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Figure 5. (A) Illustration of the preparation process of CNT@Fe-N-PC via adsorption[98], reproduced from Ref. [98] with permission. Copyright 2018 Springer Nature. (B) SEM images of the CoFe2O4 sphere, and (C) SEM, (D) TEM, (E) HAADF-STEM images of FeCo-N-HCN[99], reproduced from Ref.[99]with permission. Copyright 2021 Wiley-VCH. (F and G) TEM, (H) aberration-corrected HAADF-STEM images, and (I) EDS element mapping of CoNi-SAs/NC[103], reproduced from Ref.[103] with permission. Copyright 2019 Wiley-VCH. (J) Illustration of the fabrication process of meso-Fe-N-C, and (K) TEM image of meso-Fe-N-C[104], reproduced from Ref.[104] with permission. Copyright 2021 American Chemical Society. (L) TEM image of CoSA/N,S-HCS[105], reproduced from Ref.[105] with permission. Copyright 2020 Wiley-VCH. (M) Illustration of the fabrication process of flexible electrode based on SA@NCF/CNF, (N) digital photos of Co SA@NCF/CNF flexible electrode under rolling, bending, and twisting state, and (O) SEM image of Co SA@NCF/CNF[111], reproduced from Ref.[111] with permission. Copyright 2019 Wiley-VCH. (P) HAADF-STEM image, (Q) EDS element mapping, and (R) aberration-corrected HAADF-STEM image of Co-N/CNFs[112], reproduced from Ref.[112] with permission. Copyright 2017 American Chemical Society.
