A Combination of "Push Effect" Strategy with "Triple-Phase-Boundary Engineering" on Iron Porphyrin-Based MOFs: Enhanced Selectivity and Activity for Oxygen Reduction.

Herein, the "push effect" strategy combined with "triple-phase-boundary" (TPB) engineering was innovatively employed to target the single Fe-N 4 sites in an iron porphyrin-based metal-organic framework, with axially coordinated 4-octylpyridine groups on Fe-N 4 (named as PCN-224 (Fe)-1). The amphiphilic 4-octylpyridine groups donate sufficient electrons toward Fe-N 4 by the Fe-N(pyridine) coordination bond and simultaneously provide effective TBP reactive sites by the hydrophobic octyl terminals, resulting in enhanced ORR activity of the PCN-224 (Fe)-1 in hydrophobic octyl terminals, with an E 1/2 of 0.81 V and complete 4-electron selectivity. Furthermore, TPB engineering is utilized to construct the PCN-224 (Fe)-1-based Zn-air battery with a maximum power density of 98 mW cm -2 , demonstrating great practical application potential for molecule-based ORR catalysts. Meanwhile, the "push effect" mechanism on ORR is revealed by electron paramagnetic resonance, in situ UV-vis spectroelectrochemical analysis, and density functional theory.