High NH3 Yield Research Articles

Fe/Cu diatomic catalysts for electrochemical nitrate reduction to ammonia

Electrochemical conversion of nitrate to ammonia offers an efficient approach to reducing nitrate pollutants and a potential technology for low-temperature and low-pressure ammonia synthesis. However, the process is limited by multiple competing reactions and NO3− adsorption on cathode surfaces. Here, we report a Fe/Cu diatomic catalyst on holey nitrogen-doped graphene which exhibits high catalytic activities and selectivity for ammonia production. The catalyst enables a maximum ammonia Faradaic efficiency of 92.51% (−0.3 V(RHE)) and a high NH3 yield rate of 1.08 mmol h−1 mg−1 (at − 0.5 V(RHE)). Computational and theoretical analysis reveals that a relatively strong interaction between NO3− and Fe/Cu promotes the adsorption and discharge of NO3− anions. Nitrogen-oxygen bonds are also shown to be weakened due to the existence of hetero-atomic dual sites which lowers the overall reaction barriers. The dual-site and hetero-atom strategy in this work provides a flexible design for further catalyst development and expands the electrocatalytic techniques for nitrate reduction and ammonia synthesis.

Enhancing electroreduction activity and selectivity of N2-to-NH3 through proton-feeding adjustments in Ag@AgP2@Ni-CoP@C core-shell nanowires

The synthesis of NH3via electrochemical N2 fixation at ambient conditions has been proposed as a promising alternative to the traditional Haber-Bosch process. However, the development of highly efficient and selective electrocatalysts remains a challenge. In this study, uniform Ag@AgP2 @Ni-CoP@C core-shell nanowires were synthesized using a template-engaged strategy. The merging of conductive Ag core with active AgP2 and porous carbon-coated Ni-doped CoP shells favors the mass and electron transfers, effectively lowering the activation energy toward the reduction of N2 to NH3. Density functional theory (DFT) calculations further indicates that the sandwiched AgP2 layer plays crucial roles in promoting electrocatalytic kinetics and suppressing the competitive hydrogen evolution reactions. Benefiting from these advantages, the titled catalyst achieved a high NH3 yield of 16.84 μg h−1 mg–1cat. at −0.4 V (vs. reversible hydrogen electrode, RHE) and a high Faradaic efficiency of 21.7 % at −0.3 V vs. RHE, as well as high electrochemical and structure stability.

Optimizing Electrocatalytic Nitrogen Reduction via Interfacial Electric Field Modulation: Elevating d-Band Center in WS2-WO3 for Enhanced Intermediate Adsorption.

Electrocatalytic nitrogen reduction reaction (ENRR) has emerged as a promising approach to synthesizing green ammonia under ambient conditions. Tungsten (W) has been found to be one of the most effective ENRR catalyst, with the protonation of intermediates as the rate-determining step (RDS). Enhancing the adsorption of intermediates is crucial to increase the protonation of intermediates and thus improve the catalyst's overall performance. Herein, we aimed to construct a strong interfacial electric field in WS2-WO3 to elevate the d-band center of W, thereby strengthening the adsorption of intermediates. Experimental results demonstrated that this approach led to a significantly improved ENRR performance. Specifically, WS2-WO3 exhibited a high NH3 yield of 62.38 μg h-1mgcat-1 and a promoted faraday efficiency (FE) of 24.24 %. Furthermore, in-situ characterizations and theoretical calculations showed that the strong interfacial electric field in WS2-WO3 upshifted the d-band center of W towards the Fermi level, leading to enhanced adsorption of -NH2 and -NH intermediates on the catalyst's surface. This, resulted in a significantly promoted reaction rate of the RDS. Overall, our study offers new insights into the relationship between interfacial electric field and d-band center and provides a promising strategy to enhance the intermediates adsorption during the ENRR process.

Optimizing Electrocatalytic Nitrogen Reduction via Interfacial Electric Field Modulation: Elevating d‐Band Center in WS2‐WO3 for Enhanced Intermediate Adsorption

AbstractElectrocatalytic nitrogen reduction reaction (ENRR) has emerged as a promising approach to synthesizing green ammonia under ambient conditions. Tungsten (W) is one of the most effective ENRR catalysts. In this reaction, the protonation of intermediates is the rate‐determining step (RDS). Enhancing the adsorption of intermediates is crucial to increase the protonation of intermediates, which can lead to improved catalytic performance. Herein, we constructed a strong interfacial electric field in WS2‐WO3 to elevate the d‐band center of W, thereby strengthening the adsorption of intermediates. Experimental results demonstrated that this approach led to a significantly improved ENRR performance. Specifically, WS2‐WO3 exhibited a high NH3 yield of 62.38 μg h−1 mgcat−1 and a promoted faraday efficiency (FE) of 24.24 %. Furthermore, in situ characterizations and theoretical calculations showed that the strong interfacial electric field in WS2‐WO3 upshifted the d‐band center of W towards the Fermi level, leading to enhanced adsorption of −NH2 and −NH intermediates on the catalyst surface. This resulted in a significantly promoted reaction rate of the RDS. Overall, our study offers new insights into the relationship between interfacial electric field and d‐band center and provides a promising strategy to enhance the intermediates adsorption during the ENRR process.

Accelerating Industrial-Level NO3 - Electroreduction to Ammonia on Cu Grain Boundary Sites via Heteroatom Doping Strategy.

Although the electrocatalytic nitrate reduction reaction (NO3 - RR) is an attractive NH3 synthesis route, it suffers from low yield due to the lack of efficient catalysts. Here, this work reports a novel grain boundary (GB)-rich Sn-Cu catalyst, derived from in situ electroreduction of Sn-doped CuO nanoflower, for effectively electrochemical converting NO3 - to NH3 . The optimized Sn1% -Cu electrode achieves a high NH3 yield rate of 1.98mmol h-1 cm-2 with an industrial-level current density of -425mA cm-2 at -0.55V versus a reversible hydrogen electrode (RHE) and a maximum Faradaic efficiency of 98.2% at -0.51V versus RHE, outperforming the pure Cu electrode. In situ Raman and attenuated total reflection Fourier transform infrared spectroscopies reveal the reaction pathway of NO3 - RR to NH3 by monitoring the adsorption property of reaction intermediates. Density functional theory calculations clarify that the high-density GB active sites and the competitive hydrogen evolution reaction (HER) suppression induced by Sn doping synergistically promote highly active and selective NH3 synthesis from NO3 - RR. This work paves an avenue for efficient NH3 synthesis over Cu catalyst by in situ reconstruction of GB sites with heteroatom doping.

Modulating Lewis acidic active sites of Fe doped Bi2MoO6 nanosheets for enhanced electrochemical nitrogen fixation

Electrocatalytic nitrogen reduction reaction (NRR) for artificial ammonia synthesis under mild conditions has been considered as a promising alternative to the conventional Haber–Bosch method. The highly desired efficient NRR still faced with the mulriple challenges of adsorption and activation of N2 and limited Faraday efficiency. Here, Fe-doped Bi2MoO6 nanosheets fabricated by one step synthesis exhibits high NH3 yield rate of 71.01 μg·h−1·mg−1 and Faraday Efficiency of 80.12%. The decreased electron density of Bi in collaboration with Lewis acid active sites on Fe-doped Bi2MoO6, jointly enhance the adsorption and activation of Lewis basic N2. Benefited from surface texture optimization and the superior ability of N2 adsorption and activation, the increasing density of effective active sites greatly improve the NRR behavior. This work provides new opportunities for developing efficient and highly selective catalysts for NH3 synthesis via NRR.

Cu2+1O/Ag Heterostructure for Boosting the Electrocatalytic Nitrate Reduction to Ammonia Performance.

Electrocatalytic nitrate reduction reaction (ENO3RR) is an alternative, sustainable, and environmentally friendly value-added NH3 synthesis method under ambient conditions relative to the traditional Haber-Bosch process; however, its low NH3 yield, low Faradaic efficiency (FE), low selectivity, and low conversion rate severely restrict the development. In this work, a Cu2+1O/Ag-CC heterostructured electrocatalyst was successfully fabricated by constructing a heterogeneous interface between Cu2+1O and Ag for selective electrochemical nitrate-to-ammonia conversion. The construction of the heterogeneous interface effectively promotes the synergistic effect of the catalytically active components Cu2+1O and Ag, which enhances the material conductivity, accelerates the interfacial electron transfer, and exposes more active sites, thus improving the performance of ENO3RR. Such Cu2+1O/Ag-CC manifests a high NH3 yield of 2.2 mg h-1 cm-2 and a notable ammonia FE of 85.03% at the optimal applied potential of -0.74 V vs RHE in a relatively low concentration of 0.01 M NO3--containing 0.1 M KOH. Moreover, it shows excellent electrochemical stability during the cycle tests. Our study not only provides an efficient catalyst for ammonia electro-synthesis from ENO3RR but also an effective strategy for the construction of ENO3RR electrocatalysts for electrocatalytic applications.

Frustrated Lewis pairs-engineered boron-doped 3D carbon nitride for improved electrocatalytic nitrogen reduction

It is of great importance to explore metal-free electrocatalysts with high electrocatalytic nitrogen reduction reaction (NRR) activity for ammonia (NH3) production. This work for the first time reports a three-dimensional (3D) boron (B) doped carbon nitride with frustrated Lewis pairs and deficiencies for efficient NRR via a facile copolymerization of sodium borohydride and urea precursors. The texture and the amount of B dopants in the resultant 3D carbon nitride can be finely tuned by varying the dosage of sodium borohydride. With the optimal B-doping content, the formed honeycomb-like 3D catalyst has a high NH3 yield rate of 17.8 μg h−1 mg−1 and Faradaic efficiency of 9.85% in 0.1 M Na2SO4 and 0.05 M H2SO4 electrolyte at −1.4 V vs RHE, which is considerably better than the undoped 3D carbon nitride. Comprehensive characterizations reveal that for the B-doped 3D carbon nitride, the unique 3D structure makes more introduced cyano groups and exposed nitrogen defects, favoring the contact between the electrolyte and the active sites. The abundant unsaturated B and N atoms function as frustrated Lewis pairs to strengthen N2 chemisorption and activation, lowing the barrier of NRR and meanwhile suppressing hydrogen evolution reaction. Moreover, in-situ UV–vis spectroscopy elucidates that the optimal potential at −1.4 V vs RHE benefits free electrons to participate in the NRR reaction because it matches the conduction potential of B-UCN-15. This study provides a new avenue for the rational design of nonmetal-based catalysts for NRR.

Optimization of the surface sites of CuPc/Ce-MOF for boosting photoelectrochemical ammonia production

Photoelectrochemical reduction of nitrate (PEC NRR) to ammonia (NH3) is a promising means with water as hydrogen source under room temperature. The construction of photoelectrode with efficient light response and reaction kinetics is the core point to achieve high NH3yield efficiency. Herein, a cerium-based metal organic framework (Ce-MOF) was successfully decorated on the copper phthalocyanine (CuPc). The CuPc/Ce-MOF heterostructure exhibits the ideal nitrate catalytic reduction activity, and the NH3yield (−0.6 V versus RHE) increases to 1.58 [Formula: see text]g [Formula: see text] [Formula: see text] from 0.67 [Formula: see text]g [Formula: see text] [Formula: see text](CuPc). Besides, the cycle experiments reveal that the CuPc/Ce-MOF heterostructure has maintained good catalytic stability. This work explores the PEC NRR process mechanism of CuPc/Ce-MOF samples and provides a new idea for green NH3production.

Cu/Co bimetallic conductive MOFs: Electronic modulation for enhanced nitrate reduction to ammonia

Electrochemical reduction of nitrate to ammonia is an eco-friendly strategy to remove the nitrate pollution in waste effluents. Developing new-type electrocatalysts with high activity for NO3RR has attracted worldwide attention. Owing to the numerous active single-metal sites, electric conductivity and ordered in-plane porous structure, conductive metal–organic frameworks (cMOFs) are promising alternative to construct the next-generation NO3RR electrocatalysts. In this work, a bimetallic cMOF (CuxCoyHHTP) is proposed for efficient NO3– electroreduction to ammonia and the synergy effect between different types of single-metal sites is also revealed. As the result, the optimal Cu1Co1HHTP exhibits an outstanding electrocatalytic activity with a high NH3 yield rate of 299.9 μmol h−1 cm−2 and a large Faradic efficiency of 96.4%. Both theoretical and experimental results reveal that the Co sites can affect the electron structure of Cu sites in Cu1Co1HHTP slab and decrease the ΔG of potential determining step in NO3RR process. Moreover, the Co sites bring a higher selectivity to Cu active sites for reducing *NO2 to *NO, rather than the desorption of NO2–. The bimetallic c-MOFs strategy will innovate the design concept of next-generation catalyst, paving the way to investigate catalytic mechanism of single-metal-atom and open up their application prospects.

Self-powered electrocatalytic nitrate to ammonia driven by lightweight triboelectric nanogenerators for wind energy harvesting

Ammonia (NH3) is an essential feedstock for modern industry and agriculture, as well as a promising energy carrier owing to its high energy density (4.3 kWh kg–1) and storage security. The electrocatalytic nitrate reduction reaction to ammonia (NRA) is a promising alternative route for convenient and distributed NH3 synthesis coupled with clean energy, and is attracting widespread attention. Building a coupled system for NH3 production between NRA and clean energy capture is an exciting direction for future distributed energy utilization and conversion. Herein, a lightweight triboelectric nanogenerators (TENGs) with ultra-low start-up wind speed (3.0 m s–1) is coupled to NRA system loaded with polycrystalline copper, enabling energy harvesting in a wide wind speed band for the efficient NH3 production. An adaptation strategy for capacitor embedded in the energy conversion process is proposed to further enhance the efficiency of coupled system, achieving a high NH3 yield of 11.48 μg cm−2 h–1 with the high catalytic activity of polycrystalline copper on cathode. This work opens up a coupled electrocatalysis and natural energy capture system for the conversion of NO3– to NH3, and provides an idea for the renewable energy conversion and nitrogen cycle remediation.

Design of material regulatory mechanism for electrocatalytic converting NO/NO3−to NH3progress

AbstractNitric oxide (NO)/nitrate (NO3−) exists as the most hazardous pollutions in the air/water that severely impacts human health. Conventional disposing methods are energy‐consuming and uneconomic. Moreover, ammonia (NH3) fertilizer resources acquire urgent, eco‐friendly, and economical strategies that can remove NO/NO3−pollution and simultaneously convert nitrate species, maintaining nitrogen balance. Electrochemical nitrogen (N) reduction is attracting more attention, particularly electrocatalytic NO/NO3−reduction (ENR) to ammonia supply an approach to fixed nitrogen and generate ammonia. ENR is capable of achieving high NH3yield and Faradaic efficiency (FE), avoiding competitive hydrogen evolution reactions and easily overcoming strong N≡N triple bond (941 kJ mol−1). There are abundant research studies related to ENR for decreasing hazardous NO/NO3−and supplying profitable NH3. In this review, we discuss different electrocatalytic regulations for crystalline facet engineering, heteroatom doping, heterostructure, surface vacancy engineering, and single‐atom structure, which bring various metal/nonmetal and their combined catalysts to the preferable performance, such as reactivity, selectivity, FE, and stability. Finally, we summarize the challenges and provide the perspectives to promote the industrial application of ENR.Key PointsThis review focusing on systematically introduce the different modification strategies and regulatory mechanism to enhance the electrochemical performance for NORR/NO3RR, including crystalline facet engineering, heteroatom doping, heterostructure, surface vacancy engineering, and single atom structure.

Highly Efficient Electroenzymatic Cascade Reduction Reaction For The Conversion of Nitrite to Ammonia

AbstractThe electrochemical nitrite reduction reaction provides an alternative approach to offer sustainable ammonia source routes for repairing imbalances in the global nitrogen cycle. In this work, electrocatalysis is combined with enzymatic catalysis to provide an efficient and clean process for recoverable ammonia production. NO2− is reduced to NH3 by electroenzymatic cascade reduction reaction on a bioconjugate, in which 1‐butyl‐3‐methylimidazolium bromide (ILBMB) modified chloroperoxidase (CPO) is fixed on polyethyleneimine (PEI) modified multi‐walled carbon nanotubes (MWCNT) to from bioconjugate (CPO‐ILBMB/MWCNT‐PEI). 15N and 14N isotope labeling reveal that the NH3 species is derived from NO2− reduction. Density functional theory calculations identify that the FeII species in heme center of CPO serve as the key active site for NO2− reduction. The amino groups derived from MWCNT‐PEI not only serve as a bridge to covalently immobilize CPO but also enrich the NO2− ion at electrode/solution interface through electrostatic interactions. The low energy barrier of NO2− reduction and low adsorption free energy of the intermediate result in high Faradaic efficiency (96.4%), NH3 yield (112.7 mg h−1 mgCPO−1), and high selectivity in pH 5.0 solution. The highly efficient electroenzymatic reaction ensurespromising applications in the conversion of NO2− to NH3.

Efficient Electrocatalytic Nitrate Reduction to Ammonia Based on DNA-Templated Copper Nanoclusters

In alkaline solutions, the electrocatalytic conversion of nitrates to ammonia (NH3) (NO3RR) is hindered by the sluggish hydrogenation step due to the lack of protons on the electrode surface, making it a grand challenge to synthesize NH3 at a high rate and selectivity. Herein, single-stranded deoxyribonucleic acid (ssDNA)-templated copper nanoclusters (CuNCs) were synthesized for the electrocatalytic production of NH3. Because ssDNA was involved in the optimization of the interfacial water distribution and H-bond network connectivity, the water-electrolysis-induced proton generation was enhanced on the electrode surface, which facilitated the NO3RR kinetics. The activation energy (Ea) and in situ spectroscopy studies adequately demonstrated that the NO3RR was exothermic until NH3 desorption, indicating that, in alkaline media, the NO3RR catalyzed by ssDNA-templated CuNCs followed the same reaction path as the NO3RR in acidic media. Electrocatalytic tests further verified the efficiency of ssDNA-templated CuNCs, which achieved a high NH3 yield rate of 2.62 mg h-1 cm-2 and a Faraday efficiency of 96.8% at -0.6 V vs reversible hydrogen electrode. The results of this study lay the foundation for engineering catalyst surface ligands for the electrocatalytic NO3RR.

Controlled growth of a graphdiyne-Prussian blue analog heterostructure for efficient ammonia production

Selective and efficient ammonia (NH3) production using an electrocatalytic nitrate reduction reaction (ECNtRR) under ambient conditions provides a green and promising alternative to the traditional energy-intensive Haber–Bosch process. The challenge is in design and controlled syntheses of efficient electrocatalysts with high selectivities, high NH3 yield rates (YNH3) and long-term stabilities. Here, a freestanding three-dimensional graphdiyne-hollowed FeCoNi Prussian blue analog electrode (h-FeCoNi PBA@GDY) with highly selective and active interfaces was synthesized by in situ growth of a GDY layer on the surface of h-FeCoNi PBA and used for the ECNtRR in alkaline solution at ambient temperatures and pressures. The experimental results demonstrated that the uniquely incomplete charge transfer between metal atoms and GDY effectively enhanced the intrinsic activity and increased the number of active sites of the electrocatalyst and promoted fast redox switching and high-density charge transport at the interface, which resulted in high selectivity, activity and stability for the ECNtRR. The results indicated that the electrocatalyst showed a Faraday efficiency (FE) of 95.1% with a YNH3 of 1015.5 μmol h−1 cm−2 and excellent stability.

Photoelectrochemical N2 -to-NH3 Fixation with High Efficiency and Rates via Optimized Si-Based System at Positive Potential versus Li0/.

As a widely used commodity chemical, ammonia is critical for producing nitrogen-containing fertilizers and serving as the promising zero-carbon energy carrier. Photoelectrochemical nitrogen reduction reaction (PEC NRR) can provide a solar-powered green and sustainable route for synthesis of ammonia (NH3 ). Herein, we report an optimum PEC system with a Si-based hierarchically-structured PdCu/TiO2 /Si photocathode and well-thought-out trifluoroethanol as the proton source for lithium-mediated PEC NRR, achieving a record high NH3 yield of 43.09μg cm-2 h-1 and an excellent faradaic efficiency of 46.15% under 0.12-MPa O2 and 3.88-MPa N2 at 0.07V versus lithium(0/+) redox couple (versus Li0/+ ). PEC measurements coupled with operando characterization revealed that the PdCu/TiO2 /Si photocathode under N2 pressures facilitate the reduction of N2 to form lithium nitride (Li3 N), which reacts with active protons to produce NH3 while releasing the Li+ to reinitiate the cycle of the PEC NRR. The Li-mediated PEC NRR process is further enhanced by introducing small amount of O2 or CO2 under pressure by accelerating the decomposition of Li3 N. For the first time, this work provides mechanistic understanding of the lithium-mediated PEC NRR process and opens new avenues for efficient solar-powered green conversion of N2 -to-NH3 . This article is protected by copyright. All rights reserved.

Defective PrOx for Efficient Electrochemical NO2−-to-NH3 in a Wide Potential Range

Electrocatalytic reduction of nitrite (NO2−) is a sustainable and carbon-neutral approach to producing green ammonia (NH3). We herein report the first work on building defects on PrOx for electrochemical NO2− reduction to NH3, and demonstrate a high NH3 yield of 2870 μg h−1 cm−2 at the optimal potential of –0.7 V with a faradaic efficiency (FE) of 97.6% and excellent FEs of >94% at a wide given potential range (−0.5 to −0.8 V). The kinetic isotope effect (KIE) study suggested that the reaction involved promoted hydrogenation. Theoretical calculations clarified that there was an accelerated rate-determining step of NO2− reduction on PrOx. The results also indicated that PrOx could be durable for long-term electrosynthesis and cycling tests.

Fluorine‐Stabilized Defective Black Phosphorene as a Lithium‐Like Catalyst for Boosting Nitrogen Electroreduction to Ammonia

AbstractElectrocatalytic N2 reduction reaction (NRR) is recognized as a zero‐carbon emission method for NH3 synthesis. However, to date, this technology still suffers from low yield and low selectivity associated with the catalyst. Herein, inspired by the activation of N2 by lithium metal, a highly reactive defective black phosphorene (D−BPene) is proposed as a lithium‐like catalyst for boosting electrochemical N2 activation. Correspondingly, we also report a strategy for producing environmentally stable D−BPene by simultaneously constructing defects and fluorination protection based on topochemical reactions. Reliable performance evaluations show that the fluorine‐stabilized D−BPene can induce a high NH3 yield rate of ≈70 μg h−1 mgcat.−1 and a high Faradaic efficiency of ≈26 % at −0.5 V vs. RHE in an aqueous electrolyte. This work not only exemplifies the first stable preparation and practical application of D−BPene, but also brings a new design idea for NRR catalysts.

Fluorine-Stabilized Defective Black Phosphorene as a Lithium-Like Catalyst for Boosting Nitrogen Electroreduction to Ammonia.

Electrocatalytic N2 reduction reaction (NRR) is recognized as a zero-carbon emission method for NH3 synthesis. However, to date, this technology still suffers from low yield and low selectivity associated with the catalyst. Herein, inspired by the activation of N2 by lithium metal, a highly reactive defective black phosphorene (D-BPene ) is proposed as a lithium-like catalyst for boosting electrochemical N2 activation. Correspondingly, we also report a strategy for producing environmentally stable D-BPene by simultaneously constructing defects and fluorination protection based on topochemical reactions. Reliable performance evaluations show that the fluorine-stabilized D-BPene can induce a high NH3 yield rate of ≈70 μg h-1 mgcat. -1 and a high Faradaic efficiency of ≈26 % at -0.5 V vs. RHE in an aqueous electrolyte. This work not only exemplifies the first stable preparation and practical application of D-BPene , but also brings a new design idea for NRR catalysts.

A Plasmon Resonance Enhanced Photo‐Electrode to Promote NH3 Yield in Sustainable N2 Conversion

A key challenge for electrochemical nitrogen reduction reactions (NRR) is the difficulty for conventional catalysts to achieve high currents at low H* coverage to produce appreciable NH3 . Herein, we specially designed an Au nanoparticle-embedded ZnSe photo-electrode to solve the problem. As-designed photo-electrode achieves excellent NRR performance with a high NH3 yield (12.2 μg cm-2 h-1 ) and Faradaic efficiency (27.3 %). Our work reveals that the unique plasmon resonance effect of embedded Au nanoparticles plays a key role in increasing catalytic current when the H* coverage is decreased. Moreover, we successfully established a correlation between H* coverage and NRR performance based on theoretical calculations and experimental observations. This work paves the path for the future design of catalytic materials to overcome the selectivity and yield challenge of sustainable NH3 production.