Enhanced electrochemical nitrate reduction to ammonia with nanostructured Mo₂C on carbon nanotube-reduced graphene oxide hybrid support

Abstract

The electrochemical nitrate reduction reaction (NO₃⁻RR) is emerging as a promising method for ammonia production under ambient conditions while simultaneously addressing nitrate pollution. Due to the complexity of NO₃⁻RR, which involves multi-electron/proton transfer and competes with the hydrogen evolution reaction (HER), the development of efficient electrocatalysts with high activity and stability is crucial. In this study, we report the use of Mo₂C nanoparticles homogeneously dispersed on a carbon nanotube-reduced graphene oxide hybrid support (Mo₂C/CNT-RGO) as an effective electrocatalyst for NO₃⁻RR. The three-dimensional CNT-RGO hybrid provides a large surface area for electrolyte contact, enhanced electrical conductivity, and prevents the aggregation of Mo₂C nanoparticles. Consequently, the Mo₂C/CNT-RGO electrocatalyst demonstrated high NO₃⁻RR performance, achieving a maximum NH₃ production rate of 5.23 mg h⁻¹ cm⁻² with a faradaic efficiency of 95.9%. Mo₂C/CNT-RGO also exhibited excellent long-term stability during consecutive cycling tests. This work presents a promising strategy for developing high-performance and durable NO₃⁻RR electrocatalysts.

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Introduction

Ammonia is an indispensable chemical in various industries, including fertilizers, explosives, pharmaceuticals, and plastics.^1,2 Additionally, it is considered a promising carbon-free energy carrier, offering a high energy density of 4.32 kW h L⁻¹.^3–6 However, industrial-scale ammonia synthesis remains reliant on the energy-intensive Haber–Bosch process, which requires high temperatures (400–600 °C) and high pressures (200–350 atm). This process is heavily dependent on fossil fuels,^7–10 contributing to 1–2% of the world's energy consumption and approximately 1% of global annual greenhouse gas emissions.^2,11 Therefore, developing an eco-friendly and sustainable approach for NH₃ production is of great importance.^12–14

Recently, the electrochemical nitrogen reduction reaction (NRR) has attracted significant interest as it utilizes water as a sustainable proton source under mild conditions.^15–17 However, NRR faces significant challenges, such as extremely low faradaic efficiency and NH₃ yield, attributable to the poor solubility of N₂ in water, highly stable N≡N bond (941 kJ mol⁻¹), and competing hydrogen evolution reaction (HER).^18–22 As an alternative to NRR, the research on electrochemical nitrate reduction reaction (NO₃⁻RR) is growing extensively.^23–25 This growth is driven by substantially higher NH₃ production rates compared to NRR, owing to the high solubility of NO₃⁻ in aqueous solutions and the lower bond energy of N=O (204 kJ mol⁻¹).^26–28 Moreover, NO₃⁻ is abundantly present as a contaminant in surface and groundwater due to the excessive use of nitrogen-containing fertilizers and chemicals, posing significant health risks, such as blue baby syndrome, non-Hodgkin's lymphoma, and other cancers.^26,29 Therefore, NO₃⁻RR offers a “two birds-one stone” solution by converting nitrate pollutants into value-added ammonia while simultaneously purifying water. However, the NO₃⁻RR is a complex process involving an eight-electron and nine-proton transfer with sluggish kinetics, and it includes several intermediates (e.g., NO₂⁻, N₂, and N₂H₄).^30–35 Thus, the development of efficient electrocatalysts with high activity and stability for NO₃⁻RR is imperative.

Various noble metal-based catalysts, including Pt, Rh, and Pd, have been employed as NO₃⁻RR catalysts, demonstrating high faradaic efficiency and stability.^36–38 However, their high costs and limited availability hinder the large-scale application of NO₃⁻RR systems. Transition metal carbides (TMCs) have emerged as promising alternatives to Pt-group metals in various electrocatalytic processes due to their electronic structures, which resemble those of noble metals.^39–41 Among TMCs, molybdenum carbides (Mo₂C) have been employed as catalysts for both NRR and NO₃⁻RR owing to their high adsorption capacity and catalytic hydrogenation ability for electron-rich nitrogenous molecules.^42,43 Nevertheless, the aggregation and large particle size of Mo₂C, typically resulting from high synthesis temperatures, reduce the exposure of active sites, and consequently impair catalytic activity.⁴⁴ Therefore, there remains significant scope for improving the activity and stability of Mo₂C, particularly for NO₃⁻RR applications.

To enhance the electrocatalytic activity of Mo₂C, one effective strategy is to compound it with carbonaceous materials as catalyst supports. Carbonaceous materials, such as carbon nanotubes (CNTs) and graphene, offer a large surface area and high electrical conductivity, which can enhance the performance of loaded Mo₂C.^45–49 However, when used individually, graphene tends to stack due to van der Waals forces and strong π–π interactions between nanosheets.^50,51 Similarly, CNTs have a tendency to bundle together, which reduces their surface area and electrochemical performance.⁵² The combination of CNTs and graphene (forming a CNT-RGO hybrid) addresses the stacking and bundling challenges associated with their individual use by creating a three-dimensional structure. This hybrid CNT-RGO framework not only provides a larger contact area with the electrolyte but also facilitates improved electron transfer, thereby enhancing the overall electrocatalytic activity.

In this study, nanostructured Mo₂C supported on a CNT-RGO hybrid (Mo₂C/CNT-RGO) was prepared using a modified urea-glass route for NO₃⁻RR.^53,54 The Mo₂C/CNT-RGO composite comprised uniformly dispersed 7 nm Mo₂C nanoparticles on a three-dimensional CNT-RGO hybrid support. The resulting Mo₂C/CNT-RGO demonstrated high NO₃⁻RR activity, achieving a maximum NH₃ production rate of 5.23 mg h⁻¹ cm⁻² and a faradaic efficiency (FE) of 95.9%, outperforming the Mo₂C/CNT and Mo₂C/RGO catalysts. Additionally, it exhibited excellent long-term stability over ten consecutive cycling tests. The enhanced NO₃⁻RR performance of Mo₂C/CNT-RGO can be attributed to the synergistic interaction between the active Mo₂C nanoparticles and the CNT-RGO hybrid support, which provided a high surface area and enhanced electrical conductivity.

Experimental

Materials

Molybdenum(V) chloride (MoCl₅, 99.6%) was obtained from Alfa Aesar. GO was prepared using Hummers’ method,⁵⁵ and CNT (CM-95) was sourced from Hanwha Nanotech. Dimethyl sulfoxide-d₆ (DMSO-d₆, 99.9 atom% D), ammonium chloride (NH₄Cl, ≥99.5%), ammonium-¹⁵N chloride (¹⁵NH₄Cl, ≥98 atom% ¹⁵N), and potassium sodium tartrate tetrahydrate (KNaC₄H₄O₆, 99%) were purchased from Sigma-Aldrich. High-purity N₂ (99.999%) and Ar (99.999%) gases were purchased from Hyundai Energy. Urea (99.0%), ethyl alcohol (C₂H₅OH, 99.9%, anhydrous), Nessler's reagent, and hydrochloric acid (HCl, 35.0–37.0%) were procured from Samchun Chemicals. Nickel foam (NF, 99.5%) was obtained from Goodfellow.

Synthesis of Mo₂C/CNT-RGO

Mo₂C/CNT-RGO composites were fabricated via a modified urea-glass route. GO and CNT were first dispersed in 15 mL of ethanol at a 1 : 1 weight ratio. Separately, 1.0 g MoCl₅ was dissolved in 2.53 mL of ethanol and added to the CNT-GO solution under vigorous stirring. After 30 min of stirring, 1.75 g of urea (molar ratio of urea/Mo = 8) was introduced into the mixture, which was subsequently stirred for an additional hour. The resulting solution was dried at 100 °C in an oven to remove excess ethanol and then calcined at 750 °C (with a ramp rate of 3 °C min⁻¹) for 3 h under N₂ flow. For comparison, Mo₂C/CNT and Mo₂C/RGO were synthesized using only CNT and RGO, respectively, following the same procedure. The nominal weight content of Mo₂C in each sample was fixed at ca. 80 wt%.

Characterization

The surface morphologies of the prepared catalysts were examined using field-emission transmission electron microscopy (FE-TEM, JEOL, JEM-2100F). The crystalline structures were characterized by X-ray diffraction (XRD, Rigaku, MiniFlex 600) with Cu-Kα (1.54 Å) radiation. X-ray photoelectron spectroscopy (XPS, Thermo-Scientific, K-alpha) was employed to analyze the chemical states of the samples. The produced ammonia was detected using a UV-Vis spectrophotometer (SHIMADZU, UV 2600i), while the gaseous products from the electrochemical experiments were analyzed by gas chromatography (GC, Agilent, 8890 GC) equipped with thermal conductivity detectors (TCD) using nitrogen as the carrier gas. Proton nuclear magnetic resonance (¹H NMR, Bruker, Advance Neo 600 MHz) was conducted to identify the nitrogen source in the ammonia. Electrical conductivity measurements were performed using a four-point probe (AIT, CMT-100S).

Electrochemical measurements

Electrochemical measurements were conducted using a potentiostat (AMETEK, VersaSTAT 3) in a three-electrode cell system. To prepare the working electrode, 30 mg of the synthesized catalyst was dispersed in a mixture of ethanol and deionized (DI) water (4 mL : 2 mL), followed by ultrasonication for 20 min to ensure uniform dispersion. The resulting catalyst ink was then loaded onto a 1 × 1 cm² nickel foam substrate, achieving a mass loading of 3 mg cm⁻². The Pt wire served as the counter electrode, while an Ag/AgCl (3 M KCl) electrode was used as the reference electrode. All potentials were converted to the reversible hydrogen electrode (RHE) using the equation: E_RHE = E_Ag/AgCl + 0.059 pH + 0.197. Prior to measurements, the electrolyte (0.1 M KOH with 0.1 M NaNO₃) was purged with Ar gas for 30 min to remove dissolved O₂. Cyclic voltammetry (CV) was conducted until steady-state polarization curves were achieved, using a scan rate of 50 mV s⁻¹. Linear sweep voltammetry (LSV) measurements were performed at a scan rate of 5 mV s⁻¹, and chronoamperometry tests were conducted for 1 h at various applied potentials. Electrochemical impedance spectroscopy (EIS) was performed over a frequency range from 100 kHz to 0.1 Hz with a 5 mV amplitude, and the resulting EIS data were fitted using Z-view software. The electrochemical double-layer capacitance (EDLC) was evaluated using CV at scan rates of 20–60 mV s⁻¹ in the non-faradaic potential region (0.1–0.2 V vs. RHE).

Results and discussion

Fig. 1 presents a schematic illustration of the synthesis process for Mo₂C/CNT-RGO. Molybdenum precursor (MoCl₅) in ethanol solution was mixed with the CNT-GO solution under vigorous stirring. After adding urea, a Mo–urea complex was formed on the CNT-GO support. This complex was then annealed at 750 °C for 3 h under N₂ flow to produce the Mo₂C/CNT-RGO composite. During annealing, Mo₂C crystallization occurred, along with the simultaneous reduction of GO to RGO, thus eliminating the need for toxic gases (e.g., methane) for carbide formation or an additional reduction step for GO. This facile method resulted in the uniform dispersion of Mo₂C nanoparticles on the CNT-RGO support. For comparison, Mo₂C/CNT and Mo₂C/RGO were synthesized using only CNT and RGO, respectively, following the same procedure.

Fig. 1 Schematic illustration of the synthetic method for Mo₂C/CNT-RGO.

Fig. 2a shows the TEM image of the Mo₂C/CNT-RGO catalyst, where CNTs are randomly distributed across the RGO layers, and spherical Mo₂C particles are uniformly dispersed on the CNT-RGO hybrid support without aggregation. The average particle size of Mo₂C is approximately 7 nm. The high-resolution TEM (HRTEM) image in Fig. 2b reveals lattice fringes of 0.224 and 0.240 nm, corresponding to the (101) and (002) facets of the Mo₂C phase, respectively. Fig. 2c and e present the TEM images of Mo₂C/CNT and Mo₂C/RGO, showing that ∼8 nm Mo₂C nanoparticles are exclusively anchored onto the CNTs and RGO, respectively. Similar to Fig. 2b, lattice spacings of 0.224 and 0.240 nm were detected, confirming the presence of the Mo₂C phase (Fig. 2d and f).

Fig. 2 TEM and HRTEM images of (a and b) Mo₂C/CNT-RGO; (c and d) Mo₂C/CNT; (e and f) Mo₂C/RGO.

The XRD patterns of the prepared catalysts are presented in Fig. 3a. All catalysts exhibit identical XRD patterns, aligning with the reference XRD patterns of hexagonal Mo₂C (JCPDS No. 00-035-0787). The observed peaks at 34.4°, 37.9°, 39.4°, 52.2°, 61.6°, 69.6°, 74.6°, and 75.5° correspond to the (100), (002), (101), (102), (110), (103), (112), and (201) planes of Mo₂C, respectively. No impurity peaks, such as Mo metal or MoO_x, were detected, confirming the successful synthesis of pure Mo₂C on the CNT-RGO, CNT, and RGO supports. The absence of peaks around 10° further indicates the conversion of GO to RGO during thermal annealing.⁵⁶

Fig. 3 (a) XRD patterns of the synthesized catalysts. XPS spectra of Mo₂C/CNT-RGO for (b) C 1s, (c) Mo 3d, and (d) N 1s.

The chemical states of Mo₂C/CNT-RGO were investigated via XPS, as shown in Fig. 3b–d. The survey spectrum of Mo₂C/CNT-RGO confirms the presence of C, Mo, N, and O elements (Fig. S1a†). In the C 1s spectrum (Fig. 3b), the deconvoluted peaks at 283.2, 284.6, 285.6, and 286.5 eV correspond to the Mo₂C, C–C, C–N, and C–O bands, respectively.^57,58 Fig. S1b† shows the C 1s spectrum for GO, where broad peaks observed at 280–290 eV indicate the presence of oxygen-containing functional groups such as hydroxyl, carboxyl, and epoxy groups. The significantly reduced peak intensities in the C 1s spectrum of Mo₂C/CNT-RGO suggest the conversion of GO to RGO during synthesis. The Mo 3d spectrum in Fig. 3c is deconvoluted into Mo²⁺ (228.3/231.5 eV), Mo⁴⁺ (229.2/233.6 eV), and Mo⁶⁺ (232.5/235.6 eV).⁵⁹ The Mo⁴⁺ and Mo⁶⁺ species are attributed to MoO₂ and MoO₃, respectively, due to unavoidable surface oxidation,^42,43,60 while the Mo²⁺ species stem from the Mo₂C phase.^61–63 The N 1s spectrum (Fig. 3d) exhibits three main peaks at 396.1, 398.3, and 400.6 eV, corresponding to N–Mo, pyridinic N, and graphitic N, respectively. The peak observed at 394.4 eV is assigned to Mo 3p due to binding energy overlap.⁵⁷ Fig. S2 and S3† display the XPS results of Mo₂C/CNT and Mo₂C/RGO, with their C 1s, Mo 3d, and N 1s spectra showing similarities to Mo₂C/CNT-RGO, indicating comparable chemical states among these catalysts.

The electrical conductivities of the catalysts were measured using the four-point probe method, with results summarized in Table 1. Among the catalysts, Mo₂C/CNT-RGO exhibited the highest electrical conductivity of 3.04 × 10³ S m⁻¹, followed by Mo₂C/CNT (1.98 × 10³ S m⁻¹), and Mo₂C/RGO (0.64 × 10³ S m⁻¹).

Table 1 Electrochemical properties of samples

Sample	Resistivity [ohm cm]	Electrical conductivity × 10^3 [S m^−1]
Mo2C/CNT-RGO	3.28 × 10^−2	3.04 (±0.14)
Mo2C/CNT	5.05 × 10^−2	1.98 (±0.57)
Mo2C/RGO	1.58 × 10^−1	0.64 (±0.07)

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The high electrical conductivity, which is crucial for enhanced NO₃⁻RR activity, was effectively achieved by employing the CNT-RGO hybrid support for Mo₂C.

Electrochemical NO₃⁻RR measurements were conducted in a 0.1 M KOH solution with 0.1 M NaNO₃ under ambient conditions. LSV curves were used to investigate the electrocatalytic responses of the catalysts both in the presence and absence of NO₃⁻ (Fig. S4a†). In 0.1 M KOH (dashed line), the LSV curves displayed a delayed onset potential. However, the addition of 0.1 M NaNO₃ (solid line) resulted in significant changes, including an increase in current density and a reduction in onset potential, indicating a strong NO₃⁻ reduction response. As shown in Fig. 4a, the LSV curves for the prepared catalysts in the presence of 0.1 M NaNO₃ demonstrated that Mo₂C/CNT-RGO exhibited a higher current density across the entire potential range, indicating its superior electrocatalytic activity for nitrate reduction.

Fig. 4 Electrochemical nitrate reduction performance of the prepared catalysts: (a) LSV curves in 0.1 M KOH with 0.1 M NaNO₃, (b) Tafel plots, (c) measured capacitive currents as a function of scan rate, (d) Nyquist plots, (e) NH₃ yields, and (f) FE_NH3 at each applied potential for 1 h.

Fig. 4b presents the Tafel plots of the prepared catalysts fitted to the Tafel equation (η = b log|J| + a, where b is the Tafel slope and J is the current density). A lower Tafel slope typically signifies better reaction kinetics. The Tafel slope of Mo₂C/CNT-RGO was 140 mV dec⁻¹, which is smaller than that of Mo₂C/CNT (172 mV dec⁻¹) and Mo₂C/RGO (188 mV dec⁻¹), suggesting that Mo₂C/CNT-RGO possesses higher electrocatalytic activity.

The cyclic voltammogram (CV) curves of the catalysts at various scan rates in the non-faradaic region are shown in Fig. S5,† and the corresponding electrochemical double-layer capacitance (C_dl) values are provided in Fig. 4c. Mo₂C/CNT-RGO exhibited a larger C_dl of 25.74 mF cm⁻² compared to Mo₂C/CNT (18.93 mF cm⁻²) and Mo₂C/RGO (17.01 mF cm⁻²). The C_dl is generally proportional to the contact area between the catalyst and electrolyte. Employing the CNT-RGO hybrid support leads to a larger contact area due to its 3D network structure, contributing to the enhanced NO₃⁻RR activity of Mo₂C/CNT-RGO.^64,65 This is further supported by the adsorption capacity (q_e, the adsorbed NO₃⁻ amount per unit catalyst amount) measurements, which confirm the effectiveness of the CNT-RGO hybrid.⁶⁶ In Fig. S6,† the Mo₂C/CNT-RGO recorded a much higher q_e for NO₃⁻ (67.5 g g_cat⁻¹) compared to Mo₂C/CNT (42. 9 g g_cat⁻¹) and Mo₂C/RGO (32.8 g g_cat⁻¹), indicating that CNT-RGO provides an enhanced surface area for reactant adsorption.

Fig. 4d shows the Nyquist plots of the catalysts obtained from electrochemical impedance spectroscopy (EIS). The charge transfer resistance (R_ct) at the catalyst-electrolyte interface is represented by the semicircle in the Nyquist plot and is inversely proportional to the electrocatalytic activity. The measured R_ct values were 16.2, 33.5, and 47.5 Ω for Mo₂C/CNT-RGO, Mo₂C/CNT, and Mo₂C/RGO, respectively, suggesting faster electron transfer and thus enhanced NO₃⁻RR activity of Mo₂C/CNT-RGO.

Chronoamperometry (CA) tests were conducted over a potential range from −0.3 V to −0.6 V for 1 h (Fig. S4b†). The concentrations of NO₂⁻, NO₃⁻, and NH₃ products were quantified using the colorimetric method, with their standard calibration curves shown in Fig. S7.† As illustrated in Fig. 4e and f, the Mo₂C/CNT-RGO demonstrated a higher NH₃ yield and FE_NH3 across the entire potential range compared to Mo₂C/CNT and Mo₂C/RGO. The NH₃ yield for Mo₂C/CNT-RGO increased with more negative potentials, reaching a maximum yield of 5.23 mg h⁻¹ cm⁻² at −0.6 V (Fig. 4e). In comparison, the maximum NH₃ yields for Mo₂C/CNT and Mo₂C/RGO were 4.55 and 4.53 mg h⁻¹ cm⁻², respectively. Additionally, Mo₂C/CNT-RGO achieved a maximum FE_NH3 of 95.92% at −0.3 V and maintained FE_NH3 values above 90% up to −0.5 V (Fig. 4f), demonstrating superior performance at relatively less negative potentials compared to other reported Mo-based catalysts (Table S1†). A decreasing trend in FE_NH3 was observed at −0.6 V, primarily due to the increasing dominance of HER at more negative potentials. Although Mo₂C/CNT and Mo₂C/RGO also demonstrated notable performance with FE_NH3 values of 85.25% and 84.39% at −0.3 V, respectively, their overall activity was significantly lower than that of Mo₂C/CNT-RGO. The three-dimensional CNT-RGO hybrid support offers a larger contact area with the electrolyte (as evidenced by Fig. 4c and Fig. S6†) and exhibits higher electrical conductivity (Table 1). Consequently, when combined with the active Mo₂C, this hybrid support structure contributes to the superior NO₃⁻RR performance of Mo₂C/CNT-RGO compared to Mo₂C/CNT and Mo₂C/RGO.

Long-term stability is crucial in determining the performance of catalysts. To evaluate the stability of Mo₂C/CNT-RGO, ten consecutive electrolytic cycles were conducted at −0.3 V. As shown in Fig. 5a, both the NH₃ yield and FE_NH3 remained stable throughout the cycling tests, indicating the catalyst's good stability. The morphology of Mo₂C/CNT-RGO after the cycling test was examined using TEM. As shown in Fig. S8a,† the Mo₂C particles remain well-dispersed on the CNT-RGO hybrid support without significant aggregation. Additionally, the lattice spacings of 0.224 nm and 0.240 nm observed in Fig. S8b† correspond to the (101) and (002) planes of Mo₂C, respectively. The similar morphology of Mo₂C/CNT-RGO after the cycling test suggests its structural stability.

Fig. 5 (a) Consecutive cycling test of Mo₂C/CNT-RGO at −0.3 V, (b) FEs of different products after NO₃⁻RR electrolysis, (c) amounts of NH₃ produced at −0.3 V for 1 h under different conditions, and (d) ¹H NMR spectra of standard solutions of ¹⁴NH₄Cl and ¹⁵NH₄Cl, along with electrolyte after NO₃⁻RR using ¹⁵NO₃⁻ and ¹⁴NO₃⁻ as nitrogen sources.

Possible by-products such as NO₂⁻ and H₂ were also measured (Fig. 5b). NO₂⁻ was detected only in the potential range of −0.3 to −0.5 V and was nearly absent at −0.6 V. As the potential becomes more negative, the FE of H₂ gradually increased due to the competing HER. Nevertheless, Mo₂C/CNT-RGO maintained high selectivity for NH₃ generation across all potentials.

To identify the nitrogen source in the produced NH₃, several control experiments were performed. Conducting CA tests at −0.3 V for 1 h in the absence of NO₃⁻ and under open-circuit potential (OCP) conditions resulted in negligible ammonia formation (Fig. 5c), confirming that the produced NH₃ originated from the NO₃⁻RR. Furthermore, a ¹⁵N isotopic labeling experiment was conducted using ¹H-NMR. In Fig. 5d, standard solutions of ¹⁴NH₄Cl and ¹⁵NH₄Cl exhibited characteristic triplet peaks of ¹⁴NH₄⁺ and doublet peaks of ¹⁵NH₄⁺, respectively. When ¹⁴NO₃⁻ (from Na¹⁴NO₃) was used as the reactant, triplet peaks corresponding to ¹⁴NH₄⁺ were observed, while doublet peaks corresponding to ¹⁵NH₄⁺ appeared when ¹⁵NO₃⁻ (from Na¹⁵NO₃) was used as the reactant. These results strongly confirm that the NH₄⁺ detected in the electrolyte originated from NO₃⁻RR and not from other contaminants.

Conclusions

In summary, nanostructured Mo₂C homogeneously dispersed on a CNT-RGO hybrid support was employed as a catalyst for NO₃⁻RR. The three-dimensional CNT-RGO hybrid offered a high surface area for electrolyte contact, enhanced electrical conductivity, and effectively dispersed the Mo₂C nanoparticles, preventing aggregation. Due to these advantages, the Mo₂C/CNT-RGO catalyst exhibited superior performance compared to Mo₂C/CNT and Mo₂C/RGO, achieving a FE_NH3 of 95.9% and a maximum ammonia yield of 5.23 mg h⁻¹ cm⁻². Additionally, the Mo₂C/CNT-RGO demonstrated good stability over ten consecutive cycling tests. Control experiments and the ¹⁵N isotopic labeling experiment confirmed that the generated ammonia originated from NO₃⁻, further validating the reliability of the results. This work presents a promising strategy for designing high-performance, stable NO₃⁻RR electrocatalysts.

Data availability

The data supporting this article have been included as part of the ESI.†

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

This study was supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP) and the Ministry of Trade, Industry & Energy (MOTIE) of the Republic of Korea (No. 20224000000080). This work was also supported by the research fund of Hanyang University and KRICT (HY-202400000003499).

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Footnote

† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d4dt02817a

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