Large‐area Free‐standing Metalloporphyrin‐based Covalent Organic Framework Films by Liquid‐air Interfacial Polymerization for Oxygen Electrocatalysis

Synthesizing large‐area free‐standing covalent organic framework (COF) films is of vital importance for their applications but is still a big challenge. Herein, we reported the synthesis of large metalloporphyrin‐based COF films and their applications for oxygen electrocatalysis. The reaction of meso‐benzohydrazide‐substituted metal porphyrins with tris‐aldehyde linkers afforded free‐standing COF films at the liquid‐air interface. These films can be scaled up to 3000 cm2 area and display great mechanical stability and structural integrity. Importantly, the Co‐porphyrin‐based films are efficient for electrocatalytic O2 reduction and evolution reactions. A flexible, all‐solid‐state Zn‐air battery was assembled using the films and showed high performance with a charge–discharge voltage gap of 0.88 V at 1 mA cm−2 and high stability under bent conditions (0° to 180°). This work thus presents a strategy to synthesize functionalized COF films with high quality for uses in flexible electronics. A series of free‐standing large‐area metalloporphyrin‐based COF films, connected through dynamic covalent acylhydrazone bonds, are synthesized by liquid‐air interfacial polymerization. These films are smooth, dense, uniform, and defect free, and display high hydrolytic and mechanical stability. The Co‐based films are active for electrocatalytic oxygen reduction and evolution reactions and show promising applications in flexible Zn‐air batteries.