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–N4 sites in an iron porphyrin-based metal–organic framework, with axially coordinated 4-octylpyridine groups on Fe–N4 (named as PCN-224 (Fe)-1). The amphiphilic 4-octylpyridine groups donate sufficient electrons toward Fe–N4 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 E1/2 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.