Boosting electrocatalytic N2 reduction to NH3 on β-FeOOH by fluorine doping

Rational design of artificial Lewis pairs coupling with polyethylene glycol for efficient electrochemical ammonia synthesis

Ammonia (NH3) synthesis at mild conditions by electrocatalytic nitrogen reduction (eNRR) has received more attention and has been regarded as a promising alternative to the traditional Haber-Bosch process. Lewis acid-base pairs (LPs) can chemisorb and react with nitrogen by electronic interaction, while the tuning of the microenvironment near electrode can hinder hydrogen evolution reaction (HER) thus improving the selectivity of the eNRR. Herein, the FeOOH nanorod coupled with LPs on the surface (i.e., Fe, Fe-O) was synthesized, which could effectively drive eNRR. Meanwhile, polyethylene glycol (PEG) was introduced to serve as a local non-aqueous electrolyte system to inhibit HER. The prepared FeOOH-150 catalyst achieved outstanding eNRR performance with an NH3 yield rate of 118.07 μg h-1mgcat-1 and a Faradaic efficiency of 51.4 % at -0.6 V vs. RHE in 0.1 M LiClO4 + 20 % PEG. Both the experiment and DFT calculations revealed that the interaction of PEG with Lewis base sites could optimize nitrogen adsorption configuration and activation.

Synthesis of F-doped materials and applications in catalysis and rechargeable batteries

Elemental doping is one of the most essential techniques for material modification. It is well known that fluorine is considered to be a highly efficient and inexpensive dopant in the field of materials. Fluorine is one of the most reactive elements with the highest electronegativity (χ = 3.98). Compared to cationic doping, anionic doping is another valuable method for improving the properties of materials. Many materials have physicochemical limitations that affect their practical application in the field of catalysis and rechargeable ion batteries. Many researchers have demonstrated that F-doping can significantly improve the performance of materials for practical applications. This paper reviews the applications of various F-doped materials in photocatalysis, electrocatalysis, lithium-ion batteries, and sodium-ion batteries, as well as briefly introducing their preparation methods and mechanisms to provide researchers with more ideas and options for material modification.

Catalysis of dinitrogen activation and reduction by a single Fe13 cluster and its doped systems

Catalyzing N₂ reduction to ammonia under ambient conditions is known to be significant both in the fertilizer industry and life sciences. To unveil the synergy of multiple sites, here, we have studied the catalysis of ammonia synthesis using a typical Fe₁₃ cluster and its doped systems, Fe₁₂X (X = V, Cr, Mn, Co, Ni, Cu, Zn, Nb, Mo, Ru, and Rh). The energetics analysis showed that center substitution (X@Fe₁₂) was favored while doping single V, Cr, Co, and Mo atoms, whereas Mn, Ni, Cu, Zn, Nb, Ru, and Rh tended to form shell-doped structures (Fe₁₂X). Among all the 13 clusters, Fe₁₂Nb exhibited the lowest activation energy for N₂ dissociation; moreover, in the hydrogenation process, Fe₁₂Nb could convert N₂ to ammonia efficiently. We have fully illustrated the reaction dynamics and structural chemistry essence of these diverse 13-atom systems and propose Fe₁₂Nb as an ideal candidate for catalytic ammonia synthesis.

Phosphorus incorporation accelerates ammonia electrosynthesis over a mesoporous Au film

In this work, a phosphorus-doped mesoporous Au alloy film is grown on Ni foam (mAuP/NF) via a replacement reaction using diblock copolymers and NaH₂PO₂ as pore-forming agents and a phosphorus dopant, respectively. Due to the phosphorus doping and well-developed mesoporous structure, the obtained mAuP/NF possesses superior NH₃ yield (36.52 µg h^-1 mg^-1_cat.) and faradaic efficiency (20.32%) for ammonia electrosynthesis in neutral conditions, superior to mAu/NF.

Interface engineering of MoS2@Fe(OH)3 nanoarray heterostucture: Electrodeposition of MoS2@Fe(OH)3 as N2 and H+ channels for artificial NH3 synthesis under mild conditions

The electrocatalytic reduction of nitrogen (N₂) to ammonia (NH₃) has broad prospects for green and sustainable NH₃ production. Due to the electrocatalytic nitrogen reduction reaction (eNRR) performance of transition metal compound may be restricted with low yield rate, we develop transition metal interface engineering to improve the eNRR performance. Although the edge of MoS₂ catalyst is active, the MoS₂(001) surface is inert for N₂ electroreduction. Through the hydrothermal and electrodeposition methods, Fe(OH)₃ as N₂ and H⁺ channels coated on MoS₂ nanosheets array (MoS₂@Fe(OH)₃/CC) is synthesized. Such catalyst exhibits excellent eNRR performance in 0.1 M Na₂SO₄ with high Faradaic efficiency (2.76%) and NH₃ yield rate (4.23 × 10^-10 mol s^-1 cm^-2) at - 0.45 V (vs. RHE). This work may provide a new electrocatalyst synthesis pathway for artificial N₂ fixation. Density functional theory calculations show that electrodeposition Fe(OH)₃ can accelerate eNRR process rate of MoS₂.

Effect of local coordination on catalytic activities and selectivities of Fe-based catalysts for N2 reduction

Electrochemical reduction of nitrogen is considered as a promising route for achieving green and sustainable ammonia synthesis at ambient conditions. Transition metal atom loaded on N-doped graphene is commonly used...

MoS2 -Based Catalysts for N2 Electroreduction to NH3 - An Overview of MoS2 Optimization Strategies

The nitrogen reduction reaction (NRR) has become an ideal alternative to the Haber-Bosch process, as NRR possesses, among others, the advantage of operating under ambient conditions and saving energy consumption. The key to efficient NRR is to find a suitable electrocatalyst, which helps to break the strong N≡N bond and improves the reaction selectivity. Molybdenum disulfide (MoS2 ) as an emerging layered two-dimensional material has attracted a mass of attention in various fields. In this minireview, we summarize the optimization strategies of MoS2 -based catalysts which have been developed to improve the weak NRR activity of primitive MoS2 . Some theoretical predictions have also been summarized, which can provide direction for optimizing NRR activity of future MoS2 -based materials. Finally, an outlook about the optimization of MoS2 -based catalysts used in electrochemical N2 fixation are given.

Phosphorus modulation of a mesoporous rhodium film for enhanced nitrogen electroreduction

Electrochemical reduction of nitrogen to ammonia has received considerable attention for sustainable nitrogen fixation, but the sluggish kinetics results in unsatisfactory activity and efficiency. Designing electrocatalytic active centers for nitrogen adsorption and activation is highly desired. Herein, we present an electrodeposition method for the synthesis of a phosphorus-doped mesoporous rhodium film on nickel foam for the electrochemical synthesis of ammonia. Due to the unique combination of components and structure, the obtained catalyst not only shows excellent catalytic performance (NH₃ yield: 32.57 μg h^-1 mg^-1_cat.; faradaic efficiency: 40.86%), but also exhibits almost no decrease in activity after the durability test. This research work can provide a facile synthesis strategy for non-metal-doped porous metal based catalysts, which would be promising for the electrochemical synthesis of ammonia.

Identifying the Active Site on Graphene Oxide Nanosheets for Ambient Electrocatalytic Nitrogen Reduction

Identifying the active sites on graphene oxide (GO) nanosheets is of great importance. In situ electroreduction at different potentials is applied to control the oxygenated groups on GO surfaces. Both experiments and theoretical calculations suggest the C═O group is critical for N₂ adsorption and activation, guaranteeing the ambient electrocatalytic N₂ reduction.

Ambient Ammonia Electrosynthesis: Current Status, Challenges, and Perspectives

Ammonia (NH₃ ) electrosynthesis from atmospheric nitrogen (N₂ ) and water is emerging as a promising alternative to the energy-intensive Haber-Bosch process; however, such a process is difficult to perform due to the inherent inertness of N₂ molecules together with low solubility in aqueous solutions. Although many active electrocatalysts have been used to electrocatalyze the N₂ reduction reaction (NRR), unsatisfactory NH₃ yields and lower Faraday efficiency are still far from practical industrial production, and thus, considerable research efforts are being devoted to address these problems. Nevertheless, most reports still mainly focus on the preparation of electrocatalysts and largely ignore a summary of optimization-modification strategies for the NRR. In this review, a general introduction to the NRR mechanism is presented to provide a reasonable guide for the design of highly active catalysts. Then, four categories of NRR electrocatalysts, according to chemical compositions, are surveyed, as well as several strategies for promoting the catalytic activity and efficiency. Later, strategies for developing efficient N₂ fixation systems are discussed. Finally, current challenges and future perspectives in the context of the NRR are highlighted. This review sheds some light on the development of highly efficient catalytic systems for NH₃ synthesis and stimulates research interests in the unexplored, but promising, research field of the NRR.

Two-dimensional (2D)/2D Interface Engineering of a MoS2/C3N4 Heterostructure for Promoted Electrocatalytic Nitrogen Fixation

The electrochemical nitrogen reduction reaction (NRR) is a very efficient method for sustainable NH₃ production, but it requires effective catalysts to expedite the NRR kinetics and inhibit the concomitant hydrogen evolution reaction (HER). Two-dimensional (2D)/2D interface engineering is an effective method to design powerful catalysts due to intimate face-to-face contact of two 2D materials that facilitates the strong interfacial electronic interactions. Herein, we explored a 2D/2D MoS₂/C₃N₄ heterostructure as an active and stable NRR catalyst. MoS₂/C₃N₄ exhibited a conspicuously improved NRR performance with an NH₃ yield of 18.5 μg h^-1 mg^-1 and a high Faradaic efficiency (FE) of 17.8% at -0.3 V, far better than those of the individual MoS₂ or C₃N₄ component. Density functional theory calculations revealed that the interfacial charge transport from C₃N₄ to MoS₂ could enhance the NRR activity of MoS₂/C₃N₄ by promoting the stabilization of the key intermediate *N₂H on Mo edge sites of MoS₂ and concurrently decreasing the reaction energy barrier. Meanwhile, MoS₂/C₃N₄ rendered a more favorable *H adsorption free energy on S edge sites than on Mo edge sites of MoS₂, thereby protecting the NRR-active Mo edge sites from the competing HER and leading to a high FE.

Efficient electrocatalytic conversion of N2 to NH3 on NiWO4 under ambient conditions

The development of highly efficient and inexpensive catalysts is still a tremendous challenge for the electrocatalytic nitrogen reduction reaction (NRR), which is a promising alternative to high-temperature and high-pressure industrial technologies for the synthesis of NH3. Herein, we report a facile and large scale strategy exploiting a porous non-precious bimetallic oxide of NiWO4 for the NRR under ambient conditions. Benefiting from the above-mentioned merits, the designed electrocatalyst achieved outstanding catalytic activities in both 0.1 M HCl (NH3 yield: (40.05 ± 1.45) μg h-1 mg-1cat., Faraday efficiency (FE): (19.32 ± 0.68)% at -0.3 V) and 0.1 Na2SO4 (NH3 yield: (23.14 ± 1.75) μg h-1 mg-1cat., Farady efficiency: (10.18 ± 0.62)% at -0.3 V), and these efficiencies are superior to most of the reported non-precious metals for the NRR. Furthermore, the prepared catalyst presented excellent stability in both acidic and neutral media for up to 20 h. This work opens a constructive avenue for optimizing the catalytic performance of metal oxides and other transition metal-based catalysts for NRRs.

Plasma-engineered NiO nanosheets with enriched oxygen vacancies for enhanced electrocatalytic nitrogen fixation

Plasma technique can readily create the enriched oxygen vacancies which enable the NiO to be an active and durable catalyst for electrocatalytic fixation of N₂ to NH₃.

Unusual electrochemical N2 reduction activity in an earth-abundant iron catalyst via phosphorous modulation

FeP₂ nanoparticles-reduced graphene oxide hybrid acts as an efficient electrocatalyst for conversion of N₂ to NH₃ in 0.5 M LiClO₄, achieving a large NH₃ yield of 35.26 μg h⁻¹ mg_cat.⁻¹ and a high faradaic efficiency of 21.99%.

WO3 nanosheets rich in oxygen vacancies for enhanced electrocatalytic N2 reduction to NH3

The Haber-Bosch process for industrial-scale NH3 production suffers from harsh conditions and serious CO2 release. Electrochemical N2 reduction is an alternative approach to synthesize NH3 under ambient conditions, but it requires highly-efficient electrocatalysts for the N2 reduction reaction (NRR). In this Communication, we demonstrate that WO3 nanosheets rich in oxygen vacancies (R-WO3 NSs) exhibit greatly enhanced NRR performances. In 0.1 M HCl, such R-WO3 NSs achieve a large NH3 yield of 17.28 μg h-1 mgcat.-1 and a high faradaic efficiency of 7.0% at -0.3 V vs. a reversible hydrogen electrode, much superior to the WO3 nanosheets deficient in oxygen vacancies (6.47 μg h-1 mgcat.-1 and 1.02%). Remarkably, R-WO3 NSs also show high electrochemical stability.

Cr3C2 Nanoparticle-Embedded Carbon Nanofiber for Artificial Synthesis of NH3 through N2 Fixation under Ambient Conditions

Industrial production of NH₃ heavily depends on the conventional Haber-Bosch process under rigorous conditions with a large amount of energy consumption and carbon emissions. Electrocatalysis exhibits an intriguing prospect for the N₂ reduction reaction (NRR) at ambient conditions. In this case, a high-efficiency and low-cost catalyst is paramount. In this letter, Cr₃C₂ nanoparticles and carbon nanofiber composite (Cr₃C₂@CNF) are proposed as a noble-metal-free NRR electrocatalyst for converting N₂ to NH₃ with an excellent selectivity. The optimal Faradic efficiency and NH₃ yield rate achieved are as high as 8.6% and 23.9 μg h^-1 mg_cat.^-1 at -0.3 V vs reversible hydrogen electrode in 0.1 M HCl, respectively. Theoretical calculations show a low reaction barrier of merely 0.53 eV in the enzymatic route for this catalyst.

Facile Preparation of Carbon Shells-Coated O-Doped Molybdenum Carbide Nanoparticles as High Selective Electrocatalysts for Nitrogen Reduction Reaction under Ambient Conditions

Electrochemical nitrogen reduction reaction (NRR) has been considered as a promising alternative to the traditional Haber-Bosch process for the preparation of ammonia (NH₃) under ambient conditions. The development of cost-effective electrocatalysts with suppressive activity for hydrogen evolution reaction is critical for improving the efficiency of NRR. Herein, oxygen-containing molybdenum carbides (O-MoC) embedded in nitrogen-doped carbon layers (N-doped carbon) can be easily fabricated by pyrolyzing the chelate of dopamine and molybdate. A rate of NH₃ formation of 22.5 μg·h^-1·mg_cat^-1 is obtained at -0.35 V versus reversible hydrogen electrode with a high faradaic efficiency of 25.1% in 0.1 mM HCl + 0.5 M Li₂SO₄. Notably, the synthesized O-MoC@NC-800 also exhibits high selectivity (no formation of hydrazine) and electrochemical stability. The moderate electron structure induced by the interaction between O-MoC and N-doped carbon shells can effectively weaken the activity of hydrogen evolution reaction and increase the faradaic efficiency of NRR. Additionally, by applying the in situ Fourier transform infrared spectroscopy, an associative reaction pathway is proposed on O-MoC@NC-800. This work provides new insights into the rational design of carbon-encapsulated metal nanoparticles as efficient catalysts for NRR at ambient conditions.

Electronically Coupled SnO2 Quantum Dots and Graphene for Efficient Nitrogen Reduction Reaction

Electrocatalytic N₂ reduction reaction (NRR) provides an effective and renewable approach for artificial NH₃ production, but still remains a grand challenge because of the low NH₃ yield and Faradaic efficiency (FE). Herein, we reported that the SnO₂ quantum dots (QDs) supported on reduced graphene oxide (RGO) could efficiently and stably catalyze NRR at ambient conditions. The NRR performance of resulting SnO₂/RGO was studied by both experimental techniques and density functional theory calculations. It was found that the ultrasmall SnO₂ QDs (2 nm) grown on RGO could provide abundant sites for efficient N₂ adsorption. Significantly, the strongly electronically coupled SnO₂ QDs and RGO brought about the enhanced conductivity and the decreased work function, which led to a considerably lowered energy barrier of *N₂ → *N₂H that was the rate-determining step of the NRR process. Meanwhile, the SnO₂/RGO exhibited inferior hydrogen evolution reaction activity. As a result, the SnO₂/RGO delivered a high NH₃ yield of 25.6 μg h^-1 mg^-1 (5.1 μg cm^-2h^-1) and an FE of 7.1% in 0.1 M Na₂SO₄ at -0.5 V (vs RHE), together with the outstanding selectivity and stability, endowing it as a promising electrocatalyst for N₂ fixation.

Efficient Photoelectrochemical Route for the Ambient Reduction of N2 to NH3 Based on Nanojunctions Assembled from MoS2 Nanosheets and TiO2

Efficient nitrogen fixation under ambient conditions is an exigent task in both basic research and industrial applications. Recently, reduction of N₂ to NH₃ based on photocatalysis and/or electrocatalysis offers a possible route to the typical Haber-Bosch process. However, achieving a high yield of N₂ reduction reaction (NRR) is still a challenging goal because of the limitations of efficient catalysts. Herein, we propose a photoelectrochemical NRR route based on the rational design of MoS₂@TiO₂ semiconductor nanojunction catalysts through a facile hydrothermal synthetic method. The developed MoS₂@TiO₂ photocathode attains a high NH₃ yield rate (1.42 × 10^-6 mol h^-1 cm^-2) and a superhigh faradaic efficiency (65.52%), which is the highest record to the best of our knowledge. Moreover, MoS₂@TiO₂ exhibits high stability over 10 consecutive reaction cycles. Therefore, this work demonstrates an effective NRR photoelectrocatalyst and results in a breakthrough in the low faradaic efficiency because of the interfacial electronic coupling and synergistic effects between the MoS₂ and TiO₂ components.

Ambient electrochemical N2 reduction to NH3 under alkaline conditions enabled by a layered K2Ti4O9 nanobelt

A K₂Ti₄O₉ nanobelt effectively electrocatalyzes ambient N₂-to-NH₃ fixation. In 0.1 M KOH, a NH₃ yield of 22.88 μg h⁻¹ mg⁻¹_cat. and a faradaic efficiency of 5.87% are attained, with good selectivity and high electrochemical stability.

Dendritic Cu: a high-efficiency electrocatalyst for N2 fixation to NH3 under ambient conditions

Dendritic Cu behaves as an efficient electrocatalyst for ambient N₂-to-NH₃ fixation with a high Faradaic efficiency of 15.12% and a large NH₃ yield rate of 25.63 μg h⁻¹ mg_cat.⁻¹ at −0.40 V versus reversible hydrogen electrode in 0.1 M HCl.

A perovskite La2Ti2O7 nanosheet as an efficient electrocatalyst for artificial N2 fixation to NH3 in acidic media

The synthesis of NH3 heavily relies on the Haber-Bosch process suffering from a large amount of CO2 emission and energy consumption. Possessing eco-friendly and sustainable characteristics, electrochemical reduction is considered as a promising candidate for artificial N2 fixation under ambient conditions, but efficient electrocatalysts are crucial for the N2 reduction reaction (NRR). In this communication, we report that perovskite La2Ti2O7 nanosheets behave as an efficient NRR electrocatalyst with excellent selectivity under ambient conditions. In 0.1 M HCl, this catalyst achieves a high NH3 yield rate of 25.15 μg h-1 mgcat.-1 with a faradaic efficiency of 4.55% at -0.55 V vs. a reversible hydrogen electrode. Notably, it also shows high electrochemical stability.

TiS2 nanosheets for efficient electrocatalytic N2 fixation to NH3 under ambient conditions

TiS₂ is efficient for electrochemical N₂ fixation to NH₃ in 0.1 M Na₂SO₄, achieving a faradaic efficiency of 5.50% with an NH₃ yield of 16.02 μg h⁻¹ mg⁻¹_cat at a potential of −0.6 V vs. reversible hydrogen electrode.

Electrocatalytic N2-to-NH3 conversion using oxygen-doped graphene: experimental and theoretical studies

Oxygen-doped graphene acts as an efficient electrocatalyst for conversion of N₂ to NH₃ in 0.1 M HCl, achieving a large NH₃ yield of 21.3 μg h⁻¹ mg_cat.⁻¹ and a high FE of 12.6%.

Ceria-reduced graphene oxide nanocomposite as an efficient electrocatalyst towards artificial N2 conversion to NH3 under ambient conditions

Ultrasmall CeO₂ on the surface of rGO sheets exhibits electrocatalytic performance towards artificial N₂ conversion to NH₃ with excellent selectivity.

An Fe2O3 nanoparticle-reduced graphene oxide composite for ambient electrocatalytic N2 reduction to NH3

Fe₂O₃-rGO behaves as an Earth-abundant NRR electrocatalyst for conversion of N₂ to NH₃ in 0.5 M LiClO₄, achieving a large NH₃ yield of 22.13 μg h⁻¹ mg⁻¹_cat and a high faradaic efficiency of 5.89%.