A Janus Fe‐SnO2 Catalyst that Enables Bifunctional Electrochemical Nitrogen Fixation

Electrochemical N₂ reduction reactions (NRR) and the N₂ oxidation reaction (NOR), using H₂O and N₂, are a sustainable approach to N₂ fixation. To date, owing to the chemical inertness of nitrogen, emerging electrocatalysts for the electrochemical NRR and NOR at room temperature and atmospheric pressure remain largely underexplored. Herein, a new‐type Fe‐SnO₂ was designed as a Janus electrocatalyst for achieving highly efficient NRR and NOR catalysis. A high NH₃ yield of 82.7 μg h^?1 mg_cat.^?1 and a Faraday efficiency (FE) of 20.4 % were obtained for NRR. This catalyst can also serve as an excellent NOR electrocatalyst with a NO₃^? yields of 42.9 μg h^?1 mg_cat.^?1 and a FE of 0.84 %. By means of experiments and DFT calculations, it is revealed that the oxygen vacancy‐anchored single‐atom Fe can effectively adsorb and activate chemical inert N₂ molecules, lowering the energy barrier for the vital breakage of N≡N and resulting in the enhanced N₂ fixation performance.     

Pulsed Electrocatalysis Enabling High Overall Nitrogen Fixation Performance for Atomically Dispersed Fe on TiO2

Atomically dispersed Fe was designed on TiO₂ and explored as a Janus electrocatalyst for both nitrogen oxidation reaction (NOR) and nitrogen reduction reaction (NRR) in a two-electrode system. Pulsed electrochemical catalysis (PE) was firstly involved to inhibit the competitive hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Excitingly, an unanticipated yield of 7055.81 μmol h⁻¹ g⁻¹_cat. and 12 868.33 μmol h⁻¹ g⁻¹_cat. were obtained for NOR and NRR at 3.5 V, respectively, 44.94 times and 7.8 times increase in FE than the conventional constant voltage electrocatalytic method. Experiments and density functional theory (DFT) calculations revealed that the single-atom Fe could stabilize the oxygen vacancy, lower the energy barrier for the vital rupture of N≡N, and result in enhanced N₂ fixation performance. More importantly, PE could effectively enhance the N₂ supply by reducing competitive O₂ and H₂ agglomeration, inhibit the electrocatalytic by-product formation for longstanding *OOH and *H intermediates, and promote the non-electrocatalytic process of N₂ activation.     

ZIF-Induced d-Band Modification in a Bimetallic Nanocatalyst: Achieving Over 44 % Efficiency in the Ambient Nitrogen Reduction Reaction

The electrochemical nitrogen reduction reaction (NRR) offers a sustainable solution towards ammonia production but suffers poor reaction performance owing to preferential catalyst–H formation and the consequential hydrogen evolution reaction (HER). Now, the Pt/Au electrocatalyst d-band structure is electronically modified using zeolitic imidazole framework (ZIF) to achieve a Faradaic efficiency (FE) of >44 % with high ammonia yield rate of >161 μg mg_cat⁻¹ h⁻¹ under ambient conditions. The strategy lowers electrocatalyst d-band position to weaken H adsorption and concurrently creates electron-deficient sites to kinetically drive NRR by promoting catalyst–N₂ interaction. The ZIF coating on the electrocatalyst doubles as a hydrophobic layer to suppress HER, further improving FE by >44-fold compared to without ZIF (ca. 1 %). The Pt/Au-N_ZIF interaction is key to enable strong N₂ adsorption over H atom.     

Electrocatalytically Active Fe-(O-C2)4 Single-Atom Sites for Efficient Reduction of Nitrogen to Ammonia

Single-atom catalysts have demonstrated their superiority over other types of catalysts for various reactions. However, the reported nitrogen reduction reaction single-atom electrocatalysts for the nitrogen reduction reaction exclusively utilize metal–nitrogen or metal–carbon coordination configurations as catalytic active sites. Here, we report a Fe single-atom electrocatalyst supported on low-cost, nitrogen-free lignocellulose-derived carbon. The extended X-ray absorption fine structure spectra confirm that Fe atoms are anchored to the support via the Fe-(O-C₂)₄ coordination configuration. Density functional theory calculations identify Fe-(O-C₂)₄ as the active site for the nitrogen reduction reaction. An electrode consisting of the electrocatalyst loaded on carbon cloth can afford a NH₃ yield rate and faradaic efficiency of 32.1 μg h⁻¹ mg_cat.⁻¹ (5350 μg h⁻¹ mg_Fe⁻¹) and 29.3 %, respectively. An exceptional NH₃ yield rate of 307.7 μg h⁻¹ mg_cat.⁻¹ (51 283 μg h⁻¹ mg_Fe⁻¹) with a near record faradaic efficiency of 51.0 % can be achieved with the electrocatalyst immobilized on a glassy carbon electrode.     

Nanoporous Palladium Hydride for Electrocatalytic N2 Reduction under Ambient Conditions

The electrocatalytic nitrogen reduction reaction (NRR) is an alternative eco‐friendly strategy for sustainable N₂ fixation with renewable energy. However, NRR suffers from sluggish kinetics owing to difficult N₂ adsorption and N≡N cleavage. Now, nanoporous palladium hydride is reported as electrocatalyst for electrochemical N₂ reduction under ambient conditions, achieving a high ammonia yield rate of 20.4 μg h^?1 mg^?1 with a Faradaic efficiency of 43.6 % at low overpotential of 150 mV. Isotopic hydrogen labeling studies suggest the involvement of lattice hydrogen atoms in the hydride as active hydrogen source. In situ Raman analysis and density functional theory (DFT) calculations further reveal the reduction of energy barrier for the rate‐limiting *N₂H formation step. The unique protonation mode of palladium hydride would provide a new insight on designing efficient and robust electrocatalysts for nitrogen fixation.     

Ambient Electrosynthesis of Ammonia on a Core–Shell-Structured Au@CeO2 Catalyst: Contribution of Oxygen Vacancies in CeO2

Electrosynthesis of NH₃ through the N₂ reduction reaction (NRR) under ambient conditions is regarded as promising technology to replace the industrial energy- and capital-intensive Haber–Bosch process. Herein, a room-temperature spontaneous redox approach to fabricate a core–shell-structured Au@CeO₂ composite, with Au nanoparticle sizes below about 10 nm and a loading amount of 3.6 wt %, is reported for the NRR. The results demonstrate that as-synthesized Au@CeO₂ possesses a surface area of 40.7 m² g⁻¹ and a porous structure. As an electrocatalyst, it exhibits high NRR activity, with an NH₃ yield rate of 28.2 μg h⁻¹ cm⁻² (10.6 μg h⁻¹ mg⁻¹_cat., 293.8 μg h⁻¹ mg⁻¹_Au) and a faradaic efficiency of 9.50 % at −0.4 V versus a reversible hydrogen electrode in 0.01 m H₂SO₄ electrolyte. The characterization results reveal the presence of rich oxygen vacancies in the CeO₂ nanoparticle shell of Au@CeO₂; these are favorable for N₂ adsorption and activation for the NRR. This has been further verified by theoretical calculations. The abundant oxygen vacancies in the CeO₂ nanoparticle shell, combined with the Au nanoparticle core of Au@CeO₂, are electrocatalytically active sites for the NRR, and thus, synergistically enhance the conversion of N₂ into NH₃.     

ZIF‐Induced d‐Band Modification in a Bimetallic Nanocatalyst: Achieving Over 44 % Efficiency in the Ambient Nitrogen Reduction Reaction

The electrochemical nitrogen reduction reaction (NRR) offers a sustainable solution towards ammonia production but suffers poor reaction performance owing to preferential catalyst–H formation and the consequential hydrogen evolution reaction (HER). Now, the Pt/Au electrocatalyst d‐band structure is electronically modified using zeolitic imidazole framework (ZIF) to achieve a Faradaic efficiency (FE) of >44 % with high ammonia yield rate of >161 μg mg_cat^?1 h^?1 under ambient conditions. The strategy lowers electrocatalyst d‐band position to weaken H adsorption and concurrently creates electron‐deficient sites to kinetically drive NRR by promoting catalyst–N₂ interaction. The ZIF coating on the electrocatalyst doubles as a hydrophobic layer to suppress HER, further improving FE by >44‐fold compared to without ZIF (ca. 1 %). The Pt/Au‐N_ZIF interaction is key to enable strong N₂ adsorption over H atom.     

Boosting Electroreduction Kinetics of Nitrogen to Ammonia via Atomically Dispersed Sn Protuberance

Atomically dispersed metal catalysts show potential advantages in N₂ reduction reaction (NRR) due to their excellent activity and efficient metal utilization. Unfortunately, the reported catalysts usually exhibit unsatisfactory NRR activity due to their poor N₂ adsorption and activation. Herein, we report a novel Sn atomically dispersed protuberance (ADP) by coordination with substrate C and O to induce positive charge accumulation on Sn site for improving its N₂ adsorption, activation and NRR performance. The extended X-ray absorption fine structure (EXAFS) spectra confirmed the local coordination structure of the Sn ADPs. NRR activity was significantly promoted via Sn ADPs, exhibiting a remarkable NH₃ yield (R_NH3) of 28.3 μg h⁻¹ mg_cat⁻¹ (7447 μg h⁻¹ mg_Sn⁻¹) at −0.3 V. Furthermore, the enhanced N₂H_x intermediates was verified by in situ experiments, yielding consistent results with DFT calculation. This work opens a new avenue to regulate the activity and selectivity of N₂ fixation.     

Bio-Inspired Aerobic-Hydrophobic Janus Interface on Partially Carbonized Iron Heterostructure Promotes Bifunctional Nitrogen Fixation

Competition from hydrogen/oxygen evolution reactions and low solubility of N₂ in aqueous systems limited the selectivity and activity on nitrogen fixation reaction. Herein, we design an aerobic-hydrophobic Janus structure by introducing fluorinated modification on porous carbon nanofibers embedded with partially carbonized iron heterojunctions (Fe₃C/Fe@PCNF-F). The simulations prove that the Janus structure can keep the internal Fe₃C/Fe@PCNF-F away from water infiltration and endow a N₂ molecular-concentrating effect, suppressing the competing reactions and overcoming the mass-transfer limitations to build a robust “quasi-solid–gas” state micro-domain around the catalyst surface. In this proof-of-concept system, the Fe₃C/Fe@PCNF-F exhibits excellent electrocatalytic performance for nitrogen fixation (NH₃ yield rate up to 29.2 μg h⁻¹ mg⁻¹_cat. and Faraday efficiency (FE) up to 27.8 % in nitrogen reduction reaction; NO₃⁻ yield rate up to 15.7 μg h⁻¹ mg⁻¹_cat. and FE up to 3.4 % in nitrogen oxidation reaction).     

A Surface-Strained and Geometry-Tailored Nanoreactor that Promotes Ammonia Electrosynthesis

A surface-strained and geometry-optimized TiO₂ nanoreactor enhances the performance of electrocatalytic nitrogen fixation. The nanotubular confinement allows spatial regulation of the mass transport of nitrogen during the NRR process and offers an enlarged surface area, thus boosting the ammonia production with high selectivity. Both experimental and theoretical evidence support strained Ti³⁺ sites, demonstrating a more favorable pathway for the N₂ activation and selective NH₃ production with a faster kinetic rate than the pristine TiO₂. The TiO₂-based nanoreactor with surface and bulk structure tailoring delivered an NH₃ yield rate up to 5.50 μg h⁻¹ cm⁻² (16.67 μg h⁻¹ mg_cat⁻¹) and high faradaic efficiency of 26 % under ambient aqueous conditions. Our findings highlight the concept of lattice strain and geometry modified nanoreactors, which will have broad implications in the renewable energy catalysis and electrosynthesis of valuable products.     

ZnO Quantum Dots Coupled with Graphene toward Electrocatalytic N2 Reduction: Experimental and DFT Investigations

Electrochemical reduction of N₂ to NH₃ is a promising method for artificial N₂ fixation, but it requires efficient and robust electrocatalysts to boost the N₂ reduction reaction (NRR). Herein, a combination of experimental measurements and theoretical calculations revealed that a hybrid material in which ZnO quantum dots (QDs) are supported on reduced graphene oxide (ZnO/RGO) is a highly active and stable catalyst for NRR under ambient conditions. Experimentally, ZnO/RGO was confirmed to favor N₂ adsorption due to the largely exposed active sites of ultrafine ZnO QDs. DFT calculations disclosed that the electronic coupling of ZnO with RGO resulted in a considerably reduced activation-energy barrier for stabilization of *N₂H, which is the rate-limiting step of the NRR. Consequently, ZnO/RGO delivered an NH₃ yield of 17.7 μg h⁻¹ mg⁻¹ and a Faradaic efficiency of 6.4 % in 0.1 m Na₂SO₄ at −0.65 V (vs. RHE), which compare favorably to those of most of the reported NRR catalysts and thus demonstrate the feasibility of ZnO/RGO for electrocatalytic N₂ fixation.     

Defect Engineering Metal‐Free Polymeric Carbon Nitride Electrocatalyst for Effective Nitrogen Fixation under Ambient Conditions

Electrocatalytic nitrogen reduction reaction (NRR) under ambient conditions provides an intriguing picture for the conversion of N₂ into NH₃. However, electrocatalytic NRR mainly relies on metal‐based catalysts, and it remains a grand challenge in enabling effective N₂ activation on metal‐free catalysts. Here we report a defect engineering strategy to realize effective NRR performance (NH₃ yield: 8.09 μg h^?1 mg^?1_cat., Faradaic efficiency: 11.59 %) on metal‐free polymeric carbon nitride (PCN) catalyst. Illustrated by density functional theory calculations, dinitrogen molecule can be chemisorbed on as‐engineered nitrogen vacancies of PCN through constructing a dinuclear end‐on bound structure for spatial electron transfer. Furthermore, the N?N bond length of adsorbed N₂ increases dramatically, which corresponds to “strong activation” system to reduce N₂ into NH₃. This work also highlights the significance of defect engineering for improving electrocatalysts with weak N₂ adsorption and activation ability.     

Surface-Regulated Rhodium–Antimony Nanorods for Nitrogen Fixation

Surface regulation is an effective strategy to improve the performance of catalysts, but it has been rarely demonstrated for nitrogen reduction reaction (NRR) to date. Now, surface-rough Rh₂Sb nanorod (RNR) and surface-smooth Rh₂Sb NR (SNR) were selectively created, and their performance for NRR was investigated. The high-index-facet bounded Rh₂Sb RNRs/C exhibit a high NH₃ yield rate of 228.85±12.96 μg h⁻¹ mg⁻¹_Rh at −0.45 V versus reversible hydrogen electrode (RHE), outperforming the Rh₂Sb SNRs/C (63.07±4.45 μg h⁻¹ mg⁻¹_Rh) and Rh nanoparticles/C (22.82±1.49 μg h⁻¹ mg⁻¹_Rh), owing to the enhanced adsorption and activation of N₂ on high-index facets. Rh₂Sb RNRs/C also show durable stability with negligible activity decay after 10 h of successive electrolysis. The present work demonstrates that surface regulation plays an important role in promoting NRR activity and provides a new strategy for creating efficient NRR electrocatalysts.     

Carbon-Anchored Molybdenum Oxide Nanoclusters as Efficient Catalysts for the Electrosynthesis of Ammonia and Urea

The electrochemical NO₃⁻ reduction and its coupling with CO₂ can provide novel and clean routes to synthesize NH₃ and urea, respectively. However, their practical application is still impeded by the lack of efficient catalysts with desirable Faradaic efficiency (FE) and yield rate. Herein, we report the synthesis of molybdenum oxide nanoclusters anchored on carbon black (MoO_x/C) as electrocatalyst. It affords an outstanding FE of 98.14 % and NH₃ yield rate of 91.63 mg h⁻¹ mg_cat.⁻¹ in NO₃⁻ reduction. Besides, the highest FE of 27.7 % with a maximum urea yield rate of 1431.5 μg h⁻¹ mg_cat.⁻¹ toward urea is also achieved. The formation of electron-rich MoO_x nanoclusters with highly unsaturated metal sites in the MoO_x/C heterostructure is beneficial for enhanced catalytic performance. Studies on the mechanism reveal that the stabilization of *NO and *CO₂NOOH intermediates are critical for the NH₃ and urea synthesis, respectively.     

Durable Electrocatalytic Reduction of Nitrate to Ammonia over Defective Pseudobrookite Fe2TiO5 Nanofibers with Abundant Oxygen Vacancies

We propose the pseudobrookite Fe₂TiO₅ 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.     

Vacancy Engineering of Iron-Doped W18O49 Nanoreactors for Low-Barrier Electrochemical Nitrogen Reduction

The electrochemical nitrogen reduction reaction (NRR) is a promising energy-efficient and low-emission alternative to the traditional Haber–Bosch process. Usually, the competing hydrogen evolution reaction (HER) and the reaction barrier of ambient electrochemical NRR are significant challenges, making a simultaneous high NH₃ formation rate and high Faradic efficiency (FE) difficult. To give effective NRR electrocatalysis and suppressed HER, the surface atomic structure of W₁₈O₄₉, which has exposed active W sites and weak binding for H₂, is doped with Fe. A high NH₃ formation rate of 24.7 μg h⁻¹ mg_cat⁻¹ and a high FE of 20.0 % are achieved at an overpotential of only −0.15 V versus the reversible hydrogen electrode. Ab initio calculations reveal an intercalation-type doping of Fe atoms in the tunnels of the W₁₈O₄₉ crystal structure, which increases the oxygen vacancies and exposes more W active sites, optimizes the nitrogen adsorption energy, and facilitates the electrocatalytic NRR.     

Electrocatalytically Active Fe‐(O‐C2)4 Single‐Atom Sites for Efficient Reduction of Nitrogen to Ammonia

Single‐atom catalysts have demonstrated their superiority over other types of catalysts for various reactions. However, the reported nitrogen reduction reaction single‐atom electrocatalysts for the nitrogen reduction reaction exclusively utilize metal–nitrogen or metal–carbon coordination configurations as catalytic active sites. Here, we report a Fe single‐atom electrocatalyst supported on low‐cost, nitrogen‐free lignocellulose‐derived carbon. The extended X‐ray absorption fine structure spectra confirm that Fe atoms are anchored to the support via the Fe‐(O‐C₂)₄ coordination configuration. Density functional theory calculations identify Fe‐(O‐C₂)₄ as the active site for the nitrogen reduction reaction. An electrode consisting of the electrocatalyst loaded on carbon cloth can afford a NH₃ yield rate and faradaic efficiency of 32.1 μg h^?1 mg_cat.^?1 (5350 μg h^?1 mg_Fe^?1) and 29.3 %, respectively. An exceptional NH₃ yield rate of 307.7 μg h^?1 mg_cat.^?1 (51 283 μg h^?1 mg_Fe^?1) with a near record faradaic efficiency of 51.0 % can be achieved with the electrocatalyst immobilized on a glassy carbon electrode.     

Surface‐Regulated Rhodium–Antimony Nanorods for Nitrogen Fixation

Surface regulation is an effective strategy to improve the performance of catalysts, but it has been rarely demonstrated for nitrogen reduction reaction (NRR) to date. Now, surface‐rough Rh₂Sb nanorod (RNR) and surface‐smooth Rh₂Sb NR (SNR) were selectively created, and their performance for NRR was investigated. The high‐index‐facet bounded Rh₂Sb RNRs/C exhibit a high NH₃ yield rate of 228.85±12.96 μg h^?1 mg^?1_Rh at ?0.45 V versus reversible hydrogen electrode (RHE), outperforming the Rh₂Sb SNRs/C (63.07±4.45 μg h^?1 mg^?1_Rh) and Rh nanoparticles/C (22.82±1.49 μg h^?1 mg^?1_Rh), owing to the enhanced adsorption and activation of N₂ on high‐index facets. Rh₂Sb RNRs/C also show durable stability with negligible activity decay after 10 h of successive electrolysis. The present work demonstrates that surface regulation plays an important role in promoting NRR activity and provides a new strategy for creating efficient NRR electrocatalysts.     

Greatly Improving Electrochemical N2 Reduction over TiO2 Nanoparticles by Iron Doping

Titanium‐based catalysts are needed to achieve electrocatalytic N₂ reduction to NH₃ with a large NH₃ yield and a high Faradaic efficiency (FE). One of the cheapest and most abundant metals on earth, iron, is an effective dopant for greatly improving the nitrogen reduction reaction (NRR) performance of TiO₂ nanoparticles in ambient N₂‐to‐NH₃ conversion. In 0.5 m LiClO₄, Fe‐doped TiO₂ catalyst attains a high FE of 25.6 % and a large NH₃ yield of 25.47 μg h^?1 mg_cat^?1 at ?0.40 V versus a reversible hydrogen electrode. This performance compares favorably to those of all previously reported titanium‐ and iron‐based NRR electrocatalysts in aqueous media. The catalytic mechanism is further probed with theoretical calculations.     

Graphdiyne Interface Engineering: Highly Active and Selective Ammonia Synthesis

A freestanding 3D graphdiyne–cobalt nitride (GDY/Co₂N) with a highly active and selective interface is fabricated for the electrochemical nitrogen reduction reaction (ECNRR). Density function theory calculations reveal that the interface‐bonded GDY contributes an unique p‐electronic character to optimally modify the Co‐N compound surface bonding, which generates as‐observed superior electronic activity for NRR catalysis at the interface region. Experimentally, at atmospheric pressure and room temperature, the electrocatalyst creates a new record of ammonia yield rate (Y ) and Faradaic efficiency (FE) of 219.72 μg h^?1 mg_cat.^?1 and 58.60 %, respectively, in acidic conditions, higher than reported electrocatalysts. Such a catalyst is promising to generate new concepts, new knowledge, and new phenomena in electrocatalytic research, driving rapid development in the field of electrocatalysis.