Nitric Oxide Reduction Reaction Research Articles

Electrode Materials for NO Electroreduction Based on Dithiolene Metal–Organic Frameworks: A Theoretical Study

To quickly and efficiently screen catalytic materials with both activity and selectivity for the nitric oxide reduction reaction (NORR), we adopted a strategy that considers the activity of the side reaction hydrogen evolution reaction (HER) first. It can be seen that Fe3(THT)2 (THT = triphenylene-2,3,6,7,10,11-hexathiol) has extremely excellent HER activity, with a Gibbs free energy change (ΔG) of 0.007 eV. Based on the relationship between ΔG and theoretical exchange current density, all TM3(THT)2 can be divided into two regions: one is the absolute values of ΔG greater than 1 eV, the other is the absolute values of ΔG greater than 0 eV and less than 1eV. Obviously, the candidates with the absolute values of ΔG greater than 1 eV have poor HER performance, but this precisely provides the possibility of obtaining NORR catalytic materials with both excellent selectivity and activity. Subsequent calculation results show that the maximum ΔG change of the rate-determining step of Ta3(THT)2 is unexpectedly only 0.05 eV. Therefore, Ta3(THT)2 may be regarded as the NORR catalytic material with both excellent performance and selectivity. Based on the electron transfer and partial density of states (PDOS) analysis, it can be seen that Ta plays a crucial role in the activation stage of NO. The approach that considers the activity of the side reaction HER first may provide a new idea for rapidly screening highly selective and active NORR catalysts.

Efficient screening of single-atom Porphyrazine-coordinated transition metal catalysts for electrochemical nitric oxide reduction: Insights from first-principles calculations

The electrochemical conversion of NO to NH3 is gaining attention in green energy for its dual benefits of producing ammonia and eliminating toxic NO. However, the lack of efficient and durable electrocatalysts limits its application, highlighting the need for improved catalysts to advance this promising strategy. The emerging transition metal porphyrazine frameworks (TM − Pz), which combine the advantages of single-atom metal (SAC) centers with the coordination of surrounding 4 N ligands, present promising opportunities in the field of electrochemical catalysis. We have designed a series of 3d transition metal single-atom catalysts (SACs) and conducted high-throughput screening, based on first-principles computations, to identify effective catalysts for the electrocatalytic conversion of NO to NH3. Our findings reveal that the Ti − Pz, Fe − Pz, and V − Pz nanosheets exhibit significantly lower UL values of −0.11, −0.24, and −0.31 V, respectively, when compared to the experimentally and theoretically determined criterion of −0.32 V. The correlation between limiting potentials (UL) and a specific descriptor (φ) is particularly significant for constructing a volcano plot, which illustrates the intrinsic properties of metal atoms in various TM − Pz series and their associated remarkable nitric oxide reduction reaction (NORR) performance. Among the range of nanosheets evaluated, the Ti − Pz and Fe − Pz models emerge as particularly noteworthy, demonstrating significantly higher selectivity and NORR activity than their counterparts. This research deepens our comprehension of the distinctive and advantageous properties of SACs, presenting progressive perspectives that can directly facilitate the discovery and optimization of SACs for NORR applications.

Highly-selective Electrocatalytic Reduction of NO to NH3 using Cu Embedded WS2 Monolayer as Single-atom Catalyst: A DFT Study.

Electrocatalytic nitric oxide reduction reaction (NORR) is a promising method for generating NH3. However, developing a NORR catalyst for NH3 synthesis with low cost and high efficiency is still challenging. We here report a series of single-atom catalysts (SACs), designed by embedding nine different transition metals from Sc to Cu in S-vacant WS2 monolayer (TM@WS2), and investigate the electrocatalytic performance for NORR process using the dispersion-corrected density functional theory (DFT) calculations. Among them, Cu-based SACshows a strong binding to the WS2 surface and high selectivity towards NORR process, and also it greatly inhibits the competing hydrogen evolution reaction (HER). Through ab initio molecular dynamics (AIMD) simulations, the thermal stability of SAC is assessed and found no structure deformation even at 500 K temperature. All possible reactive pathways including distal and alternating mode at both N- and O-end configurations for NH3 production were explored. We predicted that the Cu@WS2 SAC exhibits remarkable catalytic activity and selectivity with lowest limiting potential of -0.41 V via the N-alternating pathway. Our study emphasize that the transition metal dichalcogenide (TMDC) based SACs are potential candidates for converting NO to NH3, and this opens a new avenue in designing NORR catalysts with high catalytic performance.

Selective electrosynthesis of ammonia via nitric oxide electroreduction catalyzed by copper nanowires infused in nitrogen-doped carbon nanorods

The electrochemical nitric oxide reduction reaction (eNORR) is meticulously investigated as an alternative to the energy intensive Haber-Bosch process to produce Ammonia (NH3). However, the eNORR is hindered by NH3 selectivity due to side reactions and mass-transfer limitations. In this work, we rationally designed copper nanowires (Cu NWs) infused in the lotus-root-like multi-nano-channels of the porous N-doped carbon nanorods (Cu-mNCNR) for a high selective eNORR to synthesize NH3 at ambient conditions. The optimized catalyst, Cu-mNCNR2, has achieved the highest NH3 Faradaic efficiency of 79% with NH3 yield rate of 34.5 μmol cm–2 h–1 at −0.4 VRHE. Moreover, the Cu-mNCNR2 has demonstrated a vigorous performance in the 24 h continuous NO electrolysis to produce NH3. Additionally, a prototype device, the Zn-NO battery, was demonstrated. This study shows that the rational design of a catalyst considering mass-transfer limitations is crucial to achieving high selective NH3 electrosynthesis in eNORR.

Modifying the second coordination spheres of Fe active sites for electrocatalytic nitric oxide reduction in realistic electrochemical environment

The first and second coordination spheres in the coordination microenvironment may regulate the electronic structure of single-metal atoms supported on carbon matrix, which in turn modulates the catalyst’s catalytic activity. Simulating the kinetic process of electrocatalytic nitric oxide reduction reaction (NORR) by the theoretical modeling of electrochemical microenvironments helps understand the theoretical structure–activity relationship and guides a more rational design of electrocatalysts. In this study, density functional theory calculations combined with a constant-potential/hybrid-solvent model and microkinetic modeling are employed to study NORR mechanism on the carbon-based FeN4, FeN4-O and FeN4-B catalysts with different electronegativity atoms in the second coordination spheres under −1.00 ∼ 0.40 V vs. RHE. The free energy changes of all elementary reactions for NORR on the catalysts reveal that the optimal pathways for NORR on FeN4 produce both ammonia and hydroxylamine, proceeding through the reaction intermediates *NHOH. Within −1.00 ∼ -0.37 V vs. RHE, the kinetic barriers of the rate-determining steps for NORR increase sequentially on FeN4, FeN4-O, and FeN4-B, corresponding to the sequentially decreasing reaction rate constants. At −6.00 mA∙cm−2, the electrode potential for ammonia production on FeN4 catalyst is the lowest among the catalysts at −0.70 V vs. RHE, indicating it has higher electrocatalytic activity.

Role of Interfacial Water Structure in the Electroreduction of NO over Cu2O.

The electrochemical nitric oxide reduction reaction (NORR), which utilizes water as the sole hydrogen source, has the potential to facilitate ammonia production while concurrently mitigating pollutants. However, limited research has been dedicated to characterizing the structure of interfacial water due to the challenges associated with probing this intricate system, impeding the development of more efficient catalysts for the NORR process. Herein, the Cu2O microcrystals with distinct exposed facets, including {100}, {110}, and {111}, are employed for the model catalysts to investigate interfacial water structure and intermediate species in the NORR process. The results from shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) indicated that the NORR performance in 0.1 M Na2SO4 (with heavy water as the solvent) was positively correlated to the proportion of hydrated Na+ ion water. In addition, a sequence of intermediates from the NORR, including *NOH, *NH, *NH2, and *NH3, was detected by employing a combination of multiple in situ characterization methods. Furthermore, in conjunction with experimental results and theoretical calculations, we revealed the potential reaction pathway of NORR. This study offers novel insights into the NORR mechanism and valuable guidance for the design of high-performance catalysts for ammonia production.

Computational Insights on Structural Sensitivity of Cobalt in NO Electroreduction to Ammonia and Hydroxylamine.

It has been reported that it was selective to produce ammonia on metallic cobalt in the electrocatalytic nitric oxide reduction reaction (eNORR), where hexagonal close-packed (hcp) cobalt outperforms face-centered cubic (fcc) cobalt. However, hydroxylamine is more selectively produced on a cobalt single-atom catalyst (Co-SAC). Herein, we uncover the structural sensitivity over hcp-Co, fcc-Co, and Co-SAC in eNORR by employing a recently developed constant potential simulation method and microkinetic modeling. It was found that the superior activity for ammonia production on hcp-Co can be attributed to its facile electron and proton transfer and a stronger lateral suppression effect from NO* over fcc-Co. The exceptional hydroxylamine selectivity on Co-SAC is due to the modified electronic structure, namely, a positively charged active center. It was found that it is more favorable to produce NOH* over hcp-Co and fcc-Co, while HNO* is more preferable on Co-SAC, which are firmly correlated with the vertical and strong NO adsorption on the former and the moderate adsorption on the latter. In other words, a key factor for selectivity control is the first step of NO* protonation. Therefore, the local structure and electronic structure of the catalysts can be critical in regulating the activity and selectivity in eNORR.

Performance and Emission Optimisation of an Ammonia/Hydrogen Fuelled Linear Joule Engine Generator

This paper presents a Linear Joule Engine Generator (LJEG) powered by ammonia and hydrogen co-combustion to tackle decarbonisation in the electrification of transport propulsion systems. A dynamic model of the LJEG, which integrates mechanics, thermodynamics, and electromagnetics sub-models, as well as detailed combustion chemistry analysis for emissions, is presented. The dynamic model is integrated and validated, and the LJEG performance is optimised for improved performance and reduced emissions. At optimal conditions, the engine could generate 1.96 kWe at a thermal efficiency of 34.3% and an electrical efficiency of 91%. It is found that the electromagnetic force of the linear alternator and heat addition from the external combustor and engine valve timing have the most significant influences on performance, whereas the piston stroke has a lesser impact. The impacts of hydrogen ratio, oxygen concentration, inlet pressure, and equivalence ratio of ammonia-air on nitric oxide (NO) formation and reduction are revealed using a detailed chemical kinetic analysis. Results indicated that rich combustion and elevated pressure are beneficial for NO reduction. The rate of production analysis indicates that the equivalence ratio significantly changes the relative contribution among the critical NO formation and reduction reaction pathways.

Comparative study and screening of Single-Atom and homonuclear Dual-Atom catalysts for NO reduction via electrocatalysis

Electrocatalytic technology offers a promising solution to address environmental pollution and resource scarcity. The development of high-stability and selective catalysts is crucial in this regard. This paper focuses on single-atom catalysts (SACs) and homonuclear dual-metal catalysts (DACs) constructed using transition metal atoms as active centers. Catalytic activity and selectivity of these catalysts in the nitric oxide reduction reaction (NORR) process are systematically investigated through first-principles calculations, while exploring the influence of adjacent metal atoms on their characteristics. Using a four-step screening approach, we identify Ti2-N6 as a standout candidate catalyst with a low applied voltage (-0.24 V) for selective NO catalysis and significant inhibition of competitive responses. Homonuclear DACs inherit the advantages of SACs while disrupting the inherent linear relationship, resulting in reduced applied voltage requirements and enhanced catalytic performance. This work presents an efficient catalyst screening method and highlights the unique characteristics and advantages of homonuclear DACs over SACs.

Improving nitric oxide reduction reaction through surface doping on superstructures

Electrochemical nitric oxide reduction reaction (NORR) combining the production of NH3 with the removal of atmospheric pollutant NO is regarded as a promising strategy for producing important chemicals and reducing environmental pollution. However, existing NORR electrocatalysts such as Cu(111) have disadvantages of low activity and selectivity. In this work, the Cu2Si/Cu(111) and Cu2Si/Si(111) superstructures are proposed as NORR electrocatalysts with high stability, activity and selectivity. The results indicate that doping p-block element Si on Cu(111) and transition metal Cu on Si(111) changes the surface chemical environment and local physical properties, optimizing NO adsorption energy and successfully getting rid of the energy barriers of 0.15 and 1.56 eV on Cu(111) and Si(111), respectively. It is of great interest to find that the interfacial effect suppresses the competitive hydrogen evolution reaction (HER) by improving the interlayer charge transfer and modulating Si-3pz orbital, thus ensuring the high NORR selectivity. This theoretical work paves a new way to help design better NORR electrocatalysts for producing renewable fuels from pollutant NO.

First principle investigation of nitric oxide reduction reaction for efficient ammonia synthesis over a Fe–Mo dual-atom electrocatalyst

Electrocatalytic conversion of NO-to-NH3 holds immense potential for removing contaminants and producing zero-carbon fuel. To facilitate widespread commercial adoption of this technology, electrocatalysts with exceptional stability, high activity, and selective performance are urgently desired. We developed a novel dual-atom electrocatalyst, Fe–Mo@NG, in which Fe–Mo dimer is anchored to N-doped graphite. Through the first principle calculations, it is discovered that Fe–Mo@NG provided exceptional performance in NO-to-NH3 conversion. The parallel adsorption type was found can maximize the activation of NO. And the most favorable adsorption structure exhibits a limiting potential of −0.26 eV, surpassing that of most conventional electrocatalysts. The remarkable NORR activity of Fe–Mo@NG is traced back the synergistic effect between the dual-atom active site and the electronic interactions between the active site and NO. At high coverages, the interaction between intermediates and free NO molecules may lead to the formation of N2 or N2O. Overall, our research introduces a promising dual-atom electrocatalyst with broad applicability in NO reduction reactions, providing novel insights into the dual-atom catalysts design.

Evaluating the efficiency of single-double atom catalysts in electrochemical NH3 production from NO based on CN monolayers

The electrochemical NO reduction reaction (NORR) for the synthesis of NH3 from nitric oxide (NO) presents a promising alternative to the conventional Haber process for ammonia production.

From defects to catalysis: mechanism and optimization of NO electroreduction synthesis of NH3.

Ammonia (NH₃) is a crucial industrial raw material, but the traditional Haber-Bosch process is energy-intensive and highly polluting. Electrochemical methods for synthesizing ammonia using nitric oxide (NO) as a precursor offer the advantages of operating under ambient conditions and achieving both NO reduction and resource utilization. Defect engineering enhances electrocatalytic performance by modulating electronic structures and coordination environments. In this brief review, the catalytic reaction mechanism of electrocatalytic NO reduction to NH3 is elucidated, with a focus on synthesis strategies involving vacancy defects and doping defects. From this perspective, the latest advances in various catalytic reduction systems for nitric oxide reduction reaction (NORR) are summarized and synthesized. Finally, the research prospects for NO reduction to NH₃ are discussed.

Computational screening of two-dimensional conductive metal–organic frameworks as electrocatalysts for the nitric oxide reduction reaction

Through a “four-step” screening strategy, Mo3(C6O6)2 is selected from 25 2D c-MOFs as the NORR electrocatalyst, which has a low limiting potential of −0.20 V, as well as strong capability to suppress competing H2, N2, and N2O formation.

Morphology and valence state evolution of Cu: Unraveling the impact on nitric oxide electroreduction

Ammonia (NH3) serves as a critical component in the fertilizer industry and fume gas denitrification. However, the conventional NH3 production process, namely the Haber-Bosch process, leads to considerable energy consumption and waste gas emissions. To address this, electrocatalytic nitric oxide reduction reaction (NORR) has emerged as a promising strategy to bridge NH3 consumption to NH3 production, harnessing renewable electricity for a sustainable future. Copper (Cu) stands out as a prominent electrocatalyst for NO reduction, given its exceptional NH3 yield and selectivity. However, a crucial aspect that remains insufficiently explored is the effects of morphology and valence states of Cu on the NORR performance. In this investigation, we synthesized CuO nanowires (CuO-NF) and Cu nanocubes (Cu-NF) as cathodes through an in situ growth method. Remarkably, CuO-NF exhibited an impressive NH3 yield of 0.50 ± 0.02 mg cm−2 h−1 at −0.6 V vs. reversible hydrogen electrode (RHE) with faradaic efficiency of 29.68% ± 1.35%, surpassing that of Cu-NF (0.17 ± 0.01 mg cm−2 h−1, 16.18% ± 1.40%). Throughout the electroreduction process, secondary cubes were generated on the CuO-NF surface, preserving their nanosheet cluster morphology, sustained by an abundant supply of subsurface oxygen (s-O) even after an extended duration of 10 h, until s-O depletion ensued. Conversely, Cu-NF exhibited inadequate s-O content, leading to rapid crystal collapse within the same timeframe. The distinctive current–potential relationship, akin to a volcano-type curve, was attributed to distinct NO hydrogenation mechanisms. Further Tafel analysis revealed the exchange current density (i0) and standard heterogeneous rate constant (k0) for CuO-NF, yielding 3.44 × 10−6 A cm−2 and 3.77 × 10−6 cm−2 s−1 when NORR was driven by overpotentials. These findings revealed the potential of CuO-NF for NO reduction and provided insights into the intricate interplay between crystal morphology, valence states, and electrochemical performance.

High-Throughput Screening of Effective Dual Atom Catalysts for the Nitric Oxide Reduction Reaction.

Electrochemical NO-to-NH3 conversion has been attracting more attention in the field of green energy, which, however, imposes restrictions on the catalysts. We therefore design a family of dual atom catalysts (DACs) TM1TM2@g-CN and perform high-throughput screening to position the effective catalysts for electrocatalytic NO-to-NH3 conversion from first-principles computations. We identify that TiCr@g-CN (-0.37 V), TiMo@g-CN (-0.36 V), and MnMo@g-CN (-0.43 V) are promising candidates with low overpotentials. In particular, we find that MoMo@g-CN can spontaneously reduce NO to NH3, which makes it an excellent electrocatalyst for the NO reduction reaction (NORR) to be translated to experiments. In terms of the local geometry feature and local electronic structures, we unravel the origin of the high NORR activity and high selectivity of the DAC MoMo@g-CN.

Value‐Added Aqueous Metal‐Redox Bicatalyst Batteries

AbstractThe development and utilization of electrochemical energy conversion and storage devices can maximize intermittent renewable energy and balance environmental issues. Aqueous metal‐redox bicatalyst batteries, incorporating value‐added electro‐reduction reactions during discharge process at the cathode, are considered a particularly attractive alternative for simultaneous electricity generation and valuable chemical production. In this review, for the first time, a holistic and subtle description of value‐added metal‐redox bicatalyst batteries is made, focusing on recent efforts to optimize the energy conversion/chemical production‐involved cathodic discharging reactions, including CO2 reduction reaction (CO2RR), nitrogen reduction reaction (NRR), nitric oxide reduction reaction (NORR), nitrate reduction reaction (NO3−RR), nitrite reduction reaction (NO2−RR), hydrogen evolution reaction (HER), and acetylene reduction reaction (ARR). A macroscopic understanding of design principles in terms of anodes, cathodes, and reaction parameters is provided. Some mechanism explorations, feasibility analyses, technoeconomic assessments, device combinations, and associated comparisons are involved to deepen the understanding of different systems and evaluate their application prospects. Perspectives on and opportunities for future research directions are also outlined.

Oxygen Vacancies‐Rich Metal Oxide for Electrocatalytic Nitrogen Cycle

AbstractThe development of industry and agriculture has been accompanied by an artificially imbalanced nitrogen cycle, which threatens human health and ecological environments. Electrocatalytic systems have emerged as a sustainable way of converting nitrogen‐containing molecules into high value‐added chemicals. However, the construction of high‐performance electrocatalysts remains challenging. The development of oxygen vacancy engineering strategy has promoted more research efforts to explore the structure‐activity relationship between catalytic activity and oxygen vacancies. This review systematically summarizes the recent development of oxygen vacancies‐rich metal oxides for electro‐catalyzing nitrogen cycling systems, involving electrocatalytic nitrate reduction reaction, nitric oxide reduction reaction, nitrogen reduction reaction, C─N coupling, urea oxidation reaction, and nitrogen oxidation reaction. First, the construction methods and characterization methods of oxygen vacancies are summarized. Then, the effect of oxygen vacancy on electrocatalytic activity of metal oxides is discussed in terms of regulating the electronic structures of electrocatalysts, improving the electroconductivity of catalysts, lowing the energy barrier, and strengthening adsorption and activation of intermediate species. Finally, future directions for oxygen vacancy engineering and electrocatalytic nitrogen cycle are anticipated.

Oxygen-Bridged Copper-Iron Atomic Pair as Dual-Metal Active Sites for Boosting Electrocatalytic NO Reduction.

Electrocatalytic reduction of nitric oxide (NO) to ammonia (NH3 ) is a promising approach to NH3 synthesis. However, due to the lack of efficient electrocatalysts, the performance of electrocatalytic NO reduction reaction (NORR) is far from satisfactory. Herein, it is reported that an atomic copper-iron dual-site electrocatalyst bridged by an axial oxygen atom (OFeN6 Cu) is anchored on nitrogen-doped carbon (CuFe DS/NC) for NORR. The CuFe DS/NC can significantly enhance the electrocatalytic NH3 synthesis performance (Faraday efficiency, 90%; yield rate, 112.52µmolcm-2 h-1 ) at -0.6V versus RHE, which is dramatically higher than the corresponding Cu single-atom, Fe single-atom and all NORR single-atom catalysts in the literature so far. Moreover, an assembled proof-of-concept Zn-NO battery using CuFe DS/NC as the cathode outputs a power density of 2.30mWcm-2 and an NH3 yield of 45.52µgh-1 mgcat -1 . The theoretical calculation result indicates that bimetallic sites can promote electrocatalytic NORR by changing the rate-determining step and accelerating the protonation process. This work provides a flexible strategy for efficient sustainable NH3 synthesis.

First-principles study of transition metal supported on graphyne as single atom electrocatalysts for nitric oxide reduction reaction

NH3 is an important precursor to various chemicals and carbon-free energy carriers, whereas NO is a significant environmental pollutant. The NO electrocatalytic reduction (NOER) is one of the primary methods in reducing pollution via converting NO into useful NH3. The auxiliary action of the catalyst plays a significant role in the speed of the NOER. Therefore, the development of new and inexpensive catalysts with high stability, activity, and selectivity is essential for NOER technologies. The potential of a 3d transition metal (TM) supported on graphyne (GY), as an electrocatalyst for the NOER, was systematically investigated using density functional theory calculations. The results demonstrated that Ni@GY exhibited a low limiting potential (−0.51 V), which indicates good catalytic activity. Therefore, we predict that Ni@GY is a promising and efficient single-atom catalyst for the NOER.