea (M-ATU). Cu-ATU is composed of Cu coordinated with two S and two N atoms, whereas Ni-ATU is formed by Ni with four N atoms from two ATU ligands. Remarkably, Cu-ATU with a Cu-N2S2 coordination configuration exhibits superior NO3RR activity with a NH3 yield rate of 159.8 mg h-1 mgcat-1 (-1.54 V) and Faradaic efficiency of 91.7% (-1.34 V), outperforming previously reported molecular catalysts. Compared to Ni-ATU, Cu-ATU transfers more electrons to the *NO intermediate, effectively breaking the strong sp2 hybridization system and weakening the energy of N═O bonds. The increase in free energy of *NO reduced the energy barriers of the rate-determining step, facilitating the further hydrogenation process over Cu-ATU. Our work opened up a new horizon for exploring molecular electrocatalysts for nitrate activation and paved a way for the in-depth understanding of catalytic behaviors, aligning more closely with industrial demands.

Electrocatalytic Synthesis of Urea: An In-depth Investigation from Material Modification to Mechanism Analysis

Industrial urea synthesis production uses NH3 from the Haber-Bosch method, followed by the reaction of NH3 with CO2, which is an energy-consuming technique. More thorough evaluations of the electrocatalytic C-N coupling reaction are needed for the urea synthesis development process, catalyst design, and the underlying reaction mechanisms. However, challenges of adsorption and activation of reactant and suppression of side reactions still hinder its development, making the systematic review necessary. This review meticulously outlines the progress in electrochemical urea synthesis by utilizing different nitrogen (NO3 -, N2, NO2 -, and N2O) and carbon (CO2 and CO) sources. Additionally, it delves into advanced methods in materials design, such as doping, facet engineering, alloying, and vacancy introduction. Furthermore, the existing classes of urea synthesis catalysts are clearly defined, which include 2D nanomaterials, materials with Mott-Schottky structure, materials with artificially frustrated Lewis pairs, single-atom catalysts (SACs), and heteronuclear dual-atom catalysts (HDACs). A comprehensive analysis of the benefits, drawbacks, and latest developments in modern urea detection techniques is discussed. It is aspired that this review will serve as a valuable reference for subsequent designs of highly efficient electrocatalysts and the development of strategies to enhance the performance of electrochemical urea synthesis.

High-Density Atomically Dispersed Metals Activate Adjacent Nitrogen/Carbon Sites for Efficient Ammonia Electrosynthesis from Nitrate

While electrocatalytic reduction of nitrate to ammonia presents a sustainable solution for addressing both the environmental and energy issues within the nitrogen cycle, it remains a great challenge to achieve high selectivity and activity due to undesired side reactions and sluggish reaction kinetics. Here, we fabricate a series of metal-N-C catalysts that feature hierarchically ordered porous structure and high-density atomically dispersed metals (HD M1/PNC). Specifically, the as-prepared HD Fe1/PNC catalyst achieves an ammonia production rate of 21.55 mol gcat-1 h-1 that is at least 1 order of magnitude enhancement compared with that of the reported metal-N-C catalysts, while maintaining a 92.5% Faradaic efficiency when run at 500 mA cm-2 for 300 h. In addition to abundant active sites, such high performance benefits from the fact that the high-density Fe can more significantly activate the adjacent N/C sites through charge redistribution for improved water adsorption/dissociation, providing sufficient active hydrogen to Fe sites for nitrate ammoniation, compared with the low-density counterpart. This finding deepens the understanding of high-density metal-N-C materials at the atomic scale and may further be used for designing other catalysts.

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 0.3 wt.% 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 ± 3 nmol 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.

Nitrogen fixation by alkali and alkaline earth metal hydrides assisted by plasma

The chemical behaviors of alkali and alkaline earth metal hydrides including LiH, KH, MgH2, CaH2, and BaH2 under nitrogen plasma differ significantly from one another, exhibiting an ammonia production trend that contrasts with that observed under thermal conditions. A prominent feature of KH is its ability to facilitate plasma-assisted N2 fixation without generating H2 byproduct, showing high atomic economy in utilization of hydride ions for N2 reduction.

Highly Efficient Nitrogen Reduction to Ammonia through the Cooperation of Plasma and Porous Metal-Organic Framework Reactors with Confined Water

While the ambient N2 reduction to ammonia (NH3) using H2O as hydrogen source (2N2+6H2O=4NH3+3O2) is known as a promising alternative to the Haber-Bosch process, the high bond energy of N≡N bond leads to the extremely low NH3 yield. Herein, we report a highly efficient catalytic system for ammonia synthesis using the low-temperature dielectric barrier discharge plasma to activate inert N2 molecules into the excited nitrogen species, which can efficiently react with the confined and concentrated H2O molecules in porous metal-organic framework (MOF) reactors with V3+, Cr3+, Mn3+, Fe3+, Co2+, Ni2+ and Cu2+ ions. Specially, the Fe-based catalyst MIL-100(Fe) causes a superhigh NH3 yield of 22.4 mmol g-1 h-1. The investigation of catalytic performance and systematic characterizations of MIL-100(Fe) during the plasma-driven catalytic reaction unveils that the in situ generated defective Fe-O clusters are the highly active sites and NH3 molecules indeed form inside the MIL-100(Fe) reactor. The theoretical calculation reveals that the porous MOF catalysts have different adsorption capacity for nitrogen species on different catalytic metal sites, where the optimal MIL-100(Fe) has the lowest energy barrier for the rate-limiting *NNH formation step, significantly enhancing efficiency of nitrogen fixation.

Behavior of Lithium Amide Under Argon Plasma

Alkali and alkaline earth metal amides are a type of functional materials for hydrogen storage, thermal energy storage, ion conduction, and chemical transformations such as ammonia synthesis and decomposition. The thermal chemistry of lithium amide (LiNH2), as a simple but representative alkali or alkaline earth metal amide, has been well studied previously encouraged by its potentials in hydrogen storage. In comparison, little is known about the interaction of plasma and LiNH2. Herein, we report that the plasma treatment of LiNH2 in an Ar flow under ambient temperature and pressure gives rise to distinctly different reaction products and reaction pathway from that of the thermal process. We found that plasma treatment of LiNH2 leads to the formation of Li colloids, N2, and H2 as observed by UV-vis absorption, EPR, and gas products analysis. Inspired by this very unique interaction between plasma and LiNH2, a chemical loop for ammonia decomposition to N2 and H2 mediated by LiNH2 was proposed and demonstrated.

Fluorine Domains Induced Ultrahigh Nitrogen Solubility in Ionic Liquids

Fluorinated ionic liquids (ILs) are well-known as electrolytes in the nitrogen (N2) electroreduction reaction due to their exceptional gas solubility. However, the influence of fluorinated functional group on N2 solvation and solubility enhancement remains unclear. Massive molecular dynamics simulations and free energy perturbation methods are conducted to investigate the N2 solubility in 11 traditional and 9 fluorinated ILs. It shows that the fluorinated IL of 1-Ethyl-3-methylimidazolium tris(pentafluoroethyl) trifluorophosphate ([Emim]FAP) exhibits ultrahigh solubility, 4.844 × 10-3, approximately 118 times higher than that of traditional IL 1-Ethyl-3-methylimidazolium nitrate ([Emim]NO3). Moreover, fluorinated ILs with more than 10 C-F bonds possess higher N2 solubility than others and show an exothermic nature during solvation. As the C-F bonds number in ILs decreases, the N2 solubility decreases significantly and displays the opposite endothermic behavior. To understand the ultrahigh N2 solubility in fluorinated ILs, we propose a concept of fluorine densification energy (FDE), referring to the average strength of interaction between atoms per unit volume in ILs with fluorine domains, demonstrating a linear relationship with C-F bonds. Physically, lower FDE results in lower N2-anion pair dissociation energy and higher free volume, finally enhancing the N2 solubility. Consequently, medium to long alkyl fluorine tails within a polar environment defines a distinct fluorine domain, emphasizing FDE's role in enhancing N2 solubility. Overall, these quantitative results will not only deepen the understanding of N2 solvation in ILs but may also shed light on the rational design of IL-based high-performance N2 capture and conversion technologies.

Reductive Inner-Sphere Electrosynthesis of Ammonia via a Nonelectrocatalytic Outer-Sphere Redox

Electrochemistry of outer-sphere redox molecules involves an essentially intact primary coordination sphere with minimal secondary sphere adjustments, resulting in very fast electron transfer events even without a noble metal-based electrocatalyst. Departing from conventional electrocatalytic paradigms, we incorporate these minimal reaction coordinate adjustments of outer-sphere species to stimulate the electrocatalysis of energetically challenging inner-sphere substrates. Through this approach, we are able to show an intricate 8e- and 9H+ transfer inner-sphere reductive electrocatalysis at almost half the energy input of a conventional inner-sphere electron donor. This methodology of employing outer-sphere redox species has the potential to notably improve the cost and energy benefits in electrochemical transformations involving fundamental substrates such as water, CO2, N2, and many more.

Atomically Dispersed Cu on In2O3 for Relay Electrocatalytic Conversion of Nitrate and CO2 to Urea

Urea electrosynthesis from coelectrolysis of NO3- and CO2 (UENC) holds a significant prospect to achieve efficient and sustainable urea production. Herein, atomically dispersed Cu on In2O3 (Cu1/In2O3) is designed as an effective and robust catalyst for the UENC. Combined theoretical calculations and in situ spectroscopic analysis reveal the synergistic effect of the Cu1-O2-In site and the In site to boost the UENC energetics via a relay catalysis pathway, where the Cu1-O2-In site drives *NO3 → *NH2 and the In site catalyzes *CO2 → *CO. The generated *CO is then migrated from the In site to the Cu1-O2-In site, followed by C-N coupling with *NH2 on the Cu1-O2-In site to generate urea. Consequently, Cu1/In2O3 assembled within a flow cell exhibits an impressive urea yield rate of 28.97 mmol h-1 g-1 with a urea-Faradaic efficiency (FEurea) of 50.88%.

Nanocluster-agminated amorphous cobalt nanofilms for highly selective electroreduction of nitrate to ammonia

Developing highly-efficient electrocatalysts for the nitrate reduction reaction (NITRR) is a persistent challenge. Here, we present the successful synthesis of 14 amorphous/low crystallinity metal nanofilms on three-dimensional carbon fibers (M-NFs/CP), including Al, Ti, Mn, Fe, Co, Ni, Cu, Zn, Ag, In, Sn, Pb, Au, or Bi, using rapid thermal evaporation. Among these samples, our study identifies the amorphous Co nanofilm with fine agglomerated Co clusters as the optimal electrocatalyst for NITRR in a neutral medium. The resulting Co-NFs/CP exhibits a remarkable Faradaic efficiency (FENH3) of 91.15 % at - 0.9 V vs RHE, surpassing commercial Co foil (39 %) and Co powder (20 %), despite sharing the same metal composition. Furthermore, during the electrochemical NITRR, the key intermediates on the surface of the Co-NFs/CP catalyst were detected by in situ Fourier-transform infrared (FTIR) spectroscopy, and the possible reaction ways were probed by Density functional theory (DFT) calculations. Theoretical calculations illustrate that the abundant low-coordinate Co atoms of Co-NFs/CP could enhances the adsorption of *NO3 intermediates compared to crystalline Co. Additionally, the amorphous Co structure lowers the energy barrier for the rate-determining step (*NH2→*NH3). This work opens a new avenue for the controllable synthesis of amorphous/low crystallinity metal nano-catalysts for various electrocatalysis reaction applications.

From Charge to Spin: An In-Depth Exploration of Electron Transfer in Energy Electrocatalysis

Catalytic materials play crucial roles in various energy-related processes, ranging from large-scale chemical production to advancements in renewable energy technologies. Despite a century of dedicated research, major enduring challenges associated with enhancing catalyst efficiency and durability, particularly in green energy-related electrochemical reactions, remain. Focusing only on either the crystal structure or electronic structure of a catalyst is deemed insufficient to break the linear scaling relationship (LSR), which is the golden rule for the design of advanced catalysts. The discourse in this review intricately outlines the essence of heterogeneous catalysis reactions by highlighting the vital roles played by electron properties. The physical and electrochemical properties of electron charge and spin that govern catalysis efficiencies are analyzed. Emphasis is placed on the pronounced influence of external fields in perturbing the LSR, underscoring the vital role that electron spin plays in advancing high-performance catalyst design. The review culminates by proffering insights into the potential applications of spin catalysis, concluding with a discussion of extant challenges and inherent limitations.

Oriented Synthesis of Glycine from CO2, N2, and H2O via a Cascade Process

Air contains carbon, hydrogen, oxygen, and nitrogen elements that are essential for the constitution of amino acids. Converting the air into amino acids, powered with renewable electricity, provides a green and sustainable alternative to petrochemical-based methods that produce waste and pollution. Here, taking glycine as an example, we demonstrated the complete production chain for electrorefining amino acids directly from CO2, N2, and H2O. Such a prospective Scheme was composed of three modules, linked by a spontaneous C-N bond formation process. The high-purity bridging intermediates, separated from the stepwise synthesis, boosted both the carbon selectivity from CO2 to glycine of 91.7 % and nitrogen selectivity from N2 to glycine of 98.7 %. Under the optimum condition, we obtained glycine with a partial current density of 160.8 mA cm-2. The high-purity solid glycine product was acquired with a separation efficiency of 98.4 %. This work unveils a green and sustainable method for the abiotic creation of amino acids from the air components.

Enhancement of Lithium-Mediated Nitrogen Reduction by Modifying Center Atom of Tetraalkyl-Type Ionic Liquids

The lithium-mediated nitrogen reduction reaction (Li-NRR) offers a viable alternative to the Haber-Bosch process for ammonia production. However, ethanol, a common proton carrier in Li-NRR, exhibits electrochemical instability, leading to oxidation at the anode or byproduct formation at the cathode. This study replaces alcoholic proton carriers with ionic liquids (ILs), specifically tetrabutylphosphonium chloride (TBPCl) and tetrabutylammonium chloride (TBACl), to examine how the electronegativity differences between the central atom and adjacent carbon of the cation affect catalytic performance. The results show that switching the central atom in tetraalkyl-type ILs markedly enhances performance, specifically resulting in a 1.45-fold increase in Faradaic efficiency (FE) with the transition from phosphonium to ammonium cation of ILs. Additionally, optimal IL concentrations in the electrolyte are identified to maximize ammonia yield. TBACl, in particular, demonstrates enhanced ammonia production and operational stability, achieving an ammonia yield rate of 13.60 nmol/cm2/s, an FE of 39.5 %, and operational stability for over 12 h under conditions of 10 mA/cm2 and 10 atm. This research underscores the potential of precise IL modifications for more efficient and sustainable Li-NRR.

Electrosynthesis of Ammonia from Nitrate Using a Self-Activated Carbon Fiber Paper

While electrochemically upcycling nitrate wastes to valuable ammonia is considered a very promising pathway for tackling the environmental and energy challenges underlying the nitrogen cycle, the effective catalysts involved are mainly limited to metal-based materials. Here, we report that commercial carbon fiber paper, which is a classical current collector and is typically assumed to be electrochemically inert, can be significantly activated during the reaction. As a result, it shows a high NH3 Faradaic efficiency of 87.39% at an industrial-level current density of 300 mA cm-2 for over 90 h of continuous operation, with a NH3 production rate of as high as 1.22 mmol cm-2 h-1. Through experimental and theoretical analysis, the in situ-formed oxygen functional groups are demonstrated to be responsible for the NO3RR performance. Among them, the C-O-C group is finally identified as the active center, which lowers the thermodynamic energy barrier and simultaneously improves the hydrogenation kinetics. Moreover, high-purity NH4Cl and NH3·H2O were obtained by coupling the NO3RR with an air-stripping approach, providing an effective way for converting nitrate waste into high-value-added NH3 products.

In Situ Characterization Techniques for Electrochemical Nitrogen Reduction Reaction

The electrochemical reduction of nitrogen to produce ammonia is pivotal in modern society due to its environmental friendliness and the substantial influence that ammonia has on food, chemicals, and energy. However, the current electrochemical nitrogen reduction reaction (NRR) mechanism is still imperfect, which seriously impedes the development of NRR. In situ characterization techniques offer insight into the alterations taking place at the electrode/electrolyte interface throughout the NRR process, thereby helping us to explore the NRR mechanism in-depth and ultimately promote the development of efficient catalytic systems for NRR. Herein, we introduce the popular theories and mechanisms of the electrochemical NRR and provide an extensive overview on the application of various in situ characterization approaches for on-site detection of reaction intermediates and catalyst transformations during electrocatalytic NRR processes, including different optical techniques, X-ray-based techniques, electron microscopy, and scanning probe microscopy. Finally, some major challenges and future directions of these in situ techniques are proposed.

Complex phase behavior of dihydroxyl-functionalized ionic liquids at low temperature

Here, we have synthesized six dihydroxyl-functionalized ionic liquids for phase behavior studies at low temperature via crystallographic methods, Raman spectroscopy, differential scanning calorimetry (DSC), and density functional theory (DFT) calculations. Phase varieties are observed depending on the direction and strength of hydrogen bonding. Our studies also show that the ILs could be potentially excellent phase-change thermal storage materials with nearly no change of the phase transition enthalpy.

Selective electrochemical nitrogen fixation to ammonia catalyzed by a novel microporous vanadium phosphonate via the distal pathway

Herein, a microporous organic-inorganic hybrid, vanadium phosphonate (VPn) material has been developed. With the combined advantages of the periodic organic-inorganic skeleton, a regular microporous channel with a crystalline pore wall, and good surface area, VPn displays electrocatalytic NRR activity with a selective NH3 yield (11.84 μg h-1 mgcat-1), faradaic efficiency of 26.29% at -0.6 V and high stability up to 15 h. The isotopic labeling experiment also verifies the electrosynthesis of NH3 both qualitatively and quantitatively. The theoretical simulation reveals that the associative distal route serves as the most favourable pathway during the NRR, with the first protonation step of *N2 leading to *NNH as the potential determining step.