Vapor‐Depositing Single‐Atom Iron Catalysts on Porous Carbon Nanosheets for Enhanced Oxygen Reduction

ABSTRACT

Single‐atom Fe catalysts (Fe–SACs) are recognized as the effective alternative to platinum‐based counterparts for the oxygen reduction reaction (ORR). Maximizing availability efficiency of active sites is of great significance for Fe–SACs in practical application. Herein, an efficient chemical vapor deposition route is developed to generate Fe–SACs on porous carbon nanosheets for ORR. Metal‐organic framework (ZIF‐8) is converted into highly porous and N,S‐co‐doped carbon nanosheets as Fe–SACs support. Ferrocene is sublimated and deposited on carbon nanosheet support to generate isolated single‐atomic Fe sites. Spectral and microscopic investigations confirm that Fe elements in Fe–SACs are highly dispersed in carbon support and coordinated asymmetrically with nitrogen and sulfur atoms in Fe–N₃S₁ configuration. The optimized Fe–SACs achieve outstanding alkaline ORR activity with a half‐wave potential of 0.91 V vs. RHE. After 10 000 cycles, the half‐wave potential only shows 16 mV decays. Furthermore, the rechargeable zinc–air batteries assembled with Fe–SACs as the air electrode can show a peak power density of 213 mW cm⁻² and retain a stable voltage plateau over 10 000 charge–discharge cycles. This work affords an efficient strategy for preparing highly exposed Fe–SACs for energy‐related applications.

An efficient chemical vapor deposition route is developed to prepare Fe single‐atom catalysts on porous carbon nanosheets. Fe–SACs provide enhanced ORR performance, especially for prominent durability in long‐term ORR test and charge/discharge cycling in Zn‐air battery operation.

1. Introduction

With the continuous development and advancement of sustainable clean energy technologies, oxygen‐driven energy conversion devices such as fuel cells and metal‐air batteries are gradually emerging as prospective candidates for various large‐scale applications [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]. However, their energy conversion efficiency is relatively hindered due to the sluggish ORR kinetics on the air electrodes [13, 14, 15, 16, 17]. Traditional platinum group catalysts are commonly employed to facilitate this electrochemical process and exhibit excellent ORR performances [18, 19, 20]. Nevertheless, their widespread adoption is severely curtailed by their exorbitant cost and limited availability [21, 22, 23, 24, 25]. Hence, there exists an urgent imperative to engineer a low‐cost and readily available ORR catalyst as a substitute for platinum‐based counterparts [26, 27, 28]. Recently, single‐atom catalysts have garnered substantial attention as viable alternatives to platinum‐based catalysts because of their large atomic efficiency and distinctive metal coordination centers [29, 30]. The so‐called single‐atom catalysts feature active centers composed of atomically dispersed metal sites coordinated with surrounding non‐metal species such as nitrogen to catalyze electrochemical reactions. Tremendous efforts are devoted to developing various efficient fabrication methods to synthesize single‐atom catalysts for ORR applications [31].

Single‐atom Fe catalysts have garnered extensive attention because of their outstanding ORR catalytic activity that can be comparable to Pt‐based counterparts [32, 33, 34, 35]. Anchoring single Fe atoms on carbon supports through high‐temperature pyrolysis has become a prevalent approach in current research [36, 37, 38]. However, due to the high mobility of metal atoms at elevated temperatures, Fe species may not be entirely coordinated in single dispersed state on carbon support [39]. It is possible to generate iron nanoparticles and clusters thus reducing atomic efficiency and subsequently diminishing the ORR catalytic performance [40, 41]. Additionally, metal‐organic frameworks (MOFs) are commonly used as precursors due to their uniform and abundant microporous and mesoporous structures to synthesize Fe–SACs [42, 43, 44, 45, 46, 47]. However, their 3D structures along with the derived catalysts are usually subjected inefficient participation of single‐atom active sites in ORR process because the fact that the real active sites are buried deeply within carbon layer and less capable of providing high catalytic performances [48, 49]. Therefore, it is great important to enhance the real contact area between Fe single‐atom active sites and oxygen intermediates, expose more active sites on the surface for ORR reactants, and efficiently prepare single‐atom catalysts while reducing the occurrence of metal nanoparticles and other species to improve atomic efficiency [50, 51, 52].

Herein, we present a potassium thiocyanate (KSCN) assisted pyrolysis strategy for etching polyhedral ZIF‐8 precursors into 2D porous carbon nanosheets with enriched structural defects and large specific surface area as ideal support to anchor Fe single atoms. At elevated temperatures, the molten KSCN salt can not only induce structural rearrangement of carbon support to form ultrathin 2D sheet‐like morphology but also generate highly exposed active sites and provide additional nitrogen and sulfur atoms. The gaseous ferrocene molecule is transported and deposited onto the porous structure of the carbon support under evaluated temperature and converted into iron atoms anchored by N and S species. Structural analysis confirms the isolated distribution of iron in single‐atom form in Fe–SACs without metal particle formation. Inductively coupled plasma optical emission spectroscopy (ICP‐OES) suggests that the metal loading in Fe–SACs is 0.74 wt.%. The ORR measurement shows that the optimized Fe–SACs can deliver outstanding catalytic activity and durability in 0.1 M KOH medium. The half‐wave potential is as high as 0.91 V vs. RHE. After 10 000 cycles of stability testing, the activity decay is detected to be only 16 mV. Furthermore, when employed as the air electrode materials for rechargeable zinc–air batteries, the Fe–SACs can achieve a peak power density of 213 mW cm⁻² at 330 mA cm⁻² current and exhibit long‐term stability over 10 000 charge–discharge cycles.

2. Results and Discussion

2.1. Synthesis and Characterizations of Porous Carbon Nanosheet‐Supported Fe–SACs

As illustrated in Figure 1a, this work presents the strategy of potassium thiocyanate (KSCN)‐assisted pyrolysis and chemical vapor deposition to synthesize single‐atom Fe catalysts. Initially, 2‐methylimidazole and zinc nitrate were mixed together to produce coordination reaction to fabricate polyhedral ZIF‐8 precursors (Figure S1). Subsequently, the ZIF‐8 precursors were mixed with KSCN and heated at 920°C for 2 h to obtain N,S‐doped carbon nanosheets (Figure S2). Upon elevation of the temperature, KSCN is pyrolyzed into inorganic potassium carbonate. The inorganic alkali metal carbonates can serve as 2D template for the formation of carbon nanosheets in the solid‐ state pyrolytic conversion [53]. KSCN serves not only as the carrier etchant but also as sulfur and nitrogen sources to modify the coordination environment of metal active centers. Finally, ferrocene vapor was deposited onto the surface of the porous carbon nanosheets under high temperature, forming stable coordination structures with N and S. Simultaneously, we adjusted the pyrolysis temperature and the amount of ferrocene, introducing 30, 45, and 60 mg of ferrocene at 950°C and 980°C, respectively, and named the resulting products accordingly, such as 45 mg 950 Fe–SACs. Subsequently, we evaluated the electrochemical performances of the synthesized catalysts. This method ensures that iron atoms can be stably and uniformly dispersed in the porous carbon support. Additionally, the KSCN‐assisted ZIF‐8 pyrolysis and vapor deposition route can overcome the drawbacks of the traditional and well‐developed MOFs precursor methods. In our designed preparation, the ZIF‐8 precursors are first pyrolyzed and converted into defective 2D N,S‐doped carbon nanosheets. This 2D carbon structure can serve as the most ideal support to strongly anchor single‐atom metal active sites, where all the single‐atom active sites can be exposed outside for ORR reactants to achieve real 100% atom efficiency. Therefore, compared with the traditional MOFs precursor methods, our designed process to synthesize single‐atom Fe catalysts is highly efficient. Furthermore, the present strategy can generate spatial confinement template to direct the carbon nanosheet formation, etching condition to form defect‐rich structure, and additional sulfur atoms to coordinate iron species for forming multiheteroatom‐coordinated active sites.

FIGURE 1.

Synthesis and structural characterization of Fe–SACs. (a) Schematic illustration of the proposed chemical vapor deposition procedure. (b) Typical SEM image. (c) TEM image. (d) HRTEM image and the inset showing SAED pattern. (e) AC‐HAADF‐STEM image. (f) and (g) HAADF‐STEM image and corresponding EDS elemental mappings.

Scanning electron microscopy (SEM) images (Figure 1b and Figure S3) reveal the successful transformation of the carbonaceous substrate from 3D polyhedral morphology to 2D sheet‐like structure through KSCN etching. This morphological evolution is further confirmed by transmission electron microscopy (TEM) images (Figure 1c and Figure S4), which also indicate the presence of abundant surface pores and the absence of nanoparticle formation in the material. High‐resolution TEM (HR‐TEM) image and electron selected area diffraction (SAED) pattern demonstrate the amorphous nature and defect‐rich structure of the material (Figure 1d). Figure 1e and Figure S5 present the aberration‐corrected high‐angle annular dark‐field scanning transmission electron microscopy (AC‐HAADF‐STEM) image to offer atomic‐level visualization of the material surface. The AC‐HAADF‐STEM image shows the uniform dispersion of Fe species within the carbonaceous substrate in isolated and individual atom form. The portions highlighted in circles represent the single Fe atoms, indicating the absence of Fe clusters or nanoparticles. This result suggests that the developed chemical vapor deposition method can effectively anchor Fe atoms on the defect‐rich and porous carbon substrate. STEM images and energy‐dispersive X‐ray spectroscopy (EDS) elemental mappings further demonstrate the uniform distribution of C, N, S, and Fe species across the carbonaceous substrate, reinforcing the confirmation that Fe is highly dispersed on the support without the formation of clusters or nanoparticles (Figure 1f,g and Figures S5 and S7). The metal loading of the catalyst was quantified by inductively coupled plasma optical emission spectrometry (ICP‐OES), yielding a value of 0.75 wt.% (Table S1).

X‐ray diffraction (XRD) patterns (Figure 2a) reveal two broad characteristic peaks corresponding to the pyrolytic carbon structure for all samples. No obvious peaks can be observed for Fe or Fe₂O₃ phases. This suggests that the Fe species did not aggregate into nanoparticles within the carbonaceous substrate. In Raman spectra (Figure 2b and Table S2), the D peak corresponds structural defects, while the G peak indicates the integrity of the graphitic lattice. The spectra reveal that the intensity of the D peak substantially exceeds that of the G peak for all samples, indicating a high density of structural defects. Nitrogen adsorption‐desorption measurements were conducted to evaluate Brunauer‐Emmett‐Teller (BET) surface area and porous characteristics of the materials (Figure 2c, Table S3 and Figure S8). The results demonstrate that with increasing ferrocene content and pyrolysis temperature, the average pore size of the materials exhibits an initial decrease followed by a subsequent increase overall. Concurrently, both BET surface area and total pore volume of the materials exhibit a trend of initial increase followed by a decrease. Notably, the Fe–SACs synthesized with 45 mg ferrocene at 980°C demonstrate the largest BET surface area (1243.6 m² g⁻¹) and pore volume (1.1 cm³ g⁻¹), alongside the smallest average pore size (4.3 nm). Given that the chemical vapor deposition method used for fabricating single‐atom catalysts is greatly dependent on the pore structure of substrate, the observed higher surface area and smaller average pore size are conducive to superior electrochemical performance compared to the other samples.

FIGURE 2.

Physicochemical and fine atomic structure confirmation of Fe–SACs. (a) XRD patterns. (b) Raman spectra. (c) Nitrogen adsorption‐desorption isotherms. (d) Fe K‐edge XANES profiles. (e) Fourier‐transformed EXAFS spectra. (f) WT‐EXAFS contour plots. (g) K‐space EXAFS fitting profile. (h) R‐space FT‐EXAFS fitting profile and the inset showing the atomic structure model with the cyan, brown, green, and black spheres representing Fe, S, N, and C atoms, respectively.

X‐ray photoelectron spectroscopy (XPS) was employed to confirm the elemental composition and chemical valence states of the Fe–SACs (Figures S9–S12 and Tables S4–S6). The survey XPS spectra reveal a relatively uniform elemental distribution across all samples. For the representative Fe–SACs synthesized with 45 mg ferrocene at 980°C, the nitrogen and sulfur amounts are detected to be 4.46 at% and 4.49 at%, respectively. High‐resolution N 1s spectra could be deconvoluted into three individual nitrogen species, related to pyridinic N (398.7 eV), pyrrolic N (401.6 eV), and graphitic N (403.6 eV). Additionally, the S 2p XPS spectrum shows peaks corresponding to thiophene sulfur (S 2p_3/2 at 165.0 eV and S 2p_1/2 at 168.5 eV) as well as oxidized sulfur species (163.8 eV). X‐ray absorption near‐edge structure (XANES) analysis was performed at the Fe K‐edge to elucidate the coordination environment of the active sites in Fe–SACs. The normalized XANES spectra are presented in Figure 2d. Compared to the reference spectra of Fe foil, FeO, Fe₂O₃, and FeS counterparts, the absorption edge of Fe–SACs is positioned among those of FeO and Fe₂O₃ references, suggesting that the oxidation state of Fe species lies among +2 and +3. Moreover, the Fe–SACs exhibit relatively smooth curve oscillations, which is consistent with the absence of long‐range order typical of single‐atom metal catalysts.

As shown in Figure 2e, the Fourier‐transformed (FT) k ³‐weighted EXAFS spectra reveal a prominent peak at 1.65 Å⁻¹ for Fe–SACs, related to the scattering pathway of Fe atoms coordinated with N atoms. Additionally, a peak at 2.6 Å⁻¹ is attributable to the scattering pathway of Fe–S coordination shell, indicating successful bonding between Fe and S atoms within the carbon matrix. Furthermore, no peaks corresponding to Fe–Fe interactions typically observed at 2.2 and 4.6 Å⁻¹ are detected in Fe–SACs, confirming the absence of iron clusters or nanoparticles, and underscoring the highly dispersed feature of Fe atoms. To further resolve the coordination environment in both k and R space, wavelet transform (WT) analysis of the Fe K‐edge EXAFS oscillations was carried out. The WT contour plot for Fe–SACs reveals a single intensity maximum at a low wavenumber of about 5.2 Å⁻¹, attributed to scattering from light atoms such as N and S. In contrast, the Fe foil, FeO, and Fe₂O₃ reference samples exhibit intensity maxima peaks between 7 and 8 Å⁻¹ due to contributions from Fe–Fe and Fe–O scattering pathways, highlighting a distinct difference from the pathways observed in Fe–SACs. This shift in the maximum intensity is attributed to contributions from Fe–N and Fe–S bonds. These analyses consistently indicate the atomic dispersion of Fe and its coordination with N and S atoms in Fe–SACs. The quantitative structural parameters of the central Fe active sites in Fe–SACs were obtained by the least‐squares EXAFS fitting method (Figure 2g,h and Table S7). The best‐fitting model indicates that each Fe atom in Fe–SACs is coordinated with three N atoms and one S atom in the first coordination shell within the carbon support. The fitting results show excellent agreement with the experimental data, confirming the proposed Fe–N₃S₁ configuration and reinforcing the conclusion that Fe species is atomically dispersed within the Fe–SAC architecture.

2.2. Electrocatalytic ORR Performances Over Fe–SACs

The ORR performances of Fe–SACs were first evaluated in alkaline medium (0.1 M KOH) through rotating disk electrode (RDE) measurements. Cyclic voltammetry (CV) curves (Figure 3a) reveal an obvious ORR peak at 0.910 V vs. RHE for Fe–SACs, accompanied by a large peak current density of 2.38 mA cm⁻². These values substantially exceed those of commercial Pt/C catalysts (0.848 V and 0.56 mA cm⁻², respectively), indicating the superior intrinsic activity of Fe–SACs. Linear sweep voltammetry (LSV) measurements were performed to detect the half‐wave potentials (E _1/2) of the synthesized catalysts. All Fe–SACs samples (Figures S13 and S14) exhibit higher E _1/2 values than that of commercial Pt/C catalysts. Notably, the optimized Fe–SACs (45 mg, 980°C) can achieve the highest half‐wave potential of 0.910 V vs. RHE with 5.9 mA cm⁻² limiting current density (Figure 3b). This excellent performance can be ascribed to the favorable pore architecture of the carbon support, characterized by a large specific surface area and small average pore diameter as discussed previously. The obtained half‐wave potential value outperforms that of the commercial Pt/C catalysts and the majority of recently reported non‐precious metal catalysts (Table S8 and S9), highlighting the remarkable ORR activity of the Fe–SACs.

FIGURE 3.

Electrocatalytic ORR property of Fe–SACs. (a) CV profiles in nitrogen‐ and oxygen‐saturated 0.1 M KOH electrolyte. (b) LSV plots measured under 1600 rpm rotation rate. (c) Half‐wave potential and kinetic current density values at 0.900 V vs. RHE. (d) Tafel slope curves measured under rotate rate of 1600 rpm. (e) LSV profiles under different rotation rates. (f) Comparisons of turnover frequency and mass activity at 0.850 V vs. RHE. (g) Methanol resistance measurement. (h) ORR polarization curves before and after 10 000 cycles. (i) Hydrogen peroxide yield and electron transfer.

To clarify the origin of the enhanced catalytic performance, the control experiments were performed on Fe,N–doped carbon (Fe–NC), N,S–doped carbon nanosheets (NSC), and N–doped carbon (NC). As shown in Figure S15, the LSV curves demonstrate that Fe–SACs exhibit markedly higher ORR activity than Fe–NC, NSC, and NC counterparts, suggesting that the atomically dispersed Fe species can serve as the primary active sites that is responsible for the improved ORR activity. The coordinated S atoms also contribute synergistically to the enhanced performance. The kinetic current density (J_k) at 0.900 V vs. RHE was derived from the LSV data using the Koutecky–Levich (K–L) equation (Figure 3c). The optimized Fe–SACs achieve a J_k of 8.9 mA cm⁻², significantly surpassing those of the control samples and Pt/C catalysts. This result further demonstrates the superior ORR kinetics facilitated by the atomically dispersed Fe–N₃S₁ active sites.

The ORR kinetics of Fe–SACs are further investigated by Tafel analysis. As shown in Figure 3d, the optimized Fe–SACs (45 mg, 980°C) deliver the lowest Tafel slope of 55.48 mV dec⁻¹ among all samples, which outperforms both the control samples and commercial Pt/C catalyst. This low Tafel slope is attributed to favorable ORR kinetics and rapid electron transfer at the catalyst surface. To confirm the ORR mechanism, LSV measurements were further performed on the optimized Fe–SACs at various rotation speeds ranging from 900 to 2500 rpm (Figure 3e). The corresponding K–L plots show good linearity within the potential window of 0.3–0.7 V vs. RHE (Figure S16), suggesting first‐order oxygen reduction reaction kinetics. Subsequently, the electron transfer number (n) was calculated to be 3.9 according to the K–L equation, suggesting that the Fe–SACs show four‐electron (4e⁻) ORR pathway. Mass activity (MA) and turnover frequency (TOF) are critical indicators for evaluating intrinsic activity and utilization efficiency of metal atoms in Fe–SACs catalyst.

As presented in Figure 3f, the Fe–SACs exhibit an MA of 2.77 A mg⁻¹ and a TOF of 1.87 e site⁻¹ s⁻¹ at 0.9 V vs. RHE. These values are significantly larger than that of Pt/C catalysts (MA 0.055 A mg⁻¹ and TOF 0.11 e site⁻¹ s⁻¹), indicating the excellent atom utilization and intrinsic ORR activity of the atomically dispersed Fe–N₃S₁ sites. Methanol crossover tolerance of the Fe–SACs was evaluated by chronoamperometric (CA) measurements upon methanol injection into oxygen‐saturated KOH electrolyte. The Fe–SACs deliver negligible current density fluctuation and maintain stable operation before and after methanol addition. In contrast, Pt/C catalyst displays significant current drop under identical conditions, confirming the excellent methanol crossover tolerance of Fe–SACs. Electrochemical impedance spectroscopy (EIS) was conducted to reveal the charge transfer behaviors. The Nyquist plots suggest that the Fe–SACs possess much lower charge transfer resistance (R _ct) compared to the control samples (Figure S17), indicative of enhanced electrode kinetics and more favorable electrode/electrolyte interface.

To assess the long‐term cycling durability of the Fe–SACs samples, the accelerated CV measurements were conducted under 0.2 V s⁻¹ scan rate. After 10 000 cycles, the half‐wave potential of Fe–SACs exhibits negligible negative shift of only 16 mV (Figure 2h), markedly superior to that of commercial Pt/C catalyst, which shows a decay of 64 mV under identical conditions (Figure S18). These results demonstrate the exceptional electrochemical stability of Fe–SACs for the oxygen reduction reaction. The hydrogen peroxide (H₂O₂) yield and the electron transfer number (n) of the Fe–SACs samples were calculated through rotating ring‐disk electrode (RRDE) measurements. As shown in Figure 3i, the Fe–SACs exhibit a relatively low H₂O₂ yield below 2.5% across the measured potential range, corresponding to an electron transfer number of 3.95. This value is in excellent agreement with the fitting result obtained from the K–L equation. The above analysis confirms the selectivity of its 4e⁻ transfer ORR pathway and efficient catalytic activity. Additionally, the double‐layer capacitance (C_dl) value of Fe–SACs is determined to be 58.8 mF cm⁻² (Figure S19 and Table S10), indicating a large accessible surface area and abundant active site exposure.

2.3. Zn–Air Battery Performance of Fe–SACs

The Fe–SACs were further evaluated in zinc–air batteries (ZABs) with 6 M KOH medium to realize their potential application due to their excellent oxygen reduction reaction activity. Figure 4a presents a schematic illustration of the assembled ZAB configuration, which is composed of zinc foil negative electrode and Fe–SACs‐based air cathode, alongside a Pt/C‐based counterpart for comparison. The as‐fabricated Zn–air battery could successfully power a light‐emitting diode (LED) panel, indicative of its practical applicability (Figure 4b). In addition to ORR activity, the oxygen evolution reaction (OER) performances of the air cathode are also critical for rechargeable ZAB operation during the charging process, as it governs the reaction kinetics. The OER overpotential of Fe–SACs is determined to be 447 mV at a current density of 10 mA cm⁻² from linear sweep voltammetry (LSV) measurements (Figure S20). The galvanostatic discharge performance of the assembled ZABs was investigated over a 5‐h test period (Figure 4c). The zinc–air battery assembled with Fe–SACs exhibits a stable voltage plateau ranging from 1.48 to 1.53 V, slightly outperforming the 1.46 V of the Pt/C‐based counterpart under identical conditions.

FIGURE 4.

Zn–air battery performance of Fe–SACs. (a) Schematic illustration of the configuration of assembled Zn–air batteries. (b) Digital photograph of a lighted LED panel device powered by the Zn–air batteries. (c) Open‐circuit voltage plots. (d) Discharge voltage profiles at stepwise increasing current densities. (e) Specific capacity profiles. (f) Polarization and power density curves. (g) Cycling stability at constant current density.

The rate capability of the Fe–SACs‐based zinc–air batteries was examined by galvanostatic discharge measurements at varying current densities (Figure 4d and Table S11). Compared to the Pt/C counterpart, the Fe–SACs‐based battery shows superior rate performance and maintains a higher discharge voltage plateau across all applied current densities. Moreover, upon returning the 1.0 mA cm⁻² current density, the voltage platform is fully recovered, suggesting the outstanding ORR activity and robust stability of the Fe–SACs cathode. The specific discharge capacities are normalized to the amount of consumed zinc as presented in Figure 4e. The Fe–SACs‐based battery shows a notable specific capacity of 804 mAh g⁻¹, surpassing that of the Pt/C‐based battery (757 mAh g⁻¹). This result further suggests the superior intrinsic ORR activity of the atomically dispersed Fe–N₃S₁ sites. The excellent ORR performances of Fe–SACs can be attributed to the unique asymmetric Fe–N₃S₁ coordination structure. Compared with the conventional and symmetric Fe–N₄ configuration, the asymmetric Fe–N₃S₁ structure can provide favorable electron distribution for appropriately absorbing oxygen intermediates [54, 55, 56].

The power density performances of the assembled batteries are displayed in Figure 4f. The Fe–SACs‐based battery could deliver a peak power density of 213 mW cm⁻² under a current density of 330 mA cm⁻², significantly surpassing that of the Pt/C‐based battery (130 mW cm⁻²). This remarkable improvement highlights the practical application of the Fe–SACs as high‐performance air cathode materials. Additionally, the long‐term cycling stability is considered as a critical parameter for rechargeable zinc–air batteries and evaluated at a constant current density of 5 mA cm⁻² (Figure 4g). The Fe–SACs‐based battery can maintain a relatively stable charge–discharge voltage plateau over 10 000 cycles, with a significantly lower overpotential compared to the Pt/C‐based battery. Additionally, Fe–SACs‐assembled ZABs show excellent electrochemical performances that surpass the reported catalysts (Table S12). The corresponding long‐term charge–discharge profiles (Figure S21) further confirm the exceptional cycling durability of the Fe–SACs cathode, highlighting its potential for practical energy storage applications.

3. Conclusion

In summary, we develop a vapor deposition method for the manufacture of N,S‐coordinated Fe–SACs as greatly effective ORR catalysts. The KSCN‐assisted etching of ZIF‐8 precursors can generate a highly porous sheet‐like carbon architecture with a large specific surface area and abundant structural defects. Subsequent high‐temperature sublimation of ferrocene under argon flow can facilitate the vapor deposition and anchoring of Fe atoms onto the defective carbon support, where they are stabilized through coordination with nitrogen and sulfur species. Microscopic and spectroscopic analyses evidently confirm the atomic dispersion of Fe species and reveal an asymmetric Fe–N₃S₁ coordination configuration within the carbon support. The as‐synthesized Fe–SACs show exceptional ORR activity in alkaline electrolyte, achieving a half‐wave potential of 0.91 V vs. RHE, which surpasses that of commercial Pt/C and the most previously reported M–N–C catalysts. Moreover, the Fe–SACs demonstrate remarkable durability with a negligible half‐wave potential decay of only 16 mV after 10 000 cycles. When employed as the air cathode in zinc–air batteries, the Fe–SACs achieve a peak power density of 213 mW cm⁻² at a current density of 330 mA cm⁻² and maintain a stable voltage platform over 10 000 charge–discharge cycles. This research presents an innovative strategy for the rational design of single‐atom Fe catalysts with tailored coordination environments and defect‐rich supports.

4. Experimental Section

4.1. Chemical Vapor Deposition of N,S‐Coordinated Fe–SACs

The N,S‐coordinated Fe–SACs were prepared via a facile strategy based on KSCN‐assisted pyrolysis and chemical vapor deposition. First, 2‐methylimidazole and zinc nitrate were reacted in methanol to synthesize ZIF‐8 precursors. After that, the as‐obtained ZIF‐8 powder and the KSCN etching agent were thoroughly mixed in a mass ratio of 1:0.75 in mortar with ethanol as solvent. The above mixture was subsequently heated in a tube furnace under argon atmosphere at a rate of 5°C min⁻¹ to 500°C for 2 h and then to 920°C for an additional 2 h. After naturally cooling down to room temperature, the resulting product was washed with sulfuric acid at 80°C for 12 h to remove residual impurities. The product was then thoroughly washed with deionized water and dried overnight at 60°C to obtain porous N,S‐doped carbon nanosheets. To introduce atomically dispersed Fe species, the as‐prepared carbon nanosheets (40 mg) were placed at one end of a ceramic boat, while a controlled amount of ferrocene (30, 45 and 60 mg) was placed at the opposite end of the same ceramic boat. The boat was inserted into a tube furnace with the argon gas flow directed from the ferrocene toward the carbon substrate. The system was heated to either 950°C or 980 °C at a ramp rate of 5°C min⁻¹ and held under argon to facilitate vapor‐phase deposition of Fe atoms. The resulting samples were designated according to the ferrocene mass and pyrolysis temperature; for example, 45 mg 950°C Fe–SACs corresponds to the sample prepared with 45 mg of ferrocene at 950°C.

Funding

The financial support was from the National Natural Science Foundation of China (22475017 and 52173273), the National Key Research and Development Program of China (2024YFB3713001), and the Fundamental Research Funds for the Central Universities (2022CX11013).

Conflicts of Interest

The authors declare no conflicts of interest.

Supporting information

Supporting File: smll74559‐sup‐0001‐SuppMat.pdf.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.