Haber-Bosch Research Articles

The Development, Essence and Perspective of Nitrogen Reduction to Ammonia.

Ammonia plays a pivotal role in agriculture and meanwhile holds promising potential as an energy vector for the hydrogen economy, where the nitrogen reduction to ammonia is a critical pathway for achieving sustainable development. Over the past hundred years, ammonia synthesis has undergone several breakthrough developments from Haber-Bosch process to photo/electro-catalysis and Li-mediated strategy, but still faces the challenges of low yield rate, selectivity and efficiency. Therefore, there is a pressing demand to develop efficient and green ammonia synthesis from nitrogen. This review summarizes the development of the nitrogen reduction to ammonia, highlighting six milestones during the whole journey. From the development direction, this work finds and extracts the essence of ammonia synthesis, that is the reaction pathways are affected by the energy barrier of reaction intermediates, which can be altered by proton sources, auxiliaries and catalysts. Then this work discusses the detailed overview of the significant development of proton source, auxiliaries and catalysts. Finally, based on the essence, the possible opportunities of ammonia synthesis from nitrogen reduction are presented, including the design of new ammonia synthesis pathways and efficient catalysts. The deep insight of nitrogen reduction to ammonia will provide a design guidance for efficient ammonia synthesis.

Magnetically Propelled Microrobots toward Photosynthesis of Green Ammonia from Nitrates.

Ammonia (NH₃) production is a critical industrial process, as ammonia is a key component in fertilizers, essential for global agriculture and food production. However, the current method of synthesizing ammonia, the Haber-Bosch process, is highly energy-intensive, and relies on fossil fuels, contributing substantially to greenhouse gas emissions. Moreover, the centralized nature of the Haber-Bosch process limits its accessibility in remote or resource-limited areas. Photochemical synthesis of ammonia, provides an alternate lower energy, carbon-free pathway compared to the prevailing industrial methods. The photoconversion of nitrate anions, often present in wastewater, offers a greener, more sustainable, and energy-efficient route for both ammonia-generation and wastewater treatment. Photochemical and chemical synthesis of ammonia requires intensive mass-transfer processes, which limits the efficiency of the method. To change the game, in this work, a key new technology of ammonia-generation, a catalytic ammonia generation (AmmoGen) microrobot, which converts nitrate to ammonia using renewable light energy is reported. The magnetic propulsion of the AmmoGen microrobots significantly enhances mass-transfer, and expedites the photosynthesis of ammonia. Overall, this "proof-of-concept" study demonstrates that microrobots can aid in catalytic small molecule activation and generation of value-added products; and are envisaged to pave the way toward new sustainable technologies for catalysis.

Expanded scope of chitin-derived nitrogen scaffolds enabled by the 3-acetamido-5-furfurylaldehyde (3A5F) platform

The chitin-derived platform 3-acetamido-5-furfurylaldehyde (3A5F) undergoes organocatalyzed oxidative esterification with various alcohols to produce 4-acetamidofuran-2-carboxylates, enabling streamlined access to this previously unexplored chemical space. The reaction proceeds under mild conditions, using an affordable thiazolium catalyst, molecular oxygen as the oxidant, and ethyl acetate as the solvent (if necessary). Additionally, 3A5F facilitates access to a 3-acetamidobutenolide and 5-vinylfuran-3-acetamide, valuable biogenic platforms with a broad range of potential applications. All the products contain biogenic nitrogen and have been synthesized without using building blocks derived from ammonia produced via the energy-intensive Haber process.

Interfacial Engineering of MoxSy via Boron-Doping for Electrochemical N2-to-NH3 Conversion.

The electrocatalytic synthesis of ammonia (NH3) through the nitrogen reduction reaction (NRR) under ambient temperature and pressure is emerging as an alternative approach to the conventional Haber-Bosch process. However, it remains a significant challenge due to poor kinetics, low nitrogen (N2) solubility in aqueous electrolytes, and the competing hydrogen evolution reaction (HER), which can significantly impact NH3 production rates and Faradaic efficiency (FE). Herein, a rationally designed boron-doped molybdenum sulfide (B-Mo-MoxSy) electrocatalyst is reported that effectively enhances N2 reduction to NH3 with an onset potential of -0.15V versus RHE, achieving a FE of 78% and an NH3 yield of 5.83µg h⁻¹ cm⁻2 in a 0.05m H2SO4(aq). Theoretical studies suggest that the effectiveness of NRR originates from electron density redistribution due to boron (B) doping, which provides an ideal pathway for nitrogenous species to bind with electron-deficient B sites. This work demonstrates a significant exploration, showing that Mo-based electrocatalysts are capable of facilitating artificial N2 fixation.

Two-Dimensional Bi2Se3 Nanosheets Synthesis for Efficient Electrocatalytic Production of Ammonia from Nitrate

Ammonia (NH3), a critical component for various industries, is produced through the Haber-Bosch process, which, despite its importance, is a significant source of carbon emissions and operates on a centralized model, emphasizing the need for innovative solutions to decarbonize and decentralize its production. Electrochemical nitrate (NO3–) reduction to NH3 presents a promising alternative to the Haber-Bosch process for NH3 synthesis, with the added advantage of transforming waste into a valuable resource while mitigating water pollution concerns. However, achieving a well-defined active center and catalytic selectivity in the electrochemically driven reaction remains a significant challenge. In this study, we successfully fabricated a highly selective and active 2D Bi2Se3 catalyst, which demonstrated better performance in reducing NO3– to NH3 with a Faradaic efficiency (FE) of approximately 80% (−0.3V (RHE)) and a significant yield rate of 45mgh−1mgcat−1 (0.46 mmolh−1cm−2). Furthermore, the fabricated material exhibited exceptional stability and durability, maintaining a high NO3– reduction of 80% FE even after 10 consecutive cycles of extended use and continuous operation, demonstrating its remarkable resilience and reliability. Our findings show that the prepared catalyst selectively promotes the electrochemical reduction of NO3– to NH3 while suppressing the competing hydrogen evolution reaction (HER). The charge density profile indicates a pronounced charge localization around the Se atoms, implying that the Se active sites in the 2D Bi2Se3 catalyst act as the active center for the NO3– reduction mechanism, playing a crucial role in facilitating the reaction kinetics.

Designing V Single Atom Embedded Carbon Moiety for the Electrocatalytic Nitrogen Reduction Reaction by First Principles Study.

Development of an efficient electrocatalyst for the nitrogen reduction reaction (NRR) to serve as a sustainable alternative to the Haber-Bosch process has proven highly challenging. Single atom catalysts (SACs), which have the maximum atom utilization efficiency, are among the most promising candidates. Single atoms can be incorporated to a catalytic system by doping or substitution or by attaching a molecular coordination complex to a substrate and the different insertion modes allow the chemical environment to be varied. We have used DFT to investigate vanadium SACS for NRR activity with a focus on varying the coordination environment of the V atom. Phthalocyanine, porphyrin and graphene like coordination environments with varying N-coordination have been studied. Vanadium phthalocyanine (VphN4) is the most promising of the investigated systems. It features high selectivity relative the HER reaction and relatively strong binding of N2 relatively H, which prevents poisoning of the surface by hydrogen. VphN4 also has the lowest overpotential among the studied systems. The electrocatalytic properties of VphN4 deposited as a monolayer on the Ag (111) surface have been investigated. This system, which already has been prepared, shows promising properties for use as a catalytic electrode for the NRR reaction.

Preventing Nitrite Desorption via Switching Hydrogenation Position: A Dual-Site Approach for Selective Nitrate Reduction to Ammonia.

The electrochemical nitrate reduction reaction (NO3RR), which converts harmful nitrates into valuable ammonia (NH3) with zero carbon emission, is one of the most promising alternatives to the Haber-Bosch process. However, the NO3RR process is complex and involves multiple proton-coupled electron transfers that generate intermediates or byproducts, such as NO2 -, resulting in low ammonia yields and faradaic efficiency (FE). Herein, by constructing a FeCu bimetallic catalyst (FeCu-NC), the hydrogenation position of *NO3 is switched at the FeCu dual-atom site, preventing the desorption of *NO2 intermediate. Furthermore, electron transfer from Cu to Fe sites mimics the electron flow direction in natural nitrite reductase enzymes and accelerates the reduction of *NO2 to NH3, achieving efficient conversion of NO3 - to NH3. A 24-hour electrocatalytic experiment with FeCu-NC demonstrates negligible NO2 - formation throughout the NO3RR process, with an ammonia production rate of 6.13mgh-1mgcat -1 and an impressive FE of 95%, which are remarkably superior in comparison to most of the NO3RR electrocatalysts. This work opens new avenues for the fundamental understanding of catalytic mechanisms and the development of next-generation catalysts for sustainable ammonia production.

Au-Added CuS Hollow Spheres to Regulate the Strength and Active Area of N2 Adsorption Sites for Electrochemical NH3 Production.

Ammonia is a chemical compound in considerable global demand and plays a crucial role as an environmentally friendly energy carrier for hydrogen energy storage. The electrochemical nitrogen reduction reaction (eNRR) using copper sulfide catalysts is being extensively studied as an environmentally sustainable approach to the energy-intensive Haber-Bosch process for ammonia production. In this study, we aimed to prepare CuS hollow spheres modified with Au nanoparticles using an antisolvent crystallization-based method to be used as the catalysts for eNRR. During the addition of Au to the CuS catalysts, the nitrogen adsorption strength and surface area of the CuS catalysts are significantly regulated and expanded, leading to a noticeable enhancement in electrocatalytic performance for eNRR. Specifically, the ammonia production rate of 2.4 μmol cm-2 h or jNH3 = 0.2 mA cm-2 is achieved at a selectivity of 52% in neutral aqueous electrolyte, which is more than a 2-fold increase compared to the unmodified CuS catalyst. The findings of this study can contribute to the development of sustainable and environmentally friendly ammonia production in the future.

Modulating Nitrogen Adsorption Mode and Microenvironment of Active Sites for Boosting Electrochemical Nitrogen Reduction.

Electrochemical reduction of N2(NRR) offers a sustainable approach for ammonia (NH3) synthesis, serving as a complementary to the traditional emission- and energy-intensive Haber-Bosch process. However, it faces challenges in N2 activation and competing with pronounced hydrogen evolution reaction (HER). Herein an efficient electrocatalyst comprised of ultrafine Ru nanoclusters (NCs) confined by a hydrophobic molecular layer is developed on the surface of 2D Ti3C2Tx for NRR. These experimental and theoretical calculation results demonstrate that 1) ultrafine Ru NCs dispersed on the Ti3C2Tx surface form paired active sites for N2 chemisorption in a unique tilted configuration with low-energy activation 2) the hydrophobic molecular layer modulates the local microenvironment surrounding catalytically active sites, enabling efficient N2 accumulation while repelling H2O diffusion to the active sites on the Ti3C2Tx surface, thereby leading to an increased N2 concentration and suppressed HER. As a result, an exceptionally high NH3 yield rate of 33.5µg h-1mg-1cat and Faradaic efficiency of 65.3% are obtained at -0.25V versus reversible hydrogen electrode (RHE) in 0.1m Na2SO4, outperforming those previously reported Ti3C2Tx-derived electrocatalysts. This work provides a valuable strategy for the rational design of advanced electrocatalysts by manipulating active sites and local microenvironments for efficient electrocatalysis.

Promoted Two-Step Ammonia Synthesis with CoOOH/Co foam at Ampere-Level Current Density and Nearly 100% Faraday Efficiency from Air and Water.

Ammonia (NH3) is regarded as an essential hydrogen storage material in the new energy field, and plasma-electrocatalytic synthesis of NH3 (PESA) is an alternative to the traditional Haber-Bosch process. Here, a bifunctional catalyst CoOOH/CF is proposed to enhance the PESA process. Benefiting from the efficient activation of O2 by CoOOH/CF, NOx - yield rate can reach the highest value of 171.90mmol h-1 to date. Additionally, CoOOH holds a more negative d-band center, thereby exhibiting weaker adsorption toward NO*, lowering the energy barrier for the rate determining step, resulting in a high NH3 yield rate (302.55mg h-1 cm-2 at -0.8V) with ampere-level NH3 current density (2.86 A cm-2 at -0.8V) and nearly 100% Faraday efficiency (FE, 99.8% at -0.6V). Moreover, CoOOH/CF achieves an excellent 4.54g h-1 NH3 yield rate with 97.9% FE in an enlarged electrolyzer, demonstrating the feasibility of PESA on a large scale.

Comparative life cycle assessment of carbon-free ammonia as fuel for power generation based on the perspective of supply chains

In recent years, there has been a surge in ammonia demand due to growing interest in carbon-free fuel for decarbonization. Thus, it is crucial to identify the methods to fulfill the required demand, particularly for countries with resource scarcity or lacking well-established production infrastructure. The present study compares environmental impact analysis between domestic ammonia production and import ammonia for these countries by using life cycle assessment (LCA) methodology. In these ammonia supply paths, five different production ways were applied: gray (conventional Haber-Bosch process), blue (with carbon capture and storage), green (wind, solar, and nuclear powered water electrolysis with Haber-Bosch process). The assessment showed highest global warming potential (GWP) value at 2.64 ton CO2-eq/ton NH3 for imported gray while domestic nuclear-driven ammonia had the lowest value at 0.81 ton CO2-eq/ton NH3. In addition, contrary to expectations, the human and environment impact of green ammonias were all higher than gray and blue ammonia due to the production of raw materials. This means that environmental improvements of related production process are crucial in preparation for the coming new energy regime, which then lead to the production of environmentally friendly ammonia. Lastly, these results offer valuable guideline for future energy strategy planning.

MULTI-LAYER KESTERITE-BASED PHOTOCATHODES FOR NH3 PHOTOSYNTHESIS FROM N2 REDUCTION REACTION.

The necessity of new methods to substitute the Haber-Bosch process in the NH3 synthesis, generating fewer greenhouse gases, and dispensing less energy, drove the investigation of the photoelectrocatalytic approach in the N2 reduction reaction (N2RR). For that, this work presents the synthesis and characterization of the layered CZTSSe/CdS/TiO2 photocathode decorated with Pt nanoparticles for application in NH3 production using the photoelectrocatalysis technique. The CZTSSe/CdS/TiO2-Pt characterization showed a well-designed and stable photocatalyst synthesized layer by layer with an important contribution of the Pt nanoparticles for the catalyst performance, improving the photocurrent density and the charge transfer. The N2RR in a two-compartment photochemical cell with 0.1 mol L-1 Na2SO3 and 0.05 mol L-1 H2SO4 in the cathodic and anodic chamber, respectively, using CZTSSe/CdS/TiO2-Pt and under 1 sun of light incidence and applied potential of -0.4 VAg/AgCl reached 0.22 mmol L-1 cm-2 NH3, a value 28 folds higher than using the catalyst without Pt modification. The superiority of N2RR under the photoelectrocatalysis technique was demonstrated compared to photocatalytic and electrocatalytic techniques, together with the investigation of the supporting electrolyte influence in the cathodic compartment. Additionally, that is the first time a kesterite-based photocathode has been applied to NH3 photosynthesis, showing excellent photoconversion capability.

Localized High-Concentration Electrolyte in Li-Mediated Nitrogen Reduction for Ammonia Synthesis.

The lithium-mediated nitrogen reduction reaction (Li-NRR) is a promising green alternative to the Haber-Bosch process for ammonia synthesis. The solid electrolyte interphase (SEI) is crucial for high efficiency and stability, as it regulates reactant diffusion and suppresses side reactions. The SEI properties are greatly influenced by the Li+ ion solvation structure, which is controllable through electrolyte engineering. Although anion-derived SEI enhances selectivity and stability, it has typically been engineered using high-concentration electrolytes (HCEs), which face mass transfer, viscosity, and cost issues. In this study, a localized high-concentration electrolyte (LHCE) in the Li-NRR is first introduced, enabling the formation of anion-derived SEI in a low-concentration electrolyte (LCE) by enhancing the Li-anion coordination using an antisolvent. Among various antisolvents, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) achieves the highest ammonia Faradaic efficiency (73.6 ± 2.5%), more than double that of the LCE (34.3 ± 2.8%) and exceeding the HCE (56.0 ± 2.8%). Systematic calculations and experimental analyses show that the LHCE exhibits anion-rich solvation structures and formsthin, inorganic SEI. Moreover, the LHCE has advantages of low viscosity and high N2 solubility, which facilitate mass transport. This study suggests the application of LHCE as an effective electrolyte engineering strategy to enhance the Li-NRR efficiency.

Boosting electrochemical ammonia synthesis via dynamic nitrogen carriers coupled with electron-rich Lewis acidic sites on TiO2−x nanofiber

In light of the high energy consumption and substantial carbon emissions associated with traditional NH3 production based on the Haber–Bosch process, the aqueous electrochemical nitrogen reduction reaction (NRR) offers a clean and sustainable alternative production route. Nevertheless, activating the NN bonds at room temperature is challenging due to the high bond energy, severely hindering the development and commercialization of the electrochemical NRR. Herein, we report a synergistic strategy for achieving efficient N2 activation at ambient conditions that combines electrolyte engineering with catalytic site-modulated TiO2−x nanofiber electrocatalysts. The synthesized TiO2−x nanofiber electrocatalysts contained abundant intrinsic oxygen vacancies and were further modified with hydroxyl groups to create electron-rich Lewis acidic Ti sites. Additionally, BF3 was engineered into the electrolyte microenvironment, and it could form adducts with N2, serving as a dynamic carrier for N2 transport. The electron-rich Lewis acidic sites and the dynamic carriers exerted a ‘pull–pull’ effect on N2, thereby weakening the NN bonds. Through electrochemical performance evaluation, the designed electrocatalytic scheme achieved an NH3 yield of ∼57.15 μg h−1 mg−1 and a Faradaic efficiency of ∼15.14 %. We anticipate that this methodology will provide new insights into the development of electrochemical ammonia synthesis, particularly in relation to multifaceted design.

Electrocatalysis for Urea Evolution and Oxidation Through Confining Atomic Ni Into In2O3 Nanosheet Catalysts

AbstractUrea, a highly sought‐after fertilizer, is conventionally manufactured through the energy‐intensive Haber–Bosch process but is frequently encountered as a pollutant in wastewater. Thus, achieving sustainable urea production under ambient conditions and the potential to recycle urea from wastewater represent significant eco‐economic advancements. In this study, a novel Ni‐confined In2O3 (Ni‐In2O3) electrocatalyst demonstrating outstanding capabilities in both the urea evolution reaction (UER) from nitrate and carbon dioxide and the highly efficient urea oxidation reaction (UOR) for waste urea utilization is introduced. Computational data and in situ X‐ray absorption spectroscopy (XAS) analysis demonstrate that the unique Ni‐oxygen vacancy (Ni‐Vo) local structure effectively modulates the electronic configuration of neighboring In and Ni atoms. This structural refinement results in a significantly reduced energy barrier for the potential‐determining steps (PDS) in both UER (*COOHNH2 → *CONH2) and UOR (*CO(NH2)2 → *CONHNH2). Consequently, the optimized catalysts achieve a urea evolution faradic efficiency of 19.6%, accompanied by remarkable UOR performance, attaining a 100 mA cm−2 anodic current density at a potential of 1.35 V. This work not only offers a sustainable route to urea production but also highlights the potential for efficient urea oxidation, contributing to a greener and more economically viable future for the nitrogen cycle.

Air cold plasmas as a new tool for nitrogen fixation in agriculture: underlying mechanisms and current experimental insights

Nitrogen fixation is crucial for plant growth and global agriculture, especially with the projected population growth requiring a significant increase in food production. Traditional nitrogen fixation relies on the Haber-Bosch (H-B) process, which is energy-intensive and environmentally harmful due to greenhouse gas emissions. Emerging technologies, such as cold plasma, offer promising alternatives with lower energy consumption. Cold plasma facilitates reactive nitrogen species generation under ambient conditions, potentially improving the production efficiency of nitrogen oxides (NOx). However, optimizing cold plasma nitrogen fixation requires a synergy between experimental and theoretical approaches. Accurate input data are essential for refining theoretical models, which can then guide the design of more efficient processes. This integrated approach can leverage renewable energy, operate on smaller scales, and minimize environmental impacts, making cold plasma a sustainable solution for future nitrogen fixation needs.

Sustainable ammonia and amines from chitin

Efforts are underway to explore alternative methods to the Haber-Bosch process for sustainable ammonia production, while the potential for ammonia extraction from natural nitrogenous biomass is under-exploited. Here, a synergistic catalytic strategy involving acid and modified Ru-based catalysts is communicated for the direct production of amines and ammonia from chitin. Phosphoric acid promotes the cleavage of ether bonds in biomass polymers and also serves to protect amino groups from being removed. Selective hydrogenation, deoxygenation, and amination can be achieved by controllably adjusting the ratio of Ru0/Run+. The utilization of nitrogen atoms in chitin can reach up to 95 % (21 % amines, 74 % ammonium), and the catalytic process is applicable to waste shrimp shells. This study demonstrates the possibility of efficient production of nitrogen-containing compounds from abundant biopolymers.

Chidambar Kulkarni.

"A turning point in my career was exploring the molecular design of responsive polymers and macromolecular materials as a postdoctoral scholar… My group has fun by laughing, both in lab and group meeting, as well going on fun outings like group cookouts on the beach…" Find out more about Benjamin McDonald in his Introducing… Profile.

Leveraging Soft Acid-Base Interactions Alters the Pathway for Electrochemical Nitrogen Oxidation to Nitrate with High Faradaic Efficiency.

Electrocatalytic nitrogen oxidation reaction (N2OR) offers a sustainable alternative to the conventional methods such as the Haber-Bosch and Ostwald oxidation processes for converting nitrogen (N2) into high-value-added nitrate (NO3 -) under mild conditions. However, the concurrent oxygen evolution reaction (OER) and inefficient N2 absorption/activation led to slow N2OR kinetics, resulting in low Faradaic efficiencies and NO3 - yield rates. This study explored oxygen-vacancy induced tin oxide (SnO2-Ov) as an efficient N2OR electrocatalyst, achieving an impressive Faradaic efficiency (FE) of 54.2% and a notable NO3 - yield rate (22.05µg h-1 mgcat -1) at 1.7V versus reversible hydrogen electrode (RHE) in 0.1m Na2SO4. Experimental results indicate that SnO2-Ov possesses substantially more oxygen vacancies than SnO2, correlating with enhanced N2OR performance. Computational findings suggest that the superior performance of SnO2-Ov at a relatively low overpotential is due to reduced thermodynamic barrier for the oxidation of *N2 to *N2OH during the rate-determining step, making this step energetically favorable than the oxygen adsorption step for OER. This work demonstrates the feasibility of ambient nitrate synthesis on the soft acidic Sn active site and introduces a new approach for rational catalyst design.

Reduction of N2 to NH3 using FeP(101)/TiO2 catalysts: A First-principles study

The electrochemical nitrogen reduction reaction offers an eco-friendly and sustainable way for synthesizing ammonia at room temperature, in contrast to the energy-intensive Haber-Bosch process. In this study, we demonstrate that FeP (101) is stabilized by anatase TiO2(101), resulting in the formation of a FeP/TiO2 composite. This composite shows promising potential as a catalyst for N2 electroreduction. All hydrogenation reactions are feasible and occur spontaneously, with the ∗N2-∗N2H step serving as the potential determining step (PDS) with a value of 0.59 V. In comparison to the Ru (0001) surface (1.08 V), which exhibits superior catalytic activity in nitrogen reduction reactions (NRR), the obtained value is significantly lower. FeP/TiO2 exhibits ∼100% selectivity towards ammonia synthesis as compared to the competitive hydrogen evolution process (HER). This study demonstrates that the correlation between N2 activation and the electronic structure will aid in the fundamental comprehension, design, and alteration of NRR catalysts.