Emerging two-dimensional nanomaterials for electrochemical nitrogen reduction

Defect Engineering of Metal-Based Atomically Thin Materials for Catalyzing Small-Molecule Conversion Reactions

Recently, metal-based atomically thin materials (M-ATMs) have experienced rapid development due to their large specific surface areas, abundant electrochemically accessible sites, attractive surface chemistry, and strong in-plane chemical bonds. These characteristics make them highly desirable for energy-related conversion reactions. However, the insufficient active sites and slow reaction kinetics leading to unsatisfactory electrocatalytic performance limited their commercial application. To address these issues, defect engineering of M-ATMs has emerged to increase the active sites, modify the electronic structure, and enhance the catalytic reactivity and stability. This review provides a comprehensive summary of defect engineering strategies for M-ATM nanostructures, including vacancy creation, heteroatom doping, amorphous phase/grain boundary generation, and heterointerface construction. Introducing recent advancements in the application of M-ATMs in electrochemical small molecule conversion reactions (e.g., hydrogen, oxygen, carbon dioxide, nitrogen, and sulfur), which can contribute to a circular economy by recycling molecules like H2, O2, CO2, N2, and S. Furthermore, a crucial link between the reconstruction of atomic-level structure and catalytic activity via analyzing the dynamic evolution of M-ATMs during the reaction process is established. The review also outlines the challenges and prospects associated with M-ATM-based catalysts to inspire further research efforts in developing high-performance M-ATMs.

Isocyanide Ligation Enables Electrochemical Ammonia Formation in a Synthetic Cycle for N2 Fixation

Transition-metal-mediated splitting of N2 to form metal nitride complexes could constitute a key step in electrocatalytic nitrogen fixation, if these nitrides can be electrochemically reduced to ammonia under mild conditions. The envisioned nitrogen fixation cycle involves several steps: N2 binding to form a dinuclear end-on bridging complex with appropriate electronic structure to cleave the N2 bridge followed by proton/electron transfer to release ammonia and bind another molecule of N2. The nitride reduction and N2 splitting steps in this cycle have differing electronic demands that a catalyst must satisfy. Rhenium systems have had limited success in meeting these demands, and studying them offers an opportunity to learn strategies for modulating reactivity. Here, we report a rhenium system in which the pincer supporting ligand is supplemented by an isocyanide ligand that can accept electron density, facilitating reduction and enabling the protonation/reduction of the nitride to ammonia under mild electrochemical conditions. The incorporation of isocyanide raises the N-H bond dissociation free energy of the first N-H bond by 10 kcal/mol, breaking the usual compensation between pKa and redox potential; this is attributed to the separation of the protonation site (nitride) and the reduction site (delocalized between Re and isocyanide). Ammonia evolution is accompanied by formation of a terminal N2 complex, which can be oxidized to yield bridging N2 complexes including a rare mixed-valent complex. These rhenium species define the steps in a synthetic cycle that converts N2 to NH3 through an electrochemical N2 splitting pathway, and show the utility of a second, tunable supporting ligand for enhancing nitride reactivity.

Light-driven nitrogen fixation routes for green ammonia production

The global goal for decarbonization of the energy sector and the chemical industry could become a reality by a massive increase in renewable-based technologies. For this clean energy transition, the versatile green ammonia may play a key role in the future as a fossil-free fertilizer, long-term energy storage medium, chemical feedstock, and clean burning fuel for transportation and decentralized power generation. The high energy-intensive industrial ammonia production has triggered researchers to look for a step change in new synthetic approaches powered by renewable energies. This review provides a comprehensive comparison of light-mediated N2 fixation technologies for green ammonia production, including photocatalytic, photoelectrocatalytic, PV-electrocatalytic and photothermocatalytic routes. Since these approaches are still at laboratory scale, we examine the most recent developments and discuss the open challenges for future improvements. Last, we offer a technoeconomic comparison of current and emerging ammonia production technologies, highlighting costs, barriers, recommendations, and potential opportunities for the real development of the next generation of green ammonia solutions.

Water-Driven Stacking Structure Transformation of Ultrathin Ru Nanosheets for Efficient Hydrogen Evolution Reaction

Ultrathin crystalline materials are a class of popular materials that can potentially exhibit fascinating physical and chemical properties dictated by their unique stacking freedom. However, it is challenging to achieve the controllable synthesis over their stacking structure for ultrathin crystalline materials. Herein, water is employed as a key regulatory factor to realize phase engineering in ultrathin nanosheets (NSs), thereby altering stacking faults to achieve distinct stacking arrangements. Ruthenium (Ru) NSs with consistent specific surface areas but different stacking manners are fabricated through the systematic regulation of water. Based on this, it is demonstrated that the hydrogen evolution reaction (HER) performance can be significantly influenced by their stacking structures. Further in-depth investigations reveal that the distinct stacking structures of Ru NSs, featuring a limited area of side facets, will influence the energy barrier of sluggish Volmer step in HER. Ru NSs with ABC stacking exhibit an accelerated Volmer process with outstanding catalytic activity, demonstrating a remarkably low overpotential (25 mV at 10 mA cm-2) and Tafel slope (29 mV dec-1) than most of the reported HER catalysts. The work will advance the understanding of controllable synthesis methods and illuminate the structure-activity relationships in ultrathin crystalline nanomaterials.

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.

Two-Dimensional MOF Constructed by a Binuclear-Copper Motif for High-Performance Electrocatalytic NO Reduction to NH3

Ambient electrochemical NO reduction presents a dual solution for sustainable NO reduction and NH3 synthesis. However, their complex kinetics and energy demands necessitate high-performance electrocatalysts to ensure effective and selective process outcomes. Herein, we report that a two-dimensional Cu-based metal-organic framework (MOF), {[Cu(HL)]·H2O} n , (Cu-OUC, H3L = 5-(2'-carboxylphenoxy)isophthalic acid) acts as a stable electrocatalyst with high efficiency for NO-to-NH3 conversion. Electrochemical experimental studies showed that in 0.1 M K2SO4 solution, the as-prepared Cu-OUC achieved a peak Faradaic efficiency of 96.91% and a notable NH3 yield as high as 3415.82 μg h-1 mg-1. The Zn-NO battery in aqueous solution can produce electricity possessing a power density of 2.04 mW cm-2 while simultaneously achieving an NH3 yield of 616.92 μg h-1 mg-1. Theoretical calculations revealed that the surface of Cu-OUC effectively facilitates NO activation through a two-way charge transfer mechanism of "electron acceptance and donation", with the *NO formation step being the potential-determining stage. The study pioneers the use of a MOF as an electrocatalyst for ambient NO-to-NH3 conversion.

Modulating Nitrogen Adsorption Mode and Microenvironment of Active Sites for Boosting Electrochemical Nitrogen Reduction

Electrochemical reduction of N2 (NRR) offers a sustainable approach for ammonia (NH3) synthesis, serving as a complementary to the traditional emission- and energy-intensive Haber-Bosch process. However, it faces challenges in N2 activation and competing with pronounced hydrogen evolution reaction (HER). Herein an efficient electrocatalyst comprised of ultrafine Ru nanoclusters (NCs) confined by a hydrophobic molecular layer is developed on the surface of 2D Ti3C2Tx for NRR. These experimental and theoretical calculation results demonstrate that 1) ultrafine Ru NCs dispersed on the Ti3C2Tx surface form paired active sites for N2 chemisorption in a unique tilted configuration with low-energy activation 2) the hydrophobic molecular layer modulates the local microenvironment surrounding catalytically active sites, enabling efficient N2 accumulation while repelling H2O diffusion to the active sites on the Ti3C2Tx surface, thereby leading to an increased N2 concentration and suppressed HER. As a result, an exceptionally high NH3 yield rate of 33.5 µg h-1 mg-1cat and Faradaic efficiency of 65.3% are obtained at -0.25 V versus reversible hydrogen electrode (RHE) in 0.1 m Na2SO4, outperforming those previously reported Ti3C2Tx-derived electrocatalysts. This work provides a valuable strategy for the rational design of advanced electrocatalysts by manipulating active sites and local microenvironments for efficient electrocatalysis.

Role of Interfacial Water Structure in the Electroreduction of NO over Cu2O

The electrochemical nitric oxide reduction reaction (NORR), which utilizes water as the sole hydrogen source, has the potential to facilitate ammonia production while concurrently mitigating pollutants. However, limited research has been dedicated to characterizing the structure of interfacial water due to the challenges associated with probing this intricate system, impeding the development of more efficient catalysts for the NORR process. Herein, the Cu2O microcrystals with distinct exposed facets, including {100}, {110}, and {111}, are employed for the model catalysts to investigate interfacial water structure and intermediate species in the NORR process. The results from shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) indicated that the NORR performance in 0.1 M Na2SO4 (with heavy water as the solvent) was positively correlated to the proportion of hydrated Na+ ion water. In addition, a sequence of intermediates from the NORR, including *NOH, *NH, *NH2, and *NH3, was detected by employing a combination of multiple in situ characterization methods. Furthermore, in conjunction with experimental results and theoretical calculations, we revealed the potential reaction pathway of NORR. This study offers novel insights into the NORR mechanism and valuable guidance for the design of high-performance catalysts for ammonia production.

Graphdiyne Enabled Nitrogen Vacancy Formation in Copper Nitride for Efficient Ammonia Synthesis

The electrocatalytic reduction of nitrate is promising for sustainable ammonia synthesis but suffers from slow reduction kinetics and multiple competing reactions. Here, we report a catalyst featuring copper nitride (Cu3N) anchored on a novel graphdiyne support (termed Cu3N/GDY), which is used for electrocatalytic reduction of nitrate to produce ammonia. The GDY absorbed hydrogen and enabled nitrogen (N) vacancy formation in Cu3N for the fast nitrate reduction reaction (NO3RR). Further, the distinct absorption sites formed by GDY and N vacancy enabled the excellent selectivity and stability of NO3RR. Notably, the Cu3N/GDY catalyst achieved a high ammonia yield (YNH3) up to 35280 μg h-1 mgcat.-1 and a high Faradaic efficiency (FE) of 98.1% using 0.1 M NO3- at -0.9 V versus a reversible hydrogen electrode (RHE). Using electron paramagnetic resonance (EPR) technology and in situ X-ray absorption fine structure (XAFS) spectroscopy measurement, we visualized the N vacancy formation in Cu3N and electrocatalytic NO3RR enabled by GDY. These findings show the promise of GDY in sustainable ammonia synthesis and highlight the efficacy of Cu3N/GDY as a catalyst.

Polyoxometalate-Intercalated Tremella-Like CoNi-LDH Nanocomposites for Electrocatalytic Nitrite-Ammonia Conversion

The electrocatalytic reduction of NO2- (NO2RR) holds promise as a sustainable pathway to both promoting the development of emerging NH3 economies and allowing the closing of the NOx loop. Highly efficient electrocatalysts that could facilitate this complex six-electron transfer process are urgently desired. Herein, tremella-like CoNi-LDH intercalated by cyclic polyoxometalate (POM) anion P8W48 (P8W48/CoNi-LDH) prepared by a simple two-step hydrothermal-exfoliation assembly method is proposed as an effective electrocatalyst for NO2- to NH3 conversion. The introduction of POM with excellent redox ability tremendously increased the electrocatalytic performance of CoNi-LDH in the NO2RR process, causing P8W48/CoNi-LDH to exhibit large NH3 yield of 0.369 mmol h-1 mgcat-1 and exceptionally high Faradic efficiency of 97.0% at -1.3 V vs the Ag/AgCl reference electrode in 0.1 M phosphate buffer saline (PBS, pH = 7) containing 0.1 M NO2-. Furthermore, P8W48/CoNi-LDH demonstrated excellent durability during cyclic electrolysis. This work provides a new reference for the application of POM-based nanocomposites in the electrochemical reduction of NO2- to obtain value-added NH3.

Ambient Electrochemical Ammonia Synthesis: From Theoretical Guidance to Catalyst Design

Ammonia, a vital component in the synthesis of fertilizers, plastics, and explosives, is traditionally produced via the energy-intensive and environmentally detrimental Haber-Bosch process. Given its considerable energy consumption and significant greenhouse gas emissions, there is a growing shift toward electrocatalytic ammonia synthesis as an eco-friendly alternative. However, developing efficient electrocatalysts capable of achieving high selectivity, Faraday efficiency, and yield under ambient conditions remains a significant challenge. This review delves into the decades-long research into electrocatalytic ammonia synthesis, highlighting the evolution of fundamental principles, theoretical descriptors, and reaction mechanisms. An in-depth analysis of the nitrogen reduction reaction (NRR) and nitrate reduction reaction (NitRR) is provided, with a focus on their electrocatalysts. Additionally, the theories behind electrocatalyst design for ammonia synthesis are examined, including the Gibbs free energy approach, Sabatier principle, d-band center theory, and orbital spin states. The review culminates in a comprehensive overview of the current challenges and prospective future directions in electrocatalyst development for NRR and NitRR, paving the way for more sustainable methods of ammonia production.

Jahn-Teller Distortions Induced by in situ Li Migration in λ-MnO2 for Boosting Electrocatalytic Nitrogen Fixation

Lithium-mediated electrochemical nitrogen reduction reaction (Li-NRR) completely eschews the competitive hydrogen evolution reaction (HER) occurred in aqueous system, whereas the continuous deposition of lithium readily blocks the active sites and further reduces the reaction kinetics. Herein, we propose an innovative in situ Li migration strategy to realize that Li substitutes Mn sites in λ-MnO2 instead of evolving into the dead Li. Comprehensive characterizations corroborate that the intercalation of Li+ at high voltage breaks the structural integrity of MnO6 octahedron and further triggers unique Jahn-Teller distortions, which promotes the spin state regulation of Mn sites to generate the ameliorative eg orbital configuration and accelerates N≡N bond cleavage via eg -σ and eg -π* interaction. To this end, the resulted cationic disordered LiMnO4 delivers the recorded highest NH3 yield rate of 220 μg h-1  cm-2 and a Faradaic efficiency (FE) 83.80 % in organic electrolyte.

Interstitial Boron-Modulated Porous Pd Nanotubes for Ammonia Electrosynthesis

Electrochemical conversion of nitrogen into ammonia at ambient conditions as a sustainable approach has gained significant attention, but it is still extremely challenging to simultaneously obtain a high faradaic efficiency (FE) and NH3 yield. In this work, the interstitial boron-doped porous Pd nanotubes (B-Pd PNTs) are constructed by combining the self-template reduction method with boron doping. Benefiting from distinctive one-dimensional porous nanotube architectonics and the incorporation of the interstitial B atoms, the resulting B-Pd PNTs exhibit high NH3 yield (18.36 μg h-1 mgcat.-1) and FE (21.95%) in neutral conditions, outperforming the Pd/PdO PNTs (10.4 μg h-1 mgcat.-1 and 8.47%). The present study provides an attractive method to enhance the efficiency of the electroreduction of nitrogen into ammonia by incorporating interstitial boron into porous Pd-based catalysts.

Symmetry-Breaking p-Block Antimony Single Atoms Trigger N-Bridged Titanium Sites for Electrocatalytic Nitrogen Reduction with High Efficiency

The electrochemical nitrogen reduction reaction (eNRR) under mild conditions emerges as a promising approach to produce ammonia (NH3) compared to the typical Haber-Bosch process. Herein, we design an asymmetrically coordinated p-block antimony single-atom catalyst immobilized on nitrogen-doped Ti3C2Tx (Sb SA/N-Ti3C2Tx) for eNRR, which exhibits ultrahigh NH3 yield (108.3 μg h-1 mgcat-1) and excellent Faradaic efficiency (41.2%) at -0.3 V vs RHE. Complementary in situ spectroscopies with theoretical calculations reveal that the nitrogen-bridged two titanium atoms triggered by an adjacent asymmetrical Sb-N1C2 moiety act as the active sites for facilitating the protonation of the rate-determining step from *N2 to *N2H and the kinetic conversion of key intermediates during eNRR. Moreover, the introduction of Sb-N1C2 promotes the formation of oxygen vacancies to expose more titanium sites. This work presents a strategy for single-atom-decorated ultrathin two-dimensional materials with the aim of simultaneously enhancing NH3 yield and Faradaic efficiency for electrocatalytic nitrogen reduction.

Nitrogen Electrocatalysis: Electrolyte Engineering Strategies to Boost Faradaic Efficiency

The electrochemical activation of dinitrogen at ambient temperature and pressure for the synthesis of ammonia has drawn increasing attention. The faradaic efficiency (FE) as well as ammonia yield in the electrochemical synthesis is far from reaching the requirement of industrial-scale production. In aqueous electrolytes, the competing electron-consuming hydrogen evolution reaction (HER) and poor solubility of nitrogen are the two major bottlenecks. As the electrochemical reduction of nitrogen involves proton-coupled electron transfer reaction, rationally engineered electrolytes are required to boost FE and ammonia yield. In this Review, we comprehensively summarize various electrolyte engineering strategies to boost the FE in aqueous and non-aqueous medium and suggest possible approaches to further improve the performance. In aqueous medium, the performance can be improved by altering the electrolyte pH, transport velocity of protons, and water activity. Other strategies involve the use of hybrid and water-in-salt electrolytes, ionic liquids, and non-aqueous electrolytes. Existing aqueous electrolytes are not ideal for industrial-scale production. Suppression of HER and enhanced nitrogen solubility have been observed with hybrid and non-aqueous electrolytes. The engineered electrolytes are very promising though the electrochemical activation has several challenges. The outcome of lithium-mediated nitrogen reduction reaction with engineered non-aqueous electrolyte is highly encouraging.

WOx nanoparticles coupled with nitrogen-doped porous carbon toward electrocatalytic N2 reduction

The electrocatalytic nitrogen reduction reaction (eNRR) is a sustainable and green alternative to the traditional Haber-Bosch process. However, the chemical inertness of nitrogen gas and the competitive hydrogen evolution reaction significantly limit the catalytic performance of eNRR. Although tungsten oxide-based eNRR catalysts could donate unpaired electrons to the antibonding orbitals of N2 and accept lone electron pairs from N2 to dissociate NN triple bonds, the low electrical conductivity and the influence of the variable valence of W still affect the catalytic activity. Herein, a high-performance eNRR catalyst WOx nanoparticle/nitrogen-doped porous carbon (WOx/NPC) was prepared by a one-step thermal pyrolysis method. The results reveal that WOx gradually changes from the dominant WO2 phase to the WO3 phase. WOx/NPC-700 °C with WO2 NPs anchored on the surfaces of NPC via W-N bonding could deliver a high NH3 yield of 46.8 μg h-1 mg-1 and a high faradaic efficiency (FE) of 10.2%. The edge W atomic site on WOx/NPC is demonstrated to be the active center which could activate a stable NN triple bond with an electron-donating ability. Benefiting from the covalent interaction between the WOx nanoparticles and NPC, WOx/NPC also shows high electrocatalytic stability.

Metal-Based Electrocatalysts for Selective Electrochemical Nitrogen Reduction to Ammonia

Ammonia (NH3) plays a significant role in the manufacture of fertilizers, nitrogen-containing chemical production, and hydrogen storage. The electrochemical nitrogen reduction reaction (e-NRR) is an attractive prospect for achieving clean and sustainable NH3 production, under mild conditions driven by renewable energy. The sluggish cleavage of N≡N bonds and poor selectivity of e-NRR are the primary challenges for e-NRR, over the competitive hydrogen evolution reaction (HER). The rational design of e-NRR electrocatalysts is of vital significance and should be based on a thorough understanding of the structure-activity relationship and mechanism. Among the various explored e-NRR catalysts, metal-based electrocatalysts have drawn increasing attention due to their remarkable performances. This review highlighted the recent progress and developments in metal-based electrocatalysts for e-NRR. Different kinds of metal-based electrocatalysts used in NH3 synthesis (including noble-metal-based catalysts, non-noble-metal-based catalysts, and metal compound catalysts) were introduced. The theoretical screening and the experimental practice of rational metal-based electrocatalyst design with different strategies were systematically summarized. Additionally, the structure-function relationship to improve the NH3 yield was evaluated. Finally, current challenges and perspectives of this burgeoning area were provided. The objective of this review is to provide a comprehensive understanding of metal-based e-NRR electrocatalysts with a focus on enhancing their efficiency in the future.

Renaissance of elemental phosphorus materials: properties, synthesis, and applications in sustainable energy and environment

The polymorphism of phosphorus-based materials has garnered much research interest, and the variable chemical bonding structures give rise to a variety of micro and nanostructures. Among the different types of materials containing phosphorus, elemental phosphorus materials (EPMs) constitute the foundation for the synthesis of related compounds. EPMs are experiencing a renaissance in the post-graphene era, thanks to recent advancements in the scaling-down of black phosphorus, amorphous red phosphorus, violet phosphorus, and fibrous phosphorus and consequently, diverse classes of low-dimensional sheets, ribbons, and dots of EPMs with intriguing properties have been produced. The nanostructured EPMs featuring tunable bandgaps, moderate carrier mobility, and excellent optical absorption have shown great potential in energy conversion, energy storage, and environmental remediation. It is thus important to have a good understanding of the differences and interrelationships among diverse EPMs, their intrinsic physical and chemical properties, the synthesis of specific structures, and the selection of suitable nanostructures of EPMs for particular applications. In this comprehensive review, we aim to provide an in-depth analysis and discussion of the fundamental physicochemical properties, synthesis, and applications of EPMs in the areas of energy conversion, energy storage, and environmental remediation. Our evaluations are based on recent literature on well-established phosphorus allotropes and theoretical predictions of new EPMs. The objective of this review is to enhance our comprehension of the characteristics of EPMs, keep abreast of recent advances, and provide guidance for future research of EPMs in the fields of chemistry and materials science.

Powerful Orbital Hybridization of Copper-Silver Bimetallic Nanosheets for Electrocatalytic Nitrogen Reduction to Ammonia

Electrochemical nitrogen reduction (eNRR) is a promising strategy to replace the energy- and capital-intensive Haber-Bosch process. Unfortunately, the low selectivity of the eNRR process impedes the industrial application of this approach. In this work, a highly efficient and stable NRR electrocatalyst is obtained via coreduction of Cu and Ag precursors using the holly leaves as reducing agents. The as-obtained Cu₃Ag bimetallic nanosheets exhibit excellent NRR performance with an NH₃ production rate of 31.3 μg h^-1 mg^-1_cat. and a Faradaic efficiency of 31.3% at -0.2 V vs RHE. According to density functional theory (DFT) calculation, the outstanding performance of Cu₃Ag bimetallic nanosheets could be caused by the fact that Ag optimizes the 3d orbital occupation of Cu and synergistically enhances the charge transfer during the NRR process, resulting in a suitable adsorption strength of the intermediates.

Identification of Dynamic Active Sites Among Cu Species Derived from MOFs@CuPc for Electrocatalytic Nitrate Reduction Reaction to Ammonia

Direct electrochemical nitrate reduction reaction (NITRR) is a promising strategy to alleviate the unbalanced nitrogen cycle while achieving the electrosynthesis of ammonia. However, the restructuration of the high-activity Cu-based electrocatalysts in the NITRR process has hindered the identification of dynamical active sites and in-depth investigation of the catalytic mechanism. Herein, Cu species (single-atom, clusters, and nanoparticles) with tunable loading supported on N-doped TiO2/C are successfully manufactured with MOFs@CuPc precursors via the pre-anchor and post-pyrolysis strategy. Restructuration behavior among Cu species is co-dependent on the Cu loading and reaction potential, as evidenced by the advanced operando X-ray absorption spectroscopy, and there exists an incompletely reversible transformation of the restructured structure to the initial state. Notably, restructured CuN4&Cu4 deliver the high NH3 yield of 88.2 mmol h-1 gcata-1 and FE (~ 94.3%) at - 0.75 V, resulting from the optimal adsorption of NO3- as well as the rapid conversion of *NH2OH to *NH2 intermediates originated from the modulation of charge distribution and d-band center for Cu site. This work not only uncovers CuN4&Cu4 have the promising NITRR but also identifies the dynamic Cu species active sites that play a critical role in the efficient electrocatalytic reduction in nitrate to ammonia.

Hydrogen Radical-Induced Electrocatalytic N2 Reduction at a Low Potential

Realizing efficient hydrogenation of N₂ molecules in the electrocatalytic nitrogen reduction reaction (NRR) is crucial in achieving high activity at a low potential because it theoretically requires a higher equilibrium potential than other steps. Analogous to metal hydride complexes for N₂ reduction, achieving this step by chemical hydrogenation can weaken the potential dependence of the initial hydrogenation process. However, this strategy is rarely reported in the electrocatalytic NRR, and the catalytic mechanism remains ambiguous and lacks experimental evidence. Here, we show a highly efficient electrocatalyst (ruthenium single atoms anchored on graphdiyne/graphene sandwich structures) with a hydrogen radical-transferring mechanism, in which graphdiyne (GDY) generates hydrogen radicals (H^•), which can effectively activate N₂ to generate NNH radicals (^•NNH). A dual-active site is constructed to suppress competing hydrogen evolution, where hydrogen preferentially adsorbs on GDY and Ru single atoms serve as the adsorption site of ^•NNH to promote further hydrogenation of NH₃ synthesis. As a result, high activity and selectivity are obtained simultaneously at -0.1 V versus a reversible hydrogen electrode. Our findings illustrate a novel hydrogen transfer mechanism that can greatly reduce the potential and maintain the high activity and selectivity in NRR and provide powerful guidelines for the design concept of electrocatalysts.

Disordered Au Nanoclusters for Efficient Ammonia Electrosynthesis

The electrochemical nitrogen (N₂ ) reduction reaction (N₂ RR) under mild conditions is a promising and environmentally friendly alternative to the traditional Haber-Bosch process with high energy consumption and greenhouse emission for the synthesis of ammonia (NH₃ ), but high-yielding production is rendered challenging by the strong nonpolar N≡N bond in N₂ molecules, which hinders their dissociation or activation. In this study, disordered Au nanoclusters anchored on two-dimensional ultrathin Ti₃ C₂ T_x MXene nanosheets are explored as highly active and selective electrocatalysts for efficient N₂ -to-NH₃ conversion, exhibiting exceptional activity with an NH₃ yield rate of 88.3±1.7 μg h^-1  mg_cat. ^-1 and a faradaic efficiency of 9.3±0.4 %. A combination of in situ near-ambient pressure X-ray photoelectron spectroscopy and operando X-ray absorption fine structure spectroscopy is employed to unveil the uniqueness of this catalyst for N₂ RR. The disordered structure is found to serve as the active site for N₂ chemisorption and activation during the N₂ RR process.

Recent advances in two-dimensional materials for hydrovoltaic energy technology

Hydrovoltaic energy technology that generates electricity directly from the interaction of materials with water has been regarded as a promising renewable energy harvesting method. With the advantages of high specific surface area, good conductivity, and easily tunable porous nanochannels, two-dimensional (2D) nanomaterials have promising potential in high-performance hydrovoltaic electricity generation applications. Herein, this review summarizes the most recent advances of 2D materials for hydrovoltaic electricity generation, including carbon nanosheets, layered double hydroxide (LDH), and layered transition metal oxides and sulfides. Some strategies were introduced to improve the energy conversion efficiency and the output power of hydrovoltaic electricity generation devices based on 2D materials. The applications of these devices in self-powered electronics, sensors, and low-consumption devices are also discussed. Finally, the challenges and perspectives on this emerging technology are outlined.

Highly Selective N2 Electroreduction to NH3 Using a Boron-Vacancy-Rich Diatomic NbB Catalyst

The ambient electrochemical N₂ reduction reaction (NRR) is a future approach for the artificial NH₃ synthesis to overcome the problems of high-energy consumption and environmental pollution by Haber-Bosch technology. However, the challenge of N₂ activation on a catalyst surface and the competitive hydrogen evolution reaction make the current NRR unsatisfied. Herein, this work demonstrates that NbB₂ nanoflakes (NFs) exhibit excellent selectivity and durability in NRR, which produces NH₃ with a production rate of 30.5 µg h^-1 mg_cat ^-1 and a super-high Faraday efficiency (FE) of 40.2%. The high-selective NH₃ production is attributed to the large amount of active B vacancies on the surface of NbB₂ NFs. Density functional theory calculations suggest that the multiple atomic adsorption of N₂ on both unsaturated Nb and B atoms results in a significantly stretched N₂ molecule. The weakened NN triple bonds are easier to be broken for a biased NH₃ production. The diatomic catalysis is a future approach for NRR as it shows a special N₂ adsorption mode that can be well engineered.

Hexagonal Cobalt Nanosheets for High-Performance Electrocatalytic NO Reduction to NH3

Electrocatalytic nitric oxide (NO) reduction not only provides an extremely promising strategy for ambient NH₃ generation but also alleviates the artificially disrupted N-cycle balance. However, exploring efficient electrocatalysts to enhance the NO electroreduction performance remains a significant challenge. Herein, a hexagonal-close-packed Co nanosheet (hcp-Co) is prepared and exhibits a high NH₃ yield of 439.50 μmol cm^-2 h^-1 and a Faraday efficiency of 72.58%, outperforming the face-centered cubic phase of the Co nanosheet (fcc-Co) and most reported electrocatalysts. Through the combination of density functional theory calculations and NO temperature-programmed desorption experiments, the superior catalytic NO reduction reaction (NORR) activity on the hcp-Co can be attributed to the unique electron structures and proton shuttle effect. A proof-of-concept device of Zn-NO batteries using the hcp-Co as the cathode is assembled and shows a power density of 4.66 mW cm^-2, which is superior to the reported performance in the literature so far.

A simple descriptor for the nitrogen reduction reaction over single atom catalysts

The performance of supported catalysts is largely decided by metal-support interactions, which is of great significance for the rational design of catalysts. However, how to quantify the structure-activity relationship of supported catalysts remains a great challenge. In this work, taking MoS₂ and WS₂ supported single atom catalysts (SACs) as prototypes, a simple descriptor, namely, effective d electron number (labeled as Φ), is constructed to quantitatively describe the effect of metal-support interaction on the nitrogen reduction reaction (NRR) activity. This descriptor merely consists of intrinsic properties of the catalyst (including the number of d electrons, electronegativity of the metal atoms and generalized electronegativity of the substrate atoms) and can accurately predict the limiting potential (U_L) for the NRR, with no need for any density functional theory calculations. Moreover, this descriptor possesses superb expansibility that can be applied to other materials, including other metal dichalcogenide (MoSe₂, MoTe₂, WSe₂, WTe₂ and NbS₂) and even MXene (V₂CO₂, Ti₂CO₂ and Nb₂CO₂)-supported SACs. On this basis, a fast screening of excellent NRR catalysts among these systems is performed and three promising NRR catalysts (i.e. Mo@WTe₂, Mo@V₂CO₂ and Re@NbS₂) are successfully selected with U_L as low as -0.32, -0.24 and -0.31 V, respectively. This work offers new opportunities for advancing the rapid discovery of high-efficiency NRR catalysts, and the design principle is expected to be widely applicable to other catalytic systems and beyond.

Transfer organic chloramines to monochloramine using two-step chlorination: A method to inhibit N-DBPs formation in algae-containing water treatment

Organic chloramines formed in chlorination of algae-containing water are typical precursors of nitrogenous disinfection byproducts (N-DPBs). The objective to simultaneously enhance the removal efficiency of organic chloramines and control DBP formation remains a challenge. In this study, we report a two-step chlorination strategy for transferring organic chloramines to monochloramine based on the decomposition mechanisms of mono- and di-organic chloramines, which could limit organic chloramines formation and inhibit N-DBPs formation. We demonstrated that two-step chlorination could decrease the organic chloramines formation by nearly 50% than conventional one-step chlorination. Furthermore, two-step chlorination not only blocked the pathway that organic chloramines decomposed to nitriles, but also led to the conversion of organic chloramines to monochloramine. During two-step chlorination of algal organic matter, the organic chloramine transfer proportion decreased by 6.5% and the monochloramine transfer proportion increased by 17.0%. The N-DBP formation, especially haloacetonitriles (HANs), decreased significantly as organic nitrogen became inorganic nitrogen (monochloramine) in two-step chlorination. This work further clarified the process from algal organic matter to N-DBPs, which could expand our understanding of algae-derived organic chloramines removal and DBPs control.

Phase Engineering of Metastable Transition Metal Dichalcogenides via Ionic Liquid Assisted Synthesis

Metallic group VIB transition metal dichalcogenides (1T-TMDs) have attracted great interest because of their outstanding performance in electrocatalysis, supercapacitors, batteries, and so on, whereas the strict fabrication conditions and thermodynamical metastability of 1T-TMDs greatly restrict their extensive applications. Therefore, it is significant to obtain stable and high-concentration 1T-TMDs in a simple and large-scale strategy. Herein, we report a facile and large-scale synthesis of high-concentration 1T-TMDs via an ionic liquid (IL) assisted hydrothermal strategy, including 1T-MoS₂ (the obtained MoS₂ sample was denoted as MoS₂-IL), 1T-WS₂, 1T-MoSe₂, and 1T-WSe₂. More importantly, we found that IL can adsorb on the surface of 1T-MoS₂, where the steric hindrance, π-π stacking, and hydrogen bonds of ionic liquid collectively induce the formation of the 1T-MoS₂. In addition, DFT calculation reveals that electrons are transferred from [BMIM]SCN (1-butyl-3-methylimidazolium thiocyanate) to 1T-MoS₂ layers by hydrogen bonds, which enhances the stability of 1T-MoS₂, so the MoS₂-IL performs with high stability for 180 days at room temperature without obvious change. Furthermore, the MoS₂-IL exhibits excellent HER performance with an overpotential of 196 mV at 10 mA cm^-2 in acid conditions.

Theoretical Evaluation of Electrochemical Nitrate Reduction Reaction on Graphdiyne-Supported Transition Metal Single-Atom Catalysts

The electrochemical reaction can be applied as a powerful method to eliminate the pollution of nitrate (NO₃ ^-) and as a feasible synthesis to enable the conversion of nitrate into ammonia (NH₃) at room temperature. Herein, density functional theory calculations are applied to comprehensively analyze the electrochemical nitrate reduction reaction (NO₃RR) on graphdiyne-supported transition metal single-atom catalysts (TM@GDY SACs) for the first time. It can be found that the vanadium-anchored graphdiyne (V@GDY) displays the lowest limiting potential of -0.63 V versus a reversible hydrogen electrode among the investigated systems in this work. Notably, the competing hydrogen evolution reaction is relatively restrained due to the comparatively weak adsorption of the H proton on the TM@GDY SACs. Moreover, higher energy intake is needed to overcome the energy barrier during the formation of byproducts (NO₂, NO, N₂O, and N₂) on V@GDY without applying extra electrode potential, showing the selectivity of NH₃ in the NO₃RR process. The ab initio molecular dynamics simulation denotes that the V@GDY possesses excellent structure stability at the temperature of 600 K without much distortion, compared with the initial shape, indicating the promise for synthesis. This study not only offers a feasible NO₃RR electrocatalyst but also paves the way for the development of the NO₃RR process.

Improved nitrogen reduction activity of NbSe2 tuned by edge chirality

Efficient catalysts for the electroreduction of N2 to NH3 are of paramount importance for sustainable ammonia production. Recently, it was reported that NbSe2 nanosheets exhibit an excellent catalytic activity for nitrogen reduction under ambient conditions. However, existing theoretical calculations suggested an overpotential over 3.0 V, which is too high to interpret the experimental observations. To reveal the underlying mechanism of the high catalytic activity, in this work, we assessed NbSe2 edges with different chirality and Se vacancies by using first principles calculations. Our results show that N2 can be efficiently reduced to NH3 on a pristine zigzag edge via the enzymatic pathway with an overpotential of 0.45 V. Electronic structure analysis demonstrates that the N2 molecule is activated by the back-donation mechanism. The efficient tuning of the local chemical environments by edge chirality provides a promising approach for catalyst design.

Advanced Materials for Electrochemical Energy Conversion and Storage

With the massive consumption of traditional fossil resources, environmental issues such as air pollution and greenhouse gas emissions have motivated a transition towards clean and sustainable energy sources capable of meeting the increasing energy demands of our modern society [...]

Porphyrin-Based COF 2D Materials: Variable Modification of Sensing Performances by Post-Metallization

2D nanomaterials with flexibly modifiable surfaces are highly sought after for various applications, especially in room-temperature chemiresistive gas sensing. Here, we have prepared a series of COF 2D nanomaterials (porphyrin-based COF nanosheets (NS)) that enabled highly sensitive and specific-sensing of NO₂ at room temperature. Different from the traditional 2D sensing materials, H₂ -TPCOF was designed with a largely reduced interlayer interaction and predesigned porphyrin rings as modifiable sites on its surfaces for post-metallization. After post-metallization, the metallized M-TPCOF (M=Co and Cu) showed remarkably improved sensing performances. Among them, Co-TPCOF exhibited highly specific sensing toward NO₂ with one of the highest sensitivities of all reported 2D materials and COF materials, with an ultra-low limit-of-detection of 6.8 ppb and fast response/recovery. This work might shed light on designing and preparing a new type of surface-highly-modifiable 2D material for various chemistry applications.