DyF 3 : An Efficient Electrocatalyst for N 2 Fixation to NH 3 under Ambient Conditions

Comprehensive Understanding of the Thriving Ambient Electrochemical Nitrogen Reduction Reaction

The electrochemical method of combining N₂ and H₂ O to produce ammonia (i.e., the electrochemical nitrogen reduction reaction [E-NRR]) continues to draw attention as it is both environmentally friendly and well suited for a progressively distributed farm economy. Despite the multitude of recent works on the E-NRR, further progress in this field faces a bottleneck. On the one hand, despite the extensive exploration and trial-and-error evaluation of E-NRR catalysts, no study has stood out to become the stage protagonist. On the other hand, the current level of ammonia production (microgram-scale) is an almost insurmountable obstacle for its qualitative and quantitative determination, hindering the discrimination between true activity and contamination. Herein i) the popular theory and mechanism of the NRR are introduced; ii) a comprehensive summary of the recent progress in the field of the E-NRR and related catalysts is provided; iii) the operational procedures of the E-NRR are addressed, including the acquisition of key metrics, the challenges faced, and the most suitable solutions; iv) the guiding principles and standardized recommendations for the E-NRR are emphasized and future research directions and prospects are provided.

Iron-Doped MoO3 Nanosheets for Boosting Nitrogen Fixation to Ammonia at Ambient Conditions

Nitrogen can be electrochemically reduced to produce ammonia, which supplies an energy-saving and environmental-benign route at room temperature, but high-efficiency catalysts are sought to reduce the reaction barrier. Here, iron-doped α-MoO₃ nanosheets are thus designed and proposed as potential catalysts for fixing N₂ to NH₃. The α-MoO₃ band structure is intentionally modulated by the iron doping, which narrows the band gap of α-MoO₃ and turns the semiconductor into a metal-like catalyst. Oxygen vacancies, generated by substituting Mo⁶⁺ for Fe³⁺ anions, are beneficial for nitrogen adsorption at the active sites. In 0.1 M Na₂SO₄, the Fe-doped MoO₃ catalyst reached a high faradaic efficiency of 13.3% and an excellent NH₃ yield rate of 28.52 μg h^-1 mg_cat^-1 at -0.7 V versus reversible hydrogen electrode, superior to most of the other metal-based catalysts. Theoretical calculations confirmed that the N₂ reduction reaction at the Fe-MoO₃ surface followed the distal reaction path.

A peanut shell-derived economical and eco-friendly biochar catalyst for electrochemical ammonia synthesis under ambient conditions: combined experimental and theoretical study

The electrochemical conversion of N₂ to NH₃ under ambient conditions is a highly promising alternative to the energy-intensive Haber–Bosch process. As a catalyst for electrocatalytic N₂ synthesis of NH₃, biochar is a sustainable green material.

Exploration and Investigation of Periodic Elements for Electrocatalytic Nitrogen Reduction

High demand for green ecosystems has urged the human community to reconsider and revamp the traditional way of synthesis of several compounds. Ammonia (NH₃ ) is one such compound whose applications have been extended from fertilizers to explosives and is still being synthesized using the high energy inhaling Haber-Bosch process. Carbon free electrocatalytic nitrogen reduction reaction (NRR) is considered as a potential replacement for the Haber-Bosch method. However, it has few limitations such as low N₂ adsorption, selectivity (competitive HER reactions), low yield rate etc. Since it is at the early stage, tremendous efforts have been devoted in understanding the reaction mechanism and screening of the electrocatalysts and electrolytes. In this review, the electrocatalysts are classified based on the periodic table with heat maps of Faraday efficiency and yield rate of NH₃ in NRR and their electrocatalytic properties toward NRR are discussed. Also, the activity of each element is discussed and short tables and concise graphs are provided to enable the researchers to understand recent progress on each element. At the end, a perspective is provided on countering the current challenges in NRR. This review may act as handbook for basic NRR understandings, recent progress in NRR, and the design and development of advanced electrocatalysts and systems.

Structural evolution of CrN nanocube electrocatalysts during nitrogen reduction reaction

Metal nitrides have been suggested as prospective catalysts for the electrochemical nitrogen reduction reaction (NRR) in order to obtain ammonia at room temperature under ambient pressure. Herein, we report that templated chromium nitride porous microspheres built up by nanocubes (NCs) are an efficient noble-metal-free electrocatalyst for NRR. The CrN NCs catalyst exhibits both a high stability and NH3 yield of 31.11 μg h-1 mgcat.-1 with a Faradaic efficiency (FE) of 16.6% in 0.1 M HCl electrolyte. Complementary physical characterization techniques demonstrate partial oxidation of the pristine CrN NCs during reaction. Structural characterization by means of scanning transmission electron microscopy (STEM) combining electron energy loss spectrum (EELS) and energy dispersive X-ray spectroscopy (EDX) analysis reveals the NC structure to consist of an O-rich core and N-rich shell after NRR. This gradient distribution of nitrogen within the CrN NCs upon completed NRR is distinct to previously reported metal nitride NRR catalysts, because no significant loss of nitrogen occurs at the catalyst surface.

FeVO4 porous nanorods for electrochemical nitrogen reduction: contribution of the Fe2c-V2c dimer as a dual electron-donation center

The electrocatalytic N₂ reduction reaction (NRR) offers a sustainable route for ambient NH₃ production. To ensure a high NRR efficiency, it is critically important to design active electrocatalysts which possess a strong electron-donating capability to activate the stable N[triple bond, length as m-dash]N bond and facilitate the protonation process. Herein, inspired by the FeV-cofactor as a catalytic site for biological N₂ fixation, we show that the FeVO₄ can be a highly efficient and durable NRR catalyst. The developed FeVO₄ porous nanorods delivered a favorable combination of both high NH₃ production rate (52.8 μg h^-1 mg^-1) and high faradaic efficiency (15.7%), surpassing those of nearly all the previously reported Fe- and V-based catalysts. Theoretical computations revealed that the high NRR performance of FeVO₄ originated from the Fe_2c-V_2c dimer (2c means two-fold coordinated bond) as a dual electron-donation center to effectively activate the NRR with a low overpotential.

Flower-like Hollow MoSe2 Nanospheres as Efficient Earth-Abundant Electrocatalysts for Nitrogen Reduction Reaction under Ambient Conditions

Electrocatalytic nitrogen reduction reaction (NRR) is a green and sustainable strategy for artificial nitrogen fixation but remains a significant challenge because of the lack of high-performance electrocatalysts. In this study, flower-like hollow MoSe₂ nanospheres as efficient earth-abundant NRR electrocatalysts with a high faradaic efficiency of 14.2% and an ammonia yield of 11.2 μg h^-1 mg_cat.^-1 at ambient conditions were prepared. Such excellent NRR activity can be attributed to the higher specific surface area, more active sites, and longer N₂ retention time within the shells because of the design of the hollow structure. Density functional theory calculations were performed to further understand the catalytic mechanism involved. This work demonstrates the feasibility of transition-metal selenides as NRR electrocatalysts and suggests an electrocatalyst materials structure design for efficient electrochemical nitrogen fixation.

Bismuth-Based Free-Standing Electrodes for Ambient-Condition Ammonia Production in Neutral Media

Electrocatalytic nitrogen reduction reaction is a carbon-free and energy-saving strategy for efficient synthesis of ammonia under ambient conditions. Here, we report the synthesis of nanosized Bi2O3 particles grown on functionalized exfoliated graphene (Bi2O3/FEG) via a facile electrochemical deposition method. The obtained free-standing Bi2O3/FEG achieves a high Faradaic efficiency of 11.2% and a large NH3 yield of 4.21 ± 0.14 [Formula: see text] h-1 cm-2 at - 0.5 V versus reversible hydrogen electrode in 0.1 M Na2SO4, better than that in the strong acidic and basic media. Benefiting from its strong interaction of Bi 6p band with the N 2p orbitals, binder-free characteristic, and facile electron transfer, Bi2O3/FEG achieves superior catalytic performance and excellent long-term stability as compared with most of the previous reported catalysts. This study is significant to design low-cost, high-efficient Bi-based electrocatalysts for electrochemical ammonia synthesis.

Ambient electrochemical NH3 synthesis from N2 and water enabled by ZrO2 nanoparticles

ZrO₂ nanoparticles act as an efficient electrocatalyst for ambient N₂-to-NH₃ fixation. In 0.1 M HCl, it attains a large NH₃ yield rate of 24.74 μg h⁻¹ mg_cat.⁻¹ with a faradaic efficiency of 5.0% at −0.45 V vs. RHE.

A Janus antimony sulfide catalyst for highly selective N2 electroreduction

Sb₂S₃ delivered an excellent NRR faradaic efficiency of 24.1% at −0.3 V, attributed to the Janus role of active Sb centers that contributed to the boosted NRR and the suppressed HER.

P-Doped graphene toward enhanced electrocatalytic N2 reduction

P doping greatly improves electrochemical N₂ reduction over graphene. In 0.5 M LiClO₄, P-doped graphene attains a high Faradic efficiency of 20.82% and a large NH₃ yield of 32.33 μg h⁻¹ mg_cat.⁻¹ at −0.65 V vs. RHE.

Bimetallic MnMoO4 with dual-active-centers for highly efficient electrochemical N2 fixation

MnMoO₄/RGO exhibited a combination of high NH₃ yield (60.3 μg h⁻¹ mg⁻¹) and high faradaic efficiency (14.7%), attributed to the surface-terminated Mn and Mo atoms as dual-active-centers to synergistically promote the NRR and suppress the HER.

ZrB2 as an earth-abundant metal diboride catalyst for electroreduction of dinitrogen to ammonia

ZrB₂ nanocubes show a high NH₃ production rate (37.7 μg h⁻¹ mg⁻¹) and Faradaic efficiency (18.2%), attributed to a unique tetranuclear N₂ adsorption side-on mode for ZrB₂ that could strongly activate N₂ and lower the reaction energy barrier.