Catalysts For N2 Reduction Reaction Research Articles

Oxygen vacancy optimization of the titanium carbide MXene surface for enhanced electrochemical nitrogen reduction

Electrochemical N2 reduction reaction (NRR) provides a hopeful way for sustainable NH3 production. It is the key to realize efficient NRR reaction to optimize the structure and electronic configuration of catalyst materials. Increasing the number of active centers in Ti3C2Tx MXene allows for the development of effective NRR electrocatalysts. Herein, we rationally integrated defect engineering to create oxygen vacancy-rich Ti3C2-MXene (K-Ti3C2-400) as an efficient NRR catalyst with an NH3 yield of 32.25 ± 0.8 μg·h−1·mg−1cat. at − 0.55 V and a Faradaic efficiency of 12.85 % ± 0.26 % at −0.45 V versus reversible hydrogen electrode. According to the density functional theory, oxygen vacancies can prevent the hydrogen evolution reaction by delaying H adsorption, thereby activating absorbed N2 and encouraging *N2H synthesis. This research opens up new possibilities for creating MXene-based catalysts with surface reactivity and selectivity for electrochemical N2 fixation.

Breaking linear scaling relations by strain engineering on MXene for boosting N2 electroreduction

The development of N2 reduction reaction (NRR) electrocatalysts with excellent activity and selectivity is of great significance, but adsorption-energy linear scaling relations between reaction intermediates severely hamper the realization of this aspiration. Here, we propose an elegant strain engineering strategy to break the linear relations in NRR to promote catalytic activity and selectivity. Our results show that the N–N bond lengths of adsorbed N2 with side-on and end-on configurations exhibit opposite variations under strains, which is illuminated by establishing two different N2 activation mechanisms of “P-P” (Pull-Pull) and “E-E” (Electron-Electron). Then, we highlight that strain engineering can break the linear scaling relations in NRR, selectively optimizing the adsorption of key NH2NH2** and NH2* intermediates to realize a lower limiting potential (UL). Particularly, the catalytic activity-selectivity trade-off of NRR on MXene can be circumvented, resulting in a low UL of −0.25 V and high Faraday efficiency (FE), which is further elucidated to originate from the strain-modulated electronic structures. Last but not least, the catalytic sustainability of MXene under strain has been guaranteed. This work not only provides fundamental insights into the strain effect on catalysis but also pioneers a new avenue toward the rational design of superior NRR catalysts.

Tuning Coordination Structures of Zn Sites Through Symmetry-Breaking Accelerates Electrocatalysis.

Manipulating the coordination environment of individual active sites in a precise manner remains an important challenge in electrocatalytic reactions. Herein, inspired by theoretical predictions, a facile procedure to synthesize a series of symmetry-breaking zinc metal-organic framework (Zn-MOF) catalysts with well-defined structures is presented. Benefiting from the optimized coordination microenvironment regulated by symmetry-breaking, Zn-N2 S2 -MOF exhibits the best performance of nitrogen (N2 ) reduction reaction (NRR) with NH3 yield rate of 25.07±1.57µgh-1 cm-2 and Faradaic efficiency of 44.57±2.79% compared with reported Zn-based NRR catalysts. X-ray absorption near-edge structure shows that the symmetry-breaking distorts the coordination environment and modulates the delocalized electrons around the Zn sites, which favors the formation of unpaired low-valence Znδ+ , thereby facilitating the adsorption/activation of N2 . Theoretical calculations elucidate that low-valence Znδ+ in Zn-N2 S2 -MOF can effectively lower the energy barrier of potential determining step, promoting the kinetics and boosting the NRR activity. This work highlights the relationship between the precise coordination environment of metal sites and the catalytic activity, which offers insightful guidance for rationally designing high-efficiency electrocatalysts.

Unveiling the competitive behavior by the orientated regulation of S-vacancy over MoS2 for highly effective N2 fixation

The electrochemical N2 reduction reaction (NRR) renders great potential for sustainable ammonia generation but still suffers from serious challenges, which limit the effective enhancement of catalytic performances. Herein, we skillfully utilize the asynchronous NRR and hydrogen evolution reaction (HER) activities as a function of S-vacancy (Vs) concentrations to enhance the NRR activity but sacrifice the HER activity, thus achieving the tradeoff between activity and selectivity towards the NRR. Inspired by the theoretical guidance, the optimized catalyst (FL-MoS2-20) with a suitable Vs concentration (16.30 %) renders a high NH3 yield rate of 92.95 ± 2.10 µg h−1 mg−1 and a Faradic efficiency (FE) of 20.80 ± 0.18 %, exceeding virtually all previously published MoS2-based NRR catalysts and the overwhelming majority of state-of-the-art NRR catalysts. This work broadens the potential of vacancy engineering to manage the competitive reaction on a single active site and enlightens the catalyst design in the NRR field and beyond.

Two-Dimensional Metal–Organic Framework TM Catalysts for Electrocatalytic N2 and CO2 Reduction: A Density Functional Theory Investigation

In this study, we screened novel two-dimensional metal–organic framework (MOF) materials, which can be used as efficient electrocatalysts in the N2 reduction reaction (NRR) and CO2 reduction reaction (CO2RR) through density functional theory (DFT) calculations. By systematically investigating the adsorption behaviors of N2 and CO2 in different MOF-TMs (TM = Fe, Co, Ni, Cu, Zn) and their electrocatalytic hydrogenation processes, we found that 2D MOF-Fe, MOF-Co, and MOF-Ni can be used as catalysts for electrocatalytic NRR. The free energy increase in the corresponding potential-limiting step is calculated to be 0.84 eV on MOF-Fe, 1.00 eV on MOF-Co, and 1.17 eV on MOF-Ni, all of which are less than or at least comparable to those reported values for the NRR. Moreover, only 2D MOF-Fe was identified as a suitable electrocatalyst for CO2RR. Instead of other hydrocarbons, the product CH3OH is selectively obtained in an electrocatalytic CO2 reduction reaction on a 2D MOF-Fe with a free energy increase of 0.84 eV in the potential-limiting step. Overall, the results of this study not only facilitate the potential application of 2D MOF-TMs as electrocatalysts but also provide new guidelines for rationally designing novel electrocatalysts for the NRR and CO2RR.

Zn-doped carbon nanocage and Zn-doped silicon nanocage (Zn-C52 and Zn-Si52) as catalysts of nitrogen (N2) reduction to ammonia (NH3) conversion

In this work, the capacities of Zn-doped nanocages (Zn-C52 and Zn-Si52) as catalysts for N2 reduction reaction to produce the NH3 are examined. Results shown that the ΔEadoption of Zn-C52 and Zn-Si52 nanocages are acceptable values and Zn is improved the catalytic activity of C52 and Si52 nanocages. The Zn atoms are catalytic positions of Zn-C52 and Zn-Si52 nanocages to adsorb the N2 molecule. The Zn-*NN → Zn-*NNH step through distal, enzymatic and alternating mechanisms is the potential limiting step for N2 reduction reaction. The pathway of N2 reduction reaction by alternating mechanism is as follow: Zn → Zn-*NN → Zn-*NNH → Zn-*NHNH → Zn-*NHNH2 → Zn-*NH2NH2 → Zn-*NH2 + NH3 → Zn*+ NH3. The Zn-Si52 nanocage can reduce the N2 to NH3 with lower potential limiting step than Zn-C52 nanocage. Finally, the Zn-C52 and Zn-Si52 nanocages as proposed catalysts have acceptable potential for N2 reduction reaction.

Charge transfer and vacancy engineering of Fe2O3 nanoparticle catalysts for highly selective N2 reduction towards NH3 synthesis

The development of electrocatalysts for N2 reduction reaction (NRR) is significant for scalable and renewable NH3 synthesis, but calls for a technology innovation to overcome the specific problems of low efficiency and poor selectivity. Herein, we prepare a core–shell nanostructure by coating polypyrrole (PPy) onto sulfur-doped iron oxide nanoparticles (denoted as S-Fe2O3@PPy) as the highly selective and durable electrocatalysts for NRR under ambient conditions. Sulfur doping and PPy coating remarkably improve the charge transfer efficiency of S-Fe2O3@PPy, and the interactions between PPy and Fe2O3 nanoparticles produce abundant oxygen vacancies as active sites for NRR. This catalyst achieves an NH3 production rate of 22.1 μg h−1 mgcat−1 and a very-high Faradic efficiency of 24.6%, surpassing other Fe2O3 based NRR catalysts. Density functional theory calculations show that the S-coordinated iron site can successfully activate the N2 molecule and optimize the energy barrier during the reduction process, resulting in a small theoretical limiting potential.

Plasmonic Au nanoparticles anchored 2D WS2@RGO for high-performance photoelectrochemical nitrogen reduction to ammonia

The photoelectrochemical reduction of nitrogen to ammonia (NH3) is a sustainable and cost-effective process. The photoelectrocatalysts adsorb light, activate N2, and transport electrons efficiently to achieve high-yield NH3. In the present work, gold-tungsten sulfide-anchored reduced graphene oxides (Au-WS2@RGO) are developed as highly efficient photoelectrocatalysts for the N2 reduction reaction (NRR) to synthesize NH3. The effect of Au nanoparticles loaded on WS2@RGO is optimized to achieve hierarchical 2D Au-WS2@RGO with excellent electrical conductivity, large active surface area, and unique porous network. Photoelectrocatalytic NRR of Au-WS2@RGO achieves remarkable NH3 production rates with ultrahigh NH3 yield of 34 μgh-1mgcat-1 at −0.6 V, tremendous faradaic efficiency (FE) of 16.2 %, long durability for about 14 h, and prolonged lifetime of photo-carriers. DFT calculations support the experimental findings and demonstrate that Au-WS2@RGO as an effeient NRR catalyst with low overpotential. The Au-WS2@RGO shows the highest NRR performances even in atmospheric air (AirRR) and outperforms the state-of-the-art NRR catalysts. The high AirRR performance and durability of Au-WS2@RGO make it a promising alternative to Au-based NRR catalysts in photo electrolyzers. Further, an innovative methodology will be proposed for high-efficiency urea fertilizer production using Au-WS2@RGO-based NRR photocatalysts.

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.

Fe-doped Mo2C for boosting electrocatalytic N2 reduction

• Our work designed the synthesis of 5 %Fe-doped Mo 2 C a and its catalytic performance for the NRR. • 5 %Fe-doped Mo 2 C achieves a high Faradic efficiency of 10.3 % and NH 3 yield 36.6 μg∙h −1 ∙mg −1 at 0.3 V vs RHE. • Density functional (DFT) calculations of the rate-determining step energy barriers for these catalysts further show that the 5 % Fe-doped Mo 2 C catalyst has a lower rate-determining step energy barrier (0.84 eV). • Mo 2 C, 5% Fe-doped Mo 2 C and 11.1% Fe-doped Mo 2 C catalysts for ammonia synthesis were studied theoretically and experimentally. Electrocatalytic fixation of N 2 is highlighted as a carbon-free route to generate NH 3 , which strongly demands highly efficient and durable electrocatalysts. We explored the performance of Fe-doped-Mo 2 C catalysts for ammonia nitrogen reduction synthesis. We demonstrate that 5 %Fe-doped Mo 2 C can be an effective and durable catalyst for the electrocatalytic N 2 reduction reaction (NRR). 5 %Fe-doped Mo 2 C achieves a remarkable NH 3 yield of 36.6 μg∙h −1 ∙mg −1 and high faradaic efficiency of 10.3 % at 0.3 V vs RHE, far superior to Mo 2 C nanosheets and outperforming most reported NRR catalysts. Density functional theory (DFT) shows that 5 %Fe-doped Mo 2 C activates N 2 molecule better than Mo 2 C and 11.1 %Fe-doped Mo 2 C, which is reflected by its lower energy barrier (0.84 eV). This research provides an attractive non-noble-metal catalyst for electrocatalytic NH 3 synthesis for efficient electrocatalytic N 2 fixation.

Transition metal atoms anchored on nitrogen-doped α-arsenene as efficient electrocatalysts for nitrogen electroreduction reaction

Electrocatalytic reduction of N2 to NH3 under ambient conditions, inspired by biological nitrogen fixation, is a new approach to address the current energy shortage crisis. As a result, developing efficient and low-cost catalysts is critical. The catalytic activity, catalytic mechanism, and selectivity of α-arsenene (α-Ars) catalysts anchored with various transition metal atoms and doped with different numbers of N atom were investigated for N2 reduction reaction (NRR) in this paper. Results reveal that compared with WN3-α-Ars which is coordinated with three N atoms, asym-WN2As-α-Ars that coordinated with two N atoms not only exhibits high catalytic activity (UL = −0.36 V), but can also successfully suppress the hydrogen evolution reaction (HER). It is manifested that reducing the number of coordination atoms can promote the selectivity of the transition metal (TM) loaded N-doped arsenene catalysts. Furthermore, activity origin analyses show both the charge on ∗N–NH and φ form volcano-type relationship with the limiting potential. The active center of the catalyst, which acts as the charge transporter and has the moderate ability to retrieve charges, is the most efficient in NRR. Overall, this research creates high performance NRR catalysts by varying the number of coordinating N atoms, which provides a novel idea for the development of new NRR catalysts.

MXene Quantum Dots/Copper Nanocomposites for Synergistically Enhanced N2 Electroreduction

Electrocatalytic N2 reduction reaction (NRR) represents an appealing solution for sustainable ammonia production, whereas exploring high‐efficiency NRR catalysts is highly desired but extremely challenging. Herein, we combine Ti3C2Tx‐MXene quantum dots (MQDs) with porous Cu nanosheets to design a novel heterostructured MQDs/Cu as an effective and durable NRR catalyst. Impressively, MQDs/Cu showed a synergistically enhanced NRR activity with an NH3 yield of 78.5 μg h−1 mg−1 (−0.5 V) and a Faradaic efficiency of 21.3% (−0.4 V), far superior to pure MQDs and Cu, and outperforming the majority of the state‐of‐the‐art NRR catalysts. Density function theory computations demonstrated that the synergy of MQDs and Cu enabled the creation of interfacial Cu‐Ti dimer as dual‐active‐centers to strongly activate the absorbed N2 and promote the *N2H formation, consequently resulting in the much reduced energy barriers and greatly enhanced NRR performance.

Boron Nitride Quantum Dots/Ti3C2Tx‐MXene Heterostructure For Efficient Electrocatalytic Nitrogen Fixation

Electrocatalytic N2 fixation through N2 reduction reaction (NRR) has been regarded as a promising route for sustainable NH3 synthesis, while exploring high‐performing NRR catalysts is pivotal yet challenging. Herein, BN quantum dots/Ti3C2Tx‐MXene (BNQDs/Ti3C2Tx) heterostructure is demonstrated as an efficient and durable NRR catalyst, exhibiting a high NH3 yield of 52.8 ± 3.3 μg h−1 mg−1 with an FE of 19.1 ± 1.6% at −0.4 V (vs. RHE), which stand at the high level among all reported BN‐ and MXene‐based NRR catalysts. Theoretical computations reveal that the electronic interactions between BNQDs and Ti3C2Tx enrich the electron density of B atoms at the heterointerface and endow them with enhanced electron‐donating capability for N2 activation and protonation. Meanwhile, the decorated BNQDs can block the active sites of Ti3C2Tx for hydrogen evolution, rendering a high N2‐to‐NH3 selectivity.

Ti2N nitride MXene evokes the Mars-van Krevelen mechanism to achieve high selectivity for nitrogen reduction reaction

We address the low selectivity problem faced by the electrochemical nitrogen (N2) reduction reaction (NRR) to ammonia (NH3) by exploiting the Mars-van Krevelen (MvK) mechanism on two-dimensional (2D) Ti2N nitride MXene. NRR technology is a viable alternative to reducing the energy and greenhouse gas emission footprint from NH3 production. Most NRR catalysts operate by using an associative or dissociative mechanism, during which the NRR competes with the hydrogen evolution reaction (HER), resulting in low selectivity. The MvK mechanism reduces this competition by eliminating the adsorption and dissociation processes at the sites for NH3 synthesis. We show that the new class of 2D materials, nitride MXenes, evoke the MvK mechanism to achieve the highest Faradaic efficiency (FE) towards NH3 reported for any pristine transition metal-based catalyst—19.85% with a yield of 11.33 μg/cm2/hr at an applied potential of − 250 mV versus RHE. These results can be expanded to a broad class of systems evoking the MvK mechanism and constitute the foundation of NRR technology based on MXenes.

Boosting the Electrocatalytic Conversion of Nitrogen to Ammonia on Metal-Phthalocyanine-Based Two-Dimensional Conjugated Covalent Organic Frameworks.

The electrochemical N2 reduction reaction (NRR) under ambient conditions is attractive in replacing the current Haber-Bosch process toward sustainable ammonia production. Metal-heteroatom-doped carbon-rich materials have emerged as the most promising NRR electrocatalysts. However, simultaneously boosting their NRR activity and selectivity remains a grand challenge, while the principle for precisely tailoring the active sites has been elusive. Herein, we report the first case of crystalline two-dimensional conjugated covalent organic frameworks (2D c-COFs) incorporated with M-N4-C centers as novel, defined, and effective catalysts, achieving simultaneously enhanced activity and selectivity of electrocatalytic NRR to ammonia. Such 2D c-COFs are synthesized based on metal-phthalocyanine (M = Fe, Co, Ni, Mn, Zn, and Cu) and pyrene units bonded by pyrazine linkages. Significantly, the 2D c-COFs with Fe-N4-C center exhibit higher ammonia yield rate (33.6 μg h-1 mgcat-1) and Faradaic efficiency (FE, 31.9%) at -0.1 V vs reversible hydrogen electrode than those with other M-N4-C centers, making them among the best NRR electrocatalysts (yield rate >30 μg h-1 mgcat-1 and FE > 30%). In situ X-ray absorption spectroscopy, Raman spectroelectrochemistry, and theoretical calculations unveil that Fe-N4-C centers act as catalytic sites. They show a unique electronic structure with localized electronic states at Fermi level, allowing for stronger interaction with N2 and thus faster N2 activation and NRR kinetics than other M-N4-C centers. Our work opens the possibility of developing metal-nitrogen-doped carbon-rich 2D c-COFs as superior NRR electrocatalyst and provides an atomic understanding of the NRR process on M-Nx-C based electrocatalysts for designing high-performance NRR catalysts.

Electrocatalytic N2 Reduction on FeS2 Nanoparticles Embedded in Graphene Oxide in Acid and Neutral Conditions

The development of stable, low-cost, and highly efficient electrocatalysts for the N2 reduction reaction (NRR) process is challenging but crucial for ammonia production. Herein, we demonstrate the synthesis of pyrite nanoparticles wrapped by graphene oxide (FeS2@GO) acting as a highly efficient NRR catalyst in a wide pH range. The FeS2 nanoparticles are uniformly dispersed across the GO nanosheet, thus leading to the fine exposure of active sites, the promotion of charge transfer, and the increment of a contact surface area, which are all beneficial for a desired catalyst. In the meantime, the low-coordinated Fe atoms are activated as highly active sites, which is in favor of the enhanced electrochemical performance for the NRR. Furthermore, density functional theory (DFT) calculations illustrated that the high activity of N2 reduction over the FeS2@GO catalyst arises from the well-exposed Fe active sites and the increment of charge density at the valence band edge. Benefiting from the well-optimized interface, the barrier of the addition of the first hydrogen atom to N2 forming *NNH species as the potential-determining step is as low as 0.93 eV in N2 electroreduction. The electrochemical test results reveal that, as expected, FeS2@GO exhibits high Faradaic efficiencies (4.7% in 0.1 M HCl solution and 6.8% in 0.1 M Na2SO4 solution) and advanced NH3 yields (78.6 and 27.9 μg h-1 mgcat.-1 in 0.1 M HCl and 0.1 M Na2SO4 solutions, respectively) in both acid and neutral conditions. This work offers a new avenue for exploring novel electrocatalysts, which has great promise to accelerate the practical application of the NRR.

Conversion of dinitrogen to ammonia by rhenium doped graphyne

Developing efficient catalysis for dinitrogen (N2) fixation is a very important and challenging issue in chemistry. Herein, by means of density functional theory (DFT) computations, we reported that the potential of single-atom Rhenium (Re) supported on the graphyne (Re-GY) for activating N2 and reducing it into ammonia (NH3). It is found that the adsorption energies of N2 on Re-GY for end-on/side-on configuration are −1.05/-0.56 eV, together with the N–N bond length are stretched to 1.14/1.21 Å, respectively. The hydrazine intermediate is difficult to release with adsorption energies of −1.71/1.49 eV on Re-GY for different pathways, which ensures it is sequentially hydrogenated and eventually form NH3. All the mechanisms considered are energetically favorable and the most favorable pathway is the mixed mechanism. It is worth noting that there are relatively rare researches on Re-based catalysts for N2 fixation, our findings provide a new option for the design and synthesis of catalysts for N2 reduction reaction.

Metal-free BN quantum dots/graphitic C3N4 heterostructure for nitrogen reduction reaction

Exploring high-efficiency metal-free electrocatalysts towards N2 reduction reaction (NRR) is of great interest for the development of electrocatalytic N2 fixation technology. Herein, we combined boron nitride quantum dots (BNQDs) and graphitic carbon nitride (C3N4) to design a metal-free BNQDs/C3N4 heterostructure as an effective and durable NRR catalyst. The electronically coupled BNQDs/C3N4 presented an NH3 yield as high as 72.3 μg h−1 mg−1 (-0.3 V) and a Faradaic efficiency of 19.5% (-0.2 V), far superior to isolated BNQDs and C3N4, and outperforming nearly all previously reported metal-free catalysts. Theoretical computations unveiled that the N2 activation could be drastically enhanced at the BNQDs-C3N4 interface where interfacial BNQDs and C3N4 cooperatively adsorb N2 and stabilize *N2H intermediate, leading to the significantly promoted NRR process with an ultra-low overpotential of 0.23 V.

High spin polarization ultrafine Rh nanoparticles on CNT for efficient electrochemical N2 fixation to ammonia

The electroreduction of nitrogen (N2) to ammonia (NH3) is gravely restricted by its inherent kinetic complexity and energy-intensive multi-electron steps. Most literature has reported that the first step of N2 adsorption and activation is the bottleneck of electrochemistry N2 reduction reaction (NRR). However, it is a considerable challenge to understand the design rule of catalysts with perfect performances for NRR. Here, as a proof-of-concept experiment, we apply the theoretical calculations with the experimental studies to reveal the influence of the high spin related to the size effect and the charge density related to the substrate effect on the catalytic activity of NRR catalysts. The desired ultrafine Rh nanoparticles anchored on CNT exhibit excellent NRR performances, especially high NH3 yield (26.91 μg h−1 mgcat.−1), Faradaic efficiency (23.48 %) and energy efficiency (20.50 %), outperforming most reported NRR electrocatalysts under ambient conditions, which can be attributed to excellent synergism of the high-spin polarization of Rh NPs and the charge exchange between Rh NPs and the substrate that can promote N2 adsorption and activate its intrinsic NN triple bond.