fig6

Figure 6. Synthetic procedures of (A) the CoFe-NC-PPy electrocatalyst (reproduced with permission from Elsevier, copyright 2024)^[109] and (B) the Co/CNB-x catalyst (reproduced with permission from Elsevier, copyright 2023)^[110]; (C) construction of Fe-N-C-E (Reproduced with permission from the Copyright 2024, American Chemical Society, copyright 2024)^[111]. N-C-E: Metal-nitrogen-carbon; ZIFs: zeolite imidazole frameworks; MOFs: metal-organic frameworks.