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Figure 1. 

(a) Schematic illustration detailing the synthetic pathways of ZIF-67, Co SACs, and Co NPs. (b), (d) TEM and EDS mapping images of Co SACs. (c), (e) TEM and EDS mapping images of Co NPs. (f) XRD patterns of Co SACs and Co NPs. (g) Magnetic-field-dependent magnetization for Co NPs at room temperature.

Figure 2. 

(a) Co 2p XPS spectra of Co SACs and Co NPs. (b) N 1s XPS spectra of Co SACs and Co NPs. (c) XANES spectra at Co K-edge for Co foil, CoO, Co₂O₃, Co SACs, and Co NPs. (d) Coordination number fitting of FT-EXAFS for Co SACs. (e) FT-EXAFS spectra of Co foil, CoO, Co₂O₃, Co SACs, and Co NPs. (f) Wavelet transform (WT)-EXAFS spectra of Co foil, CoO, Co₂O₃, Co SACs, and Co NPs.

Figure 3. 

(a) LSV of Co SACs and Co NPs in electrolyte with and without 0.5 M KNO₃. (b) FE of NH₃ for NC, Co SACs, and Co NPs. (c) FE of NH₃ and NO₂⁻ for Co NPs. (d) NH₃ yield rate for NC, Co SACs, and Co NPs. (e) ¹H NMR spectra of the postreaction electrolyte using 0.5 M K¹⁵NO₃ or K¹⁴NO₃ as the precursor. (f) Comparison of the NO₃RR performance of Co NPs in this work with state-of-the-art literature results. (g) Cyclic stability test of Co NPs over 20 consecutive cycles.

Figure 4. 

Operando ATR-FTIR spectra of (a) Co NPs, and (b) Co SACs at various applied potentials. (c) DEMS analysis of Co NPs. (d) EPR spectra of blank control, NC, Co SACs, and Co NPs.

Figure 5. 

(a) Reaction schematic for NO₃RR. (b) Reaction energy barrier diagrams of Co NPs and Co SACs. (c) PDOS of Co NPs and Co SACs after adsorption of *NO₃. (d) The ΔG_*NO3 and charge transfer number of Co NPs and Co SACs.