Ambient Ammonia Synthesis via Electrochemical Reduction of Nitrate Enabled by NiCo2 O4 Nanowire Array

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.

Revealing the Electro-oxidation Mechanism of 5-Aminotetrazole on Nickel-Based Oxides and Synthesizing 5,5'-Azotetrazolate Salts

With the gradual expansion of the application of organic electromechanical synthesis in the field of energetic materials, it is necessary to explore deeply the mechanisms behind the organic electromechanical oxidation of energetic materials in order to develop efficient electrocatalysts. Electrochemical synthesis of 5,5'-azotetrazolate (ZT) salts is not only environmentally friendly and efficient but also can replace oxygen evolution reaction (OER) combined with hydrogen production, significantly reducing the battery voltage of overall water splitting (OWS) and achieving low energy consumption hydrogen production. Here, we prepared the Co-modified nickel-based oxide electrodes (Ni3-xCoO4/carbon cloth (CC), x = 1, 2) as a medium to reveal the oxidative coupling mechanism of 5-aminotetrazole (5-AT). Experimental and theoretical calculations verified that Ni-catalyzed oxidative coupling of 5-AT is a proton-coupled electron transfer (PCET) process, including electron transfer of electrocatalytic intermediates (Ni2+-O + OH- = Ni3+-O(OH) + e-) and spontaneous dehydrogenation process (Ni3+-O(OH) + X-H = Ni2+-O + X•). The Ni3+-O(OH) is an extremely fast nonreducing electron transfer center that serves as a chemical oxidant to directly abstract hydrogen atoms from the 5-AT. Simultaneously, the synergistic effect of Co doping on the electric cloud around Ni causes the upshift of the d-band centers, which is conducive to the easier adsorption of OH*, forming the generation of active intermediate Ni3+-O(OH). Thus, Ni2CoO4/CC has higher Faraday efficiency (FE) and yield for the oxidation reaction of 5-AT, with a yield of approximately 72.3% after electrolysis at 1.7 V vs reversible hydrogen electrode (RHE).

Regulation of the Fe/Ni ratio on the morphology of FexNiyO4 and the performance of nitrate reduction in ammonia synthesis

The combination of theoretical calculations and experimental synthesis provides valuable insights into the performance of FexNiyO4 as a catalyst for ammonia (NH3) synthesis through the electrocatalytic nitrate reduction reaction (eNO3-RR). Here, an observation of a volcano-shaped trend in the theoretical calculations reveals that the catalytic activity of FexNiyO4 for NH3 synthesis varies with the Fe/Ni ratio. The subsequent experimental syntheses of FexNiyO4 with different Fe/Ni ratios validate this trend and demonstrate the morphological changes associated with the varying Fe/Ni ratios. The evolution of the FexNiyO4 morphology from nanosheets to sea urchin-like structures, nanowires and nanoflowers composed of rotated nanosheets as the Fe/Ni ratio increases further supports the influence of the composition on the resulting morphology. This morphological diversity can be attributed to the specific growth conditions and self-assembly processes involved in the synthesis. The correlation between the Fe/Ni ratio, morphology and NH3 yield reinforces the theoretical calculations. The observed volcanic trend in the NH3 yield, consistent with the theoretical predictions, indicates that there is an optimal Fe/Ni ratio (Fe2NiO4) with the highest NH3 yield of 12.51 mg h-1 cm-2 at -1.1 V. The excellent Faradaic efficiency of 95.97 % in neutral solution further highlights the suitability of Fe2NiO4 as a catalyst for NH3 synthesis through eNO3-RR. Moreover, the remarkable stability of FexNiyO4, regardless of the Fe/Ni ratio, is an important finding. The consistent performance of FexNiyO4 indicates its potential for long-term and practical applications in NH3 synthesis. Furthermore, the observed morphological changes, volcano-shaped trend in the NH3 yield and remarkable stability of FexNiyO4 highlight its potential as a promising catalyst.

Electrocatalytic Nitrate Reduction on Metallic CoNi-Terminated Catalyst with Industrial-Level Current Density in Neutral Medium

Green ammonia synthesis through electrocatalytic nitrate reduction reaction (eNO3RR) can serve as an effective alternative to the traditional energy-intensive Haber-Bosch process. However, achieving high Faradaic efficiency (FE) at industrially relevant current density in neutral medium poses significant challenges in eNO3RR. Herein, with the guidance of theoretical calculation, a metallic CoNi-terminated catalyst is successfully designed and constructed on copper foam, which achieves an ammonia FE of up to 100% under industrial-level current density and very low overpotential (-0.15 V versus reversible hydrogen electrode) in a neutral medium. Multiple characterization results have confirmed that the maintained metal atom-terminated surface through interaction with copper atoms plays a crucial role in reducing overpotential and achieving high current density. By constructing a homemade gas stripping and absorption device, the complete conversion process for high-purity ammonium nitrate products is demonstrated, displaying the potential for practical application. This work suggests a sustainable and promising process toward directly converting nitrate-containing pollutant solutions into practical nitrogen fertilizers.

Two-dimensional Cu Plates with Steady Fluid Fields for High-rate Nitrate Electroreduction to Ammonia and Efficient Zn-Nitrate Batteries

Nitrate electroreduction reaction (eNO3 -RR) to ammonia (NH3) provides a promising strategy for nitrogen utilization, while achieving high selectivity and durability at an industrial scale has remained challenging. Herein, we demonstrated that the performance of eNO3 -RR could be significantly boosted by introducing two-dimensional Cu plates as electrocatalysts and eliminating the general carrier gas to construct a steady fluid field. The developed eNO3 -RR setup provided superior NH3 Faradaic efficiency (FE) of 99 %, exceptional long-term electrolysis for 120 h at 200 mA cm-2, and a record-high yield rate of 3.14 mmol cm-2 h-1. Furthermore, the proposed strategy was successfully extended to the Zn-nitrate battery system, providing a power density of 12.09 mW cm-2 and NH3 FE of 85.4 %, outperforming the state-of-the-art eNO3 -RR catalysts. Coupled with the COMSOL multiphysics simulations and in situ infrared spectroscopy, the main contributor for the high-efficiency NH3 production could be the steady fluid field to timely rejuvenate the electrocatalyst surface during the electrocatalysis.

Structure and Electron Engineering for Nitrate Electrocatalysis to Ammonia: Identification and Modification of Active Sites in Spinel Oxides

Cobalt spinel oxides, which consist of tetrahedral site (AO4) and octahedral site (BO6), are a potential group of transition metal oxides (TMO) for electrocatalytic nitrate reduction reactions to ammonia (NRA). Identifying the true active site in spinel oxides is crucial to designing advanced catalysts. This work reveals that the CoO6 site is the dominant site for NRA through the site substitution strategy. The suitable electronic configuration of Co at the octahedral site leads to a stronger interaction between the Co d-orbital and the O p-orbital in O-containing intermediates, resulting in a high-efficiency nitrate-to-ammonia reduction. Furthermore, the substitution of metallic elements at the AO4 site can affect the charge density at the BO6 site via the structure of A-O-B. Thereafter, Ni and Cu are introduced to replace the tetrahedral site in spinel oxides and optimize the electronic structure of CoO6. As a result, NiCo2O4 exhibits the best activity for NRA with an outstanding yield of NH3 (15.49 mg cm-2 h-1) and FE (99.89%). This study introduces a novel paradigm for identifying the active site and proposes an approach for constructing high-efficiency electrocatalysts for NRA.

Unveiling Cutting-Edge Developments in Electrocatalytic Nitrate-to-Ammonia Conversion

The excessive enrichment of nitrate in the environment can be converted into ammonia (NH3) through electrochemical processes, offering significant implications for modern agriculture and the potential to reduce the burden of the Haber-Bosch (HB) process while achieving environmentally friendly NH3 production. Emerging research on electrocatalytic nitrate reduction (eNitRR) to NH3 has gained considerable momentum in recent years for efficient NH3 synthesis. However, existing reviews on nitrate reduction have primarily focused on limited aspects, often lacking a comprehensive summary of catalysts, reaction systems, reaction mechanisms, and detection methods employed in nitrate reduction. This review aims to provide a timely and comprehensive analysis of the eNitRR field by integrating existing research progress and identifying current challenges. This review offers a comprehensive overview of the research progress achieved using various materials in electrochemical nitrate reduction, elucidates the underlying theoretical mechanism behind eNitRR, and discusses effective strategies based on numerous case studies to enhance the electrochemical reduction from NO3 - to NH3. Finally, this review discusses challenges and development prospects in the eNitRR field with an aim to guide design and development of large-scale sustainable nitrate reduction electrocatalysts.

Selective Reduction of Aqueous Nitrate to Ammonium with an Electropolymerized Chromium Molecular Catalyst

Nitrate (NO3-) is a common nitrogen-containing contaminant in agricultural, industrial, and low-level nuclear wastewater that causes significant environmental damage. In this work, we report a bioinspired Cr-based molecular catalyst incorporated into a redox polymer that selectively and efficiently reduces aqueous NO3- to ammonium (NH4+), a desirable value-added fertilizer component and industrial precursor, at rates of ∼0.36 mmol NH4+ mgcat-1 h-1 with >90% Faradaic efficiency for NH4+. The NO3- reduction reaction occurs through a cascade catalysis mechanism involving the stepwise reduction of NO3- to NH4+ via observed NO2- and NH2OH intermediates. To our knowledge, this is one of the first examples of a molecular catalyst, homogeneous or heterogenized, that is reported to reduce aqueous NO3- to NH4+ with rates and Faradaic efficiencies comparable to those of state-of-the-art solid-state electrocatalysts. This work highlights a promising and previously unexplored area of electrocatalyst research using polymer-catalyst composites containing complexes with oxophilic transition metal active sites for electrochemical nitrate remediation with nutrient recovery.

Engineering the Co(II)/Co(III) Redox Cycle and Coδ+ Species Shuttle for Nitrate-to-Ammonia Conversion

Electroreduction of waste nitrate to valuable ammonia offers a green solution for environmental restoration and energy storage. However, the electrochemical self-reconstruction of catalysts remains a huge challenge in terms of maintaining their stability, achieving the desired active sites, and managing metal leaching. Herein, we present an electrical pulse-driven Co surface reconstruction-coupled Coδ+ shuttle strategy for the precise in situ regulation of the Co(II)/Co(III) redox cycle on the Co-based working electrode and guiding the dissolution and redeposition of Co-based particles on the counter electrode. As result, the ammonia synthesis performance and stability are significantly promoted while cathodic hydrogen evolution and anodic ammonia oxidation in a membrane-free configuration are effectively blocked. A high rate of ammonia production of 1.4 ± 0.03 mmol cm-2 h-1 is achieved at -0.8 V in a pulsed system, and the corresponding nitrate-to-ammonia Faraday efficiency is 91.7 ± 1.0%. This work holds promise for the regulation of catalyst reactivity and selectivity by engineering in situ controllable structural and chemical transformations.

Designing Efficient Nitrate Reduction Electrocatalysts by Identifying and Optimizing Active Sites of Co-Based Spinels

Cobalt-based spinel oxides (i.e., Co3O4) are emerging as low-cost and selective electrocatalysts for the electrochemical nitrate reduction reaction (NO3-RR) to ammonia (NH3), although their activity is still unsatisfactory and the genuine active site is unclear. Here, we discover that the NO3-RR activity of Co3O4 is highly dependent on the geometric location of the Co site, and the NO3-RR prefers to occur at octahedral Co (CoOh) rather than tetrahedral Co (CoTd) sites. Moreover, CoOhO6 is electrochemically transformed to CoOhO5 along with the formation of O vacancies (Ov) during the process of NO3-RR. Both experimental and theoretic results reveal that in situ generated CoOhO5-Ov configuration is the genuine active site for the NO3-RR. To further enhance the activity of CoOh sites, we replace inert CoTd with different contents of Cu2+ cations, and a volcano-shape correlation between NO3-RR activity and electronic structures of CoOh is observed. Impressively, in 1.0 M KOH, (Cu0.6Co0.4)Co2O4 with optimized CoOh sites achieves a maximum NH3 Faradaic efficiency of 96.5% with an ultrahigh NH3 rate of 1.09 mmol h-1 cm-2 at -0.45 V vs reversible hydrogen electrode, outperforming most of other reported nonprecious metal-based electrocatalysts. Clearly, this work paves new pathways for boosting the NO3-RR activity of Co-based spinels by tuning local electronic structures of CoOh sites.

Fluidization and Application of Carbon Nano Agglomerations

Carbon nanomaterials are unique with excellent functionality and diverse structures. However, agglomerated structures are commonly formed because of small-size effects and surface effects. Their hierarchical assembly into micro particles enables carbon nanomaterials to break the boundaries of classical Geldart particle classification before stable fluidization under gas-solid interactions. Currently, there are few systematic reports regarding the structural evolution and fluidization mechanism of carbon nano agglomerations. Based on existing research on carbon nanomaterials, this article reviews the fluidized structure control and fluidization principles of prototypical carbon nanotubes (CNTs) as well as their nanocomposites. The controlled agglomerate fluidization technology leads to the successful mass production of agglomerated and aligned CNTs. In addition, the self-similar agglomeration of individual ultralong CNTs and nanocomposites with silicon as model systems further exemplify the important role of surface structure and particle-fluid interactions. These emerging nano agglomerations have endowed classical fluidization technology with more innovations in advanced applications like energy storage, biomedical, and electronics. This review aims to provide insights into the connections between fluidization and carbon nanomaterials by highlighting their hierarchical structural evolution and the principle of agglomerated fluidization, expecting to showcase the vitality and connotation of fluidization science and technology in the new era.

Phase-Regulated Active Hydrogen Behavior on Molybdenum Disulfide for Electrochemical Nitrate-to-Ammonia Conversion

Electrochemical reduction of nitrate waste is promising for environmental remediation and ammonia preparation. This process includes multiple hydrogenation steps, and thus the active hydrogen behavior on the surface of the catalyst is crucial. The crystal phase referred to the atomic arrangements in crystals has a great effect on active hydrogen, but the influence of the crystal phase on nitrate reduction is still unclear. Herein, enzyme-mimicking MoS2 in different crystal phases (1T and 2H) are used as models. The Faradaic efficiency of ammonia reaches ≈90 % over 1T-MoS2 , obviously outperforming that of 2H-MoS2 (27.31 %). In situ Raman spectra and theoretical calculations reveal that 1T-MoS2 produces more active hydrogen on edge S sites at a more positive potential and conducts an effortless pathway from nitrate to ammonia instead of multiple energetically demanding hydrogenation steps (such as *HNO to *HNOH) performed on 2H-MoS2 .

Rare earth oxide based electrocatalysts: synthesis, properties and applications

As an important strategic resource, rare earths (REs) constitute 17 elements in the periodic table, namely 15 lanthanides (Ln) (La-Lu, atomic numbers from 57 to 71), scandium (Sc, atomic number 21) and yttrium (Y, atomic number 39). In the field of catalysis, the localization and incomplete filling of 4f electrons endow REs with unique physical and chemical properties, including rich electronic energy level structures, variable coordination numbers, etc., making them have great potential in electrocatalysis. Among various RE catalytic materials, rare earth oxide (REO)-based electrocatalysts exhibit excellent performances in electrocatalytic reactions due to their simple preparation process and strong structural variability. At the same time, the electronic orbital structure of REs exhibits excellent electron transfer ability, which can reduce the band gap and energy barrier values of rate-determining steps, further accelerating the electron transfer in the electrocatalytic reaction process; however, there is a lack of systematic review of recent advances in REO-based electrocatalysis. This review systematically summarizes the synthesis, properties and applications of REO-based nanocatalysts and discusses their applications in electrocatalysis in detail. It includes the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), hydrogen oxidation reaction (HOR), oxygen reduction reaction (ORR), carbon dioxide reduction reaction (CO2RR), methanol oxidation reaction (MOR), nitrogen reduction reaction (NRR) and other electrocatalytic reactions and further discusses the catalytic mechanism of REs in the above reactions. This review provides a timely and comprehensive summary of the current progress in the application of RE-based nanomaterials in electrocatalytic reactions and provides reasonable prospects for future electrocatalytic applications of REO-based materials.

Bifunctional bimetallic oxide nanowires for high-efficiency electrosynthesis of 2,5-furandicarboxylic acid and ammonia

It is an appealing avenue for electrosyntheis of high-valued chemicals at both anode and cathode by coupling 5-hydroxymethylfurfural (HMF) oxidation and nitrate reduction reactions simultaneously, while the development such bifunctional electrocatalysts is still in its infancy with dissatisfied selectivity and low yield rate. Here, we first report that Zn-doped Co3O4 nanowires array can be served as an efficient and robust dual-functional catalyst for HMF oxidation and nitrate reduction at ambient conditions. Specifically, the catalyst shows a faradaic efficiency of 91 % and a yield rate of 241.2 μmol h-1 cm-2 for 2,5-furandicarboxylic acid formation together with a high conversion of nearly 100 % at a potential of 1.40 V. It also displays good cycling stability. Besides, the catalyst is capable of catalyzing the reduction of nitrate to NH3, giving a maximal faradaic efficiency of 92 % and a peak NH3 yield rate of 4.65 mg h-1 cm-2 at a potential of -0.70 V. These results surpass those obtained using pristine Co3O4 and are comparable to those of state-of-the-art electrocatalysts. Moreover, the catalyst is further employed as the cathode catalyst to assemble a Zn-nitrate battery, giving a peak power density of 5.24 mW cm-2 and a high yield rate of 0.72 mg h-1 cm-2. Theoretical simulations further reveal that Zn-doping favors the adsorption and dissociation of nitrate and HMF species and reduces the energy barrier as well. Our work demonstrates the potential interest of Co3O4-based materials for the highly selective production of valuable feedstocks via ambient electrolysis.

Electrocatalytic nitrate-to-ammonia conversion on CoO/CuO nanoarrays using Zn-nitrate batteries

Zn-NO3- batteries can generate electricity while producing NH3 in an environmentally friendly manner, making them a very promising device. However, the conversion of NO3- to NH3 involves a proton-assisted 8-electron (8e-) transfer process with a high kinetic barrier, requiring high-performance catalysts to realize the potential applications of this technology. Herein, we propose a heterostructured CoO/CuO nanoarray electrocatalyst prepared on a copper foam (CoO/CuO-NA/CF) that can electrocatalytically and efficiently convert NO3- to NH3 at low potential and achieves a maximum NH3 yield of 296.9 μmol h-1 cm-2 and the Faraday efficiency (FE) of 92.9% at the -0.2 V vs. reversible hydrogen electrode (RHE). Impressively, Zn-NO3- battery based on the monolithic CoO/CuO-NA/CF electrode delivers a high NH3 yield of 60.3 μmol h-1 cm-2, FENH3 of 82.0%, and a power density of 4.3 mW cm-2. This study provides a paradigm for heterostructured catalyst preparation for the energy-efficient production of NH3 and simultaneously generating electrical energy.

Rod-Shaped Spinel Co3O4 and Carbon Nitride Heterostructure-Modified Fluorine-Doped Tin Oxide Electrode as an Electrochemical Transducer for Efficient Sensing of Hydrazine

Engineering low-cost and efficient materials for sensing hydrazine (HA) is critical given the adverse effects of high concentrations on humans. We report an efficient electrode made up of rod-shaped Co3O4/g-C3N4 (Co3O4/graphitic carbon nitride (GCN))-coated fluorine-doped tin oxide as a desirable electrode for the detection of HA. GCN is synthesized by the thermal decomposition of melamine, Co3O4, and the heterostructure is grown by a hydrothermal process. The as-prepared materials were characterized by using spectroscopic and microscopic techniques. The voltammetric studies showed that HA can be oxidized at a lower onset potential of 0.24 V vs reference Ag/AgCl, and the composite yielded a significantly enhanced oxidation peak current than the pure components because of the high electrocatalytic activity and the synergy between Co3O4 and GCN. By employing chronoamperometry, the proposed sensor can detect HA in a wide range with a high sensitivity of 819.52 μA mM-1 cm-2 and a detection limit of 3.14 μM. The high conductivity of Co3O4, enhanced electroactive surface area, the rich redox couples of Co2+/Co3+, and the additional catalytic sites from GCN are responsible for the high performance of the heterostructure.

Cu doping in FeP enabling efficient electrochemical nitrate reduction to ammonia in neutral media

Electrochemical nitrate reduction to ammonia (NH3) not only provides a promising strategy for green NH3 synthesis, but also removes harmful nitrates from water. Herein, a Cu-doped FeP electrocatalyst was prepared for nitrate reduction, which achieved a high NH3 faradaic efficiency of 92.5% and a high NH3 yield of 0.787 mmol h-1 cm-2 in a neutral electrolyte, greatly surpassing its FeP counterpart.

Ag-Co3 O4 -CoOOH-Nanowires Tandem Catalyst for Efficient Electrocatalytic Conversion of Nitrate to Ammonia at Low Overpotential via Triple Reactions

The electrocatalytic conversion of nitrate (NO3 ‾) to NH3  (NO3 RR) offers a promising alternative to the Haber-Bosch process. However, the overall kinetic rate of NO3 RR is plagued by the complex proton-assisted multiple-electron transfer process. Herein, Ag/Co3 O4 /CoOOH nanowires (i-Ag/Co3 O4  NWs) tandem catalyst is designed to optimize the kinetic rate of intermediate reaction for NO3 RR simultaneously. The authors proved that NO3 ‾ ions are reduced to NO2 ‾ preferentially on Ag phases and then NO2 ‾ to NO on Co3 O4  phases. The CoOOH phases catalyze NO reduction to NH3  via NH2 OH intermediate. This unique catalyst efficiently converts NO3 ‾ to NH3  through a triple reaction with a high Faradaic efficiency (FE) of 94.3% and a high NH3  yield rate of 253.7 μmol h-1  cm-2  in 1 M KOH and 0.1 M KNO3  solution at -0.25 V versus RHE. The kinetic studies demonstrate that converting NH2 OH into NH3  is the rate-determining step (RDS) with an energy barrier of 0.151 eV over i-Ag/Co3 O4  NWs. Further applying i-Ag/Co3 O4  NWs as the cathode material, a novel Zn-nitrate battery exhibits a power density of 2.56 mW cm-2  and an FE of 91.4% for NH3  production.

Boosting Electrocatalytic Nitrate-to-Ammonia via Tuning of N-Intermediate Adsorption on a Zn-Cu Catalyst

The renewable-energy-powered electroreduction of nitrate (NO3 - ) to ammonia (NH3 ) has garnered significant interest as an eco-friendly and promising substitute for the Haber-Bosch process. However, the sluggish kinetics hinders its application at a large scale. Herein, we first calculated the N-containing species (*NO3 and *NO2 ) binding energy and the free energy of the hydrogen evolution reaction over Cu with different metal dopants, and it was shown that Zn was a promising candidate. Based on the theoretical study, we designed and synthesized Zn-doped Cu nanosheets, and the as-prepared catalysts demonstrated excellent performance in NO3 - -to-NH3 . The maximum Faradaic efficiency (FE) of NH3 could reach 98.4 % with an outstanding yield rate of 5.8 mol g-1  h-1 , which is among the best results up to date. The catalyst also had excellent cycling stability. Meanwhile, it also presented a FE exceeding 90 % across a wide potential range and NO3 - concentration range. Detailed experimental and theoretical studies revealed that the Zn doping could modulate intermediates adsorption strength, enhance NO2 - conversion, change the *NO adsorption configuration to a bridge adsorption, and decrease the energy barrier, leading to the excellent catalytic performance for NO3 - -to-NH3 .

Surface-Reconstructed Copper Foil Free-Standing Electrode with Nanoflower Cu/Ce2O3 by In Situ Electrodeposition Reduction for Electrocatalytic Nitrate Reduction to Ammonia

The electrocatalytic reduction of nitrate to ammonia (NRA) is considered to be a promising and environmentally friendly alternative to the Haber-Bosch process. Herein, a simple in situ electrodeposition-reduction method is proposed, which allows for the surface reconstruction and modification of copper foil by introducing cerium. The surface modification results in the formation of Cu/Ce2O3 nanoflowers on the copper electrode surface. Additionally, density functional theory calculations demonstrate that Ce2O3 enhances the adsorption of NO3-. Compared with a pure copper electrode, the NRA performance of surface-reconstructed copper is greatly improved, with the maximum ammonia yield rate and the highest Faradaic efficiency from 24.8% to 73.0% and from 0.081 to 0.386 mmol h-1 cm-2, respectively. The 15N isotope labeling experiment confirms that the nitrogen source in the ammonia originated from nitrate.

Fe and Cu Double-Doped Co3O4 Nanorod with Abundant Oxygen Vacancies: A High-Rate Electrocatalyst for Tandem Electroreduction of Nitrate to Ammonia

The electrochemical nitrate reduction reaction (NO3RR) is an attractive green alternative to the conventional Haber-Bosch method for the synthesis of NH3. However, this reaction is a tandem process that involves multiple steps of electrons and protons, posing a significant challenge to the efficient synthesis of NH3. Herein, we report a high-rate NO3RR electrocatalyst of Fe and Cu double-doped Co3O4 nanorod (Fe1/Cu2-Co3O4) with abundant oxygen vacancies, where the Cu preferentially catalyzes the rapid conversion of NO3- to NO2- and the oxygen vacancy in the Co3O4 substrate can accelerate NO2- reduction to NH3. In addition, the introduction of Fe can efficiently capture atomic H* that promotes the dynamics of NO2- to NH3, improving Faradaic efficiency of the produced NH3. Controlled experimental results show that the optimal electrocatalyst of Fe1/Cu2-Co3O4 exhibits good performance with high conversion (93.39%), Faradaic efficiency (98.15%), and ammonia selectivity (98.19%), which is significantly better than other Co-based materials. This work provides guidance for the rational design of high-performance NO3RR catalysts.

Electrochemical Postmodification-Induced Surface Atom Rearrangement over Cu Nanodendrites for Enhanced Electrosynthesis of Ammonia from Nitrate

Utilizing nitrate from wastewater as a N-source for ammonia synthesis via electrocatalysis is of significance for both environmental protection and ecological nitrogen cycle balance, which requires high-performance electrocatalysts to drive selective nitrate-to-ammonia transformation. In this work, an electrochemical postmodification strategy was developed to regulate the surface structure of presynthesized Cu nanodendrites at the atomic level. A combination of physicochemical characterization and electrochemical study demonstrates that such a treatment could induce surface Cu atom rearrangement and result in increased electrochemically active surface area and high density of surface-active sites, disclosing a high electrocatalytic nitrate-to-ammonia capability, with an optimal NH3 yield rate of 0.2238 mmol h-1 cm-2 and a corresponding Faradaic efficiency of 94.43%. This study may provide a guiding design avenue for atomic arrangement engineering of metallic nanocrystals via electrochemical postmodification for nitrate reduction reaction and other energy conversion electrocatalysis.

Pd-Doped Co3 O4 Nanoarray for Efficient Eight-Electron Nitrate Electrocatalytic Reduction to Ammonia Synthesis

Ammonia (NH3 ) is an indispensable feedstock for fertilizer production and one of the most ideal green hydrogen rich fuel. Electrochemical nitrate (NO3 - ) reduction reaction (NO3 - RR) is being explored as a promising strategy for green to synthesize industrial-scale NH3 , which has nonetheless involved complex multi-reaction process. This work presents a Pd-doped Co3 O4 nanoarray on titanium mesh (Pd-Co3 O4 /TM) electrode for highly efficient and selective electrocatalytic NO3 - RR to NH3 at low onset potential. The well-designed Pd-Co3 O4 /TM delivers a large NH3 yield of 745.6 µmol h-1 cm-2 and an extremely high Faradaic efficiency (FE) of 98.7% at -0.3 V with strong stability. These calculations further indicate that the doping Co3 O4 with Pd improves the adsorption characteristic of Pd-Co3 O4 and optimizes the free energies for intermediates, thereby facilitating the kinetics of the reaction. Furthermore, assembling this catalyst in a Zn-NO3 - battery realizes a power density of 3.9 mW cm-2 and an excellent FE of 98.8% for NH3 .

Coordinative Stabilization of Single Bismuth Sites in a Carbon-Nitrogen Matrix to Generate Atom-Efficient Catalysts for Electrochemical Nitrate Reduction to Ammonia

Electrochemical nitrate reduction to ammonia powered by renewable electricity is not only a promising alternative to the established energy-intense and non-ecofriendly Haber-Bosch reaction for ammonia generation but also a future contributor to the ever-more important denitrification schemes. Nevertheless, this reaction is still impeded by the lack of understanding for the underlying reaction mechanism on the molecular scale which is necessary for the rational design of active, selective, and stable electrocatalysts. Herein, a novel single-site bismuth catalyst (Bi-N-C) for nitrate electroreduction is reported to produce ammonia with maximum Faradaic efficiency of 88.7% and at a high rate of 1.38 mg h-1 mgcat -1 at -0.35 V versus reversible hydrogen electrode (RHE). The active center (described as BiN2 C2 ) is uncovered by detailed structural analysis. Coupled density functional theory calculations are applied to analyze the reaction mechanism and potential rate-limiting steps for nitrate reduction based on the BiN2 C2 model. The findings highlight the importance of model catalysts to utilize the potential of nitrate reduction as a new-generation nitrogen-management technology based on the construction of efficient active sites.

Constructing Ru@C3 N4 /Cu Tandem Electrocatalyst with Dual-Active Sites for Enhanced Nitrate Electroreduction to Ammonia

Electroreduction of nitrate to ammonia reaction (NO₃ ^- RR) is considered as a promising carbon-free energy technique, which can eliminate nitrate from waste-water also produce value-added ammonia. However, it remains a challenge for achieving satisfied ammonia selectivity and Faraday efficiency (FE) due to the complex multiple-electron reduction process. Herein, a novel Tandem electrocatalyst that Ru dispersed on the porous graphitized C₃ N₄ (g-C₃ N₄ ) encapsulated with self-supported Cu nanowires (denoted as Ru@C₃ N₄ /Cu) for NO₃ ^- RR is presented. As expected, a high ammonia yield of 0.249 mmol h^-1  cm^-2 at -0.9 V and high FE_NH3 of 91.3% at -0.8 V versus RHE can be obtained, while achieving excellent nitrate conversion (96.1%) and ammonia selectivity (91.4%) in neutral solution. In addition, density functional theory (DFT) calculations further demonstrate that the superior NO₃ ^- RR performance is mainly resulted from the synergistic effect between the Ru and Cu dual-active sites, which can significantly enhance the adsorption of NO₃ ^- and facilitate hydrogenation, as well as suppress the hydrogen evolution reaction, thus lead to highly improved NO₃ ^- RR performances. This novel design strategy would pave a feasible avenue for the development of advanced NO₃ ^- RR electrocatalysts.

Interfacial Engineering of Bimetallic Ni/Co-MOFs with H-Substituted Graphdiyne for Ammonia Electrosynthesis from Nitrate

The electrochemical synthesis of ammonia is highly dependent on the coupling reaction between nitrate and water, for which an electrocatalyst with a multifunctional interface is anticipated to promote the deoxygenation and hydrogenation of nitrate with water. Herein, by engineering the surface of bimetallic Ni/Co-MOFs (NiCoBDC) with hydrogen-substituted graphdiyne (HsGDY), a hybrid nanoarray of NiCoBDC@HsGDY with a multifunctional interface has been achieved toward scale-up of the nitrate-to-ammonia conversion. On the one hand, a partial electron transfers from Ni²⁺ to the coordinatively unsaturated Co²⁺ on the surface of NiCoBDC, which not only promotes the deoxygenation of *NO₃ on Co²⁺ but also activates the water-dissociation to *H on Ni²⁺. On the other hand, the conformal coated HsGDY facilitates both electrons and NO₃^- ions gathering on the interface between NiCoBDC and HsGDY, which moves forward the rate-determining step from the deoxygenation of *NO₃ to the hydrogenation of *N with both *H on Ni²⁺ and *H₂O on Co²⁺. As a result, such a NiCoBDC@HsGDY nanoarray delivers high NH₃ yield rates with Faradaic efficiency above 90% over both wide potential and pH windows. When assembled into a galvanic Zn-NO₃^- battery, a power density of 3.66 mW cm^-2 is achieved, suggesting its potential in the area of aqueous Zn-based batteries.

Nano-Polycrystalline Cu Layer Interlaced with Ti3+-Self-Doped TiO2 Nanotube Arrays as an Electrocatalyst for Reduction of Nitrate to Ammonia

The electrochemical nitrate reduction reaction (NO₃RR) is considered as a promising strategy to degrade nitrate-containing wastewater and synthesize recyclable ammonia at atmospheric pressure and room temperature. In this work, the copper oxides-derived nano-polycrystalline Cu (NPC Cu) was integrated with Ti³⁺-self-doped TiO₂ nanotube arrays (NTA) to fabricate the NPC Cu/H-TiO₂ NTA. Ti³⁺-self-doped TiO₂ NTAs and the NPC Cu facilitate electron transfer and mass transportation and create abundant active sites. The unique nanostructure in which Cu nano-polycrystals interlace with the TiO₂ nanotube accelerates the electron transfer from the substrate to surface NPC Cu. The density functional theory calculations confirm that the built-in electric field between Cu and TiO₂ improves the adsorption characteristic of the NPC Cu/H-TiO₂ NTA, thereby converting the endothermic NO₃^- adsorption step into an exothermic process. Therefore, the high NO₃^- conversion of 98.97%, the Faradic efficiency of 95.59%, and the ammonia production yield of 0.81 mg cm^-2 h^-1 are achieved at -0.45 V vs reversible hydrogen electrode in 10 mM NaNO₃ (140 mg L^-1)-0.1 M Na₂SO₄. This well-designed NPC Cu/H-TiO₂ NTA as an effective electrocatalyst for the 8e^- NO₃RR possesses promising potential in the applications of ammonia production.

Electrochemical generation of hydrogen peroxide from a zinc gallium oxide anode with dual active sites

Electrochemical water oxidation enables the conversion of H₂O to H₂O₂. It holds distinct advantages to the O₂ reduction reaction, which is restricted by the inefficient mass transfer and limited solubility of O₂ in aqueous media. Nonetheless, most reported anodes suffer from high overpotentials (usually >1000 mV) and low selectivity. Electrolysis at high overpotentials often causes serious decomposition of peroxides and leads to declined selectivity. Herein, we report a ZnGa₂O₄ anode with dual active sites to improve the selectivity and resist the decomposition of peroxides. Its faradaic efficiency reaches 82% at 2.3 V versus RHE for H₂O₂ generation through both direct (via OH^-) and indirect (via HCO₃^-) pathways. The percarbonate is the critical species generated through the conversion of bicarbonate at Ga-Ga dual sites. The peroxy bond is stable on the surface of the ZnGa₂O₄ anode, significantly improving faradaic efficiency.

Constructing Co@TiO2 Nanoarray Heterostructure with Schottky Contact for Selective Electrocatalytic Nitrate Reduction to Ammonia

Electrochemical nitrate (NO₃ ^- ) reduction reaction (NO₃ ^- RR) is a potential sustainable route for large-scale ambient ammonia (NH₃ ) synthesis and regulating the nitrogen cycle. However, as this reaction involves multi-electron transfer steps, it urgently needs efficient electrocatalysts on promoting NH₃  selectivity. Herein, a rational design of Co nanoparticles anchored on TiO₂  nanobelt array on titanium plate (Co@TiO₂ /TP) is presented as a high-efficiency electrocatalyst for NO₃ ^- RR. Density theory calculations demonstrate that the constructed Schottky heterostructures coupling metallic Co with semiconductor TiO₂  develop a built-in electric field, which can accelerate the rate determining step and facilitate NO₃ ^- adsorption, ensuring the selective conversion to NH₃ . Expectantly, the Co@TiO₂ /TP electrocatalyst attains an excellent Faradaic efficiency of 96.7% and a high NH₃  yield of 800.0 µmol h^-1  cm^-2  under neutral solution. More importantly, Co@TiO₂ /TP heterostructure catalyst also presents a remarkable stability in 50-h electrolysis test.

Oxygen Vacancy Induced Strong Metal-Support Interactions on Ni/Ce0.8Zr0.2O2 Nanorod Catalysts for Promoting Steam Reforming of Toluene: Experimental and Computational Studies

To develop an efficient Ni-based steam reforming catalyst for tar removal from the products of biomass gasification, Ni/Ce_0.8Zr_0.2O₂ nanorods were designed. The Ni/Ce_0.8Zr_0.2O₂ nanorod was used as a catalyst in steam reforming of toluene, which was regarded as a model compound of biomass gasification tar. At gas hourly space velocity (GHSV) of 24,000 h^-1 and Ni loading of 5 wt %, the 5Ni/Ce_0.8Zr_0.2O₂ nanorod catalyst achieved 100% of toluene conversion at 600 °C. After 10 h of operation, toluene conversion still reached 87.6%, and the carbon deposition rate was only 1.9 mg/g_cat h^-1. The experimental results demonstrated that the 5Ni/Ce_0.8Zr_0.2O₂ nanorod catalyst showed much higher catalytic activity and coking resistance than other Ni-based catalysts reported in the literature. Through different characterization technologies and density functional theory calculations, it was confirmed that the excellent catalytic performance was attributed to the strong metal-support interaction (SMSI) between Ni and the {100} facet of Ce_0.8Zr_0.2O₂. The special surface structure of {100} allowed Ni atoms to anchor to the surface oxygen vacancies and maintained its reduced state by electron transport between surface atoms. The anchored Ni facilitated oxygen vacancies formation and H₂O dissociation on the support, while the support modulated the electronic structure of Ni, which promoted its ability to toluene activation.

Enabled Efficient Ammonia Synthesis and Energy Supply in a Zinc-Nitrate Battery System by Separating Nitrate Reduction Process into Two Stages

The aqueous electrocatalytic reduction of NO₃ ^- into NH₃ (NitrRR) presents a sustainable route applicable to NH₃ production and potentially energy storage. However, the NitrRR involves a directly eight-electron transfer process generally required a large overpotential (<-0.2 V versus reversible hydrogen electrode (vs. RHE)) to reach optimal efficiency. Here, inspired by biological nitrate respiration, the NitrRR was separated into two stages along a [2+6]-electron pathway to alleviate the kinetic barrier. The system employed a Cu nanowire catalyst produces NO₂ ^- and NH₃ with current efficiencies of 91.5 % and 100 %, respectively at lower overpotentials (>+0.1 vs. RHE). The high efficiency for such a reduction process was further explored in a zinc-nitrate battery. This battery could be specified by a high output voltage of 0.70 V, an average energy density of 566.7 Wh L^-1 at 10 mA cm^-2 and a power density of 14.1 mW cm^-2 , which is well beyond all previously reported similar concepts.

Theoretical Evaluation of Highly Efficient Nitrate Reduction to Ammonia on InBi

Electrocatalytic reduction of nitrate to ammonia has become a popular approach for wastewater treatment and ammonia production. However, the development of highly efficient electrocatalysts remains a great challenge. Herein, we systematically studied the potential of InBi for nitrate reduction to ammonia (NRA) based on density functional theory (DFT) calculations. Our results reveal that InBi exhibits high activity for NRA via an O-end pathway, where the free energy evolution of all intermediates is downhill in the most favorable elementary steps. The activation of nitrate originates from the strong orbital hybridization between oxygen and indium atoms, leading to an enhanced charge transfer as well as NO₃^- adsorption. In particular, the competing hydrogen evolution reaction (HER) is effectively suppressed due to the weak adsorption of proton. Our study not only proves the great electrocatalytic potential of InBi as a novel catalyst for NRA but also points out a new way to design NRA electrocatalysts for practical applications.

Self-Supported Pd Nanorod Arrays for High-Efficient Nitrate Electroreduction to Ammonia

Electrochemical nitrate (NO₃ ^- ) reduction to ammonia (NH₃ ) offers a promising pathway to recover NO₃ ^- pollutants from industrial wastewater that can balance the nitrogen cycle and sustainable green NH₃ production. However, the efficiency of electrocatalytic NO₃ ^- reduction to NH₃ synthesis remains low for most of electrocatalysts due to complex reaction processes and severe hydrogen precipitation reaction. Herein, high performance of nitrate reduction reaction (NO₃ ^- RR) is demonstrated on self-supported Pd nanorod arrays in porous nickel framework foam (Pd/NF). It provides a lot of active sites for H* adsorption and NO₃ ^- activation leading to a remarkable NH₃ yield rate of 1.52 mmol cm^-2  h^-1 and a Faradaic efficiency of 78% at -1.4 V versus RHE. Notably, it maintains a high NH₃ yield rate over 50 cycles in 25 h showing good stability. Remarkably, large-area Pd/NF electrode (25 cm² ) shows a NH₃ yield of 174.25 mg h^-1 , be promising candidate for large-area device for industrial application. In situ FTIR spectroscopy and density functional theory calculations analysis confirm that the enrichment effect of Pd nanorods encourages the adsorption of H species for ammonia synthesis following a hydrogenation mechanism. This work brings a useful strategy for designing NO₃ ^- RR catalysts of nanorod arrays with customizable compositions.

Bioinspired Cobalt Oxide Nanoball Synthesis, Characterization, and Their Potential as Metal Stress Absorbants

Massive accumulation of heavy metals in agricultural land as a result of enhanced levels of toxicity in the soil is an emerging global concern. Among various metals, zinc contamination has severe effects on plant and human health through the food chain. To remove such toxicity, a nanotechnological neutralizer, cobalt oxide nanoballs (Co₃O₄ Nbs) were synthesized by using the extract of Cordia myxa. The Co₃O₄ Nbs were well characterized via UV-vis spectrophotometry, scanning electron microscopy, and X-ray diffraction techniques. Green-synthesized Co₃O₄ Nbs were exposed over Acacia jacquemontii and Acacia nilotica at different concentrations (25, 50, 75, and 100 ppm). Highly significant results were observed for plant growth by the application of Co₃O₄ Nbs at 100 ppm, thereby increasing the root length (35%), shoot length (48%), fresh weight (44%), and dry weight (40%) of the Acacia species with respect to the control. Furthermore, physiological parameters including chlorophyll contents, relative water contents, and osmolyte contents like proline and sugar showed a prominent increase. The antioxidant activity and atomic absorption supported and justified the positive response to using Co₃O₄ Nbs that mitigated the heavy-metal zinc stress by improving the plant growth. Hence, the biocompatible Co₃O₄ Nbs counteract the zinc toxicity for governing and maintaining plant growth. Such nanotechnological tools can therefore step up the cropping system and overcome toxicity to meet the productivity demand along with the development of agricultural management strategies.

Construction of Frustrated Lewis Pair Sites in CeO2-C/BiVO4 for Photoelectrochemical Nitrate Reduction

Photoelectrochemical nitrate reduction reaction (PEC NIRR) could convert the harmful pollutant nitrate (NO₃^-) to high-value-added ammonia (NH₃) under mild conditions. However, the catalysts are currently hindered by the low catalytic activity and slow kinetics. Here, we reported a heterostructure composed of CeO₂ and BiVO₄, and the "frustrated Lewis pairs (FLPs)" concept was introduced for understanding the role of Lewis acids and Lewis bases on PEC NIRR. The electron density difference maps indicated that FLPs were significantly active for the adsorption and activation of NO₃^-. Furthermore, carbon (C) improved the carrier transport ability and kinetics, contributing to the NH₃ yield of 21.81 μg h^-1 cm^-2. The conversion process of NO₃^- to NH₃ was tracked by ¹⁵NO₃^- and ¹⁴NO₃^- isotopic labeling. Therefore, this study demonstrated the potential of CeO₂-C/BiVO₄ for efficient PEC NIRR and provided a unique mechanism for the adsorption and activation of NO₃^- over FLPs.

Perovskites with Enriched Oxygen Vacancies as a Family of Electrocatalysts for Efficient Nitrate Reduction to Ammonia

Electrochemical nitrate reduction to ammonia (NRA) provides an efficient, sustainable approach to convert the nitrate pollutants into value-added products, which is regarded as a promising alternative to the industrial Haber-Bosch process. Recent studies have shown that oxygen vacancies of oxide catalysts can adjust the adsorption energies of intermediates and affect their catalytic performance. Compared with other metal oxides, perovskite oxides can allow their metal cations to exist in abnormal or mixed valence states, thereby resulting in enriched oxygen vacancies in their crystal structures. Here, the catalytic activities of perovskite oxides toward NRA catalysis with respect to the amount of oxygen vacancies are explored, where four perovskite oxides with different crystal structures (including cubic LaCrO₃ , orthorhombic LaMnO₃ and LaFeO₃ , hexagonal LaCoO₃ ) are chosen and investigated. By combining X-ray photoelectron spectroscopy, electron paramagnetic resonance spectroscopy and electrochemical measurements, it is found that the amount of oxygen vacancies in these perovskite oxides surprisingly follow the same order as their activities toward NRA catalysis (LaCrO₃  < LaMnO₃  < LaFeO₃  < LaCoO₃ ). Further theoretical studies reveal that the existence of oxygen vacancies in LaCoO₃ perovskite can decrease the energy barriers for reduction of *HNO₃ to *NO₂ , leading to its superior NRA performance.

Durable Electrocatalytic Reduction of Nitrate to Ammonia over Defective Pseudobrookite Fe2 TiO5 Nanofibers with Abundant Oxygen Vacancies

We propose the pseudobrookite Fe₂ TiO₅ nanofiber with abundant oxygen vacancies as a new electrocatalyst to ambiently reduce nitrate to ammonia. Such catalyst achieves a large NH₃ yield of 0.73 mmol h^-1  mg^-1 _cat. and a high Faradaic Efficiency (FE) of 87.6 % in phosphate buffer saline solution with 0.1 M NaNO₃ , which is lifted to 1.36 mmol h^-1  mg^-1 _cat. and 96.06 % at -0.9 V vs. RHE for nitrite conversion to ammonia in 0.1 M NaNO₂ . It also shows excellent electrochemical durability and structural stability. Theoretical calculation reveals the enhanced conductivity of this catalyst and an extremely low free energy of -0.28 eV for nitrate adsorption at the presence of vacant oxygen.

Sub-nm RuOx Clusters on Pd Metallene for Synergistically Enhanced Nitrate Electroreduction to Ammonia

The electrochemical nitrate reduction to ammonia reaction (NO3RR) has emerged as an appealing route for achieving both wastewater treatment and ammonia production. Herein, sub-nm RuOx clusters anchored on a Pd metallene (RuOx/Pd) are reported as a highly effective NO3RR catalyst, delivering a maximum NH3-Faradaic efficiency of 98.6% with a corresponding NH3 yield rate of 23.5 mg h-1 cm-2 and partial a current density of 296.3 mA cm-2 at -0.5 V vs RHE. Operando spectroscopic characterizations combined with theoretical computations unveil the synergy of RuOx and Pd to enhance the NO3RR energetics through a mechanism of hydrogen spillover and hydrogen-bond interactions. In detail, RuOx activates NO3- to form intermediates, while Pd dissociates H2O to generate *H, which spontaneously migrates to the RuOx/Pd interface via a hydrogen spillover process. Further hydrogen-bond interactions between spillovered *H and intermediates makes spillovered *H desorb from the RuOx/Pd interface and participate in the intermediate hydrogenation, contributing to the enhanced activity of RuOx/Pd for NO3--to-NH3 conversion.

Boosting Electrocatalytic Ammonia Synthesis of Bio-Inspired Porous Mo-Doped Hematite via Nitrogen Activation

Electrochemical N₂ reduction reaction (NRR) emerges as a highly attractive alternative to the Haber-Bosch process for producing ammonia (NH₃) under ambient circumstances. Currently, this technology still faces tremendous challenges due to the low ammonia production rate and low Faradaic efficiency, urgently prompting researchers to explore highly efficient electrocatalysts. Inspired by the Fe-Mo cofactor in nitrogenase, we report Mo-doped hematite (Fe₂O₃) porous nanospheres containing Fe-O-Mo subunits for enhanced activity and selectivity in the electrochemical reduction from N₂ to NH₃. Mo-doping induces the morphology change from a solid sphere to a porous sphere and enriches lattice defects, creating more active sites. It also regulates the electronic structures of Fe₂O₃ to accelerate charge transfer and enhance the intrinsic activity. As a consequence, Mo-doped Fe₂O₃ achieves effective N₂ fixation with a high ammonia production rate of 21.3 ± 1.1 μg h^-1 mg_cat.^-1 as well as a prominent Faradaic efficiency (FE) of 11.2 ± 0.6%, superior to the undoped Fe₂O₃ and other iron oxide catalysts. Density functional theory (DFT) calculations further unravel that the Mo-doping in Fe₂O₃ (110) narrows the band gap, promotes the N₂ activation on the Mo site with an elongated N≡N bond length of 1.132 Å in the end-on configuration, and optimizes an associative distal pathway with a decreased energy barrier. Our results may pave the way toward enhancing the electrocatalytic NRR performance of iron-based materials by atomic-scale heteroatom doping.

Single-Step Synthesis of Fe-Fe3 O4 Catalyst for Highly Efficient and Selective Electrochemical Nitrogen Reduction

Nitrogen reduction electrocatalysts are highly attractive for catalytic science. However, most electrocatalysts are limited by their low faradaic efficiency, poor ammonia yield, and tedious and costly catalyst synthesis process. In this work, Fe-based oxide composite nanoparticles with steady chemical states are prepared by a single-step green procedure under ambient conditions. The resulting Fe-Fe₃ O₄ demonstrates remarkable activity and selectivity for nitrogen reduction reaction (NRR) with the highest faradaic efficiency of 53.2±1.8 % and NH₃ yield rate of 24.6±0.8 μg h^-1  mg_cat. ^-1 at -0.4 V (vs. RHE) in 0.1 m Na₂ SO₄ electrolyte. Characterization experiments and theoretical calculation reveal that Fe-Fe₃ O₄ exhibits significantly enhanced charge transfer capability and suppresses the competitive HER process.

In Situ Derived Co2B Nanosheet Array: A High-Efficiency Electrocatalyst for Ambient Ammonia Synthesis via Nitrate Reduction

Ambient ammonia synthesis via electrochemical nitrate (NO3-) reduction is regarded as a green alternative to the Haber-Bosch process. Herein, we report the in situ derivation of an amorphous Co2B layer on a Co3O4 nanosheet array on a Ti mesh (Co2B@Co3O4/TM) for efficient NH3 production via selective electroreduction of NO3- under ambient conditions. In 0.1 M PBS and 0.1 M NaNO3, Co2B@Co3O4/TM exhibits a maximum Faradaic efficiency of 97.0% at -0.70 V and a remarkable NH3 yield of 8.57 mg/h/cm2 at -1.0 V, with durability for stable NO3--to-NH3 conversion over eight recycling tests and 12 h of electrolysis. Additionally, it can be applied as an efficient cathode material for Zn-NO3- batteries to produce NH3 while generating electricity. The catalytic mechanisms on Co2B@Co3O4 are further revealed by theoretical calculations.

In Situ Growth of Fe2O3 Nanorod Arrays on Carbon Cloth with Rapid Charge Transfer for Efficient Nitrate Electroreduction to Ammonia

Electrochemical reduction of nitrate to ammonia (NH3), a green NH3 production route upon combining with renewable energy sources, is an appealing and alternative method to the Haber-Bosch process. However, this process not only involves the complicated eight-electron reduction to transform nitrate into various nitrogen products but simultaneously suffers from the competitive hydrogen evolution reaction, challenged by a lack of efficient catalysts. Herein, the in situ growth of Fe2O3 nanorod arrays on carbon cloth (Fe2O3 NRs/CC) is reported to exhibit a high NH3 yield rate of 328.17 μmol h-1 cm-2 at -0.9 V versus RHE, outperforming most of the reported Fe catalysts. An in situ growth strategy provides massive exposed active sites and a fast electron-transport channel between the carbon cloth and Fe2O3, which accelerates the charge-transport rate and facilitates the conversion of nitrate to NH3. In situ Raman spectroscopy in conjunction with attenuated total reflection Fourier transform infrared spectroscopy reveals the catalytic mechanism of nitrate to NH3. Our study provides not only an efficient catalyst for NH3 production but also useful guidelines for the pathways and mechanism of nitrate electroreduction to NH3.

High-Efficiency Electrochemical Nitrate Reduction to Ammonia on a Co3O4 Nanoarray Catalyst with Cobalt Vacancies

Electrocatalytic nitrate reduction reaction (NO₃RR) affords a bifunctional character in the carbon-free ammonia synthesis and remission of nitrate pollution in water. Here, we fabricated the Co₃O₄ nanosheet array with cobalt vacancies on carbon cloth (v_Co-Co₃O₄/CC) by in situ etching aluminum-doped Co₃O₄/CC, which exhibits an excellent Faradaic efficiency of 97.2% and a large NH₃ yield as high as 517.5 μmol h^-1 cm^-2, better than the pristine Co₃O₄/CC. Theoretical calculative results imply that the cobalt vacancies can tune the local electronic environment around Co sites of Co₃O₄, increasing the charge and reducing the electron cloud density of Co sites, which is thus conducive to adsorption of NO₃^- on Co sites for greatly enhanced nitrate reduction. Furthermore, the v_Co-Co₃O₄ (311) facet presents excellent NO₃RR activity with a low energy barrier of about 0.63 eV on a potential-determining step, which is much smaller than pristine Co₃O₄ (1.3 eV).