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Article

ZnCu Metal–Organic Framework Electrocatalysts for Efficient Ammonia Decomposition to Hydrogen

by
Mingguang Ouyang
,
Geng Chen
,
Weitao Ning
,
Xiaoyang Wang
*,
Xiaojiang Mu
and
Lei Miao
*
Guangxi Novel Battery Materials Research Center of Engineering Technology, State Key Laboratory of Featured Metal Materials and Life-Cycle Safety for Composite Structures, School of Physical Science and Technology, Guangxi University, Nanning 530004, China
*
Authors to whom correspondence should be addressed.
Energies 2025, 18(14), 3871; https://doi.org/10.3390/en18143871
Submission received: 13 June 2025 / Revised: 11 July 2025 / Accepted: 16 July 2025 / Published: 21 July 2025
(This article belongs to the Special Issue Advanced Energy Conversion Technologies Based on Energy Physics)
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Abstract

The electrocatalytic decomposition of ammonia represents a promising route for sustainable hydrogen production, yet current systems rely heavily on noble metal catalysts with prohibitive costs and limited durability. A critical challenge lies in developing non-noble electrocatalysts that simultaneously achieve high active site exposure, optimized electronic configurations, and robust structural stability. Addressing these requirements, this study strategically engineered Cu-doped ZIF-8 architectures via in situ growth on nickel foam (NF) substrates through a facile room-temperature hydrothermal synthesis approach. Systematic optimization of the Cu/Zn molar ratio revealed that Cu0.7Zn0.3-ZIF/NF achieved optimal performance, exhibiting a distinctive nanoflower-like architecture that substantially increased accessible active sites. The hybrid catalyst demonstrated superior electrocatalytic performance with a current density of 124 mA cm−2 at 1.6 V vs. RHE and a notably low Tafel slope of 30.94 mV dec−1, outperforming both Zn-ZIF/NF (39.45 mV dec−1) and Cu-ZIF/NF (31.39 mV dec−1). Combined XPS and EDS analyses unveiled a synergistic electronic structure modulation between Zn and Cu, which facilitated charge transfer and enhanced catalytic efficiency. A gas chromatography product analysis identified H2 and N2 as the primary gaseous products, confirming the predominant occurrence of the ammonia oxidation reaction (AOR). This study not only presents a noble metal-free electrocatalyst with exceptional efficiency and durability for ammonia decomposition but also demonstrates the significant potential of MOF-derived materials in sustainable hydrogen production technologies.

1. Introduction

In recent years, as energy policy has shifted towards greener/sustainable technologies, hydrogen has emerged as a desirable energy source [1,2]. However, due to the inherent limitations of hydrogen with regard to storage and transportation, an increasing number of researchers are seeking a high-density hydrogen storage medium [3]. Ammonia exhibits a mass hydrogen storage density of up to 17.6 wt%, which is significantly higher than that of traditional materials such as methanol and water. Moreover, ammonia can be produced in substantial quantities through the Haber–Bosch process and transported using existing storage and transportation methods, thereby providing a substantial supply of low-cost hydrogen storage materials [4]. In addition, the electrocatalytic ammonia oxidation reaction (AOR) for hydrogen production offers a green and efficient alternative [5], featuring a theoretical voltage of 0.06 V, significantly lower than conventional water electrolysis (1.23 V) [6,7,8]. Additionally, this technology demonstrates important applications in ammonia fuel cells [7,8,9,10] and ammonia–nitrogen wastewater treatment [11,12]. Consequently, electrolytic ammonia hydrogen production represents a highly promising pathway for hydrogen generation.
However, the electrolytic AOR is a six-electron proton-coupled process with a high kinetic barrier that severely limits electrolysis efficiency. This results in slow reaction kinetics and increased energy requirements to overcome the reaction barrier [13], thereby restricting ammonia decomposition application. Consequently, developing low overpotential electrocatalysts for ammonia decomposition anode catalysts is imperative. Currently, AOR catalysts are categorized as either noble metal catalysts [14,15,16] or non-noble metal catalysts [17,18]. While noble metal catalysts reduce the reaction barriers effectively, most suffer from poor stability due to strong N* that causes rapid catalyst deactivation [3,4,19]. Meanwhile, considering that the raw materials of noble metal catalysts are too expensive, researchers started to search for cheap catalysts for efficient AOR. As a result, more and more research has focused on non-noble metal catalysts, and the current studies on non-noble metal catalysts are mainly focused on transition metal alloys [20], transition metal oxides [21], transition metal phosphorus/sulfides [22,23], and other types of catalysts. Compared with noble metal catalysts, the stability of non-noble metal catalysts has been substantially improved, Nevertheless, they exhibit substantially higher overpotentials than noble metal catalysts. Key challenges involve high kinetic barriers and catalyst stability issues. Noble metal catalysts undergo rapid deactivation owing to strong N* adsorption, while non-noble metal catalysts (e.g., transition metal alloys/oxides) exhibit limited activity.
Metal–organic frameworks (MOFs) feature high specific surface areas and tunability, enabling applications in energy, gas adsorption/desorption, and catalysis [24,25,26]. Although their high specific surface areas and abundant unsaturated metal sites provide numerous catalytic active sites, most MOFs exhibit poor conductivity due to insufficient charge carriers and transport pathways. Additionally, limited aqueous stability constrains their practical use in electrocatalysis [27,28,29,30,31,32,33]. In contrast to most MOFs, zeolitic imidazolate framework-8 (ZIF-8) demonstrates excellent water stability and low cost. We therefore selected ZIF-8 to explore the MOF potential in electrocatalytic ammonia decomposition. To enhance conductivity and active site utilization, ZIF-8 was synthesized in situ on nickel foam (NF) [34,35]. Given the established electrocatalytic performance of Cu-based catalysts in AOR [36,37,38,39,40], we introduced copper doping to provide additional active sites for improved AOR activity [41,42].
In this study, CuxZn1-x-ZIF/NF anodic catalysts were synthesized via a simple room-temperature aqueous synthesis method for AOR application. The materials were systematically characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) to analyze their crystal structures and chemical states. The SEM results demonstrated that the microstructures of Cu0.7Zn0.3-ZIF/NF with the unusual “nanoflower” structure exposed a greater number of active sites, thereby facilitating the catalytic reaction. The SEM results demonstrated that the microstructure of Cu0.7Zn0.3-ZIF/NF, featuring the distinctive “nanoflower” configuration, exhibited an increased number of active sites and thereby promoted the catalytic reaction. Moreover, electrochemical tests demonstrated that the Cu0.7Zn0.3-ZIF/NF catalyst exhibited a current density of up to 124 mA/cm2 (1.6 V vs. RHE). Subsequent chronoamperometry (i-t) tests further corroborated the remarkable stability of the catalyst. In this paper, Cu-doped ZIF-8/NF catalysts were synthesized by a simple room-temperature hydrothermal method. These catalysts have efficient electrocatalytic AOR performance and provide a new strategy for the application of MOF in electrocatalysis.

2. Materials and Methods

2.1. Synthesis of CuxZn1-x-ZIF/NF Catalysts

Preparation method: all reagents were directly used without further refinement. CuxZn1-x-ZIF/NF catalysts were synthesized via a room-temperature aqueous synthesis method, as shown in Figure 1. Briefly, 1.08 g of 2-methylimidazole (98%, Aladdin, Wallingford, CT, USA) and 0.66 g (2.2 mmol) of zinc nitrate hexahydrate (99%, Sinopharm Chemical Reagent Co., Ltd., Shanghai, China) were dissolved and mixed separately and then added to NF with full stirring for 3 h to make ZIF-8 grow uniformly on the NF surface. Finally, this mixture was dried in a 60 °C vacuum. The Zn-ZIF/NF catalyst was obtained by drying in a drying oven for 6 h; the molar ratio of the fixed metal source to 2-methylimidazole was kept constant. For Cu doping using copper nitrate trihydrate compounds (97%, Aladdin), the molarities of Cu and Zn sources were fixed at 2.2 mmol, and the catalysts were prepared by weighing x of the Cu source molarities/metal molarities and were denoted as CuxZn1-x-ZIF/NF, respectively.

2.2. Material Characterization

The surface morphology and microstructure of the catalysts were analyzed using a ZEISS Gemini 300 SEM (Zeiss, Oberkochen, Germany) at a 5 kV working voltage. X-ray energy-dispersive spectroscopy (EDS) mapping was performed at an acceleration voltage of 15 kV to acquire elemental composition. The phase structure of the catalyst was characterized using an A24A10 X-ray powder diffractometer from BRUKER AXS GMBH in Karlsruhe, Germany. Cu-Kα (λ = 1.54056 Å) was used as the X-ray radiation source, and all operating parameters were set to 40 kV and 40 mA. In the actual test, a scanning rate of 8°/min was selected for scanning in the range of 3–50°. The acquisition of transmission electron microscopy (TEM) data was performed using a JEOL JEM-2100plus from Akishima, Japan. X-ray photoelectron spectroscopy (XPS) signals were recorded using a monochromatic Al Kα X-ray source (1486.6 eV) and Thermo Scientific K-Alpha XPS (Waltham, MA, USA). The binding energy of C 1 s at 284.8 eV was utilized as a calibration standard.

2.3. Electrochemical Testing

All the electrochemical measurements of the AOR were carried out at room temperature using a CHI660E electrochemical workstation (CH Instruments, Shanghai, China), a three-electrode system consisting of a graphite rod as the counter electrode, a Hg/HgO electrode (filled with 1 mol/L KOH solution) as the reference electrode, and a prepared catalyst as the working electrode. The electrochemical tests were carried out in 1 M KOH + 1 M NH3·H2O electrolyte. The AOR performance was tested by recording linear sweep voltammetry (LSV) at a scan rate of 10 mV/s in the range of −0.4 V to 0.8 V vs. Hg/HgO. The OER performance of the catalysts was confirmed by the LSV recorded at the same scan rate in 1 M KOH electrolyte. Electrochemical impedance spectroscopy (EIS) was performed in the frequency range of 0.01–100,000 Hz to measure the resistance of the catalysts at the 1 M KOH working electrode for the prepared catalysts. All catalysts were activated in 1 M KOH electrolyte, and the activation process was confirmed by cyclic voltammetry (CV) curves. The measured potentials were converted to RHE by the following equation:
E (vs. RHE) = E (vs. Hg/HgO) + E(Hg/HgO) (vs. NHE) + 0.059 × pH
Chrono-current measurements usually involve the application of a constant voltage to the working electrode in order to check the change in its current. In this study, the electrode was tested for AOR stability at 0.6 V vs. Hg/HgO. Double-layer capacitance (Cdl) was determined by performing a CV scan of the catalyst in the range of 10–120 mV/s at a potential range without the Faraday process. This test was performed to obtain the electrochemically active surface area (ECSA) of the catalyst. Finally, the gases produced by the electrochemical reaction were directly analyzed by an online gas chromatograph (GC).

3. Results

3.1. Physical Characterization

In situ grown CuZn-ZIF/NF catalysts were synthesized on NF by a simple room-temperature hydrothermal method. In order to reveal the effect of different levels of Cu doping on the morphology of the catalysts, the catalyst materials were observed using a scanning electron microscope (SEM). As shown in Figure 2a of the microscopic morphology of the Zn-ZIF/NF catalyst, a clear dodecahedral crystal structure with sharp edges attached to the NF surface can be clearly seen. This indicates the successful preparation of the Zn-ZIF/NF catalyst. When Cu doping was up to 30%, it exhibited a structure similar to that of the original Zn-ZIF/NF, indicating that Cu doping had some influence on the morphology of the catalyst. As Cu is further doped to 50%, it appears to have a completely different microstructure from that of the parent, showing a peculiar nanoflower structure, which further verifies the effect of Cu doping on the catalyst’s microscopic morphology. Meanwhile, the XRD pattern (Figure S1) reveals distinct changes, and its entirely different peak structure from Zn-ZIF/NF is primarily attributed to the coordination of Cu with 2-methylimidazole ligands [43]. This evidence suggests that the morphological changes may be related to the coordination of Cu and dimethylimidazole. When Cu was doped to 70%, it still showed the nanoflower structure, and this special structure of branching and hollowing provided a high porosity for the catalyst, which in turn promoted the transport of reactants and gaseous products, and more active sites would be exposed on its surface, contributing to the continuation of the catalytic reaction [42]. However, the internal architecture in these nanodendrites was not observed under TEM (Figure S2), which is similar to the structure of most MOF materials [43,44]. With the further increase in Cu doping, the catalyst material further grows from the original nanoflower structure to a nanosphere when the metal in the catalyst material is completely replaced by Cu (Figure 2e). At this point, only Cu is coordinated with 2-methylimidazole. However, when Cu and Zn coexist, the morphological changes observed result from the combined effects of Cu coordination with 2-methylimidazole and Zn-Cu electron transfer. To further elucidate the Zn-Cu electron transfer, we performed a detailed electronic structure analysis, as shown in Figure S3. The band structure along the high-symmetry paths Γ-X-U|K-Γ-L-W-X and Γ-M-K-Γ-A-L-H-A|L-M|H-K reveals enhanced valence band dispersion along the Γ→L path with band crossing at EF, while localized conduction bands emerge near the K region. The Fermi level intersects hybridized bands at U|K and forms an energy gap at M. The projected density of states shows broadened Zn 3d states below EF (−4 to −2 eV) and Cu 3d states near EF with an unoccupied peak at +0.5 eV, alongside significant Zn/Cu orbital hybridization. These features directly corroborate the Zn→Cu charge transfer mechanism: The enhanced valence band dispersion along Γ-L indicates electron delocalization consistent with Zn electron depletion, while the conduction band localization near K reflects state localization corresponding to Cu electron capture, with the EF crossing at U|K confirming interfacial charge transfer channels that align with real-space differential charge density observations. EDS was utilized to ascertain the elemental compositions of the Cu0.7Zn0.3-ZIF/NF (Figure 2f) and Cu0.5Zn0.5-ZIF/NF (Figure S4) catalysts. The corresponding EDS mapping demonstrated that the structures in the nanoflowers were predominantly composed of the elements C, N, and Zn, thereby indicating that the elemental composition of the Cu0.7Zn0.3-ZIF/NF was similar to that of ZIF-8. Combined with the coordination of Cu with 2-methylimidazole ligands confirmed by XRD (Figure S1) [43], we propose that it forms a ZIF-like derivative. Additionally, the uniform distribution of Cu elements on the NF surface was found to facilitate the uniform distribution of active sites for the AOR reaction [41]. Furthermore, the EDS data (Figures S5 and S6) demonstrate that the Cu/Zn atomic ratio in Cu0.7Zn0.3-ZIF/NF and Cu0.5Zn0.5-ZIF/NF approximates the doping ratio, thereby indicating the successful introduction of Cu.
In order to further explore the reasons for the changes in the catalyst micro-morphology, the CuxZn1-x-ZIF/NF series catalysts were examined using X-ray photoelectron spectroscopy (XPS). The XPS results of the catalysts are shown in Figure 3. As illustrated in Figure 3a, the Zn 2p spectra for various catalysts are presented, and the investigation revealed the presence of two primary positions of spectral peaks, with locations in the vicinity of 1021 and 1044 eV, respectively. It has been confirmed that the presence of Zn2+ has been detected [38]. The binding energy at Zn 2p1/2 shows a gradual increase with elevated Cu doping, from 1021.78 eV for Zn-ZIF/NF to 1021.96 eV for Cu0.7Zn0.3-ZIF/NF, which is mainly attributed to the electron density redistribution induced by the high electronegativity of Cu [36]. Cu pulls electrons from the Zn-N ligand environment through metal–ligand bonding, enhancing the effective nuclear charge of Zn. This fine-tuning of the electronic structure optimizes the Lewis acidity of the Zn site, which significantly enhances the ammonia decomposition activity. From the Cu 2p spectrum (Figure 3b), it is evident that all samples exhibited two prominent peaks in the Cu 2p1/2 region, located at 933 and 934 eV, respectively. These peaks have been identified as Cu+ and Cu2+ species [36,39]. Specifically, the binding energies of the main peaks of the Cu 2p decreased in comparison to those of the Cu-ZIF/NF when the added Cu reached 50% and 70%. This decline was primarily attributable to electron transfer between Cu and Zn, a finding that aligns with the observations made in the Zn 2p spectra. Furthermore, the electron gain of Cu was reflected in its valence change, and the Cu+ content of Cu0.5Zn0.5-ZIF/NF and Cu0.7Zn0.3-ZIF/NF was higher than that of Cu-ZIF/NF (56%), reaching 64% and 80%, respectively. The electron transfer between Zn and Cu provided a sufficient active site for the AOR [37]. This results in a significant enhancement of the speed and efficiency of hydrogen production. Consequently, despite the similarity in microstructure exhibited by the Cu0.5Zn0.5-ZIF/NF and Cu0.7Zn0.3-ZIF/NF catalysts, the latter exhibited a higher content of Cu+. This result indicates that the higher AOR activity observed in the Cu0.7Zn0.3-ZIF/NF catalyst is due to its higher content of Cu+ (See Figure S7).

3.2. AOR Performance of Catalysts

To evaluate the AOR performance of each catalyst, measurements were conducted on a typical three-electrode system within a 1 M KOH + NH3·H2O electrolyte. The intrinsic activity of the catalysts was tested by LSV. As shown in Figure 4a, the Cu0.7Zn0.3-ZIF/NF catalyst had a potential of only 1.4 V (vs. RHE) at a current density of 10 mA/cm2, representing the lowest potential among all catalysts, highlighting its superior performance. Furthermore, it delivered an excellent current density of 124 mA/cm2 at 1.6 V vs. RHE. This enhanced activity is attributed not only to the “nanoflower” microstructure, which provides more exposed active sites and a large interfacial contact area, but also to the contribution of additional Cu sites to AOR performance. In conclusion, the negligible AOR activity of pure NF further confirms that Cu0.7Zn0.3-ZIF/NF provides the essential active sites for the reaction.
It is well known that the AOR competes with the oxygen evolution reaction (OER) in the process of ammonia electrolysis, and additional tests were performed to confirm that the observer activity primarily stemmed from ammonia oxidation rather than water splitting. A comparison of the LSV curves for the AOR and OER (Figure 4b) reveals significantly higher current densities for the AOR, despite the OER exhibiting a lower onset potential at 10 mA/cm2. To unequivocally identify the reaction occurring in the 1 M KOH + NH3·H2O electrolyte, gaseous products were analyzed by online GC. The results (Figure 4c) show that the reaction products consist predominantly of H2 and N2, with only a minor amount of O2, confirming that the primary process is an AOR. The Tafel slope analysis (Figure 4d) yielded values of 39.45, 31.39, and 30.94 mV dec−1 for Zn-ZIF/NF, Cu-ZIF/NF, and Cu0.7Zn0.3-ZIF/NF, respectively. The lower Tafel slope of the Cu0.7Zn0.3-ZIF/NF catalyst compared to both Zn-ZIF/ NF and Cu-ZIF/NF indicates superior electrochemical activity, and evidence was found to suggest that an elevated level of Cu+ is capable of significantly augmenting the catalytic activity of the AOR [37].
To better understand the electrochemical properties, double–double layer capacitance (Cdl) and electrochemical ac impedance spectroscopy (EIS) tests were performed (Figure 4e). The Cdl values ranked as follows: Cu0.7Zn0.3-ZIF/NF (20.09 mF cm−2) > Zn-ZIF/NF (10.58 mF cm−2) > Cu-ZIF/NF (9.94 mF cm−2). Cu0.7Zn0.3-ZIF/NF exhibits a higher Cdl than the recently reported Ni1Cu3@Ni-NDC (12.69 mF cm−2) [39], indicating abundant exposed active sites that facilitate catalyst–reactant contact and further demonstrating its superior performance. This large Cdl likely originates from the high BET of the ZIF material, with Cu doping further enhancing material defect density, leading to an increased electrochemically active surface area (ECSA). Additionally, Cu-doped catalysts (except Cu0.3Zn0.7-ZIF/NF, Figure S7) show a higher Cdl than Zn-ZIF/NF or Cu-ZIF/NF alone, which suggests a Zn-Cu synergistic effect that enhances catalytic performance.
The EIS results revealed that the complete substitution of Zn by Cu in 2-methylimidazole coordination significantly reduced Rct, which was 0.90 and 0.67 Ω for the Cu0.7Zn0.3-ZIF/NF and Cu-ZIF/NF catalysts. The lower Rct of Cu0.7Zn0.3-ZIF/NF correlates with its high AOR activity, as reduced Rct facilitates rapid electron transfer, thereby enhancing catalytic reactions and explaining the observed high AOR activity.
In addition to the above tests, stability is a crucial metric for catalytic performance. As shown in Figure S9, the i-t results of Cu0.7Zn0.3-ZIF/NF demonstrate excellent stability exceeding 10 h, further confirming its superior catalytic performance. Moreover, to better evaluate this catalyst, we compared it with the recently reported catalysts. Figure 4g shows that it exhibited the highest activity across various potentials, further evidencing its exceptional AOR performance. For a more direct comparison with prior studies, Table 1 summarizes the current density of selected catalysts at specified potentials. The data clearly demonstrate that our catalyst achieves 124 mA/cm2 at 1.6 V vs. RHE, significantly outperforming other catalysts. Notably, this performance substantially exceeds the 54 mA/cm2 reported for the recent MOF-based Ni1Cu3@Ni-NDC AOR catalyst, further highlighting the superior activity of Cu0.7Zn0.3-ZIF/NF. Furthermore, at a higher potential of 1.7 V, it delivers an even higher current density of 195 mA/cm2, further confirming its exceptional performance under elevated voltage conditions.

4. Conclusions

In this study, the electrocatalytic ammonia decomposition performance was significantly enhanced by the synergistic effect of Cu-doped ZIF-8/NF and structural modifications. The “nanoflower” structure of Cu0.7Zn0.3-ZIF/NF increased the exposure of active sites and the reactant transport efficiency, and its high porosity and uniform Cu distribution promoted the AOR kinetics. XPS confirmed the induction of electron transfer between Zn and Cu due to Cu doping, whereby Cu0.7Zn0.3-ZIF/NF exhibited the highest Cu+ content, providing sufficient active sites for the AOR and resulting in excellent catalytic performance. The catalyst achieved a current density of 124 mA/cm2 at 1.6 V vs. RHE, which was the highest at all potentials when compared with catalysts studied in recent years, and the Tafel slope (30.94 mV dec−1) indicated its efficient charge transfer characteristics. The poor conductivity of MOF materials was solved by the composite strategy of conductive substrate NF and ZIF-8, which provides a new idea for the application of non-noble metal catalysts in the field of energy conversion. The dynamic valence modulation and bimetallic synergistic mechanism can be further explored in the future.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/en18143871/s1, Figure S1: XRD diffraction patterns of each catalyst; Figure S2: TEM of Cu0.7Zn0.3-ZIF/NF; Figure S3: The band structure diagram of (a) Zn and (b) Cu, and (c) differential density of states results for Zn and Cu are presented herewith. In the band structure diagram of zinc, zinc is represented by gray, whereas copper is represented by blue; Figure S4: EDS of Cu0.5Zn0.5-ZIF/NF; Figure S5: Elemental atomic content ratio distribution diagram of Cu0.7Zn0.3-ZIF/NF catalyst; Figure S6: Elemental atomic content ratio distribution diagram of Cu0.5Zn0.5-ZIF/NF catalyst. Figure S7: LSV curves for each ratio of catalysts; Figure S8: Cdl performance of each catalyst; Figure S9: Stability testing of Cu0.7Zn0.3-ZIF/NF catalysts.

Author Contributions

Methodology, M.O. and G.C.; Investigation, G.C. and W.N.; Data curation, M.O.; Writing—original draft, M.O., G.C. and W.N.; Writing—review & editing, X.W., X.M. and L.M.; Supervision, X.W.; Project administration, L.M.; Funding acquisition, X.W. and L.M. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the Natural Science Foundation of Guangxi Province (Grant No. AB25069268), Basic Ability Promotion Project for Young College Teachers in Guangxi Zhuang Autonomous Region (Grant No. 2025KY0041) and the National Natural Science Foundation of China (Grant No. U21A2054).

Data Availability Statement

The original contributions presented in the study are included in the article/Supplementary Materials, and further inquiries can be directed to the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. CuxZn1-x-ZIF/NF catalyst preparation flow.
Figure 1. CuxZn1-x-ZIF/NF catalyst preparation flow.
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Figure 2. SEM images of (a) Zn-ZIF/NF, (b) Cu0.3Zn0.7-ZIF/NF, (c) Cu0.5Zn0.5-ZIF/NF, (d) Cu0.7Zn0.3-ZIF/NF, and (e) Cu-ZIF/NF; (f) EDS elemental mapping images of Cu0.7Zn0.3-ZIF/NF.
Figure 2. SEM images of (a) Zn-ZIF/NF, (b) Cu0.3Zn0.7-ZIF/NF, (c) Cu0.5Zn0.5-ZIF/NF, (d) Cu0.7Zn0.3-ZIF/NF, and (e) Cu-ZIF/NF; (f) EDS elemental mapping images of Cu0.7Zn0.3-ZIF/NF.
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Figure 3. XPS spectra of each CuxZn1-x-ZIF/NF catalyst: (a) Zn 2p; (b) Cu 2p.
Figure 3. XPS spectra of each CuxZn1-x-ZIF/NF catalyst: (a) Zn 2p; (b) Cu 2p.
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Figure 4. Electrochemical performance tests of CuxZn1-x-ZIF/NF in a three-electrode system: (a) LSV curves of each catalyst in 1 M KOH + NH3·H2O; (b) LSV curves of Cu0.7Zn0.3-ZIF/NF catalysts in 1 M KOH containing ammonia (without ammonia); (c) Cu0.7Zn0.3-ZIF/NF catalysts’ GC curves; (d) Tafel slope of each catalyst; (e) Cdl of each catalyst; (f) EIS comparison of each catalyst; (g) AOR performance of Cu0.7Zn0.3-ZIF/NF catalysts in comparison with other studies. Comparison [6,11,12,17,18,21,24,39,45,46,47,48,49,50,51,52].
Figure 4. Electrochemical performance tests of CuxZn1-x-ZIF/NF in a three-electrode system: (a) LSV curves of each catalyst in 1 M KOH + NH3·H2O; (b) LSV curves of Cu0.7Zn0.3-ZIF/NF catalysts in 1 M KOH containing ammonia (without ammonia); (c) Cu0.7Zn0.3-ZIF/NF catalysts’ GC curves; (d) Tafel slope of each catalyst; (e) Cdl of each catalyst; (f) EIS comparison of each catalyst; (g) AOR performance of Cu0.7Zn0.3-ZIF/NF catalysts in comparison with other studies. Comparison [6,11,12,17,18,21,24,39,45,46,47,48,49,50,51,52].
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Table 1. Comparison of AOR performance with the literature.
Table 1. Comparison of AOR performance with the literature.
CatalystElectrolytesAnode Potential (vs. RHE)Current Density (mA/cm2)Ref.
Cu0.7Zn0.3-ZIF/NF1 M KOH + 1 M NH31.6 V124This work
1.7 V195
Ni1Cu1Co0.5-S-T/CP1 M NaOH + 0.2 M NH4Cl1.6 V96Ref. [12]
NiCu3@Ni-NDC0.5 M KOH + 55 mM NH31.6 V54Ref. [39]
LNCO55-Ar0.5 M KOH + 55 mM NH4Cl1.6 V14Ref. [6]
Ni2P/NF1 M KOH + 5000 mg/L NH31.6 V8.2Ref. [18]
α-Fe2O30.1 M NaClO4 + 0.5 M NH31.6 V2.13Ref. [46]
Ni1Cu3-S-T/CP1 M NaOH + 0.2 M NH4Cl1.69 V110Ref. [24]
Ni1Cu3-N-C1 M NaOH + 0.2 M NH4Cl1.69 V88Ref. [21]
Ni4Cu5Fe1/C0.5 M KOH + 55 mM NH31.72 V92Ref. [52]
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Ouyang, M.; Chen, G.; Ning, W.; Wang, X.; Mu, X.; Miao, L. ZnCu Metal–Organic Framework Electrocatalysts for Efficient Ammonia Decomposition to Hydrogen. Energies 2025, 18, 3871. https://doi.org/10.3390/en18143871

AMA Style

Ouyang M, Chen G, Ning W, Wang X, Mu X, Miao L. ZnCu Metal–Organic Framework Electrocatalysts for Efficient Ammonia Decomposition to Hydrogen. Energies. 2025; 18(14):3871. https://doi.org/10.3390/en18143871

Chicago/Turabian Style

Ouyang, Mingguang, Geng Chen, Weitao Ning, Xiaoyang Wang, Xiaojiang Mu, and Lei Miao. 2025. "ZnCu Metal–Organic Framework Electrocatalysts for Efficient Ammonia Decomposition to Hydrogen" Energies 18, no. 14: 3871. https://doi.org/10.3390/en18143871

APA Style

Ouyang, M., Chen, G., Ning, W., Wang, X., Mu, X., & Miao, L. (2025). ZnCu Metal–Organic Framework Electrocatalysts for Efficient Ammonia Decomposition to Hydrogen. Energies, 18(14), 3871. https://doi.org/10.3390/en18143871

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