2D Metal Porphyrin-Based MOFs and ZIF-8 Composite-Derived Carbon Materials Containing M–Nx Active Sites as Bifunctional Electrocatalysts for Zinc–Air Batteries

The main impediment to the development of zinc–air batteries is the sluggish kinetics of the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). Transition metal N-doped carbon catalysts offer a promising alternative to noble metal catalysts, with metal–organic framework (MOF)-derived carbon material catalysts being particularly noteworthy. Here, we synthesized MxP-Z-C carbon catalysts by combining two-dimensional (2D) metal porphyrin-based MOFs (MxPMFs, x = Fe, Co, Ni, Mn) and three-dimensional zeolitic imidazole framework-8 (ZIF-8) through electrostatic interaction, followed by carbonization. ZIF-8 was inserted between the layers of MxPMFs to prevent its Π–Π stacking, allowing the active sites to become fully exposed. MxP-Z-C demonstrated an impressive catalytic activity for both the ORR and the OER reactions. Among them, FeP-Z-C showed the best catalytic activity. The half-wave potential for ORR was 0.92 V (vs the reversible hydrogen electrode (RHE)), while the overpotential for the OER was 290 mV. In addition, the zinc–air battery assembled by FeP-Z-C exhibited high power density (133.14 mW cm–2) and significant specific capacity (816 mAh gZn–1), indicating considerable potential as a bifunctional catalyst for electronic devices.