Ampere-level current density ammonia electrochemical synthesis using CuCo nanosheets simulating nitrite reductase bifunctional nature

Orchestrated electron transfer in reduced polyoxometalate-based coordination architectures for facilitating nitrate-to-ammonia electrosynthesis

The electrochemical nitrate reduction to ammonia (ENRA) process is critically hindered by sluggish multistep proton/electron transfer kinetics, limiting its practical viability for sustainable ammonia (NH3) synthesis. To address this challenge, we designed a bioinspired family of polyoxometalate (POM)-based crystalline electrocatalysts-(HNCP)2[M(H2O)3]2[MMo12(HPO4)4(PO4)4O30] (where HNCP = 2-(4-carboxyphenyl)imidazo(4,5-f)(1,10) phenanthroline and M = Ni, Co, or Fe; denoted as M-P4Mo6)-by mimicking the cluster geometry and proton-coupled electron transfer (PCET) dynamics of natural nitrate reductase (NR) for the efficient conversion of nitrate (NO3-) to NH3. Among them, Ni-P4Mo6 demonstrates highly effective ENRA performance, achieving a Faradaic efficiency (FE) of 91.0 % at -1.2 V vs. reversible hydrogen electrode (RHE) and an NH3 yield rate of 7.4 mg h-1 mg-1cat. at -1.3 V vs. RHE. In situ Fourier transform infrared spectroscopy (in situ FTIR) captures critical nitrogen valence transitions (N5+ → N-3). Density functional theory (DFT) calculations reveal a collaborative mechanism: directional electron delocalization from the POM skeleton to the Ni center synergistically optimizes the d-band electronic structure, reducing the energy barrier of *NO3 adsorption (*denotes the adsorbed state, Gibbs free energy (ΔG) = 0.13 eV) and effectively suppressing hydrogen evolution. In this work, we establish a universal electronic structure engineering paradigm for designing high-efficiency POM electrocatalysts, opening new avenues for sustainable NH3 synthesis.

Self-supported copper-cobalt oxide hybrid electrode for bifunctionally electrocatalytic nitrate reduction and methanol oxidation reactions

Electrochemical nitrate reduction reaction (NO3RR) to ammonia (NH3) is a sustainable approach to upcycle nitrate (NO3-) pollutant, the further pairing of cathodic NO3RR with anodic methanol oxidation reaction (MOR) enables coproduction of NH3 and formate chemicals by electrolysis at enhanced energy efficiency. Bifunctional catalytic electrode for both reactions is crucial for achieving such a target. In view of the strong NO3- adsorption ability of copper (Cu) and the high active hydrogen adsorption ability of cobalt (Co) based compound, the catalyst composed of Cu and Co elements facilitates the deoxidation and complete hydrogenation of NO3- into NH3. In addition, the Cu- and Co-containing material is also possible catalyst or precatalyst for MOR. Herein, a self-supported Cu-cobalt oxide (CoO) hybrid onto nickel foam substrate, denoted as Cu-CoO/NF electrode, was fabricated by electrodeposition at negative potential. Due to the relaying effect of Cu and CoO components during NO3RR, the Cu-CoO/NF achieved a decent faradaic efficiency (FE) of 84 ± 4 % and an NH3 yield of 0.40 ± 0.02 mmol h-1 cm-2 at a high operation potential of -0.1 V. Moreover, the Cu-CoO/NF demonstrated high MOR property for formate production at significantly reduced potential (over 0.2 V) compared to the oxygen evolution reaction. The NO3RR-MOR coelectrolyser enabled coproduction of NH3 and formate at reduced energy consumption. This work provides a promising paradigm for pairwise production of valuable chemicals via rational design of catalytic electrode and construction of coelectrolysis system.

Laser-induced PdCu alloy catalysts for highly efficient and stable electrocatalytic nitrate reduction to ammonia

The electrochemical reduction reaction of nitrate (NO3RR) to ammonia is an environmentally friendly approach that can treat wastewater as well as find an alternative to the energy-intensive Haber-Bosch process. The use of adhesives partially to adhere to the NO3RR electrocatalysts, leading to sluggish kinetics, poor stability and poor scalability. Herein, we report the synthesis of PdCu alloy catalysts via a direct laser writing method, demonstrating their exceptional performance in the electrochemical reduction of nitrate. The Pd0.55Cu0.45 alloy exhibited a remarkable ammonia production rate of 30.55 mg h-1 cm-2 under neutral electrolyte conditions and maintained stable operation for over 1500 h. Density functional theory (DFT) calculations and experimental analyses revealed that the PdCu alloy's enhanced activity stems from its lower energy barrier for the rate-determining step (*NO → *NOH) and improved mass transfer capabilities. The alloy's electronic properties and geometric configuration, fine-tuned by the laser-induced synthesis method, facilitate the conversion of NO2- and suppress the hydrogen evolution reaction (HER), thereby significantly enhancing the selectivity and activity of the NO3RR process. This study provides a sustainable and efficient pathway for ammonia synthesis and offers insights into the design of advanced catalysts for environmental and energy applications.

Advances in electrocatalytic nitrate reduction to ammonia over Cu-based catalysts

Ammonia (NH3) is a critical basic material for both the agricultural and pharmaceutical industries. Traditionally, NH3 synthesis has relied on the Haber-Bosch process, which is characterized by high greenhouse gas emissions and stringent reaction conditions. As a more sustainable and cost-effective alternative, electrocatalytic NH3 synthesis has gained increasing attention. Nitrate (NO3-), a common pollutant in water and soil, is considered a promising nitrogen source for NH3 production due to its high solubility and relatively low N=O bond dissociation energy. This makes it particularly suitable for electrocatalytic nitrate reduction to ammonia (NRA), a process with significant potential for addressing nitrate pollution while contributing to NH3 production. However, challenges such as slow reaction kinetics and poor product selectivity persist in the NRA process. To overcome these challenges, the selection and optimization of catalysts are crucial for improving NRA performance. Among the various catalysts explored, copper-based (Cu) catalysts have attracted widespread attention due to their unique electronic structure and outstanding catalytic performance. This review provides a comprehensive analysis of the application and reaction mechanisms of Cu-based catalysts in NRA, along with an overview of testing systems and evaluation metrics used in the field. Additionally, it highlights current challenges and outlines future research directions to support the continued development of Cu-based materials for NRA applications.

Nitrogen-doped graphene encapsulating Fe2N for enhanced electrocatalytic conversion of nitrate to ammonia

This study reports the synthesis of a nitrogen-doped graphene encapsulating iron nitride (Fe2N@NC) electrocatalyst with outstanding activity for the NO3RR, achieving excellent faradaic efficiency (FE) for NH3 of 96.11% and high NH3 yield rate of 618.35 mmol h-1 gcat-1 at -0.5 V versus the reversible hydrogen electrode (RHE). Furthermore, the catalyst maintains an FE exceeding 90% across a broad range of potentials (from -0.3 to -0.7 V vs. RHE) and 85% across a wide range of concentrations (from 0.01 M to 0.5 M). Electron transfer between Fe and the support results in the formation of electron-deficient Fe. The experimental results demonstrated that electron-deficient Fe enhances the adsorption of NO3-. Furthermore, doping with Fe effectively utilizes *H radicals and inhibits the hydrogen evolution reaction (HER), thereby enhancing the activity of the NO3RR.

Synthesis of Ultrathin Mesoporous CuxRu Nanomeshes for Efficient Kilowatt-Level Nitrate Reduction to Ammonia

The electrochemical conversion of abundant nitrate ions from industrial wastewater and polluted groundwater into value-added ammonia represents an important route for the sustainable development of human society. However, developing efficient and stable catalysts remains a huge challenge. Herein, the synthesis of ultrathin mesoporous CuxRu nanomeshes is reported via a theory-guided ion exchange method for efficient nitrate reduction to ammonia. The prepared CuxRu nanomeshes are composed of Cu atoms anchored ultrathin mesoporous Ru nanomeshes, with a thickness of ≈2-3 nm and a pore distribution between 2 and 10 nm. It offers a high nitrate reduction performance, including a positive onset potential (0.41 V), a high ammonia Faradaic efficiency (94.5%) and a highest ammonia mass activity (0.7 A mg-1) at 0 V up to date. Moreover, a kilowatt-level nitrate reduction is first verified in a flow electrolyzer, with the fastest reported NO3 - removal velocity of 12.4 mmol min-1. In situ characterizations and theoretical calculations clearly reveal that Cu atoms can balance the energy barriers in nitrate reduction and competitive hydrogen evolution reactions, leading to improved catalytic performance.

Tuning Nitrogen Configurations in Nitrogen-Doped Graphene Encapsulating Fe3C Nanoparticles for Enhanced Nitrate Electroreduction

Electrochemical nitrate reduction reaction (NO3RR) offers a promising technology for the synthesis of ammonia (NH3) and removal of nitrate in wastewater. Herin, we fabricate a series of Fe3C nanoparticles in controllable pyridinic-N doped graphene (Fe3C@NG-X) by a self-sacrificing template method for the NO3RR. Fe3C@NG-10 exhibits high catalytic performance with a Faradaic efficiency (FE) of 94.03 % toward NH3 production at -0.5 V vs. Reversible hydrogen electrode (RHE) and an NH3 yield rate of 477.73 mmol h-1 gcat -1. Additionally, the catalyst also has a FE above 90 % across a broad potential range and NO3 - concentration range (12.5-500 mM). During the electrocatalytic process, the material experienced structural reconstruction, forming Fe/Fe3C@NG-X heterojunction. Experimental investigations demonstrate that the remarkable electrocatalytic activity is attributed to the high proportion of pyridinic-N content, and the reconstruction further enhances the overall reduction process.

Low-dimensional materials for ammonia synthesis

Ammonia is an essential chemical due to its immense usage in agriculture, energy storage, and transportation. The synthesis of "green" ammonia via carbon-free routes and renewable energy sources is the need of the hour. In this context, photo- and/or electrocatalysis proves to be highly crucial. Low-dimensional materials (LDMs), owing to their unique properties, play a significant role in catalysis. This review presents a vast library of LDMs and broadly categorizes their catalytic performance according to their dimensionality, i.e., zero-, one-, and two-dimensional catalysts. The rational design of LDMs can significantly improve their catalytic performance, particularly in reducing small molecules like dinitrogen, nitrates, nitrites, and nitric oxides to synthesize ammonia via photo- and/or electrocatalysis. Additionally, converting nitrates and nitrites to ammonia can be beneficial in wastewater treatment and be coupled with CO2 co-reduction or oxidative reactions to produce urea and other valuable chemicals, which are also discussed in this review. This review collates the works published in recent years in this field and offers some fresh perspectives on ammonia synthesis. Through this review, we aim to provide a comprehensive insight into the catalytic properties of the LDMs, which are expected to enhance the efficiency of ammonia production and promote the synthesis of value-added products.

A Cu0.76Co2.24O4/γ-Cu2(OH)3Cl composite catalyst for efficient neutral nitrate reduction

The electrocatalytic nitrate reduction reaction (eNO3-RR) is an environmentally friendly process that converts nitrate wastewater into high-value ammonia (NH3). However, the multi-step electron and proton transfer in this reaction leads to slow kinetics and competitive reactions, making it challenging to achieve energy-efficient performance. Herein, a Cu0.76Co2.24O4/γ-Cu2(OH)3Cl (CCOC) composite has been prepared as an electrocatalyst for the eNO3-RR. The CCOC catalyst demonstrated an outstanding NH3 yield rate of 10.71 mg h-1 cm-2 and a remarkable faradaic efficiency (FE) of 95.9% in a 0.5 M Na2SO4 neutral solution containing 0.1 M NO3-, surpassing most reported catalysts under neutral conditions. In situ investigations demonstrated that Cu0.76Co2.24O4 with high-valent Cuδ+ and Coδ+ significantly enhances H2O dissociation and proton production while also promoting the adsorption of NO3- and *NH intermediates. These properties contribute to the high NH3 selectivity and activity observed under neutral conditions. This work demonstrates Cu0.76Co2.24O4/γ-Cu2(OH)3Cl as a promising candidate for the sustainable and efficient production of NH3 through the eNO3-RR, offering new insights into efficient nitrate reduction in neutral environments.

Anodic Oxidation-Induced Interfacial Regulation of Nanoporous Co2P/CoOOH for Electrocatalytic Nitrate Reduction to Ammonia

The rechargeable Zn-nitrate battery presents a promising strategy for renewable energy conversion, ammonia production, and sewage treatment. Despite achieving excellent performance with transition metal-based electrocatalysts, the structure evolution of the electrocatalyst during Zn-nitrate battery charging/discharging and the corresponding reaction mechanism on nitrate reduction reaction (NO3RR) are still unclear. Inspired by the structural reconstruction in the charging process, nanoporous Co2P/CoOOH prepared by dealloying and anodic oxidation is reported as an electrocatalyst for NO3RR, achieving remarkable catalytic performance (ammonia yield rate: 1.93 mmol h-1 cm-2, Faradaic efficiency: 94.18%) with a high cathodic energy efficiency of 34.51%. Additionally, the assembled rechargeable Zn-nitrate battery delivers a power density of 31.99 mW cm-2 with a high charge-discharge stability. In-situ spectroscopy investigation reveals the generation of a Co2P/Co3O4 heterosturcture through a synergetic redox reaction involving the cobalt species and nitrate ions during NO3RR, which enhances the approach of potassium-ionized water and improves ammonia generation kinetics by regulating the NO2- and *NH2 generation. Density functional theoretical calculation further illustrates that Co2P/Co3O4 heterostructure optimizes the adsorption of the *NO intermediate and enables an energetically favorable rate-limiting *NOH formation step. The unique structural evolution and nitrate activation mode of cobalt-based heterostructure would provide new insights on designing efficient electrocatalysts for nitrate reduction and rechargeable Zn-nitrate battery.

Pd-based bimetallic nanosheets for a highly efficient nitrate reduction reaction

The PdNi NS catalyst exhibits outstanding nitrate electroreduction performance, achieving a high NH3 yield rate of 181 μmol h-1 cm-2, a superior FENH3 of 99.6%, and long durability over 20 cycles at -0.77 V (vs. RHE). This work not only introduces a high performance electrocatalyst for ammonia production, but also provides a new perspective on Zn-NO3- batteries.

Square-Planar Tetranuclear Cluster-Based High-Symmetry Coordination Metal-Organic Polymers for Efficient Electrochemical Nitrate Reduction to Ammonia

Metal-organic polymers (MOPs) are gaining booming attention as atomically precise single-site catalysts for electrochemical nitrate-to-ammonia conversion owing to their regular structures and tunable functionalities. However, a molecular-level understanding is still lacking for the design of more efficient MOP electrocatalysts. Here, we report the construction of high-symmetry coordination MOPs (Mn-TATB, Fe-TATB, and Co-TATB), utilizing square-planar tetranuclear building units [M4(μ4-O)(CO2)8] (M = Mn, Fe, or Co) bridged by 2,4,6-tris(4-carboxyphenyl)-1,3,5-triazine (H3TATB) ligands. These MOPs possess distinct coordination motifs with well-defined porosity, high-density catalytic sites, accessible mass transfer channels, and nanoconfined chemical environments. Benefited from the unique metal-organic coordination framework, Co-TATB demonstrated a remarkable ammonia production Faradaic efficiency (FENH3) of ∼98% across a wide potential range (-0.7 to -1.0 V (vs RHE)) in the electrocatalytic nitrate reduction reaction (NITRR) and maintained stable performance over a long duration when tested in a flow cell at an industrially relevant current density of ∼332.1 mA cm-2. Furthermore, in situ spectroscopic analyses, combined with theoretical calculations, elucidate the intrinsic reaction pathway of the Co-TATB model during the NITRR process. These findings offer insightful perspectives on the strategic design of electrocatalysts with symmetrical configurations for the purification of nitrate-containing wastewater and the green synthesis of ammonia.

In Situ Tailored Frustrated Lewis Pairs on Asymmetric Bi─Ov─In Motifs Domino-Direct High-Efficiency Urea Electrosynthesis

The green urea synthesis via co-electrolysis of waste nitrate and CO2 is alluring but challenging, especially with insufficient selectivity caused by thermodynamic differences and kinetic mismatch between multi-step conversion processes. Here, a domino effect-oriented electrosynthesis strategy is showcased to steer cascade reactions in upgrading nitrate and CO2 toward urea of high selectivity on Bi-doped In2O3 with asymmetric oxygen vacancies (Ov). The conventionally arbitrary reaction mode can be vectored and re-customized by stable and cumulative *NH2 intermediates in situ derived from priority nitrate reduction reaction, which not only form surface frustrated Lewis pairs (SFLPs, Bi─Ov─In─NH2) with Bi Lewis acid sites to synergistically adsorb and activate CO2 but also provide more opportunities for sluggish C─N coupling, delivering an unprecedented urea Faradic efficiency of 80.2% and an impressive urea yield of 2.38 × 103 µg h-1 mgcat. -1 at -0.4 V versus RHE. The atomically dispersed Bi sites promote the protonation of *NO to form nucleophilic *NH2 intermediates, which can be stabilized in the electrophilic region mediated by asymmetric Ov, permitting two nucleophilic attacks to complete the C─N coupling. The domino modeling protocol via positioning a specific intermediate in situ tailors the parallel conversion process and may guide selectivity control of electrosynthesis.

Active Hydrogen Enrichment on Cu6Sn5-type High Entropy Intermetallics for Efficient Nitrate Reduction Reaction

Electrocatalytic nitrate reduction reaction (NO3RR) provides a feasible strategy for green ammonia production and the treatment of nitrate pollution in wastewater. The generation of active hydrogen (H*) plays an important role in improving the selectivity, yield rate, and Faradaic efficiency of ammonia products. Here, structurally ordered nanoporous Cu6Sn5-type high entropy intermetallics (HEI) with extremely superior performance toward NO3RR is demonstrated. The optimal nanoporous (Cu0.25Ni0.25Fe0.25Co0.25)6Sn5 HEI delivers a high NH3 Faradaic efficiency of 97.09 ± 1.15% and excellent stability of 120 h at the industrial level current density of 1 A cm-2, accordingly directly converting NO3 ‒ to high-purity (NH4)2HPO4 with near-unity efficiency. Theoretical calculations combined with experimental results reveal that the ordered multi-site nature of the nanoporous HEI can simultaneously promote water dissociation, reduce the reaction-free energy of the hydrogenation process, and suppress hydrogen evolution. This work provides the design of the precious-metal-free HEI for sustainable NH3 synthesis and paves insights into the H* enrichment mechanism.

Manipulation of Hydrogen Transfer Behaviors by RhCu Alloying Enables an All-in-one Sustainable "Furfural-Nitrate" System

Nitrate and furfural are typical wastes mainly from industrialization and agriculturalization progresses, and their clean conversions are still very challenging for a sustainable future. Nevertheless, scant attention has been devoted to the core issues: the rational integration of two wastes recycling and the targeted manipulation of hydrogen (H*) transfer behaviors to address their sluggish reaction kinetics. Herein, we report an all-in-one electrochemical energy system that is thermodynamically designed by coupling nitrate reduction (NO3RR) and furfural oxidation reactions (FORs) together. Particularly, the poor kinetics for both electrode reactions are efficaciously optimized by the bifunctional electrocatalyst of RhCu alloy nanowires on copper foam (RhCu NW/CF) with highly improved dual-directional H*-modulation performances, thus initializing NO3RR for NH3 synthesis at +0.31 V and driving FOR for H2 harvest at an onset potential lower than 0 V. Eventually, such integrated "Furfural-Nitrate" system can simultaneously effectuate the electricity energy supply (10.76 mW cm-2), wastewater purification, cathodic hydrogen storage (NH3), anodic H2 production, and biomass upgrading. Hence, it provides a promising perspective of "turning waste into treasure" in a rational manner, justifying its all-in-one property in addressing the global challenge of sustainable energy.

Boosting Urea Electrosynthesis via Asymmetric Oxygen Vacancies in Zn-Doped Fe2O3 Catalysts

Urea electrosynthesis from CO2 and nitrate (NO3 -) provides an attractive pathway for storing renewable electricity and substituting traditional energy-intensive urea synthesis technology. However, the kinetics mismatching between CO2 reduction and NO3 - reduction, as well as the difficulty of C─N coupling, are major challenges in urea electrosynthesis. Herein, we first calculated the free energy of *CO, *OCNO, and *NOH formation over defect-rich Fe2O3 catalysts with different metal dopants, which showed that Zn dopant was a promising candidate. Based on the theoretical study, we developed Zn-doped defect-rich Fe2O3 catalysts (Zn-Fe2O3/OV) containing asymmetric Zn-OV-Fe sites. It exhibited an outstanding urea faradaic efficiency of 62.4% and the remarkable recycling stability. The production rate of urea was as high as 7.48 mg h-1 mgcat -1, which is higher than most of the reported works to date. Detailed control experiments and in situ spectroscopy analyses identified *OCNO as a crucial intermediate for C─N coupling. The Zn-Fe2O3/OV catalyst with asymmetric Zn-OV-Fe sites showed enhanced *CO coverage and promoted *OCNO formation, leading to high efficiency toward urea production.

Interfacial Water Structure Modulation on Unconventional Phase Non-Precious Metal Alloy Nanostructures for Efficient Nitrate Electroreduction to Ammonia in Neutral Media

Electrocatalytic nitrate reduction reaction (NO3RR) has been recognized as a sustainable route for nitrate removal and value-added ammonia (NH3) synthesis. Regulating the surface active hydrogen (*H) behavior is crucial but remains a formidable challenge, especially in neutral electrolytes, greatly limiting the highly selective NH3 formation. Herein, we report the controlled synthesis of heterophase hcp/fcc non-precious CuNi alloy nanostructures for efficient NH3 electrosynthesis in neutral media. Significantly, hcp/fcc Cu10Ni90 exhibits excellent performance with NH3 Faradaic efficiency and yield rate of 98.1% and 57.4 mg h-1 mgcat -1, respectively. In situ studies suggest that the high proportion of interfacial K+ ion hydrated water (K+-H2O) on hcp/fcc Cu10Ni90 creates high *H coverage via boosting interfacial water dissociation, enabling the rapid hydrogenation kinetics for NH3 synthesis. Theoretical calculations reveal that the superior NO3RR performance of hcp/fcc Cu10Ni90 originates from both the existence of hcp phase to improve the electroactivity and the high Ni content to guarantee an efficient active hydrogen supply. The strong interaction between Ni and Cu also optimizes the electronic structures of Cu sites to realize fast intermediate conversions with low energy barriers. This work provides a novel strategy to optimize surface *H behavior via tuning interfacial water structure by crystal phase control.

Single-atom Fe anchored graphdiyne for high-efficiency nitrate-to-ammonia conversion under ambient conditions

The electrocatalytic conversion of wastewater nitrate (NO3-) to ammonia (NH3) under industrial-grade current densities at ambient conditions presents a sustainable alternative to the energy-intensive Haber-Bosch process, yet remains fundamentally challenging. Here, a highly efficient NO3- to NH3 electrocatalyst with single Fe atoms dispersed on graphdiyne (GDY) is constructed through an in situ growth method. Experimental analysis demonstrates the formation of high-density atomic active sites on GDY, ensuring the high intrinsic activity of the electrocatalyst. Besides, the newly formed sp-C-Fe chemical bonds bridged GDY and Fe atoms providing a well-defined channel for selectively and efficiently transferring electrons from the active sites to the reactants/key intermediates, allowing for selective NO3- activation and efficient protonation. This atomic-scale electronic modulation enables exceptional nitrate reduction performance, achieving record-high faradaic efficiency (45.48%) and ammonia yield (202.34 μmol h-1 cm-2) while maintaining operational stability.

Elucidating Relay Catalysis on Copper Clusters With Satellite Single Atoms for Enhanced Urea Electrosynthesis

Relay catalysis represents significant efficacy in alleviating competition among different reactants during coupling reactions. However, a comprehensive understanding of the reaction mechanism underlying relay catalysis for the urea electrosynthesis remains challenging. Herein, we have developed a catalyst (CuAC-CuSA@NC) comprising Cu atomic clusters (CuAC) with satellite Cu─N4 single atoms (CuSA) sites on the nitrogen-doped porous interconnected carbon skeleton (NC), enabling elucidation of a relay catalysis process for co-reduction of CO2 and NO3 -. The designed CuAC-CuSA@NC catalyst exhibits an approximately threefold higher urea yield rate compared to that of CuSA@NC at -1.3 V versus RHE. Ex-situ experimental results and in-situ attenuated total reflection surface-enhanced infrared absorption spectroscopy analysis reveal a formation sequence between the *NH2 and *NH2CO species on CuAC-CuSA@NC with increasing reduction potential. The combination of theoretical calculations further elucidates that the relay catalysis pathway involves "CuAC" sites facilitating the conversion of *NO3 to *NOx, followed by a hydrogenation process to form *NH2 with *H from water dissociation promoted by "CuSA" sites, which subsequently couples with *CO2 to produce urea. This work provides novel insights into the investigation of coupling reactions, but not limit to, urea synthesis.

Alloyed Rhodium-Copper Nanocavities with Optimized Chemisorption of Hydrogen Radicals for Efficient Nitrate-to-Ammonia Electrocatalysis

Electrocatalytic reduction of waste nitrate (NO3 -) in water represents a sustainable and economic route for selective electrosynthesis of recycled ammonia (NH3), but their performance still falls behind the needed. Herein, bimetallic rhodium-copper nanocavities (RhCu NCs), featuring open nanocavities in mesoscopic structure and well-alloyed composition at atomic level, are demonstrated as a high-performance electrocatalyst for efficient nitrate-to-ammonia (NO3 --to-NH3) electrocatalysis in a neutral condition. In comparison to other counterpart electrocatalysts, the best RhCu NCs deliver superior NO3 --to-NH3 performance at a very positive potential of -0.10 V versus RHE with Faradaic efficiency of 97.5%, yield rate of 8.1 mg h-1 mg-1, energy efficiency of 39%, and cycling stability of reaching 15 cycles. The combination of kinetic analysis, in situ Raman spectroscopy, and density functional theory calculation reveals that active hydrogen radicals can be kinetically formed and selectively consumed by the nitrogen intermediates to promote the [2e + 6e] tandem pathway of NO3 - reduction for efficient NH3 electrosynthesis. The work thus provides some insights into designing functional tandem electrocatalysts for selective electrosynthesis of multi-electron products from various electrocatalytic reactions.

Harnessing Spin-Lattice Interplay in Metal Nitrides for Efficient Ammonia Electrosynthesis

Metal nitrides, renowned for their spin-lattice-charge interplay, offer vast potential in catalysis, electronics, and energy conversion. However, spin polarization manipulation in these nitrides remains a challenge for multi-electron electrocatalytic processes. This study introduces Co3Mo3N with a low-spin polarization configuration, achieved by incorporating spin-free lattice Mo with 4d orbitals into high-spin polarization Co4N. This innovation delivers outstanding nitrate-to-ammonia electrosynthesis, ranking among the best to date. Mo inclusion induces competing magnetic exchange interactions, reducing the spin polarization degree and enabling rate-determining step of NO2* to NO-OH* conversion via vertex-sharing NMo6 octahedra. A paired electro-refinery with a Co3Mo3N cathode achieves 2 000 mA cm-2 at 2.28 V and sustains an industrial-scale current of 1 000 mA cm-2 for 2,100 h, with an NH3 production rate of ≈70 mg NH3 h-1 cm-2. This work establishes a transformative platform for spin polarization degree-engineered electrocatalysts, driving breakthroughs in energy conversion technologies.

Selective Urea Electrosynthesis from CO2 and Nitrate on Spin-Polarized Atomically Ordered PdCuCo

The electrocatalytic conversion of NO3 - and CO2 into urea features a potential means of reducing carbon footprint and generating value-added chemicals. Nonetheless, due to the limited efficiency of carbon-nitrogen (C─N) coupling and the competing side reaction that forms ammonia, the urea selectivity and production yield have remained low. In this work, a spin-polarized cobalt-doped, atomically ordered PdCu intermetallic compound (denoted as PdCuCo) is developed as an efficient urea electrosynthesis catalyst. The Pd and Cu serve as the adsorption sites for CO2 and NO3 -, respectively, and the spin-polarized Co sites promote the adsorption of *NO intermediate, followed by hydrogenation of *NO at its N-terminal to form *HNO, instead of at its O-terminal. The difference in the hydrogenation position switches the subsequent reaction pathway to produce urea, in contrast to the PdCu or Ni-doped PdCu intermetallic compounds with main product selectivity of ammonia. The PdCuCo electrocatalyst exhibited an outstanding electrosynthesis of urea from NO3 - and CO2, including a Faradaic efficiency of 81%, a high urea yield of 227 mmol gcat. -1 h-1, and a notable electrochemical stability of >260 h, suggesting the attractive potential of designing spin-polarized catalytic sites for carbon-nitrogen coupling processes.

CoWO4 nanoparticles with dual active sites for highly efficient ammonia synthesis

The electrochemical reduction reaction of NO3- (NO3RR) represents a promising green technology for ammonia (NH3) synthesis. Among various electrocatalysts, Co-based materials have demonstrated considerable potential for the NO3RR. However, the NH3 production efficiency of Co-based materials is still limited due to challenges in the competitive hydrogen evolution reaction (HER) and hydrogenating oxynitride intermediates (*NOx). In this study, tungsten (W) and cobalt (Co) elements are co-incorporated to form cobalt tungstate (CoWO4) nanoparticles with dual active sites of Co2+ and W6+, which are applied to optimize the hydrogenation of NOx and decrease the HER, thereby achieving a highly efficient NO3RR to NH3. Theoretical calculations indicate that the Co sites in CoWO4 facilitate the adsorption and hydrogenation of *NOx intermediates, while W sites suppress the competitive HER. These dual active sites work synergistically to enhance NH3 production from the NO3RR. Inspired by these calculations, CoWO4 nanoparticles are synthesized using a simple ion precipitation method, with sizes ranging from 10 to 30 nm. Electrochemical performance tests demonstrate that CoWO4 nanoparticles exhibit a high faradaic efficiency of 97.8 ± 1.5% and an NH3 yield of 13.2 mg h-1 cm-2. In situ Fourier transform infrared spectroscopy characterizes the enhanced adsorption and hydrogenation behaviors of *NOx as well as a minimized HER on CoWO4, which contributes to the high efficiency and selectivity to NH3. This work introduces CoWO4 nanoparticles as an electrocatalytic material with dual active sites, contributing to the design of electrocatalysts for NH3 synthesis.

Efficient Ammonia Electrosynthesis from Pure Nitrate Reduction via Tuning Bimetallic Sites in Redox-Active Covalent Organic Frameworks

Electrocatalytic nitrate reduction reaction (NITRR) represents a promising approach for ammonia synthesis, but existing application has been constrained by the complex proton-coupled electron transfer and the sluggish kinetics induced by various intermediates. Herein, we synthesized a series of metalized covalent organic frameworks: NiTP-MTAPP MCOFs (M = 2H, Co, Cu, and Fe), based on dual redox-active centers: thiophene-substituted Ni-bis(dithiolene) ligand-Ni[C2S2(C4H2SCHO)2]2 and metallic porphyrin. Through regulating the adsorption and desorption of species at the catalytic sites, we have identified the optimal NITRR electrocatalyst: NiTP-CoTAPP MCOF, which achieved the highest faradaic efficiency (FE) of approximately 85.6% at -0.8 V (vs. RHE) in pure nitrate solution, with an impressive yield rate of 160.2 mmol h-1 g-1 cat. The generation of active hydrogen at [NiS4] sites achieved dynamic equilibrium with the timely hydrogenation reaction at CoN4 sites, effectively suppressing the hydrogen evolution reaction. Moreover, the incorporation of thiophene (TP) groups and metal ions facilitates charge transfer. Density functional theory (DFT) calculations demonstrated the reduction in energy barriers at different catalytic sites. The CoN4-NiS4 system exhibited the optimal adsorption-to-desorption capability and the lowest energy barrier (0.58 eV) for the rate-determining step (*NO → *HNO), which is supported by the moderate d-band center and Bader charge value.

Multivariate covalent organic frameworks with tailored electrostatic potential promote nitrate electroreduction to ammonia in acid

The direct synthesis of ammonia from nitrate (NO3-) reduction in acid is a promising approach for industrialization. However, the difficulty arises from the intense competition with the inevitable hydrogen evolution reaction, which is favoured due to the overwhelming protons (H+). Here, we systematically explore and rationally optimize the microenvironment using multivariate covalent organic frameworks (COFs) as catalyst adlayers to promote the nitrate-to-ammonia conversion in acid. With the application of tailored positive electrostatic potential generated over the multivariate COFs, both the mass transfer of NO3- and H+ are regulated via appropriate electrostatic interactions, thus realizing the priority of NO3RR with respect to HER or NO3--to-NO2-. As a result, an NH3 yield rate of 11.01 mmol h-1 mg-1 and a corresponding Faradaic efficiency of 91.0% are attained, and solid NH4Cl with a high purity of 96.2% is directly collected in acid; therefore, this method provides a practical approach for economically valorising wastewater into valuable ammonia.

Subnanometric Nickel Phosphide Heteroclusters with Highly Active Niδ+-Pδ- Pairs for Nitrate Reduction toward Ammonia

The development of efficient electrocatalysts for the neutral nitrate reduction reaction (NO3-RR) toward ammonia (NH3) is essential to address the environmental issues caused by NO3- but remains considerably challenging owing to the sluggish reaction kinetics of NO3-RR in neutral media. Herein, we report subnanometric heteroclusters with strongly coupled nickel-phosphorus (Ni-P) dual-active sites as electrocatalysts to boost the neutral NO3-RR. Experimental and theoretical results reveal that the subnanometric feature of Ni-P heteroclusters promotes the electron transfer from Ni to P, generating Niδ+-Pδ- active pairs, in which Niδ+ species are highly active for the NO3-RR and Pδ- tunes the interfacial water hydrogen bonding network to promote the water dissociation step and accelerate proton transfer during the NO3-RR. Consequently, in the neutral NO3-RR, Ni-P heteroclusters exhibit a large NH3 yield rate of 0.61 mmol h-1 cm-2 at -0.8 V versus reversible hydrogen electrode, which is 2.8- and 3.3-fold larger than those on Ni-P nanoparticles and Ni clusters, respectively, and the generated NH3 exists as NH4+ in electrolytes. This study offers an efficient approach to boosting electrocatalytic reactions with multiple intermediates by designing subnanometric heteroclusters with strongly coupled active sites.

Mechanistic Insights into the CO2-Assisted NO Electrochemical Deoxygenation and Hydrogenation

Electrocatalytic NO reduction to NH3 holds significant potential for pollutant treatment and resource recovery. Herein, we report that the introduction of CO2 on octahedral oxide-derived copper (o-OD-Cu) significantly enhances the electrochemical reduction of NO to NH3. With 10% NO in a CO2 environment, the Faradaic efficiency for NH3 production in a flow cell remains around 80% over a wide current density range from 20 to 250 mA cm-2. At a current density of 250 mA cm-2, the yield can reach up to 1403.9 µmol cm-2 h-1, which is 3.71 times higher than without CO2 and surpasses the performance reported in similar literature. Moreover, even at a low concentration of 1% NO, the Faradaic efficiency can reach a maximum of 70.11% at a current density of 20 mA cm-2. In situ investigations and theoretical calculations revealed that, in the coexistence of NO and CO2, the NO reduction pathway involves a unique route wherein *CO and *COOH, produced from CO2 reduction, can respectively promote the deoxygenation of *NO and hydrogenation of *N by acquiring O atoms from *NO and providing H atoms for the sustained hydrogenation of *N, thereby accelerating the conversion process of NO to NH3.

Enhanced p-d Orbital Coupling in Unconventional Phase RhSb Alloy Nanoflowers for Efficient Ammonia Electrosynthesis in Neutral Media

Phase control provides a promising approach for physicochemical property modulation of metal/alloy nanomaterials toward various electrocatalytic applications. However, the controlled synthesis of alloy nanomaterials with unconventional phases remains challenging, especially for those containing both p- and d-block metals. Here, we report the one-pot synthesis of ultrathin RhSb alloy nanoflowers (NFs) with an unconventional 2H phase. Using 2H RhSb NFs as an electrocatalyst for nitrite reduction reaction in neutral media, the optimal NH3 Faradaic efficiency and yield rate can reach up to 96.8% and 47.2 mg h-1 mgcat -1 at -0.3 and -0.6 V (vs. reversible hydrogen electrode), respectively. With 2H RhSb NFs as a bifunctional cathode catalyst, the as-assembled zinc-nitrite/methanol batteries deliver a high energy efficiency of 96.4% and improved rechargeability with 120-h stable running. Ex/in situ characterizations and theoretical calculations have demonstrated that the phase change of RhSb from face-centered cubic (fcc) to 2H has optimized the electronic structure through stronger interactions between Rh and Sb by p-d orbital couplings, which improves the adsorption of key intermediates and reduces the reaction barriers of nitrite reduction to guarantee the efficient electrocatalysis. This work offers a feasible strategy of boosting the electrocatalytic performance of alloy nanostructures by integrating phase control and p-d orbital coupling.

Tuning the Acid Hardness Nature of Cu Catalyst for Selective Nitrate-to-Ammonia Electroreduction

Electrocatalytic nitrate reduction reaction (NO3RR) in alkaline electrolyte presents a sustainable pathway for energy storage and green ammonia (NH3) synthesis. However, it remains challenging to obtain high activity and selectivity due to the limited protonation and/or desorption processes of key intermediates. Herein, we propose a strategy to regulate the acid hardness nature of Cu catalyst by introducing appropriate modifier. Using density functional theory calculations, we firstly identified that the BaO-modified Cu showed optimal Gibbs free energies for key NO3RR steps, including the protonation of *NO and the desorption of *NH3. Experimentally, the BaO-modified Cu catalyst exhibited 97.3 % Faradaic efficiency (FE) for NH3 with a yield rate of 356.9 mmol h-1 gcat -1. It could also maintain high activity across a wide range of applied potentials and nitrate substrate concentrations. Detailed experimental and theoretical studies revealed that the Ba species could modulate the local electronic states of Cu, enhance the electron transfer rate, and optimize the adsorption/protonation/desorption processes of the N-containing intermediates, leading to the excellent catalytic performance for NO3 --to-NH3.

Mechanism of oxygen vacancy engineering CoOX/Fe3O4 regulated electrocatalytic reduction of nitrate to ammonia

To enhance the activity of the nitrate reduction reaction (NO3-RR), the development of oxygen vacancies electrocatalysts is a promising approach for improving the efficiency of ammonia synthesis. However, the mechanism by which oxygen vacancies regulate NO3-RR to ammonia remains poorly understood. In this study, a series of CoOX/Fe3O4 composite catalysts derived from ZIF-67 containing oxygen vacancies (OVs) were synthesized to elucidate the role of OVs on the activity and selectivity of ammonia synthesis. Structural characterization revealed that the concentration of OVs in the catalysts increased with the addition of iron ions. Electrochemical experiments and theoretical calculations demonstrated that OVs promote interfacial electron transfer, alter the adsorption conformation of NO3* on the catalyst surface, and reduce the activation energy barrier of NO3*. Nonetheless, we observed that high concentrations of OVs exhibited a preference for the product NO2- at high potentials, which we attribute to the strong adsorption of NO* by the OVs, impeding the subsequent hydrogenation process. Additionally, electron paramagnetic resonance (EPR) and activated hydrogen (H*) quenching experiments indicated that the catalyst was unable to deliver substantial amounts of H* in the buffered electrolyte, resulting in low ammonia productivity. The ammonia Faraday current efficiency (FE) of CoOX/Fe3O4-90 in 0.1 M KOH and 0.1 M NO3- was 82.22 %, with an ammonia production rate of 1.09 mmol h-1 cm-2.

Bias-Free Solar-Driven Ammonia Coupled to C3-Dihydroxyacetone Production through Photoelectrochemistry

Conversion of solar energy into value-added chemicals through photoelectrochemistry (PEC) holds great potential for advancing sustainable development but limits by high onset potential which affects energy conversion efficiencies. Herein, we utilized a CuPd cocatalyst-modified Sb2(S,Se)3 photocathode (CuPd/TSSS) to achieve an ultra-low onset potential of 0.83 VRHE for photoelectrochemical ammonia synthesis. Meanwhile, we achieved unbiased NH3 production by synthesizing major value-added C3-dihydroxyacetone (DHA) through glycerol oxidation on the BiVO4 photoanode with the loading Pd cocatalyst, instead of a traditional solar water oxidation reaction. The PEC integrated system stably produced 11.98 μmol cm-2 of NH3 and 201.9 mmol m-2 of DHA over 5 h with ~80 % faradaic efficiency without applying additional bias. In situ analysis and theoretical calculations confirmed high catalytic activity for ammonia synthesis at the CuPd/TSSS photocathode and enhanced selectivity for DHA at the Pd/BiVO4 photoanode. This design represents a breakthrough in directly utilizing solar energy, nitrate-containing wastewater, and biomass waste for ammonia and highly value-added C3 production, which addresses increasing energy demands while decreasing environmental impact.

Polyoxometalates for the catalytic reduction of nitrogen oxide and its derivatives: from novel structures to functional applications

Nitrogen oxide and its derivatives, including nitroaromatic hydrocarbons and various other nitro compounds, are commonly used in industrial applications such as synthesizing drugs, dyes, pesticides, and explosives. However, these compounds are also highly toxic to the environment. Their long-term accumulation can significantly affect air and water quality and disrupt ecosystems. Thus, efficiently converting these harmful compounds into more valuable products through catalytic processes is an urgent challenge in chemical catalysis. In this regard, polyoxometalates (POMs) have emerged as promising inorganic molecular catalysts for the reduction of nitrogen oxide and its derivatives. Their unique structure, excellent redox properties, and versatile catalytic abilities contribute to their effectiveness. This review provides an overview of recent advancements in the POM-catalyzed reduction of nitrogen oxide and its derivatives, focusing on reducing nitroaromatic hydrocarbons and nitrogen oxides. Additionally, we discuss the reaction mechanisms involved in the catalytic process, explore the potential of POMs' structural features for the rational design and optimization of catalytic performance, and highlight future directions for developing POM-based catalysts.

Tailoring the Catalytic Activity of Metal Catalysts by Laser Irradiation

In recent years, the rapid advancements in laser technology have garnered considerable interest as an efficient method for synthesizing electrocatalytic nanomaterials. This review delves into the progress made in laser-induced nanomaterials for electrocatalysis, providing a comprehensive overview of the synthesis strategies and catalytic mechanisms involved in defect engineering, morphology tuning, and heterostructure formation. The review highlights the various laser-induced synthesis techniques in producing nanomaterials with enhanced electrocatalytic properties. It discusses the underlying mechanisms through which laser irradiation can induce defects, modify morphology, and create heterostructures in nanomaterials, ultimately leading to improved catalytic performance. The comprehensive summary of these synthesis strategies and catalytic mechanisms provides valuable insights for researchers interested in utilizing laser technology for the fabrication of advanced electrocatalytic materials. Furthermore, this review identifies the existing challenges and outlines future directions within this booming research field. By addressing the current limitations and discussing potential avenues for exploration, the review provides important guidance for researchers looking to design and fabricate laser-induced nanomaterials with desirable properties for advanced electrocatalysis and beyond.

Intensifying Interfacial Reverse Hydrogen Spillover for Boosted Electrocatalytic Nitrate Reduction to Ammonia

Rational regulation of active hydrogen (*H) behavior is crucial for advancing electrocatalytic nitrate reduction reaction (NO3RR) to ammonia (NH3), yet in-depth understanding of the *H generation, transfer, and utilization remains ambiguous, and explorations for *H dynamic optimization are urgently needed. Herein we engineer a Ni3N nanosheet array intimately decorated with Cu nanoclusters (NF/Ni3N-Cu) for remarkably boosted NO3RR. From comprehensive experimental and theoretical investigations, the Ni3N moieties favors water dissociation to generate *H, and then *H can rapidly transfer to the Cu via unique reverse hydrogen spillover mediating interfacial Ni-N-Cu bridge bond, thus increasing *H coverage on the Cu site for subsequent deoxygenation/hydrogenation. More impressively, such intriguing reverse hydrogen spillover effect can be further strengthened via elegant engineering of the Ni3N/Cu heterointerface with more intimate contact. Consequently, the NF/Ni3N-Cu with Cu nanoclusters intimate anchoring presents record NH3 yield rate of 1.19 mmol h-1 cm-2 and Faradaic efficiency of 98.7 % at -0.3 V vs. RHE, being on par with the state-of-the-art ones. Additionally, with NF/Ni3N-Cu as the cathode, a high-performing Zn-NO3 - battery can be assembled. This contribution illuminates a novel pathway to optimize *H behavior via distinct reverse hydrogen spillover for promoted NO3RR and other hydrogenation reactions.

Highly selective electrocatalytic reduction of nitrate to ammonia over a copper-cobalt bimetallic catalyst

The electrocatalytic nitrate reduction reaction (NitRR) is a promising alternative to the traditional Haber-Bosch process. However, the competitive hydrogen evolution reaction results in poor NH3 selectivity (S NH3). Here, a Cu-Co bimetallic catalyst supported on biomass-derived porous carbon (Cu-Co/BPC) is designed and synthesized. Interestingly, the catalyst presents a high NH3 yield rate of 9114.1 ± 244.8 μg h-1 cm-2 at -1.4 V (vs. RHE) and a high faradaic efficiency (FE) of 84.5 ± 1.6% at -1.0 V (vs. RHE). Notably, the S NH3 of Cu-Co/BPC catalyst is kept above 94.2% under a broad range from -1.0 to -1.4 V (vs. RHE), indicating the high NitRR-to-NH3 selectivity of Cu-Co/BPC. The combination of in situ characterization and experimental results indicates that the electron transfer occurs between Cu and Co, and many active sites are generated for adsorption and activation of N[double bond, length as m-dash]O double bonds, and hydrogenation reactions occur with adjacent H protons to improve the selectivity of NH3.

Intermetallic PtSn Nanosheets with p-d Orbital Hybridization for Selective Hydroxylamine Electrosynthesis

The electrocatalytic nitrate reduction to hydroxylamine (NH2OH) is a challenging catalytic process that has gained significant attention. However, its performance is hindered by the low selectivity of the electrocatalysts. Here, intermetallic PtSn nanosheets with p-d orbital hybridization have been synthesized, which significantly enhances the performance of electrocatalytic nitrate reduction to NH2OH. The Faradaic efficiency of NH2OH reaches a maximum of 82.83 ± 1.55% at -0.10 V versus the reversible hydrogen electrode (vs RHE), and the yield of NH2OH achieves 6.15 ± 0.32 mmol h-1 mgcat-1 at -0.25 V vs RHE. Mechanistic studies reveal that p-d orbital hybridization between p-block Sn and d-block Pt effectively enhances nitrate adsorption and NH2OH desorption to boost electrochemical NH2OH synthesis. Given their excellent performance in the electrochemical synthesis of NH2OH, PtSn nanosheets are utilized as the cathode in an alkaline-acid hybrid Zn-NO3- battery to facilitate the production of NH2OH, achieving an NH2OH FE of 80.42%.

Efficient co-production of ammonia and formic acid from nitrate and polyester via paired electrolysis

Paired electrolysis, which integrates a productive cathodic reaction, such as the nitrate reduction reaction (NO3-RR) with selective oxidation at the anode, offers an intriguing way to maximize both atomic and energy efficiency. However, in a conventional design, the NO3-RR is often coupled with the anodic oxygen evolution reaction, leading to substantial energy consumption while yielding low-value oxygen. Here, we report a hybrid electrolysis system that combines cathodic reduction of nitrate to ammonia and anodic oxidation of polyethylene-terephthalate-derived ethylene glycol (EG) to formic acid (FA), utilizing oxygen-vacancy-rich (OV) Co3O4 and Cu doped Ni(OH)2 as the cathode and anode, respectively. Remarkably, this paired electrolysis system demonstrates a faradaic efficiency (FE) of 92% for cathodic ammonia production and a FE of 99% for anodic FA production, while reducing the cell voltage by 0.54 V compared to the conventional NO3-RR system at the same current density of 100 mA cm-2. Experimental investigations combined with theoretical calculations reveal that the OV introduction effectively addresses the insufficient NO3- adsorption and hydrogenation on bare Co3O4. Additionally, Cu incorporation increases the Ni-O covalency, resulting in an improved EG adsorption ability. This work presents a promising way for waste management via paired electrolysis.

Efficient Electrocatalytic Conversion of Nitrate in Water with Anderson-Type Polyoxometalate-Modified Co-MOF

The electrochemical conversion of nitrate to ammonia has garnered growing attention, as it aims to reduce carbon emissions and promote environmental sustainability. Nevertheless, developing an electrocatalyst that exhibits outstanding activity, selectivity, and stability is still a significant challenge. Here, we report three Anderson-type polyoxometalates (POMs)-modified cobalt metal-organic framework (Co-MOF), namely, Co-MOF/MMo6 (M = Fe, Co, Ni) composite electrocatalyst, fabricated using an easy standing method. Among them, POMs not only facilitated the formation of lamellar structures with a high specific surface area of Co-MOF as a morphology regulator but also contributed to electron transfer between Co-MOF as an electron-rich cluster, achieving an enhancement in the catalytic performance of NO3RR to NH3. In particular, Co-MOF/NiMo6 exhibits NO3RR performance with maximal Faradaic efficiency of 98.2% at -0.8 V vs the reverse hydrogen electrode (vs reversible hydrogen electrode (RHE)) and NH3 yield rate of up to 10.88 mg h-1 mgcat.-1, better than most previously reported MOF-based catalysts. By in situ spectrometric measurement, we demonstrate that the NH3 formation via a kinetically favored pathway of NO3- → *NO3 → *NO2 → *NO → *NH2OH → *NH3. This work indicates the considerable potential of POM-based MOF materials for the electrochemical NO3RR to NH3.

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.

Promoting *NO2 Hydrogeneration on Cobalt-Doped Copper Oxides for Selective Ammonia Electrosynthesis from Nitrate

Electrochemical nitrate reduction reaction (NO3RR) driven by renewable energy has attracted extensive attention, which can realize nitrate degradation and ammonia production simultaneously under ambient conditions. Copper-based catalysts are the most widely used due to their high activity but are subject to low selectivity owing to intermediate nitrite accumulation. This work has reported cobalt-doped copper oxide (Co/CuO) composites, while introduced Co sites accelerate the hydrogenation of nitrogen species. The prepared Co/CuO composites realize a 93.9 % Faradaic efficiency at the applied potential of -0.4 V (vs. RHE), yielding ammonia at 0.5441 mmol⋅h-1 cm-2. The exceptional stability of Co/CuO composites has also been affirmed by following continuous recycling tests. In situ characterization confirms that the existence of Co sites is prone to conversion of *NO2 to *NH2, thus exhibiting high performance for NO3RR.

Overcoming Energy-Scaling Barriers: Efficient Ammonia Electrosynthesis on High-Entropy Alloy Catalysts

Electrochemically converting nitrate (NO3 -) to value-added ammonia (NH3) is a complex process involving an eight-electron transfer and numerous intermediates, presenting a significant challenge for optimization. A multi-elemental synergy strategy to regulate the local electronic structure at the atomic level is proposed, creating a broad adsorption energy landscape in high-entropy alloy (HEA) catalysts. This approach enables optimal adsorption and desorption of various intermediates, effectively overcoming energy-scaling limitations for efficient NH3 electrosynthesis. The HEA catalyst achieved a high Faradaic efficiency of 94.5 ± 4.3% and a yield rate of 10.2 ± 0.5 mg h-1 mgcat -1. It also demonstrated remarkable stability over 250 h in an integrated three-chamber device, coupling electrocatalysis with an ammonia recovery unit for continuous NH3 collection. This work elucidates the catalytic mechanisms of multi-functional HEA systems and offers new perspectives for optimizing multi-step reactions by circumventing adsorption-energy scaling limitations.

Boosting Amino Acid Synthesis with WOx Sub-Nanoclusters

The conversion of nitrate-rich wastewater and biomass-derived blocks into high-value products using renewably generated electricity is a promising approach to modulate the artificial carbon and nitrogen cycle. Here, a new synthetic strategy of WOx sub-nanoclusters is reported and supported on carbon materials as novel efficient electrocatalysts for nitrate reduction and its coupling with α-keto acids. In acidic solutions, the NH3-NH2OH selectivity can also optimized by adjusting the potential, with the total FE exceeding 80% over a wide potential range. After introducing α-keto acids, the WOx/D-CB electrode achieves remarkable activity and selectivity toward C2-C6 amino acids. For glycine and alanine, impressive FEs of 49.34% and 38.22% based on transitional metal oxides can be obtained, surpassing those of WOx nanoclusters with larger size. In situ analysis and mechanistic studies reveal the critical role of WOx sub-nanoclusters in reducing the energy barriers of key steps in alanine synthesis. This work opens up new insights into the rational design of cluster catalysts to promote electrochemical amino acid synthesis.

Capturing Copper Single Atom in Proton Donor Stimulated O-End Nitrate Reduction

Ammonia (NH3) is vital in global production and energy cycles. Electrocatalytic nitrate reduction (e-NO3RR) offers a promising route for nitrogen (N) conversion and NH3 synthesis, yet it faces challenges like competing reactions and low catalyst activity. This study proposes a synergistic mechanism incorporating a proton donor to mediate O-end e-NO3RR, addressing these limitations. A novel method combining ultraviolet radiation reduction, confined synthesis, and microwave treatment was developed to create a model catalyst embedding Cu single atoms on La-based nanoparticles (p-CNCusLan-m). DFT analysis emphasizes the critical role of La-based clusters as proton donors in e-NO3RR, while in situ characterization reveals an O-end adsorption reduction mechanism. The catalyst achieves a remarkable Faraday efficiency (FENH3) of 97.7%, producing 10.6 mol gmetal -1 h-1 of NH3, surpassing most prior studies. In a flow cell, it demonstrated exceptional stability, with only a 9% decrease in current density after 111 hours and a NH3 production rate of 1.57 mgNH3/h/cm-2. The proton donor mechanism's effectiveness highlights its potential for advancing electrocatalyst design. Beyond NH3 production, the O-end mechanism opens avenues for exploring molecular-oriented coupling reactions in e-NO3RR, paving the way for innovative electrochemical synthesis applications.

Self-Triggering a Locally Alkaline Microenvironment of Co4Fe6 for Highly Efficient Neutral Ammonia Electrosynthesis

Electrochemical nitrate reduction reaction (eNO3-RR) to ammonia (NH3) holds great promise for the green treatment of NO3- and ambient NH3 synthesis. Although Fe-based electrocatalysts have emerged as promising alternatives, their excellent eNO3-RR-to-NH3 activity is usually limited to harsh alkaline electrolytes or alloying noble metals with Fe in sustainable neutral electrolytes. Herein, we demonstrate an unusual self-triggering localized alkalinity of the Co4Fe6 electrocatalyst for efficient eNO3-RR-to-NH3 activity in neutral media, which breaks down the conventional pH-dependent kinetics restrictions and shows a 98.6% NH3 Faradaic efficiency (FE) and 99.9% NH3 selectivity at -0.69 V vs RHE. The synergetic Co-Fe dual sites were demonstrated to enable the optimal free energies of eNO3-RR-to-NH3 species and balance water dissociation and protonation of adsorbed NO2-. Notably, the Co4Fe6 electrocatalysts can attain a high current density of 100 mA cm-2 with a high NH3 FE surpassing 96% and long-term stability for over 500 h eNO3-RR-to-NH3 in a membrane electrode assembly (MEA) electrolyzer. This work provides insight into tailoring the self-reinforced local-alkalinity on the Fe-based alloy electrocatalysts for eNO3-RR-to-NH3 and thus avoids alkaline electrolytes and noble metals for practical sustainable nitrate upcycling technology.

Selenium-Deficient FeSe2/Fe3O4 Electrocatalyst for Nitrate Reduction to Ammonia

Electrocatalytic reduction of NO3 - is a green and sustainable method that not only helps to treat industrial pollutants in wastewater, but also produces valuable chemicals. However, the slow dynamics of the proton-coupled electron transfer process results in a high barrier and low conversion efficiency. In this work, the Se-deficient FeSe2/Fe3O4 heterojunction was synthesized, which showed excellent electrochemical performance in 0.1 M nitrate reduction reaction, superior to most currently reported catalysts. The high activity of Se-deficient FeSe2/Fe3O4 is due to the synergistic effect between FeSe2 and Fe3O4 to achieve relay catalytic NO3 - reduction. Among them, the Se-deficient FeSe2 contributes to NO3 - deoxygenation and subsequent hydrogenation, and Fe3O4 promotes H2O decomposition to provide H proton, jointly promote NO3RR. Finally, the online differential electrochemical mass spectra (DEMS), in situ Raman and DFT calculation confirmed the optimal pathway for NO3RR to NH3 on Se-deficient FeSe2/Fe3O4(100). This strategy of relay catalysis provides a potential way to treat wastewater with high concentration nitrate.

"Soft armor" regulates the electrocatalytic microenvironment for nitrate reduction to ammonia to greatly enhance stability

An interfacial "soft armor" of hydrogel coating on FeOOH nanowire/Ti mesh structures regulates the electrolytic microenvironment, attracts reductive intermediates, prevents catalyst failure, and enables continuous, stable ammonia production from nitrate electrocatalysis for 60 hours at a rate of 8.64 mg h-1 cm-2, boosting the nitrate-to-ammonia conversion efficiency and durability.

Solar-Driven High-Rate Ammonia Production from Wastewater Coupled with Plastic Waste Reforming

Solar-powered electrochemical NH3 synthesis offers the benefits of sustainability and absence of CO2 emissions but suffers from a poor solar-to-ammonia yield rate (SAY) due to a low NH3 selectivity, large bias caused by the sluggish oxygen evolution reaction, and low photocurrent in the corresponding photovoltaics. Herein, a highly efficient photovoltaic-electrocatalytic system enabling high-rate solar-driven NH3 synthesis was developed. A high-performance Ru-doped Co nanotube catalyst was used to selectively promote the nitrite reduction reaction (NO2RR), exhibiting a faradaic efficiency of 99.6% and half-cell energy efficiency of 52.3% at 0.15 V vs the reversible hydrogen electrode, delivering a high NO2RR selectivity even in electrolytes with high NO3- and low NO2- concentrations. Thus, the promoted NO2RR was coupled with the ethylene glycol oxidation reaction and a perovskite photovoltaic cell to achieve the highest SAY reported to date (146 ± 1 μmol h-1 cm-2) and stable operation.

Unraveling the Structural Evolution of Cobalt Sulfides in Electrocatalytic NO3RR: the Inescapable Influence of Cl. Inorg Chem 2025;64:2787-2794. [PMID: 39915902 DOI: 10.1021/acs.inorgchem.4c04780] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Electrochemical nitrate reduction (NO3RR) to ammonia is an attractive approach for mitigating NO3- pollution and producing valuable NH3. Cobalt-sulfur compounds are widely considered to be potential electrocatalysts for NO3RR. However, there is still a lack of research on the probable structural evolution, long-term stability, and reactive sites of cobalt-based sulfides during catalysis. Herein, we have employed three cobalt sulfides (CoSx, where x = 8/9, 2, 1.097) with different sulfur contents as catalysts for electrocatalytic NO3RR under alkaline conditions. At -0.8 V vs RHE, all these CoSx show promising performances that Faradaic efficiencies of >80% and a high yield of >1780 mmol h-1 gcat-1 for NH3 production are achieved. Through a combination of X-ray diffraction (XRD), transmission electron microscopy (TEM), and other characterizations, it is revealed that all these cobalt sulfides are easily converted into cobalt hydroxide during the NO3RR. This phenomenon is seemingly contradictory to the thermodynamic prediction that, according to the Pourbaix diagram, these CoSx compounds should be stable even under the catalytic condition. We suggest that this is due to the presence of Cl- ions in the electrolyte that promote the transformation of CoSx toward Co(OH)2. Chloride ions are commonly found in both industrial settings and natural water bodies and are challenging to remove. The evolved Co(OH)2 species is proposed to be responsible for catalyzing NO3RR, especially during a long-term catalytic process. This study highlights the inevitable structural evolution of CoSx catalysts under current alkaline electrocatalytic NO3RR conditions, offering theoretical guidance for the judicious selection and design of future catalysts.

Enhancing Low-Concentration Electroreduction of NO to NH3 via Potential-Controlled Active Site-Intermediate Interactions

Electronic defect states in catalysts are recognized as highly effective active sites for enhancing the low-concentration electroreduction of NO to NH3 (NORR). Their structures dynamically evolve with applied electrode potentials, allowing the active sites to adjust interactions with intermediates, thereby improving electrocatalytic performance. However, the dynamic changes in these interactions under applied potentials remain poorly understood, hindering the design of more diverse electrocatalytic systems. Herein, we developed a strategy that unitizes electrode potential to control the interactions between active sites and intermediates over oxygen vacancy-modified TiO2 (VO-TiO2-x) to enhance NORR performance. By combining state-of-the-art constant inner potential (CIP) DFT calculations with in situ (spectro)electrochemical measurements, we investigated how the electrode potential influences these interactions in NORR. The results clearly demonstrate that applying an external potential alters the spatial symmetry of degenerate orbitals of Ti3+ to facilitate the generation of key intermediates for NO-to-NH3 conversion. Therefore, the VO-TiO2-x catalyst exhibited superior NORR performance with a NH3 Faradaic efficiency up to 76.4 % and a high NH3 yield rate of 632.9 μg h-1 mgcat. -1 under 1.0 vol % NO atmosphere, which is competitive with those of previously reported works under higher NO concentration (above 10 vol %). Remarkably, the NORR process achieved a record-breaking NH3 yield of 2292.7 μg h-1 mgcat. -1 in a membrane electrode assembly (MEA) electrolyzer under the same conditions. This study opens a new avenue for enhancing electrocatalytic activity by adjusting operating conditions, thereby transcending the limitations of material design.

Precise structural regulation of copper-based electrocatalysts for sustainable nitrate reduction to ammonia

The electrocatalytic reduction of nitrate to ammonia (NRA) technology not only achieves the effective removal of nitrates in the environment but also produces value-added products-NH3. In recent years, copper-based materials have shown tremendous application prospects in this field due to their excellent conductivity, moderate cost, and their proximity of d orbital energy levels to the LUMO π∗ molecular orbitals of nitrate. This review starts with copper-based catalysts to elucidate the reaction mechanisms of NRA and its influencing factors, while summarizing and analyzing the principles and pros and cons of various modification strategies. Then, we will explore the impact of different modification strategies on improving NRA performance and the underlying theoretical mechanisms. Finally, this review proposes the current challenges and prospects of copper-based materials, aiming to provide a reference for the further development and industrial application of copper-based catalysts.