Catalysts For Reduction Of Nitrogen Research Articles

Transition metal single-atom supported on W2N3 as efficient electrocatalysts for the nitrogen reduction reaction: A DFT study

The problems of poor Faraday efficiency and high overpotential usually limit electrochemical nitrogen reduction (NRR) catalysts. In this paper, 28 different transition metal single-atoms (TM-SAs) supported on W2N3 (TM@W2N3) were designed by density functional theory (DFT) for catalytic N2 reduction. The stability, N2 activation capacity, selectivity and NRR mechanism of TM@W2N3 were analyzed. Following the screening process, only 9 TM@W2N3 (TM=Sc, Ti, V, Co, Cu, Y, Mo, Ag, W) structures were identified as exhibiting high stability, strong activation capacity and high NRR selectivity. And then N2 activation mechanism of V@W2N3, Mo@W2N3 and W@W2N3, as well as the Gibbs free energies of its four NRR reaction pathways were further discussed. The overpotentials (η) of Mo@W2N3 and V@W2N3 to NRR are 0.129 V and 0.470 V, respectively. The overpotential (η) of W@W2N3 is the lowest at 0.059 V, while its catalytic activity is the highest. V@W2N3 and W@W2N3 are more likely to follow the distal pathway for NRR, while Mo@W2N3 is more likely to follow the enzymatic pathway. This study offers some theoretical foundation and reference for the design of new and efficient electrocatalytic NRR catalysts.

Screening transition metal and nonmetal atoms co-doped graphyne as efficient single-atom catalysts for nitrogen reduction

Despite the great potential of electrocatalytic nitrogen reduction reaction (NRR) for more sustainable and energy-efficient ammonia (NH3) production, significant challenges remain, including low activity and poor selectivity of currently available catalysts. In this study, we systematically investigate the electrocatalytic NRR performance of 43 types of single-atom catalysts (SACs) constructed by introducing single transition metal (TM) or/and nonmetal (NM) atoms in graphyne (TM-NM-GY) through first-principles calculations. It is found that Mn-, Os-, B-, Ti-B-, V-B-, Cr-B-, Ru-B-, and Os-B-GY exhibit remarkable efficiency for NRR, showcasing overpotentials lower than 0.34 V. Particularly, Os-B-GY stands out by demonstrating ultra-high catalytic activity, selectivity, and stability for NRR as well as good experimental feasibility, with an impressively low overpotential of merely 0.13 V. The co-doping of Os and B allows for adjusting moderately positive charge densities around Os, which enables strong d-2π* coupling between Os and N2. As a result, the N≡N triple bond is remarkably weakened, facilitating the subsequent NRR process. Moreover, benefiting from the cooperative doping of NM and TM, the potential limiting step is changed, which breaks the inherent linear volcanic relationship between the free energy of the critical intermediate N2H* and limiting potential (UL) on the sole TM-doped system, further enhancing the activity and selectivity. We anticipate that the insights gained from this comprehensive and systematic study can offer valuable guidance for the design and synthesis of novel and highly efficient SACs toward NRR.

Combined Effect of Pressure and Temperature on Nitrogen Reduction Reaction in Water

The synthesis of ammonia starting from nitrogen and using electrochemical processes is considered an interesting strategy to produce ammonia in a sustainable way. However, it requires not only the development of efficient catalysts for nitrogen reduction but also the optimization of the operating conditions of the employed electrochemical devices. In this work, we optimize the kinetics and the thermodynamics of the electrocatalytic nitrogen reduction reaction in water by developing a pressurized H-cell that may operate at temperatures up to 80 °C. Ni foam with low Au loading (0.08 mg cm−2) has been adopted as a catalyst at the cathode. Ammonia has been produced during chronoamperometry experiments in a saturated N2 atmosphere and measured by the indophenol blue method. The effect of voltage, temperature, and pressure has been studied. The nitrogen reduction experiments have been repeated under saturated Ar. To remove contributions due to environmental contamination, we determined the net value as the difference between the produced ammonia in N2 and in Ar. The ammonia yield increases by increasing the temperature and the pressure. The best results have been obtained by using the combined effects of temperature and pressure. Operating at 5 bar of saturated N2 and 75 °C, a production rate of 6.73 μg h−1·cm−2 has been obtained, a value corresponding to a 5-fold enhancement, compared to that obtained under ambient conditions and room temperature.

“Capture-activation-recapture” mechanism-guided design of double-atom catalysts for electrocatalytic nitrogen reduction

Compared with the traditional industrial nitrogen fixation, electrocatalytic methods, especially those utilizing double-atom catalysts containing nonmetals, can give good consideration to the economy and environmental protection. However, the existing “acceptance-donation” mechanism is only applicable to bimetallic catalysts and nonmetallic double-atom catalysts containing boron atoms. Herein, a novel “capture-activation-recapture” mechanism for metal-nonmetal double-atom catalyst is proposed to solve the problem by adjusting the coordination environments of nonmetallic atoms and utilizing the activation effect of metal atoms on nitrogen. Based on this mechanism, the nitrogen reduction reaction (NRR) activity of 48 structures is calculated by density functional theory calculation, and four candidates are selected as outstanding electrocatalytic nitrogen reduction catalysts: Si-Fe@NG (UL = –0.14 V), Si-Co@NG (UL = –0.15 V), Si-Mo@BP1 (UL = 0 V), and Si-Re@BP1 (UL = –0.02 V). The analyses of electronic properties further confirm “capture-activation-recapture” mechanism and suggest that the difference in valence electron distribution between metal and Si atoms triggers the activation of N≡N bonds. In addition, a machine learning approach is utilized to generate an expression and an intrinsic descriptor that considers the coordination environment to predict the limiting potential. This study offers profound insight into the synergistic mechanism of TM and Si for NRR and guidance in the design of novel double-atom nitrogen fixation catalysts.

Bismuth-doped manganese molybdenum bimetallic oxide nanorods as a highly efficient nitrogen reduction catalyst

Bi-doped MnMoO4 nanorods prepared by a simple hydrothermal method exhibit an excellent electrocatalytic nitrogen gas reduction performance at −0.40 V vs. RHE.

Enhancing electrochemical N2 reduction at mild conditions with FexOy co-deposited on amorphous MoS2

Electrochemical reduction of N2 can lead to the clean and sustainable production of NH3 under environmental conditions. However, limited progress has been made as most catalysts lack efficient activity for N2 fixation. Here, we report FexOy co-deposited on amorphous MoS2 supported on a gas diffusion layer electrode (GDL) as an effective catalyst for N2 reduction. The catalysts were prepared by electrodeposition, a simple and low-cost method. Physical characterizations revealed the amorphous nature of MoS2 and while FexOy was evenly distributed over MoS2. In 0.1 M Na2SO4, GDL/MoS2-Fe-1 exhibited an NH3 yield of 7.38 µmol h−1 cm−2, a value almost 2 times greater than that obtained for MoS2/GDL and a faradaic efficiency of 54.9 % at ˗0.2 V vs. reversible hydrogen electrode (RHE) at 25 ℃. Also, the catalyst displayed high stability and durability, retaining almost 93 % of its original values after recycling tests. The amorphous MoS2-FexOy provides new insight into designing efficient and robust catalysts for nitrogen reduction.

Electrochemical N2-to-NH3 with high faradaic efficiency on ZrO2/carbon quantum dots catalysts in neutral electrolyte

Electrochemical nitrogen reduction (NRR) to synthesize NH3 is limited by low Faraday efficiency (FE). Developing electrocatalysts that can efficiently adsorb/activate N2 and suppress hydrogen evolution reaction (HER) to enhance FE is needed. In this work, x-ZrO2/CQDs-T series catalysts were successfully prepared. The results demonstrate that: (I) The appropriate introduction of carbon quantum dots (CQDs) effectively enhances the surface adsorption capacity of ZrO2/CQDs for N2. (II) By high-temperature calcination eliminates the alkaline functional group (-NH2) of CQDs, which reduces the basicity of ZrO2/CQDs catalyst and inhibits the adsorption of protons on the catalyst surface. (III) Due to the semiconductor properties of ZrO2, the charge transfer efficiency of ZrO2/CQDs catalyst is significantly reduced, thereby weakening the binding of electrons to the adsorbed protons. As a result, 1-ZrO2/CQDs-750 catalyst appropriately and effectually restricts the accessibility of protons/electrons and promotes more N2 molecules to occupy active sites, thus achieving up to 66.62 % FE, which is superior to most reported NRR catalysts so far. Meanwhile, electrochemical in situ ATR-SEIRAS technique reveals that 1-ZrO2/CQDs-750 catalyst surface occurs in associative alternating reactions. The introduction of CQDs not only effectively affects the adsorption of N2 and N-related intermediates on ZrO2/CQDs catalyst and limits the proton/electron accessibility to improve FE of NRR, but also promotes the exposure of active sites to increase NH3 yield.

The Construction of Surface-Frustrated Lewis Pair Sites to Improve the Nitrogen Reduction Catalytic Activity of In2O3.

The construction of a surface-frustrated Lewis pairs (SFLPs) structure is expected to break the single electronic state restriction of catalytic centers of P-region element materials, due to the existence of acid-base and basic active canters without mutual quenching in the SFLPs system. Herein, we have constructed eight possible SFLPS structures on the In2O3 (110) surface by doping non-metallic elements and investigated their performance as electrocatalytic nitrogen reduction catalysts using density functional theory (DFT) calculations. The results show that P atom doping (P@In2O3) can effectively construct the structure of SFLPs, and the doped P atom and In atom near the vacancy act as Lewis base and acid, respectively. The P@In2O3 catalyst can effectively activate N2 molecules through the enzymatic mechanism with a limiting potential of -0.28 eV and can effectively suppress the hydrogen evolution reaction (HER). Electronic structure analysis also confirmed that the SFLPs site can efficiently capture N2 molecules and activate N≡N bonds through a unique "donation-acceptance" mechanism.

High-throughput computational screening of doped transition metal oxides as catalysts for nitrogen reduction

High-throughput computational screening of doped transition metal oxides as catalysts for nitrogen reduction

Built-in Electric Field-Induced Work Function Reduction in C-Co3O4 for Efficient Electrochemical Nitrogen Reduction.

Co3O4 is a highly selective catalyst for the electrochemical conversion of N2 to NH3. However, the large work function (WF) of Co3O4 leads to unsatisfactory activity. To address this issue, a strong built-in electric field (BIEF) was constructed in Co3O4 by doping C atoms (C-Co3O4) to reduce the WF for improving the electrocatalytic performance. C-Co3O4 exhibited a remarkable NH3 yield of 38.5 μg h-1 mgcat-1 and a promoted FE of 15.1% at -0.3 V vs RHE, which were 2.2 and 1.9 times higher than those of pure Co3O4, respectively. Kelvin probe force microscopy (KPFM), zeta potential, and ultraviolet photoelectron spectrometry (UPS) confirmed the formation of strong BIEF and WF reduction in C-Co3O4. Additionally, in situ Raman measurements and density functional theory (DFT) calculations revealed the relationship between BIEF and WF and provided insights into the reaction mechanism. Our work offers valuable guidance for the design and development of more efficient nitrogen reduction catalysts.

Exploring Various Catalysts for Nitrogen Reduction to Ammonia

Electrochemical nitrogen reduction reaction (eNRR), one of the most studied problems in catalysis, has the potential to replace the century-old Haber-Bosch process for ammonia synthesis. However, a low-cost, highly selective and efficient catalyst for eNRR is yet to be discovered. Metal based catalysts have been at the heart of numerous studies for eNRR, however there has been a shift towards metal-free catalysts due to their environmentally benign nature and low cost. In this study, we analyze 2D boron-based electrocatalysts for nitrogen reduction and explore the effect of carbon substitution on their activity. Using first-principles calculations, we demonstrate that pristine and carbon (C) substituted 𝛼 borophene catalyze eNRR at exceptionally low limiting potentials of -0.33 V and -0.25 V, respectively. These 𝛼 borophene based catalysts also show high selectivity towards eNRR over the competing hydrogen evolution reaction (HER). Our results show that C-substituted 𝛼 borophene exhibits outstanding catalytic activity towards eNRR via the distal pathway with a small activation barrier of 0.56 eV, almost half the value reported for Ru (0001). Finally, we identify two novel descriptors, adsorption energy of *NNH and charge transfer to *N2, which can be used in high-throughput screening of catalysts for eNRR. These findings demonstrate the strong potential of metal-free borophene based catalysts for efficient electrochemical reduction of N2, enabling low-cost and sustainable NH3 synthesis.We revisit the nitrogenase FeM cofactor (M=Fe/Mo/V) based catalysts for eNRR to decipher the key mechanism at play. Further, catalysts based on transition metal nitrides (TMNs) and transition metal dichalcogenides (TMDCs) are also being explored for the study and compared with the state-of-the-art materials available. The dominance of one NRR mechanism like the Mars Van Krevelen (MvK) mechanism on TMNs over others like the dissociative NRR is also examined. These findings will provide a more comprehensive and elaborate view of the ammonia synthesis for N2 reduction reaction space.

High efficiency carbon nanotubes-based single-atom catalysts for nitrogen reduction

Carbon-based single-atom catalysts (SACs) for electrochemical nitrogen reduction reaction (NRR) have received increasing attention due to their sustainable, efficient, and green advantages. However, at present, the research on carbon nanotubes (CNTs)-based NRR catalysts is very limited. In this paper, using FeN3@(n, 0) CNTs (n = 3 ~ 10) as the representative catalysts, we demonstrate that the CNT curvatures will affect the spin polarization of the catalytic active centers, the activation of the adsorbed N2 molecules and the Gibbs free energy barriers for the formation of the critical intermediates in the NRR processes, thus changing the catalytic performance of CNT-based catalysts. Zigzag (8, 0) CNT was taken as the optimal substrate, and twenty transition metal atoms (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Nb, Mo, Tc, Ru, Rh, Pd, W, Re, Ir, and Pt) were embedded into (8, 0) CNT via N3 group to construct the NRR catalysts. Their electrocatalytic performance for NRR were examined using DFT calculations, and TcN3@(8, 0) CNT was screened out as the best candidate with a low onset potential of − 0.53 V via the distal mechanism, which is superior to the molecules- or graphene-support Tc catalysts. Further electronic properties analysis shows that the high NRR performance of TcN3@(8, 0) CNT originates from the strong d-2π* interaction between the N2 molecule and Tc atom. TcN3@(8, 0) CNT also exhibits higher selectivity for NRR than the competing hydrogen evolution reaction (HER) process. The present work not only provides a promising catalyst for NRR, but also open up opportunities for further exploring of low-dimensional carbon-based high efficiency electrochemical NRR catalysts.

Two-dimensional carbon nanosheets loaded with NiCo bimetallic catalysts for efficient electrocatalytic reduction of nitrogen to ammonia

Ammonia, one of the most produced chemicals, is mainly produced by the Haber Bosch process, under high-temperature, high-pressure, and energy-intensive conditions. Therefore, electrocatalytic nitrogen reduction is an attractive alternative method under ambient conditions. In this paper, two-dimensional carbon nanosheets (CNS) are firstly prepared by a modified Hummer method, and then Co and Ni bimetal load on CNS are prepared by a hydrothermal method to investigate their electrocatalytic nitrogen reduction reaction (NRR) properties. CNS has a porous sheet structure, and the NiCo oxide nanoflower structure with zigzag folding grows on the surface of CNS, which is beneficial to improve the contact area of the catalyst with N2, increasing the number of active sites, and better improve the performance of N2 reduction NH3 synthesis. At −0.34 V, the NH3 yield reaches a maximum of 22.18 μg·h−1·mg−1, and the Faradaic efficiency (FE) is 4.50 %, both of which are about twice as high as that of pure CNS, which is superior to other metal-doped electrocatalysts used for N2 reduction. This study provides an effective method for the design of electrocatalysts with high N2 reduction performance for ammonia synthesis. The catalytic mechanism is further explored by the theoretical calculations of DFT.

Strategies to improve the catalytic activity of Fe-based catalysts for nitrogen reduction reaction

Electrochemical ammonia synthesis from N2 under mild condition is considered a promising strategy to store energy produced by renewable sources, but it is affected by the lack of efficient catalysts for nitrogen reduction. In this work Fe-based nanoparticles with different morphology are deposited on carbon cloth via drop-casting and chemical reduction. The catalyst activity has been evaluated by cyclic voltammetry and chronoamperometry, using a 0.01 M phosphate buffered electrolyte (PBS). The produced ammonia has been determined through the indophenol method. As effective strategy to improve the catalytic activity, the morphology and particle size have been optimized and an electrochemical activation procedure has been implemented. Activation increases the available active sites and is related to higher amount of oxygen vacancies and Fe+2/Fe+3 ratio. Catalysts with optimized morphology produce ammonia at −0.35 V vs RHE with yield of 26.44 μg mgcat−1h−1 and Faradaic efficiency of 20.4%, more than five times higher than without activation.

A Review of Transition Metal Nitride-Based Catalysts for Electrochemical Nitrogen Reduction to Ammonia

Electrochemical nitrogen reduction (NRR) has attracted much attention as a promising technique to produce ammonia at ambient conditions in an environmentally benign and less energy-consuming manner compared to the current Haber–Bosch process. However, even though much research on the NRR catalysts has been conducted, their low selectivity and reaction rate still hinder the practical application of the NRR process. Among various catalysts, transition metal nitride (TMN)-based catalysts are expected to be promising catalysts for NRR. This is because the NRR process can proceed via the unique Mars–Van Krevelen (MvK) mechanism with a compressed competing hydrogen evolution reaction. However, a controversial issue exists regarding the origin of ammonia produced on TMN-based catalysts. The instability of the TMN-based catalysts can lead to ammonia generation from lattice nitrogen instead of supplied N2 gas. Thus, this review summarizes the recent progress of TMN-based catalysts for NRR, encompassing the NRR mechanism, synthetic routes, characterizations, and controversial opinions. Furthermore, future perspectives on producing ammonia electrochemically using TMN-based catalysts are provided.

Advances in Semiconductor-Based Nanocomposite Photo(electro)catalysts for Nitrogen Reduction to Ammonia.

Photo(electro)catalytic nitrogen fixation technology is a promising ammonia synthesis technology using clean solar and electric energy as the driving energy. Abundant nitrogen and water as raw materials uphold the principle of green and sustainable development. However, the generally low efficiency of the nitrogen reduction reaction has seriously restricted the application and development of this technology. The paper introduces the nitrogen reduction process and discusses the main challenges and differences in the current photo(electro)catalytic nitrogen fixation systems. It focuses on promoting the adsorption and activation of N2 and the resolution and diffusion of NH3 generated. In recent years, reviews of the modification strategies of semiconductor materials in light of the typical cases of nitrogen fixation have been reported in the literature. Finally, the future development trend of this field is analyzed and prospected.

Design of molecular M[sbnd]N[sbnd]C dual-atom catalysts for nitrogen reduction starting from surface state analysis

Under electrocatalytic conditions, the state of a catalyst surface (e.g., adsorbate coverage) can be very different from a pristine form due to the existing conversion equilibrium between water and H- and O-containing adsorbates. Dismissing the analysis of the catalyst surface state under operating conditionsmay lead to misleading guidelines for experiments. Given that confirming the actual active site of the catalyst under operating conditions is indispensable to providing practical guidance for experiments, herein, we analyzed the relations between the Gibbs free energy and the potential of a new type of molecular metal-nitrogen-carbon (MNC) dual-atom catalysts (DACs) with a unique 5 N-coordination environment, by spin-polarized density functional theory (DFT) and surface Pourbaix diagram calculations. Analyzing the derived surface Pourbaix diagrams, we screened out three catalysts, N3-Ni-Ni-N2, N3-Co-Ni-N2, and N3-Ni-Co-N2, to further study the activity of nitrogen reduction reaction (NRR). The results display that N3-Co-Ni-N2 is a promising NRR catalyst with a relatively low ΔG of 0.49 eV and slow kinetics of the competing hydrogen evolution. This work proposes a new strategy to guide DAC experiments more precisely: the analysis of the surface occupancy state of the catalysts under electrochemical conditions should be performed before activity analysis.

Theoretical design toward highly efficient single-atom catalysts for nitrogen reduction by regulating the “acceptance-donation” mechanism

Single-atom catalysts (SACs) show great potential for driving electrochemical nitrogen reduction reaction (NRR). However, the lack of physico-chemical understanding of the ambiguous activation mechanism impedes the development of electrocatalysts. In this work, using first principles calculations, we tuned NRR activity and elucidated regulation mechanism of N2 activation by constructing SACs based on defective Ti2CO2 and Ti2NO2 MXenes. Interestingly, Mo@Ti2CO2-v and W@Ti2CO2-v show excellent NRR activity and selectivity with low limiting potentials of –0.27 and –0.27 V at the first hydrogenation (*N2→*NNH) and the last hydrogenation (*NH2→*NH3) steps via distal pathway, respectively. The intrinsic activity tendency can be related to adsorption energy of intermediate *NNH (ΔE(*NNH)). Furthermore, electronic structure analysis demonstrates that number of unpaired electrons in d orbitals (Nun-d) determines occupation of d orbitals, thus regulating the “acceptance-donation” mechanism. Particularly, transition metals with Nun-d of 5 and 4 show moderate “acceptance-donation” interaction, thus achieving encouraging NRR performance. Moreover, ΔE(*NNH) and Nun-d can be considered as promising descriptors for screening and designing effective SACs. Finally, our investigation not only contributes to discovery of novel SACs toward NRR, but also provides insightful guidance for other electrochemical reactions with high bond-order molecules and multi-electron steps, such as ORR and CO2RR.

Electrocatalytic nitrogen fixation performance of two-dimensional Metal-Organic Frameworks Cu3(C6O6) and TM/Cu3(C6O6) from first-principle study

Electrochemical nitrogen reduction reaction can convert N2 into NH3 under ambient conditions, which is a friendly method of ammonia synthesis. Many studies have shown that two-dimensional Metal-Organic Framework (2D-MOF) materials have potential applications in the field of catalysis. In this paper, we systematically studied different single-atom catalysts (SACs) TM/Cu3(C6O6) by the density functional theory (DFT), and screened out two suitable candidate catalysts. Fe/Cu3(C6O6) and Co/Cu3(C6O6) catalysts have the excellent catalytic activity with the limiting potentials of −0.92 V and −0.97 V respectively. And it reveals that doping transition metal atoms can effectively improve the catalytic activity of Cu3(C6O6). Interestingly, we analyzed the electronic band structures and the density of state (DOS) of the catalysts, the results show that they have metallic properties and have good electrical conductivity. Therefore, Fe/Cu3(C6O6) and Co/Cu3(C6O6) are promising catalysts for NRR. Our study provides a new idea for the design of high-efficiency nitrogen reduction catalysts.

Two-Dimensional Carbon Nanosheets Loaded with Nico Bimetallic Catalysts for Efficient Electrocatalytic Reduction of Nitrogen to Ammonia

Two-Dimensional Carbon Nanosheets Loaded with Nico Bimetallic Catalysts for Efficient Electrocatalytic Reduction of Nitrogen to Ammonia