Nitrogen-mediated microenvironment optimization of Fe-N4 sites by ligand exchange strategy on dual MOF precursor for enhanced oxygen reduction reaction performance

The catalytic performance of single-atom catalysts primarily depends on their coordination environment. To date, research on the catalytic regulation of SACs has predominantly concentrated on the first and second coordination structures of the central atom. In this study, we demonstrate that regulating the nitrogen-mediated non-coordinated microenvironment beyond the second coordination sphere of SACs is also crucial for optimizing catalytic performance. A dual metal-organic framework precursor, ZIF-L@ZIF-8/Fc, was constructed using the “MOF@MOF” strategy, wherein ferrocene was in situ anchored within the cages of ZIF-L@ZIF-8. Notably, a ligand exchange strategy was adopted, where the 1,2,4-triazole-3,5-diamine ligand underwent ligand exchange with the dimethylimidazole ligand in the ZIF-L@ZIF-8/Fc precursor, and the e-Fe SA /CSNC catalyst rich in Fe-N 4 active sites was formed through pyrolysis. Density functional theory confirmed that the ligand exchange strategy optimized the non-coordinated microenvironment of the Fe-N 4 active sites. Consequently, the e-Fe SA /CSNC catalyst exhibits excellent performance across the entire pH range, with half-wave potentials of 0.95 V, 0.81 V, and 0.83 V in alkaline, acidic, and neutral media, respectively. Furthermore, the e-Fe SA /CSNC-based zinc-air battery and quasi-solid-state zinc-air battery show long-term cycling stability, during which the intrinsic morphology of ZIF-L is maintained, exhibiting excellent overall performance.