Nitric Oxide Reduction Reaction Research Articles

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.

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.

Unveiling “Sabatier principle” for electrocatalytic nitric oxide reduction on single cluster catalysts: A DFT and machine learning guideline

As a revolutionary chemical engineering, the electrocatalytic synthesis of ammonia (NH3) has become one alternative option for green hydrogen storage. However, under the guidance of Sabatier principle, favored single atom catalyst (SAC) hardly gets rid of the perplexity of element selection. Here, a span-new structure-activity correlation for nitric oxide reduction reaction (NORR) was well-proposed on single cluster catalyst (SCC), which not only contributes to improve the activity with the cluster growth, but also breaks the consistent pattern of catalytic performance toward designed SAC. By performing DFT calculations, Co4@GaS was selected out because of its unexceptionable activity, only −0.06 V for working potential rarely reported yet. More eye-catching, as the displacement of activity descriptors obtained from elusory electronic characteristics only, a universal expression that handles free energy change was put forward with the assistance of machine learning (ML). This work may open a fresh avenue for the rational and straightforward design of desirable catalysts and even the development of interdisciplinary in chemistry.

Hexagonal Cobalt Nanosheets for High-Performance Electrocatalytic NO Reduction to NH3

Electrocatalytic nitric oxide (NO) reduction not only provides an extremely promising strategy for ambient NH3 generation but also alleviates the artificially disrupted N-cycle balance. However, exploring efficient electrocatalysts to enhance the NO electroreduction performance remains a significant challenge. Herein, a hexagonal-close-packed Co nanosheet (hcp-Co) is prepared and exhibits a high NH3 yield of 439.50 μmol cm-2 h-1 and a Faraday efficiency of 72.58%, outperforming the face-centered cubic phase of the Co nanosheet (fcc-Co) and most reported electrocatalysts. Through the combination of density functional theory calculations and NO temperature-programmed desorption experiments, the superior catalytic NO reduction reaction (NORR) activity on the hcp-Co can be attributed to the unique electron structures and proton shuttle effect. A proof-of-concept device of Zn-NO batteries using the hcp-Co as the cathode is assembled and shows a power density of 4.66 mW cm-2, which is superior to the reported performance in the literature so far.

Defective 1Tˊ-MoX2 (X = S, Se, Te) monolayers for electrocatalytic ammonia synthesis: Steric and electronic effects on the catalytic activity

Point defects, including both vacancy (Vd) and antisite defects (Ad) are common in transition metal dichalcogenides (TMDs). Both types of defects are produced due to the deviation from stoichiometric ratio of precursor materials and both point defects can serve as active sites in catalytic reactions. In this study, by means of first-principles calculations, the activities of single-point defective 1T′–MoX2 (X = S, Se, Te) monolayers for the electrocatalytic nitrogen reduction reaction (eNRR) and nitric oxide reduction reaction (eNORR) are investigated. Our results show that these catalysts have great potential toward eNRR and eNORR by exhibiting low limiting potentials (UL). For eNRR, the antisite defects (UL’s are −0.45, −0.31 and −0.27 V for 1T′–MoS2@SAd, 1T′–MoSe2@SeAd and 1T′–MoTe2@TeAd) have better catalytic activity than the vacancy defects (UL’s are −0.94, −0.53 and −0.36 V for 1T′–MoS2@SVd, 1T′–MoSe2@SeVd and 1T′–MoTe2@TeVd). All the calculated UL’s are much smaller than that of the Ru (0001) surface (UL = −0.98 V), the benchmark catalyst for eNRR. For eNORR, except for the 1T′–MoS2@SVd catalyst, antisite defects still perform better (UL’s are correspondingly −0.45, 0 and 0 V for 1T′–MoS2@SVd, 1T′–MoSe2@SeVd and 1T′–MoTe2@TeVd; for vacancy defects, they are 0, −0.13 and −0.36 V). In addition, for eNRR, the hydrogen evolution reaction (HER) is effectively inhibited over the 1T′–MoTe2@TeVd, 1T′–MoS2@SAd, 1T′–MoSe2@SeAd and 1T′–MoTe2@TeAd catalysts. Meanwhile, for eNORR, HER is inhibited over all six catalysts. During the eNORR process at at high NO concentration, except for the 1T′–MoSe2@SeVd and 1T′–MoTe2@TeVd catalysts, the other four show better selectivity toward NH3 than the byproducts of N2O/N2. The activity superiority of the antisite defects is mainly steric, i.e., the steric hindrance is larger at the bowl-shaped vacancy defect. In contrast, the activity difference among the catalysts with the same type of defects is largely electronic, which can be represented by work function. For example, the capability of N2/NO activation and electron transfer increases with the decreasing value of work function:1T′–MoS2@SAd (5.62 eV) < 1T′–MoSe2@SeAd (5.10 eV) < 1T′–MoTe2@TeAd (4.53 eV). Overall, these catalysts are promising for electrochemical ammonia synthesis from N2 and NO. This work may also be useful to the rational design of TMD-based catalysts.

Single atomic cerium sites anchored on nitrogen-doped hollow carbon spheres for highly selective electroreduction of nitric oxide to ammonia

Electrocatalytic nitric oxide reduction reaction (NORR) at ambient environments not only offers a promising strategy to yield ammonia (NH3) but also degrades the NO contaminant; however, its application depends on searching for high-performance catalysts. Herein, we present single atomic Ce sites anchored on nitrogen-doped hollow carbon spheres that are capable of electro-catalyzing NO reduction to NH3 in an acidic solution, achieving a maximal Faradaic efficiency of 91 % and a yield rate of 1023 μg h−1 mgcat.−1 at –0.7 V vs RHE for NH3 formation, both of which outperform these on Ce nanoclusters and approach the best-reported results. Meanwhile, the single atomic Ce catalyst shows good structural and electrochemical stability during the 30-h NO electrolysis. Furthermore, when the single atomic Ce catalyst was used as cathodic material in a proof-of-concept of Zn–NO battery, it delivers a maximal power density of 3.4 mW cm−2 and a high NH3 yield rate of 309 μg h−1 mgcat.−1. Theoretical simulations suggest that the Ce-N4 active moiety can not only activate NO molecules via a strong electronic interaction but also reduce the free energy barrier of *NO transition to *NOH intermediate as the limiting step, and therefore boosting the NORR kinetics and suppressing the competitive hydrogen evolution.

Coupling a Main-Group Metal with a Transition Metal to Create Biatom Catalysts for Nitric Oxide Reduction

Developing efficient biatom catalysts for renewable energies is becoming increasingly worthwhile, yet it remains a great challenge. Herein, by means of large-scale first-principles calculations, we report a design principle of coupling main-group metal with transition metal (TM) to explore biatom catalysts for nitric oxide reduction reaction (NORR), namely, $\mathrm{Mg}/\mathrm{Al}/\mathrm{Ga}\ensuremath{-}\mathrm{TM}$ dimers anchored on nitrogen-doped graphene. We propose a comprehensive screening strategy to recognize promising candidates of such catalysts. Following this strategy, we screen $\mathrm{Mg}\ensuremath{-}\mathrm{Ni}@\mathrm{NC}$ and $\mathrm{Ga}\ensuremath{-}\mathrm{Cr}@\mathrm{NC}$ out of 24 candidates as promising biatom catalysts with high activity and selectivity for direct $\mathrm{NO}$-$\mathrm{to}$-${\mathrm{NH}}_{3}$ conversion. Such high catalytic activity is related to the synergetic interatomic interactions. Moreover, based on the interplay between main-group metal and TM centers, we propose a ``donation-backdonation-redonation'' mechanism to characterize $\mathrm{NO}$ activation. In addition, $\mathrm{\ensuremath{\Delta}}{\ensuremath{\epsilon}}_{s/p\ensuremath{\rightarrow}d}$ is identified as an efficient quantitative descriptor to prereduce the number of such catalyst candidates. Our work opens a strategy for rational design of biatom catalysts toward NORR.

Using ternary steric hindrance synergy of a defective MoS2 monolayer to manipulate the electrocatalytic mechanism toward nitric oxide reduction: a first-principles and machine learning study

The complex competing electroreduction reaction pathways in the nitric oxide reduction reaction are guided in the expected direction by taking advantage of the innate steric hindrance of defective MoS2.

Activating dual atomic electrocatalysts for the nitric oxide reduction reaction through the P/S element.

The development of efficient atomic electrocatalysts to resolve the activity and selectivity issues of the nitric oxide reduction reaction (NORR) has increasingly received more attention but is still challenging. The current research on the dual atomic NORR electrocatalyst is exclusively focused on TM atoms. Herein, we propose a novel mechanism of introducing a P/S element, which takes advantage of finite orbitals to active the transition metal (TM) atoms of dual atomic electrocatalysts for NORR. The finite orbitals can hinder the capture of the lone pair electrons of NO but modulate the electronic configurations of the neighboring TM and thus the "donation-backdonation" mechanism can be realized. Through large-scale first-principles calculations, the catalytic performance of a series of P/S-TM biatoms supported by the monolayer CN (P/S-TM@CN) is evaluated. According to a "four-step" screening strategy, P-Cu@CN and S-Ni@CN are successfully screened as promising catalysts with outstanding activity and high selectivity for direct NO-to-NH3 conversion. Moreover, we identify Δεd-p as a valid descriptor to evaluate the adsorption of NO on such catalysts, allowing for reducing the number of catalytic candidates. Our work thus provides a new direction for the rational design of dual atomic electrocatalysts.

Isolated Electron‐Rich Ruthenium Atoms in Intermetallic Compounds for Boosting Electrochemical Nitric Oxide Reduction to Ammonia

AbstractThe direct electrochemical nitric oxide reduction reaction (NORR) is an attractive technique for converting NO into NH3 with low power consumption under ambient conditions. Optimizing the electronic structure of the active sites can greatly improve the performance of electrocatalysts. Herein, we prepare body‐centered cubic RuGa intermetallic compounds (i.e., bcc RuGa IMCs) via a substrate‐anchored thermal annealing method. The electrocatalyst exhibits a remarkable NH4+ yield rate of 320.6 μmol h−1 mg−1Ru with the corresponding Faradaic efficiency of 72.3 % at very low potential of −0.2 V vs. reversible hydrogen electrode (RHE) in neutral media. Theoretical calculations reveal that the electron‐rich Ru atoms in bcc RuGa IMCs facilitate the adsorption and activation of *HNO intermediate. Hence, the energy barrier of the potential‐determining step in NORR could be greatly reduced.