Electrocatalytic green ammonia production beyond ambient aqueous nitrogen reduction

Advanced Microwave Strategies Facilitate Structural Engineering for Efficient Electrocatalysis

In the dynamic realm of energy conversion, the demand for efficient electrocatalysis has surged due to the urgent need to seamlessly integrate renewable energy. Traditional electrocatalyst preparation faces challenges like poor controllability, elevated costs, and stringent operational conditions. The introduction of microwave strategies represents a transformative shift, offering rapid response, high-temperature energy, and superior controllability. Notably, non-liquid-phase advanced microwave technology holds promise for introducing novel models and discoveries compared to traditional liquid-phase microwave methods. This review examines the nuanced applications of microwave technology in electrocatalyst structural engineering, emphasizing its pivotal role in the energy paradigm and addressing challenges in conventional methods. The ensuing discussion explores the profound impact of advanced microwave strategies on electrocatalyst structural engineering, highlighting discernible advantages in optimizing performance. Various applications of advanced microwave techniques in electrocatalysis are comprehensively discussed, providing a forward-looking perspective on their untapped potential to propel transformative strides in renewable energy research. It provides a forward-looking perspective, delving into the untapped potential of microwaves to propel transformative strides in renewable energy research.

Photocatalytic NO x removal and recovery: progress, challenges and future perspectives

The excessive production of nitrogen oxides (NO x ) from energy production, agricultural activities, transportation, and other human activities remains a pressing issue in atmospheric environment management. NO x serves both as a significant pollutant and a potential feedstock for energy carriers. Photocatalytic technology for NO x removal and recovery has received widespread attention and has experienced rapid development in recent years owing to its environmental friendliness, mild reaction conditions, and high efficiency. This review systematically summarizes the recent advances in photocatalytic removal, encompassing NO x oxidation removal (including single and synergistic removal and NO3 - decomposition), NO x reduction to N2, and the emergent NO x upcycling into green ammonia. Special focus is given to the molecular understanding of the interfacial nitrogen-associated reaction mechanisms and their regulation pathways. Finally, the status and the challenges of photocatalytic NO x removal and recovery are critically discussed and future outlooks are proposed for their potential practical application.

Phase Engineering of High-Entropy Alloy for Enhanced Electrocatalytic Nitrate Reduction to Ammonia

Directly electrochemical conversion of nitrate (NO3 -) is an efficient and environmentally friendly technology for ammonia (NH3) production but is challenged by highly selective electrocatalysts. High-entropy alloys (HEAs) with unique properties are attractive materials in catalysis, particularly for multi-step reactions. Herein, we first reported the application of HEA (FeCoNiAlTi) for electrocatalytic NO3 - reduction to NH3 (NRA). The bulk HEA is active for NRA but limited by the unsatisfied NH3 yield of 0.36 mg h-1 cm-2 and Faradaic efficiency (FE) of 82.66 %. Through an effective phase engineering strategy, uniform intermetallic nanoparticles are introduced on the bulk HEA to increase electrochemical active surface area and charge transfer efficiency. The resulting nanostructured HEA (n-HEA) delivers enhanced electrochemical NRA performance in terms of NH3 yield (0.52 mg h-1 cm-2) and FE (95.23 %). Further experimental and theoretical investigations reveal that the multi-active sites (Fe, Co, and Ni) dominated electrocatalysis for NRA over the n-HEA. Notably, the typical Co sites exhibit the lowest energy barrier for NRA with *NH2 to *NH3as the rate-determining step.

Achieving Decentralized, Electrified, and Decarbonized Ammonia Production

The rapid reduction in the cost of renewable energy has motivated the transition from carbon-intensive chemical manufacturing to renewable, electrified, and decarbonized technologies. Although electrified chemical manufacturing technologies differ greatly, the feasibility of each electrified approach is largely related to the energy efficiency and capital cost of the system. Here, we examine the feasibility of ammonia production systems driven by wind and photovoltaic energy. We identify the optimal regions where wind and photovoltaic electricity production may be able to meet the local demand for ammonia-based fertilizers and set technology targets for electrified ammonia production. To compete with the methane-fed Haber-Bosch process, electrified ammonia production must reach energy efficiencies of above 20% for high natural gas prices and 70% for low natural gas prices. To account for growing concerns regarding access to water, geospatial optimization considers water stress caused by new ammonia facilities, and recommendations ensure that the identified regions do not experience an increase in water stress. Reducing water stress by 99% increases costs by only 1.4%. Furthermore, a movement toward a more decentralized ammonia supply chain driven by wind and photovoltaic electricity can reduce the transportation distance for ammonia by up to 76% while increasing production costs by 18%.

Carbon Support Enhanced Mass Transfer and Metal-Support Interaction Promoted Activation for Low-Concentrated Nitric Oxide Electroreduction to Ammonia

The electrochemical NO reduction reaction (NORR) is a promising approach for both nitrogen cycle regulation and ammonia synthesis. Due to the relatively low concentration of the NO source and poor solubility of NO in solution, mass transfer limitation is a serious but easily overlooked issue. In this work, porous carbon-supported ultrafine Cu clusters grown on Cu nanowire arrays (defined as Cu@Cu/C NWAs) are prepared for low-concentration NORR. A high Faradaic efficiency (93.0%) and yield rate (1180.5 μg h-1 cm-2) of ammonia are realized on Cu@Cu/C NWAs at -0.1 V vs a reversible hydrogen electrode (RHE), which are far superior to those of Cu NWAs and other reported performances under similar conditions. The construction of a porous carbon support can effectively decrease the NO diffusion kinetics and promote NO coverage for subsequent highly effective conversion. Moreover, the favorable metal-support interaction between ultrafine Cu clusters and carbon support enhances the adsorption of NO and decreases the barrier for *HNO formation in comparison with that of pure Cu NWAs. Overall, the whole NORR can be fully strengthened on Cu@Cu/C NWAs at low NO concentrations.

Bridging Together Theoretical and Experimental Perspectives in Single-Atom Alloys for Electrochemical Ammonia Production

Ammonia is an essential commodity in the food and chemical industry. Despite the energy-intensive nature, the Haber-Bosch process is the only player in ammonia production at large scales. Developing other strategies is highly desirable, as sustainable and decentralized ammonia production is crucial. Electrochemical ammonia production by directly reducing nitrogen and nitrogen-based moieties powered by renewable energy sources holds great potential. However, low ammonia production and selectivity rates hamper its utilization as a large-scale ammonia production process. Creating effective and selective catalysts for the electrochemical generation of ammonia is critical for long-term nitrogen fixation. Single-atom alloys (SAAs) have become a new class of materials with distinctive features that may be able to solve some of the problems with conventional heterogeneous catalysts. The design and optimization of SAAs for electrochemical ammonia generation have recently been significantly advanced. This comprehensive review discusses these advancements from theoretical and experimental research perspectives, offering a fundamental understanding of the development of SAAs for ammonia production.

Li-Mediated Electrochemical Nitrogen Fixation: Key Advances and Future Perspectives

The electrochemical nitrogen reduction reaction holds great potential for ammonia production using electricity generated from renewable energy sources and is sustainable. The low solubility of nitrogen in aqueous media, poor kinetics, and intrinsic competition by the hydrogen evolution reaction result in meager ammonia production rates. Attributing measured ammonia as a valid product, not an impurity, is challenging despite rigorous analytical experimentation. In this regard, Li-mediated electrochemical nitrogen reduction is a proven method providing significant ammonia yields. Herein, fundamental advances and insights into the Li-mediated strategy are summarized, emphasizing the role of lithium, reaction parameters, cell designs, and mechanistic evaluation. Challenges and perspectives are presented to highlight the prospects of this strategy as a continuous, stable, and modular approach toward sustainable ammonia production.

Cu doping in FeP enabling efficient electrochemical nitrate reduction to ammonia in neutral media

Electrochemical nitrate reduction to ammonia (NH3) not only provides a promising strategy for green NH3 synthesis, but also removes harmful nitrates from water. Herein, a Cu-doped FeP electrocatalyst was prepared for nitrate reduction, which achieved a high NH3 faradaic efficiency of 92.5% and a high NH3 yield of 0.787 mmol h-1 cm-2 in a neutral electrolyte, greatly surpassing its FeP counterpart.

3D cauliflower-like Ni foam: a high-efficiency electrocatalyst for ammonia production via nitrite reduction

A 3D cauliflower-like Ni foam on titanium plate (Ni foam/TP) shows high electrocatalytic performance for ambient ammonia (NH3) synthesis via nitrite (NO2-) reduction. In 0.1 M phosphate-buffered saline solution with 0.1 M NO2-, such Ni foam/TP attains a high NH3 Faradaic efficiency (FE) of 95.9% and a large NH3 yield of 742.7 μmol h-1 cm-2 at -0.8 V. Its Zn-NO2- battery offers a high power density of 6.2 mW cm-2 and an NH3 FE of 90.1%.

Metal-organic framework-derived Cu nanoparticle binder-free monolithic electrodes with multiple support structures for electrocatalytic nitrate reduction to ammonia

Electrocatalytic nitrate reduction to ammonia, which removes nitrates from aquatic ecosystems, is a potential alternative to the classical Haber-Bosch process. Nevertheless, the selectivity of ammonia is often affected by the toxic by-product nitrite. Here, the polyhedral-supported Cu nanoparticle binder-free monolithic electrode (Cu-BTC-Cu) is synthesized by the in situ electroreduction of Cu metal-organic framework (Cu-MOF) precursors. The Cu-BTC-Cu displays a high ammonia yield of 4.00 mg h-1 cm-2cat and a faradaic efficiency of 83.8% in 0.05 M K2SO4 (pH = 7), greatly outperforming the rod-supported (Cu-BTEC-Cu) and unsupported (Cu-BDC-Cu) Cu nanoparticle monolithic electrodes. Impressively, the Cu-BTC-Cu can inhibit significantly the release of by-product NO2- and present favourable stability after 10 consecutive cycles. These preeminent properties can be attributed to the polyhedral structure, which enables better dispersion of Cu nanoparticles and brings more active sites. Moreover, the reaction mechanism of Cu-BTC-Cu is analysed by electrochemical in situ characterization and several key intermediates are captured. This work provides new insights into the modification of the electrocatalytic nitrate reduction activity of Cu-based catalysts and ideas for the design of high-efficiency electrodes.

Guiding catalytic CO2 reduction to ethanol with copper grain boundaries

The grain boundaries (GBs) in copper (Cu) electrocatalysts have been suggested as active sites for CO₂ electroreduction to ethanol. Nevertheless, the mechanisms are still elusive. Herein, we describe how GBs tune the activity and selectivity for ethanol on two representative Cu-GB models, namely Cu∑3/(111) GB and Cu∑5/(100) GB, using joint first-principles calculations and experiments. The unique geometric structures on the GBs facilitate the adsorption of bidentate intermediates, *COOH and *CHO, which are crucial for CO₂ activation and CO protonation. The decreased CO-CHO coupling barriers on the GBs can be rationalized via kinetics analysis. Furthermore, when introducing GBs into Cu (100), the product is selectively switched from ethylene to ethanol, due to the stabilization effect for *CH₃CHO and inapposite geometric structure for *O adsorption, which are validated by experimental trends. An overall 12.5 A current and a single-pass conversion of 5.18% for ethanol can be achieved over the synthesized Cu-GB catalyst by scaling up the electrode into a 25 cm² membrane electrode assembly system.

CoFe nanoalloys encapsulated in nitrogen-doped carbon for efficient nitrite electroreduction to ammonia

Electrochemical nitrite (NO₂^-) reduction to ammonia (NH₃) can not only remove harmful NO₂^- in wastewater, but also produce valuable NH₃. Herein, a CoFe nanoalloy encapsulated in nitrogen-doped carbon (CoFe-NC) electrocatalyst was fabricated for nitrite reduction, which achieved a high NH₃ Faraday efficiency of 94.5%, and a large NH₃ yield of 4050.6 μg h^-1 cm^-2 in a neutral electrolyte.

An Integrated Electrochemical System for Synergistic Cathodic Nitrate Reduction and Anodic Sulfite Oxidation

Electrochemical reduction of nitrate has broad application prospects. However, in traditional electrochemical reduction of nitrate, the low value of oxygen produced by the anodic oxygen evolution reaction and the high overpotential limit its application. Seeking a more valuable and faster anodic reaction to form a cathode-anode integrated system with nitrate reaction can effectively accelerate the reaction rate of the cathode and anode, and improve the utilization of electrical energy. Sulfite, as a pollutant after wet desulfurization, has faster reaction kinetics in its oxidation reaction compared to the oxygen evolution reaction. Therefore, this study proposes an integrated cathodic nitrate reduction and anodic sulfite oxidation system. The effect of operating parameters (cathode potential, initial NO₃^--N concentration, and initial SO₃^2--S concentration) on the integrated system was studied. Under the optimal operating parameters, the nitrate reduction rate in the integrated system reached 93.26% within 1 h, and the sulfite oxidation rate reached 94.64%. Compared with the nitrate reduction rate (91.26%) and sulfite oxidation rate (53.33%) in the separate system, the integrated system had a significant synergistic effect. This work provides a reference for solving nitrate and sulfite pollution, and promotes the application and development of electrochemical cathode-anode integrated technology.

Beyond Purification: Highly Efficient and Selective Conversion of NO into Ammonia by Coupling Continuous Absorption and Photoreduction under Ambient Conditions

Although the selective catalytic reduction technology has been confirmed to be effective for nitrogen oxide (NO_x) removal, green and sustainable NO_x re-utilization under ambient conditions is still a great challenge. Herein, we develop an on-site system by coupling the continuous chemical absorption and photocatalytic reduction of NO in simulated flue gas (C_NO = 500 ppm, GHSV = 18,000 h^-1), which accomplishes an exceptional NO conversion into value-added ammonia with competitive conversion efficiency (89.05 ± 0.71%), ammonia production selectivity (95.58 ± 0.95%), and ammonia recovery efficiency (>90%) under ambient conditions. The anti-poisoning capacities, including the resistance against factors of H₂O, SO₂, and alkali/alkaline/heavy metals, are also achieved, which presents strong environmental practicability for treating NO_x in flue gas. In addition, the critical roles of corresponding chemical absorption and catalytic reduction components are also revealed by in situ characterizations. The emerging strategy herein not only achieves a milestone efficiency for sustainable NO purification but also opens a new route for contaminant resourcing in the near future of carbon neutrality.

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.

In situ modification of d-band in core-shell structure for efficient hydrogen storage via electrocatalytic N2 fixation

The electrochemical N₂ reduction reaction (NRR) into NH₃, especially powered by clean and renewable electricity, is a promising alternative to the capital- and energy-intensive Haber–Bosch process. However, the inert N Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> N bond and the frantic competition of the hydrogen evolution reaction lead to a poor NH₃ yield rate and faradaic efficiency (FE). Here, we in situ construct a series of two-dimension core/shell V₂O₃/VN nanomeshes with a gradient nitride-layer thickness. Among them, V₂O₃/VN-2 exhibits the highest FE of 34.9%, an excellent NH₃ yield rate of 59.7 μg h⁻¹ mg_cat.⁻¹, and outstanding cycle stability, exceeding those of most of the NRR electrocatalysts reported to date. First-principles calculations reveal that the d-band center of VN shifts up in a nearly linear manner with the decrease of nitride-layer thickness, and V₂O₃/VN-2 with a d-band center closer to the Fermi level can strengthen the d–2π* coupling between the catalyst and N₂ molecule, notably facilitating the N₂-into-NH₃ conversion.

In 2D core/shell V₂O₃/VN nanomeshes with a gradient nitride-layer thickness, the V₂O₃ core can tune the d-band structure of the VN shell, strengthen the interaction between N₂ and the active site, and thus enhance electrochemical NRR performance.