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Article

Constructing of Ni-Nx Active Sites in Self-Supported Ni Single-Atom Catalysts for Efficient Reduction of CO2 to CO

by
Xuemei Zhou
†,
Chunxia Meng
†,
Wanqiang Yu
,
Yijie Wang
,
Luyun Cui
,
Tong Li
and
Jingang Wang
*
Institute for Advanced Interdisciplinary Research (iAIR), School of Chemistry and Chemical Engineering, University of Jinan, Jinan 250022, China
*
Author to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Nanomaterials 2025, 15(6), 473; https://doi.org/10.3390/nano15060473
Submission received: 19 February 2025 / Revised: 16 March 2025 / Accepted: 19 March 2025 / Published: 20 March 2025
(This article belongs to the Special Issue Recent Progress on Single-Atom and Nanocluster Materials)
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Abstract

:
The electrochemical carbon dioxide reduction reaction (CO2RR) represents a promising approach for achieving CO2 resource utilization. Carbon-based materials featuring single-atom transition metal-nitrogen coordination (M-Nx) have attracted considerable research attention due to their ability to maximize catalytic efficiency while minimizing metal atom usage. However, conventional synthesis methods often encounter challenges with metal particle agglomeration. In this study, we developed a Ni-doped polyvinylidene fluoride (PVDF) fiber membrane via electrospinning, subsequently transformed into a nitrogen-doped three-dimensional self-supporting single-atom Ni catalyst (Ni-N-CF) through controlled carbonization. PVDF was partially defluorinated and crosslinked, and the single carbon chain is changed into a reticulated structure, which ensured that the structure did not collapse during carbonization and effectively solved the problem of runaway M-Nx composite in the high-temperature pyrolysis process. Grounded in X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS), nitrogen coordinates with nickel atoms to form a Ni-N structure, which keeps nickel in a low oxidation state, thereby facilitating CO2RR. When applied to CO2RR, the Ni-N-CF catalyst demonstrated exceptional CO selectivity with a Faradaic efficiency (FE) of 92%. The unique self-supporting architecture effectively addressed traditional electrode instability issues caused by catalyst detachment. These results indicate that by tuning the local coordination structure of atomically dispersed Ni, the original inert reaction sites can be activated into efficient catalytic centers. This work can provide a new strategy for designing high-performance single-atom catalysts and structurally stable electrodes.

1. Introduction

The rapid industrialization and extensive consumption of fossil fuels have driven a sustained increase in atmospheric CO2 emissions, posing global challenges such as climate change, sea-level elevation, ocean acidification [1,2,3]. To realize carbon peaking and carbon neutrality objectives, it is crucial to develop strategies that simultaneously mitigate atmospheric CO2 levels and convert this greenhouse gas into value-added products [4,5]. Electrochemical CO2 reduction reaction (CO2RR) technology has emerged as a promising solution, enabling the transformation of CO2 into industrially relevant chemicals and fuels (e.g., CO, CH3OH, C2H4) through sustainable pathways [6]. Notably, CO stands out as a versatile chemical feedstock for synthesizing essential industrial compounds including methanol and phosgene [7], making its production via CO2RR particularly valuable for carbon resource utilization. The CO2RR process involves a complex multi-step mechanism where proton-coupled electron transfer (PCET) constitutes the rate-determining step [8]. However, the inherent stability of CO2 molecules, primarily due to their high C=O bond energy (~806 kJ·mol−1) [9], imposes substantial activation barriers that necessitate high overpotentials. This thermodynamic limitation not only leads to excessive energy consumption but also intensifies competing side reactions, particularly the hydrogen evolution reaction (HER) [10]. Therefore, the rational design of electrocatalysts that can effectively lower activation potentials while maintaining high product selectivity and catalytic efficiency represents a critical scientific challenge that demands immediate attention [11].
The catalysts for the reduction of CO2 to CO included metal-based catalysts [12], alloy catalysts [13], metal oxides [14], carbon-based catalysts (doped carbon materials) [15], single-atom catalysts (SACs) [16,17]. Precious metal catalysts (notably Au [18], Ag [19], and Pd [20]) demonstrate superior performance owing to their distinctive electronic configurations, optimized adsorption energetics, and rapid charge transfer kinetics. Nevertheless, practical deployment of these catalysts faces three fundamental constraints: prohibitive material costs, limited natural abundance, and insufficient mechanistic understanding of active sites. Carbon-supported nonprecious metal catalysts (e.g., Ni [21], Fe [22]) present cost advantages but confront intrinsic electronic structure limitations. The mismatch between their Fermi levels/electron density distributions and the energy requirements for optimal CO2 adsorption results in unstable adsorbate configurations and elevated activation barriers [23]. This electronic incompatibility, coupled with insufficient CO2 binding strength, leads to inefficient molecular capture and HER dominance under low overpotentials [24]. Additional challenges include maintaining homogeneous active site distribution, as aggregation phenomena during synthesis cause site blocking and performance degradation [25]. The emergence of single-atom catalysis (SACs) since 2011 has fundamentally transformed CO2RR through dual synergistic mechanisms [26]: (1) Electronic modulation via metal-support interactions (e.g., Fermi level adjustment through charge transfer) enhances d-electron density near the Fermi level, effectively lowering CO2 activation barriers; (2) Atomic-level coordination engineering (e.g., tailoring N coordination numbers in M-Nx configurations) enables precise control over intermediate stabilization (e.g., *COOH) while suppressing HER. These characteristics, combined with near-theoretical atomic utilization, allow SACs to overcome the efficiency-selectivity paradox inherent to conventional catalysts. Particularly noteworthy are nitrogen-doped carbon matrices that simultaneously stabilize single metal atoms through robust M-N bonds and provide secondary active sites (e.g., pyridinic N) to synergistically enhance CO2 adsorption and proton transfer [27]. Among SAC configurations, Ni-based systems have emerged as frontrunners due to their optimal d-band positioning for intermediate binding [28]. The Ni-N4-C configuration is prone to form *COOH due to the presence of high free energy barriers [29,30]. However, the central metal atom geometry and electronic configuration can be changed by strategies such as screening the substrate and changing the coordination environment [31,32,33]. Axial modification of the Ni-N4 active center by heteroatom (N, P, B, and other atoms) doping method can promote CO2 activation, lower the free energy barrier required for the formation of *COOH, and promote the dissociation of CO, thus improving the kinetics and catalytic activity [34,35,36,37]. For example, Zhang et al. developed a new catalyst Ni6@Ni-N3 to unsaturated Ni-N3 sites by integrating Ni nanoclusters. Ni6@Ni-N3 exhibited up to 99.7% CO Faraday efficiency at 500 mA cm−2 under −1.15 V vs. RHE [38]. For instance, Zhao et al. developed MOF-derived Ni SACs with engineered coordination environments, which the faraday efficiency of CO could achieve 95.6% at −0.65 V vs. RHE [39]. Current research focuses on overcoming two critical synthesis challenges: (i) preventing metal aggregation during precursor reduction and pyrolysis, and (ii) developing self-supporting architectures. The fiber membrane treated with defluorination, and cross-linking operations does not collapse after carbonization and can maintain its structural integrity. Therefore, it can effectively solve the problem of uncontrolled M-Nx compounding in high-temperature pyrolysis [40,41]. Metal-doped EFCMs processed through nitrogenation and carbonization form binder-free electrodes that eliminate adhesive-induced site blocking, thereby enhancing both catalytic activity and operational stability [42].
In this study, electrospinning technology was used to fabricate a PVDF-Ni composite precursor with a high specific surface area and a nanoporous structure. The precursor was subjected to high-temperature carbonization and nitrogen doping, successfully resulting in the formation of a Ni-N4-C structure-based single-atom catalyst. During the carbonization process, defluorination and cross-linking of the PVDF fibers preserved the original three-dimensional network structure, allowing the material to be directly utilized as a self-supporting electrode. This eliminated the instability issues often associated with the detachment of powder catalysts. The self-supported catalyst demonstrated excellent selectivity in the electrochemical reduction of CO2 to CO.

2. Materials and Methods

2.1. Materials

Polyvinylidene difluoride (99%, (CH2CF2) n) were purchased from Solvay. Nickel chloride hexahydrate (99.9%, NiCl2·6H2O), N,N-dimethylformamide (99.9%, DMF), nano magnesium oxide (99.9%, MgO), acetone (99.9%, CH3COCH3), p-xylene diamine (99%, C6H4(CH2NH2)2) were from Shanghai McLean Reagent Co., Ltd. Argon (99.7%, Ar), carbon dioxide (99.9%, CO2) and ammonia (99.9%, NH3) were from Jinan Yao tian Instrument Jinan., China.

2.2. Preparation of Catalysts

Three types of catalysts, namely Ni-doped PVDF catalyst carbonized in an argon-ammonia blended atmosphere (Ni-N-C), Ni-doped PVDF catalyst carbonized in an argon environment (Ni-C), and PVDF carbonized under an ammonia atmosphere (N-C), were synthesized. Taking Ni-N-CF as an example: 1.2 g of polyvinylidene fluoride tetrachloroethylene (PVDF) was mixed thoroughly with 4 mL of acetone and 6 mL of N, N dimethylformamide (DMF). An amount of 0.0012 g of nickel (II) chloride hexahydrate (NiCl2·6H2O) was added into it. Throughout 12 h of magnetic agitation at 25 °C, the precursor mixture gradually transformed into a viscously uniform system suitable for subsequent spinning processes. The spinning solution was loaded into a 10 mL medical syringe and electrospun under a high-voltage electric field of 20 kV. The process parameters were set as follows: needle-to-collector distance was 15 cm, collector rotation speed was 80 rpm, and peristaltic pump flow rate was 1.02 mL h−1. The resulting fibrous membrane, denoted as Ni-PVDF, was vacuum-dried at 80 °C for 12 h and subsequently densified using a hot press (2 MPa, 120 °C). A cross-linking solution was prepared by mixing 15 mL of methanol, 1 g of NaOH, 4 g of 1,4-phenylenediamine, and 2 g of MgO nanoparticles. The Ni-PVDF membrane underwent sequential treatments: (1) immersion in 1 M HNO3 for 1 h; (2) rinsing with deionized water for 6 h; (3) ultrasonic cleaning in methanol and n-hexane for 2 h each. This cleaning cycle was repeated three times, followed by vacuum drying at 60 °C. Controlled carbonization was performed in a tube furnace under an Ar/NH3 mixed gas flow (1:2). The temperature was ramped at 5 °C min−1 to 1000 °C and maintained for 2 h, yielding nitrogen-doped nickel-carbon composites (denoted as Ni-N-CF). Control samples were prepared under modified conditions: (1) N-CF synthesized without nickel precursors; (2) Ni-CF obtained via carbonization in pure Ar atmosphere.

2.3. CO2 Reduction Reaction Measurements

All electrochemical tests involved in this experiment were carried out using a traditional three-electrode system in CO2 saturated NaHCO3 solution (0.5 mol/L) using a closed classical H electrolyzer equipped with an electrochemical workstation (CHI660D, Shanghai Chenhua Instrument Shanghai, China). The prepared catalyst carbon fiber membrane was cut into a rectangle of 2 cm × 1 cm as the working electrode (to ensure that its area immersed in the electrolyte was 1 cm × 1 cm), the reference electrode was a saturated calomel electrode (SCE), and the Pt piece was the counter electrode. The left and right chambers were filled with 15 mL of CO2-saturated NaHCO3 solution (0.5 mol/L) during testing. Prior to testing the CO2RR performance, a 30 min purge was performed with a 30-sccm flow rate of Ar to test the LSV, followed by a 30 min purge with a 30-sccm flow rate of CO2 to test the LSV. The two LSV curves were compared to derive a range of potentials for the test. A potential was applied to the catalyst during the test using an electrochemical workstation, and after 1 h of reaction, 10 mL of gas was removed using a syringe and kept sealed to test the gas phase product. The liquid phase products were tested by removing 10mL of liquid phase products. The gas phase and liquid phase data were tested at different voltages. All applied potentials were converted into reversible hydrogen electrode (RHE) using the following equation: E (vs. RHE) = E (vs. SCE) + 0.24 + 0.059 × pH. The gas-phase products were analyzed by online gas chromatography (GC, HF-901, Shandong Huifen Instrument Jinan, China) equipped with a thermal conductivity detector (TCD) and a flame Ionization detector (FID). No liquid products were detected by nuclear magnetic resonance (NMR) spectrometer.

3. Results and Discussion

The synthesis procedure of the Ni-based N-doped carbon fiber catalyst (Ni-N-CF) is shown in Figure 1a. The preparation process of the catalyst in this study mainly involved three key steps. First, the precursor was prepared using electrospinning technology. Second, the precursor underwent defluorination and cross-linking to form a stable carbon skeleton structure. Finally, the target sample was obtained by nitrogen-doped carbonization at a high temperature of 1000 °C. The specific preparation procedure is described in detail in the Supporting Information, experimental section. Figure 1b,e are digital photographs of the Ni-PVDF fiber membrane before and after carbonization. It can be observed that Ni-N-CF did not exhibit significant shrinkage after calcination. A cross-sectional image was obtained using SEM, measuring the average thickness of the electrode to be 180 ± 5 μm (Figure S1, Supporting Information). The electrode has a single-layer structure, but its interior consists of numerous intersecting fibers, with no additional functional layers stacked on top. SEM results demonstrate that the internal structure of both Ni-PVDF (Figure 1c,d) and Ni-N-CF (Figure 1f,g) fiber membranes maintained a similar three-dimensional mesh structure before and after carbonization. Infrared evidence (Figure S2, supporting information) showed that the double bonds of different carbon chains within PVDF underwent cross-linking to form a network structure [43,44]. The surface of the Ni-PVDF fibers was relatively smooth, while after carbonization, the fiber surface exhibited noticeable pits and irregular rough structures. Fiber diameter analysis revealed that the average fiber diameter before carbonization was approximately 0.72 μm (Figure S3, supporting information), and after carbonization, it increased slightly to 0.76 μm (Figure S4, supporting information). These results indicated that a three-dimensional network self-supporting catalyst with a stable structure has been prepared.
Structural characterization of the catalyst was conducted using TEM, SAED, EDS, and nitrogen adsorption–desorption analysis. As shown in Figure 2a, the Ni-N-CF catalyst exhibits a uniform internal architecture with distinct brightness variations, revealing a well-developed porous structure. Contact angle measurements (Figure S5, supporting information) demonstrate significantly enhanced hydrophilicity (contact angle reduced from 115.2° to 11.92°) after nitrogen doping and carbonization, which facilitates CO2 adsorption/desorption processes. Atomic-scale imaging in Figure 2b reveals a characteristic 0.34 nm lattice spacing corresponding to the (002) plane of graphitic carbon, with no observable metallic Ni crystalline phases, consistent with the diffuse SAED pattern (inset). As shown in Figure S6 (supporting information), the XRD patterns exhibit two characteristic diffraction peaks at 23° and 40°, corresponding to the (002) and (111) crystallographic planes of amorphous carbon, respectively. Elemental mapping in Figure 2c confirms the homogeneous distribution of C, N, O, and Ni throughout the carbon nanofibers, indicating excellent metal dispersion. Nitrogen sorption analysis reveals a type IV isotherm with H3 hysteresis (Figure 2d), characteristic of mesoporous materials, yielding a remarkable specific surface area of 606.83 m2·g−1 for Ni-N-CF-73-fold higher than uncarbonized Ni-PVDF (8.36 m2·g−1). The corresponding pore size distribution (Figure 2e) confirms a hierarchical pore structure spanning micro- (<2 nm), meso- (2–50 nm), and macropores (>50 nm), with a total pore volume of 0.55 cm3·g−1. This three-dimensional interconnected porosity not only provides abundant active sites through structural defects created during N-doping but also establishes efficient transport pathways for CO2 molecules and electrolyte ions [45,46].
The phase composition and structure of the Ni-N-CF, Ni-CF, and N-CF catalysts were systematically characterized using HAADF-STEM, Raman spectroscopy, XPS, and XAFS. Figure 3a,b shows HAADF-STEM images at different magnifications. No large Ni nanoparticles were observed; the bright spots (regions indicated by red circles) in the images correspond to Ni single atoms [47]. Figure 3c displays the Raman spectra featuring characteristic D (1340 cm−1) and G (1590 cm−1) bands [48]. The progressive increase in ID/IG ratio from 2.35 (N-CF) to 2.53 (Ni-N-CF) with simultaneous Ni/N doping suggests enhanced graphitic ordering [49]. Furthermore, a 5 cm−1 positive shift in the G-band position observed for Ni-N-CF compared to Ni-CF indicates nitrogen-induced lattice distortion, which generates structural defects exposing additional active sites for catalytic reactions [50]. To further investigate the relationship between the electronic structure of the catalyst and its catalytic activity, XPS analysis was performed. The results in Figure S7 (supporting information) revealed that Ni-N-CF contained only nitrogen (N), carbon (C), and oxygen (O); Ni-CF exhibited carbon and oxygen, while N-CF showed the presence of nitrogen and oxygen. Figure 3d showed the high-resolution N1s spectrum of the Ni-N-CF catalyst. Compared to the N1s spectrum of N-C shown in Figure S8 (supporting information), a distinct Ni-N bond peak was observed at 399.5 eV, indicating that Ni metal atoms form a stable Ni-N structure within the carbon fiber framework through coordination with N atoms. Additionally, peaks for pyridinic nitrogen (398.3 eV), pyrrolic nitrogen (400.8 eV), graphitic nitrogen (402.1 eV), and oxidized nitrogen (403.8 eV) were also observed, confirming the presence of various nitrogen doping types in the catalyst [51,52]. In particular, the high content of pyridinic nitrogen was likely to facilitate the activation of CO2 molecules, thereby promoting the catalytic reaction [53,54,55]. The content of pyridinic nitrogen in the Ni-N-CF catalyst was significantly higher than that in the Ni-CF catalyst (Figure S9, supporting information). Further analysis of the high-energy-resolution O 1s spectrum of the Ni-CF catalyst demonstrated the existence of Ni-O bonds (Figure S10, supporting information). The XAFS spectrum of the Ni K-edge was characterized (as shown in Figure 3e) to gain deeper insights into the chemical state and coordination environment of Ni. An analysis of this figure revealed a slight right shift for Ni-N-CF, indicating that the average oxidation state of Ni atoms in the catalyst was above zero. As shown in Figure 3e, the Ni K-edge XANES spectra show that the near-edge absorption energy of Ni-N-C was located between those of the Ni foil and NiO, indicating that the average valence state of Ni in Ni-N-C was between 0 and +2. The fingerprint peak was around 8336 eV, which was assigned to the 1s-4pz transition of the square planar Ni-N4 moiety [56]. Figure 3f displayed the Fourier transform of the EXAFS spectrum with k3-weighted χ(k) function, where only one peak at 1.39 Å was observed in Ni-N-CF, corresponding to the Ni-N bond [16]. This indicated that Ni atoms were isolated and dispersed on the nitrogen-doped carbon support. The ICP-MS analysis (Table S1, Supplementary Materials) indicated that the Ni content in Ni-N-CF was 0.08 wt%. The above results demonstrate the successful preparation of the Ni-N-CF single-atom catalyst.
To investigate the catalytic activity of the Ni-N-CF catalyst designed, particularly the advantages of the N-doped mesh self-supporting structure, we conducted CO2RR tests using a three-electrode system in an H-type electrolytic cell. All applied potentials were referenced to the reversible hydrogen electrode (RHE) in this work. As the LSV curve in Figure 4a, the Ni-N-CF catalyst showed a more significant increase in the current density for CO2 in CO2-saturated NaHCO3, which was attributed to the CO2 reduction. At −0.65 V vs. RHE, Ni-N-CF exhibited a current density of 2.8 mA cm−2, surpassing N-C (0.1 mA cm−2) and Ni-CF (1.5 mA cm−2). The activity and selectivity of the Ni-N-CF catalyst were tested after one hour of electrolysis at a constant potential. Only CO and H2 were detected over the whole investigated potential range. The maximum FE of CO reached 92% at −0.65 V vs. RHE (Figure 4b), which the selectivity of Ni-N-CF for reduction to CO was much higher than N-C (1%) and Ni-CF (3%) (Figure 4c). In addition, Figure 4d showed that the current density for CO2RR of Ni-N-CF was superior to that of other catalysts at all tested potentials. The results obtained from XPS, aberration-corrected microscopy, XANES, and electroreduction data indicated that nitrogen doping keeps nickel in a low oxidation state, and Ni-N was the main active site for CO2RR in Ni-N-CF. This confirms the significant role of nitrogen doping in enhancing the performance of Ni-CF, thereby strengthening the argument for the synergistic mechanism between nickel single atoms and nitrogen doping. As shown in Figure 4e, during the continuous 12 h CO2 reduction to CO reaction at -0.65 V vs. RHE, the Ni-N-CF catalyst exhibits no significant decay in FE and current density, indicating its robust stability. In addition, compared to other recently reported Ni-N4 catalysts, Ni-N-CF seems to exhibit superior selectivity for CO products in CO2 RR [39,57,58,59,60,61,62,63] (Table S2, supporting information). These results indicated that Ni-N4-C species possess excellent activity and selectivity, with Ni-N being the decisive catalytic site in the carbon dioxide reduction process. This is consistent with reported findings in the literature on M-N-C catalysts [64,65].

4. Conclusions

In summary, we propose a rational design and simple synthesis method to construct an atomically dispersed nitrogen-doped three-dimensional network carbon nanofiber membrane (Ni-N-CF) electrocatalyst. The network structure formed after the cross-linking of PVDF fiber membrane can inhibit the structural collapse during carbonization. The Ni single atoms and nitrogen doping form Ni-N coordination on the self-supported porous fiber membrane, which is beneficial for the reduction of CO2 to CO. The Ni-N-CF structure exhibits excellent selectivity for CO production (with a Faradaic efficiency of 92%) and long-term stability for CO2RR at a low overpotential (−0.65 V RHE). XPS, XAFS, and electrochemical performance analyses confirm that Ni-N is the main active site of Ni-N-CF. This study provides a practical and efficient approach for developing atomically scaled three-dimensional electrocatalysts.

Supplementary Materials

The following supporting information can be downloaded at: www.mdpi.com/article/10.3390/nano15060473/s1, Figure S1: Different cross-sections of the same catalyst in SEM and their dimensions; Figure S2: Infrared spectra of PVDF, PVDF after defluorination and PVDF after cross-linking; Figure S3: Diameter distribution of Ni-PVDF membrane fibers; Figure S4: Fiber diameter distribution chart of Ni-PVDF membrane after carbonization; Figure S5: Contact angles of Ni-PVDF membrane before and after carbonization; Figure S6: XRD spectra of Ni-N-CF, Ni-CF and N-CF catalyst; Figure S7: XPS spectra of Ni-N-CF, Ni-CF and N-CF catalyst; Figure S8: XPS spectra of N-CF. (a) XPS survey spectra. (b) N 1s; Figure S9: XPS spectra of Ni-N-CF. (a) XPS survey spectra. (b) Ni 2p. (c) C 1s and (d) O 1s; Figure S10: XPS spectra of Ni-CF. (a) XPS survey spectra. (b) N 1s. (c) C 1s and (d) Ni 2p; Table S1: ICP-MS Data Table of Ni-N-CF; Table S2: Comparison of recent Ni-N4 electrocatalysts for CO2RR to CO.

Author Contributions

X.Z.: writing—original draft preparation, methodology. C.M.: data curation, writing—reviewing and editing. W.Y.: data curation, writing. Y.W.: writing—reviewing and editing. L.C.: writing—reviewing and editing. T.L.: reviewing and editing. J.W.: methodology, supervision. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by City-school integration development strategic project of Jinan (JNSX2021015), the Major Science and Technology Innovation Project of Shandong Province (2024ZLGX01) and Jinan University Cultivation Fund of University of Jinan (XKY2310).

Data Availability Statement

Data are contained within the article and supplementary materials.

Acknowledgments

The authors extend their gratitude to Zhang qian from Shiyanjia Lab (www.shiyanjia.com, URL (accessed on 17 July 2023)) for providing invaluable assistance with the XPS analysis.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Zhong, J.-W.; Yang, X.-F.; Wu, Z.-L.; Liang, B.-L.; Huang, Y.-Q.; Zhang, T. State of the art and perspectives in heterogeneous catalysis of CO2 hydrogenation to methanol. Chem. Soc. Rev. 2020, 49, 1385–1413. [Google Scholar] [CrossRef]
  2. Duan, X.-C.; Xu, J.-T.; Wei, Z.-X.; Ma, J.-M.; Guo, S.-J.; Wang, S.-Y.; Liu, H.-K.; Dou, S.-X. Metal-free carbon materials for CO2 electrochemical reduction. Adv. Mater. 2017, 29, 1701784. [Google Scholar]
  3. Chu, S.; Majumdar, A. Opportunities and challenges for a sustainable energy future. Nature 2012, 488, 294–303. [Google Scholar] [PubMed]
  4. Liu, M.-J.; Zhan, L.-S.; Wang, Y.-C.; Zhao, X.; Wu, J.; Deng, D.-N.; Jiang, J.-B.; Zheng, X.-R.; Lei, Y.-P. Achieving integrated capture and reduction of CO2: A promising electrocatalyst. J. Mater. Sci. Technol. 2023, 165, 235–243. [Google Scholar]
  5. Zhang, X.-Y.; Xue, D.-P.; Jiang, S.; Xia, H.-C.; Yang, Y.-L.; Yan, W.-F.; Hu, J.-S.; Zhang, J.-N. Rational confinement engineering of MOF-derived carbon-based electrocatalysts toward CO2 reduction and O2 reduction reactions. InfoMat 2021, 4, e12257. [Google Scholar]
  6. Liu, J.-Z.; Wang, Y.-T.; Jiang, H.; Jiang, H.-B.; Zhou, X.-D.; Li, Y.-H.; Li, C.-Z. Ag@Au core-shell nanowires for nearly 100 % CO2-to-CO electroreduction. Chem. Asian J. 2020, 15, 425–431. [Google Scholar]
  7. Daiyan, R.; Chen, R.; Kumar, P.; Bedford, N.-M.; Qu, J.-T.; Cairney, J.-M.; Lu, X.; Amal, R. Tunable syngas production through CO2 electroreduction on cobalt–carbon composite electrocatalyst. ACS Appl. Mater. Interfaces 2020, 12, 9307–9315. [Google Scholar] [CrossRef]
  8. Li, C.-C.; Zhang, T.-T.; Liu, H.; Guo, Z.-Y.; Liu, Z.-L.; Shi, H.-J.; Cui, J.-L.; Li, H.; Li, H.-H.; Li, C.-Z. Steering CO2 electroreduction to C2+ products via enhancing localized *CO coverage and local pressure in conical cavity. Adv. Mater. 2024, 36, 2312204. [Google Scholar]
  9. Su, J.-W.; Pan, D.-H.; Dong, Y.; Zhang, Y.-Y.; Tang, Y.-L.; Sun, J.; Zhang, L.-J.; Tian, Z.-Q.; Chen, L. Ultrafine Fe2C iron carbide nanoclusters trapped in topological carbon defects for efficient electroreduction of carbon dioxide. Adv. Energy Mater. 2023, 13, 2204391. [Google Scholar]
  10. Zheng, T.-T.; Jiang, K.; Ta, N.; Hu, Y.-F.; Zeng, J.; Liu, J.-Y.; Wang, H.-T. Large-scale and highly selective CO2 electrocatalytic reduction on nickel single-atom catalyst. Joule 2019, 3, 265–278. [Google Scholar] [CrossRef]
  11. Liu, M.-H.; Liu, S.-J.; Xu, Q.; Miao, Q.-Y.; Yang, S.; Hanson, S.; Chen, G.-Z.; He, J.; Jiang, Z.; Zeng, G.-F. Dual atomic catalysts from COF-derived carbon for CO2RR by suppressing HER through synergistic effects. Carbon. Energy 2023, 5, e300. [Google Scholar] [CrossRef]
  12. Jing, X.; Dong, X.; Liu, C.-X.; Li, J.-W.; Dai, Y.-Z.; Xue, W.-Q.; Luo, L.-H.; Ji, Y.; Zhang, X.; Li, X.; et al. Turning copper into an efficient and stable CO evolution catalyst beyond noble metals. Nat. Commun. 2024, 15, 5998. [Google Scholar]
  13. Li, J.-W.; Zeng, H.-L.; Dong, X.; Ding, Y.-M.; Hu, S.-P.; Zhang, R.-H.; Dai, Y.-Z.; Cui, P.-X.; Xiao, Z.; Zhao, D.-H.; et al. Selective CO2 electrolysis to CO using isolated antimony alloyed copper. Nat. Commun. 2023, 14, 340. [Google Scholar] [CrossRef]
  14. Azaiza-Dabbah, D.; Wang, F.; Haddad, E.; Solé-Daura, A.; Carmieli, R.; Poblet, J.M.; Vogt, C.; Neumann, R. Heterometallic transition metal oxides containing lewis acids as molecular catalysts for the reduction of carbon dioxide to carbon monoxide with bimodal activity. J. Am. Chem. Soc. 2024, 146, 27871–27885. [Google Scholar] [CrossRef]
  15. Yun, H.; Yoo, S.; Son, J.; Kim, J.-H.; Wu, J.-W.; Jiang, K.; Shin, H.; Hwang, Y.-J. Strong cation concentration effect of Ni–N–C electrocatalysts in accelerating acidic CO2 reduction reaction. Chem 2025, 102461. [Google Scholar] [CrossRef]
  16. Cho, J.-H.; Ma, J.-H.; Lee, C.-H.; Lim, J.-W.; Kim, Y.; Jang, H.-Y.; Kim, J.; Seo, M.-g.; Choi, Y.-H.; Jang, Y.-J.; et al. Crystallographically vacancy-induced MOF nanosheet as rational single-atom support for accelerating CO2 electroreduction to CO. Carbon Energy 2024, 6, e510. [Google Scholar] [CrossRef]
  17. Wang, C.; Chen, B.-R.; Ren, H.-A.; Wang, X.-Y.; Li, W.-J.; Hu, H.-C.; Chen, X.-Y.; Liu, Y.-Q.; Guan, Q.-X.; Li, W. Stabilizing Ni single-atom sites through introducing low-valence Ni species for durably efficient electrochemical CO2 reduction. Appl. Catal. B-Environ. 2025, 368, 125151. [Google Scholar] [CrossRef]
  18. Zhu, W.-L.; Michalsky, R.; Metin, Ö.; Lv, H.; Guo, S.-J.; Wright, C.-J.; Sun, X.-L.; Peterson, A.-A.; Sun, S.-H. Monodisperse Au nanoparticles for selective electrocatalytic reduction of CO2 to CO. J. Am. Chem. Soc. 2013, 135, 16833–16836. [Google Scholar] [CrossRef]
  19. Liu, S.-B.; Tao, H.-B.; Zeng, L.; Liu, Q.; Xu, Z.-H.; Liu, Q.-X.; Luo, J.-L. Shape-dependent electrocatalytic reduction of CO2 to CO on triangular silver nanoplates. J. Am. Chem. Soc. 2017, 139, 2160–2163. [Google Scholar] [CrossRef]
  20. Chang, Q.-W.; Kim, J.; Lee, J.-H.; Kattel, S.; Chen, J.-G.; Choi, S.-I.; Chen, Z. Boosting activity and selectivity of CO2 electroreduction by prehydridizing Pd nanocubes. Small 2020, 16, 2005305. [Google Scholar] [CrossRef]
  21. Yang, H.-B.; Hung, S.-F.; Liu, S.; Yuan, K.-D.; Miao, S.; Zhang, L.-P.; Huang, X.; Wang, H.-Y.; Cai, W.-Z.; Chen, R.; et al. Atomically dispersed Ni(i) as the active site for electrochemical CO2 reduction. Nat. Energy 2018, 3, 140–147. [Google Scholar]
  22. Gu, J.; Hsu, C.-S.; Bai, L.-C.; Chen, H.-M.; Hu, X.-L. Atomically dispersed Fe3+ sites catalyze efficient CO2 electroreduction to CO. Science 2019, 364, 1091–1094. [Google Scholar] [PubMed]
  23. Wang, J.-J.; Wang, G.-J.; Zhang, J.-F.; Wang, Y.-D.; Wu, H.; Zheng, X.-R.; Ding, J.; Han, X.-P.; Deng, Y.-D.; Hu, W.-B. Inversely tuning the CO2 electroreduction and hydrogen evolution activity on metal oxide via heteroatom doping. Angew. Chem. Int. Ed. 2021, 60, 1–6. [Google Scholar]
  24. Ma, M.-B.; Tang, Q. Axial coordination modification of M–N4 single-atom catalysts to regulate the electrocatalytic CO2 reduction reaction. J. Mater. Chem. C 2022, 10, 15948–15956. [Google Scholar]
  25. Jiang, X.-X.; Zhao, Y.-X.; Kong, Y.; Sun, J.-J.; Feng, S.-Z.; Lu, X.; Hu, Q.; Yang, H.-P.; He, C.-X. Support effect and confinement effect of porous carbon loaded tin dioxide nanoparticles in high-performance CO2 electroreduction towards formate. Chin. Chem. Lett. 2025, 36, 109555. [Google Scholar]
  26. Yang, X.-F.; Wang, A.-Q.; Qiao, B.-T.; Li, J.; Liu, J.-Y.; Zhang, T. A new frontier in heterogeneous catalysis. Acc. Chem. Res. 2013, 46, 1740–1748. [Google Scholar] [CrossRef] [PubMed]
  27. Jiang, H.-L.; Zhang, Y.; Jiao, L.; Yang, W.-J.; Xie, C.-F. Rational fabrication of low-coordinate single-atom Ni electrocatalysts by MOFs for highly selective CO2 reduction. Angew. Chem. Int. Ed. 2021, 60, 7607–7611. [Google Scholar]
  28. Chen, Y.-Q.; Zhang, J.-R.; Yang, L.-J.; Wang, X.-Z.; Wu, Q.; Hu, Z. Recent advances in non-precious metal–nitrogen–carbon single-site catalysts for CO2 electroreduction reaction to CO. Electrochem. Energy Rev. 2022, 5, 11. [Google Scholar] [CrossRef]
  29. Li, X.-G.; Bi, W.-T.; Chen, M.-L.; Sun, Y.-X.; Ju, H.-X.; Yan, W.-S.; Zhu, J.-F.; Wu, X.-J.; Chu, W.-S.; Wu, C.-Z.; et al. Exclusive Ni–N4 sites realize near-unity CO selectivity for electrochemical CO2 reduction. J. Am. Chem. Soc. 2017, 139, 14889–14892. [Google Scholar]
  30. Huang, J.-R.; Qiu, X.-F.; Zhao, Z.-H.; Zhu, H.-L.; Liu, Y.-C.; Shi, W.; Liao, P.-Q.; Chen, X.-M. Single-product faradaic efficiency for electrocatalytic of CO2 to CO at current density larger than 1.2 A cm−2 in neutral aqueous solution by a single-atom. Nanozyme Angew. Chem. Int. Ed. 2022, 61, e202210985. [Google Scholar]
  31. Xu, F.; Wang, X.-H.; Liu, X.; Li, C.-Y.; Fan, G.-H.; Xu, H. Computational screening of TMN4 based graphene-like BC6N for CO2 electroreduction to C1 hydrocarbon products. Mol. Catal. 2022, 530, 112571. [Google Scholar]
  32. Xu, S.-X.; Ding, Y.-X.; Du, J.; Zhu, Y.; Liu, G.-Q.; Wen, Z.-B.; Liu, X.; Shi, Y.-B.; Gao, H.; Sun, L.-C.; et al. Immobilization of iron phthalocyanine on pyridine-functionalized carbon nanotubes for efficient nitrogen reduction reaction. ACS Catal. 2022, 12, 5502–5509. [Google Scholar]
  33. Zheng, W.-Q.; Zhu, R.; Wu, H.-J.; Ma, T.; Zhou, H.-J.; Zhou, M.; He, C.; Liu, X.-K.; Li, S.; Cheng, C. Tailoring bond microenvironments and reaction pathways of single-atom catalysts for efficient water electrolysis. Angew. Chem. Int. Ed. 2022, 61, e202208667. [Google Scholar]
  34. Ping, D.; Huang, S.-G.; Wu, S.-D.; Zhang, Y.-F.; Wang, S.-W.; Yang, X.-Z.; Han, L.-F.; Tian, J.-F.; Guo, D.-J.; Qiu, H.-J.; et al. Confinement effect and 3D design endow unsaturated single Ni atoms with ultrahigh stability and selectivity toward CO2 Electroreduction. Small 2023, 20, 2309014. [Google Scholar]
  35. Ping, D.; Feng, Y.-C.; Wu, S.-D.; Yi, F.; Cheng, S.-Y.; Wang, S.-W.; Tian, J.-F.; Wang, H.; Yang, X.-Z.; Guo, D.-J.; et al. Maximizing surface single-Ni sites on hollow carbon sphere for efficient CO2 electroreduction. ACS Sustain. Chem. Eng. 2024, 12, 3034–3043. [Google Scholar]
  36. Cui, Y.; Ren, C.-J.; Li, Q.; Ling, C.-Y.; Wang, J.-L. Hybridization state transition under working conditions: Activity origin of single-atom catalysts. J. Am. Chem. Soc. 2024, 146, 15640–15647. [Google Scholar] [CrossRef]
  37. Mao, Z.-C.; Wei, G.-P.; Liu, L.-L.; Hao, T.-T.; Wang, X.-J.; Tang, S.-B. Synergistic effect of multi-metal site provided by Ni-N4, adjacent single metal atom, and Fe6 nanoparticle to boost CO2 activation and reduction. J. Colloid. Interface Sci. 2025, 679, 860–867. [Google Scholar] [PubMed]
  38. Zhang, W.-Y.; Mehmood, A.; Ali, G.; Liu, H.; Chai, L.-Y.; Wu, J.; Liu, M. Nickel nanocluster-stabilized unsaturated Ni–N3 atomic sites for efficient CO2-to-CO electrolysis at industrial-level current. Angew. Chem. Int. Ed. 2025, e202424552. [Google Scholar]
  39. Zhao, C.-G.; Dai, X.-Y.; Yao, T.; Chen, W.-X.; Wang, X.-Q.; Wang, J.; Yang, J.; Wei, S.-Q.; Wu, Y.; Li, Y.-D. Ionic exchange of metal–organic frameworks to access single nickel sites for efficient electroreduction of CO2. J. Am. Chem. Soc. 2017, 139, 8078–8081. [Google Scholar]
  40. Ren, X.-Y.; Liu, H.; Wang, J.-G.; Yu, J.-Y. Electrospinning-derived functional carbon-based materials for energy conversion and storage. Chin. Chem. Lett. 2024, 35, 109282. [Google Scholar]
  41. Hajikhani, M.; Lin, M.-S. A review on designing nanofibers with high porous and rough surface via electrospinning technology for rapid detection of food quality and safety attributes. Trends Food Sci. Technol. 2022, 128, 118–128. [Google Scholar] [CrossRef]
  42. Chang, M.-Y.; Ren, W.-H.; Ni, W.-Y.; Lee, S.; Hu, X.-L. Ionomers modify the selectivity of Cu-catalyzed electrochemical CO2 reduction. ChemSusChem 2023, 16, e202201687. [Google Scholar] [CrossRef]
  43. Wang, X.-J.; Wang, Y.-J.; Cui, L.-Y.; Gao, W.-Q.; Li, X.; Liu, H.; Zhou, W.-J.; Wang, J.-G. Coordination-based synthesis of Fe single-atom anchored nitrogen-doped carbon nanofibrous membrane for CO2 electroreduction with nearly 100% CO selectivity. Chin. Chem. Lett. 2024, 35, 110031. [Google Scholar] [CrossRef]
  44. Koh, D.; McCool, B.A.; Deckman, H.; Lively, R. Reverse osmosis molecular differentiation of organic liquids using carbon molecular sieve membranes. Science 2016, 353, 804–807. [Google Scholar] [CrossRef]
  45. Yao, Y.-J.; Gao, M.-X.; Zhang, Y.-Y.; Zheng, H.-D.; Hu, H.-H.; Yin, H.-Y.; Wang, S.-B. Nonprecious bimetallic (Mo, Fe)-N/C nanostructures loaded on PVDF membrane for toxic Cr VI reduction from water. J. Hazard. Mater. 2020, 389, 121844. [Google Scholar] [CrossRef] [PubMed]
  46. Liu, C.-J.; Wang, Z.; Zong, X.; Jin, Y.-M.; Li, D.; Xiong, Y.-P.; Wu, G. N- & S-co-doped carbon nanofiber network embedded with ultrafine Ni-Co nanoalloy for efficient oxygen electrocatalysis and Zn–air batteries. Nanoscale 2020, 12, 9581–9589. [Google Scholar]
  47. Chen, Y.-B.; Zou, L.-L.; Liu, H.; Chen, C.; Wang, Q.; Gu, M.; Yang, B.; Zou, Z.-Q.; Fang, J.-H.; Yang, H. Fe and N Co-doped porous carbon nanospheres with high density of active sites for efficient CO2 electroreduction. J. Phys. Chem. C. 2019, 123, 16651–16659. [Google Scholar] [CrossRef]
  48. Wu, S.-D.; Lv, X.-N.; Ping, D.; Zhang, G.-W.; Wang, S.-W.; Wang, H.; Yang, X.-Z.; Guo, D.-J.; Fang, S.-M. Highly exposed atomic Fe–N active sites within carbon nanorods towards electrocatalytic reduction of CO2 to CO. Electrochim. Acta 2020, 340, 135930. [Google Scholar] [CrossRef]
  49. Ping, D.; Dong, C.-J.; Zhao, H.; Dong, X.-F. A novel hierarchical RuNi/Al2O3–carbon nanotubes/Ni foam catalyst for selective removal of CO in H2-rich fuels. Ind. Eng. Chem. Res. 2018, 57, 5558–5567. [Google Scholar] [CrossRef]
  50. Liu, J.; Song, P.; Ruan, M.-B.; Xu, W.-L. Catalytic properties of graphitic and pyridinic nitrogen doped on carbon black for oxygen reduction reaction. Chin. J. Catal. 2016, 37, 1119–1126. [Google Scholar] [CrossRef]
  51. Hou, Y.; Qiu, M.; Zhang, T.; Ma, J.; Liu, S.-H.; Zhuang, X.-D.; Yuan, C.; Feng, X.-L. Efficient electrochemical and photoelectrochemical water splitting by a 3D nanostructured carbon supported on flexible exfoliated graphene foil. Adv. Mater. 2016, 29, 1604480. [Google Scholar] [CrossRef] [PubMed]
  52. Chen, Y.-Z.; Wang, C.-M.; Wu, Z.-Y.; Xiong, Y.-J.; Xu, Q.; Yu, S.-H.; Jiang, H.-L. From bimetallic metal-organic framework to porous carbon: High surface area and multicomponent active dopants for excellent electrocatalysis. Adv. Mater. 2015, 27, 5010–5016. [Google Scholar] [CrossRef] [PubMed]
  53. Geng, D.-S.; Chen, Y.; Chen, Y.-G.; Li, Y.-L.; Li, R.-Y.; Sun, X.-L.; Ye, S.-Y.; Knights, S. High oxygen-reduction activity and durability of nitrogen-doped graphene. Energy Environ. Sci. 2011, 4, 760. [Google Scholar] [CrossRef]
  54. Qu, L.-T.; Liu, Y.; Baek, J.; Dai, L.-M. Nitrogen-doped graphene as efficient metal-free electrocatalyst for oxygen reduction in fuel cells. ACS Nano 2010, 4, 1321–1326. [Google Scholar] [CrossRef]
  55. Kattel, S.; Wang, G.-F. A density functional theory study of oxygen reduction reaction on Me–N4 (Me = Fe, Co, or Ni) clusters between graphitic pores. J. Mater. Chem. A 2013, 1, 10790. [Google Scholar] [CrossRef]
  56. Zhang, X.-M.; Zhai, P.-L.; Zhang, Y.-X.; Wu, Y.-Z.; Wang, C.; Ran, L.; Gao, J.-F.; Li, Z.-W.; Zhang, B.; Fan, Z.-Z.; et al. Engineering single-atomic Ni-N4-O sites on semiconductor photoanodes for high-performance photoelectrochemical water splitting. J. Am. Chem. Soc. 2021, 143, 20657–20669. [Google Scholar]
  57. Gong, L.; Chen, B.-T.; Gao, Y.; Yu, B.-Q.; Wang, Y.-H.; Han, B.; Lin, C.-X.; Bian, Y.-Z.; Qi, D.-D.; Jiang, J.-Z. Covalent organic frameworks based on tetraphenyl-p-phenylenediamine and metalloporphyrin for electrochemical conversion of CO2 to CO. Inorg. Chem. 2022, 9, 3217–3223. [Google Scholar] [CrossRef]
  58. Lyu, X.; Anastasiadou, D.; Raj, J.; Wu, J.-J.; Bai, Y.-C.; Li, J.-L.; Cullen, D.-A.; Yang, J.; Gonçalves, L.-P.-L.; Lebedev, O.-I.; et al. Large-scale synthesis of metal/nitrogen Co-doped carbon catalysts for CO2 electroreduction. Electrochim. Acta 2023, 455, 142427. [Google Scholar] [CrossRef]
  59. Chen, J.-X.; Wei, X.-F.; Cai, R.-M.; Ren, J.-Z.; Ju, M.; Lu, X.-Q.; Long, X.; Yang, S.-H. Composition-Tuned surface binding on CuZn-Ni catalysts boosts CO2RR selectivity toward CO generation. ACS Materials Lett. 2022, 4, 497–504. [Google Scholar] [CrossRef]
  60. Wang, F.-Y.; Liu, Y.; Song, Z.-L.; Miao, Z.-C.; Zhao, J.-P. Ni-N-Doped carbon-modified reduced graphene oxide catalysts for electrochemical CO2 reduction reaction. Catalysts 2021, 11, 561. [Google Scholar] [CrossRef]
  61. Sheng, J.-Y.; Gao, M.-S.; Zhao, N.; Zhao, K.; Shi, Y.-A.; Wang, W. Bimetallic Ni/Fe functionalized, 3D printed, self-supporting catalytic-electrodes for CO2 reduction reaction. Fuel 2025, 382, 133703. [Google Scholar]
  62. Liu, E.; Liu, T.-X.; Ma, X.-J.; Zhang, Y.-P. The electrocatalytic performance of Ni–AlO(OH)3@RGO for the reduction of CO2 to CO. New J. Chem. 2022, 46, 12023. [Google Scholar]
  63. Cheng, Y.; Zhao, S.-Y.; Li, H.-B.; He, S.; Veder, J.-P.; Johannessen, B.; Xiao, J.-P.; Lu, S.-F.; Pan, J.; Chisholm, M.-F.; et al. Unsaturated edge-anchored Ni single atoms on porous microwave exfoliated graphene oxide for electrochemical CO2. Appl. Catal. B Environ. 2019, 243, 294–303. [Google Scholar]
  64. Varela, A.-S.; Ju, W.; Bagger, A.; Franco, P.; Rossmeisl, J.; Strasser, P. Electrochemical reduction of CO2 on metal-nitrogen-doped carbon catalysts. ACS Catal. 2019, 9, 7270–7284. [Google Scholar]
  65. Lin, L.; Li, H.-B.; Yan, C.-C.; Li, H.-F.; Si, R.; Li, M.-R.; Xiao, J.-P.; Wang, G.-X.; Bao, X.-H. Synergistic catalysis over iron-nitrogen sites anchored with cobalt phthalocyanine for efficient CO2 electroreduction. Adv. Mater. 2019, 31, 1903470. [Google Scholar]
Nanomaterials 15 00473 g001
Figure 1. (a) Schematic diagram of the formation of Ni-N-CF (b) Digital image of Ni-PVDF before carbonization. (c,d) SEM images of Ni-PVDF at different magnifications before carbonization. (e) Digital image of Ni-N-CF after carbonization. (f,g) SEM images of Ni-N-CF at different magnifications after carbonization.
Figure 1. (a) Schematic diagram of the formation of Ni-N-CF (b) Digital image of Ni-PVDF before carbonization. (c,d) SEM images of Ni-PVDF at different magnifications before carbonization. (e) Digital image of Ni-N-CF after carbonization. (f,g) SEM images of Ni-N-CF at different magnifications after carbonization.
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Figure 2. (a) TEM image of Ni-N-CF. (b) HRTEM image (inset is the SAED image) of Ni-N-CF. (c) Elemental mapping analysis of Ni-N-CF and the distributions of C, N, Ni, and O elements. (d) N2 adsorption–desorption isotherm of Ni-N-CF and Ni-PVDF catalysts. (e) Pore size distribution plot of Ni-N-CF and Ni-PVDF catalysts.
Figure 2. (a) TEM image of Ni-N-CF. (b) HRTEM image (inset is the SAED image) of Ni-N-CF. (c) Elemental mapping analysis of Ni-N-CF and the distributions of C, N, Ni, and O elements. (d) N2 adsorption–desorption isotherm of Ni-N-CF and Ni-PVDF catalysts. (e) Pore size distribution plot of Ni-N-CF and Ni-PVDF catalysts.
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Figure 3. (a,b) HAADF-STEM images of Ni-N-CF. (c) The Raman spectra of Ni-N-CF, Ni-CF, and N-CF. (d) N 1s spectra of Ni-N-CF catalysts. (e) Ni K-edge XANES of the Ni foil, Ni-N-C, and NiO. (f) EXAFS spectra at the Ni K-edge for Ni-N-CF.
Figure 3. (a,b) HAADF-STEM images of Ni-N-CF. (c) The Raman spectra of Ni-N-CF, Ni-CF, and N-CF. (d) N 1s spectra of Ni-N-CF catalysts. (e) Ni K-edge XANES of the Ni foil, Ni-N-C, and NiO. (f) EXAFS spectra at the Ni K-edge for Ni-N-CF.
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Figure 4. (a) LSV curves of Ni-N-CF in Ar-saturated 0.5 M NaHCO3 solution and LSV curves in CO2 saturated 0.5 M NaHCO3 solution of N-CF, Ni-CF and Ni-N-CF. (b) Faradaic efficiency of CO product in CO2RR on Ni-N-CF at various cathode potentials. (c) Faradaic efficiency CO product in CO2RR on N-CF, Ni-CF, and Ni-N-CF at −0.65 V vs. RHE. (d) The partial current density for CO production of Ni-N-CF, Ni-CF, and N-CF at different voltages. (e) Stability test of Ni-N-CF at −0.65 V vs. RHE over 12 h.
Figure 4. (a) LSV curves of Ni-N-CF in Ar-saturated 0.5 M NaHCO3 solution and LSV curves in CO2 saturated 0.5 M NaHCO3 solution of N-CF, Ni-CF and Ni-N-CF. (b) Faradaic efficiency of CO product in CO2RR on Ni-N-CF at various cathode potentials. (c) Faradaic efficiency CO product in CO2RR on N-CF, Ni-CF, and Ni-N-CF at −0.65 V vs. RHE. (d) The partial current density for CO production of Ni-N-CF, Ni-CF, and N-CF at different voltages. (e) Stability test of Ni-N-CF at −0.65 V vs. RHE over 12 h.
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MDPI and ACS Style

Zhou, X.; Meng, C.; Yu, W.; Wang, Y.; Cui, L.; Li, T.; Wang, J. Constructing of Ni-Nx Active Sites in Self-Supported Ni Single-Atom Catalysts for Efficient Reduction of CO2 to CO. Nanomaterials 2025, 15, 473. https://doi.org/10.3390/nano15060473

AMA Style

Zhou X, Meng C, Yu W, Wang Y, Cui L, Li T, Wang J. Constructing of Ni-Nx Active Sites in Self-Supported Ni Single-Atom Catalysts for Efficient Reduction of CO2 to CO. Nanomaterials. 2025; 15(6):473. https://doi.org/10.3390/nano15060473

Chicago/Turabian Style

Zhou, Xuemei, Chunxia Meng, Wanqiang Yu, Yijie Wang, Luyun Cui, Tong Li, and Jingang Wang. 2025. "Constructing of Ni-Nx Active Sites in Self-Supported Ni Single-Atom Catalysts for Efficient Reduction of CO2 to CO" Nanomaterials 15, no. 6: 473. https://doi.org/10.3390/nano15060473

APA Style

Zhou, X., Meng, C., Yu, W., Wang, Y., Cui, L., Li, T., & Wang, J. (2025). Constructing of Ni-Nx Active Sites in Self-Supported Ni Single-Atom Catalysts for Efficient Reduction of CO2 to CO. Nanomaterials, 15(6), 473. https://doi.org/10.3390/nano15060473

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