Modulating intermediate coverage on atomically dispersed Co modified Cu2O for efficient nitrate reduction across a wide temperature range

Electrocatalytic nitrate reduction to ammonia (NITRR) provides a sustainable avenue for simultaneous nitrate mitigation and ammonia synthesis, but the sluggish surface hydrogen migration during NITRR remains a major bottleneck. Here, we show a barrierless hydrogen transfer pathway along intramolecular hydrogen bonds between hydroxyls of hydroxyl-rich nanocavities for efficient nitrate electroreduction to ammonia. This nanocavity is constructed via electrochemical reduction-assisted selective Sr ions leaching on the La0.4Sr0.6FeO3-δ perovskites. Combined experimental and theoretical investigations reveal that the nanocavity features nanocavity-like architecture with hydroxyl-enriched walls, boosting active hydrogen generating and hopping for NO3- hydrogenation. Benefiting from such unusual intramolecular hydrogen transfer, the surface nanoconcaved La0.4Sr0.6FeO3-δ achieves a Faradaic efficiency of 97.81 % and an ammonia yield rate of 51.37 mg h-1 cm-2 at -0.8 V versus reversible hydrogen electrode (RHE), surpassing nanocavity-free counterpart and ranking among superior NITRR catalysts. Ampere-level current density of nitrate-to-ammonia conversion are further realized in a renewable-energy-powered electrolyzer at a very low cell voltage of 2.23 V. Techno-economic analysis underscores dual benefits of this process including economic viability in ammonia synthesis and environmental impact in nitrate remediation.

The traditional Haber-Bosch method suffers from harsh conditions and high energy consumption, while electrocatalytic nitrate reduction to ammonia (ENRA) is a green route for ammonia synthesis and can serve as a cathode reaction for Zn-nitrate batteries. Its development is limited by sluggish intermediate hydrogenation and severe hydrogen evolution reaction (HER). Herein, we develop topology-engineered isomeric polyoxometalate (POM)-confined bimetallic metal-organic framework (MOF) electrocatalysts (NH2-MIL-53, -88, -101). Flexible NH2-MIL-88(FeNi) enables tight encapsulation of [PW12O40]3- (PW12) clusters via the "breathing effect", yielding PW12@NH2-MIL-88(FeNi) with synergistically modulated electronic distribution and proton transfer. Combined experimental and theoretical studies reveal that confined PW12 induces electronic redistribution over Fe/Ni centers, concurrently strengthening NO3 - adsorption on Fe and accelerating *NO2 hydrogenation on Ni. Beyond electronic effects, PW12 loosens the rigid hydration layer and forms conjugated acid-base pairs with MOF amino groups, promoting proton diffusion, boosting *NO2 hydrogenation, and suppressing HER. Thus, PW12@NH2-MIL-88(FeNi) achieves an NH3 yield rate of 20.1mg h-1 mgcat. -1 with a Faradaic efficiency of 98.6% under neutral electrolytes. When used as a cathode in rechargeable Zn-nitrate batteries, it delivers a peak power density of 13.2mW cm-2. This study establishes a generalizable paradigm for engineering interfacial proton transport and electronic properties via POM confinement in MOFs.

Metal-support interactions provide a powerful tool to tailor the catalytic activities of metallic catalysts. Amorphous materials can serve as an effective support matrix to form unique crystalline-amorphous interfaces and modulate the electronic structure of active metals. However, robust synthetic strategies for precise structural control remain underdeveloped. Here, we report the laser-shocked synthesis of heterostructures including bimetallic CuNi, CuFe, CuCo, and medium-entropy CuFeCoNi heterostructures, where crystalline metal nanoparticles are anchored on amorphous hydroxide supports. The heterostructures are characterized by an interfacial electronic distribution that improves catalytic activities. With CuNi as an example for nitrate reduction reaction, the laser-engineered heterophase CuNi achieves an NH3 production rate of 92.18mg/h/mgcat with 98.6% Faradaic efficiency (FE), substantially superior to standalone crystalline CuNi or amorphous CuNi hydroxide. The CuNi heterostructure maintains a stable FE(NH3) of ∼90% up to 80h while improving current density from 75 to 120mA/cm2 due to the robust amorphous layer and dynamic amorphous/crystalline reconstruction. In situ characterization and theoretical calculations reveal that the amorphous/crystalline interface regulates the balance between reactive hydrogen species and reaction intermediates, effectively suppressing the competing hydrogen evolution and promoting cascade nitrate-to-nitrite and nitrite-to ammonia conversion. This work provides a general and viable strategy for producing high-performance supported catalysts.

Ammonia, as a crucial feedstock in the chemical industry, is traditionally synthesized via the energy-intensive and high-carbon-emission Haber-Bosch process, which contradicts sustainable development goals. The electrocatalytic nitrate reduction reaction (NO3RR) for ammonia synthesis has emerged as a research hotspot due to its low energy consumption and environmental friendliness. However, existing catalysts still suffer from high overpotentials, competitive hydrogen evolution reaction (HER), and intermediate accumulation. In this study, we successfully fabricated copper-doped cobalt phosphide (Cu-CoP) catalysts through hydrothermal and phosphidation strategies, systematically investigating their NO3RR performance and mechanism. Experimental results demonstrate that Cu-CoP exhibits exceptional catalytic activity at -0.65 V vs RHE, achieving a Faradaic efficiency of 96.2% and an ammonia production rate of 7.06 mg cm-2 h-1, significantly outperforming undoped CoP catalysts. Through comprehensive characterization and theoretical calculations, we reveal that Cu incorporation not only optimizes the electronic structure of Co sites to facilitate water dissociation and *H generation, but also enables efficient nitrate adsorption at Cu sites while suppressing *H dimerization, thereby synergistically enhancing NO3RR selectivity and kinetics. This work provides insights for designing high-performance nonprecious metal NO3RR catalysts and elucidates the cooperative mechanism of dual active sites.

Cu-based nanocatalysts have been widely studied for the electrochemical nitrate reduction reaction (NO3RR) to ammonia, yet their activity and selectivity remain limited. Herein, we demonstrate that lattice-strained Au3Cu, achieved by organizing Cu@Au3Cu core-shell nanocrystals (NCs), facilitates efficient high-concentration nitrate electroreduction to ammonia. Typically, an NH3 yield rate of 265.2 mg h-1 mgcat-1 is achieved, which is superb among reported Cu-Au catalysts. In situ experiments confirm that the strained Au3Cu promotes water dissociation under alkaline conditions, ensuring enhanced *H surface coverage to support efficient hydrogenation. Density functional theory (DFT) calculations further demonstrate the strain-induced upward shift of the d-band center strengthens NO3- adsorption and activation. More critically, the compressive strain within the Au3Cu shell drastically contracts Au-Cu interatomic distances, which achieves a substantial reduction in the energy barrier for hydrogen spillover from Au to Cu sites. These integrated effects collectively lower the energy barrier (0.12 eV) for forming the key reaction intermediate *NHO during the rate-determining step, boosting the overall NO3RR kinetics. Integrating the NO3RR catalyst into a Zn-NO3- battery as the cathode achieves a power density of 5.91 mW cm-2 and FE of 90.5% for NH3 production, highlighting the potential for energy-efficient nitrate-to-ammonia conversion.

Efficient nitrate removal from low carbon-to-nitrogen (C/N) wastewater remains challenging due to the scarcity of electron donors in conventional biological denitrification. To address this limitation, a synergistic system coupling manganese-catalyzed iron-carbon micro-electrolysis (IMC-ME) with biological denitrification was developed. Under carbon-deficient conditions (C/N = 2), the coupled system achieved 90.1% nitrate removal and 77.2% total nitrogen (TN) removal, substantially outperforming the standalone biological process (49.4% TN removal). Mechanistically, manganese dioxide functioned as a cathodic catalyst, accelerating zero-valent iron corrosion and continuously generating Fe2+ and atomic hydrogen [H] as inorganic electron donors. This electrochemical process induced a shift in the microbial community from Proteobacteria to Bacteroidota dominance. Notably, the system selectively enriched Zoogloea, enhancing biofilm stability, and Thiobacillus, indicating the activation of iron-dependent autotrophic denitrification pathways. This integration of chemical reduction and biological metabolism provides a promising strategy for deep nitrogen removal in organic-substrate-limited waters.

Nitrate (NO3 -) pollution poses a critical environmental threat by contaminating water resources and disrupting the global nitrogen cycle. The electrochemical nitrate reduction reaction (NO3RR) in alkaline media offers a dual solution: mitigating nitrate contamination while enabling sustainable ammonia (NH3) production. However, the scarcity of free protons (H+) at high pH hampers efficient NO3 --to-NH3 conversion. Here, we report a sub-stoichiometric covalent organic framework PEPy-2CHO-TTA, synthesized by microwave-assisted [4 + 3 + 2] polycondensation strategy, which retains pendant unreacted aldehyde groups oriented toward the pore channels. This framework-intrinsic integration of polar aldehyde functionalities enhances water uptake and promotes the formation of a structured hydration network within the pores, enabling localized proton transfer that overcomes proton deficiency under alkaline conditions. As a result, PEPy-2CHO-TTA COF achieves a Faradaic efficiency (FE) exceeding 95% and an NH3 yield rate of 5.87mgh-1cm-2 which is among the highest reported for metal-free or metal-based porous electrocatalysts. Isotope labelling using K15NO3 confirms that the produced ammonia originates exclusively from nitrate reduction. DFT calculations reveal a multi-step eight-electron reduction pathway with the NO-to-NHO transformation as the potential-determining step. This work introduces a new design paradigm for COF electrocatalysts, where pendant aldehydes within the framework serve as molecular handles for water-mediated proton transport, enabling efficient nitrate reduction under alkaline conditions, without external acidification or metal catalysts.

Enhancing nitrogen retention in low C/N food waste digestate composting: synergistic effects of biochar and nitrifying inoculation.

Removal of nitrate by aerobic denitrification granular sludge under strongly alkaline and low carbon to nitrogen ratio conditions: Performance and mechanism.

Electrocatalytic nitrate reduction (NO3 -RR) offers a promising route for simultaneous nitrate remediation and sustainable ammonia (NH3)synthesis. However, its efficiency is limited by low NH3 selectivity, insufficient Faradaic efficiency (FE), and high overpotential, primarily due to inadequate active hydrogen (*H) supply and nitrite (NO2-) accumulation. Herein, we report an Fe─Co tandem catalyst (FeCo/C-0.5) with an optimized Fe/Co ratio that achieves 98% NH3 selectivity and 89.68% FE at -0.33V vs. RHE, with a yield of 14.12mgh-1mgcat -1. Combining in situ FTIR, Raman, DEMS, and DFT calculations, we demonstrate that Fe─Co synergy accelerates H2O dissociation and establishes a dynamic *H balance, suppressing the hydrogen evolution reaction (HER) while maintaining adequate *H supply for hydrogenation. Furthermore, NO2 - generated at Fe sites is rapidly reduced to NH3 at adjacent Co sites, thereby eliminating NO2 - accumulation and enabling high NH3 selectivity at low potentials. The catalyst also demonstrates robust stability in simulated wastewater containing Cl- and SO4 2-, and achieves a power density of 6.63mWcm-2 in a Zn-NO3 - battery, which underscores its practical potential.

Efficient nitrate reduction over Fe-Cu bimetals under UV irradiation: Performance and mechanisms.

Synergistic doping enables efficient nitrate electrosynthesis via dual-regulation of surface polarity and competitive reactions

The electrochemical nitrate reduction reaction (NO3RR) represents a promising strategy for wastewater remediation and sustainable ammonia (NH3) production. However, its practical application is hindered by low selectivity and competition from the hydrogen evolution reaction (HER). Herein, a series of PtBi-CoX (X = 4.9, 5.3, and 6.1) ternary alloy nanoplates was synthesized via a one-pot method with tunable Co content. Structural characterization indicates that Co incorporation does not significantly alter the hexagonal crystal structure of the PtBi phase. Electrochemical measurements reveal that the NO3RR performance varies with PtBi-CoX (X = 4.9, 5.3, 6.1), with PtBi-Co5.3 exhibiting the optimal balance of activity and selectivity among the studied samples. At −0.5 V vs. RHE, it achieves a Faradaic efficiency (FE) of 97.75 ± 0.75% and an NH3 yield rate of 9.33 ± 0.50 mg h−1 mgcat−1 under the tested conditions. In addition, the catalyst exhibits relatively suppressed HER activity compared to samples with higher Co content, along with good stability. These findings provide useful insights into the design of PtBi-based ternary alloy catalysts for efficient nitrate reduction.

The electrocatalytic nitrate reduction reaction (eNO3 -RR) provides a sustainable pathway for ammonia synthesis and nitrate wastewater remediation, yet its efficiency is fundamentally limited by the sluggish kinetics of the multistep conversion process. Herein, we elucidate how alkali-metal cations regulate the interfacial microenvironment to boost the ammonia production performance of eNO3 -RR. Using winged carbon coaxial nanocables as model catalysts, among the alkali-metal cations investigated, Cs+ enhances the local electric field that strengthens the adsorption of *NOx intermediates, whereas Li+ more effectively promotes the interfacial water reorganization to facilitate adsorbed hydrogen atom (*H) formation. Crucially, Na+ achieves the most favorable balance between these two complementary processes, thereby enabling efficient coupling between *NOx intermediates and *H throughout the nitrate reduction pathway. This balanced interplay delivers an NH3 yield rate of 94.9g h-1 gcat. -1 in a Na+-mediated neutral electrolyte. The strategy exhibits broad applicability across diverse electrolytes and catalyst systems, offering a general design principle for steering complex hydrogenation-related catalytic transformations via rational electrolyte engineering.

ABSTRACT The electrocatalytic nitrate reduction reaction (eNO 3 − RR) provides a sustainable pathway for ammonia synthesis and nitrate wastewater remediation, yet its efficiency is fundamentally limited by the sluggish kinetics of the multistep conversion process. Herein, we elucidate how alkali‐metal cations regulate the interfacial microenvironment to boost the ammonia production performance of eNO 3 − RR. Using winged carbon coaxial nanocables as model catalysts, among the alkali‐metal cations investigated, Cs + enhances the local electric field that strengthens the adsorption of *NO x intermediates, whereas Li + more effectively promotes the interfacial water reorganization to facilitate adsorbed hydrogen atom ( * H) formation. Crucially, Na + achieves the most favorable balance between these two complementary processes, thereby enabling efficient coupling between *NO x intermediates and *H throughout the nitrate reduction pathway. This balanced interplay delivers an NH 3 yield rate of 94.9 g h −1 g cat. −1 in a Na + ‐mediated neutral electrolyte. The strategy exhibits broad applicability across diverse electrolytes and catalyst systems, offering a general design principle for steering complex hydrogenation‐related catalytic transformations via rational electrolyte engineering.

Tunable-crystallinity N-doped carbon supports synergizing with Fe active sites for efficient nitrate electroreduction

Engineering pore structure of bamboo-derived porous carbons via pyrolysis behavior of various organic potassium salts for efficient nitrate removal by capacitive deionization

Dynamic cycling of surface lattice hydrogen on OH-terminated metal borides drives efficient nitrate electroreduction for aquatic pollution mitigation.

Electrocatalytic nitrate reduction (NO₃RR) offers a promising route for sustainable ammonia synthesis and wastewater treatment, yet designing highly active and selective catalysts remains challenging. Herein, we construct an N-bridge anchored asymmetric AgCu dual-atomic catalyst on Ti₃C₂T_x MXene (AgCu DAC/Ti₃C₂T_x) for efficient nitrate electroreduction. The unique N-bridged structure stabilizes the asymmetric AgCu dual sites, enabling synergistic adsorption and activation of nitrate intermediates. In situ X-ray absorption fine structure (XAFS) spectroscopy confirms the dynamic evolution of the Ag-Cu coordination under reaction conditions, revealing their maintained heteronuclear pairing and electronic coupling during NO₃RR. As a result, the AgCu DAC/ Ti₃C₂T_x catalyst achieves a high NH₃ Faradaic efficiency of ~97.1% with an exceptional yield rate of ~3.1 mg h^-1 cm^-2 at −0.5 V vs. RHE, surpassing most reported dual-atom catalysts. This work provides insights into the design of asymmetric dual-atomic sites for multi-step catalytic reactions.