Electrocatalytic Synthesis Of Ammonia Research Articles

Sulfur‐Vacancy Defective MoS2 as a Promising Electrocatalyst for Nitrogen Reduction Reaction under Mild Conditions

AbstractDeveloping low‐cost and efficient nanomaterials to transform nitrogen to ammonia under mild conditions is an attractive topic in chemistry and is significant for sustaining agriculture and life. In this work, the catalytic performance of three types of MoS2 electrocatalysts is systematically investigated. The density of states shows noticeable improvement in the electrical conductivity for sulfur‐vacancy defective MoS2 (VS‐MoS2) than that of pure MoS2, as it facilitates the following electrocatalytic nitrogen reduction reaction (NRR). VS‐MoS2 possesses excellent NRR catalytic performance with a limiting potential of −0.48 V, an outstanding NH3 average yield of 29.55 μg h−1 mgcat.−1 at −0.5 V versus reversible hydrogen electrode (RHE), and a high faraday efficiency of 4.58 % at −0.3 V vs RHE. The hydrogenation of *N‐NH to *NH‐NH is the rate determining step of the enzymatic mechanism. These results demonstrate the feasibility of VS‐MoS2 for electrocatalytic ammonia synthesis.

Sustainable nitrogen fixation over Ru single atoms decorated Cu2O using electrons produced from photoelectrocatalytic organics degradation

Electrocatalytic ammonia (NH3) synthesis requires electrons, usually from the oxygen evolution reaction (OER) conducted on the dark anode. To meet the thermodynamic potential of the OER and smoothly transfer charge, a high bias voltage is often required, which, however, increases energy consumption. Here, we demonstrate that using photoanode instead of dark anode can remarkably reduce the energy required. Electrons for NH3 synthesis originally provided via OER are replaced by photoelectrons, and the power input for driving charge transfer can be partially or even eliminated completely depending on the Fermi level of photoanode. In view of this, we substituted the OER with photoelectrocatalytic bisphenol A degradation (~99.6%) and achieved abundant electrons supply for NH3 synthesis over Ru single atoms embedded Cu2O (yield: ~37.4 μg h−1 mg−1cat., FE: ~17.1%) at low voltage. Compared with the individual NH3 synthesis, the integrated system reduces energy consumption by ~ 51.8%. Life cycle assessment shows that this system is more sustainable and economically viable.

Regulating nitrogenous adsorption and desorption on Pd clusters by the acetylene linkages of hydrogen substituted graphdiyne for efficient electrocatalytic ammonia synthesis

Precious metal Pd has the intrinsic superiority in adsorbing N2 molecule and wrecking the high cleavage barrier of the N≡N bond, however, its over-strong adsorption ability is unfavorable to the desorption of the produced NH3 during the electrochemical N2 reduction (NRR), which weighs heavily against the NH3 productivity. Here we demonstrate that the high electron-density of acetylene linkages of hydrogen substituted graphdiyne can regulate the nitrogen adsorption and NH3 desorption on the active Pd sites (Pd/HsGDY), resulting in impressive electrocatalytic NRR performance. The optimized Pd/HsGDY features an ultrahigh Faraday efficiency of 44.45% and an NH3 yield of 115.93 mg g−1 h−1 (or 11.59 µg cm−2 h−1). Density functional theory calculations reveal that the acetylene linkages in HsGDY can tune the d band center of active Pd atoms by downward shifting it from the Fermi level. This favors the hydrogenation of nitrogen on HsGDY-tuned Pd sites and benefits the desorption of produced NH3 from the catalyst surface to recover active sites induced by heat dissipation during the exothermic hydrogenation processes, resulting in a selectively facilitated electrosynthesis of NH3.

Precise synthesis of Fe–N2 with N vacancies coordination for boosting electrochemical artificial N2 fixation

The construction of definitive correlation between structure and catalytic properties for electrochemical artificial N2 fixation is still challenging yet significative. Herein, we have explored the coordinative unsaturation (Fe-N2) in isolated Fe atoms with nitrogen vacancies (VN, which are located at the opposite coordination sites of the Fe atom) on interconnected carbon for electrocatalytic ammonia synthesis. Benefiting from dual active centers (Fe-N2 and VN) and the spin density on both of them, the novel catalyst exhibits a synergistic improvement of catalytic activity, selectivity, and stability. This work guides the design of the catalyst theoretically and synergistically and combines the advantages of Fe-N2 with VN structure creation, defect and spin-state engineering introduction toward the concurrent fulfillment of effective N2 adsorption and activation. We believe our strategy will incite more investigation into designing high-performance catalysts with well-defined coordinative unsaturation single-atom active sites for ambient ammonia synthesis and other energy conversion system.

High-Throughput Screening of a Single-Atom Alloy for Electroreduction of Dinitrogen to Ammonia.

Exploring electrocatalysts with high activity, selectivity, and stability is essential for the development of applicable electrocatalytic ammonia synthesis technology. By performing density functional theory calculations, we systematically investigated the potential of a series of transition-metal-doped Au-based single-atom alloys (SAAs) as promising electrocatalysts for nitrogen reduction reaction (NRR). The overall process for the Au-based electrocatalyst suffers from the limiting potential arising from the first hydrogenation step of the reduction of *N2 to *NNH. However, SAAs showed to be favorable toward lowering free energy barriers by increasing the binding strength of N2. According to simulation results, three descriptors were proposed to describe the first hydrogenation step ΔG(*N2 → *NNH): ΔG(*NNH), d-band center, and d/√Em. Eight doped elements (Ti, V, Nb, Ru, Ta, Os, W, and Mo) were initially screened out with a limiting potential ranging from -0.75 to -0.30 V. Particularly, Mo- and W-doped systems possess the best activity with a limiting potential of -0.30 V each. Then, the intrinsic relationship between the structure and potential performance was analyzed using machine learning. The selectivity, feasibility, and stability of these candidates were also evaluated, confirming that SAA containing Mo, Ru, Ta, and W could be outstanding NRR electrocatalysts. This work not only broadens our understanding of SAA application in electrocatalysis, but also leads to the discovery of novel NRR electrocatalysts.

Anionic Biopolymer Assisted Preparation of MoO2@C Heterostructure Nanoparticles with Oxygen Vacancies for Ambient Electrocatalytic Ammonia Synthesis.

Recently, Mo-based metal catalysts are widely applied in the electrocatalytic nitrogen reduction reaction (NRR) due to the lower binding energy between the Mo atom and N atom. The design of a Mo-based catalyst@carbon heterostructure and the introduction of anion vacancies are effective measures to improve their NRR performance. In this research, the cross-linked Vo-MoO2@C (Vo means oxygen vacancies) heterostructure nanoparticles with rich oxygen vacancies are first synthesized via pectin assisted hydrothermal reaction followed by calcination and treating with NaBH4 solution. Vo-MoO2@C exhibits good electrocatalytic NRR performance with an ammonia yield rate of 9.75 μg h-1 mg-1 at -0.5 V (RHE) and a Faraday efficiency (FE) of 3.24% at -0.3 V (RHE) under ambient conditions.

Scalable Production of Cobalt Phthalocyanine Nanotubes: Efficient and Robust Hollow Electrocatalyst for Ammonia Synthesis at Room Temperature.

Electrocatalytic ammonia (NH3) synthesis through the nitrogen reduction reaction (NRR) under ambient conditions presents a promising alternative to the famous century-old Haber-Bosch process. Designing and developing a high-performance electrocatalyst is a compelling necessity for electrochemical NRR. Specific transition metal based nanostructured catalysts are potential candidates for this purpose owing to their attributes such as higher actives sites, specificity as well as selectivity and electron transfer, etc. However, due to the lack of a well-organized morphology, lower activity, selectivity, and stability of the electrocatalysts make them ineffective at producing a high NH3 yield rate and Faradaic efficiency (FE) for further development. In this work, stable β-cobalt phthalocyanine (CoPc) nanotubes (NTs) have been synthesized by a scalable solvothermal method for electrochemical NRR. The chemically synthesized CoPc NTs show excellent electrochemical NRR due to high specific area, greater number of exposed active sites, and specific selectivity of the catalyst. As a result, CoPc NTs produced a higher NH3 yield of 107.9 μg h-1 mg-1cat and FE of 27.7% in 0.1 M HCl at -0.3 V vs RHE. The density functional theory calculations confirm that the Co center in CoPc is the main active site responsible for electrochemical NRR. This work demonstrates the development of hollow nanostructured electrocatalysts in large scale for N2 fixation to NH3.

One-step electrocatalytic synthesis of ammonia and acetone from nitrogen and isopropanol in an ionic liquid

Using a prepared ionic liquid with high N2 solubility as the electrolyte and isopropanol as the proton source, we achieved the one-step electrocatalytic synthesis of ammonia and acetone with considerable ammonia yield and high faradaic efficiency.

Electrocatalytic Activity of Lanthanum Chromite-Based Composite Cathode for Ammonia Synthesis from Water and Nitrogen

The electrocatalytic ammonia synthesis using water (along with nitrogen) as a hydrogen source is proposed as an alternative green and clean technology to the energy-intensive and CO2-emitting process (Haber-Bosch) for ammonia production. Besides, a selective electrocatalyst for ammonia synthesis versus the competing hydrogen evolution remains elusive. This study aims to investigate the electrocatalytic activity of non-noble metal Co and Fe-free perovskite oxide-based composite cathode (La0.75Sr0.25Cr0.5Mn0.5O3-δ-Ce0.8Gd0.18Ca0.02O2-δ) towards ammonia synthesis from H2O and N2. The electrocatalyst was synthesized via a sol-gel process and characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Ammonia was successfully with a maximum formation rate of 2.5 × 10-10mol s-1cm-2and Faradaic efficiency of 0.52% at 400 oC and applied voltage of 1.4 V. The results demonstrated that the proposed non-noble metal-based electrocatalyst is a promising material for the carbon-free ammonia synthesis process.

Recent Progress on Electrocatalytic Synthesis of Ammonia Under Amibent Conditions

Recent Progress on Electrocatalytic Synthesis of Ammonia Under Amibent Conditions

Electrocatalytic Synthesis of Ammonia Using a 2D Ti3 C2 MXene Loaded with Copper Nanoparticles.

As an energy-saving and environmentally friendly ammonia synthesis method, electrocatalytic nitrogen reduction reaction (NRR) has received a great deal of attention. There is thus an urgent need to find high-efficiency electrocatalysts for the NRR. In this work, a Cu/Ti3 C2 composite catalyst was prepared and demonstrated excellent selectivity under environmental conditions, which could efficiently convert N2 into NH3 electrochemically. In 0.1 M KOH, Cu/Ti3 C2 can achieve a high Faradaic efficiency of 7.31 % and a high NH3 production rate of 3.04 μmol h-1 cm-2 at -0.5 V vs. RHE. Moreover, the material also exhibits superior electrochemical stability and durability. At the same time, density functional theory (DFT) shows that, compared with Ti3 C2 , Cu/Ti3 C2 exhibits a wider conduction and valence band and a larger Fermi level, thus indicating that Cu plays a vital role in the enhancement of the catalytic activity and conductivity of Ti3 C2 -based materials. This work provides a feasible strategy for designing high-efficiency MXene-based NRR electrocatalysts.

Recent Advances in the Application of Structural‐Phase Engineering Strategies in Electrochemical Nitrogen Reduction Reaction

AbstractAmmonia (NH3) exists as an important chemical raw material in the chemical industry and national economy of all countries in the world. The widely used Haber–Bosch ammonia synthesis process not only requires a large amount of highly purified hydrogen, but also is inseparable from high‐temperature and high‐pressure reaction conditions, resulting in numerous problems that cannot be fundamentally solved in terms of safety, efficiency, cost, etc. It is considered to be an alternative technology with great potential to achieve the synthesis of ammonia under normal temperature and pressure making use of electrochemical nitrogen reduction reaction (NRR), which utilizes water in aqueous solution systems in replacement of hydrogen as hydrogen source. This paper succinctly explains the basic mechanism for electrocatalytic ammonia synthesis from the reduction of nitrogen in aqueous solution systems. Based on the research progress in the past year, the principles and related researches of constructing electrocatalysts of NRR using five structural‐phase strategies including defect engineering, interface engineering, strain engineering, atomic ordering engineering, and single‐atom engineering are reviewed. Finally, this paper provides an outlook to the future research and application.

Theory-guided construction of electron-deficient sites via removal of lattice oxygen for the boosted electrocatalytic synthesis of ammonia

Rational design of catalytic sites to activate the inert N≡N bond is of paramount importance to advance N2 electroreduction. Here, guided by the theoretical predictions, we construct a NiFe layered double hydroxide (NiFe-LDH) nanosheet catalyst with a high density of electron-deficient sites, which were achieved by introducing oxygen vacancies in NiFe-LDH. Density functional theory calculations indicate that the electron-deficient sites show a much lower energy barrier (0.76 eV) for the potential determining step compared with that of the pristine NiFe-LDH (2.02 eV). Benefiting from this, the NiFe-LDH with oxygen vacancies exhibits the greatly improved electrocatalytic activity, presenting a high NH3 yield rate of 19.44 µg·h−1·mgcat−1, Faradaic efficiency of 19.41% at −0.20 V vs. reversible hydrogen electrode (RHE) in 0.1 M KOH electrolyte, as well as the outstanding stability. The present work not only provides an active electrocatalyst toward N2 reduction but also offers a facile strategy to boost the N2 reduction.

Molybdenum and boron synergistically boosting efficient electrochemical nitrogen fixation

Ammonia production consumes ~2% of the annual worldwide energy supply, therefore strategic alternatives for the energy-intensive ammonia synthesis through the Haber-Bosch process are of great importance to reduce our carbon footprint. Inspired by MoFe-nitrogenase and the energy-efficient and industrially feasible electrocatalytic synthesis of ammonia, we herein establish a catalytic electrode for artificial nitrogen fixation, featuring a carbon fiber cloth fully grafted by boron-doped molybdenum disulfide ( B-MoS 2 /CFC) nanosheets. An excellent ammonia production rate of 44.09 μg h –1 cm –2 is obtained at −0.2 V versus the reversible hydrogen electrode (RHE), whilst maintaining one of the best reported Faradaic efficiency (FE) of 21.72% in acidic aqueous electrolyte (0.1 M HCl). Further applying a more negative potential of −0.25 V renders the best ammonia production rate of 50.51 μg h –1 cm –2 . A strong-weak electron polarization (SWEP) pair from the different electron accepting and back-donating capacities of boron and molybdenum (2 p shell for boron and 5 d shell for molybdenum) is proposed to facilitate greatly the adsorption of non-polar dinitrogen gas via N ≡ N bond polarization and the first protonation with large driving force. In addition, for the first time a visible light driven photo-electrochemical (PEC) cell for overall production of ammonia, hydrogen and oxygen from water + nitrogen, is demonstrated by coupling a bismuth vanadate BiVO 4 photo-anode with the B-MoS 2 /CFC catalytic cathode. A catalytic electrode B-MoS 2 /CFC is established for artificial nitrogen fixation, displaying the excellent ammonia production rate of 44.09 μg h –1 cm –2 and Faradaic efficiency of 21.72% in acidic aqueous electrolyte at −0.2 V. A supposed strong-weak electron polarization pair is inferred from the different electron accepting and back-donating capacities of boron and molybdenum (2 p shell for boron and 5 d shell for molybdenum), which may facilitate the adsorption of nonpolar dinitrogen and its first protonation greatly. • A carbon fiber cloth fully grafted by boron-doped molybdenum disulfide ( B-MoS 2 /CFC) nanosheets was prepared. • An excellent ammonia production rate of 44.09 μg h –1 cm –2 was obtained in 0.1 M HCl. • A strong-weak electron polarization pair of 2 p shell for B and 5 d shell for Mo was proposed to facilitate the N ≡ N bond polarization. • A visible light driven photo-electrochemical cell for overall production of NH 3 , H 2 and O 2 from H 2 O + N 2 , was demonstrated.

Efficient Ambient Electrocatalytic Ammonia Synthesis by Nanogold Triggered via Boron Clusters Combined with Carbon Nanotubes.

Currently, the development of stable electrochemical nitrogen reduction reaction (ENRR) catalysts with high N2 conversion activity and low cost to instead of the traditional Haber-Bosch ammonia production process of high-energy consumption remains a great challenge for researchers. Here, we have immobilized reductive closo-[B12H11]- boron clusters on a carbon nanotubes (CNT) surface and have successfully prepared a novel Au-CNT catalyst with extraordinary ENRR activity after adding HAuCl4 to the CNT-[B12H11]- precursor. The excellent properties of ammonia yield (57.7 μg h-1 cm-2) and Faradaic efficiency (11.97%) make it possible to achieve using this Au-CNT catalyst in large-scale industrial production of ammonia. Furthermore, its outstanding cyclic stability and long-term tolerability performance make it one of the most cost-effective catalysts to date. Here, by means of density functional theory we disclose the associative mechanism of N2-to-NH3 conversion on the Au(111) surface, providing visual theoretical support for the experimental results.

Considering Electrocatalytic Ammonia Synthesis via Bimetallic Dinitrogen Cleavage

Despite advances in the development of molecular catalysts capable of reducing dinitrogen to ammonia using proton donors and chemical reductants, few molecular electrocatalysts have been discovered. This Perspective considers the prospects of electrocatalyst development based on a mechanism featuring the cleavage of N2 into metal nitride complexes. By understanding the factors that control the reactivity of individual steps along the electrochemical N2 cleavage path, opportunities for new advances are identified. Ligand design principles for facile electrochemical N2 binding, formation of bridging N2 complexes, thermal or photochemical N2 cleavage, and conversion of a nitride ligand into ammonia are described, featuring recent advances and the authors’ collaborative work on rhenium complexes.

Boosting Electrocatalytic Nitrogen Fixation with Co–N3 Site-Decorated Porous Carbon

Electrocatalytic ammonia (NH3) synthesis under ambient temperature and pressure is an emerging sustainable method for dinitrogen (N2) fixation, providing a potential environmentally benign pathway ...

Current Progress of Electrocatalysts for Ammonia Synthesis Through Electrochemical Nitrogen Reduction Under Ambient Conditions.

Ammonia, one of the most important chemicals and carbon-free energy carriers, is mainly produced by the traditional Haber-Bosch process operated at high pressure and temperature, which results in massive energy consumption and CO2 emissions. Alternatively, the electrocatalytic nitrogen reduction reaction to synthesize NH3 under ambient conditions using renewable energy has recently attracted significant attention. However, the competing hydrogen evolution reaction (HER) significantly reduces the faradaic efficiency and NH3 production rate. The design of high-performance electrocatalysts with the suppression of the HER for N2 reduction to NH3 under ambient conditions is a crucial consideration for the development of electrocatalytic NH3 synthesis with high FE and NH3 production rate. Five kinds of recently developed electrocatalysts classified by their chemical compositions are summarized, with particular emphasis on the relationship between their optimal electrocatalytic conditions and NH3 production performance. Conclusions and perspectives are provided for the future design of high-performance electrocatalysts for electrocatalytic NH3 production. The Review can give practical guidance for the design of effective electrocatalysts with high FE and NH3 production rates.

Recent Advances in Noble-Metal-Free Catalysts for Electrocatalytic Synthesis of Ammonia under Ambient Conditions.

Ammonia is an essential chemical for producing fertilizers and energy carriers. However, the industrial Haber-Bosch process causes huge CO2 emissions and energy waste. As a promising alternative for Haber-Bosch process, electrochemical synthesis of ammonia has drawn much attention. Catalysts, as a vital part of electrochemical nitrogen reduction reaction (NRR), have developed rapidly in recent years. Compared to noble-metal catalysts, noble-metal-free catalysts possess a low-cost advantage. In this review, noble-metal-free catalysts, including metal-based materials, metal organic frameworks (MOFs), MXenes, and metal-free materials, are summarized. In addition, effective design strategies are discussed, along with the main problems and some potential directions of noble-metal-free NRR catalysts.

Accelerated Dinitrogen Electroreduction to Ammonia via Interfacial Polarization Triggered by Single-Atom Protrusions

Summary Electrocatalytic N2 reduction reaction (NRR) offers a promising low-energy, sustainable ammonia-synthesizing alternative to Haber-Bosch reaction. One roadblock lying in access to high-performance ammonia electrosynthesis emanates from the unsatisfied ability of electrocatalysts to wreck N≡N bond. Here, we report that interfacial polarization is an efficient scenario to enhance N≡N fracture to boost electrocatalytic ammonia synthesis. As a proof-of-concept demonstration, protrusion-shaped Fe single-atom catalysts immobilized onto MoS2 nanosheets engender electric fields to polarize N2. The resultant interfacial polarization fields between Fe-MoS2 and N2 drive the injection of more electrons into N2 antibonding orbitals in a fast manner, leading to a superior ammonia-evolving rate (36.1 ± 3.6 mmol g−1 h−1 or 97.5 ± 6 μg h−1 cm−2) at low applied potential. Similar phenomena are applicable in Co-MoS2, Cu-MoS2, Rh-MoS2, or Ru-MoS2, suggesting the potential universality of our interfacial polarization concept in upgrading wide-scope catalysis.