Electrochemical Fabrication of Porous Au Film on Ni Foam for Nitrogen Reduction to Ammonia

Electrochemical reduction of N₂ to NH₃ provides an alternative strategy to replace the industrial Haber–Bosch process for facile and sustainable production of NH₃. The development of efficient electrocatalysts for the nitrogen reduction reaction (NRR) is highly desired. Herein, a micelle‐assisted electrodeposition method is presented for the direct fabrication of porous Au film on Ni foam (pAu/NF). Benefiting from its interconnected porous architectonics, the pAu/NF exhibits superior NRR performance with a high NH₃ yield rate of 9.42 µg h^?1 cm^?2 and a superior Faradaic efficiency of 13.36% at ?0.2 V versus reversible hydrogen electrode under the neutral electrolyte (0.1 m Na₂SO₄). The proposed micelle‐assisted electrodeposition strategy is highly valuable for future design of active NRR catalysts with desired compositions toward various electrocatalysis fields.     

Light Field-Enhanced Single-Site Cu Electrocatalyst for Nitrogen Fixation

Direct electrocatalytic reduction of N₂ to NH₃ under mild conditions is attracting considerable interests but still remains enormous challenges in terms of respect of intrinsic catalytic activity and limited electrocatalytic efficiency. Herein, a photo-enhanced strategy is developed to improve the NRR activity on Cu single atoms catalysts. The atomically dispersed Cu single atoms supported TiO₂ nanosheets (Cu SAs/TiO₂) achieve a Faradaic Efficiency (12.88%) and NH₃ yield rate (6.26 µg h⁻¹ mg_cat⁻¹) at −0.05 V versus RHE under the light irradiation field, in which NH₃ yield rate is fivefold higher than that under pure electrocatalytic nitrogen reduction reaction (NRR) process and is remarkably superior in comparison to most of the similar type electrocatalysts. The existence of external light field improves electron transfer ability between Cu O and Ti O, and thus optimizes the accumulation of surface charges on Cu sites, endowing more electrons involved in nitrogen fixation. This work reveals an atomic-scale mechanistic understanding of field effect-enhanced electrochemical performance of catalysts and it provides predictive guidelines for the rational design of photo-enhanced electrochemical N₂ reduction catalysts.     

P-Block Metal-Based Electrocatalysts for Nitrogen Reduction to Ammonia: A Minireview

Electrochemical nitrogen reduction reaction (NRR) to ammonia (NH₃) using renewable electricity provides a promising approach towards carbon neutral. What's more, it has been regarded as the most promising alternative to the traditional Haber-Bosch route in current context of developing sustainable technologies. The development of a class of highly efficient electrocatalysts with high selectivity and stability is the key to electrochemical NRR. Among them, P-block metal-based electrocatalysts have significant application potential in NRR for which possessing a strong interaction with the N 2p orbitals. Thus, it offers a good selectivity for NRR to NH₃. The density of state (DOS) near the Fermi level is concentrated for the P-block metal-based catalysts, indicating the ability of P-block metal as active sites for N₂ adsorption and activation by donating p electrons. In this work, we systematically review the recent progress of P-block metal-based electrocatalysts for electrochemical NRR. The effect of P-block metal-based electrocatalysts on the NRR activity, selectivity and stability are discussed. Specifically, the catalyst design, the nature of the active sites of electrocatalysts and some strategies for boosting NRR performance, the reaction mechanism, and the impact of operating conditions are unveiled. Finally, some challenges and outlooks using P-block metal-based electrocatalysts are proposed.     

Highly Selective N2 Electroreduction to NH3 Using a Boron-Vacancy-Rich Diatomic Nb?B Catalyst

The ambient electrochemical N₂ reduction reaction (NRR) is a future approach for the artificial NH₃ synthesis to overcome the problems of high-energy consumption and environmental pollution by Haber–Bosch technology. However, the challenge of N₂ activation on a catalyst surface and the competitive hydrogen evolution reaction make the current NRR unsatisfied. Herein, this work demonstrates that NbB₂ nanoflakes (NFs) exhibit excellent selectivity and durability in NRR, which produces NH₃ with a production rate of 30.5 µg h⁻¹ mg_cat⁻¹ and a super-high Faraday efficiency (FE) of 40.2%. The high-selective NH₃ production is attributed to the large amount of active B vacancies on the surface of NbB₂ NFs. Density functional theory calculations suggest that the multiple atomic adsorption of N₂ on both unsaturated Nb and B atoms results in a significantly stretched N₂ molecule. The weakened NN triple bonds are easier to be broken for a biased NH₃ production. The diatomic catalysis is a future approach for NRR as it shows a special N₂ adsorption mode that can be well engineered.     

Salt‐Templated Construction of Ultrathin Cobalt Doped Iron Thiophosphite Nanosheets toward Electrochemical Ammonia Synthesis

Exploiting efficient electrocatalysts for electrochemical nitrogen reduction (NRR) is highly desired and deeply meaningful for realizing sustainable ammonia (NH₃) production under ambient conditions. The Fe protein contains one [Fe₄S₄] cluster and P cluster, which play an important role for transfer electron during the nitrogen fixing of nitrogenases. Based on the understanding of nitrogenase, the rising‐star 2D iron thiophosphite (FePS₃) nanomaterials may be highly active electrocatalysts toward NRR due to the ideal elemental composition. In this work, 2D FePS₃ nanosheets are successfully synthesized by a facile salt‐templated method. The FePS₃ nanosheets show better electrocatalytic NH₃ yield and faradaic efficiency (FE) than Fe₂S₃, which demonstrates that the P element indeed improves the NRR activity of Fe‐S. Theoretically, Co incorporation not only effectively prompts the conductivity of FePS₃, but also enhances the catalytic activities of Fe‐edge sites. Experimentally, Co‐doped FePS₃ (Co‐FePS₃) nanosheets exhibit a remarkable electrocatalytic performance toward NRR, such as high NH₃ yield rate of 90.6 µg h^?1 mg_cat^?1, high FE of 3.38%, and an excellent long‐term stability. Being the first theoretical and experimental report regarding FePS₃‐based electrocatalyst toward NRR, this work represents an important beginning to the family of metal thiophosphite as advanced electrocatalysts toward NRR.     

Identifying the Origin of Ti3+ Activity toward Enhanced Electrocatalytic N2 Reduction over TiO2 Nanoparticles Modulated by Mixed-Valent Copper

The ambient electrocatalytic N₂ reduction reaction (NRR) enabled by TiO₂ has attracted extensive recent attention. Previous studies suggest the formation of Ti³⁺ in TiO₂ can significantly improve the NRR activity, but it still remains unclear what kinds of Ti³⁺ are effective. Herein, it is demonstrated that mixed-valent Cu acts as an effective dopant to modulate the oxygen vacancy (V_O) concentration and Ti³⁺ formation, which markedly improves the electrocatalytic NRR performance. In 0.5 m LiClO₄, this electrocatalyst attains a high Faradic efficiency of 21.99% and a large NH₃ yield of 21.31 µg h⁻¹ mg_cat.⁻¹ at –0.55 V vs reversible hydrogen electrode, which even surpasses most reported Ti-based NRR electrocatalysts. Using density function theory calculations, it is evidenced that mixed-valent Cu ions modulate the TiO₂ (101) surface with multiple oxygen vacancies, which is beneficial for generating different Ti³⁺ 3d¹ defect states localized below the Fermi energy. N₂ activation and adsorption are effectively strengthened when Ti³⁺ 3d¹ defect states present the splitting of e_g and t_2g orbitals, which can be modulated by its coordination structure. The synergistic roles of the three ion pairs formed by the V_O defect, including Cu¹⁺–Ti⁴⁺, Ti³⁺–Ti⁴⁺ and Ti³⁺–Ti³⁺, are together responsible for the enhanced NRR performance.     

FeOOH quantum dots decorated graphene sheet: An efficient electrocatalyst for ambient N2 reduction

Electrochemical N₂ reduction offers a promising alternative to the Haber-Bosch process for sustainable NH₃ synthesis at ambient conditions, but it needs efficient catalysts for the N₂ reduction reaction (NRR). Here, we report that FeOOH quantum dots decorated graphene sheet acts as a superior catalyst toward enhanced electrocatalytic N₂ reduction to NH₃ under ambient conditions. In 0.1 M LiClO₄, this hybrid attains a large NH₃ yield rate and a high Faradaic efficiency of 27.3 µg·h⁻¹·mg⁻¹_cat. and 14.6% at −0.4 V vs. reversible hydrogen electrode, respectively, rivalling the current efficiency of all Fe-based NRR electrocatalysts in aqueous media. It also shows strong durability during the electrolytic process.

     

A Generalized Surface Chalcogenation Strategy for Boosting the Electrochemical N2 Fixation of Metal Nanocrystals

Electrocatalytic nitrogen reduction reaction (NRR) is a promising process relative to energy-intensive Haber–Bosch process. While conventional electrocatalysts underperform with sluggish paths, achieving dissociation of N₂ brings the key challenge for enhancing NRR. This study proposes an effective surface chalcogenation strategy to improve the NRR performance of pristine metal nanocrystals (NCs). Surprisingly, the NH₃ yield and Faraday efficiency (FE) (175.6 ± 23.6 mg h^–1 g^–1_Rh and 13.3 ± 0.4%) of Rh-Se NCs is significantly enhanced by 16 and 15 times, respectively. Detailed investigations show that the superior activity and high FE are attributed to the effect of surface chalcogenation, which not only can decrease the apparent activation energy, but also inhibit the occurrence of the hydrogen evolution reaction (HER) process. Theoretical calculations reveal that the strong interface strain effect within core@shell system induces a critical redox inversion, resulting in a rather low valence state of Rh and Se surface sites. Such strong correlation indicates an efficient electron-transfer minimizing NRR barrier. Significantly, the surface chalcogenation strategy is general, which can extend to create other NRR metal electrocatalysts with enhanced performance. This strategy open a new avenue for future NH₃ production for breakthrough in the bottleneck of NRR.     

Electrochemical Ammonia Synthesis via Nitrogen Reduction Reaction on a MoS2 Catalyst: Theoretical and Experimental Studies

The discovery of stable and noble‐metal‐free catalysts toward efficient electrochemical reduction of nitrogen (N₂) to ammonia (NH₃) is highly desired and significantly critical for the earth nitrogen cycle. Here, based on the theoretical predictions, MoS₂ is first utilized to catalyze the N₂ reduction reaction (NRR) under room temperature and atmospheric pressure. Electrochemical tests reveal that such catalyst achieves a high Faradaic efficiency (1.17%) and NH₃ yield (8.08 × 10^?11 mol s^?1 cm^?1) at ?0.5 V versus reversible hydrogen electrode in 0.1 m Na₂SO₄. Even in acidic conditions, where strong hydrogen evolution reaction occurs, MoS₂ is still active for the NRR. This work represents an important addition to the growing family of transition‐metal‐based catalysts with advanced performance in NRR.     

Formation of B?N?C Coordination to Stabilize the Exposed Active Nitrogen Atoms in g‐C3N4 for Dramatically Enhanced Photocatalytic Ammonia Synthesis Performance

It is an important issue that exposed active nitrogen atoms (e.g., edge or amino N atoms) in graphitic carbon nitride (g‐C₃N₄) could participate in ammonia (NH₃) synthesis during the photocatalytic nitrogen reduction reaction (NRR). Herein, the experimental results in this work demonstrate that the exposed active N atoms in g‐C₃N₄ nanosheets can indeed be hydrogenated and contribute to NH₃ synthesis during the visible‐light photocatalytic NRR. However, these exposed N atoms can be firmly stabilized through forming B? N? C coordination by means of B‐doping in g‐C₃N₄ nanosheets (BCN) with a B‐doping content of 13.8 wt%. Moreover, the formed B? N? C coordination in g‐C₃N₄ not only effectively enhances the visible‐light harvesting and suppresses the recombination of photogenerated carriers in g‐C₃N₄, but also acts as the catalytic active site for N₂ adsorption, activation, and hydrogenation. Consequently, the as‐synthesized BCN exhibits high visible‐light‐driven photocatalytic NRR activity, affording an NH₃ yield rate of 313.9 µmol g^?1 h^?1, nearly 10 times of that for pristine g‐C₃N₄. This work would be helpful for designing and developing high‐efficiency metal‐free NRR catalysts for visible‐light‐driven photocatalytic NH₃ synthesis.     

Electrocatalytic N2 reduction to NH3 with high Faradaic efficiency enabled by vanadium phosphide nanoparticle on V foil

To develop highly efficient electrochemical catalysts for N₂ fixation is important to sustainable ambient NH₃ production through the N₂ reduction reaction (NRR). Herein, we demonstrate the development of vanadium phosphide nanoparticle on V foil as a high-efficiency and stable catalyst for ambient NH₃ production with excellent selectivity. The high Faradaic efficiency of 22% with a large NH₃ yield of 8.35 × 10⁻¹¹ mol·s⁻¹·cm⁻² was obtained at 0 V vs. the reversible hydrogen electrode in acid solution, superior to all previously studied V-based NRR catalysts. Density functional theory calculations are also utilized to have an insight into the catalytic mechanism.

     

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.     

Controllable Exfoliation of MOF-Derived Van Der Waals Superstructure into Ultrathin 2D B/N Co-Doped Porous Carbon Nanosheets: A Superior Catalyst for Ambient Ammonia Electrosynthesis

The electrocatalytic nitrogen reduction reaction (NRR) to synthesize NH₃ under ambient conditions is a promising alternative route to the conventional Haber–Bosch process, but it is still a great challenge to develop electrocatalysts’ high Faraday efficiency and ammonia yield. Herein, a facile and efficient exfoliation strategy to synthesize ultrathin 2D boron and nitrogen co-doped porous carbon nanosheets (B/N C NS) via a metal–organic framework (MOF)-derived van der Waals superstructure, is reported. The results of experiments and theoretical calculations show that the doping of boron and nitrogen can modulate the electronic structure of the adjacent carbon atoms; which thus, promotes the competitive adsorption of nitrogen and reduces the energy required for ammonia synthesis. The B/N C NS exhibits excellent catalytic performance and stability in electrocatalytic NRR, with a yield rate of 153.4 µg·h⁻¹·mg⁻¹ cat and a Faraday efficiency of 33.1%, which is better than most of the reported NRR electrocatalysts. The ammonia yield of B/N C NS can maintain 92.7% of the initial NRR activity after 48 h stability test. The authors’ controllable exfoliation strategy using MOF-derived van der Waals superstructure can provide a new insight for the synthesis of other 2D materials.     

Hierarchical Nanospheres with Polycrystalline Ir&Cu and Amorphous Cu2O toward Energy-Efficient Nitrate Electrolysis to Ammonia

Electrochemical reduction reaction of nitrate (NITRR) provides a sustainable route toward the green synthesis of ammonia. Nevertheless, it remains challenging to achieve high-performance electrocatalysts for NITRR especially at low overpotentials. In this work, hierarchical nanospheres consisting of polycrystalline Iridium&copper (Ir&Cu) and amorphous Cu₂O (Cu_xIr_yO_z NS) have been fabricated. The optimal species Cu_0.86Ir_0.14O_z delivers excellent catalytic performance with a desirable NH₃ yield rate (YR) up to 0.423 mmol h⁻¹ cm⁻² (or 4.8 mg h⁻¹ mg_cat⁻¹) and a high NH₃ Faradaic efficiency (FE) over 90% at a low overpotential of 0.69 V (or 0 V_RHE), where hydrogen evolution reaction (HER) is almost negligible. The electrolyzer toward NITRR and hydrazine oxidation (HzOR) is constructed for the first time with an electrode pair of Cu_0.86Ir_0.14O_z//Cu_0.86Ir_0.14O_z, yielding a high energy efficiency (EE) up to 87%. Density functional theory (DFT) calculations demonstrate that the dispersed Ir atom provides active site that not only promotes the NO₃⁻ adsorption but also modulates the H adsorption/desorption to facilitate the proton supply for the hydrogenation of *N, hence boosting the NITRR. This work thus points to the importance of both morphological/structural and compositional engineering for achieving the highly efficient catalysts toward NITRR.     

B?N Pairs Enriched Defective Carbon Nanosheets for Ammonia Synthesis with High Efficiency

Electrochemical synthesis has garnered attention as a promising alternative to the traditional Haber–Bosch process to enable the generation of ammonia (NH₃) under ambient conditions. Current electrocatalysts for the nitrogen reduction reaction (NRR) to produce NH₃ are comprised of noble metals or transitional metals. Here, an efficient metal‐free catalyst (BCN) is demonstrated without precious component and can be easily fabricated by pyrolysis of organic precursor. Both theoretical calculations and experiments confirm that the doped B? N pairs are the active triggers and the edge carbon atoms near to B? N pairs are the active sites toward the NRR. This doping strategy can provide sufficient active sites while retarding the competing hydrogen evolution reaction (HER) process; thus, NRR with high NH₃ formation rate (7.75 µg h^?1 mg_cat. ^?1) and excellent Faradaic efficiency (13.79%) are achieved at ?0.3 V versus reversible hydrogen electrode (RHE), exceeding the performance of most of the metallic catalysts.     

Rhenium Suppresses Iridium (IV) Oxide Crystallization and Enables Efficient,Stable Electrochemical Water Oxidation

IrO₂ as benchmark electrocatalyst for acidic oxygen evolution reaction (OER) suffers from its low activity and poor stability. Modulating the coordination environment of IrO₂ by chemical doping is a methodology to suppress Ir dissolution and tailor adsorption behavior of active oxygen intermediates on interfacial Ir sites. Herein, the Re-doped IrO₂ with low crystallinity is rationally designed as highly active and robust electrocatalysts for acidic OER. Theoretical calculations suggest that the similar ionic sizes of Ir and Re impart large spontaneous substitution energy and successfully incorporate Re into the IrO₂ lattice. Re-doped IrO₂ exhibits a much larger migration energy from IrO₂ surface (0.96 eV) than other dopants (Ni, Cu, and Zn), indicating strong confinement of Re within the IrO₂ lattice for suppressing Ir dissolution. The optimal catalysts (Re: 10 at%) exhibit a low overpotential of 255 mV at 10 mA cm⁻² and a high stability of 170 h for acidic OER. The comprehensive mechanism investigations demonstrate that the unique structural arrangement of the Ir active sites with Re-dopant imparts high performance of catalysts by minimizing Ir dissolution, facilitating *OH adsorption and *OOH deprotonation, and lowering kinetic barrier during OER. This study provides a methodology for designing highly-performed catalysts for energy conversion.     

Porous and Partially Dehydrogenated Fe2+-Containing Iron Oxyhydroxide Nanosheets for Efficient Electrochemical Nitrogen Reduction Reaction (ENRR)

The design and development of efficient catalysts for electrochemical nitrogen reduction reaction (ENRR) under ambient conditions are critical for the alternative ammonia (NH₃) synthesis from N₂ and H₂O, wherein iron-based electrocatalysts exhibit outstanding NH₃ formation rate and Faradaic efficiency (FE). Here, the synthesis of porous and positively charged iron oxyhydroxide nanosheets by using layered ferrous hydroxide as a starting precursor, which undergoes topochemical oxidation, partial dehydrogenated reaction, and final delamination, is reported. As the electrocatalyst of ENRR, the obtained nanosheets with a monolayer thickness and 10-nm mesopores display exceptional NH₃ yield rate (28.5 µg h⁻¹ mg_cat.⁻¹) and FE (13.2%) at a potential of −0.4 V versus RHE in a phosphate buffered saline (PBS) electrolyte. The values are much higher than those of the undelaminated bulk iron oxyhydroxide. The larger specific surface area and positive charge of the nanosheets are beneficial for providing more exposed reactive sites as well as retarding hydrogen evolution reaction. This study highlights the rational control on the electronic structure and morphology of porous iron oxyhydroxide nanosheets, expanding the scope of developing non-precious iron-based highly efficient ENRR electrocatalysts.     

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.     

Introducing High-Valence Iridium Single Atoms into Bimetal Phosphides toward High-Efficiency Oxygen Evolution and Overall Water Splitting

Single atoms are superior electrocatalysts having high atomic utilization and amazing activity for water oxidation and splitting. Herein, this work reports a thermal reduction method to introduce high-valence iridium (Ir) single atoms into bimetal phosphide (FeNiP) nanoparticles toward high-efficiency oxygen evolution reaction (OER) and overall water splitting. The presence of high-valence single Ir atoms (Ir⁴⁺) and their synergistic interaction with Ni³⁺ species as well as the disproportionation of Ni³⁺ assisted by Fe collectively contribute to the exceptional OER performance. In specific, at appropriate Ir/Ni and Fe/Ni ratios, the as-prepared Ir-doped FeNiP (Ir₂₅-Fe₁₆Ni₁₀₀P₆₄) nanoparticles at a mass loading of only 35 µg cm⁻² show the overpotential as low as 232 mV at 10 mA cm⁻² and activity as high as 1.86 A mg⁻¹ at 1.5 V versus RHE for OER in 1.0 m KOH. Computational simulations confirm the vital role of high-valence Ir to weaken the adsorption of OER intermediates, favorable for accelerating OER kinetics. Impressively, a Pt/C||Ir₂₅-Fe₁₆Ni₁₀₀P₆₄ two-electrode alkaline electrolyzer affords a current density of 10 mA cm⁻² at a low cell voltage of 1.42 V, along with satisfied stability. An AA battery with a nominal voltage of 1.5 V can drive overall water splitting with obvious bubbles released.