Atomic-dispersed copper simultaneously achieve high-efficiency removal and high-value-added conversion to ammonia of nitrate in sewage

Single-atom catalysts for electrocatalytic nitrate reduction into ammonia

Ammonia (NH3) is a versatile and important compound with a wide range of uses, which is currently produced through the demanding Haber-Bosch process. Electrocatalytic nitrate reduction into ammonia (NRA) has recently emerged as a sustainable approach for NH3synthesis under ambient conditions. However, the NRA catalysis is a complex multistep electrochemical process with competitive hydrogen evolution reaction that usually results in poor selectivity and low yield rate for NH3synthesis. With maximum atom utilization and well-defined catalytic sites, single atom catalysts (SACs) display high activity, selectivity and stability toward various catalytic reactions. Very recently, a number of SACs have been developed as promising NRA electrocatalysts, but systematical discussion about the key factors that affect their NRA performance is not yet to be summarized to date. This review focuses on the latest breakthroughs of SACs toward NRA catalysis, including catalyst preparation, catalyst characterization and theoretical insights. Moreover, the challenges and opportunities for improving the NRA performance of SACs are discussed, with an aim to achieve further advancement in developing high-performance SACs for efficient NH3synthesis.

Copper-based electro-catalytic nitrate reduction to ammonia from water: Mechanism, preparation, and research directions

Global water bodies are increasingly imperiled by nitrate pollution, primarily originating from industrial waste, agricultural runoffs, and urban sewage. This escalating environmental crisis challenges traditional water treatment paradigms and necessitates innovative solutions. Electro-catalysis, especially utilizing copper-based catalysts, known for their efficiency, cost-effectiveness, and eco-friendliness, offer a promising avenue for the electro-catalytic reduction of nitrate to ammonia. In this review, we systematically consolidate current research on diverse copper-based catalysts, including pure Cu, Cu alloys, oxides, single-atom entities, and composites. Furthermore, we assess their catalytic performance, operational mechanisms, and future research directions to find effective, long-term solutions to water purification and ammonia synthesis. Electro-catalysis technology shows the potential in mitigating nitrate pollution and has strategic importance in sustainable environmental management. As to the application, challenges regarding complexity of the real water, the scale-up of the commerical catalysts, and the efficient collection of produced NH3 are still exist. Following reseraches of catalyst specially on long term stability and in situ mechanisms are proposed.

Optimization of "sulfur-iron-nitrogen" cycle in constructed wetlands by adjusting siderite/sulfur (Fe/S) ratio

Sulfur-siderite autotrophic denitrification (SSAD) has been proved to solve the key problem of low nitrogen removal efficiency caused by the shortage of carbon source in constructed wetlands (CWs). In this study, five vertical flow constructed wetlands (VFCWs) were constructed with different Fe/S ratios (0/0, 0/1, 1/1, 2/1 and 1/2) to optimizing SSAD process, labeled S.0, S.1, S.2, S.3 and S.4. The results showed that the best NO3--N and TN removal rates were achieved with a Fe/S ratio of 2:1 (S.3), which were 96.26 ± 1.40% and 93.63 ± 3.12%, respectively. The abundance of denitrification genes (nirS, nirK and nosZ) in S.3 was significantly increased. Illumina high-throughput sequencing analysis indicated that the abundance and diversity of microorganisms involved in the "Sulfur-Iron-Nitrogen" cycle were enriched in S.3. The current study provided that the "Sulfur-Iron-Nitrogen" cycle in CWs was optimized by adjusting Fe/S ratio, and more types of denitrifying bacteria could be enriched, thereby enhancing nitrogen removal.

Functional partitioning synergistically enhances multi-scenario nitrate reduction

The promising electrocatalytic nitrate reduction reaction (eNitRR) for distributed ammonia synthesis requires the fine design of functionally compartmentalised and synergistically complementary integrated catalysts to meet the needs of low-cost and efficient ammonia synthesis. Herein, the partitionable CoP3 and Cu3P modules were built on the copper foam substrate, and the functional differentiation promoted the catalytic performance of the surface accordion-like CoP3/Cu3P@CF for eNitRR in complex water environment. Where the ammonia yield rate is as high as 23988.2 μg h-1 cm-2, and the Faradaic efficiency is close to 100 %. With CoP3/Cu3P@CF as the core, the assembled high-performance Zn-nitrate flow battery can realize the dual function of ammonia production and power supply, and can also realize the continuous production of ammonia with high selectivity driven by solar energy. The ammonia recovery reaches 753.9 mg L-1, which shows the superiority of CoP3/Cu3P@CF in multiple application scenarios and provides important experience for the vigorous development of eNitRR. Density functional theory calculation reveal that CoP3 and Cu3P sites play a relay synergistic role in eNitRR catalyzed by CoP3/Cu3P@CF. CoP3 first promotes the activation of NO3- to *NO3H, and then continuously provides proton hydrogen for the eNitRR on the surface of Cu3P, which relays the synergistic catalytic effect to promote the efficient conversion of NO3- to NH3. This study not only develops a catalyst that can promote the efficient reduction of NO3- to ammonia through an easy-to-obtain innovative strategy, but also provides an alternative strategy for the development of eNitRR that is suitable for multiple scenarios and meets the production conditions.

Self-supported iron-doped cobalt-copper oxide heterostructures for efficient electrocatalytic denitrification

The electrocatalytic reduction of nitrate ions (NO3-) to nitrogen gas (N2) has emerged as an effective approach for mitigating nitrate pollution in water bodies. However, the development of efficient and highly selective cathode materials remains challenging. Conventional copper-based catalysts often exhibit low selectivity because they strongly adsorb oxygen. In this study, a straightforward solvothermal and pyrolysis method was used to grow iron-doped cobalt-copper oxide heterogeneous structures on copper foam surfaces (Fe-CoO/CuO@CF). Then, the effects of the applied potential, initial NO3- concentration, Cl- concentration, electrolyte pH, and different catalysts on the catalyst performance were investigated. Compared with recently reported congeners, Fe-CoO/CuO@CF is less expensive and exhibits outstanding activity for NO3- reduction. Meanwhile, under a cathode potential of - 1.31 V vs. Ag/AgCl, Fe-CoO/CuO@CF degrades 98.6 % of NO3- in 200 min. In addition, when employing a method inspired by NH4+ removal by breakpoint chlorination, N2 selectivity over Fe-CoO/CuO@CF was raised from 10 % without Cl- to 99.7 % when supplemented with Cl-. The catalyst demonstrated excellent cyclic stability, maintaining a high electrocatalytic activity for the conversion of NO3- to N2 gas over eleven cycles. Moreover, Fe-CoO/CuO@CF enabled 63.7 % removal of NO3- from wastewater (50 mg/L NO3--N) prepared from natural water, with 100 % conversion to N2. Computational studies showed that iron doping decreased the free energy change of the intermediate of NO3- reduction reaction. This study provides an effective strategy for the electrochemical reduction of nitrate to nitrogen gas and offers good prospects for addressing nitrate pollution.

Efficient Electrochemical Nitrate Removal by Ordered Ultrasmall Intermetallic AuCu3 via Enhancing Nitrate Adsorption

Developing a high-performance electrocatalyst for synthesizing ammonia from nitrate represents a promising solution for addressing wastewater pollution and achieving sustainable ammonia production. However, it remains a formidable challenge. Herein, an intermetallic AuCu3 electrocatalyst with high-density active sites is designed and prepared for an efficient nitrate electroreduction to generate ammonia. Remarkably, the Faraday efficiency and yield rate of ammonia at -0.9 V are 97.6% and 75.9 mg h-1 cm-2, respectively. More importantly, after 10 cycles of testing, the removal rate of nitrate can still reach 95.2%. Electrochemical in situ Fourier transform infrared analysis indicates that AuCu3 IM can promote the adsorption of nitrate and enhance ammonia production from nitrate. *NH3, *NO, and *NO2 have been proven to be active intermediates. Theoretical and experimental studies show that the Au site can provide a large amount of *H for nitrate reduction, and the Cu site is conducive to the reduction of nitrate to produce nitrogen-containing products. Meanwhile, AuCu3 intermetallic compounds (AuCu3 IM) can inhibit the dimerization of *H. The power density and ammonia yield of the assembled Zn-nitrate battery reached 2.17 mW cm-2 and 71.2 mg h-1 cm-2, respectively.

Novel insights into carbon nanomaterials enhancing anammox for nitrogen removal: Effects and mechanisms

Carbon nanomaterials (CNMs) possess the properties including large specific surface area, high porosity, and stable chemical structures, presenting significant application advantages in wastewater treatment. Indeed, CNMs are considered to be added to anammox systems to strengthen anammox function, especially to resolve the challenge of anammox technology, i.e., the slow growth rate of anammox bacteria, as well as its high environmental sensitivity. This paper systematically reviews the promotion effects and mechanisms of CNMs on the nitrogen removal performance of anammox system. Among the zero-, one-, and two-dimensional CNMs, two-dimensional CNMs have best promoting effect on the nitrogen removal performance of anammox system due to its excellent conductivity and abundant functional groups. Then, the promotion effects of CNMs on anammox process are summarized from the perspective of anammox activity and bacteria abundance. Furthermore, CNMs not only enhance the anammox process, but also stimulate the coupling of denitrification pathways with anammox, as well as the improvement of system operational stability (alleviating the inhibitions of low temperature and pH fluctuation), thus contributing to the promoted nitrogen removal performance. Essentially, CNMs are capable of facilitating microbial immobilization and electron transfer, which favor to improve the efficiency and stability of anammox process. Finally, this review highlights the gap in knowledge and future work, aiming to provide a deeper understanding of how CNMs can strengthen the anammox system and provide a novel perspective for the engineering of the anammox process.

Self-supported P-doped NiFe2O4 micro-sheet arrays for the efficient conversion of nitrite to ammonia

The nitrite reduction reaction (NO2-RR) is an important process for eliminating toxic nitrites from water while simultaneously producing high-value ammonia under ambient conditions. For the aim to improve the NO2-RR efficiency, we designed a new synthetic strategy to prepare a phosphorus-doped three-dimensional NiFe2O4 catalyst loaded onto a nickel foam in-situ and evaluated its performance for the reduction of NO2- to NH3. The catalyst achieved a high Faradaic efficiency (FE) of 95.39%, and an ammonia (NH3) yield rate of 34788.51 µg h-1 cm-2 at - 0.45 V vs. RHE. A high NH3 yield rate and FE were maintained after 16 cycles at - 0.35 V vs. RHE in an alkaline electrolyte. This study provides a new direction for the rational design of highly stable electrocatalysts for the conversion of NO2- to NH3.

Modulating the Active Hydrogen Adsorption on Fe─N Interface for Boosted Electrocatalytic Nitrate Reduction with Ultra-Long Stability

The electrocatalytic reduction of nitrate (NO3 - ) to nitrogen (N2 ) is an environmentally friendly approach for efficient N-cycle management (toward a nitrogen-neutral cycle). However, poor catalyst durability and the competitive hydrogen evolution reaction significantly impede its practical application. Interface-chemistry engineering, utilizing the close relationship between the catalyst surface/interface microenvironment and electron/proton transfer process, has facilitated the development of catalysts with high intrinsic activity and physicochemical durability. This study reports the synthesis of a nitrogen-doped carbon-coated rice-like iron nitride (RL-Fe2 N@NC) electrocatalyst with excellent electrocatalytic nitrate-reduction reaction activity (high N2 selectivity (≈96%) and NO3 - conversion (≈86%)). According to detailed mechanistic investigations by in situ tests and theoretical calculations, the strong hydrogenation ability of iron nitride and enhanced nitrate enrichment of the system synergistically contribute to the rapid hydrogenation of nitrogen-containing species, increasing the intrinsic activity of the catalyst and reducing the occurrence of the competing hydrogen-evolution side reaction. Moreover, RL-Fe2 N@NC shows excellent stability, retaining good NO3 - -to-N2 electrocatalysis activity for more than 40 cycles (one cycle per day). This paper could guide the interfacial design of Fe-based composite nanostructures for electrocatalytic nitrate reduction, facilitating a shift toward nitrogen neutrality.

Transition Metal Single-Atom Catalysts for the Electrocatalytic Nitrate Reduction: Mechanism, Synthesis, Characterization, Application, and Prospects

Excessive accumulation of nitrate in the environment will affect human health. To combat nitrate pollution, chemical, biological, and physical technologies have been developed recently. The researcher favors electrocatalytic reduction nitrate reaction (NO3 RR) because of the low post-treatment cost and simple treatment conditions. Single-atom catalysts (SACs) offer great activity, exceptional selectivity, and enhanced stability in the field of NO3 RR because of their high atomic usage and distinctive structural characteristics. Recently, efficient transition metal-based SACs (TM-SACs) have emerged as promising candidates for NO3 RR. However, the real active sites of TM-SACs applied to NO3 RR and the key factors controlling catalytic performance in the reaction process remain ambiguous. Further understanding of the catalytic mechanism of TM-SACs applied to NO3 RR is of practical significance for exploring the design of stable and efficient SACs. In this review, from experimental and theoretical studies, the reaction mechanism, rate-determining steps, and essential variables affecting activity and selectivity are examined. The performance of SACs in terms of NO3 RR, characterization, and synthesis is then discussed. In order to promote and comprehend NO3 RR on TM-SACs, the design of TM-SACs is finally highlighted, together with the current problems, their remedies, and the way forward.

Electrochemical nitrogen fixation on single metal atom catalysts

The electrochemical reduction of nitrogen (eNRR) offers a promising alternative to the Haber-Bosch (H-B) process for producing ammonia under moderate conditions. However, the inertness of dinitrogen and the competing hydrogen evolution reaction pose significant challenges for eNRR. Thus, developing more efficient electrocatalysts requires a deeper understanding of the underlying mechanistic reactions and electrocatalytic activity. Single atom catalysts, which offer tunable catalytic properties and increased selectivity, have emerged as a promising avenue for eNRR. Carbon and metal-based substrates have proven effective for dispersing highly active single atoms that can enhance eNRR activity. In this review, we explore the use of atomically dispersed single atoms on different substrates for eNRR from both conceptual and experimental perspectives. The review is divided into four sections: the first section describes eNRR mechanistic pathways, the second section focuses on single metal atom catalysts (SMACs) with metal atoms dispersed on carbon substrates for eNRR, the third section covers SMACs with metal atoms dispersed on non-carbon substrates for eNRR, and the final section summarizes the remaining challenges and future scope of eNRR for green ammonia production.

Metal-organic framework-derived Cu nanoparticle binder-free monolithic electrodes with multiple support structures for electrocatalytic nitrate reduction to ammonia

Electrocatalytic nitrate reduction to ammonia, which removes nitrates from aquatic ecosystems, is a potential alternative to the classical Haber-Bosch process. Nevertheless, the selectivity of ammonia is often affected by the toxic by-product nitrite. Here, the polyhedral-supported Cu nanoparticle binder-free monolithic electrode (Cu-BTC-Cu) is synthesized by the in situ electroreduction of Cu metal-organic framework (Cu-MOF) precursors. The Cu-BTC-Cu displays a high ammonia yield of 4.00 mg h-1 cm-2cat and a faradaic efficiency of 83.8% in 0.05 M K2SO4 (pH = 7), greatly outperforming the rod-supported (Cu-BTEC-Cu) and unsupported (Cu-BDC-Cu) Cu nanoparticle monolithic electrodes. Impressively, the Cu-BTC-Cu can inhibit significantly the release of by-product NO2- and present favourable stability after 10 consecutive cycles. These preeminent properties can be attributed to the polyhedral structure, which enables better dispersion of Cu nanoparticles and brings more active sites. Moreover, the reaction mechanism of Cu-BTC-Cu is analysed by electrochemical in situ characterization and several key intermediates are captured. This work provides new insights into the modification of the electrocatalytic nitrate reduction activity of Cu-based catalysts and ideas for the design of high-efficiency electrodes.

Boron-cluster-based porous BCN material modified electrode for electrochemical determination of morphine in serum

Porous highly boron-doped BCN (p-BCN) was produced by using a boron cluster salt (closo-[B₁₂H₁₂]^2-) as the boron-based precursor and SiO₂ as a hard template. The synthesized p-BCN was used in an electrochemical sensor for the ultrasensitive and highly selective detection of morphine (MOP). The optimal conditions for MOP detection were determined by optimizing the experimental conditions. Under these optimal conditions, the p-BCN-based sensor exhibited excellent MOP detection performance (working potential of 0.2 V). Specifically, it showed a detection range of 0.05 to 200 μM and a detection limit of 17.8 nM. Notably, the p-BCN-based electrochemical sensor was successfully applied to the determination of MOP in human blood, and the results showed satisfactory recovery and accuracy. Therefore, this sensor can be used as an effective platform for the detection of MOP in human blood samples.

Interfacially Engineered Nanoporous Cu/MnOx Hybrids for Highly Efficient Electrochemical Ammonia Synthesis via Nitrate Reduction

Electrochemical reduction of nitrate to ammonia (NH₃ ) not only offers a promising strategy for green NH₃ synthesis, but also addresses the environmental issues and balances the perturbed nitrogen cycle. However, current electrocatalytic nitrate reduction processes are still inefficient due to the lack of effective electrocatalysts. Here 3D nanoporous Cu/MnO_x hybrids are reported as efficient and durable electrocatalysts for nitrate reduction reaction, achieving the NH₃ yield rates of 5.53 and 29.3 mg h^-1 mg_cat. ^-1 with 98.2% and 86.2% Faradic efficiency in 0.1 m Na₂ SO₄ solution with 10 and 100 mm KNO₃ , respectively, which are higher than those obtained for most of the reported catalysts under similar conditions. Both the experimental results and density functional theory calculations reveal that the interface effect between Cu/MnO_x interface could reduce the free energy of rate determining step and suppress the hydrogen evolution reaction, leading to the enhanced catalytic activity and selectivity. This work provides an approach to design advanced materials for NH₃ production via electrochemical nitrate reduction.

Theoretical insights into dissociative-associative mechanism for enhanced electrochemical nitrate reduction to ammonia

The development of electrochemical nitrate reduction reaction (NO₃RR) is a "two birds-one stone" method, which can not only remove NO₃^- pollutant, but also produce valuable ammonia (NH₃). However, a mechanistic understanding of the nitrate reduction process remains very limited. Herein, we highlighted a dissociative-associative mechanism for the NO₃RR, in which the N-O bond of nitrate is initially broken to form *O and *NO₂ intermediate adsorbed on two active sites (dissociation process) and then subsequently hydrogenated and reduced to ammonia (association process). By taking a series of diatomic site catalysts (CuTM/g-CN and CuTM/N₆C, TM= Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn) as models, we systematically investigate the dissociative-associative mechanism for the NO₃RR and compared with the Cu-based single-atom catalysts which follows the traditional directly associative mechanism. Density functional theory (DFT) calculations show that dissociative-associative mechanism is energetically favorable on seven catalysts (CuTi/g-CN, CuV/g-CN, CuMn/g-CN, CuCo/g-CN, CuV/N₆C, CuCr/N₆C and CuFe/N₆C) with the significantly reduced limiting potential of - 0.14 V to - 0.47 V. Specifically, an efficiently screening strategy was proposed to determine the dissociative-associative or directly associative mechanism for NO₃RR. This work can provide useful guideline for the rational design and development of NO₃RR electrocatalysts.

Electron Modulation and Morphology Engineering Jointly Accelerate Oxygen Reaction to Enhance Zn-Air Battery Performance

Combining morphological control engineering and diatomic coupling strategies, heteronuclear FeCo bimetals are efficiently intercalated into nitrogen-doped carbon materials with star-like to simultaneously accelerate oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The half-wave potential and kinetic current density of the ORR driven by FeCoNC/SL surpass the commercial Pt/C catalyst. The overpotential of OER is as low as 316 mV (η₁₀ ), and the mass activity is at least 3.2 and 9.4 times that of mononuclear CoNC/SL and FeNC/SL, respectively. The power density and specific capacity of the Zn-air battery with FeCoNC/SL as air cathode are as high as 224.8 mW cm^-2 and 803 mAh g^-1 , respectively. Morphologically, FeCoNC/SL endows more reactive sites and accelerates the process of oxygen reaction. Density functional theory reveals the active site of the heteronuclear diatomic, and the formation of FeCoN5C configuration can effectively tune the d-band center and electronic structure. The redistribution of electrons provides conditions for fast electron exchange, and the change of the center of the d-band avoids the strong adsorption of intermediate species to simultaneously take into account both ORR and OER and thus achieve high-performance Zn-air batteries.

Iron-Based Nanocatalysts for Electrochemical Nitrate Reduction

Nitrate has a high level of stability and persistence in water, endangering human health and aquatic ecosystems. Due to its high reliability and efficiency, the electrochemical nitrate reduction reaction (NO₃ RR) is regarded as the best available option for mitigating excess nitrate in water and wastewater, especially for the removal of trace levels of nitrate. One of the most critical factors in the electrochemical reduction are the catalysts, which directly affect the reaction efficiency of nitrate removal. Iron-based nanocatalysts, which have the advantages of nontoxicity, wide availability, and low cost, have emerged as a promising electrochemical NO₃ RR material in recent years. This review covers major aspects of iron-based nanocatalysts for electrochemical NO₃ RR, including synthetic methods, structural design, performance enhancement, electrocatalytic nitrate reduction test, and reduction mechanism. The recent progress of iron-based nanocatalysts for electrochemical NO₃ RR and the mechanism of functional advantages for modified structures are reviewed from the perspectives of loading, doping, and assembly strategies, in order to realize the conversion from pollutant nitrate to harmless nitrogen or ammonia and other sustainable products. Finally, challenges and future directions for the development of low-cost and highly-efficient iron-based nanocatalysts are explored.

Atom-dispersed copper and nano-palladium in the boron-carbon-nitrogen matric cooperate to realize the efficient purification of nitrate wastewater and the electrochemical synthesis of ammonia

Electrochemical nitrate reduction reaction (NIRR) driven by sustainable energy is not only expected to realize the green production of ammonia under ambient conditions, but also a promising way to purify nitrate wastewater. The ammonia yield rate and Faradaic efficiency of NIRR catalyzed by Pd10Cu/BCN constructed with structural constraints and pre-embedded reducing agent strategies were as high as 102,153 μg h^-1 mg_cat.^-1 and 91.47%, respectively. Pd10Cu/BCN can remove nearly 100% of 50 mg L^-1 NO₃^- without NO₂^- residue within 10 h, and the realization of this effect does not require the participation of any chloride. Control experiments and DFT calculations explain the efficient operation mechanism of NIRR on Pd10Cu/BCN, where the Pd and CuN4 sites play the role of synergistic catalysis. Compared with the reported literature, Pd10Cu/BCN with good biocompatibility has become an outstanding representative of NIRR catalyst, which provides an alternative way for the green production of ammonia and the purification of nitrate wastewater.

Cu Nanoparticle-Decorated Boron-Carbon-Nitrogen Nanosheets for Electrochemical Determination of Chloramphenicol

In the present work, irregular Cu nanoparticle-decorated boron-carbon-nitrogen (Cu-BCN) nanosheets were successfully synthesized. A Cu-BCN dispersion was deposited on a bare glassy carbon electrode (GCE) to prepare an electrochemical sensor (Cu-BCN/GCE) for the detection of chloramphenicol (CAP) in the environment. Cu-BCN was characterized using high-resolution scanning transmission electron microscopy (HRSTEM), scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis, and X-ray photoelectron spectroscopy (XPS). The performance of the Cu-BCN/GCE was studied using electrochemical impedance spectroscopy (EIS), and its advantages were proven by electrode comparison. Differential pulse voltammetry (DPV) was used to optimize the experimental conditions, including the amount of Cu-BCN deposited, enrichment potential, deposition time, and pH of the electrolyte. A linear relationship between the CAP concentration and current response was obtained under the optimized experimental conditions, with a wide linear range and a limit of detection (LOD) of 2.41 nmol/L. Cu-BCN/GCE exhibited high stability, reproducibility, and repeatability. In the presence of various organic and inorganic species, the influence of the Cu-BCN-based sensor on the current response of CAP was less than 5%. Notably, the prepared sensor exhibited excellent performance in real-water samples, with satisfactory recovery.

A vacancy engineered MnO2-x electrocatalyst promotes nitrate electroreduction to ammonia

The NO₃^- reduction reaction (NO₃RR) has recently emerged as a potential approach for sustainable and efficient NH₃ production, whereas exploring high-performance NO₃RR electrocatalysts is highly desirable yet challenging. Herein, we attempted to construct O-vacancies (OVs) on MnO₂ nanosheets and the resulting OV-rich MnO_2-x showed a high NH₃ yield of 3.34 mg h^-1 cm^-2 (at -1.0 V vs. RHE) and an excellent FE of 92.4% (at -0.9 V vs. RHE), together with the outstanding stability. DFT calculations reveal that OVs on MnO₂ serve as catalytic centers to enhance NO₃^- adsorption and dissociation, reduce the energy barriers of hydrogenation steps and thus promote NO₃^--to-NH₃ conversion.

Boosted nitrate electroreduction to ammonia on Fe-doped SnS2 nanosheet arrays rich in S-vacancies

The electrochemical nitrate reduction reaction (NO₃RR) not only holds great potential for the removal of NO₃^- contaminants from the environment, but also potentially provides a renewable-energy-driven NH₃ synthesis method to replace the Haber-Bosch process. Herein, we report that Fe-doped SnS₂ nanosheets enriched with S-vacancies can be used as an efficient NO₃RR catalyst, showing a high NH₃ yield of 7.2 mg h^-1 cm^-2 (at -0.8 V) and a faradaic efficiency of 85.6% (at -0.7 V). Density functional theory (DFT) calculations revealed that S-vacancies on Fe-SnS₂ serve as the main active sites for the NO₃RR and the Fe-doping can further regulate the electronic structure of S-vacancies to optimize the binding energies of NO₃RR intermediates, resulting in reduced energy barriers and enhanced NO₃RR activity.

Atomically Dispersed Cu Sites on Dual-Mesoporous N-Doped Carbon for Efficient Ammonia Electrosynthesis from Nitrate

The industrial Haber-Bosch process for ammonia synthesis is extremely important in modern society. However, it is energy intensive and leads to severe pollution, which has motivated eco-friendly NH₃ synthesis research. Electroreduction of contaminant nitrate ions back to NH₃ is an effective complement but is still limited by low NH₃ yields and nitrate-to-NH₃ selectivities. In this study, the electrochemical nitrate reduction reaction (NTRR) is carried out over a single-atom Cu catalyst. Atomically dispersed Cu sites anchored on dual-mesoporous N-doped carbon framework display excellent NTRR performance with NH₃ production rate of 13.8 mol NH 3  g_cat ^-1  h^-1 and NO₃ ^- -to-NH₃ faradaic efficiency (FE) of 95.5 % at -1.0 V. Cu-N-C catalyst can sustain continuous 120 h NTRR test in the simulated NH₃ synthesis scenarios with large current density (about 200 mA cm^-2 ) and amplified volume of NO₃ ^- solution (9 times). Theoretical calculations reveal that atomically dispersed Cu₁ -N₄ sites reduce the energy barrier of potential-determining step in NTRR and promote the decomposition of primary intermediate in NO₃ ^- -to-N₂ process. These findings provide a guideline for the rational design of highly active, selective and durable electrocatalysts for the NTRR.