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Article

Hydrogenation-Facilitated Spontaneous N-O Cleavage Mechanism for Effectively Boosting Nitrate Reduction Reaction on Fe2B2 MBene

by
Yuexuan He
,
Zhiwen Chen
* and
Qing Jiang
*
Key Laboratory of Automobile Materials, Ministry of Education, School of Materials Science and Engineering, Jilin University, Changchun 130022, China
*
Authors to whom correspondence should be addressed.
Molecules 2025, 30(8), 1778; https://doi.org/10.3390/molecules30081778
Submission received: 19 March 2025 / Revised: 14 April 2025 / Accepted: 14 April 2025 / Published: 15 April 2025
(This article belongs to the Special Issue Inorganic Chemistry in Asia)
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Abstract

:
The electrochemical reduction of toxic nitrate wastewater to green fuel ammonia under mild conditions has become a goal that researchers have relentlessly pursued. Existing designed electrocatalysts can effectively promote the nitrate reduction reaction (NO3RR), but the study of the catalytic mechanism is not extensive enough, resulting in no breakthroughs in performance. In this study, a novel mechanism of hydrogenation-facilitated spontaneous N-O cleavage was explored based on density functional theory calculations. Furthermore, the Ead−*OH (adsorption energy of the adsorbed *OH) was used as a key descriptor for predicting the occurrence of spontaneous N-O bond cleavage. We found that Ead−*OH < −0.20 eV results into spontaneous N-O bond cleavage. However, excessively strong adsorption of OH* hinders the formation of water. To address this challenge, we designed the eligible Fe2B2 MBene, which shows excellent catalytic activity with an ultra-low limiting potential for NO3RR of −0.22  V under this novel reaction mechanism. Additionally, electron-deficient Fe active sites could inhibit competing hydrogen evolution reactions (HERs), which provides high selectivity. This work may offer valuable insights for the rational design of advanced electrocatalysts with enhanced performance.

1. Introduction

Nitrate (NO3−) has become a common, environmentally harmful pollutant, especially abundant in domestic and industrial wastewater [1]. Consequently, removing NO3− pollutant from water sources has become a worldwide and urgent problem [2,3,4]. To overcome the pollution problem, significant efforts have been made to developing sustainable technologies for converting pollutants into viable energy sources [5,6]. Specifically, the conversion of NO3− pollution to harmless value-added ammonia (NH3) by electrochemical reduction has received much attention [7,8,9,10], which protects the environment while gaining valuable energy. NH3 serves as a crucial chemical feedstock for fertilizer production while simultaneously emerging as a promising candidate for clean energy storage and sustainable fuel applications [11,12,13]. However, the industrial production of NH3 remains predominantly reliant on the energy-intensive Haber–Bosch (H-B) process, which operates under extreme reaction conditions (350–500 °C and 150–350 atm), accounting for approximately 1–2% of global energy consumption and contributing significantly to greenhouse gas emissions [14,15,16,17,18]. The electrocatalytic synthesis of NH3 by NO3− reduction reaction (NO3RR) at ambient conditions is considered a promising alternative to the H-B method [19]. However, electrocatalytic NO3RR is a complex and difficult process involving multiple electron transfers, while also inevitably competing with hydrogen evolution reactions (HERs). Thus, there is an urgent need to find efficient and highly selective catalysts for NO3RR.
The design of catalysts under traditional reaction mechanisms is guided by the Sabatier principle [20,21], while the inherent linear scaling relationships between adsorption strengths of multiple similar intermediates impose fundamental limitations on catalytic activity, creating significant challenges in performance optimization. Normally, the first hydrogenation (*NO3 → *NO3H) step usually has a large change in Gibbs reaction free energy (ΔG) [22,23], indirectly suggesting that the insufficient intermediate interactions may exacerbate the difficulty of activation [24,25,26]. Undoubtedly, the generally accepted reaction mechanism makes it difficult to break this relationship of a significant increase in energy for hydrogenation without deoxygenation, clearly implying that an innovative understanding of the NO3RR reaction mechanism is necessary.
Surprisingly, the intermediates are found to be lower in energy after N-O bond cleavage than before [27]. However, this non-spontaneous N-O bond cleavage needs to overcome a large energy barrier, making the reaction difficult. Inspired by these thoughts, a brand-new reaction mechanism of hydrogenation-facilitated spontaneous N-O cleavage is proposed for NO3RR, which circumvents the inherent limitations of conventional reaction mechanisms, and is expected to accelerate hydrogenation and N-O cleavage simultaneously, resulting in better catalytic performance.
Fortunately, we detected hydrogenation-facilitated spontaneous N-O cleavage on traditional metal catalysts (such as Fe, Co, Ni and Cu) when Ead-*OH < −0.20 eV. Fe has shown the most negative Ead−*OH of the above metals; however, the catalytic performance of Fe for NO3RR is not satisfactory [28]. The essential reason is that the strong adsorption of Fe is unfavorable for intermediates releasing, which can be regulated efficiently by modulating the electronic structure and coordinated environment. Notably, B could utilize empty orbitals to accept electrons from Fe-3d orbitals inducing local orbital electron-deficient Fe sites, which help regulate adsorption. These moderate electron-deficiency Fe sites without excessive electron loss do not hinder the “acceptance–donation” behavior between Fe-3d orbitals and NO3−-π* orbitals, implying that Fe2B2 still has the potential for high NO3RR catalytic activity. In addition, Fe sites with positive charge have poor binding strength with protons, which is able to improve the NH3 synthesis selectivity.
With these thoughts in mind, a novel transition metal boride (MBene) catalyst, Fe2B2, is designed in this work according to the proposed mechanism. We investigate the NO3− electroreduction catalytic performance of Fe2B2 through density functional theory (DFT) calculations. Abundant Fe active sites on the surface enables hydrogenation-facilitated spontaneous N-O cleavage. Also, the electron-deficient Fe atoms result in the inhibition of the competitive HER. Our results demonstrate that Fe2B2 shows exceptional catalytic performance for NO3RR with an ultra-low potential of −0.22 V under the new mechanism with superior selectivity.

2. Results and Discussion

2.1. Hydrogenation-Facilitated Spontaneous N-O Cleavage Mechanism

To explore hydrogenation-facilitated spontaneous N-O cleavage mechanism, the first hydrogenation of *NO3 (*NO3H) on several transition metal (TM)-stabilized surfaces are calculated, including the (110) facet of Fe, as well as the (111) and (001) facets of Co, Ni, Cu, Ag and Au (Figure S1, Supplementary Materials). Simultaneously, the adsorption energies of *OH (Ead−*OH) on corresponding surfaces are calculated, as illustrated in Figure 1a. Selecting Ead−*OH as an effective descriptor, a tendency for spontaneous N-O cleavage is established where there is a threshold. As a groundbreaking finding, the N-O bond of *NO3H intermediate cleaves spontaneously when the value of Ead−*OH is negative than −0.20 eV. Cu-based catalysts are one of the most promising catalysts available for NO3RR [29], whose first hydrogenation step is the potential-determining step (PDS) of the whole pathway, based on previous studies [30]. The ΔG of its first hydrogenation step is calculated as 0.48 eV with the optimized structure pictured in Figure 1a, which is still hard to overcome. In addition, N-O bond-breaking in a *NO3H intermediate on Cu catalyst is also kinetically difficult, as evidenced by calculating the energy barrier through transition state (TS) searching (Figure S2). Hence, even though Cu catalyst is one of the high-activity catalysts, there is still space to improve the catalytic performance for NO3RR.
Fe has the most negative Ead−*OH, as shown in Figure 1a, giving rise to the prediction that it would enable the easiest spontaneous N-O cleavage, whose structural optimization process is illustrated in Figure 1b. However, too strong an adsorption is not conducive to the subsequent transformation–desorption of intermediate substances [31,32]. To address this issue, Fe2B2 MBene has been proposed. The d-band center (Ɛd) of Fe2B2 and Fe calculated are −2.24 and −2.14 eV, respectively (Figure S3). Compared with Fe, the Ɛd of Fe2B2 is farther from Fermi level, resulting in a tendency for weaker adsorption [33,34]. Notably, Ead−*OH of Fe2B2 calculated is −0.47 eV, which meets the criterion of less than −0.20 eV for the hydrogenation-facilitated spontaneous N-O cleavage mechanism.

2.2. Structures and Stability of Fe2B2

The optimized geometric structure of pristine 2D Fe2B2 is illustrated in Figure 2a, where Fe active sites are fully exposed on the surface. The crystal structure of layered Fe2B2 is an accordion-like configuration composed of layers of B atoms inserted into the subsurface of Fe-based frameworks. The dynamical stability of Fe2B2 was assessed by frequency calculations. Figure 2b presents the frequency dispersion analysis of the fully optimized Fe2B2 structure, which exhibits no significant imaginary frequencies, confirming its kinetic stability. The thermodynamic stability of Fe2B2 is also evaluated through the molecular dynamics (MD) simulation with a constant temperature of T = 500 K (Figure 2c). Four snapshots of Fe2B2 at the time of 0.3, 2.9, 5.0, and 7.2 ps, respectively, are almost the same, providing strong evidence for the high thermodynamic stability of the system. The exceptional dynamical and thermodynamic stability of Fe2B2 ensures sustained catalytic performance and long-term durability in NO3RR applications. Simultaneously, MBenes are experimentally considered to have good stability in acid-base solutions. Fe2B2, as one of the MBenes, is expected to likewise have this property [35]. Moreover, the interaction between Fe and B atoms is verified by the charge density difference (Figure S4), where the pronounced charge redistributions indicate strong chemical interactions. From Hirshfeld charge analysis, the electron transfers from Fe to B in the Fe2B2 system and the surface Fe atom has a positive charge of +0.17 e. The direction of electron transfer is consistent with the Pauling electronegativity values for Fe (1.83) and B (2.04) [36].
To understand the electronic properties of Fe2B2, we calculated the band structure as shown in Figure 2d. Obviously, there is no band gap near the Fermi level and some bands across the Fermi level, which means there are metallic conductor characteristics. Additionally, to further investigate the electron structure of Fe2B2, the partial density of states (PDOS) is calculated to evaluate the interaction between B and Fe atoms (Figure 2e). There are significant hybridizations between Fe-3d and adjacent B-2p orbitals revealed by the strong overlaps. The strong interaction and stable chemical bond between Fe and B atoms are confirmed by the PDOS projected on the d orbitals and the p orbitals.

2.3. NO3− Adsorption and Activation

The adsorption of NO3− on Fe2B2 as the initial step is one of the necessary conditions for ensuring the smooth progress of the NO3RR. Given the structure of Fe2B2, two adsorption configurations are considered: NO3− on the top site and on the bridge site, as illustrated in Figure 3a. The calculated adsorption energy (Ead) values of NO3− on the top and bridge sites are −0.66 and −1.62 eV, respectively. Thus, the bridge site NO3− is the optimal adsorption configuration, which will be focused on in the following section. In view of the Hirshfeld charge analysis, 0.163 e− transfers into the NO3− molecule. The charge density difference between Fe2B2 and the adsorbed NO3− in Figure 3b obviously shows electron transfer. The charge acceptance and donation take place on both Fe atoms and the NO3− molecule, which are responsible for the activation of NO3−. Additionally, unpaired electrons in Fe-3d orbitals decrease after adsorption, leading to a significant reduction in the magnetic moment of Fe atom from 1.56 μB to 0.45 μB. The main reason for the reduction in total magnetic moment is that the empty d orbitals in the Fe atoms could receive the lone-pair electrons of NO3−, which means that the charge transfer between Fe and NO3− induces a change in the spin magnetic moment.
In addition, to gain fundamental insights into the bonding characteristics during NO3− activation, we conducted a comparative analysis of the interaction between NO3− and Fe2B2 using the projected density of states (PDOS) before and after adsorption (Figure 3c). Before NO3− adsorption, Fe-3d states possess strong peaks around Fermi level, which facilitates efficient electron transfer during the NO3− activation. After NO3− adsorption, significant orbital overlap between O-2s and -2p orbitals and Fe-3d orbitals emerges, demonstrating that the hybridizing occurs. The Fe-3d orbitals accept the lone-pair electrons from the NO3− molecule to form stable bonding states. These results reveal that the NO3− molecule is effectively activated and active for subsequent protonation.

2.4. NO3RR Performance of Fe2B2

The potential for nitrate protonation must be assessed before examining the specific reaction pathway. We find that Fe2B2 satisfies the criterion (Ead−*OH < −0.20 eV) to achieve N-O cleavage. There still are numerous bare active sites on the Fe2B2 surface after capturing the NO3− molecule. With the aid of these active sites, *NO3H is decomposed into *NO2 and *OH fragments, attributed to a cleavage effect. The reaction Gibbs free energy of *NO2*OH formation (ΔG*NO2*OH) calculated is −1.91 eV, indicating that the N-O bond cleaves spontaneously, while the adsorption configuration is also considered in Figure 4a. We further calculate the PDOS of decomposed *NO2*OH on Fe2B2 surface. The PDOS in Figure 4b shows the significant orbital hybridization between Fe2B2 and *NO2*OH where the remarkable overlap of p-d orbitals near the Fermi level is present. This mitigates the inherent intrinsic linkage of the intermediate and hinders the energy rise. Analogously, the cleavage is also realized in *NO*OH and *HN*OH on Fe2B2 (Figure S5 and Figure 4b). The corresponding structures before and after the optimization of each hydrogenation-facilitated N-O cleavage step are provided in Figure S6.
On these bases, a brand-new reaction mechanism called spontaneous N-O cleavage mechanism for NO3RR on Fe2B2 is put forward, as exhibited in Figure S7. For the electron-deficient surface of Fe2B2, the NO3− molecule is first adsorbed at the bridge site with ∆G*NO3− = −1.25 eV and then the follow protonation steps based on the new mechanism (Figure 4c). After the first hydrogenation step, protonation initiates the decomposition of intermediate *NO3H into *NO2 and *OH fragments. The ∆G value for the formation of *NO2*OH is −1.91 eV. Subsequently, the H proton tends to attack *OH to form the first H2O molecule and release from Fe2B2 surface, which is the PDS with the maximal ∆G value of 0.22 eV and UL = −0.22 V vs. RHE. Likewise, the *NO2H separates into *NO and *OH with ∆G  =  −0.85 eV in the third hydrogenation process. After that, the second H2O molecule also continually releases with a ∆G value of −0.09 eV. Next, the free energy changes for both pathways of *NO hydrogenation (*NO → *HNO and *NO → *NOH) are calculated with the detailed results provided in Figure S8. The formation of *NOH is undesirable with ΔG*NOH = 0.79 eV, which is much higher than ΔG*HNO (−0.08 eV), suggesting that the *HNO pathway is better. Hence, *HNO hydrogenates to decomposed *NH and *OH fragments (ΔG*HN*OH = −1.17 eV). In subsequent reaction steps, the protons continue to drive the transformation of remaining intermediates, ultimately yielding the third H2O molecule and the desired NH3 product. The ∆G value for releasing H2O is −0.33 eV. And ∆G values for *NH2 and *NH3 formations are −0.48 and −0.36 eV, respectively. Finally, we performed comparative calculations of NO3RR performance between Fe(110) and Fe2B2 (Figure S9). The results show that the maximal ΔG of Fe is 0.91 eV, which is much higher than that of Fe2B2 (0.22 eV). Furthermore, we also considered the implicit solvation effect and the calculation shows that the maximal ∆G value for PDS of Fe2B2 is 0.31 eV, confirming that Fe2B2 still maintains excellent NO3RR catalytic activity under this condition (Figure S10). So far, the ability of this reaction mechanism to effectively lower the energy changes has been almost verified. Encouragingly, compared with traditional reaction mechanism, the novel mechanism of the catalysis ensures the stability of adsorption and promotes the activation step through spontaneous N-O cleavage, thereby strongly validating our initial hypothesis.

2.5. Selectivity Toward NH3 Synthesis

Furthermore, owing to the presence of competitive reaction of HER, selectivity is the focus of NO3RR catalysts in addition to high catalytic activity. An optimal NO3RR electrocatalyst must mitigate detrimental H species from poisoning and inhibit the competing HER during the NH3 synthesis process. The initial hydrogen adsorption step is a prerequisite and fundamental thermodynamic requirement for the entire HER process. Here, the calculated H+ adsorption free energy (∆E*H) on Fe sites is −0.27 eV, which is more positive than ∆E*NO3 (Figure S11), suggesting that NO3− rather than H+ tends to adsorb on the active sites. Obviously, the electron-deficient Fe sites contribute to the superior selectivity. Additionally, we also calculate the adsorption of H+ in the presence of an applied corresponding limiting potential to comprehensively evaluate the adsorption selectivity under the corresponding UL of NO3RR (Figure S11). The negative value of −0.49 eV shows the adsorption of NO3− remains much stronger than that of H+. These results imply that the active sites still preferentially adsorb NO3− at the operating potential, indicating that Fe2B2 still has an excellent selectivity towards NO3RR.

3. Computational Methods

In this study, all first-principles calculations were performed using spin-polarization density functional theory (DFT) and implemented in the Dmol3 code in Material Studio [37,38]. The exchange–correlation effect is treated by the generalized gradient approximation (GGA) with Perdew–Burke–Ernzerhof (PBE) functional [39,40]. The Grimme method for DFT-D correction is applied to describe the van der Waals forces [41]. The DFT semi-core pseudopotential (DSPP) method is implemented for the treatment of core electrons with the basis set of double numerical plus polarization (DNP) set as 4.4 [38,42]. The convergence criteria is set to 1.0 × 10−5 hartree (Ha) for the energy change, 2.0 × 10−3 Ha Å−1 for the gradient and 5.0 × 10−3 Å for the displacement, respectively. A smearing value of 0.005 Ha is chosen to speed up convergence. All atoms are fully relaxed during the calculations. The 3 × 3 supercell of 2D Fe2B2 (001) with 4 layers of atoms is built and the vacuum gap is 15 Å to avoid the interaction between periodic structures in z-direction. The k-point grid is set as 4 × 4 × 1 in Brillouin zone. Before geometrical optimization, the initial spin of Fe is set to 4. The atomic charges are calculated by Hirshfeld analysis to further study the nature of charge transfer [43,44]. To investigate the N-O bond cleavage, linear synchronous transit/quadratic synchronous transit (LST/QST) methods of the transition state (TS) are used [45].
In this work, the adsorption energy (Ead−*M, M denotes the corresponding species) is defined as
Ead−*M = E*M − E* − EM
where E*M represents the total energy of the catalyst and adsorbed material, E* is the energy of the isolated catalyst and EM is the energy of the corresponding adsorbate molecule in the independent gas state.
The electrochemical NO3RR process involved net transfer of 9 protons and 8 electrons (NO3− + 9H+ + 8e− → NH3 + 3H2O) and is calculated based on the computational hydrogen electrode (CHE) model proposed by Nørskov et al. [46,47]. The free energy of a proton–electron pair at the chemical potential of 0 V vs. RHE under standard reaction conditions (pH = 0, 298.15 K, 1 atm) is equivalent to 1/2 H2(g) [48,49]. According to this theory, the Gibbs reaction free energy change (ΔG) is determined by
ΔG = ΔE + ΔZPE − TΔS
where ΔE, ΔZPE, T and ΔS are the change in electronic reaction energy, the zero-point energy (ZPE), the temperature (298.15 K) and the entropy difference between products and reactants, respectively. In addition, the limiting potential (UL) of each step is defined as
UL = −ΔGmax/e
where ΔGmax denotes the Gibbs free energy change at the highest elementary step for the pathway during the NO3− reduction process, which means the potential-determining step. The entropy values for gas-phase molecules are obtained from the standard values of thermodynamics [50].

4. Conclusions

In conclusion, we used DFT calculations to synthetically investigate the potential of Fe2B2 as an efficient and selective electrocatalyst for NO3RR. Using Fe2B2 as a prototype, guided by cleavage idea, we have successfully proposed a brand-new mechanism for NO3RR, namely a spontaneous N-O cleavage mechanism. As found, Fe2B2 exhibits remarkable NO3RR performance with an ultra-low limiting potential of −0.22 V vs. RHE under the new mechanism. In addition, electron-deficient Fe active sites also exhibit outstanding NO3RR selectivity and significantly inhibit the competing HER, even at the applied potential of NO3RR. Thus, Fe2B2 emerges as a promising candidate electrocatalyst for NO3RR due to its outstanding catalytic activity and superior selectivity. Collectively, our work establishes a novel reaction mechanism and provides valuable guidance for future catalyst design.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/molecules30081778/s1, Figure S1: The geometry optimized *NO3H (*NO2*OH) adsorption configurations on the surface of transition metals (TM). Figure S2: Dissociation process of *NO3H to *NO2*OH on Cu (111). Figure S3: The partial density of states (PDOS) plots of Fe2B2 and Fe (110). The d-band centers are also highlighted in the PDOS curves. Figure S4: The atomic electron density maps of Fe2B2 surface. The blue and yellow isosurfaces represent electron density accumulation and depletion, respectively. Figure S5: (a) The reaction free energy changes of *NO2 to *NO*OH and the corresponding structure on Fe2B2 surface. (b) The reaction free energy changes of *HNO to *HN*OH and the corresponding structure on Fe2B2 surface. Figure S6: The corresponding adsorption configurations of *NO3H (*NO2*OH), *NO2H (*NO*OH) and *HNOH (*HN*OH) before (left) and after (right) geometry optimization on Fe2B2 surface. Figure S7: The brand-new reaction mechanism of intermediate separation strategy. Figure S8: Protonation of *NO on Fe2B2, including two competitive pathways of *NOH and *HNO. Figure S9: The Gibbs free energy change diagram for NO3RR on Fe2B2 surface and Fe(110). Figure S10: The Gibbs free energy change diagram for NO3RR on Fe2B2 surface incorporating the implicit solvation effect. Figure S11: The calculated the adsorption energy of *NO3 and *H on Fe2B2 surface.

Author Contributions

Y.H.: Writing—original draft preparation, formal analysis and data curation. Z.C.: Writing—review and editing, supervision and funding acquisition. Q.J.: Writing—review and editing, supervision and funding acquisition. All authors have read and agreed to the published version of the manuscript.

Funding

This research was supported by the National Natural Science Foundation of China (No. 52130101).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data are contained within the article.

Conflicts of Interest

The authors declare no conflicts of interest.

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Molecules 30 01778 g001
Figure 1. (a) The adsorption energies of *OH (Ead−*OH) on several TM surfaces. (b) The NO3H adsorption configurations before (left) and after (right) geometry optimization on Fe (110).
Figure 1. (a) The adsorption energies of *OH (Ead−*OH) on several TM surfaces. (b) The NO3H adsorption configurations before (left) and after (right) geometry optimization on Fe (110).
Molecules 30 01778 g001
Molecules 30 01778 g002
Figure 2. (a) The geometric structures of the Fe2B2 surface with the corresponding distance between atoms. The purple and pink balls represent Fe and B atoms, respectively. (b) The frequency distribution of geometrically optimized Fe2B2. (c) Four structural fragments from MD simulation during a total time of 7.5 ps. (d) The band structure of Fe2B2. (e) The PDOS of Fe and B atoms of the Fe2B2 surface. The Fermi level is set at an energy of zero, as indicated by the gray dotted line.
Figure 2. (a) The geometric structures of the Fe2B2 surface with the corresponding distance between atoms. The purple and pink balls represent Fe and B atoms, respectively. (b) The frequency distribution of geometrically optimized Fe2B2. (c) Four structural fragments from MD simulation during a total time of 7.5 ps. (d) The band structure of Fe2B2. (e) The PDOS of Fe and B atoms of the Fe2B2 surface. The Fermi level is set at an energy of zero, as indicated by the gray dotted line.
Molecules 30 01778 g002
Molecules 30 01778 g003
Figure 3. (a) The top and side views for NO3− adsorbed at different adsorption sites on Fe2B2 surface and the corresponding adsorption energy values. (b) The electron density difference of NO3− adsorbed at the bridge site of Fe2B2 surface, where blue and yellow regions denote electron accumulation and depletion, respectively. (c) The PDOS of Fe atoms on Fe2B2 surface, NO3− adsorbed at the bridge site and an isolated NO3− molecule.
Figure 3. (a) The top and side views for NO3− adsorbed at different adsorption sites on Fe2B2 surface and the corresponding adsorption energy values. (b) The electron density difference of NO3− adsorbed at the bridge site of Fe2B2 surface, where blue and yellow regions denote electron accumulation and depletion, respectively. (c) The PDOS of Fe atoms on Fe2B2 surface, NO3− adsorbed at the bridge site and an isolated NO3− molecule.
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Molecules 30 01778 g004
Figure 4. (a) The reaction free energy changes of *NO3 to *NO2*OH on Fe2B2 and the corresponding structures of decomposed *NO2*OH adsorbed on the Fe2B2 surface. (b) The PDOS of Fe atoms and *NO2*OH, *NO*OH and *HN*OH on the Fe2B2 surface. (c) The Gibbs free energy change diagram for NO3RR and the corresponding adsorption configuration of intermediates on the Fe2B2 surface (* represents the active site).
Figure 4. (a) The reaction free energy changes of *NO3 to *NO2*OH on Fe2B2 and the corresponding structures of decomposed *NO2*OH adsorbed on the Fe2B2 surface. (b) The PDOS of Fe atoms and *NO2*OH, *NO*OH and *HN*OH on the Fe2B2 surface. (c) The Gibbs free energy change diagram for NO3RR and the corresponding adsorption configuration of intermediates on the Fe2B2 surface (* represents the active site).
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MDPI and ACS Style

He, Y.; Chen, Z.; Jiang, Q. Hydrogenation-Facilitated Spontaneous N-O Cleavage Mechanism for Effectively Boosting Nitrate Reduction Reaction on Fe2B2 MBene. Molecules 2025, 30, 1778. https://doi.org/10.3390/molecules30081778

AMA Style

He Y, Chen Z, Jiang Q. Hydrogenation-Facilitated Spontaneous N-O Cleavage Mechanism for Effectively Boosting Nitrate Reduction Reaction on Fe2B2 MBene. Molecules. 2025; 30(8):1778. https://doi.org/10.3390/molecules30081778

Chicago/Turabian Style

He, Yuexuan, Zhiwen Chen, and Qing Jiang. 2025. "Hydrogenation-Facilitated Spontaneous N-O Cleavage Mechanism for Effectively Boosting Nitrate Reduction Reaction on Fe2B2 MBene" Molecules 30, no. 8: 1778. https://doi.org/10.3390/molecules30081778

APA Style

He, Y., Chen, Z., & Jiang, Q. (2025). Hydrogenation-Facilitated Spontaneous N-O Cleavage Mechanism for Effectively Boosting Nitrate Reduction Reaction on Fe2B2 MBene. Molecules, 30(8), 1778. https://doi.org/10.3390/molecules30081778

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